Thinking of picking up a procharger or other intercooled supercharger kit. My 385 c.i. LT1 is running 11:1 compression with Mahle forged Powerpak pistons. They are the high silicone forging alloy (4032 if I remember right) so they are not as boost friendly as the ***** to the wall forgings but should be a good bit more detonation resistant than the stock cast pistons.
DCR was around 8.7:1 with a 218/224 CC XFI cam. I'm setup with a wideband O2 datalogger so guessing on the tuning wouldn't be a issue. Crankshaft horsepower right now is in the high 400 range. Wondering if anyone has experience with what sort of boost this setup could handle with good tuning assuming excellent reliabilty is very important.

 

With 11:1 CR and 8.7:1 DCR, assuming pump gas, you might be able to run one of these.




Benefits of Installing an Electric Supercharger

Lightweight and compact for any engine compartment
Reinforced Plastic ABS housing (NO RUST!!!)
Low voltage draw leaving more power for you engine!!
2-3 PSI Boost
up to 45hp
HUGE gains on hp when used WOT (wide open throttle)
Simple connections for quick installation


Go over 3psi and you will have to take so much timing out the engine that it won't run.

 

Hey man,
I actually posted a link to those on ebay several months back. Funny stuff.
I think alcohol/water injection is probably on the agenda if I do a supercharger install. Having installed and tuned a few supercharger kits before I'd make an educated guess of around 6 to 10 psi with vapor phase refrigeration (alcohol/water injection) Still just a guess on this particular combo as far as how much boost it would likely tolerate. Anyone else have any useful input?

 

with a very good meth set up and conservitive tune you might get 6-8psi for a little wile, with 11:1 and 4032 pistons.. the deck is stacked against you.. IMO it would be foolish. Why risk a nicly built 385 just too say you are supercharged.. put different pistons in it if your gonna do it. You could sell the ones you have recoup a little dough and not be out too much and it will actually last

 

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Those things work great for supercharging the leaves out of your front yard too!!!

Ken R.

 

OK,

Thanks for the replies.

The DCR on the stock LT1 motor is reputed to be around 8.5:1 and I've seen 6 pounds run on the stock pistons for a good long while with careful tuning. The only way I see to interpret the replies so far is that a .2 increase in DCR screws the pooch and you'll blow your pistons with very little boost or that 4032 pistons are at best a slight improvement to the stock hypereutectic castings. May be true but I'd expect the forging to be significantly more detonation tolerant than the cast piston. Maybe the improvement in grain structure ( less brittle) isn't worth a hoot and the high silicone content holding heat in the dome is the true key to breaking pistons under detonation. If that's true I guess we could all go to low silicone cast pistons and save money on the race forgings

Has anyone actually killed a set of 4032 pistons or am I looking at speculation? Important distinction in my book.



Thanks, Michael.

 

A stock LT1 motor will detonate when you get into more than a couple of pounds of boost under load. Timing retard can save the motor along with running it very rich. However, the power gains on such a 6lb setup are pretty insignificant. A good H/C setup will be faster, a hell of lot more reliable, and no more expensive - especialy when you factor in the cost of a rebuild. That's why people advise against boosting a stock LT1. LS1's make a lot more power with low boost and don't seem as prone to blowing up. I am not sure why this is so.

As far as the original post goes, much of the same logic applies. The pistons are sturdier though and if he has a decent set of heads will get a greater power increase with a low level of boost. But the answer is going to be that no one really knows. A few cars with similar setups, even if every one had already shown great durability, would not be enough proof of "excellent reliability". Just looking at it statistically: if excellent reliability is, for example, lasting 30,000 miles with a less than 5% chance of a major engine malfunction how many examples would it take to predict this to a 95% confidenece interval? Just an offhand guess is a couple of hundred. I doubt that there are that many similar setup out there. And the more variability in the setups and the conditions of use, the larger the sample would need to be.

That's why I really have to just shake my head when I see posts in response to questions like "how long will it last" that take the form of "I already have 2,000 miles on mine and no problems so far, so you should be fine." Seriously, that means next to nothing. And a couple of examples with 5 or 10,000 miles means little more. It wouldn't surprise me if there is a QC person lurking who could explain it better. But the only honest answer to your question from people here would be "I have no idea" or posting their own experience with you understanding how little that might actually mean to you.

My answer is "I have no idea" but my opinon based on extrapolation is that there is a better than 25% chance but a less than 95% chance that you would achieve "excellent reliability". Of course, a lot depends on conditions of operation, fuel used, etc. which you have not specified. And you have never indicated what you consider excellent reliability to be.

Rich

 

The LS1 is a better air pump. 6 psi on an LS1 might be 9 on an LT1 with similar pulley setup. Not sure why they last longer either.

 

Good post.

As far as heads and cam, I've taken car of that and like the setup so that won't be an option here other than a possible cam change if it would be worthwhile. The heads went 270 on the intake side if I remember right so a 5 or 6 pounds of boost would be a nice increase, I'd guess maybe 125 to 150 HP.

By excellent reliability I mean that the pistons are operating within their capabilities such that if you don't lean out the motor or tune it poorly so they do the death rattle they run indefinitely, say 50k or even 100k miles without failing. I don't realistically expect anyone to speak to that question but if there are folks who've run the 4032 pistons under boost for say 10k or 25k hard miles without any trouble that would be a good indicator that they can hold up long term for me. I don't run around at WOT all the time.

In my setup the engine wouldn't see the full boost even 5% of the time, probably less than 1%. It's a daily driver that isn't really ragged a lot. The vast majority of the time it's at less than 1/2 throttle and under 4500 RPM's. If it was setup for 6 psi at say 5500 RPM's it would see the 6psi occasionally but rarely for more than a few seconds. Most of the running would be anywhere from no boost to maybe 3 or 4 psi.

I'm running somewhere near 500HP now but want to be able to run and hide from a stocker with nitrous. I may just slap on a nitrous kit but if the supercharger would work out I'd probably prefer that for convenience. The initial cost difference is not a big factor and nitrous starts to catch up with the cost of a used SC kit pretty quick if you actually use it.

There are no guarantees, that's for sure. I'm just trying to make an educated decision.

Thanks, Michael