Looking for indepth cam advice with a 4.6 mod motor

[MalcolmV8]

Hey Guys,

This question is on my 03 Cobra with a 4.6. I know there's a lot of really smart guys on here working with the 302s and 4.6s so I thought I'd reach out here.

Reason for change:
First I'll preface this and let you know my main reason for looking into cams is purely the awesome sound. Especially at idle. I know it's an expensive mod just for sound but I've had the car for almost 12 years now so I have to change things up from time to time to keep it interesting.

Relevant specs on car:
I rebuilt the motor in 09 and went with -19cc dished pistons giving me a static CR of 8.1:1. Dumbest thing I've ever done with the car {punch self in face LOL}. That low CR killed throttle response, HP, and gas mileage. It is what it is and I don't plan on rebuilding the engine right now so I live with it.
The car currently has a 2.9 Whipple supercharger and is tuned for both 91 pump gas with methanol injection and also for E85. I switch back and forth due to the PITA of getting E85.
The car is at 27.5 PSI of boost and dynos around 705 whp or there about on E85 (without spraying the nitrous). It still has the stock exhaust manifolds on it so I'm sure that's a restriction. I'll be switching to long tubes this winter which should drop the boost down a few PSI and increase HP a little bit.

Concerns:
So my huge concern is that I already have such low CR. Adding more aggressive cams usually lowers the dynamic CR so I'm afraid that putting in some cams will kill HP. While I don't necessarily expect a huge (if any) HP increase with some cams I certainly don't want to kill HP just for the sound of cams.
Also a huge concern is drivability since I do 99% of driving on the road with this car. Granted its not my primary daily drive but a fun weather driver so I can live with a little bit of not so stock. I don't want it to be like a POS though dying at idle, stalling on take off, bogging and then jerking forward at low RPMs and basically just a horrible street car.

I've asked around on the forums and some local guys and I get everything from "Crower Stage 3 cams drive like stock if your tuner knows what he's doing" to "they sucked so bad I went back to stock cams". So that's kind of up in the air. I will say I got a lot more responses of "it drives like close to stock" than not. As for tuner... well I tune my own stuff so we'll see how that goes

OK so googling around this is the best I could find for what the specs are on the stock 03 Cobra cams.

INT: 190 deg @ .050/.394 lift
EXH: 196 deg @ .050/.397 lift
114 LSA, no advance

Looking around I see the main two companies making cams for the 03 Cobras that guys are getting is Crower and Comp. Listening to youtube videos I wouldn't even consider Crower Stage 2 cams. They sound so close to stock idling it would be a waste of my time and money. Stage 3 is where it sounds awesome.

For reference here are the Crower Stage 2 specs
INT/EXH - Dur @ .050” Lift: 206°/206° RR: 1.8/1.8 Gross Lift: .475”/.475” LSA: 114° RPM: Idle to 5900 Redline: 6400

Crower Stage 3 (the ones I'm considering)
INT/EXH - Dur @ .050” Lift: 212°/212° RR: 1.8/1.8 Gross Lift: .484”/.484” LSA: 114° RPM: Idle to 6200 Redline: 6700


The Comp cams Stage 3 sound even nastier in youtube videos so I assume this an even less street friendly cam. Here are the three Comp cam specs for comparison sake.

Comp - 106260
RPM - 1200 to 5800
Duration Intake 257
Duration Exhaust 259
Lobe Seperation 116
Dur @ .050 lift intake: 222 exhaust: 224
Intake Centerline 114
Valve lift intake: 0.475 exhaust: 0.45

Comp - 106360
RPM - 1500 to 6000
Duration Intake 265
Duration Exhaust 267
Lobe Seperation 116
Dur @ .050 lift intake: 230 exhaust: 232
Intake Centerline 114
Valve lift intake: 0.475 exhaust: 0.45

Comp - 106460
RPM - 2000 to 6400
Duration Intake 273
Duration Exhaust 275
Lobe Seperation 116
Dur @ .050 lift intake: 238 exhaust: 240
Intake Centerline 114
Valve lift intake: 0.475 exhaust: 0.45

