Engine's going to the machine shop.
Thread Starter
Racer
Joined: Aug 2010
Posts: 344
Likes: 0
From: Lebbrownsville Indiana
Engine's going to the machine shop.
Monday the heads and shortblock are getting dropped off a the machine shop for a much needed bath, and some work. I'm installing a miniram, cam and headers and my question is: What compression ration will work for me on pump gas? IIRC, the car came stock with 9.5:1 compression on the '88 Z51. I was thinking about a bump to 10.5-11:1 for a little more bang.
Will 10.5-11:1 work with 92 octane fuel without too much detonation? IIRC, the aluminum heads help some when raising compression. This is my first aluminum headed SBC build, so any and all suggestions are appreciated.
Will 10.5-11:1 work with 92 octane fuel without too much detonation? IIRC, the aluminum heads help some when raising compression. This is my first aluminum headed SBC build, so any and all suggestions are appreciated.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
Are you running stock heads which ones?
Lots depends on cam timing events, too. When the valves open/close etc
The typical cam spec #s you see posted dont tell the whole story.
You can ping a motor do death with a small cam just as easily as a large one if its not right. leave a little wiggle room so youre not pulling timing all the time to get it to run. All got to work together, cam compression etc.
Need more info on your ride. Year gearing, auto etc etc. More the better.
Riding the cusp of 91 oct now with 11.5:1. Most wouldnt want to drive it though.
Lots depends on cam timing events, too. When the valves open/close etc
The typical cam spec #s you see posted dont tell the whole story.
You can ping a motor do death with a small cam just as easily as a large one if its not right. leave a little wiggle room so youre not pulling timing all the time to get it to run. All got to work together, cam compression etc.
Need more info on your ride. Year gearing, auto etc etc. More the better.
Riding the cusp of 91 oct now with 11.5:1. Most wouldnt want to drive it though.
Thread Starter
Racer
Joined: Aug 2010
Posts: 344
Likes: 0
From: Lebbrownsville Indiana
88 Z51 4+3, 3.07 rear, stock 113 heads, THIS CAM, 24lb injectors, hedman headers, air pump removed, no egr, a little port work on the heads will be done to smooth them out, valve job, al light mill. Block is getting tanked, likely .030 over and decked. Light polish on the crank, and obviously new bearings/pistons/etc with oil pump.
Car is mostly an auto-x/trackday/toy. AC will be functional in this plastic EZ-bake oven.
Car is mostly an auto-x/trackday/toy. AC will be functional in this plastic EZ-bake oven.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
without figuring the nitty gritty 10.5 should be fine.
if you can at least spend some time in the bowls that will help. smoothing things our has netted me zero on the bench.
if you can at least spend some time in the bowls that will help. smoothing things our has netted me zero on the bench.
Le Mans Master
Joined: Mar 2002
Posts: 5,889
Likes: 2
From: Castro Valley Calif.
St. Jude Donor '03 thru '26
The static CR is governed by a number of factors, rod length, piston comp height, block deck height, head gasket, and chamber size to name a few. The two biggest things when considering pushing the envelope on a pump gas motor are quench (as Larry mentioned earlier) and the dynamic CR. Here's a great read on DCR, with a calculator at the bottom: http://cochise.uia.net/pkelley2/DynamicCR.html
Want to have some fun & really open your eyes to the importance of cam selection & DCR? Run the calculator and change the cam's advance plus or minus a few degrees. That makes a significant difference on your valve timing and the DCR.
Want to have some fun & really open your eyes to the importance of cam selection & DCR? Run the calculator and change the cam's advance plus or minus a few degrees. That makes a significant difference on your valve timing and the DCR.
Le Mans Master
Joined: Mar 2002
Posts: 5,889
Likes: 2
From: Castro Valley Calif.
St. Jude Donor '03 thru '26
113s are the newer aluminum heads, no? At any rate, I'd question them with a miniram and a 5600 rpm cam...
I's think 190-195s would be a better choice for an rpm motor...?
I's think 190-195s would be a better choice for an rpm motor...?
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Team Owner
Joined: Jan 2003
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From: Summerland B.C. Canada
The static CR is governed by a number of factors, rod length, piston comp height, block deck height, head gasket, and chamber size to name a few. The two biggest things when considering pushing the envelope on a pump gas motor are quench (as Larry mentioned earlier) and the dynamic CR. Here's a great read on DCR, with a calculator at the bottom: http://cochise.uia.net/pkelley2/DynamicCR.html
Want to have some fun & really open your eyes to the importance of cam selection & DCR? Run the calculator and change the cam's advance plus or minus a few degrees. That makes a significant difference on your valve timing and the DCR.
Want to have some fun & really open your eyes to the importance of cam selection & DCR? Run the calculator and change the cam's advance plus or minus a few degrees. That makes a significant difference on your valve timing and the DCR.
I have a similar cam in my 355 Super ram build. With new pistons and a .020 decked block(reduce quench), my compression came out to 8.5 dynamic. Acceptable for pump gas.
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Just for fun, you should try the Pkelly calc linked in this thread. Figure out dynamic compress before and after.
