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Old 07-01-2004, 07:19 PM
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Turbo SBC Rotating Assembly

My twin turbo Chevelle experiment is over. Well at least my all cast small journal 327 is. If I lay the boost to it (7psig), number 5 piston smacks the spark plug and she starts this awful death rattle that goes away shortly after I fix the plug and run her for a few seconds. If I drive normal she runs fine, but I have no will power so this has happened four times in the last week.


Anyway I have $2000 to spend on an all forged rotating assembly to go in a four bolt main 350 I have. I've found a few balanced kits with 4340 eagle or scat cranks, 4340 H beam rods and forged pistons for around $1800. I think I can piece one together a little cheaper on ebay and have it balanced, but I think I'd rather have a new assembly from a reputable source.

The new motor is going to be a test mule for turbo and PC based engine/vehicle management systems. I want a 4.030 bore X 3.25 or 3.00 stroke that I can spin to 8k, lay lots of boost to and not have to worry about it melting down or coming apart.

I know crank discussions get pretty heated sometimes but any advice from you guys with super/turbocharged drag motor experience would be greatly appreciated.

Thanks,
Kevin

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Old 07-01-2004, 08:06 PM
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I don`t think the piston is hitting the spark plug, it`s likely mechanical damage from the piston coming apart. in the past number 5 and 7 holes in the small block chevy, especially number 7, always ran on the lean side due to the firing order being after the other, so 5 would rob 7. both 5 and 7 had mixture problems with the earlier intakes that weren`t very efficient. also another problem was the spark plug wires, crossfire would set in from the same problem of one firing after the other and them being side by side, and if this problem is present, no matter what kind of assembly you have it won`t last long, so on your next build make sure you run the best spiral core ignition wire you can afford and keep the 5 & 7 plug wires at least a inch apart from the other.
I know this don`t answer your question, but is something important to look into.
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Old 07-01-2004, 08:17 PM
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Try a surface gap plug while you tune the engine and get a handle on the mixture.

Just a thought.
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Old 07-02-2004, 06:05 AM
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I'm not trying to fix the old motor. The electrodes on five and sometimes three are getting hammered shut. Five will actually push it up far enough to break the insulator. I'll find out whats causing it when and if I tear it down.

The new motor will be multiport injected, with distributorless ignition and have thermocouples monitoring EGT at each cylinder. We've been playing with an Opto 22 Ultimate Brain and modules on an automation project at work and are thinking about trying it out on a motor. I'm wanting to build a test mule that can take some abuse.

Thanks,
Kevin
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Old 07-02-2004, 07:20 AM
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I would buy one of those Cola's on ebay for $520. Nice crank. Get a set of I-Beam rods not the stock type but after market, spend the money on turbo specific pistons, custom, and get 10 just in case. You'll be ahead of the game.

Chris
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Old 07-02-2004, 07:32 AM
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Here's a link with multiple choice combinations available at reasonable prices.

http://www.flatlanderracing.com/rotate-chevy08.html

RA35CC15 looks like it would fit your budget with balancing and small parts included. I'd recommend sticking with the standard 5.7" length rods to keep the rings down from the piston crown and away from too much heat.

Good luck with the project.

Larry
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Old 07-02-2004, 07:49 PM
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I dont know how you feel about the foreign stuff, but suggesting eagle I guess you are okay with it. I got a set of Ibeam rods with 7/16 bolts at www.dirttrackthunder.com for $450. They are rated to 800HP and 8500RPM, but are foreign stuff. Also scored a 4340 eagle crank for $325 on ebay on clearance. About the same for my SRP pistons on ebay. If you watch long enough you can find some really good deals. I would definately spend some money on high end pistons like SRP, JE, Wiesco etc.

On another note, I am not sure why you want to spin a turbo engine that hard. You can make just as much power in lower RPM with a little more boost. Unless you are going to use some seriously large turbos and a large cam, which will be a tuning nightmare on EFI, I would stick to about 6500RPM......but that is just me. Would be much easier on parts to use more boost and less RPM

Chris
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Old 07-02-2004, 09:29 PM
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Chris,
I wasn't aware that Eagle was foreign. I have a brand new 4340 eagle crank for my 454. I bought it off ebay for $340. I heard some complaints about them but its rated for 8000Rpm and 1500 hp. It's going in my 1488 pound Quad Turbo T. I don't think I'll have the balls to break it.

For my Chevelle, I'll agree I don't need to spin a turbo motor that high, but I don't want to have to worry about breaking stuff. I used to spin my 327 to six grand, but with the turbos it never saw over 4 because I just makes so much torque. Although I did floor it once with the secondaries still disabled. I was rolling in 2nd gear at 1200 rpm. It instantly blew both head gaskets. The Chevelle will be spending time at the track and may get a full tube pro-streetment. My wife is going back to work next month, for the first time in nine years. It's time to build the car how I've always wanted without getting too crazy.

Larry,
That dragonslayer kit looks like it should do the trick. Although I don't spend time at the track, I've never heard any complaints about Callies parts.


Thanks guys,
Kevin
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