Another concern is air intake temps. I'd never heard of this till I started researching cams but it appears reversion is a real issue. With the overlap you can have the exhaust pressure pushing into the intake manifold in idle and low RPM cruise since the manifold is at a lower intake temp. This causes high IAT2s which is horrible on a blower car as intake temps are the enemy and cause timing to be pulled and HP to drop. It's actually such a huge problem on my car I've purchased a Killer Chiller (http://killerchiller.com/) and will be installing that this winter too. For those not familiar it's a unit that uses the car's A/C to chill the supercharger coolant and it keeps IAT2 temps drastically down. My IAT2 temps cruising on the highway at 70mph on a summer day is normally around 135F. When romping on the car 140s and 150s are common and terrible because I can feel the power fade even without pulling timing. I've read people experiencing IAT2s of 150 ~ 160 at idle with cams due to reversion. Granted that will cool once you get on the throttle some and driving but how long? This might be a real issue for me. Or maybe the killer chiller will keep this under control? It's hard to know.

So my three main questions are:

1) Will cams drop my dynamic CR even further to where I will loose HP? OR will the increased air flow provided by the cams increase HP even if CR drops. Bare in mind I'm at 27.5 PSI of boost so there's plenty of air to go around the motor can consume it.

2) Drivability. Does the Crower stage 3 cam look in the realm of a cam that can be made to drive decent on the street? If not what are your suggestions?

3) How big of an issue is air intake temps with reversion?

Any other info or help is greatly appreciated.

[cgrey8]

...1) Will cams drop my dynamic CR even further to where I will loose HP? OR will the increased air flow provided by the cams increase HP even if CR drops. Bare in mind I'm at 27.5 PSI of boost so there's plenty of air to go around the motor can consume it...

You may not loose a LOT of HP, but the potential is there. There's also the possibility that you'll increase by being able to push more boost. However on Windsors, if you put a radical cam with boost, you wind up loosing PSI because at lower RPMs, the added overlap literally just allows air and fuel to blow right to the exhaust. Boosted engines don't "need" wide duration cams to make power. They actually tend to prefer a milder cam, analyzed from an efficiency standpoint. However people do put more aggressive cams on boosted engines specifically to drop the DCR so the engine doesn't ping at boost. IMO, that's a hack.

...2) Drivability. Does the Crower stage 3 cam look in the realm of a cam that can be made to drive decent on the street? If not what are your suggestions?...

212/212 isn't an aggressive duration, at least it isn't on Windsors. It's a quite reasonable streetable duration. So I can't fault them for duration. The LSA of 114 is also very conservative as well.

...3) How big of an issue is air intake temps with reversion?...

On a boosted engine AT boost, it's hardly an issue. I know high boost temps are not good, but reversion only exists at mild to moderate throttle conditions (i.e. when there's vacuum in the intake to draw the cylinder charge back up). But yes, the wider the duration of the intake lobe, the more reversion you get, hence the more hot air gets shoved back up into the intake.


Because of your decision to go with the -19cc pistons, you've kind of locked yourself into what you have. While 212/212 isn't aggressive, it's a substantial jump from 190/196 and will kill fuel economy and low RPM throttle response even further. I hate to say it, but replacing those pistons is the "better" thing to be doing. I know that's expensive, but that's my opinion.

[MalcolmV8]

You may not loose a LOT of HP, but the potential is there. There's also the possibility that you'll increase by being able to push more boost. However on Windsors, if you put a radical cam with boost, you wind up loosing PSI because at lower RPMs, the added overlap literally just allows air and fuel to blow right to the exhaust. Boosted engines don't "need" wide duration cams to make power. They actually tend to prefer a milder cam, analyzed from an efficiency standpoint. However people do put more aggressive cams on boosted engines specifically to drop the DCR so the engine doesn't ping at boost. IMO, that's a hack.

I see claims of people making 100 whp more just with the cams. Even on the old stock Eaton blowers I've seen guys pick up close to 100 whp with cams so they definitely make HP over the stock 03 Cobra cams. My concern of course is I have such low compression.
With methanol injection on my pump gas tune and of course E85 I don't have detonation or ping concerns.

212/212 isn't an aggressive duration, at least it isn't on Windsors. It's a quite reasonable streetable duration. So I can't fault them for duration. The LSA of 114 is also very conservative as well.

Glad to hear you don't think it's to aggressive for street driving. Or at least reasonable.

