Destroking a 347
Destroking a 347 I searched but could not find any info on this subject. Has anybody ever destroked a 347 into a 327cid field or a 302. I know the 5.3L is a 325 cid, but Iam talking about a forged balanced and blueprinted assy. A big valved, big cam motor and got some hp numbers. I would have to guess that it would wind up quick and run out of steam compared to a stroker cid motor on a long haul.
I guess all I see is just no place like displacment threads. I guess its food for thought. Hell with prices on parts it probably the same cost to stroke it up then down.
I guess all I see is just no place like displacment threads. I guess its food for thought. Hell with prices on parts it probably the same cost to stroke it up then down.
Best thing going IMO would be 408ci . 6.0lL Iron blocks are pretty affordable nowadays . Rods , pistons , cranks are around the same prices. Bigger cylinder bore has more cylinder head options in valve sizes and an stroker could use the Gm single plane intake without as much effect on torque . 11:1 402 .30over 408 with the new and upcoming 240cc TFS heads with a long runner fuelinjected carb style intake with a cam in the 250's-270's @.050 should produce around 550-600rwhp 500+ rwtq . I would take displacement myself but if you want to destroke go longrod to keep the piston near TDC longer . A Solid Roller 302 Lsx would be cool ,8500rpms . It would only be good for a lightweight car . It takes torque though to move our wholly mammoths.
6.0L block with a 3.0" stroke crank will make your 302, but why bother? I think you're looking at something completely custom. It's not like making a 302 SBC and matched combos say a 346 built to spin to 8500 rpm and make power throughout will make more of it than a 302 built to spin to 8500 rpm and make power throughout. The idea is to have the torque come on sooner, not later.
You could look to see if anyone already makes a forged crank for the 4.8's. Those motors are just destroked 5.3's. Put that in a 6.0 block or better yet an LS2 block if you can land one for cheap. Even a stock 4.8 crank could likely handle big power and rpms with main studs and a light piston/rod combo. In a lightweight car such as a Foxbody notchback, that would be a fun little setup. Plus running true duals out the back with full size mufflers is a non-issue in those things. 
Jason
Jason
Originally Posted by tylerdurden
I searched but could not find any info on this subject. Has anybody ever destroked a 347 into a 327cid field or a 302. I know the 5.3L is a 325 cid, but Iam talking about a forged balanced and blueprinted assy. A big valved, big cam motor and got some hp numbers. I would have to guess that it would wind up quick and run out of steam compared to a stroker cid motor on a long haul.
I guess all I see is just no place like displacment threads. I guess its food for thought. Hell with prices on parts it probably the same cost to stroke it up then down.
I guess all I see is just no place like displacment threads. I guess its food for thought. Hell with prices on parts it probably the same cost to stroke it up then down.
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TECH Addict
Joined: Jun 2005
Posts: 2,660
Likes: 14
From: England
Originally Posted by Zinc
What if you're building an open track or auto-x car, where big torque at lower RPM's isn't always the best thing?
And for Auto-X I would have thought a broad power band and flat torque curve would onnly be a benefit.
The only time I can see a less torquey higher reving setup being any help is if you race in a class with a displcement limit. And also if it's in a lightweight car. I know of a lightweight Caterham like, it used a Rover V8 and would lock the rear wheels when you down shifted from 3rd to 2nd. Way too much torque for the weight of the car.
TECH Resident
Joined: Jan 2003
Posts: 855
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From: AUSTIN TX
Originally Posted by KCS
Destroking isn't a good idea unless there is a race class your trying to make that limits displacement under 346 ci. You'll just lose torque everywhere, and spend a fortune on the valvetrain to survive the RPM needed to make the same power as a larger motor turning less RPM. Someone did do it along time ago and it was a dissapointment.
Also, from my understanding, you would have to run different intake setup as most of the LSX style setups are designed to make peak power in the 6400-6500 range (not including the sheet metal or carb style intakes). I actually have a car that I am building a destroked motor for, but that is because when I started the project I was planning on running in a lbs per ci class. I no longer have that ambition, but already have the parts so will most likely finish it and then build something bigger and better later.
TECH Enthusiast
Joined: Jul 2006
Posts: 747
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From: sofla
FWIW I believe the Daytona prototypes which use the Pontiac LSX motors are limited to 302ci. These things obviously scream, but as was stated earlier, you'll spend a fortune just keeping the valvetrain alive. Good luck either way...
CTS-V race cars in SCCA last year ran a destroked 7.0L that was destroked to 5.7. they were imposed an artifical rev limiter on them because they were kicking everyones ***.
used the LS7s 4.125 bore and the 4.8L trucks crank
personaly i want to see it done in street trim because it can obviously be done.
used the LS7s 4.125 bore and the 4.8L trucks crank
personaly i want to see it done in street trim because it can obviously be done.
Originally Posted by tylerdurden
I searched but could not find any info on this subject. Has anybody ever destroked a 347 into a 327cid field or a 302. I know the 5.3L is a 325 cid, but Iam talking about a forged balanced and blueprinted assy. A big valved, big cam motor and got some hp numbers. I would have to guess that it would wind up quick and run out of steam compared to a stroker cid motor on a long haul.
I guess all I see is just no place like displacment threads. I guess its food for thought. Hell with prices on parts it probably the same cost to stroke it up then down.
I guess all I see is just no place like displacment threads. I guess its food for thought. Hell with prices on parts it probably the same cost to stroke it up then down.
Why go smaller..?? .. there is nothing to gain with a smaller motor.. unles you want to make less power..the only reason would be to comply with some sort of cubic inch displacement rule of a sacantioning body ..
