badblackta

I have been thinking about what I want to do when I rebuild my motor, and have been toying with the notion of de-stroking it. What I am thing about doing is putting a shorter crank and connecting rods and boring the block like .30 over. Not sure on the complete specs to do it but I want to make it like a 302. What I heard people used to do was put a crank out of a 283 v-8 in a 350, but I have no idea where I could get a custom crank and rods like that from. Any input?

OldSStroker

Try this thread:


http://web.camaross.com/forums/showt...threadid=79881

Stephen 87 IROC

Destroking is good for a high reving, long running engine like in Nascar. They run around for 2-3 hours at close to 8000 rpm. Because they're running at high rpms so long, they don't need torque which is built at low rpms with long strokes. They build the engines with large bores (more hp) and short stroke (less torque). Using aftermarket blocks a Nascar engine will have a bore size larger than a 400 SBC but because of the short stroke will only be around 358 CID.

For stop and go driving or drag racing you want to build torque because that's what you'll use the most. Build a 383 or a 400 for the longer stroke torque.

You can't really build a good 302 with factory parts any more. The old 283 cranks used small journal rods. In 1969 all SBC engines went to large journal rods.

DarthIROC

Wow that was a while ago. If I knew then what I know now :P

The only real reason to build a 302, unless your going to circle track it is to say "I have a 302" They are cool motors, with a neat history. ANd lets face it, turning a small block to 8000+ RPM's is just awesome.

But for more common apps, like driving on the street, or drag racing the car you would do better with a 383 or 406 type set-up.

badblackta

Well cool. I still dont know though. I know the stroker motors make alot of power an torque down low but I know a guy the has an altered class corvette that he used to race that has a 302 in it (was a 350) and he turns it to like 11,000 rpms. The car was fast too like 8 seconds. I was thinking of just building something I could turn real high. Probably will just build a stroker 396 and be done with it.

OldSStroker

Torque production depends more on displacement and breathing ability than stroke length.

A 350 has about 16% more displacement that a 302, and a 383 has about 9-1/2% more than a 350. The extra torque you see comes mostly from the displacement. If you don't increase the breathing ability when you stroke, you push the torque peak down due to reaching best volumetric efficiency at a lower rpm. This is sometimed explained by the longer stroke having more "arm", but, IMO, it's more airflow related.

Destroking a 350 and keeping the same bore size and head/manifold flow and cam will move both torque peak and hp peak up, and you may see a disproportionate loss of low end torque mainly because of the extra flow potential and overlap.

In other words, if the head/manifold/cam combination flows say 500 cfm at it's most efficient point, which is probably where and engine produces max torque, the rpm where that flow occurs will change (inversely) with displacement.

HP is torque and rpm, so making the same torque at a higher rpm makes more hp, of course. Piston speed is one of the limiting factors in max sustainable rpm, so short strokes help keep that down as well as keeping friction down.

The trend for high power, high rpm racing engines is as large a bore as practical, with the stroke then chosen to determine displacement. Nextel Cup and Formula 1 engines are good examples. 358 inch Cup engines have about the 3.25 stroke of a 327, and 183 inch (10 cyl) F1 engines have about half the Cup engine stroke, but turn just about twice the rpm.

OEM production engines have very different criteria for bore and stroke combinations. A BMW M3 engine with a power peak at 7900 has a 3.58 stroke, while the BMW F1 engine, with a power peak about 18000 has approximately a 1.55 inch stroke. They have very similar piston speeds at power peak, which is about the same as a Cup engine at power peak. They M3 engine seems to have a fairly high warranty cost. Piston speed related? Good chance, IMO.

My $.02

cnorton

If you're interested in a cast crank that will bolt into an LT1 block you might wish to explore the L99 engine combination. The L99 V8 was available only in the 1994-5 Caprice and displaced 265 cubic inches (or 4.3 liters). The bore/stroke figures on that engine are precisely the same as that of a 1955 Chevy. The most significant difference from the LT1 configuration is the fact that it uses a 5.94" connecting rod.

dave96dcm

Also the L99 has a 3" stroke so with a stock bore (4") it will be a 302.