On a boosted engine AT boost, it's hardly an issue. I know high boost temps are not good, but reversion only exists at mild to moderate throttle conditions (i.e. when there's vacuum in the intake to draw the cylinder charge back up). But yes, the wider the duration of the intake lobe, the more reversion you get, hence the more hot air gets shoved back up into the intake.


Because of your decision to go with the -19cc pistons, you've kind of locked yourself into what you have. While 212/212 isn't aggressive, it's a substantial jump from 190/196 and will kill fuel economy and low RPM throttle response even further. I hate to say it, but replacing those pistons is the "better" thing to be doing. I know that's expensive, but that's my opinion.

I think the problem is that high IAT2 temps at idle or low cruise heat soak the intake and or sensor because when you get back on the gas or even WOT they don't just suddenly drop. It takes a good 10 minutes plus of highway cruising with good airflow to bring temps back down.

How much do you think it'll kill fuel economy? That's kinda scary lol. I already only get 8 to 10 (mostly in the 8s) mpg on E85 and around 10 to 12 (mostly closer to the 10s) on pump gas.

I've known for years replacing the pistons is what I need to do. It's hard to tear down a "perfectly" good working motor to a bare block and machine and rebuild just to get better pistons. Honestly if I have to tear down to a bare block I'll probably set this iron block aside and grab an aluminum teksid block for weight savings and start over. Like you said, so expensive. I guess I need to think about it. I probably need to just bite the bullet and rebuild a new motor.... ug. Or maybe just put some cams on and if it sucks put the stock ones back and keep them aside for when I do rebuild the motor.

[cgrey8]

...I think the problem is that high IAT2 temps at idle or low cruise heat soak the intake and or sensor because when you get back on the gas or even WOT they don't just suddenly drop. It takes a good 10 minutes plus of highway cruising with good airflow to bring temps back down...

That makes perfect sense that it would take that long to reduce the heat soak at cruise. You are still fighting reversion at cruise due to lower RPMs and being at vacuum loads. At WOT though, the heat soak is gone in about 3 seconds and the intake equalizes to what ever the temp of the boosted air is. So from a normal street condition, this isn't a big deal. But on the track, during those 3 seconds a good tune will be withholding spark advance due to high ACT (aka IAT) temps. The loss of 3 seconds worth of being able to give the engine that spark advance is noticeable.

...How much do you think it'll kill fuel economy? That's kinda scary lol. I already only get 8 to 10 (mostly in the 8s) mpg on E85 and around 10 to 12 (mostly closer to the 10s) on pump gas...

I couldn't honestly say. However if you are already in the 10MPG range on pump gas, I wouldn't think it would be much. There's a massive amount of inefficiency already there. I can't imagine going from stock cams to a mild 212/212 profile cam would do THAT much damage. Like I said, 212/212 is a mild profile. Interestingly, it's the stock duration of the 93-95 302 Cobra cams (different LSA though).

...I've known for years replacing the pistons is what I need to do. It's hard to tear down a "perfectly" good working motor to a bare block and machine and rebuild just to get better pistons...

I wouldn't remachine the block. There's no reason to. I can't think of a reason why a machinist would need to mess with the block. Just replace the pistons and rings. Simple tear-down and rebuild...unless of course you get into it and see something you don't like.

...Honestly if I have to tear down to a bare block I'll probably set this iron block aside and grab an aluminum teksid block for weight savings and start over...

I thought your Cobra was the aluminum block. In that case, I have to 100% agree. Sell the cast iron and replace it with an aluminum block with the components you want. That's not any less expensive. But it's the better bang for the buck...although it is big bucks.

I think we all do things in our builds that in hindsight, we wish we had done differently.

[MalcolmV8]

That makes perfect sense that it would take that long to reduce the heat soak at cruise. You are still fighting reversion at cruise due to lower RPMs and being at vacuum loads. At WOT though, the heat soak is gone in about 3 seconds and the intake equalizes to what ever the temp of the boosted air is. So from a normal street condition, this isn't a big deal. But on the track, during those 3 seconds a good tune will be withholding spark advance due to high ACT (aka IAT) temps. The loss of 3 seconds worth of being able to give the engine that spark advance is noticeable.

It's definitely not 3 seconds on these cars. Especially not with the bigger twin screw blowers. If I just nail it WOT the temps stay where they are and keep climbing. The whole entire blower and blower cooling system is heat soaked. Hence looking at the Killer Chiller which I hear works wonders by using the AC to chill it down.

