The Stovebolt Site Forums The Shop Area Engine Shop how effective are performance pistons?

ive been looking all over the place for some performance pistons to put in my 292. im not looking for custom fabricated pistons, but more on the cheaper side. anyone able to steer me in the right direction? also, how well do they work to begin with? do they provide a big enough of a difference to make the cost of them worth it?

Try 307 V8 pistons.(They don't fit)((( Sorry, I had my 230/250 on the brain, use the propane slugs in the 292, but I think it only gives 9:1)))Brian

look at pistons for propane if I remember correctly they work out at about 10/1

307 V-8 pistons fit a 250, which has a different bore size and compression distance than a 292, I believe. Are you looking for a compression increase? Get yourself a Speed-Pro piston catalog, and try to find a piston with a similar bore diameter, compression height, and wrist pin size, and possibly a similar wrist pin offset. There are 3 types of pistons, cast, Hypereutectic cast, and forged pistons. The cast pistons are good for stock rebuilding, the hyper types are considerably stronger, and fit with reduced skirt clearance, and the forged ones are mostly good for race-only applications because of the wide skirt clearance they have to run. Forged pistons in an engine that has to run mufflers make a lot of noise. The wide clearance also promotes a little oil consumption, not a problem in a racing situation, but it's a pain in a street machine.
Jerry

Jerry,I know a lot of guys who run forged pistons on the street engines.Never heard any complaints about oil consumption for any piston noise once the engine is run for a minute.Proper engineered forged pistons run at .055 clearance,which tightens up some when they get warm.Now you're not going to get zero oil usage,but I hear about a quart every 2000 -2500 miles, not bad,most stock old 6's use more oil than that
There are the so called propane cast pistons available at stocker prices for 292's. They are advertised at 9-1 compression ,good for a street engine with a mild cam.
Raising compression adds maybe 10 percent power,better throttle response and better fuel mileage if you can avoid big domes, no problem in a 292,as flat top pistons at zero deck height gives over 10-1 compression.In return you will need high test fuel.

hmm, alot of high tech here. ive heard about the flat top pistons producing higher compression compared to the stock 292 pistons with their reverse deflectors. anyone know who i should call to get me some of them?

.055" is nearly 1/16". The only engines I've seen with that much clearance are air-cooled radial aircraft engines, big ones! I assume you mean .0055"? Standard machine shop practice for clearancing cast pistons is a maximum of .001" per inch of bore, so a 4" bore piston could have .004" as an outside limit. It's more common to have somewhere in the neighborhood of .0025" clearance on pistons up to about 350 Chevy size, 4.00". Hypereutectic pistons can supposedly run with as little as .0005", because the have virtually no heat expansion. The forged racing pistons we run on the circle track engines have about .005" to .010", depending on the type of racing they're going to do. Anything over .005" sounds like a bunch of ball peen hammers working on the cylinder walls, and the rings don't seal well for more than 500 miles. Of course, the rings and bearings aren't intended to last over 1,000 miles on a round track race engine, and the alcohol-fueled drag engines are usually rebuilt after one pass down the strip. At the end of a roundtrack season, cylinders with zero-gap rings are barrel-shaped, with most of the wear in the middle of the stroke, due to the sloppy piston fit. Doing race-engine tricks on the street is not only nonproductive, it's horribly expensive for no good reason.
Jerry

I don't know, Like I said,I know lot's a guys running forged pistons on the street with no unusual problems.I'm running forged Venolia pistons in my 302 project.Venolia themselves recomended .005 clearance on this 4.030 bore engine,they told me to expect no piston noise and ring seal that lasts as long as a cast piston in a performance street engine.
Many Chevy Big Blocks came with forged pistons from the factory,the current 454-425 hp crate motor has forged pistons and a 2 year guarantee.Mopars of past used forged pistons in the 440 6 Pak engine and Street Hemis
Currently,the new 7 liter Z06 Vette has forged pistons as did the LS6 version I believe.Many Japanese performance cars have forged pistons,notably the turbo supercharged models.

all chevy 366 and 427 tall deck truck engines run forged pistons with extra ring

Murdoc,

Look up TRW, Silv-o-Lite, Federal. All make pistons both stock and high performance applications. I don't know of HP pistons for the 292 but a call to the above could produce some!

