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Old 07-15-2006, 11:43 AM
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Piston Help??? 383 Stroker Compression

I bought a full eagle rotating assembly the other day. Its a fully forged kit with 6.0 inch rods. It cam with SRP -5 pistons. I have Dart 72 head and i figured my compression to be about 9.6:1. I am now planing to run the engine this summer and but a supercharger on it next summer. I was looking into superchargers and keeping this thing on pump gas. I found i would need about a 8.5 compresion to run 6 psi boost.
Should i return the pistons and get -16 domed pistons to give me a compression of like 8.6??
or
Can my pistons be machined down to size next summer?? If so what does this usually cost??

Would i be better off to just return my -5 pistons and live with 8.6 compression until i get my supercharger??

Any help plz??
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Old 07-15-2006, 11:50 AM
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If you plan on keeping the engine together until you get the blower, get the dished pistons now. It will run pretty decent even with 8.6:1 compression.

tom
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Old 07-15-2006, 11:59 AM
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thats kinda what im leaning towards. the only thing is that im not 100% sure im goin to get a blower. What would the difference between like 8.5 and 9.5 as like hp or 1/4 mile time??
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Old 07-15-2006, 12:22 PM
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A lot of guys will tell me "I have 3.08 gears but I'm going to put in 4.11s" or "I don't have a blower now but I'm going to......."

Rarely to they follow through.

I tell them to build for what they HAVE, not what the are (maybe) going to have....



tom
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Old 07-15-2006, 05:25 PM
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Ditto with Tom, build it for what you have now.
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Old 07-15-2006, 05:47 PM
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Is the rotating assembly already balanced? If so, changing to a different piston would require the assembly to be rebalanced if the pistons aren't equal to each other in weight.

Bob
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Old 07-15-2006, 05:49 PM
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Several testers have done the GM crate engine 350 cubes rated 290 hp and then hopped it up for the mags. The thing comes with cast pistons of 8.0/1 and iron heads and puny cam, and with air gap and Demon made 350 hp. Compression in the mid 8s doesn't seem to harm a SBC 350 much and they will run on cruddy gas that will be $ 4 gallon soon.

I'd do 8.5 compression NOW, with good heads of course. (or keep my blower down to 4 psi= it still looks good)

"You can build a 420 hp (SBC 350) engine with a fuel problem, or a 400 hp engine that will run on junk gas." Steve Henderson, engine builder.


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Old 07-15-2006, 06:39 PM
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Taken from the Knowledge Base if one wants to read.
http://www.chevymania.com/tech/383.htm

Ryan's Small Block Chevy Dynoed Combos (about 100 of them).
http://www.ryanscarpage.50megs.com/combos1.html
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Old 07-15-2006, 06:55 PM
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Quote:
Originally Posted by 89SDime
thats kinda what im leaning towards. the only thing is that im not 100% sure im goin to get a blower. What would the difference between like 8.5 and 9.5 as like hp or 1/4 mile time??

The general consensus among engine builders is that each full number of compression, 1.0, is about 4% hp, in the range of 8-11/1. As the compression gets higher the % increase gets less. (probably due to pop up pistons ruining the flame travel and the necessity for more timing advance)

So on a 420 hp engine the loss of one full number of compression, from 9.5 to 8.5, would give you about 403 hp. You MIGHT notice the difference in street driving, but the gas pump would certainly see the difference.

David Vizard, noted engine builder, who writes for PHR, Engine Masters, etc., leans more towards 2% change per full compression number.


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Old 07-15-2006, 07:04 PM
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Quote:
Originally Posted by machine shop tom
A lot of guys will tell me "I have 3.08 gears but I'm going to put in 4.11s" or "I don't have a blower now but I'm going to......."

Rarely to they follow through.

I tell them to build for what they HAVE, not what the are (maybe) going to have....



tom
Agree 100% on that, I wanted to run a blower on mine but then I realized how much 2 grand really is.. and that's not even including the price of 2 carburetors, most likely need cooling upgrades, new air filters, that air scoop setup over the carbs, etc. Lotssss of mulahhh. Maybe when I'm more financially stable and can toss around a bit of money here and there. I have plenty of power for now so I'm perfectly fine with what I got.
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Old 07-22-2006, 03:31 PM
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I was just looking to save money in the long run. Instead of have this problem when i buy a blower. I never thought about the balancing issue.

Im just think that i should run 8.5 compression now because u said i would lose little horse power and would save me alot in the future.

I dont understand this "but the gas pump would certainly see the difference."

Would having lower compression save gas??

I guess i could return my rotation assembly and get on with dished pistons.
I was wondering about my heads? I have Dart 215 Iron Eagles. Should i upgrade to aluminum or have some work done to them???
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