I couldn't honestly say. However if you are already in the 10MPG range on pump gas, I wouldn't think it would be much. There's a massive amount of inefficiency already there. I can't imagine going from stock cams to a mild 212/212 profile cam would do THAT much damage. Like I said, 212/212 is a mild profile. Interestingly, it's the stock duration of the 93-95 302 Cobra cams (different LSA though).

Yeah the low compression really hammered me on gas mileage. Not that I drive the car for gas mileage but with such a small gas tank it actually becomes an issue. Our local drag strip in KC closed down a couple years ago and now we go up north to Osborne MO which has an 1/8th mile track. It's a solid hours drive each way with 1 E85 pump along the way fairly close to my house. So about 15 minutes into the drive I pull over and fill up. I get to Osborne, made about 13 ~ 15 passes and barely made it home. Limping along very easily on the highway and barely made it back to the E85 pump with about 1 or 2 gallons in the tank. Fill up and go home. People always tell me "well that's not the car you buy for gas mileage" and while yes that's true but it becomes an issue when I'm burning through 2 to 3 tanks a weekend playing around lol. You pay to play right?

I wouldn't remachine the block. There's no reason to. I can't think of a reason why a machinist would need to mess with the block. Just replace the pistons and rings. Simple tear-down and rebuild...unless of course you get into it and see something you don't like.

You know that's exactly what I thought. I called Diamond Pistons since that's what I'm running to get some info on some replacement pistons with less of a dish and the tech was horrified I was considering that. He said that's a really bad idea because my pistons and or rings would not seat properly. He said I should have a machine shop hone it out 1 to 2 thousands to get a fresh surface and then order pistons with 1 or 2 thousands oversize to match what the machine shop did.

I thought your Cobra was the aluminum block. In that case, I have to 100% agree. Sell the cast iron and replace it with an aluminum block with the components you want. That's not any less expensive. But it's the better bang for the buck...although it is big bucks.

Prior year Cobras where. For the supercharged 03/04 models Ford went to the cast iron block. The only reason they gave was "reliability issues with aluminum" but no further details so the real reason is not clear. There are plenty of guys pushing over 1000 whp on aluminum blocks for long periods of time with no issues so clearly they do just fine. From what I've dug up my stock block is 155 lbs where as a teksid is 85 lbs and the newer 05 and up WAP blocks are supposed to be even stronger than teksid and from what I read only weighs 80 lbs. Seems there are no downsides to going aluminum other than money.

I think we all do things in our builds that in hindsight, we wish we had done differently.

Isn't that the truth!

[cgrey8]

...It's definitely not 3 seconds on these cars. Especially not with the bigger twin screw blowers. If I just nail it WOT the temps stay where they are and keep climbing. The whole entire blower and blower cooling system is heat soaked. Hence looking at the Killer Chiller which I hear works wonders by using the AC to chill it down...

Yes, I forgot it's not a centrifugal plumbed up to the engine, it's a screw mounted to the top of the engine. Yeah, heat soak on those is not going away in 3 seconds.

...He said I should have a machine shop hone it out 1 to 2 thousands to get a fresh surface and then order pistons with 1 or 2 thousands oversize to match what the machine shop did...

Hone it yourself with a honing brush and a drill. But I do agree with oversizing the pistons by the amount you hone. Basically you are just scuffing the surface a tad so the new rings have something rough to break in against. That doesn't require a lot of hone...just a roughening of the surface, which is probably about .001" worth of metal that will get removed in both the hone AND the reseating of new rings. The hone alone isn't likely to measure that much removal. But once the rings knock down those rough edges smooth again, that's where your .001-.002" oversize comes in.

Or is there some detail about honing mod motors that makes them more difficult/risky than traditional engines?

Of course if you go aluminum, I'm assuming you can order whatever size steel sleeves you want. I don't know anything about them, but I assume you can re-sleeve them similar to big diesels.

[MalcolmV8]

Or is there some detail about honing mod motors that makes them more difficult/risky than traditional engines?

Of course if you go aluminum, I'm assuming you can order whatever size steel sleeves you want. I don't know anything about them, but I assume you can re-sleeve them similar to big diesels.

