302 Compression ratio troubles

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Jan 23, 2009 | 12:38 PM

motorhead66

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From: Lincoln, NE

302 Compression ratio troubles

I am rebuilding the 302 for my 78' F150 4x4 and I am having a hard time getting a good solid estimate on my compression ratio. For starters I can't seem to get a rock solid cyclinder head volume. The casting number is C9TE-C which on the internet indicates a 58.2cc head but in the book that I purchased it indicates that it is a 69cc head. Can anyone confirm exactly what CC my heads are? I have run the numbers several times and I keep coming up with an average of 8.3:1 with a .041" gasket. Is this a good average CR for a 302? Does anyone suggest a thinner gasket to pump this up alittle? Is there a thinner gasket available? Here are my numbers so feel free to run the them and check my work.

Bore: 4.030"
Stroke: 3.0"
Deck height: .026"
Gasket: .041" X 4.1" suggestions are welcome
Piston volume: 3cc flat with 4 valve reliefs and a center divit
Head volume: 69cc exact volume is questionable.

Feel free to edit the numbers as you see fit.
Thanks for your help and advise.

Jan 23, 2009 | 12:48 PM

Conanski

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Joined: Jun 2006

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From: Ottawa, Ontario

These are '69 heads so I seriously doubt they have the larger chambers. If the heads are indeed 69cc(you'll have to measure them to be sure), they are not a good choice IMO, there's no reason to run anything less that 9:1 on either a carb or EFI motor.

Jan 23, 2009 | 12:54 PM

MBDiagMan

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From: NE Texas

I have a chart at home that should show that head. Without looking though, C9 means a design from 1969. There should not have been any 69cc heads in 69. I would think that 58cc would be correct. If it is correct and you are describing flat top pistons, you are looking at about 9.5:1 compression ratio.

Using a 302 to haul around a 4X4, believe me, you will need all the compression and anything else you can come up with to build torque. My 78 4X4 has a mild 400 and doesn't haul the big thing around good enough to suit me.

For this heavy truck you need low speed torque and LOTS OF IT! Don't even think about camming this engine up or anything like that. In fact about the only mod that would give you any significant low speed torque increase would be small tube, full length headers. The problem with that is that I doubt you can get any for a 302 in a 78 4X4. The trucks originally came with a 300 I-6, a 351M or a 400.

Jan 23, 2009 | 02:10 PM

Kemicalburns

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From: Bend,OR

man you sure got a woody for those long tube headers dont you. haha long tube headers have there purpose but can not be run in every application not to mention getting the exhaust routed properly is also a pain and causes some pretty harsh bends to get around the Tcase.

if you run the right combo of parts there are ways to get the results you want but remember there is no replacment for displacement and its gonna cost regardless.

Jan 23, 2009 | 02:34 PM

MBDiagMan

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Joined: Dec 2004

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From: NE Texas

I'll tell you what! Go do some dyno work and gather some data. You will find that for the money and effort spent, you won't find anything else that will add low speed torque like small tube, full length headers.

The only other thing that will add SIGNIFICANT low speed torque in such quantity is adding displacement, particularly due to more stroke.

Sure, you can cam up, manifold up, and head up, but you will be moving the torque peak to a higher RPM. This will drastically improve your horsepower calculation, but it will kill the low speed torque which is what is needed in one of these heavy trucks with big tires. BTDT!

Nothing is as simple and inexpensive for the torque gain as headers. Shorties will NOT make a significant low speed torque improvement.

You are correct about the trouble fitting an exhaust system in this four wheel drive chassis. I have one so I know the restriction that you're talking about. That said, what sounds easier and more effective, a total engine build or a little work bolting on headers and then a trip to the muffler shop?

Jan 23, 2009 | 02:38 PM

MBDiagMan

Cargo Master

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From: NE Texas

Ski always comes through with the details. His table shows 58 CC as I expected.

Jan 23, 2009 | 05:30 PM

motorhead66

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From: Lincoln, NE

Thanks guys for all your insight into this matter. Your feedback is always great. I am actually running a great pair of hookers on my transition 302 (the one I am running until i get this one ready or until it melts down, an old 302 from a Granada) a fellow 4x4er at a well know Nebraskan salvage yard suggested using a set of headers from a 77 bronco small tube long style. they fit great except for the clutch linkage was in the way, and ends of the headers turn inward at the end. I took them to a welder buddy and we massaged the ends to point more aft. All I notice is that the engine breathes much better. The sucky part is that there isn't any standard exhaust systems for this application so the duals that I had installed were "bent to fit". With all the restrictive corners the headers are kinda canceled out.