Cost of custom pistons can be expensive for little gain for street use.

Cast pistons in a 292 should handle anything you would build for the street. After all, the 292 is a "grunt" engine!

A 292 has potential to deliver more than grunt, supercharged @ 4-5 psi boost, 4 barrel carb, cam, head work(of coarse!) and a few other tid bits done to it dynoed 325 HP with cast pistons and it stays together! Not bad for a UPS truck engine!

Jerry, I know I've asked this before...but what does the compression for a 250 with 307 pistons work out to? I'd like to stay around 9:1-9.5:1. The stock 8.5:1 is hopelessly low.

thanks hothot6 i really need to find some quick, my whole projects come to a stand still because of this

I believe the static ratio (without getting into cam timing) is about 9.5:1. The actual compression pressure will vary according to when the intake valve closes, because no pressure can begin building until both valves are closed. That's the reasom we use such high static ratios on race engines. The actual cylinder pressure isn't much more than stock, but when we use up almost half the compression stroke with a long-duration cam, it's necessary to squeeze the remaining cylinder volume tighter to get the same pressure as with a stock cam. If you don't change cams along with the higher-compression pistons, it's possible to get very high cylinder pressures, and lots of detonation, or an engine that needs premium fuel all the time. I'm very spooky about a stock-cam engine with static compression above 9.5:1. The most recent 250 I built with 307 pistons also got a .050" head milling job, uses a stock cam, and doesn't detonate. I believe we're right on the verge of too much compression on that one, though!
Jerry

Jerry, thanks for the info. I have a rather lumpy cam for my 250, but it will be calmed down by slightly lower-than-stock ratio rocker arms. For the rest, it's going to be fuel injected with computer-controlled timing, so approximately 9.5:1 should work out great!

Frank McGurk says in his inline 6 manual:
If you go from 8:1 to 9:1 youg gain 10% HP and better milage. You can have Wayne make some McGurk style "Powerdome" forged pistens for you. They offered ma a set custom made for arround 600$.

Frank

why not cut the head to raise compression?

When a dish-top piston can be replaced by a flattop, it's simpler, and less expensive to do that substitution, especially if pistons are being bought anyway in the course of a rebuild. The term "performance" pistons might be a little misleading. Racing pistons are custom-made, and don't meet some of the needs of a street engine, specifically quiet operation and long life. Street-engine pistons are designed to give tens of thousands of miles of trouble-free operation, and do it quietly. In order to run with minimum clearance, cast pistons have an expansion-limiting piece of metal called a "strut" cast into the wrist pin bosses. This piece cannot be incorporated into a forged piston, so running clearance must be increased when forged pistons are used. Most pistons are "cam-ground" to minimize the clearance necessary between the piston skirt and the cylinder wall. As the piston reaches operating temperature, it gets rounder, and clearance is equalized all the way around. Even street-type forged pistons have somewhat of a cam shape, but the lack of a stabilizing strut makes the cam shape less effective. A lot of race-type forged pistons are round, or nearly so, and must have lots of clearance. They rattle, and don't last long. If a street-type forged piston is run, and clearanced properly, it will work OK. If a racing piston is used in a street application, it will be noisy, short-lived, and contribute to rapid cylinder wear and oil consumption.
Jerry

So how does one know if they are buying a street-type forged piston or a racing-only forged piston? They aren't advertised that way. What brands sell the street-type forged? Speedpro I hope, since I run those on my Corvette's 427.