When the machine shop bored and honed my block they had torque plates on it. I don't know how required that would be for just a honing.

I'm starting to think I need to just find an aluminum block and rebuild my motor with about 10:1 compression and the cams I want. That will give me quite the monster and a fun car.

I'm pretty sure if all I do this winter is the cams that next winter I'll be tearing it down anyways for pistons and exchanging blocks. Might as well do it all at once since a cam swap on these motors is a ton of work anyways. No sense in doing all that twice.

[cgrey8]

Yeah, you can't bore an engine without torque plates. Otherwise the bores won't be round once you put the torque to the head bolts. So they have to bore the engine while the head bolt threads and surrounding metal are under stress.

But honing isn't about removing metal. In the case of a freshly bored cylinder, the walls of the cylinder are too rough. Too much of the rings would get eaten up during their break-in seating. The hone smooths the rough cuts down so the rings don't get wear too much. And it just makes sense to hone the block with the torque plates in place. Why not?

In the case of a seasoned block, the opposite is true. There's not enough roughness for the rings to break-in in a reasonable amount of time. Without a hone on slick walls, you might be looking at 10+kmiles for the rings to seat instead of 300-500 miles. Some argue the rings may never seat properly. I tend to disagree with that assessment, although I have no facts to base that theory on...only the understanding that metal wears regardless how smooth and lubed it is. So it's my belief that they would eventually seat. But what is undeniable is during that time, they may or may not be sealing worth a damn giving you excessive blow-by. In a boosted application, that's a lot of fuel getting in the crank case. Interestingly, the harder you drive an engine where the rings aren't seated, the more wall-wash the cylinders get. That can help the rings seat but that fuel is also getting into the oil and can increase wear where you don't want it (crank bearings, valvetrain, etc). So yeah, you wanna hone the walls. It doesn't take much to scuff the walls enough to give the rings a surface to wear into. Whether you want to take the block to a machinist to do it or not is completely up to you.

[MalcolmV8]

If I do stick with the cast iron block I'd probably have a machine shop hone it. I honed my honda block myself when I built it and honestly it's not nearly as easy to do with a honing tool in a drill as it is with the fancy equipment at the machine shop. It also didn't look nearly as pretty. It worked though and that motor held up to 20 PSI for a couple years of daily driving no problem. However anything really high HP I'd get professionally done.

I've started looking at prices and teksid blocks can be had for around $400 quite easily. I'm really leaning towards that route.

[MalcolmV8]

Chris,

What's your opinion on flat top pistons? I have a guy telling me that's the way to go. He actually built his motor that way (same car as me). He says the very tiny quench area gives an artificial octane increase due to detonation resistance. He says when an engine gets in the .065-.125 quench range the risk of detonation greatly increases. With a flat top piston he keeps the quench space tiny and runs this setup on pump gas.

Mind you that's 10.7 static CR and 8.7 DCR which seems way to high to me. On the other hand I don't want to dismiss this to quickly or lightly as he does compare that to the new Coyote motors which have 11.0:1 SCR and run boosted applications very well. Now the boosted Coyotes I've personally seen so I know that's true. I've never understood how they get away with 11.0 CR and boost on pump gas but they do. He claims it's the flat top pistons and the tiny quench among other things.

So I got to work calculating things. This is the best I can do on stock specs.

Stock SCR is 8.5. A lot of the specs I was able to find on forums and google.



Here's best guess at stock cam specs. I need to use actual duration and not duration at .050" to calculate valve closing event to try and work out DCR. Depending on which site you find the Cobra specs seem to have this

INT: 184 or 190 deg @ .050/.394 lift
EXH: 196 deg @ .050/.397 lift
114 lobe center, no advance
duration 232/240



So based on that and grabbing the intake valve closing at 50 ABDC we can work out the dynamic stroke



So going back to the first tab we were on I can check the little box for dynamic stroke and get the DCR of 7.5



So now trying to work out new specs you'll notice I have the bore .020 over and a 0 CC (flat top piston) which puts me at a SCR of 10.7



This time I put in the Crower Stage 3 cam specs. Notice how big the valve overlap becomes over stock in addition to the intake valve now closing at 63 ABDC

Crower Stage 3 specs again for reference
INT/EXH - Dur @ .050” Lift: 212°/212° Advertized Duration: 258/258 RR: 1.8/1.8 Gross Lift: .484”/.484” LSA: 114° RPM: Idle to 6700 Redline: 7200



The dynamic stroke calculation



And finally back to DCR. Notice it's 8.7 which is my huge concern with the flat top piston



So looking around I did find this chart too which supports the theory of been way out of pump gases DCR range.



