ssrogers

If I put in a 4" crank, but left the bore stock, would that give me a torque curve that peaks way to soon?

When ever I use DynoSim, the torque peaks at about 4000rpm. To me that seems a little low. Isn't it? However, this is not an LS1. It just a 350 SB engine that I built on DynoSim to be close to the LS1 and make about the same power. So, I was hoping that somebody that knows how an actual LS1 would respond to something like this would be able to help me out.

By the way,
Before you think that it was just the engine that I built. I started that engine with the LS1 bore/stroke and the peaks (HP and Tq) were closer to that of the LS1. Then when I changed the stroke to 4" thats when the peak moved and of course the hp peak move because the hp calculation is so dependent on torque.

Steven

Hysteria

The crank thing is like this, take a bicycle with a long throw on the crank and you will notice that it is easy to push the crank over but it is really hard to pedal it fast because of the long distance your legs are traveling. Now take the same bike and put a short throw crank in it and you will notice that it is hard to pedal at first and once it gets going it can be pedaled real fast until you reach an incline. Torque is a wonderful thing. The problem with using a SB chevy is the 9.025 deck height, 4.00 crank must be used with at least a 6.00 rod and that leaves a piston that has a 1.00 compression height and a terrible R/S ratio. Bike thing again, long throw+short legs=low RPM. It is also like the '70-'80 SB 400's, a 3.75 stroke by 4.125 bore. It would seem this thing would rev really well but chevy put a stinking 5.565 rod in it.

ssrogers

I'm pretty sure the rods would need to be 6.125

So, do you think it's a bad idea? I couldn't really tell. Your post seemed almost neutral. It's like you were hinting that it was not a good thing to do.

But, most of those engine packages use 4" crank and a 6.125" rod and they make a lot of power. I just thought that if I left the bore stock that that would save me some labor cost and I could reuse my stock pistons. But, I would still be gaining some cubic inches and torque. See?


Steven

Hysteria

With the LS1 deck height being 9.240 you can use the 6.125 rod and it would be a lot better R/S ratio. One thing is you will not be able to use the stock pistons because the crank and rod change will cause the pistion to be .116" or more out of the block. The purchase of new pistons is required with the proper compression height, 1.130" or so. I am neutral on the engine because it has its advantages as long as you know it will not be a revver. Most 382 all stroke combos that have a good set of heads and a 220-228 cam usually peak the torque out at 4400 rpm around the 488 ft.lb. mark at the ground and the peak HP usually around 5600-5800 rpm around 440 or so at the ground. All #'s are through a M6 tranny.