243 heads questions
Thread Starter
Burning Brakes
Joined: Jan 2007
Posts: 833
Likes: 2
From: Boca FL
243 heads questions
I have a bare set and I have the light weight valves for them; will I need to do anything special to install those using Comp 918 springs? Will I need shorter push rods and will the use of a thinner head gasket and or shaved heads change the length needed?
How much to shave off stock 243s to get the 62cc chambers; is this preferred over the thinner gaskets or vise versa?
Mods will be going into/onto a 99 LS1 with 56000 mi.:
TSP228R 581/581 114LSA Comp 918 springs
KOOKS 1 3/4 with hiflow cats, 3" to the back
243 heads
Still looking for that 200.00 LS6 intake. (curse those other biders on ebay, lol)
Just running the Blackwing, hiflow air bridge, and the 85mm MAF now.
Looking to get close to the 400 mark, with good torque under the curve, just a street driver with no track interest, (not yet anyway).
Thanks to all that can help. Steve
How much to shave off stock 243s to get the 62cc chambers; is this preferred over the thinner gaskets or vise versa?
Mods will be going into/onto a 99 LS1 with 56000 mi.:
TSP228R 581/581 114LSA Comp 918 springs
KOOKS 1 3/4 with hiflow cats, 3" to the back
243 heads
Still looking for that 200.00 LS6 intake. (curse those other biders on ebay, lol)
Just running the Blackwing, hiflow air bridge, and the 85mm MAF now.
Looking to get close to the 400 mark, with good torque under the curve, just a street driver with no track interest, (not yet anyway).
Thanks to all that can help. Steve
Last edited by coanan; Jan 28, 2008 at 08:42 PM.
Safety Car
Joined: May 2006
Posts: 3,799
Likes: 1
From: Northern Virginia
St. Jude Donor '08
You want to avoid the 918 springs. There have been reports of failures with these. Go with the 921s instead.
Milling the heads will increase the compression ratio, which will bump up HP + TQ.
Milling the heads will increase the compression ratio, which will bump up HP + TQ.
Drifting
Joined: Mar 2002
Posts: 1,298
Likes: 12
From: Salt Lake City UT
Lightweight valves make using 918 springs possible but it may be safer going to patriot dual or 921 comps. I am not sure lift with your cam but it probably is around .590 at .050. This is pushing close to upper limits of 918 springs. Again the lightweight valves make this more tolerable.
I believe the lightweight valves are slightly longer than standard non hollow valve 243 heads so you may need to check for correct pushrod length.
If you run 62 cc heads (milled 65 stock approx .015) and run a Cometic .040 head gasket you will probably have approx. 11.1 compression ratio. This may let you use a 7.350 or 7.400 (stock length) pushrod.
I have a similar setup and run 7.350 pushrods but I do not have the lightweight valves.
Always double check for correct pushrod length. This setup should net you approx. 410 RWHP.
I believe the lightweight valves are slightly longer than standard non hollow valve 243 heads so you may need to check for correct pushrod length.
If you run 62 cc heads (milled 65 stock approx .015) and run a Cometic .040 head gasket you will probably have approx. 11.1 compression ratio. This may let you use a 7.350 or 7.400 (stock length) pushrod.
I have a similar setup and run 7.350 pushrods but I do not have the lightweight valves.
Always double check for correct pushrod length. This setup should net you approx. 410 RWHP.
Last edited by J.R.; Jan 28, 2008 at 09:35 AM. Reason: correct info
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
I have a bare set and need valves and spring seats. I have a chance to buy the light weight valves for them; will I need to do anything special to install those using Comp 918 springs? Will I need shorter push rods and will the use of a thinner head gasket and or shaved heads change the length needed?
Will the valves and spring seats work from the 853, 241, 806 heads? Really need to keep the costs down and was hoping for donated valves and spring seats. LOL.
How much to shave off stock 243s to get the 62cc chambers; is this preferred over the thinner gaskets or vise versa?
Mods will be going into/onto a 99 LS1 with 56000 mi.:
TSP228R 114LSA Comp 918 springs
KOOKS 1 3/4 with hiflow cats, 3" to the back
243 heads
Still looking for that 200.00 LS6 intake. (curse those other biders on ebay, lol)
Just running the Blackwing, hiflow air bridge, and the 85mm MAF now.
Looking to get close to the 400 mark, with good torque under the curve, just a street driver with no track interest, (not yet anyway).
Thanks to all that can help. Steve
Will the valves and spring seats work from the 853, 241, 806 heads? Really need to keep the costs down and was hoping for donated valves and spring seats. LOL.
