Porting GT40/Explorer/Cobra lower intakes

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cgrey8
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Porting GT40/Explorer/Cobra lower intakes

Post by cgrey8 »

TMoss Porting Tech Doc>Stock Engine Intake Ramblings
I read this article years ago by Tom Moss of TMoss porting touting how he recommends porting stock intakes over buying aftermarket intakes for EFI systems because the stock intakes, after being ported, actually perform better across the street RPM range. While the aftermarket intakes win the MAX HP numbers, his dyno tests prove that a stock ported intake will actually produce higher AVERAGE HP numbers across the RPM range that is typically used on the street. I believe in stock form, the Cobra intakes are good to about 350hp. The Explorer intake is slightly more conservative and only gets to about 330hp. In either case, they become a restriction getting there and to get any higher, you really need to port them. But when ported, they are good to around 400hp. That seemed like a LOT to me at the time, but I couldn't deny actual dyno tests.

I communicated with Tom a few times asking for clarification on certain things in his documents and we also discussed my intentions for the 331 that I'm now in the process of. He told me that while there is potential in porting the GT40p heads, far more of the potential will be unleashed in porting the intake. Well now that I have one of these intakes off the engine to look at, I'm starting to see what he was talking about.

First off, the ports in the Explorer intake are noticeably smaller than the ports in the mating GT40p head. Just opening them up and doing nothing more would be a huge benefit and where a majority of the gains come from. Notice the difference between the GT40p port (typical of all) and the intake's #8 cylinder port:
Image
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Also note that there's room to port the head port slightly larger, but not much. However it's going to take quite a bit of cutting and grinding to get the intake port as large as the head port is in stock form.

Another tip Tom says I'd need to do is weld up the knees of the stock intake to allow me to port the #1 and #5 port runners straight. In stock form, almost all of the ports have a bend in them as they "straighten" the air to enter the head. However the front two ports (#1 & 5) are the worst. The #8 port is the straightest port in the entire intake. Notice as I progress from #8 back to #5...
Port 8:
Image

Port 7:
Image

Port 6:
Image

Port 5:
Image

Besides the output ports, notice how much material needs to be taken out deep in the ports to get these things straight...hence the need for those 6" shank porting bits.

The port gets longer and more deviated. The passenger side is almost the same. However the issue is not quite as bad on the passenger side since the head accepts air in at the same angle that the runners are pointing. On the driver's side, the intake is moving the air "forward", but the heads pull the air backward on that side of the engine which slows the air down more for the driver's side as compared to the passenger side.

Here's where you really see the need to weld up the intake before porting:
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My intention with these pics is to illustrate where the welds would need to go and just how much would need to be welded up. Any ideas on how much a shop would charge to puddle up enough aluminum in those knees to allow me to port the intake properly?
...Always Somethin'

89 Ranger Supercab, 331, ported GT40p heads w/1.6RRs, Crane Powermax 2020 cam, ported Explorer lower, FMS Explorer (GT40p) headers, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, A9L w/Moates QuarterHorse, Innovate LC-1, James Duff traction bars, iDelta DC Fan controller

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Re: Porting GT40/Explorer/Cobra lower intakes

Post by MalcolmV8 »

My local shop usually charges $30 cash for most small jobs like that.

Is there a local porting shop you can use to do that? Seems like one of those jobs where a lot of skill and practice on many intakes would do you some good. I imagine a porting shop would have a flow bench too so they could match the runners. Either way keep us updated with pics. Interesting stuff.
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Re: Porting GT40/Explorer/Cobra lower intakes

Post by cgrey8 »

I'll be doing the porting myself, but I need someone with aluminum welding abilities and skills to weld up those knees.
...Always Somethin'

89 Ranger Supercab, 331, ported GT40p heads w/1.6RRs, Crane Powermax 2020 cam, ported Explorer lower, FMS Explorer (GT40p) headers, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, A9L w/Moates QuarterHorse, Innovate LC-1, James Duff traction bars, iDelta DC Fan controller

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Re: Porting GT40/Explorer/Cobra lower intakes

Post by cgrey8 »

Here's another TMoss document talking about the virtues of the GT40 lower:
What are the Power Capabilities of the GT40 Family Intakes?
...Always Somethin'

89 Ranger Supercab, 331, ported GT40p heads w/1.6RRs, Crane Powermax 2020 cam, ported Explorer lower, FMS Explorer (GT40p) headers, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, A9L w/Moates QuarterHorse, Innovate LC-1, James Duff traction bars, iDelta DC Fan controller

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Re: Porting GT40/Explorer/Cobra lower intakes

Post by cgrey8 »

I took my intake to the welding shop to have the knees puddled up before I port it. I showed it to them and they thought it'd take some time to puddle up enough aluminum to fill the area I circled. So I emailed Tom Moss and got a response back later that day. Tom confirmed that the knees on the bottom of the intake don't need to be welded up. He's never had an issue with those areas needing welding attention. So I called the welding shop back and got them to only weld on the top, not the bottom. That saved me about $50. So this is what I got for $40...

Runner 1:
Image
Image

Runner 5:
Image
Image

Once I get done porting the heads, I'll begin port work on the intake. I'll post pics of that progress as I get to them. I almost expect the intake porting to go faster than the heads...8 less ports and aluminum is softer than cast iron so it'll likely cut faster.


Now if I can just get the welds cleaned up to look this pretty:
Image
Of course this intake was bead-blasted before the welds were done and the welder used shield gas, which it appears wasn't used or wasn't used heavily enough on my welds hence all the bubbles. As long as the welds are solid, that's all I really care about since these are not load-bearing...just holding back atmosphere. It would've been nice if they were cleaner looking on the outside though.
...Always Somethin'

89 Ranger Supercab, 331, ported GT40p heads w/1.6RRs, Crane Powermax 2020 cam, ported Explorer lower, FMS Explorer (GT40p) headers, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, A9L w/Moates QuarterHorse, Innovate LC-1, James Duff traction bars, iDelta DC Fan controller

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