Info on L98 Corvette Heads - The 1947 - Present Chevrolet & GMC Truck Message Board Network

JRB · 05-28-2006, 11:45 PM

I am putting together a TPI system on my 67 327. Now the heads that I am going to put on it have 58cc chambers. I know this is going to pump up the compression on this thing big time. I am guessing 10 to 1 or higher. I also know that the burn characteristics is different from Iron to Aluminum heads. Has anyone put something similar together and what kind of outcome did you have with it? Thanks in advance for any info you can give.

JRB

67_C-30 · 05-29-2006, 12:33 AM

You shouldn't have any problems. We've run as high as 11:1 engines with a aluminum heads and EFI. Aluminum heads dissipate heat much better than do iron heads allowing more CR on pump gas. Depending on what pistons you use, you are going to be a little over 10:1. The numbers below are for a 2 valve relief 7cc flattop piston, figured with a .030" overbore (which is actually a 331 cu in engine)

Compression Ratios
58-10.3
62-9.8
64-9.6
76-8.4

**MikeB** · 05-29-2006, 10:14 AM

Do a Google search on "compression ratio calculator" and you will get thousands of hits. You may also want to learn about "dynamic compression ratio", which factors in your cam's intake valve closing point. This calculation is a more accurate indication of cylinder pressure.

If your 327 has flat top pistons w/ 4 valve reliefs, 9.025" deck height, and .038" gaskets, your static CR with 58cc heads will be around 9.6:1 -- which is no issue at all with aluminum heads and even a mild cam.

qksilver · 05-29-2006, 09:25 PM

Mike is right, those heads won't bump you that high.

Karl Hoh · 05-29-2006, 11:01 PM

A general rule of thumb was to add 1 point of compression when going from iron to aluminum heads to compensate for faster heat dissipation of the aluminum. Remember, the more heat in the heads, the better combustion efficeincy you will have. Combustion efficiency is the key to making HP.

JRB · 05-30-2006, 11:12 AM

Thanks for the Info.
I am bidding on a set of heads on EBAY and the bidding is up to 325 clams. The thing is with another 100 dollars in shipping I am at 425 for a set of heads that have 90000miles on them. I contacted a person at superflow heads in Vancouver Washington and they can get me a set of brand new CNC heads exactly the same as the ones on ebay for 625. I think I am going to spend the extra 200 and get the new ones.
JRB

05-28-2006, 11:45 PM	#1
JRB Senior Member Join Date: Nov 2005 Location: Portland Oregon Posts: 287	Info on L98 Corvette Heads I am putting together a TPI system on my 67 327. Now the heads that I am going to put on it have 58cc chambers. I know this is going to pump up the compression on this thing big time. I am guessing 10 to 1 or higher. I also know that the burn characteristics is different from Iron to Aluminum heads. Has anyone put something similar together and what kind of outcome did you have with it? Thanks in advance for any info you can give. JRB

05-29-2006, 12:33 AM	#2
67_C-30 I have a radical idea! Join Date: Jan 2005 Location: Sweet Home Alabama! Posts: 6,513	Re: Info on L98 Corvette Heads You shouldn't have any problems. We've run as high as 11:1 engines with a aluminum heads and EFI. Aluminum heads dissipate heat much better than do iron heads allowing more CR on pump gas. Depending on what pistons you use, you are going to be a little over 10:1. The numbers below are for a 2 valve relief 7cc flattop piston, figured with a .030" overbore (which is actually a 331 cu in engine) Compression Ratios 58-10.3 62-9.8 64-9.6 76-8.4 __________________ '67 C-30 Dually Pickup 6.2 Turbo Diesel, NP435 ‘72 C-10 SWB , 350 4bbl, TH350 '69 C-10 SWB , 250 L6, 3 OTT '69 GMC C3500, dump truck, 351 V6, NP435 '84 M1009 CUCV Military Blazer 67 C-30 Turbodiesel build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254096 My trucks http://s226.photobucket.com/albums/d...ediafilter=all Member of the 1-Ton Club!

05-29-2006, 10:14 AM	#3
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	Re: Info on L98 Corvette Heads Do a Google search on "compression ratio calculator" and you will get thousands of hits. You may also want to learn about "dynamic compression ratio", which factors in your cam's intake valve closing point. This calculation is a more accurate indication of cylinder pressure. If your 327 has flat top pistons w/ 4 valve reliefs, 9.025" deck height, and .038" gaskets, your static CR with 58cc heads will be around 9.6:1 -- which is no issue at all with aluminum heads and even a mild cam. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

05-29-2006, 09:25 PM	#4
qksilver Senior Member Join Date: Dec 2004 Location: Southern Pines NC Posts: 3,853	Re: Info on L98 Corvette Heads Mike is right, those heads won't bump you that high.

05-29-2006, 11:01 PM	#5
Karl Hoh A little east of nowhere Join Date: Feb 2006 Location: LaBroquerie,Manitoba Canada Posts: 168	Re: Info on L98 Corvette Heads A general rule of thumb was to add 1 point of compression when going from iron to aluminum heads to compensate for faster heat dissipation of the aluminum. Remember, the more heat in the heads, the better combustion efficeincy you will have. Combustion efficiency is the key to making HP. __________________ 68 C10 250 4spd 69 C20 327 4spd 69 910 250 3spd 80 K10 350 4spd 76 C60 366 5spd school bus "THERE'S NOTHING YOU CAN BREAK THAT SOMEONE CAN'T BE PAID TO REPAIR"

05-30-2006, 11:12 AM	#6
JRB Senior Member Join Date: Nov 2005 Location: Portland Oregon Posts: 287	Re: Info on L98 Corvette Heads Thanks for the Info. I am bidding on a set of heads on EBAY and the bidding is up to 325 clams. The thing is with another 100 dollars in shipping I am at 425 for a set of heads that have 90000miles on them. I contacted a person at superflow heads in Vancouver Washington and they can get me a set of brand new CNC heads exactly the same as the ones on ebay for 625. I think I am going to spend the extra 200 and get the new ones. JRB



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