Well, finally found this site...I thought TeamSR had kicked us all out!!

Anyways, since I am always on the lookout for turbo info, I have come across a thing on RPW's site about how they "rarely endorse the use of forged pistons". Why would this be?

And, what is the difference between Hypereutectic pistons and forged pistons, and which would be more suitable for a turbo'd engine?

Thanks,

Mav

EDIT: also, in the CNK turbo kit he says he has 8.5:1 Turbo pistons. What are they made of, or how are they made?

[ December 29, 2002, 09:53 PM: Message edited by: Mav ]

 

CNK's are Hyper-u's.

Read this.

For under 300 WHP, Hyper-U's should be just fine. For over 300 WHP, go with forged.

Forged require larger pistion/ring to cylinder wall clearances, because the forged pistions expand more when heated. When cold, the "gap" caused by the excess clearances causes "piston slap" where the pistion skirts can scrap/rub the cylinder walls causing scoring/wear within the cylinder. Once heated, the Forged pistions expand, improving ring seal, and enlarge to reduce the "gap/space" that causes pistion slap.

With a "road" going engine, expect to re-hone your cylinders in as few as 50,000 miles with forged pistions. You can also not put the engine under load/stress/high rpm until the forged pistions are warmed up. This means 120 seconds of engine warm up in mild climates to 15+ minutes of engine warm up in very cold climates. The longer the warm up, the worse the wear in the cylinders as the "slap" is worse at colder tempatures, and it also occurs for a longer period of time.

Hyper-U's don't have this disadvantage, but they are not as strong as forged.

[ December 30, 2002, 01:16 AM: Message edited by: Random ]

 

Different applications require different solutions. In the Mopar turbo camp, hypereutectics are the devil... the motors are etonation prone, and HU's tend to shatter. On the flip side, the blocks are extremely high nickel content cast iron, and forged pistons, while noisy, last at least a couple hundred thousand miles. Both motors I've torn down, both with over 80,000 miles on stock pistons, still had the cross-hatching from the factory bore left in them.

What good is this information to you? First, it's a warning that HU's will *not* handle detonation, and to be carfeul with your air-fuel ratios and timing. Second, if you find the Beta block is a good material (i.e. not too soft, get it rockwell tested at a metallurgist if you can), and use the proper rings, AND stay out of the better half of the loud pedal while the engine is warming, forged pistons will give you great service AND detonation resistance.

Another word... thousand upon thousands of dodge turbo owners are still using the factory cast non-HU pistons, even to the 300 HP level. If you can find a properly reinforced cast piston, it may be lighter than a forged slug and handle a reasonable amount of boost.

YMMV.

 

I am enlightened. Thanks Random and Mike for the clarification. It gets dang cold in my area sometimes, so methinks CNK pistons will do fine.

Thanks!

Mav

 

all I am gonna say is at idle. with a stock motor. and the defrost and everything turned on.

in 10f weather, with snow on the hood.

It took over and hour for it to BEGIN to warm up.

 

Shaddoh. Next time, don't turn the defroster on till the car it warm. It warms up faster if you don't blow/draw cold air over the heater core! tongue.gif

 

One of the questions i forgot to ask you...

 

dohhh stupid on my behalf

I thought the idea was for the thermostat to stay closed sooner to make hot air.

course I then realized later. the intake for the air systemw as packe with snow.

super cold air smile.gif

 

I don't mean don't drive it, I meant don't stress it. It's actually bad for any motor to sit there at idle (read: low oil pressure) cold. Drive off, just... slowly smile.gif

My morning routine with my Daewoo is basically crank it, scrape the windows, turn the air register to recirc/defrost/full hot/full air, then drive off, and then keep it under 3000 RPM, usually under 2500. The car is usually warm in 4 to 5 minutes, and there've been some 20 degree days.

The dodge... I gave it hell in the mornings, because I knew the engine was already toast (rings are shot), and the thermostat isn't functioning properly anyways so the motor has trouble warming up on a nice 60 degree day. Of course, that's a high nickel block with 110,000 miles on it and a nearly dead clutch, it's not like I care. Once I finish building the turbo replacement motor though, it'll get the same treatment the 'Woo does, except with an after-run, which I may automate.