Oh sh!t

MRHP

 
Supporting Member 1
Well, my buddy is getting a 383 stroker put together for his 71 camaro. Calculated compression is 10.7 dynamic 8.8 and cranking compression 234. Iron head, tunnel ram, 4 speed, 3.73 gears. Wants to run on pump gas on the street. I am concerned about it rattling with such high compression. The tunnel ram will help by drawing cool air into the motor, but I am unsure if it will be enough. What to I do? Oh, double hump heads, hardened seats, stainless valves, solid flat tap pet cam, cam is still being debated at the moment. I just don't want a non running piece of sh!t that I have to try and tune. What are your recommendations?
 

Don Jacks

Well Seasoned Member
Supporting Member 3
What in the world are you running for a camshaft to make that much cranking compression????????? With those antique heads,I would not want more than 185 cranking for todays gas.The 10.7 part isnt really out of line as long as the quench is good.
 

MRHP

 
Supporting Member 1
All the info is theoretical, running through a program. I don't recall the cam grind, but it is a pretty aggressive Voodoo cam. I will see if I can find the grind. Block will be 0 decked or possibly .005 in the hole with a .041 head gasket. Yes, the cranking compression has me worried the most. My stroker 09 has 200-205 cranking and barely runs on pump gas.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
Well,in that case the program is off for some reason.Assemble the thing and test the cranking compression.Theres no way that engine will make 230 plus psi,more than likely on a Voodo cam,175-180.With those heads,your max timming will come in about 37-38 degrees.
 

MRHP

 
Supporting Member 1
10120704 lunati I think is the cam. I can check for sure Monday. I run locked timing at 36 and it runs good now as a 350 9.7 compression, with a tad smaller Voodoo cam. I just don't want a tuning nightmare. Thanks for the insight.
 

1961BelAir427

Well Known Member
Supporting Member 3
I agree with Don. You'd need over 12:1 static CR and a cam with short duration to build that much cranking compression probably. I believe your 10.7:1 and a cam to compliment the intended use with tunnel ram will be less than 200 psi cranking.
 

Ishiftem

Well Known Member
Supporting Member 2
Well we had a 406 sbc with 76cc chambers and flat top 4 valve relief pistons. The cam was a Isky 270 hydraulic flat tappet. Stone cold it had a cranking compression of 210! Couldn't drive it on a hot day with 93 octane. The static ratio on that engine was only 9.7:1. The program might not be far off.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
Now you can understand the importance of a good quench.With those old "smog" heads[76cc] that engine had none.That was done back then to reduce nox.That old ISKY ,like the Comp high energy series cams,was designed to increase tourque by pumping up the cranking pressure making the engine think that it had more compression.
 

Ishiftem

Well Known Member
Supporting Member 2
It sure did! When it was cold out that thing pulled way harder then it had a right to.
 

MRHP

 
Supporting Member 1
Sure hope you fellas are right. I wasn't all that concerned, until talking to the machinist. He got me worried. My buddy says he trusts me with the tuning, but if it goes south, it's all on me!
 

Don Jacks

Well Seasoned Member
Supporting Member 3
I would have preferred a much better,more moderm head design[why people expect this old tech stuff to work well on todays fuels is beyond me],but with that modern cam design,at 10.7 you'll be okay,just down about 40 hp over what could be made for about the same money.
 

MRHP

 
Supporting Member 1
I told my buddy to build the engine with these heads, and in the future if he gets some $$$ buy some aluminum heads.
 

MRHP

 
Supporting Member 1
The machine shop wasn't sure until he mocks it up. Quench I remember is optimum .035-.045 but acceptable up to .060. After that you loose the benefit of it. I like a tight quench, but turning the engine hard and piston rock also has a place in the equation.
 
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