So re-doing those formulas above shooting for a 8.1 ~ 8.2 DCR or so puts me at about 10.0 ~ 10.1 SCR which is around a -4 ~ -5 CC dish. That to me makes more sense but some are saying I'd actually be better off with the flat top because of the better quench.

What are your thoughts on that?

Also bare in mind I'm not limited to purely my 91 pump gas. When running 91 pump I spray water/methanol which lets me get away with a lot. Of course that's under boost. In normal driving it's not spraying. However I'd not be opposed to running Torco in my gas if I have to. Lots of guys run it with great success and lots of boost and timing. I choose water/meth because long term it's cheaper but at this point a few bucks on gas is not bothering me. Also in the summer I do run a lot of E85. I'm just trying to avoid making this an extreme E85 only car that couldn't even run on pump gas.
I know I'm trying to get it all. Great power on E85 and still "sorta" run on pump gas with water/meth or even Torco.

Thanks

[cgrey8]

...What's your opinion on flat top pistons? I have a guy telling me that's the way to go. He actually built his motor that way (same car as me). He says the very tiny quench area gives an artificial octane increase due to detonation resistance. He says when an engine gets in the .065-.125 quench range the risk of detonation greatly increases. With a flat top piston he keeps the quench space tiny and runs this setup on pump gas...

You are talking to someone that knows their stuff. Flat tops are superior for a number of reasons.

• It's been determined that the best combustion chamber is the one with the smallest amount of surface area. Adding dish to a piston, adds surface area. Ironically this flies right in the face of the Dodge Hemi philosophy, but also explains why Hemis are so notorious for running great and instead of barely pinging right when they hit the edge, they explode to the point of destruction as soon as they detonate leaving no room for error in commanded spark.
• The construction of flat tops is simpler so they are often stronger AND lighter than a dished piston.
• Larger surface area is also more surface area exposed to heat. Flat tops don't melt as easily as dished pistons. This one doesn't mean they won't melt. It just means they will resist it more than a dished one.

As for quench, ideal quench is in the .035-.040" range. Some people will squeeze down to .030". And I've heard others say they machine the engine down to quench in the .020s. The vast majority of the benefits are gotten by .040". Tighter quench has minimal improvement, but it's not a LOT. However the benefits of quench diminish as you move away from .040" until you reach .060". After that, quench is assumed to not exist. Larger quench pads improve the benefits. Aluminum heads also improve it. Thus aluminum heads don't require a large of a quench pad as cast iron heads do.

...Mind you that's 10.7 static CR and 8.7 DCR which seems way to high to me. On the other hand I don't want to dismiss this to quickly or lightly as he does compare that to the new Coyote motors which have 11.0:1 SCR and run boosted applications very well..

There's articles out there that talk about people that try to solve their detonation problems with thicker head gaskets and make their problem worse. So it's possible to go from 10:1 down to 9.5:1 by using a thicker head gasket and thus make their detonation problems worse. The point is quench is good. The other point is quench doesn't eliminate the potential. However if you are running E85, you'll have no problem with CR in the 10s. You might have to just control your foot when running pump gas IF you have issues with detonation.

...Now the boosted Coyotes I've personally seen so I know that's true. I've never understood how they get away with 11.0 CR and boost on pump gas but they do. He claims it's the flat top pistons and the tiny quench among other things...

The main thing that gets them this is direct injection. If you don't inject the fuel until you are ready for it, then it's impossible for it to detonate on you. That works up to about 3000RPMs for cruising. Above that and at hard throttle, Direct Injection engines have regular port injectors to make up the fuel demand that the DI just doesn't have the capacity and flow ability to deliver. Direct Injectors have a TINY window to get their fuel delivered hence why they typically run fuel pressures well over 1000PSI. Port injectors don't have nearly as narrow of a window hence why they don't require but 40-60PSI rail pressures.

