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-   -   compression for street 383 question?? (http://www.hotrodders.com/forum/compression-street-383-question-229199.html)

demarques_191 02-04-2013 09:52 PM

compression for street 383 question??
 
Can someone tell me if i run this bottom end kit Scat Engine Rotating Assemblies 1-40805-1 - SummitRacing.com and used 70cc chamber edelbrock performer rpm heads for my 383 chevy, will it be street usable? I want to be below 10.1 compression.... Thanx

Now i got a email from Summitracing and they said using these pistons with the 64cc head...
"Based on a .025" deck and a .040" thick head gasket the compression ratio will be about 10.47:1. Pump gas may not make it. If a Zero deck block the compression moves to 11.11:1.

AC"

So im thinking if i went to a 70cc it should put me at 9.5 to 10.1 ...

vinniekq2 02-04-2013 10:02 PM

10 or less is safe.depends on camshaft profile etc.
match the parts to the power you want/need,not what is available inone suppliers catalogue

demarques_191 02-04-2013 10:14 PM

i can always count on the homie for his strong and accurate advice!!! And your right, all im trying to do is find a kit that consist of a forged crank, i beam rods and 9.5 pistons and rings for it... ive even seen the eagle 4140 forged crank... found one online for 400.00.. but only thing is i have to coordinate my parts together

1Gary 02-04-2013 10:55 PM

Vinnie or for that matter,anyone else is going to tell you the same thing.Using SCR formulas you should big picture game plan a build of the stacked parts.

Real general rule of thumb is iron heads limit it to 9.5 and aluminum heads just shy of that by a point.

Understand chamber design matters vs piston design.Being down .025 in the hole isn't where I would want it.And with all this,there isn't any 87 or 89 gas to come into play.


Wallace Racing - Automotive Calculators

You being in the game now should get used to figuring out your own SCR's and DCR's. Just run what you figured out back passed us before you buy.

68NovaSS 02-05-2013 12:56 AM

Keep in mind there are no "9.5" pistons", any piston that results in a 9.5:1 c.r. is a piston with a particular top design, dished, domed, flat, and the sum of other parts, bore, combustion chamber volume, deck height, head gasket thickness, etc. So consider all factors in the equation before you fall victim to what some manufacturer or seller might call a xx.x:1 c.r. piston.

LJM97Z 02-05-2013 01:33 AM

If this helps you any, I'm running a "true" 10.4 compression in my 406 with "IRON" heads, My cranking pressure is 210-215, it runs great on pump 91 premium, The cam is not that big either, 224/234 @50 on a 112 LSA, Your cam will be your limiting factor when it comes to compression & pump gas, You CAN run 11.1 on pump gas with aluminum heads, its done all the time, You don't necessarily need a big can neither, just stay on one with a larger LSA, like a 112-114, If your going to run an aluminum head, shoot for a solid 10.5 compression & you will be fine.

ssmonty 02-05-2013 08:17 PM

demarques_191,
On an earlier thread you mentioned using 64cc heads,5.7 rods, with a 5cc flat top piston, and I said it would give you over 11:1 CR.
The kit your refering to now(1-40805-1) has 6" rods and pistons with a dish/2 valve reliefs and specs at 19.6cc volume. I come up with a CR of 9.03:1 if the piston is .025" in the hole with a 64cc head. I get 8.5:1 CR if I switch to 70cc head.
If you haven't got either one yet(heads or rotating assy) you might want to look at a kit 1-40755B1(2 piece RMS,forged crank, the good 6" rods w/7/16" bolts, forged pistons w/5cc flat tops. bearings, and internally balanced from SCAT) and buy heads with 70cc chamber to get 9.8:1 CR with .040" gasket and pistons .025" in the hole. Pretty much what I'm doingexcept I had to bore out to .040" over instead of 4.030". Kit 1-40755-1 comes without bearings and is unbalanced. Just a thought.
ssmonty

1Gary 02-06-2013 03:33 AM

Edit:
When I made the statement of iron heads and aluminum heads,what I meant to say was the SCR on aluminum heads should be just shy of 10.5 or more like 10.0.But in that range of 10.0 to 10.5.

cobalt327 02-06-2013 08:09 AM

I was looking for a cam that was used in a dyno test and ran across this: How To Build A Kick-***, Pump-Gas, NPAA 680HP Small-Block Chevy - Car Craft Magazine

I do not intend to start another war about SCR vs. DCR. But this tends to support, at least in part, the idea that even nearing the extreme ends of the spectrum that more cam and more compression can run on pump gas. The engine is a big sbc, made 680 hp from about 440 ci (equivalent to a 355 making about 550 hp). Compression is 11.4:1 w/34 degrees total timing. AFR aluminum big port (245cc) heads.

To be honest, had this come up elsewhere, my opinion would have been to not run it on pump gasoline. They don't say what pump gas was used, but presumably it wasn't some ringer 100 octane race gas from a pump. And if it WAS, they need to have their *** kicked.

vinniekq2 02-06-2013 08:20 AM

pump gas
 
Quote:

Originally Posted by cobalt327 (Post 1643243)
I was looking for a cam that was used in a dyno test and ran across this: How To Build A Kick-***, Pump-Gas, NPAA 680HP Small-Block Chevy - Car Craft Magazine

I do not intend to start another war about SCR vs. DCR. But this tends to support, at least in part, the idea that even nearing the extreme ends of the spectrum that more cam and more compression can run on pump gas. The engine is a big sbc, made 680 hp from about 440 ci (equivalent to a 355 making about 550 hp). Compression is 11.4:1 w/34 degrees total timing. AFR aluminum big port (245cc) heads.

To be honest, had this come up elsewhere, my opinion would have been to not run it on pump gasoline. They don't say what pump gas was used, but presumably it wasn't some ringer 100 octane race gas from a pump. And if it WAS, they need to have their *** kicked.

sounds familiar,my 434 uses 10.75 SCR,Dart 227 heads with porting,runs on pump gas.


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