I want the engine to be very solid at 300rwhp. I'm torn between using NPR or Probe pistons. My Supra is my daily driver, so I didn't originally want a forged piston because I've heard they are prone to piston slap on cold starts. I've also seen the broken NPR pistons threads. Which is the better choice?
7M build. Pistons?
- Thread starter jake8790
- Start date
If you don't need to bore, then stock pistons.
I just went through this decision process myself, with up to a 450 WHP goal, and essentially it came down to that the stock pistons were good enough, with room to spare. The pistons aren't the weak point, really.
I was considering the Probe pistons because they're relatively inexpensive, but still more than just buying rings for the pistons that I already have, so I'll buy rings for the pistons that I already have.
Forged pistons undergo more thermal expansion than the stock hypereutectic pistons, which means that they have to have wider tolerances when cold, since they heat to a closer tolerance fit. This can allow piston slap while the pistons are cold, however a short warm-up period is all that's required to avoid the problem. They're stronger, and sometimes lighter, though I think that the weight difference is negligible for the 7M engine, so... No real advantage.
I just went through this decision process myself, with up to a 450 WHP goal, and essentially it came down to that the stock pistons were good enough, with room to spare. The pistons aren't the weak point, really.
I was considering the Probe pistons because they're relatively inexpensive, but still more than just buying rings for the pistons that I already have, so I'll buy rings for the pistons that I already have.
Forged pistons undergo more thermal expansion than the stock hypereutectic pistons, which means that they have to have wider tolerances when cold, since they heat to a closer tolerance fit. This can allow piston slap while the pistons are cold, however a short warm-up period is all that's required to avoid the problem. They're stronger, and sometimes lighter, though I think that the weight difference is negligible for the 7M engine, so... No real advantage.
My block needs to be bored over and the machine shop needs the pistons. I'm still torn and don't know what to order. Will the NPR's hold up fine? Mods include 3" turbo back, intake, and stock ct at 10 lbs. I do have a wideband. I will probably upgrade to a 57 trim eventually.
All I can tell you, is that my Probe's don't slap when cold.
But as stated above- they're not necessary for a 300WHP build.
But as stated above- they're not necessary for a 300WHP build.
Forged is a good way to future proof a build in case you change plans and want more power later...
If you're concerned about Slap just have the Pistons coated and close down the PtoB clearence a couple of thou.
If you're concerned about Slap just have the Pistons coated and close down the PtoB clearence a couple of thou.
Ive had no problems with stock NPR's in my 7m. Shot peened rods and all ARP hardware. Made 343 whp at 13.4 psi on 60 trim CT26 with lex/550's last dyno.
Its now bumped up to 18psi with methanol injection, running maftpro speed density. Has to be an easy 400+ whp now. No issues so far, just have to have a GOOD tune with ZERO detonation.
Its now bumped up to 18psi with methanol injection, running maftpro speed density. Has to be an easy 400+ whp now. No issues so far, just have to have a GOOD tune with ZERO detonation.
