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-   -   SBC 350 (https://www.racingjunk.com/forums/showthread.php?t=33324)

shopper 03-26-2013 11:33 AM

SBC 350
 
I will re-post think I posted the first one in gerneral discussions, ok here we go, I need some advise if it is possible, I have a lack of information, A friend of mine gave me a chevy 350 .060 over roller motor, (brand new) ok the problem I am having is the compression is to high and I have to run racing fuel so the valves wont rattle, I need advice on what brand and cc heads aluminum or cast iron and intake I should run to make this motor a Pump gas street engine, oh yeah I know the cam lift is over .500, does anyone have any suggestion.

Thanks
Steve

zipper06 03-26-2013 03:53 PM

Do you know if you have dome pistons or not :?:


Zip.

hotrod1994 03-26-2013 04:52 PM

depend on the pistons but a 76cc aluminum heads might get ya to premium pump gas but it all depends on the pistons

shopper 03-26-2013 05:01 PM

They are flat top pistons

markdunlap 03-26-2013 05:55 PM

sbc350
 
With flat top pistons on a 350 engine I would not think you would have too high of compression to cause this problem, unless you have heads with small cc chambers like 58. Going to 64 to 76 cc heads would lower the compression.

Camshaft duration could effect dynamic compression some too.


Are you sure you do not have excessive ignition timing?

Does your distributor have mechanical and vacuum advance or is it locked out? The advance curve may be too quick.

shopper 03-26-2013 06:02 PM

Yes it has vacuum advance, yeah I'm trying to get as much power as possible and still be very streetable, I've got it torn down to a short block and was hoping not to have to totally disassemble it, but I know with out a lot of specs it's a big guess

fast75vega 03-26-2013 07:32 PM

Re: sbc350
 

Originally Posted by markdunlap
With flat top pistons on a 350 engine I would not think you would have too high of compression to cause this problem, unless you have heads with small cc chambers like 58. Going to 64 to 76 cc heads would lower the compression.

Camshaft duration could effect dynamic compression some too.


Are you sure you do not have excessive ignition timing?

Does your distributor have mechanical and vacuum advance or is it locked out? The advance curve may be too quick.

i was thinking the same thing mark ... cant see the compression with flat tops being high enough to cause the problem? id look at the timimg :wink:

hotrod1994 03-26-2013 10:07 PM

definitely check your timing flat tops with 64 cc heads should get ya 10:1 er so maybe 10.5:1. witch is ok for premium pump gas assuming its tuned properly, 34-36 degrees of total timing is about normal for a sbc......

make sure your not leaning it out too much, an improper air fuel mixture will cause pre ignition as well....

if none of this works you could also try retarding your cam timing some to help reduce cylinder pressure and your dynamic compression ratio....

your dynamic compression needs to be about 8:1 with iron heads, if you know your cam specs and such there are calculators online to help you figure out your dynamic compression ratio......

dynamic compression should be around 8:1 for pump gas and static compression around 10:1.....

also check your quench height or "squish" witch is the distance from tdc to the top of the deck and your gasket thickness added together, a large quench area will also make it more prone to pre ignition .060 is about the max quench height they say you should run on a hi perf engine

hope this helps
-logan

shopper 03-28-2013 06:18 AM

Ok thank's for all input

oldandtired 04-01-2013 10:33 AM

With all the different size SBC harmonic balancers and timing covers, make sure your timing tab is in the zero position.


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