low compression 383 intended for boost, supercharger must wait
#1
low compression 383 intended for boost, supercharger must wait
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.
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.
#4
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
Originally Posted by sssalah
Changing the pistons later will require rebalancing the crank. So best bet would be to use some fun gas.
#5
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
Rich
#6
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.
#7
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
Rich
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.
#8
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
#10
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
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
#11
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
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