Which pistons?

**Dale Pearman** · February 21, 2001, 02:23 PM

Re: Which pistons?

Cost is the least important factor when I build an engine for myself. I always order custom forged pistons for my driver. These pistons are specified for the rods I intend to use as well the goal of zero deck height. Usually a tad has to be taken off the top to achieve a tad less that zero deck height in practice.

In the engine I'm presently building I used JE pistons designed for floating pin rods of 5.7 inch length. There's a tad of a dish in the top to achieve a 10.1 to 1 static compression ratio with 461X heads. This numbers matching block has a 4340 steel lightweight crank with a stroke of 3.625. A high lift-short duration mechanical roller cam with a handmade shaft-mounted roller rocker system is also used. With an aluminum flywheel this engine is "tractor" engineering at it's best!

I just don't like the idea of the ungodly large compression ring gap needed for hypereutectic pistons. They have their advantages and I'm sure will work just fine if you ALWAYS keep the engine out of detonation or precombustion. However, the tops of these pistons contain so much heat that I'm uncomfortable with the idea. I'm just old-fashioned I guess but I know how many times I unaviodably get into detonating for a variety of reasons and I don't mind the "rattle" of forged pistons at all. The extra wall clearance allows for plenty of oil to splash around as well.

Dale.

**Joe L.** · February 21, 2001, 06:11 PM

Re: Which pistons?

Shane----

I have gone over this quite a few times, but I'll do it again. This time I'll "frame" my response a little differently.

When selecting engine components one needs to decide what is the appropriate component for the specific application. In many circumstances, the choice may be "overkill", but there is nothing lost except money. For example, 4 bolt main blocks are really not necessary for most street applications, but they help some folks sleep better at night and there is no negative consequence of using a 4 bolt main block. Roller rocker arms or roller tipped rocker arms don't produce very much benefit in a street engine, either, but there is no negative consequence of using them, in most cases.

Forged crankshafts are not necessary in most street engines, too. But, aside from cost and the slight extra ductility that cast nodular iron provides, there is no negative consequence to using one. So, if it makes you sleep better at night and you don't mind the extra cost, by all means, use one.

Expensive, "trick" forged rods are also uneccessary in most street engines. Virtually all Chevy rods are forged steel (except aftermarket aluminum jobs), so a good magnaflux, shot peening, resizing and ARP rod bolt installation will provide more than enough rod for virtually any street application with quite a margin in reserve. But, if you want to used high cost, super strength forged pistons in your engine, you sacrifice nothing except for dollars.

With pistons, it's different, though. Forged pistons DO provide the highest strength. No question about it. But, there is a DOWNSIDE to forged pistons. Piston wear resistance, oil control (due to "looser" piston-to-wall clearances required), and noise are three primary problems.

Cast pistons provide excellent wear properties, excellent oil control, and are vrtually noise-free. However, cast pistons are not strong enough to withstand the rigors of a high performance street engine. That's why GM first went to the use of forged pistons for Corvettes in 1962 for 340 and 360 hp engine applications. GM continued the use of forged pistons in all Corvette solid lifter engines from 1962 through 1972, and the L-79, L-46, and L-82 hydraulic lifter, special high performance engines built during 1965-81.

In the last 15 years, or so, a form of a cast piston has become available which is far stronger than the cast pistons of yore. This piston construction was made possible by the development of high silicon aluminum alloys (hypereutectic). These alloys allow a piston to be manufactured which is nearly as strong as forged, but with the advantages of cast. Just about the best of all worlds.

Of course, forged pistons are still the best choice for racing engines. For these engines absolute strength is the most important quality that a piston can have. Wear resistance, oil control, and noise control are totally irrelevant.

For street applications, though, the hypereutectic cast pistons provide more strength than is necessary, plus the wear resistance, oil control, and noise reduction which are also important for street operation. So, it sort of sums up like this: if you use forged pistons, you get more strength than is necessary for street operation, but you also get inferior wear resistance, oil control, and noise control. If you use hypereutectic cast pistons you still get more strength than is necessary for street operation (but not by as wide a margin as with forged pistons), but you also get superior wear resistance, oil control, and noise control.

As I have stated many times before, GM has not used a forged piston in ANY PRODUCTION engine since the L-82 went out of production after 1981. The Corvette LT5 (ZR-1) (90-95), LT1 (92-96), LT4 (96), LS1 (97-01), and LS6 (01) all use hypereutectic cast pistons. The ZZ-series crate engines, including the 430 hp ZZ-430 engine, all use hypereutectic cast pistons. Only the 454/502 cubic inch high performance crate engines, which are SERVICE engines validated to marine standards, use forged pistons.

I might also add that a set of HIGH QUALITY hypereutectic cast pistons is NOT inexpensive. If you check the price of Keith Black-Silvolite hypereutectic pistons you will find prices that are close to those of forged pistons. And, if you check the price of Mahle hypereutectic cast pistons (like those used in LT5, LT1, LT4, LS1, and LS6 engines) you will find the price comparable to or higher than many forged pistons. Unfortunately, Mahle, the world's largest manufacturer of pistons, does not currently manufacture pistons for 327 cid or big block Chevrolet engines. I wish they did.

Finally, one of the reasons for the cost difference between cast and forged pistons is the VAST difference in PRODUCTION QUANTITIES. Like everything else, when you produce something in large quantities and are tooled up for the task with high rate production machinery, the cost per unit can be much lower than low production pieces like forged pistons.

