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Author Topic:   max compression ratio
justin
Member
posted February 05, 2002 08:26 PM
What is the max compression ration I can run on a 355 chevy with cast iron vortec heads while using a racing fuel such as Turbo Blue?


sdhnc29
Member
posted February 05, 2002 10:19 PM
If your allowed to use a domed piston , you can run 14.5:1 with no problems !

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


sdhnc29
Member
posted February 05, 2002 10:21 PM
But I'd invest in at least 112 octane fuel . I like VP !!!

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


justin
Member
posted February 06, 2002 10:31 AM
We're only allowed to use flat-top pistons. I heard that the max. comp. was around 9.1:1. Does this sound correct?


sdhnc29
Member
posted February 06, 2002 10:38 PM
No , you can get mid to high 12's with only a limited amount of work to the heads , using a flat top -5cc 2 valve relief piston . I'd have to look at my notes at work , but if my memory serves me correctly , you can angle mill the Vortec's .080" then take an additional .015" flat mill . Using the type of piston I described , and a Ferrea .035" thick 4.060" bore head gasket , with a zero deck , you'd end up with 12.7:1 . If your rules allow you to stick the piston out of the hole , you can hang her out a few thousandths , and be at 13:1 . But to do this , you'd need to run a very stable piston , such as a JE .

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


dirtracers
Member
posted February 14, 2002 08:19 PM
what class are you running from the sound of it you are a bomber or pure stock you dont need to do any thing to the heads my brother has a set of the vortecs and he had a $4000 motor when it broke he put a stock motor with dished pistons in it and it ran just as good and as a matter of fact he started 3rd row inside and was in the lead on the 3rd lap when he cut a right rear tire.


Machinah
Member
posted February 15, 2002 04:08 AM
Dirtracer is right. If you are running in one of these classes, there is not much that you have to do to your motor other than use OEM type stuff. These cars are so heavy and you are racing on dirt. The chassis setup will get you fast laps and too powerful of a motor may be too hard to control on the throttle, lots of wheel spin.


ryan
Member
posted February 15, 2002 12:40 PM
You guys have to remember that all rules aren't the same. our street stocks are only a second behind the late models the only rule difference in the motors is that the g.n. can run roller setups.


o5racer
Member
posted February 15, 2002 10:23 PM
OK i just dont really see how you can get 13 to 1 with a flat top piston. not with a 355 any way. my engine is a speed pro flat top 15 deck with steel shim head gaskets and a set of cammel backs angle milled .090 to get a 55 cc. chamber. everyone i talked to said it should be between 11 and 11.5 to one. if i put them on a 406 then i might be able to get 13 to 1, but on a 355 i just dont see how its possible.


sdhnc29
Member
posted February 15, 2002 11:34 PM
To begin with , your heads are not angle milled enough . Unlike the Vortecs , the older heads can be angle milled much farther , due to the deck thickness being thicker . First of all , you must plug the bottom row of water hole's , we use crack repair pins for this . Then you angle mill your head .150" , re correct the intake face back to stock angle , and re correct the exhaust face back to stock angle . After this , you must spot face all the head bolt holes . While the head is in the mill , you also correct the angle of the head bolt holes .

As for pistons , like I said previously , you must use an actual 2 valve relief piston , and not one that has universal relief's (same size , interconnecting relief's). You must also be sure to only cut the pistons the bare minimum for valve to piston clearance , which will usually leave you with an intake and exhaust pocket that has a combined volume of -5cc's .

Next , be sure your piston is out of the bore .005" . Use a Ferrea head gasket that has a fire ring diameter of 4.060" , and is .035" thick . Your piston to head clearance is now at the minimum , .030" .

13:1 is not a problem ! It takes more work than 11:1 , and a lot of shop's either don't want to spend the time doing this , or just don't have the capabilities . Stock heads are easy compared to the Iron Eagle's that we do !! Our limited late models are limited to a 215 Iron Eagle's , and a flat top piston . I just finished a run of 8 set's of these heads , all 8 set's have 37cc chamber's . The Iron Eagles that I did last year were at 39cc's , so as you can see , I found a little more that I could cut off of them this year . Our limited engines run at 15:1 ! Every day I hear people say it's impossible to get a 15:1 flat top limited engine using Iron Eagle's , yet every day I manage to make one !

If your interested , I have a set of 492's that I finished the other day , they might help you bump your compression up a bit . Email me if your interested , or feel free to call at any time .

Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


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