Block is back from machine shop (temporarily)

[cgrey8]

I need the following things:

• Combustion Chamber CC. In this case, I'd be using 58cc.
• Piston deck clearance (how far in the hole or above the deck the pistons are at TDC). Your link below indicates a 1.165" compression height. ASSUMING a block deck of exactly 8.200", that puts the piston in the hole .010". Math to figure this is Deck Clearance = Block Deck Height - Rod Length - 1/2 stroke - Compression Height of Piston
• Piston dish CC. For flattops, this is the CC of the valve reliefs. Your link below suggests this is 5cc dish.
• Head gasket crush thickness you plan to use
• Exact Cam PN. I'm assuming you are talking XE264HR-12, although Comp Cams often makes an HR-12 and HR-14 version of their XE series cams and the numbers are often a good bit different.
• Engine's CID including any boring and stroking. Your link indicates this kit is for a 331 stroker that IS NOT bored .030" over (piston bore of 4.000"). So actual CID is 327, not 331.
• Connecting Rod length. 331/347 stroker hits have a 5.4" and 5.315" option. Your link shows this kit to use a 5.4" rod.

With that info, I can run the DCR numbers and see what it comes up to. Some of this info you may not be able to know until the machine shop measures it for you or you get parts to install and get a measurement from. Engine builders often assemble a stroker kit without the piston rings so they can verify fit on everything. If you have parts, but aren't ready to assemble the engine yet, that might be an option for you to get deck clearance values.

The CC of the pistons should be posted on the piston's website for whatever model piston you got.

Latest edits made in RED after OP posted a link to which stroker kit is being used.

[Soul]

http://www.coasthigh.com/Ford-331-Flat- ... f331-1.htm

this is the kit I ordered (30 over)
Rod Length 5.400

[cgrey8]

I thought of more stuff I need so I edited the original post. Read up for details...

[Dave]

Chris, that link is kind of confusing on the bore size. Up on top they do say it's bored 0.030 over but down below they say "base bore of 4.000". I think that's where the confusion is coming in.
Dave

[cgrey8]

I made some assumptions about gasket crush thickness. If you use the same gaskets I'm going to use (FelPro 1011-2), then your crush thickness will be .039" which yields the following numbers:

The quench isn't that great with the pistons in the hole. But the DCR is below the 8.5 mark which is good. As-is, you should be good to run premium without too much trouble although things can be improved. If you do deck the block down to make the pistons even with the deck, your quench will tighten to much better values:

The tighter quench pushes you closer to 8.5, but with aluminum heads, I wouldn't be worried about that with a well planned quench. Either setup pretty much requires that you run 91 octane premium. If you can get 92/93 octane in your area, then the max goes to about 8.7. This also assumes a 180° T-stat. A 160° will afford you a tad more. And obviously a 195° Tstat lowers these max numbers. Notice:

(these numbers are a tad conservative, but good a good guide to plan against)

Dave, if the bore is actually 4.030", then the DCR values will go up by ~.1 point for both counts. In that case, I'd say you may want to split the difference and deck so the pistons come to about .005" from the deck. That number (including the .030" overbore) would look like this:

This keeps you below 8.5 DCR and gets you into the "meaningful" quench distance range. A .045" quench isn't ideal, but it is in the range of being beneficial/meaningful. If I had the choice, I'd take it over a solution that put me at something greater.

[Dave]

Chris, another question, why is the stroke in your data chart listed as 2.5801? It's only giving a displacement of 260 ci. I do sometimes read what is posted.
Dave

[cgrey8]

Static Compression Ratio (SCR) calculations would use a 3.25" stroke. If I unselect the checkbox, I get this:

However given this is a Dynamic Compression Ratio (DCR) calculation, the stroke shown is the "effective" stroke, or the portion of the stroke from when the intake valve closes to TDC. The calculator comes up with the effective stroke length based on the cam specs, crank stroke, and rod length.

