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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.

shopper 04-01-2013 02:27 PM

The heads I took off of the motor was shaved to almost the spark plug holes but I don't have ant clue on the CC

hotrod1994 04-01-2013 07:00 PM

take them to machine shop and have the cc volume checked but i think there way to low

64cc head should get ya 10:1 er so...

my world products 64's have plenty of room from the deck of the head to the plug hole

roadkill2 04-02-2013 06:09 AM

Kind of a SWAG but it sounds like somebody with a milling machine had a bad idea and made scrap out of those heads . .

But Hotrod's probably right. Go have them measured . .

TheYellaBrick 04-02-2013 12:49 PM

They could have been from a past 'case of beer' bench racing in a machine shop experiment :shock: 8) 8) :lol: :lol: :oops: :roll:

hotrod1994 04-02-2013 06:45 PM

there had to be at least a case of beer in the man behind the cnc machine :shock:

shopper 04-03-2013 01:00 PM

Sounds good I will take them to a machine shop and see what CC they are, another question this is a roller motor and the #3 & #5 lifters are different than the rest they are rollers but instead of the bar assembly that connects at the top of the two lifters these have like a middle brace between the two lifters and with springs in them, I'm scratching my head on this.

hotrod1994 04-03-2013 01:30 PM

hmmm idk why that would be it seem as if the guy just threw this thing together with spare parts

roadkill2 04-03-2013 02:15 PM


Originally Posted by hotrod1994
hmmm idk why that would be it seem as if the guy just threw this thing together with spare parts

X2 . . . . . A "Handy Grenade" . . Whatever he had handy, he built a grenade out of. . .

shopper 04-03-2013 03:25 PM

Got me thinking the same thing

shopper 04-03-2013 03:29 PM

I really appreciate all you guys input on this motor it sure has help me make a decision

hotrod1994 04-04-2013 07:32 AM

no problem any other questions just feel free to ask
-logan

shopper 04-15-2013 04:48 PM

Well I took a chance and put the engine back together with the heads that came with it, I installed it in my 73 Camaro with a 4-speed and the engine is awesome so far, you guys was right I adjusted the valves and maybe that was the problem the first time, but now there is no spark knock or nothing she runs great on pump gas, you know I said the last time I had to run racing fuel, I didn't think that there was that much difference between a stick and auto tranny just by the way a engine would perform, WOW!

hotrod1994 04-15-2013 04:49 PM

glad everything worked out for ya!!


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