How much to shave off stock 243s to get the 62cc chambers; is this preferred over the thinner gaskets or vise versa?
Mods will be going into/onto a 99 LS1 with 56000 mi.:
TSP228R 114LSA Comp 918 springs
KOOKS 1 3/4 with hiflow cats, 3" to the back
243 heads
Still looking for that 200.00 LS6 intake. (curse those other biders on ebay, lol)
Just running the Blackwing, hiflow air bridge, and the 85mm MAF now.
Looking to get close to the 400 mark, with good torque under the curve, just a street driver with no track interest, (not yet anyway).
Thanks to all that can help. Steve
Seats are part of the seal if you use the new design (02+) and you can get them from GM. Shims can be bought from Comp that go right over the top of the seat/seal. They are available as individual thicknesses or as a kit with all three thicknesses. You want the 1.25" OD shims shown below.
Milling will increase compression, thinner gasket provides better quench and will allow more timing. Consider both, but use a dynamic compression calculator to sort it out. If you go thinner, surface finish on the heads is critical so don't let just anyone mill them. The requirements for the surface finish can be found on Cometics web site.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Tech Contributor
Joined: Sep 2005
Posts: 1,731
Likes: 82
From: New Market AL
Comp has redesigned the 918 beehive springs, and they will replace your older 918 springs with a brand new set. This is from my personal experience, and not some urban legand. I called their tech support, and gave them the batch number from the 918's that I had recently purchased (off Ebay no less). They said that batch was not on their watch list, but that they would prefer to swap them out anyway. I received a set of new design springs 2 days later, with a return shipping label for my original set. Not bad customer service there. 
The new 918 springs have been tumbled, which provides the bling finish. The max. lift is up from .600" to a conservative .620". I have around 4000 miles on my 918 springs, with zero problems.
The new 918 springs have been tumbled, which provides the bling finish. The max. lift is up from .600" to a conservative .620". I have around 4000 miles on my 918 springs, with zero problems.
Thread Starter
Burning Brakes
Joined: Jan 2007
Posts: 833
Likes: 2
From: Boca FL
Comp has redesigned the 918 beehive springs, and they will replace your older 918 springs with a brand new set. This is from my personal experience, and not some urban legand. I called their tech support, and gave them the batch number from the 918's that I had recently purchased (off Ebay no less). They said that batch was not on their watch list, but that they would prefer to swap them out anyway. I received a set of new design springs 2 days later, with a return shipping label for my original set. Not bad customer service there.
The new 918 springs have been tumbled, which provides the bling finish. The max. lift is up from .600" to a conservative .620". I have around 4000 miles on my 918 springs, with zero problems.
The new 918 springs have been tumbled, which provides the bling finish. The max. lift is up from .600" to a conservative .620". I have around 4000 miles on my 918 springs, with zero problems.
Thread Starter
Burning Brakes
Joined: Jan 2007
Posts: 833
Likes: 2
From: Boca FL
If you don't have the valve springs, consider the PAC 1518's. Much better spring that will last longer.
Seats are part of the seal if you use the new design (02+) and you can get them from GM. Shims can be bought from Comp that go right over the top of the seat/seal. They are available as individual thicknesses or as a kit with all three thicknesses. You want the 1.25" OD shims shown below.
Milling will increase compression, thinner gasket provides better quench and will allow more timing. Consider both, but use a dynamic compression calculator to sort it out. If you go thinner, surface finish on the heads is critical so don't let just anyone mill them. The requirements for the surface finish can be found on Cometics web site.
Seats are part of the seal if you use the new design (02+) and you can get them from GM. Shims can be bought from Comp that go right over the top of the seat/seal. They are available as individual thicknesses or as a kit with all three thicknesses. You want the 1.25" OD shims shown below.
Milling will increase compression, thinner gasket provides better quench and will allow more timing. Consider both, but use a dynamic compression calculator to sort it out. If you go thinner, surface finish on the heads is critical so don't let just anyone mill them. The requirements for the surface finish can be found on Cometics web site.
1. Are the factory seals with the seats the way to go?
2. I also read to use the Exh. Seals on the In. side also, (good or bad idea)?
3. Are the shims required and how do you know which thickness?
I will more than likely just do one or the other:
1. Mill heads to 62cc and use the OEM gasket
2. Stock chambers and the Cometic gasket
Or should I do both:
1. Mill heads to 62cc and use the Cometic gasket
Looking for the best bang without the headaches.
What’s the dynamic compression calculator, can someone help me out? Thanks
Last edited by coanan; Feb 1, 2008 at 03:51 PM.
