Im told on another thread that a turbo with my speed pro hyperwhatever pistons would be a bad idea, that they are brittle and highly susceptible to pre ignition.

so, my question is, do superchargers run at a lower temp then turbos, (seems like they would) and would that lower temp mean that a preignition problem would be less likely?

and if i toned down the boost to say 5 psi, would that give me a worthwhile power boost for the money?
and would it lower the chance of preignition?

OR should i just give it as much boost as it can take, wait for them to blow up, and then get forged pistons?

as I understand it, spark knock jsut blows a hole int he top of the piston and would be unlikely to damage other components?

 

Hypereutectic. A high strength cast piston having 12% or more silicon content. I would feel safe running up to 10lbs of boost on cast pistons (hypereutectic or normal eutectic). Depending on the set up. Intercooling or water-injection, close control of fuel and spark: all part of the package.

It's detonation that Hypers have an issue with. When you start cranking up the boost the chance of detonation increases. If you play safe (see above), don't worry about it , BUT boost is addictive and forged piston become part of the "fix"

 

soo, 6-8 pounds of boost, inter cooled, with tight fuel control, and have fun till i blow them up.

the term "when they pop they pop hard" bothers me.

WHEN i break them, not if, will it likely take out other parts on their way?

 

see, im not sure its worth the risk of that.

and i almost certainly will never have a car with 20 pounds of boost.

 

I think a lot of times you just blow a head gasket - if you are lucky.

 

a broken piston i can handle, big holes in the block, unintentionally removed valves, blown up body panels, those are bad.

 

I'm really worried about this w/ my build (11 psi boost on stock bottom end). Its running fine now, but id hate to have bad gas blow it up.

I got mild detonation this summer when my meth/water injection system malfunctioned and I got a pop, sensation of lack of power, and black smoke out the exhaust.

This when I was 'opening it up' as I left a toll booth in western PA.

The meth system had an alarm buzzer going off, but I couldn't hear it over engine roar. I've since wired a failsafe relay to cutout fuel injectors.

When this incident (the toll-booth incident) occurred, I had a datalog hooked up and it indicated my suspiscion. At 5100 rpm, 10 psi boost (and rising as rpm increased) there was a severe knock retard event resulting in 10 degrees (max I had allowed) of retard. If the knock retard didnt occur and I stayed on the gas, Im guessing the engine would have blown up?

In fact, heres the frame from my scantool when this event occurred!



It shows 20 degrees spark advance (at 5100 rpm) was commanded and you see only what 10 degrees advance occurring. This is because 10 degrees of knock retard knocked off that timing.

Now, Ive hooked up a device called a 'Casper knock gauge' so I have a direct real-time view of what my knock sensors of doing.

This is a second event (not full-fledge detonation like the toll-booth incident, but pre-detonation) w/ some knock retard

Look at this dyno pull:

http://www.youtube.com/watch?v=J-KIP...&feature=feedu

When the second light on the casper knock gauge (the 2nd gauge in the middle of the dash) lights up, my datascan indicated 83 knock counts and 5 degrees of knock retard - so I immediately let up on the gas and aborted the dyno pull.

In case you are curious, I was running 21 degrees of spark advance (commanded) w/ meth injection when this occurred. This event also occurred around 5100 to 5200 rpm.

In this incident the meth/water injection system was working properly (if it wasnt then the car wouldnt have rev'd that high due to fuel relay cutout).

Now, there are some flaws to the casper knock retard gauge. Mainly, the LED's light up based on input from my a Buick Grand National ESC module spliced into my knock sensor circuit. So those LED's are telling me what knock sensor input would command knock retard on a buick grand national and not the actual retard that my ECM is pulling.

I wish I could splice it into my ECM to know exactly what my knock sensors are doing, but this gauge relies upon a buick grand national ESC. The LT-1 v-8 has knock control integrated directly into the ECM and not a separate module (required for casper gauge to function). Perhaps, I could wire in an L98 ESC module and have a better indication about what would command knock based on a v-8 platform...

but for the moment... I know that the 3rd green light indicates 5 degrees of retard ! which is too much and I should back off.

 

[U]DETONATION[/U

In the interest of helping all new comers to the land of forced induction (or extreme high compression ratios on a N/A engine like 12:1) lets first describe detonation or engine ping. It's not really pre-igniton although both end up with same effect.

If an engine detonates you can hear it as a pinging sound (assuming you are not too old with dead ears or you are running a floMaster exhaust - ! LOL). Maybe you've been at a traffic light and the guy/gal next to you sounded like a broken marble machine and you wondered what the hell was that? Not a diesel (lower sound) but kinda of like a diesel at a higher note !!!!!!

So what is detonation or engine ping ??? OMG it's the worst thing you can possibly think of. It will destroy any engine no matter how well built or with whatever components !!!!

Engine ping or detonation [or pre-ignition with a further definition] is the piston banging around in the cylinder (and it should never do that !). What you hear is the actual piston 'slapping' the cylinder wall as the "rings" collapse and allow metal to metal contact. Not only do we have metal to metal contact but we have an enormous amount of cylinder gas pass by the piston rings (as they collapse) and become BLOW-BY !!!

All of the above is a result of detonation: the flame front expands so quickly as to become an explosion as opposed to a controlled burn. Any high performance engine can demonstrate detonation if fed a bad load of gas (like 87 vs 93 octane).

The end result is an explosion - where the rising psiton meets an expanding gas. Who or what gives ? In the case of cast pistons (hyperutectic) the piston. In the case of forged pistons well the rod bearings first then other components of the rotaing assembly.

Bottom line is detonation will KILL all engines !!!!!!!!! But if your engine has cast pistons the pistons fail first. If forged pistons you'll blow an actual hole in the piston or break a rod or break a crank !!! In any case detonation is the enemy !!!!!!

More later if you want - I've got to run just now ........

VTY - greg

 

ok... i completed my previous post. in this thread..

I was working and busy earlier....

 

The best analogy I can give about hyperteutic pistons is they are like a correlle dish.

A little bit harder to break than a regular dish, but when it does break.... It shatters and explodes!

 

I didn't want to take the chance and had a short block built that could take more than what I was going to throw at it.

 

Obviously forged will handle more power. That being said, the supercharged pontiac gtp uses cast pistons (probably not as good as speed pro) and runs 6 psi.

 

this thread has been interesting, some solid information.

My budget may make the choice for me long before i have to make it for myself (dang kids and braces and all the rest)

Still the question remains, can i go ahead with the planned 6 pounds of boost for a few years untill I am ready to rebuild the bottom end again?

I cant afford to rebuild the bottom end i just rebuilt!

 

Go ahead. You will be fine.

 

Cadillac CTS-V, Subaru WRX (07+ and up), Mazdaspeed 3:

What do these all have in common?

They are OEM forced induction and do not used forged pistons. They are hyperteutic!

In reality though I think they should have forged components, but likely some exec made the corporate decision to save costs and 'pocket' the difference as a bonus.