...Crower Stage 3 specs again for reference
INT/EXH - Dur @ .050” Lift: 212°/212° Advertized Duration: 258/258 RR: 1.8/1.8 Gross Lift: .484”/.484” LSA: 114° RPM: Idle to 6700 Redline: 7200



The dynamic stroke calculation



And finally back to DCR. Notice it's 8.7 which is my huge concern with the flat top piston



So looking around I did find this chart too which supports the theory of been way out of pump gases DCR range.

...

I based my 331 on that chart as well and was told by experts that the chart is a tad conservative to help people not to oversize. Follow the chart, and you are SAFE. So, I sized the combustion chambers and the gasket thickness to give me 8.4 DCR. And after being built, I think actual numbers have me in the 8.35 range. With a 180 degree Tstat, I could not run 87 octane. I had to run 89 to keep from pinging at cruising conditions. Interestingly, my T-stat failed (a fail-open Tstat) and I couldn't get the engine above 140 and so I figured before I replaced it, I'd try 87 octane. Between the broken T-stat and some reduced spark advance in my tune, I found I COULD run 87 octane. So I replaced the T-stat with a 160 and have been running 87 ever since. Now I did have to pull spark advance form all areas AND this did reduce the MAX HP a tad. But I was OK with that.

My point being, I'm running 87 octane regular on an 8.35 DCR CAST IRON headed engine and I believe that possible because of special attention being paid to quench. It did take a 160 degree Tstat to do it though.

So if you aim for 8.7 on a tight quench aluminum headed engine, I wouldn't be surprised if you have no problems on premium. And if you need to reduce the T-stat, that's another option. I'm assuming you are running a 196??? If it's 196, rebuild it with a 180. And if it has ping issues on premium, then try a 160. Although I wouldn't be surprised if the 180 will work just fine for you despite 8.7 DCR.

Now the catch is you are boosting to some seriously high pressures. I don't how how this will affect how high of boost you'll be able to get. Again on E85, no problems. E85 would probably tolerate you going to 12:1. 91 octane premium has limits. I'm just fortunate I live in an area where 93 octane is Premium. Then you say...

...Also bare in mind I'm not limited to purely my 91 pump gas. When running 91 pump I spray water/methanol which lets me get away with a lot. Of course that's under boost. In normal driving it's not spraying. However I'd not be opposed to running Torco in my gas if I have to. Lots of guys run it with great success and lots of boost and timing. I choose water/meth because long term it's cheaper but at this point a few bucks on gas is not bothering me. Also in the summer I do run a lot of E85. I'm just trying to avoid making this an extreme E85 only car that couldn't even run on pump gas.
I know I'm trying to get it all. Great power on E85 and still "sorta" run on pump gas with water/meth or even Torco...

I think you have a great chance of doing that particularly when you have others that have done it, are driving it, and are recommending it.

And from my personal experience with a cast iron GT40p headed 331, I know 8.35 is quite possible on REGULAR. I don't see why 8.7 isn't attainable on premium particularly given you have aluminum heads, particuarly if your heads have a fair quench pad. Windsor heads have HUGE quench pads. 4v heads have less room for quench pads, but if people are still recommending quench for those heads and reporting benefits, then I have to believe the pads are big enough to be worth doing.

[MalcolmV8]

Chris, sorry for the delayed response. I've been going over this in my head so much I got side tracked with responding.

...Now the boosted Coyotes I've personally seen so I know that's true. I've never understood how they get away with 11.0 CR and boost on pump gas but they do. He claims it's the flat top pistons and the tiny quench among other things...

The main thing that gets them this is direct injection. If you don't inject the fuel until you are ready for it, then it's impossible for it to detonate on you. That works up to about 3000RPMs for cruising. Above that and at hard throttle, Direct Injection engines have regular port injectors to make up the fuel demand that the DI just doesn't have the capacity and flow ability to deliver. Direct Injectors have a TINY window to get their fuel delivered hence why they typically run fuel pressures well over 1000PSI. Port injectors don't have nearly as narrow of a window hence why they don't require but 40-60PSI rail pressures.

