7MGTE - OEM Piston Capability Question

[Grandavi]

Just wondering if I understand this correctly and looking for clarity so if I discuss it, I dont come across as an idiot.

Just rebuilt my shortblock and had to do a lot of talking/searching/reading prior to ensure I dont do it twice. Now I think I may have misunderstood something and want to see if I understand it properly.

7MGTE engine with rebuilt shortblock using OEM bearing/rods/rings/pistons.
(ignore the head gasket.. its metal with ARP studs)

Mods - 550 injectors, Lexus AFM upgrade, AEM AFPR, AEM UEGO Wideband, 57 TRIM CT26 (DM), 3" turbo back exhaust, HKS EVC-S Boost controller.
(no upgrade to intercooler yet)

Now, I asked around and was told that I would not want to run this higher than 15 psi boost on OEM pistons (not talking HP here) because they aren't considered "safe" at that level. I want to run a bit higher, so I went with Wiseco pistons (which has its own little problem potentials but have nothing to do with this question).

Is this incorrect or can you run higher boost on OEM's safely?

I may have been told to limit my boost because I have no stand alone system so have limited control of what happens to the engine tune-wise...


Just dont want to repeat incorrect information...

 

[OfnaRcR4]

I've been running 18+ on mine no problems.

 

[Enraged]

15 psi on a stock turbo and 15 psi on a T4 are not the same thing...

 

[adampecush]

what's wrong with wisecos?

power won't kill your pistons (within reason), a poor tune will. I consider significantly upping the boost on the stock computer with a stock intercooler and a CT26 upgrade a poor tune. YMMV.

 

[hvyman]

It's all in your tune. Can max the 57 trim out with no problems as long as your tuned.

1 good detonation with stock pistons high higher boost levels and there toast.

 

[Grandavi]

Yeah, not talking about the wisecos, I got them (and paid the extra) because I was under the impression that it was unsafe to run OEMs at 15 psi or higher. Just was checking if this was true. I would have preferred to stay OEM if that was possible (money and other small issues) Stand alone would solve some of the issues, but thats not an expense I am ready for yet. (its the last thing I want to do in reality... it will be done.. but only as the very last stage)

What I am reading is with my setup (no standalone), running high boost on OEMs would not be wise. With a stand alone, it would be acceptable.

With the setup I currently have, I want to run at 14 psi as normal and 21 psi at high boost (rare use.. just to do it). Detonation would hammer either piston (OEM or Wiseco), so my only gaurd against that is watching the wideband for any variations. It wont tune, but it will show me if something is wonky and prevent engine death. But with OEM, I have been told (even with everything running correctly) not to run 15 psi+ boost because they aren't safe at higher boost.

Am I getting this all correct now? I actually dont know what the max potential (psi) is with the DM 57 Trim CT26. From reading, 21 is safe.

As a sidenote, to go above 500 hp (even with a standalone) water/meth is recommended to hold back on the detonation potentials. (this is Canada gas.. 91 octane)

 

[Enraged]

by the time you see something wrong on the gauge, the damage is already done.

again, PSI is NOT a measure of power, as the CFM of a turbo will vary depending on the turbo size. Whoever is telling you this is misleading you.

"Safe" is dependant on your tune. 21 psi, tuned to a steady 10.5:1 or 11:1 will likely be fine, but if you can't tune your fuel properly, and the AFR is not stable, you will likely break something.

as for water/meth, lots of people run more than 500rwhp without it. Again, it comes back to the tuning, ignition, and fuel systems.

As for Canada gas, 10 seconds of searching got me this: http://forums.beyond.ca/showthread/t-334891.html . Looks like you can get 94 at Husky/Mohawk.

 

[adampecush]

The advantage you have with a standalone is timing control, which will help fend off detonation. Forged pistons will be far more tolerant, but I wouldn't push 21 psi through a stock intercooler with the stock computer, no matter what pistons you are using.

As far as fuel is concerned, Husky and Petro Canada both sell 94 octane. I'll be well above 500 hp on 94 octane and won't be running meth thanks to an efficient turbo and intercooler setup. At the last tuning day up here, a soarer with low compression on a cylinder put down mid 600s on pump gas without meth.

