Just trying to establish some concrete limits from those who actually have some personal experience with the scenario.

I understand the Syclone and Typhoon run hypereutectics but I'm not sure of the boost levels for them or the Grand National. I'm currently running 7-8psi on an ~2002 3100 V6 short block originally equipped with aluminum heads now bolted to the Fiero intake and heads for a safe compression ratio of around 8:1. It runs very strong.

I will be replacing the engine with a complete late model 3400 that will have a little head chamber work to try and bring compression down to just under 9:1 if material permits. The plan is to run 15 psi with a reground roller cam to turbo specs under the turbo gp ECM. I have run as high as 12psi on a 2.8 with cast pistons but this was before I acquired the knowledge and equipment to reprogram and burn chips. Eventually a ring land broke, but then that was with no detonation protection and primitive fuel delivery modification.

If I were running an automatic 4T60 series or higher which could handle considerable more power I would strongly consider forged pistons but the manual tranny has its limits and I believe it is in more danger from a 15 psi power increase than the stock pistons so I'm trying to avoid investing in areas that are already of sufficient strength.

I have run up to 15 psi in my 3.4l DOHC car. As long as you don't get detonation, these pistons are very durable. I have about 50k miles on them with the turbo. Good control is the key to keeping any engine alive. I definitely beat the crap out of my car too.

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86 GT, 5-Speed
87 GT, 3.4l DOHC Turbo
95 BMW M3
02 Nissan Altima 3.5SE

INTERCOOLER??????

watercooled turbo?? helps a little but more for longer turbo life

adding an intercooler will allow more boost to be used before detination
it is all about temps
cooler the intake air post turbo compression
the more boost before BANG goes the motor

a rich A/F mix and a retarded spark setting will allow more boost
but both hurt power
lean advanced motors make more power but go BOOM quicker

most anti-knock sensors just retard the spark

BTW by the time you hear a knock it is way too late

my hauler is my second turbo volvo wagon

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Question wonder and be wierd
are you kind?

just because pistons are cast doesnt make them weak...just look at the cast SRT4 pistons...the key as stated before is tuning, good air/fuel control, detonation is your worst enemy

i personally haven't had good luck with hyperutectic pistons, i had a set in my turbo daytona and i broke 2 of them. The first time i was running 26psi boost and the second time i was only running 20psi. Hyperutectic pistons are fine but at the first sign of detonation they will shatter into pieces, not like a forged that can take the abuse.

If you want to keep the Hyper Pistons I would invest in Water/Alky injection kit. I have heard nothing but good things about using water injection in most turboed/supercharged vehicles (plus it'll clean your engine a bit)....and if you plan on putting more power thru the engine you can switch to alky and can up the boost some more safely once its tuned. I've heard that once detonation occurs with Hyper pistons they'll shatter like glass. Either way...I would think about water/alky injection for a little insurance.

Thanks for the input, I incorporated an intercooler from the ford SC 3.8 and am aware of the detonation issue as well as the brittle nature of this type of piston and will probably taper the timing advance down to 0 deg advance at 15 psi once I have a few solid reference points at the max boost level settings in a few other factory turbo cars such as the sunbird and Grand National. I think 2 deg retard per 1 psi is the general rule. I'll do some risky experiments with the tuning issue on the engine already in the car before removal to reduce the chance of damage to the replacement. As for the cast pistons I can't ignore the fact that detonation or not the increased pressures are going to produce a tremendous increase in load on the ring lands so the cast piston compared to the stronger piston has to have an earlier failing point but more importantly from what I remember about the cast piston in the fiero it was more the design of the piston that made it weaker at that location.

[This message has been edited by Joseph Upson (edited 06-24-2005).]

I had a Typhoon and they run 15 lbs stock. I never looked at what type of pistons they run stock but lost of people ran more than 18 psi all the time. How much boost were you geting away with on your stock 2.8? I want to turbo it untill I do the motor swap but I dont want to blow it up to soon.

I blew a piston on a stock 105k 3.4 DOHC, blew it BAD I had a chunk of piston ring under my throttle plate and piston jammed not only in the intake valves of that cyl, but another cyl as well. Its mostly about luck in my opinion, though I may have had a problem with fuel delivery, it seemed to set the injectors to wide open whenever the engine was dogged, dunno

The 2.8 was stock with no chip modification and poor fuel control, it was also a bit on the loud side with free flowing exhaust so it is possible I was getting detonation and wasn't able to hear it due to that. I ran upwards of about 9 psi and pushed it as high as 12 with an intercooler but due to space and lack of equipment to install it correctly I removed the intercooler. a considerable amount of time went by before the piston failed. I wanted to use the 749 computer but it lacks the ability to run the DIS system on the 3400 and since the TGP computer is tuned for an engine much closer in displacement it's the wiser choice. Tuning for 2 psi increments until 15psi is reached should prove safe enough to avoid damaging the engine.

The late genera V6 has a nice design and runs very smooth so a performance cam increasing duration and .020 spacers under the variable rate springs should make it reach 7000 rpm easy actually 7500 since it's already close to 7K. I want to keep the power closer to the high rpm end to distribute torque load though it may not see rpm that high. I have also looked at pictures of the cylinder head and will check into the possibility of having the exhaust port reqworked to fit an intake valve, there appears to be enough room.