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Old 02-18-2008, 10:09 AM
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Hypereutectic pistons and turbos?

I'm getting ready to build a very one-off turbocharged engine, and the only appropriate pistons that I can find are hypereutectic. Does anybody have any experience with running hypereutectic pistons in a turbocharged engine (I'll be running about 15-18 psi max), or know if the pistons will hold up? I was planning on running forged pistons, but so far I haven't found anything applicable.....

(FYI, I need flat top "3.78 pistons with a crown that's thick enough to cut my own valve reliefs and compression height of around "1 3/8 +/-. There are some chevy 305 pistons that will work, but none that I've found are forged)

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Old 02-18-2008, 10:16 AM
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cast would be better than hypers for turbo charging... I'm sure there's forged 305 pistons out there somewhere though.
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Old 02-18-2008, 10:27 AM
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Any of the major piston manufacturers like Wiseco or JE can do a custom set of forged pistons. They will cost you some dollars but why mess around with cast stuff when you will just end up melting them?
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Old 02-18-2008, 11:05 AM
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http://cgi.ebay.com/ebaymotors/KEITH...QQcmdZViewItem
Forged 305 pistons

Shane
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Old 02-18-2008, 01:00 PM
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Buick Grand Nationals had Cast pistons in them from the factory. They will work fine as long as you keep your fuel and timing correct.




Larry
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Old 02-18-2008, 01:10 PM
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Hyp's will be fine as long as you avoid detonation. Cast pistons (including Hyp's) are very strong, but brittle. Forged pistons will actually yield sooner, but their malleability allows them to absorb more detonation impact before failing.

The issue isn't strength; they're both very strong. The issue is if you abuse them with detonation. Its literally like hitting the piston with a hammer. A forged piston will absorb it for a while, a cast piston will shatter.

Corky Bell (who literally wrote a book about turbocharging) actually prefers Hyp's in many applications.
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Old 02-18-2008, 01:33 PM
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Thanks for the info guys.

For what its worth, the problem isn't with finding forged pistons, but with finding "machine to fit" forged pistons. The bore and pin diameter for the 305 is correct for my application, but these are actually going into a 2.3L mercedes/cosworth engine. No matter what, I'll need to machine the top of the piston for valve reliefs and probably cut the compression surface to match my deck height. I've seen Corky Bell's book any number of times, but haven't picked it up just because I don't know who he is or wether the book is useful and/or accurate.

I'll be running a standalone EFI and spark controller, so assuming I can figure out how to tune things properly, detonation shouldn't be a problem. I'm also planning to investigate adding a knock sensor-retard circuit, but haven't even looked into that one yet.

My major concern was that since I'll be running substantially more boost than a stock GN or other turbo car, I didn't know if there are any established do's and don'ts for pistons and relatively high boost levels.
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Old 02-18-2008, 03:02 PM
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I'd run an Hyp 305 piston to 10 or 12 psi. Any more and I'd start thinking about forged.
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Old 02-18-2008, 04:43 PM
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I run 12 to 14 psi with my cast pistons on a 280zx turbo engine. I don't run any more due to poor engine management. However, other turbo Z owners do run up to 20 psi on their stock cast pistons with good efi systems.

Make sure to use low impedance injectors because they have much better control at low duty cycles.
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Old 02-18-2008, 07:04 PM
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4.3 vortec engines have hypers in them. and us 4.3 guys beat the crap out of them. i have run over 15 psi on my stock engine. and there is a guy trying to blow up a stock engine, way over 20psi. and he has not blow it yet. proper tuning is the answer.
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Old 02-19-2008, 09:42 AM
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Well, that's good news. I guess the next question is how aggressively/conservatively you guys are tuning the engines, and how much power you are extracting from them?

This is a relatively low budget project for me, but I'm still planning on taking the car to Bonneville at some point after I finish it, so I'm going to keep the tuning as aggressive as I can without blowing the engine up. Based on the results from one or two other people who have turbocharged these engines (using stock internal components), I'm expecting to achieve in the neighborhood of about 450 hp +/-. The stock rods seem to start failing around the 100hp per cylinder mark, so I'm switching to H-beam rods in the standard 5.7" chevy size. The chevy and MB pistons have different size wristpins, so I either have to re-bush the rods for whatever pistons I use, or just use pistons with the .927" wristpin. Since anything other than a 100% stock piston will need custom valve pockets anyway, I figure it's easier to start with something that fits.
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Old 02-19-2008, 09:57 AM
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In theory, the engine needs to make 200 hp without a turbo to make 450hp on 18 psi of boost.
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Old 02-19-2008, 10:10 AM
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Quote:
the only appropriate pistons that I can find are hypereutectic
Well, those aren't appropriate at all. Any piston mfr will make what you need. I would never play that game - use a hyper piston in a forced induction motor.

Quote:
Buick Grand Nationals had Cast pistons in them from the factory
The 'factory' use of that material doesn't warrant it's use in a performance application. Factory stuff is not always the best, and pales in comparison to aftermarket, application specific products. A lot of people do what you're about to and get away with it. The thing is, nobody who wastes their motor this way is going to be bragging about it. JMO
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Old 02-19-2008, 10:39 AM
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Stroke,
I was really hoping that the level of honesty on this forum is higher than that. From what I can tell, there aren't too many kiddies on here.... So I'd expect most members to admit if they had a bad experience with subgrade engine parts... That being said, you've got a good point and I'll remember to take all the testimonials with a grain of salt.

454C10,
The engine in question makes 185hp in stock form (with a substandard K-jetronic CIS fuel injection system, intentionally restricted intake system, and very mild cam specs). The cosworth/mercedes 2.3-16 was a homologation car built so that Mercedes could race the 190E platform in FIA and DTM race circuits. Getting these engines to 200hp+ as a NA engine is a cinch. The original cosworth prototype produced 320bhp as a NA engine, and race tuners like AMG squeezed about another 50 out of it for the race prepped cars.....

Needless to say, 450 with a turbo is very realistic for this engine. The guy who helped me with the turbo header design is building a semi-street drag car on the same platform. He is shooting for between 750-1000 hp with his engine, but since I plan to use the stock drivetrain and drive more than 1320 feet at a time, I can't really go the same route.

Last edited by Hal9000; 02-19-2008 at 10:44 AM.
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Old 02-19-2008, 12:37 PM
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JMO, as is, honesty isn't enough, I suggest you research your piston idea a bit further. There are 2.0ish 4 bangers making 1000+HP with turbos. There are motors such as yours bending Carrillo rods too. If you think your hyper piston is going to survive (far from that point) I've got news for you, they will be the rods demise for sure - amongst other parts. High RPM high output engines tend to require high end parts, or at least parts designed to be used in the application. Have you called any piston mfrs? I'm sure if everything were perfect and everything stayed that way you could run more boost and attain higher HP with those type pieces. I stick by my guns though in that dept. and cannot offer a pro (vs con) opinion for this scene as far as piston material. If it were my own and I wanted to see what could be done it'd be a different deal. In any case, keep this forum up to date with what you do. I'd be scared to risk what you don't seem to have a problem with.

Again, JMO.

Quote:
My major concern was that since I'll be running substantially more boost than a stock GN or other turbo car, I didn't know if there are any established do's and don'ts for pistons and relatively high boost levels
IMHO
Do use a forged piston
Do not use a Hyper piston

I'll bet these are not hypers
ROSS 4 Cylinder Custom Pistons
Also
Link to Custom Order Form

I have never worked for, nor accepted payment from, any parts manufacturer or supplier. I am not an advertising agent or compensated promoter of any product, service, or entity.
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