Here is an OEM piston at no more than 16 psi with no EGR. Hell, this may have happened at low rpm acceleration.

 

[Enraged]

one other thing, regarding a standalone. it is a big expense initially, but when you start considering the cost of something breaking due to a shitty tune on piggybacks, it soon becomes a better decision in the long run.

 

[hvyman]

Megasquirt. cheapest ems out there and can even run e85. Full sequential fuel and ignition if wired up for it.

and ms3 pro comes out jan first.

 

[hvyman]

Megasquirt. cheapest ems out there and can even run e85. Full sequential fuel and ignition if wired up for it.

and ms3 pro comes out jan first.

 

[Grandavi]

hmm... okay.. now I dont feel safe running without standalone.. lol.

My tune will be okay, but it is on stock electronics... so I think I will hold off on going higher boost until I can afford to swap in a standalone. Will do the intercooler first.. as that is slated for next September. Will just run 14 psi until then and not overstress anything.
The last thing I want to do is a second engine build. The power isn't a necessity as I wont be on a track, I just want to have it in the end. It is a Supra... after all...

In the end, I guess, I would have been better off staying OEM (my power goals are 400'ish.. not higher). The engine wont be running until the first week of the new year and with the wiseco pistons, I have to worry about a bit of piston slap setting off the knock sensors... (at least.. thats what I am assuming)...

 

[Insidious Surmiser]

if you're serious about making power... it's just like I stated in a previous thread... stock shortblock should hold 700hp w/ a good tune. Although you will want to run a AEM ems, and find a damn good tuner. TBH though on stock electronics, and intercooler, I didn't feel safe running over 12 psi on my stock ct.

 

[adampecush]

with the wiseco pistons, I have to worry about a bit of piston slap setting off the knock sensors... (at least.. thats what I am assuming)...

say what?

no, you won't have to worry provided the pistons were installed in accordance with Wiseco's specified tolerances.

piston slap happens when the motor is cold, and because forged pistons have a higher coefficient of thermal expansion than cast, larger cold clearances are needed with forged pistons.

 

[Grandavi]

maybe i worded that wrong.. they rattle more because of the reasons you just gave. This isn't truly piston slap that would damage anything but if its too much it can set off the knock sensors.

Your explanation makes a lot of sense though. Thank you.

 

[Poodles]

The stock ECU looks for knock at a certain time, outside of that it's not looking for it and won't trim timing.

 

[Grandavi]

If I understand it all correctly, if your running under 700 hp (crank?) then Oem pistons are up to the task?

I looked at the mega squirt. It looks like it would do nicely, not sure who can tune with it in Calgary.

Without it, I am now thinking, I am relying on everything functioning properly or risking problems if anything goes squirrelly.

A 7m build is not as easy as people make it seem in discussions...

 

[adampecush]

maybe i worded that wrong.. they rattle more because of the reasons you just gave. This isn't truly piston slap that would damage anything but if its too much it can set off the knock sensors.

Your explanation makes a lot of sense though. Thank you.

no problem. at operating temperature, there is no difference in clearance between forged and cast. From what I've been told by others, wisecos don't really slap on cold start a whole lot either.

 

[IJ.]

I ran Tri coatings on my Pistons so had to close up the PtoB clearences as they never expanded fully when warm.

 

[Grandavi]

Well after reading this, I think I am going to have to go stand alone. I am thinking of using the Apexi Power FC Engine Management Stand Alone as the shop that is fixing my vehicle is a dealer for them and can tune with it.
With the tuning + Stand alone and installation, I think I gotta sock away about 3000.00...

another little pebble in the bucket...

At least with my shortblock built with forged, I can opt out for a bigger turbo later on if I want, so I dont mind the fact I overbuilt a little. Would have saved me a bit to just go OEM pistons though as they would have stood up to my desired power. (I dont really plan on going much over 400 HP with the 550's and 57TrimCT26). Dont want 700 HP.. I would be too tempted to use it on the street.. lol. No self-control...