383 power
04-10-2006, 10:22 PM
#21
He said he has 8.6cc pistons (dished), not 8.6:1 CR. Whitebird, is this number right? That's a very small dish for a blower piston. Sure it's not 18.6?
I think the LT4 heads have a nominal 54cc chamber, right?
I don't know how far down in the bore your piston tops out, but somewhere around .025" is pretty normal.
For gasket thickness I'll use a stock LT4 at .043"
Bore=4.03"
Stroke=3.75"
Calculated CR is 11.02. Pretty close since the LT4 is 10.8 and you have a stroked motor which increases the compression ratio. This is too high if you are prepping the motor for a blower. Somewhere around 9.5:1 is great for a centrifugal blower - you'll still be snappy on when not boosting but not too high so you can't boost to the double digits with a good intercooler.
Would you consider a small solid roller cam? I'm running a 230/236, .575/.584" net lift 112LSA Comp Cams Extreme Street Roller on my blown 383 A4 and it is great. If you want something more radical you could do the next lobes up: 236/242 on a 114LSA. I wanted a really good idle though, so I stayed with the smaller. I'm running 7.5# after the throttle and FMIC on a static CR of 9.6:1.
I do recommend you get a good port job done on those heads. Whether you stay NA or add the blower, the porting will pay off. Adding a blower is pretty much going to guarantee you need a stout tranny and rearend.
Jim
My Site: http://home.mindspring.com/~jim_fisk/id1.html
I think the LT4 heads have a nominal 54cc chamber, right?
I don't know how far down in the bore your piston tops out, but somewhere around .025" is pretty normal.
For gasket thickness I'll use a stock LT4 at .043"
Bore=4.03"
Stroke=3.75"
Calculated CR is 11.02. Pretty close since the LT4 is 10.8 and you have a stroked motor which increases the compression ratio. This is too high if you are prepping the motor for a blower. Somewhere around 9.5:1 is great for a centrifugal blower - you'll still be snappy on when not boosting but not too high so you can't boost to the double digits with a good intercooler.
Would you consider a small solid roller cam? I'm running a 230/236, .575/.584" net lift 112LSA Comp Cams Extreme Street Roller on my blown 383 A4 and it is great. If you want something more radical you could do the next lobes up: 236/242 on a 114LSA. I wanted a really good idle though, so I stayed with the smaller. I'm running 7.5# after the throttle and FMIC on a static CR of 9.6:1.
I do recommend you get a good port job done on those heads. Whether you stay NA or add the blower, the porting will pay off. Adding a blower is pretty much going to guarantee you need a stout tranny and rearend.
Jim
My Site: http://home.mindspring.com/~jim_fisk/id1.html
04-11-2006, 09:09 AM
#23
Originally Posted by DeltaT
He said he has 8.6cc pistons (dished), not 8.6:1 CR. Whitebird, is this number right? That's a very small dish for a blower piston. Sure it's not 18.6?
My dyslexia must be kickin' in. 
I read 8.6 and "blower piston". And 8.6 cc piston is NOT a blower piston. It'd be crazy to put a blower on an 11:1 motor, IMO.