**Dale Pearman** · February 21, 2001, 08:43 PM

You're One Good Super Salersman Joe!

I just get a "rush" listening to all the advantages of hypereutics. I agree with you whole-heartedly. You make a great case for those pistons.

I'll remenber all those advantages next week when I order a set of Ross forged pistons for my next street engine project.

That's what makes the world go round! Individualism and mutual respect. We ARE having fun aren't we?

HAVE to let you in on this one. The rods in my driver's engine are NOS GMMilitary small journal rods that were packed in cosmolene and bore US Army labels. They are of the last design small journal but tighter tolerances and slightly better steel. I polished the beams, installed ARP bolts, bushed the piston ends, balanced and re-sized them and shot peened for Rockwell (140?). I would match these rods with the best that Crower produces at half the total investment.

The reason I'm using my shaft mounted roller rocker system is that I have owned it for the past 17 years and don't know what to do with it otherwise. Sure can't sell it and regain my investment. I would NEVER again buy such a contraption for the street. Also my 870 block remains a two bolt main. None of this 10,000 RPM stuff for me!

Dale.

**Joe L.** · February 21, 2001, 09:08 PM

Re: You're One Good Super Salersman Joe!

Dale-----

And I don't even own a single share of stock in, have any other proprietary interest in, or am employed by any hypereutectic piston manufacturer.

**John H.** · February 21, 2001, 09:52 PM

Some Coincidence.....

We use Mahle hypereutectic pistons in the Viper (changed from Mahle forged two years ago - testing showed the hypers provided better oil control, less noise, and reduced emissions, with no difference in durability) - they are, however, nearly the same price as forged - Mahle makes GOOD pistons. Incidentally, Dale, Vipers also use Rhodes (roller) lifters (and a fully-machined forged crank that would look great under a glass-top coffee table). Wait'll you see the innards of the 2003 Viper 500/500/500 engine - all we saved was the main bearing shells and the head gaskets from the current one! Fun job.......

**Duke W.** · February 21, 2001, 10:04 PM

From a pragmatic standpoint...

I agree with Joe 100 percent, but I need to add one "emotional" factor. SHP and FI engines with mechanical lifters and .0035" clearance forged pistons have a unique mechanical sound that is only exceeded in quality by a Columbo V-12. Part of this unique cacophony is piston noise. Without the OEM type forged pistons that are reasonably priced from Federal Mogul (nee TRW automotive) the engine just won't have that special visceral appeal.

Duke

**Craig S.** · February 22, 2001, 12:14 AM

Re: From a pragmatic standpoint...

Well said Duke. I like the slight slap on warm up, and the sound. My 67 L79 was rebuilt by the prior owner and was blueprinted and balanced about 3000 miles ago, but unfortunately has cast pistons(brand = ??) when I peered up when I pulled the pan just to inspect. I hate to pull down a new engine build that is glass smooth to 6000 rpm, but it bugs the hell out of me knowing the forged slugs are missing! It just sounds too quiet at idle- fortunately, the sidepipes help this problem out!.....and I just love the forged TRW's in my 81 454 pickup with the comp cams 270 straight up with 105cc closed chamber 69 oval port heads.....I know, not the best combination these days but it's got plenty of grunt and top end!

Does anyone know if Federal Mogul (TRW) still makes a .030 over slug for the L79 with the original 11.0 to 1? If so, what part number are they? I am hoping my almost fresh 0.030 over holes + a light hone will still have the right clearance for the TRW's and give me the compression and slap I long for....(borderline pinging, etc). I have no clue if I have a 151 cam but want to replace it just to know for sure. I think the Revs Rhodes lifter idea sounds great too!.....Craig (living in the past)....:D

**Duke W.** · February 22, 2001, 02:30 AM

Part number

Federal Mogul p/n L2166NF-30. They're also available in standard, 20, 40, and 60 thou over. Just change the suffix.

Duke

**George Daina** · February 22, 2001, 10:55 AM

Are you building a grocery getter......

or do you plan to buzz it a few times? Not to rain on anyone's parade, suggest you check with your local Chevy/Pontiac service dept. and inquire on a service bulletin re: 2000-2001 LS-1 engines. Seems the good oil control qualities, that everyone is expounding, have gone south because said drivers of above model year vehicles have a tendency to buzz their cars.

I would also contact owners who's engines use forged pistons and ask their opinion regarding oil control and consumption.

Let me be the first to state "What oil consumption? Plugs are clean and I'm as happy as a clam." For the same price, I'm sticking with the forged pistons. Let the grocery getters build their motors with hyper pistons.

**Dale Pearman** · February 22, 2001, 02:06 PM

Re: Some Coincidence.....

When hydraulic roller lifters first came out, John Rhodes told me to send him a set and he'd enlarge the hole for modification to variable duration hydraulic roller lifters. This was about the same time that I was perfecting an independent ignition system (HEI); one complete system for each cylinder.

There are times when I wish I could have worked as an R & D man in the auto industry.

Vipers ARE awesome aren't they?

Dale.

**Joe L.** · February 22, 2001, 09:39 PM

Re: Some Coincidence.....

John-----

VERY, VERY, VERY interesting, indeed! Thanks for providing that information.

**Craig S.** · February 23, 2001, 02:16 AM

Re: Part number- THX DUKE! *NM*

Which pistons?

Which pistons?

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