Most of the super-expensive pistons are race equipment. For instance, the rotating assembly for a Chevy 350 race engine I priced out recently went something like this: Crankshaft: custom-machined billet, 38-Lb. weight, $2,800.00. (A stock crank weighs 55 Lbs.) Connecting rods: Tool steel H-beam rods with Honda-size rod journals, $1,100.00. Pistons: Forged, lightweight, short-skirt, weight-matched to crankshaft counterweights, $1,000.00. Total-Seal piston rings, $240.00. Once this assembly is balanced and installed in a specially-clearanced block, all we need to buy is a set of race-prepared cylinder heads, $2,500.00 (minimum), and a cam, lifters, and pushrods, etc., $1,500.00 or so, plus a few other high-dollar bits & pieces. All this for an engine that will need rebuilding about mid-season, or 1,000 miles, whichever comes first.

Street-type forged pistons will usually run about 50% or more cost than similar cast pistons, and won't require special thickness rings, etc. One telltale property of a race piston will be a 1/16" thick, file-fitted compression ring. The rings will come with slightly more length than necessary, so the ends of the ring will butt together when the engine builder tries to install it in the cylinder. The ends of every ring will have to be filed to a specified clearance, depending on the application, closer for drag-race engines that don't get up to much running temperature, and larger clearances for roundtrack engines that come up to running temp and stay there for a while. Then, there are the "zero-gap" rings, that have a second piece in the top, and sometimes the second ring, that overlaps the conventional end gap. These must be file-fitted, also.

None of the above is desireable on a street engine. It's just not necessary, and does nothing to help reliability, or long life. Speed-Pro makes both race and street pistons, but it's pretty easy to spot the difference. If the pistons cost less than $100.00 each, they're probably for street use.
Jerry

1/16 inch compression rings with a 3/16 oil ring is the norm today for hi performance street engines.
On the 302 GMC inline I just built,got Venolia forged pistons,1/16 inch rings.Venolia recomended the narrow compression rings for street use,same as the machinist who bored the block.I figure Venolia been making pistons for 50 years,they gotta know something.
I was also told by several piston manufacturers the way the forged piston is machined is what controls expansion and the fit in the cylinder.
My GMC runs .005 clearance on the pistons,there is no mechanical piston noise at all,not even when started on a chilly morning.

Jerry, I just picked up a set of flat-top 307 .020"-over pistons from eBay for my 250 (it's standard-bore, and in good shape, so if it needs more than .020" to clean it up, I'll just deal with it). Anything to look out for with the pins not being offset on the 307s?

If there's a notch in the top of the piston, or an "F" cast into it, that's the front. Wrist pin offset is to make sure the piston skirt is pressed firmly against the cylinder wall before the spark plug fires. Otherwise, you'll get a piston slap as the fuel/air mixture burns. It's usually possible to look at the wrist pin area and see that the pin is a little off-center. I don't think I've ever seen a set of smallblock Chevy pistons, except for really exotic racing stuff, that didn't have at least some pin offset. What brand are they? Drop me an email if you have problems deciding which way to install them.
Jerry

Jerry, they are Keith Black/Silvolite #1438.

Here's a tech spec. page from the Silvolite catalog. These look like a pretty good set of street pistons, not quite as fancy as Speed-Pro, but very serviceable for street and/or mild high-performance use.

http://kb-silvolite.com/spistons.php?action=details&S_id=240

I usually use Speed-Pro hypereutectic cast pistons in the claimer engines I build. They're such a hard alloy it takes a carbide cutter to machine them!
Jerry

man ive been looking EVERYWHERE and i havent seen any "performance" pistons available for the 292 that dont have to be custom made. this means of course that each piston is gonna be costing me a little more than $100 per piston. at that price im really having trouble believing that the differnce between the stock ones is worth the price, any one else agree with me?

Give me a little time, and I'll look through a couple of piston manufacturers' catalogs I've got. I think I can come up with a close matchup for a 292. It might requre a little fitting, but there's usually something that's close enough to improve the performance. I wound up with flathead Ford V-8 pistons in an air-cooled Volkswagen engine many years ago! Hottest thing on the street!
Jerry

thanks Hotrod, i appreciate it. thanks to all yall, i dont know what id do without your imput and this wonderful source of information.