The larger the duration cam, the further up the bore the piston is before the intake valve is closed. At high RPMs, that's more time for more air to get shoved into the cylinder thanks to high velocity airflow and the air's inertia. However at low RPMs, the air doesn't have nearly enough inertia to hold itself in the chamber while the intake valve is open and the piston is moving upwards in the bore. The result is a portion of the cylinder charge gets pushed back up into the intake. This is why high duration "big" cams don't make as much torque at low RPMs as milder cams (less air being held in the cylinders which effectively reduces the CID of the engine at those RPMs). It's also why wider duration cams have a harder time producing vacuum in the intake at idle. On EFI, this isn't a big deal, but carbs need a combination of vacuum or airflow through the venturis to atomize fuel into the air as it is aspirated into the engine. So weak vacuum at idle (low flow) is not good for carbed engines. To combat this on big cammed engines, you can use a dual-plane intake. Dual Plane intakes separate sequentially firing cylinders so that the cylinder aspirating air in on its intake stroke doesn't have its vacuum being killed by a cylinder that is pushing air back into the intake on its compression stroke with the intake valve still open.

Make sense?

[Soul]

Chris,

Your amazing for running that stuff for me, yes it is .30 over kit, there are actually 2 listed in there. Yes the 264-12 is the one I was going to run, for headgaskets and stuff that is greek to me, I'll probably clone the leftovers as to what you made it

[cgrey8]

I'll need to rerun the calculations assuming the XE264HR-12. All my calcs were based on the XE264HR-14. There won't be much difference, if any. But I'll check just to make sure there aren't some surprises in the numbers. If I find significant discrepancies, I'll repost new captures.

[cgrey8]

Well, it does change things some going to the XE264HR-12 (Comp PN: 35-349-8). That adds a little more to the effective stroke which in turn ups the DCR. The durations are the same but Comp changed the Intake Centerline and Lobe Separation Angle on this cam as compared to the XE264HR-14. Notice what it does to the calculation:

If you haven't bought RRs for the AFRs, then get 1.7RRs and use the XE264HR-14 (Comp PN:35-320-8) since it is specifically designed to work with 1.7RRs. It won't hurt it to run 1.6s, the valves just won't open as far as they would with the 1.7s. AFR heads can really take advantage of the wider opening at the higher RPM/Flow conditions allowing that cam to continue a strong pull right to 6000RPMs no question. At lower RPMs, you'd never be able to tell the difference between 1.6s and 1.7s.

If you already have the XE264HR-12, then that's going to be pushing things to try to optimize quench AND maintain below 8.5 DCR. If I had to choose though, I'd choose a tighter quench vs "hoping" that going with a lower compression will keep the ping away. There's been reports of people with 10:1 SCR engines that lowered the SCR down to 9.5 using thicker gaskets and wound up with worse ping than he had with the thinner gaskets purely due to the loss of quench. Proper quench is that important. So for the tiny difference in performance between the two cams, I'd go with the XE264HR-14.

[Soul]

Ya the xe264-14 with 1.7's look like they would be a better fit, the head decking has me concerned ( I'm still kinda new to all this, quench vs Compression ). I'll do some research so I understand better what your telling me that way I can contribute something back to the conversation. I really appreciate you taking the time to crunch this stuff for me. I'm just scared I will get to high and pump gas will be an issue.

[cgrey8]

That's why you do this analysis NOW...before the engine is built.

[Soul]

lol ya I know, this engine build was from a ford engine builders book is where I'm stealing the majority of it from. They did 185 afrs on a flat top 331, and they used the xe264-12 cam. Like a said b4 and can't stress enough I'm glad there is some one to keep me from screwing up

[cgrey8]

There's a possibility that the engine builder's book was using pistons with deeper valve reliefs. 5cc for flat top piston dish is fairly shallow. There's a possibility they were using dual-relief pistons (reliefs for both standard and TFS heads). With effectively 4 sets of relief eyebrows cut into the piston, the dish volume can get upwards of 10cc. That much volume will drop the CR significantly...more than enough for the XE264HR-12 to be used on premium pump gas. So while they did it, if you don't get EVERYTHING identical to what they did, then you may not be as impressed as they were with what you end up with.

The good news is you don't have to be exact. You just need to know what to look out for and you won't be disappointed.

[Soul]

OH now that you said that they were using pistons for twisted wedge heads...