I'm building up a 383 this summer that I ultimately intend to supercharge with a Procharger D-1 next summer. however, its going to be till next summer until I'll have the time/money to do the supercharger, so this summer I'm concentrating on building the engine. I'm planning for a 9:1 compression ratio to handle up to 15# of boost on pump gas.

Since the supercharger won't be coming for a while, should I do high compression pistons now and swap to dished when I add the blower, or build it once and deal with the low compression until then?

My planned build:
VRE 383 Speed pack (Dragonslayer crank, Compstar rods, Diamond pistons)
Ai 210cc Trickflows or Ai or LE3 LT4s (corresponding piston dish for chamber size)
Associated custom blower cam
36-40# injectors for now
Hawks long-tube headers

I know I'll be down on performance compared to a higher compression ratio N/A so I'll more than likely had some nitrous to the mix in the mean time until I do the supercharger.

 

Sounds like the exact same plan I have for next year.

 

Changing the pistons later will require rebalancing the crank. So best bet would be to use some fun gas.

 

then I'll let you know how it runs when I get it in

good point, I didn't think about that. low compression it is

 

You can get away with pistons that are up to ~30gms lighter (more on a big block) with no noticible effects. Some engine builders do this kind of overbalancing deliberately. Going heavier on an already balanced assembly is not a good idea. Though a small difference would be ok.

Rich

 

Agreed, plus there might be a slight difference in the size of the pistons. I think an engine builder checks the piston size before he puts the finishing touch on the bores, to get a perfect fit for whatever the application is.

 

I just checked the Diamond catalog and the difference between a flat-top and the dished blower pistons is about 20grams heavier for the dished. answers that question then.

 

You might get away with that. I am not an expert in balancing - but I have done the lighter piston thing a few times times with no abnormal wear issues and no noticible difference in percieved vibration. What I have been told is that while that kind of overbalancing is ok, underbalancing (heavier piston) is more of a problem. The theory behind overbalancing is that on a blower motor, it decreases the force on the bearing as the piston approaches BDC. This makes sense, the piston is going down while the counterweight's net force is upward. A heavier piston would increase the load under the same circumstances. Of course, near TDC the forces are reversed, but since they are less there to begin with the overbalancing makes a certain amount of sense.

Rich

 

since I'm ordering a balanced rotating assembly, I think I'll just leave it alone

 

I think you made a good descision to build the blower motor now and run with it "all natural" while waiting for the future forced induction set up.

I just built an 8.6:1 F2 blower motor (383LT1) using Ai's top of the line heads/cam/valvetrain. The thing still makes monster torque and hp on an engine dyno (all natural). Maybe a bit sluggish at low rpm but you'll still have a hard time not noticing 500+ ft-lb of torque.

Heck, depending on the cam, maybe you can run junk gasoline "sans-blower'.

Karl Ellwein

 

Karl, thanks for the reply, thats what I like to hear. Ai Trickflows is what I'm leaning to for the top end, although I won't be pushing quite the same amount of power through it as that F2 will