C4 Decking heads, up the compression
Thread Starter
5th Gear
Joined: Apr 2010
Posts: 5
Likes: 0
From: Perth Western Australia
C4 Decking heads, up the compression
Hi, I have recently purchased my first Corvette(first American Car). It is a 1988 C4. I want to up the performance a little without spending a lot of money. I am thinking of getting the heads cleaned up and decking them 20 - 40 thou to bring up the compression and a sett of headers. Any thoughts would be appreciated. Thanks
Race Director
Joined: Jun 2004
Posts: 13,957
Likes: 706
From: WI
That's an option, you could add a thinner head gasket thought too. I used the 1094 and it worked well. Headers are good but the rest of the exhaust back is really poor stock so address that as well. If you will have the heads off I would do light porting and port matching then add new springs and 1.6 roller rockers.
Tech Contributor
Joined: Oct 2008
Posts: 3,729
Likes: 190
From: Custer, WI
That's an option, you could add a thinner head gasket thought too. I used the 1094 and it worked well. Headers are good but the rest of the exhaust back is really poor stock so address that as well. If you will have the heads off I would do light porting and port matching then add new springs and 1.6 roller rockers.
Man speaks the truth. lol
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
I agree...intake gasket is too thick for the quench/knocking issue. (Google quench). Yours is twice recommended range.
I also REALLY like the idea of having your head shop swap springs and do some pocket head porting while the head is off. That plus, headers/exhaust will be helpful. Add (at least) bigger tubes to your intake (if not bigger base as well) to complete the package.
That's probably the best/cheapest upgrade(s) you can make.
I also REALLY like the idea of having your head shop swap springs and do some pocket head porting while the head is off. That plus, headers/exhaust will be helpful. Add (at least) bigger tubes to your intake (if not bigger base as well) to complete the package.
That's probably the best/cheapest upgrade(s) you can make.
Pro
Joined: Jun 2009
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From: OR
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Thread Starter
5th Gear
Joined: Apr 2010
Posts: 5
Likes: 0
From: Perth Western Australia
Define doing the heads? What I mean is pulling the heads off, looking at how I can clean up factory casting, porting, valve springs even seats and valves if neaded. I would also like to know if anyone has had there factory heads decked(20 - 40 thou) to bring the compression ratio up. With decking and a thinner gasket, I would like to bring the comp ratio up from 9.5:1 to around 10.5:1. I have done this other motors for excellent results( and near no extra cost whilst the heads are off).
Last edited by Sven1steve; Apr 14, 2010 at 02:34 AM.
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Le Mans Master
Joined: Jul 1999
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From: jackson nj
I was going to have my 89's heads "re-done" for drag racing, even though I only am building a 5200-5500 rpm engine combo. One of the things I was having done was to increase the valve size from 1.94/1.5 to 2.0/1.55 (like the LT-4 and LS-1) but with the cost of changing the valves, springs, comp valve job and milling it was over 1K. Then I contacted and purchased Freedom heads from Patriot for $800 with CNC chambers, 58cc chambers, 2.02/1.60 valves and springs. The "plans" for my car may include higher the 5500 rpm, which is why I went with the larger valves, but even at lower RPM's you should see decent power gains, and I would consider a cam change at the same time as your half way there already. Also, when installing my headers the car did not pickup any power or ET, but in all fairness, I did not do a custom tune as the $300+ cost for the one mod did not seem worth the expense (and subsiquent cost to retune for the H/C change coming), so I'd stay with the stock tubular manifolds if you don't plan on going "deep" into mods, that will save some money for you.