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Old 10-01-2010, 04:05 PM
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Blown 383 Questions

Hello everyone. I have a 383 with stock GM block bored 30 over, 0 decked and line honed mains. Crank is a scat 4340 forged 3.75 stroke, Rods are Scat 4340 forged I-beam 6.0", Pistons are Diamond 31cc dish forged. Main Caps are studded with ARP studs, rod bolts are 7/16 ARP aswell. The heads are AFR street eliminator 195. They have 65cc Chambers. The cam is a Comp Solid roller with duration of 255/262 @ .050 LSA of 114 and
a centerline of 110. Lobe lift is 0.383 for intake and exhaust. I will be running 1.6 ratio roller rockers. This should give me 0.593 lift intake and exhaust factoring in the 0.020 valve lash. I will be using 7/16 pushrods. I also have Comps 977 valve springs. One top is a weiand 6-71 with 2 holley 600cfm blower carbs. For exhaust it has open headers with 1.75 primarys. I'm looking to have about 650hp out of this combo. Please let me know if my goal is realistic. Any advise would be appriciated this is my first blower motor and I have already learned a few hard/expensive lessons. Thanks, Chris
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Old 10-01-2010, 04:19 PM
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Quote:
Originally Posted by 383Eliminator
Hello everyone. I have a 383 with stock GM block bored 30 over, 0 decked and line honed mains. Crank is a scat 4340 forged 3.75 stroke, Rods are Scat 4340 forged I-beam 6.0", Pistons are Diamond 31cc dish forged. Main Caps are studded with ARP studs, rod bolts are 7/16 ARP aswell. The heads are AFR street eliminator 195. They have 65cc Chambers. The cam is a Comp Solid roller with duration of 255/262 @ .050 LSA of 114 and
a centerline of 110. Lobe lift is 0.383 for intake and exhaust. I will be running 1.6 ratio roller rockers. This should give me 0.593 lift intake and exhaust factoring in the 0.020 valve lash. I will be using 7/16 pushrods. I also have Comps 977 valve springs. One top is a weiand 6-71 with 2 holley 600cfm blower carbs. For exhaust it has open headers with 1.75 primarys. I'm looking to have about 650hp out of this combo. Please let me know if my goal is realistic. Any advise would be appriciated this is my first blower motor and I have already learned a few hard/expensive lessons. Thanks, Chris
Chris
Don't know how much boost you are going to run but those springs are very weak for a blower application, Remember boost will try to hold the intake valves open. 155 @ the seat and 420 over the nose is very weak!!!

Stock main caps at 650 horse is iffy and adding studs does nothing to make the caps stronger as they are just a grey cast iron caps with good hardware.

Did you have the cylinder sonic tested for thickness before you spent any money on your project??
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Old 10-01-2010, 04:40 PM
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Block and valve springs

Hello agian. They guy doing my machine work did sonic test the block and assuredme the the thrust side of the cylinders were good. I would have to ask him how think they actually were. As for the valve springs I called Comp Cams and AFR and they both pointed me towards the 977. Can I put a shim on those springs to give them a little more seat pressure? And if I could how thick would I need to go? I plan on about 10 lbs of boost. Thanks for the quick response.
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Old 10-01-2010, 04:50 PM
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Quote:
Originally Posted by 383Eliminator
Hello agian. They guy doing my machine work did sonic test the block and assuredme the the thrust side of the cylinders were good. I would have to ask him how think they actually were. As for the valve springs I called Comp Cams and AFR and they both pointed me towards the 977. Can I put a shim on those springs to give them a little more seat pressure? And if I could how thick would I need to go? I plan on about 10 lbs of boost. Thanks for the quick response.
Solid roller cam should have more pressure then that I have some circle track engines that run that much preesure and they are running flat tappet cams.

If you float a valve with a roller lifter they will break for sure.

We build some high end SBC blower engines with 8-71's and ty valves and these are chipped at 9500 RPM and we run 460 at the seat and 1250 over the nose.

Are you running steel valves??? which will make it worse!!!
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Old 10-01-2010, 04:59 PM
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Valve springs

Wow.. That's alot. So any suggestions on what springs I should run? I don't think I will ever get over 6500 RPM's. The heads have 8mm steel valve in it. Same as LS1 valves. I just looked at lunati and most of their springs are 210 lbs at the seat.
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Old 10-01-2010, 06:55 PM
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Another valve spring question

If I have to change my springs because of the boost can I just change the springs for the intake valves and leave the exhaust as it is? Will this mess anything up?
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Old 10-01-2010, 07:34 PM
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I would send a email to AFR, they should know about the heads, they made them.
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Old 10-02-2010, 05:35 AM
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Quote:
Originally Posted by 383Eliminator
Wow.. That's alot. So any suggestions on what springs I should run? I don't think I will ever get over 6500 RPM's. The heads have 8mm steel valve in it. Same as LS1 valves. I just looked at lunati and most of their springs are 210 lbs at the seat.
We are running up to 28 pounds of boost and these engines build about 1600 horse and run on alky.

I would even go higher then that.

Good luck
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