Humm to the best of my knowledge the Coyotes do not have Direct Injection. Unless they started this recently. I've also never heard of DI not been able to give enough fuel and requiring additional regular injectors. In fact my daily driver is a BMW 335XI which is twin turbo and DI and requires no additional injectors. With just a tune you can push these cars to 400 whp and I've seen guys swap turbos, E85, and get around 700 whp on the stock DI system. So I'd have to say DI can supply all the fuel you need and then some.
The only reason I've ever seen a DI motor have supplemental injectors in the intake track is to clean them. A common problem with DI cars is the oily fumes and mess that recirculates from the PCV system gunks up in the intake runners on the heads and back side of the valves. It actually does it really bad because there's no gasoline ever been sprayed there to clean it off.
In fact here's a pic of what the intake parts and valves looked like on my head when I pulled the intake manifold.



Here's what it looked like after blasting with some walnut shells and soaking in solvent etc.



This maintenance is required every 30 ~ 50k miles or so. Major PITA I did not know about until I purchased a DI car. Now I'd read online that one of the manufactures (I think maybe it was Audi but I forget) added some regular injectors in the intake runner which mists a small amount of fuel just to keep the intake clean and eliminates this maintenance.

I'm assuming you are running a 196??? If it's 196, rebuild it with a 180. And if it has ping issues on premium, then try a 160. Although I wouldn't be surprised if the 180 will work just fine for you despite 8.7 DCR.

I'm running a 170 which is the only aftermarket option available for my car. It's custom made by a guy who separates a 170F t-stat and assembles with the factory cobra back piece that blocks off the pipe. Although I will point out the car puts out a lot of heat and in summer it'll easily be 200F + just because the cooling system can't keep up. I've tried massive Mishimoto radiator, shroud, cooling fans etc. In the end the stock factory radiator, fan and shroud actually worked the best so I switched back to the stock setup. When the weather is cooler it can maintain around 180 ~ 186F. In winter weather obviously it'll run 170 but that doesn't do me any good because it's not a winter driven car.


I appreciate all the feedback and info. I'm seriously considering flat top pistons now.

[plowboy34]

WOW!! that's crazy....how many miles did you have on yours when you found that??

[MalcolmV8]

WOW!! that's crazy....how many miles did you have on yours when you found that??

That was just 50k miles. From what I've read cleanings should be done every 30 to 50k. As nasty as that looks I did not see any degradation in gas mileage or seat of the pants performance. I'm sure there was a small amount, had to be the way it looks, but nothing I noticed. Since the cleaning doesn't make a substantial difference to mileage or power I opt for 50k intervals rather than 30k

[cgrey8]

The 3000RPM thing I was referring to must be outdated info. That's from something I read with Ford's first endeavor into Direct Injection. The systems ran something like 3000PSI to overcome the pressure of air compression AND combustion...and to inject a relatively large amount of fuel in a very short period of time. But they were also using DI to do Just-In-Time (JIT) fuel delivery to avoid detonation so they could run 11:1 SCR on 87 octane pump gas. Normal combustion happens with a spark igniting fuel and a flame front starting at the spark and radiating toward the pistons. While seemingly immediate, there was a definite travel of the flame in the combustion chamber. Detonation is where the pressure builds to the point that the fuel below the flame front ignites and now you have far more fuel burning producing far more pressure than the engine is in a position to handle. Their DI philosophy was to deliver the fuel during combustion so the entire fuel payload wasn't in the cylinder all at once and capable of spontaneous detonation of the entire payload as happens with port injectors. But to do that requires some pretty precise timing and consistency. With modern day processors and controllers capable of well over 1GHz speeds, that's now quite attainable.

However it sounds like based on what you are saying, newer DI systems are finding that they can simply fire the injector earlier and earlier approaching more what port injection accomplished and thus they can use the same DI system without "auxiliary" port injectors to make up the difference. So at lower RPMs and loads, they can do the JIT fuel delivery but as the RPMs and loads go up, they just fire the injector earlier and earlier and basically attain the same conditions the auxiliary port injectors accomplished. Or perhaps they just found a more accurate high-flow-high-pressure direct injector design??? I don't know. I'd like to.

As for the cake in there, yeah that's pretty typical of what PCV does. The 302 I rebuilt into a 331 had cake far worse than that in the upper and lower intake. It was quite a pain cleaning all that gum out of there. I have noticed that neither my old 302 nor the 331 cake like that with the synthetic oil I use. It still has a definite film, but it doesn't seem to cake nearly so much. Was the engine you are showing there using synthetic oil???