grammerman

I'm looking for some first or second had info. on how the 4032 pistons hold up to abuse. Posted a question in forced induction on how much boost the 4032 pistons will tolerate and haven't found any first hand info. so far. The consensus in there has been that 3 or 4 psi is the max. but it's not clear that anyone has actually done it with 4032 pistons to find out. If done I'll run alcahol/water injection or a big intercooler. Hopefully someone in here has killed a set or two with or without boost and can chime in.

I'm running the Mahle Powerpak 4032 forgings at 11:1, DCR of around 8.7:1. Thinking of installing a mild supercharger kit (4-8 psi) but I've never personally seen any of these 4032 pistons have the wood put to them so durability is a big ?

I know the cast/hypereutectic pistons I've seen fail under detonation often shatter and most of the time the top ring land has frag'ed. A ring land breaking off can often be traced to a stock ring end gap that closed up. My end gaps were setup loose for possible boost/nitrous in the future. I've seen the standard race type forgings get rattled like hell on the dyno and often hold together and eventually burn a hole through the crown. I haven't seen any failed 4032 pistons or actually killed them myself so I just don't know how stout they are when stressed with boost/nitrous or detonation in general. I'd assume they'd be significantly stouter than a cast piston but how much?

I have seen the stock pistons hold up for a for a good while under 8 psi of boost with alcohol injection and a very long time under 6 psi with an intercooler and careful tuning. My DCR is just a tick higher than the stock LT1 engine so that seems to be a fair comparison. Seems reasonable from experience with other forged pistons and how they fail that the 4032's should be significantly more detonation resistant than a cast piston but I'd like to hear from people who have more experience with them.

Anyone have some experience with these forgings they can clue me in on?

Thanks, Michael.

SStrokerAce

11:1 with boost? You seem to be pushing it right there. That's just looking for detonation on pump gas. Which will kill any piston. I don't know if I would go that way.... either lower the compression or don't run the boost. Maybe look at a TFS casting for what you are doing, that will easily put 10-15cc more volume in the chambers.

4032 alloy is not bad, it gets a bad name for some odd reason but it's a much better alloy for street motors rather than 2618 which is a lower silicon content allow that normally runs a looser piston to wall clearance. 4032 is much stronger than hyper cast pistons, but has the good wear qualities like them due to the high (11-13.5% silicon content)

2618 is a alloy that is used in applications where a weight/strength ratio needs to be good. A 4032 part most times is going to be heavier for the same strength.

Here is some good reading:
http://www.popularhotrodding.com/tec...ns_and_cranks/

Or if you dare go to a ricer site:
http://www.dsmtalk.com/forums/showthread.php?t=170505

FWIW the DSM guys are actually dam smart, that is a good post for reading and saves me doing the work!

Bret

grammerman

Thanks for the links Bret. I'm considering going with alcohol/water injection on top of a supercharger. Certainly running straight pump gas the boost limit would be pretty low.


The turbo guys run pretty darn high levels of boost using straight alcohol injection on top of pump gas. I'm thinking that a alcohol or alcohol/water (windshield washer fluid) injection system would make this completely doable with no detonation problems. Methanol pulls something like 3 or 4 times the heat from the combustion charge as gasoline when it evaporates. Really effective stuff for supressing detonation if you add enough of it.

My motor's approx. 8.7:1 DCR is not too far from detonation on good pump gas normally aspirated. With a intercooler I'd think the max. safe boost would be a few pounds. From the way I understand it the real problem with pushing the envelope on compression ratio or boost and not breaking pistons is keeping the combustion charge cool enough so it doesn't detonate.

I wonder why you don't see NA engines with much higher compression ratios that use methanol enrichment under high load to control detonation. Seems like it would make for a considerably more efficient, powerful and responsive engine. Maybe it's just too much trouble and expense for the power increase you'd get from bumping compression from 11:1 NA to 14 or 16:1 ?


Anyway, I'm thinking that a alcohol injection system would let you run a healthy amount of boost on these pistons at 8.7 DCR without hammering them with detonation. I've seen race forgings get ventilated on the dyno in just a few seconds of heavy detonation so it's nothing to play with. Unless you like working on your engine that is

Later, Michael

SStrokerAce

Why not just change the cam to match the boost as well?

I've seen high VE% NA motors run like poo with high DCR's on pump gas, so I can't think that even with the help adding boost to increase the VE% to 140+ would be good for that.

Bret