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Author Topic:   compression
eaton89
Dirt Freak

Total posts: 268
posted January 26, 2005 08:28 PM  
Can I run a 406 sbc with 186 heads with no combustion chamber work and a 10.2 to 1 compression on pump gas(96 to 97 oct)safely?
I meant 91! Thanks for pointing that out Leapinlizard!!

[This message has been edited by eaton89 (edited January 27, 2005).]

leapinlizard
Dirt Freak

Total posts: 402
posted January 27, 2005 08:36 AM  
Yep. Not a problem at all. Where are you getting pump gas at 96 Octane?

eaton89
Dirt Freak

Total posts: 268
posted January 27, 2005 08:01 PM  
That is a good point! I meant 91 octane. I should of read what I typed. I was thinking mid grade. I wish I could get 96 or 97.


New question!! Can I run 10.2 to 1 on 91 oct?
Man what an ediot!

racer s
Dirt Forum Racer

Total posts: 83
posted January 27, 2005 08:31 PM  
I been doing some engine research so correct me if i'm wrong folks but I believe with cast iron heads 9.7 to 1 is the highest you would want on pump gas

[This message has been edited by racer s (edited January 27, 2005).]

leapinlizard
Dirt Freak

Total posts: 402
posted January 28, 2005 07:55 AM  
It's pretty safe to 10 to 1. Remember you get bad tanks of fuel once in a while when buying at the pump.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 28, 2005 09:04 AM  
Cam specs and timing will play into this as well. You wouldnt be able to run a stock cam 10:1 on 91 octane but might get by with bigger duration like 230+ because its not building as much cylinder pressure until later in the rpm range. Also you wouldnt want to push your timing advance too far in fear of detonation. If you had more effecient heads like the vortecs that didnt need as much timing that would help too.
FYI: I built a big block 408 for a guy awhile back, closed chamber heads, about 9.5:1 and aroudn 224-230 duration cam and he runs it on 89 octane and never had trouble.

If you wanted to you could mix some race gas with your pump gas to raise it up to say 94(depends on the concentration). You should be more than safe there plus the lead in the race gas will be good on the valve seats.



eaton89
Dirt Freak

Total posts: 268
posted January 28, 2005 06:45 PM  
Cant run race fuel and compression limits are 10 to 1. The pistons I was looking at were about 10.2 or close. I think I better back off a little so I dont burn it down. Thanks for the responds!!

DAYTONA392005
Dirt Roller

Total posts: 9
posted January 28, 2005 10:37 PM  
tranny fluid will increase octane fairly inexpensive

eaton89
Dirt Freak

Total posts: 268
posted January 28, 2005 10:54 PM  
Havent heard that one. Does this really work. ? how much do you add and how much will it raise. Is it detectable in a fuel test for race fuel. Not sure how all that works.

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