Murdoc,
Have you seen/read this article on the build-up of a 292 street engine? 292 build
-David

OK, here's what I've dug up so far- - - - -The 292 and the 250 have the same bore size, 3 7/8", same as the 307 V-8. The only problem with using the 307 pistons in the 292 is the fact they would stick out the top of the block 1/4" because of the 292's longer stroke!

What we need is a connecting rod 1/4" shorter, or a piston with the wrist pin 1/4" closer to the top. I think I've found a rod that will work, with a little tweaking. A Mazda con rod, Federal Mogul part # R25BL, is very close to 292 dimensions. It would require grinding the 292 crank to Mazda specs, and running the Mazda rod and bearing. The wrist pin end can be made to fit with a bushing for an International farm tractor, and the added advantage of a full-floating wrist pin is gained. I'm going to have to acquire a set of Mazda 4-cylinder rods, from a 1797 or 1970 CC engine and see if they can be adapted.

I'm going to continue to look for 3 7/8" bore pistons with the right compression height. Pistons, rods, etc. dont know what engine they're in, so I do a lot of this type of parts swapping.
Jerry

Shorter rods on a 292 is a bad idea,they are a little on the short side allready.A shorter rod will increase the angle of the rod at mid stroke,putting more side load on the cylinder walls,a problem with the stock rods in performance 292's.
Why reinvent the wheel? find a suitable piston or have custom ones made for 500 bucks.

Hotrod lincoln, I think you've had a brain fart and forgotten that the 292 has a 10.875" deck as opposed to the 9.150" of the 250. A 307 or 250 piston would be .370" below the deck in a 292.
Instead of rods that are .250" shorter, find some rods that are 1/4" longer and cheap and you would really have something. 230 pistons also have a 3.875" dia, but they have a compression height of 1.795". That is 2.025" - 1.795" = .230". The 7.00" rods from Sissell's are .240" longer than stock. I'm sure Sissell's steel rods are nice, but $11-1200 rods with stock cast 230 pistons sounds too weird to think about.
The 230 pistons should weigh a lot less than 292 pistons and if I'm not mistaken, have a smaller dish than even a 250. 292 LPG pistons weigh in at 35 grams more than stock 292 and they are not cheap. Prices vary widely, from $45 to $80 each.
You find some cheap 1/4" longer rods and you'll have my attention.

mugsy,

yeah ive read through that webpage like three times before!! its funny cause its the first thing that always pops up when i google "chevy 292" its a great source of information tho, thanks for bringing it up on this thread.

Yeah, it's especially useful for me 'cause it mentions shops here in the San Diego area. I'll be checkin' out the machine shop that did the work when I'm ready to do my 292.
-David

OK, Richard, you got me there! I was not considering the difference in deck height! That's what I get for not having a block specification book handy when I start window-shopping piston and rod catalogs! Mea culpa!
:rolleyes: :rolleyes: :rolleyes:
Jerry

I have allways run a forged piston in everthing we ever built on the street. No noise with .005 to .006. No oil cosumption.I sure would never build one for the street if i was going to put a blower turbo or gigle juice to it with out forged pistons.Now some of these motors are run 10 years and over 100000 miles no problems. Every engine builder has a diff way. I know what you mean with a race forged piston but thats a total diff animal.Some of our long rod motors have such a small wist pin and thin piston they would not last on the street.Have you gotten a 6 3/8 rod in a 355 yet? Not many have. Our IMCA motor with a 2 ring coated forged piston only runs a .003 cyl wall clearance. Before we used coatings we up around .008 in the IMCA car but thats all old tech now.Have you seen the 28 lb crank yet LOL. Just a bit more cash but its so pretty you wont want to put it in a motor.
Oh well cant talk to much about the IMCA motor as its 19 grand with a claim of 1500 bucks so we will keep that stuff secret.Never know who reads this stuff LOL
My twist on forged,ask your motor man and piston guy.It changes weekly. Only forged for me. Cast and hype are for ash trays. LOL