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Old 01-06-2013, 02:57 PM
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SBC Engine build advice

HI, JUST STARTING A ENGINE BUILD AND WILL NEED GUIDANCE AND GOOD ADVICE PLEASE.
1ST TOTAL REBUILD. BEEN READING THREADS AND COLLECTING PARTS FOR A WHILE NOW.
STREET USE MOTOR WITH RWYB IN MIND.MODEL A COUPE.
SO ITS A SBC 327 SHORT MOTOR +30
THIS WILL BE RUN ON PUMP GAS 97 OCTANE AND WITH A 6-71 BLOWER.
5% UNDERDRIVEN
STOCK CRANK 2.1 JOURNAL WITH A NEW 0.10 GRIND AND A 2ND KEY WAY MILLED IN FOR DOUBLE GROVED BALANCER.
RODS IBEAM 5.7 ARP BOLTS.
HEADS CAST DOUBLE HUMP 64cc, 2.02 INTAKE, 1.6 EXHAUST & VALVES S/S.
1.5 ROLLER ROCKERS & GUIDE PLATES

LOOKING FOR ANY ADVISE ON PARTS:
HYPR PISTONS DISHED OR FORGED?

(LIST OF PARTS I HAVE SPARE)
CAM? (NEW COMP CAM 268XE)
LIFTERS? (NEW STOCK HYDR)
VALVE SPRINGS? (HAVE DOUBLE SPRINGS 358lbs)
PUSH RODS?

HOPE YOU CAN HELP WITH MY GOAL.
CHEERS

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Old 01-06-2013, 03:04 PM
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Definitly go for the forged pistons if running a blower.
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Old 01-06-2013, 03:16 PM
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Just thought that forged pistons would be noisier running than hydro.....
I have read that hydro break like glass (detonation)
But hopefully not going their.

Cheers chap
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Old 01-06-2013, 04:45 PM
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Ive never had noisy forged pistons? Sounds like a fun build. Over build for reliability,you dont need a lot of power for that car.Looks like its in the 500 ish area.An 850 carb will be enough for a cruiser
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Old 01-06-2013, 04:51 PM
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Quote:
Originally Posted by newboldspeed View Post
Just thought that forged pistons would be noisier running than hydro.....
I have read that hydro break like glass (detonation)
But hopefully not going their.
Cheers chap
First, let's get the nomenclature correct. What you're referring to, I think, is hypereutectic (High-per-you-tech-tick) pistons that use more silicon in the alloy than standard cast pistons. Hypers are still cast, but the material they're cast from makes them a little tougher than cast pistons.

Detonation will break or melt pistons no matter what they're made of. Think of it as swinging a sledgehammer down onto the piston crown or holding a cutting torch flame in the middle of the piston crown. Something is gonna give. If you have detonation under control, you could use cheapo cast pistons and have them last forever. It's all in the tune.

Here are some basic recommendations from Blower Drive Service....
Blower Drive Service: We Deliver Horse Power! - Blower Drive Systems, Blower Kits, Blower Cams, Custom Carb Service
Blower Drive Service: We Deliver Horse Power! - Blower Drive Systems, Blower Kits, Blower Cams, Custom Carb Service
Blower Drive Service: We Deliver Horse Power! - Blower Drive Systems, Blower Kits, Blower Cams, Custom Carb Service
Blower Drive Service: We Deliver Horse Power! - Blower Drive Systems, Blower Kits, Blower Cams, Custom Carb Service
Blower Drive Service: We Deliver Horse Power! - Blower Drive Systems, Blower Kits, Blower Cams, Custom Carb Service

By looking at the tech charts, you can see that a small bore 6-71 that is underdriven by 5% on a 327 CID motor will make 7 lbs of boost. Looking further at the charts, you will see that the maximum static compression ratio you should use for 7 lbs on pump gas is about 8.0:1.

It appears to me that you have not thought this combination through completely. With 64cc heads, I cannot find a suitable dish size in a 327 piston. Largest dish I find is 13cc's (KB158 hyper) and that will make 9.0:1 in a 327 with 64cc heads. You may be able to have Ross or one of the other manufacturers make 327 8.0:1 pistons for you, but plan on taking out a loan to pay for them. You'll need a 25cc dish to reach 8.0:1 with 64cc heads, or you could change to 76cc heads and do it with a 327 flat-top piston.
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Old 01-06-2013, 05:30 PM
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That's making things better to understand. Thanks techinspector1

I do have 76cc cast heads 1.72/1.50 valves. But then......
will the valves be large enough for a blown motor. Mmmmm.

whats you thoughts?

Last edited by newboldspeed; 01-06-2013 at 05:46 PM.
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Old 01-06-2013, 08:12 PM
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Quote:
Originally Posted by newboldspeed View Post
That's making things better to understand. Thanks techinspector1
I do have 76cc cast heads 1.72/1.50 valves. But then......
will the valves be large enough for a blown motor. Mmmmm.
whats you thoughts?
I'm of the opinion that most everyone misinterprets what is necessary to make a blower motor work. For a street motor with up to 6 lbs of boost, you don't need a double-throwdown camshaft and sewer-pipe heads. The blower will compensate for a plethora of errors and still make good power (25%-40% increase over stock) at street rpm's, on cast iron exhaust manifolds and stock head gaskets. Just as in the remainder of life, there are varying degrees of success, based on the combination of parts used.
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Old 01-07-2013, 04:03 AM
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Hi, Not sure what this means
you don't need a double-throwdown camshaft and sewer-pipe heads.

I think your saying that the blower will make a good street motor out of stock heads and a mild cam.
The rotating assembly needs to be in good shape i.e
crank, ibeam rods & 8.1 c/r pistons for the 76cc heads. once this is built up you have a base for a street blown motor that will perform well at 5% underdriven.

not to get carried away with all the performance options avalible.
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Old 01-12-2013, 01:45 PM
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Been looking at AFR Heads for the blown motor build.
75cc chambers to go with flat top pistons on ibeam rods. 8;1 C/R.

Could anyone recommend the most suited to a street blown motor.

I'm not understanding all the cfm and flows etc.

cheers
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Old 01-12-2013, 02:36 PM
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Just keep in touch with Tech, he has a lot of knowledge and is right on the money with the 76cc heads and the 8:1.
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Old 01-13-2013, 07:05 AM
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Beware that 97 octane in UK is the same as 93 in the US.

Blower cams typically have wide lobe separation angles like 114 degrees.

Cast pistons can be used for low boost, say under 10 psi. However, timing and fuel ratio tuning will be less tolerate to mistakes.

On a 350 street build, I would use 7.5-8.0, 10 psi of boost, a cam around 210/220 on 114 LSA, with a good set of aftermarket heads. Expect around 550hp/550ftlbs with this build.

Good exhaust will be important. Headers and dual 3 inch pipes.

Best to just lock the ignition timing. Try 24 - 28 degrees.
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