I know this isn't the right way to do things, but is it possible to swap stock cast pistons for forged pistons if there is no ridge at the top of the cylinders and the motor has low miles and all the bearing clearances check out with a plastigauge?

 

bearings are cheap i'd just use new ones. have the block measured , you may not need to have it machined oversized. just hone it, or have it honed and use new bearings and rings. guess i'd change oil pump too while i was at it.

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ICON Motorsports

1st & 3rd

[This message has been edited by ede (edited January 24, 2001).]

 

Thanks ede. Is there a way to check the bores and hone it myself? I've seen cylinder hones made for a drill motor. Is that what I would need?

 

you need a dial bore gauge to check the bores, or a inside mike. the hone will work like you seen for a drill. a quick and easy way to check the bore is to use a 12" feeler gauge and check the piston to bore clearance. it'll give you an idea if it's too far gone, more than how close it is. you check diameter, out of roundness and taper in the bores. i've rebuilt several low budget engines for people that needed bored oversize for sure and they didn't have the money to do it so i used standard sized parts, and they've worked out good, all things considered.

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ICON Motorsports

1st & 3rd

 

Thanks again ede. If it turns out that the motor needs overboring, I'll go for a full rebuild, but I don't want to rebuild a running motor with low miles just because I want forged pistons. My plan is tp get a Vortec 350 from a wrecked 96-98 GM truck and swap cam's, and put on an edelbrock carb and intake, but I want to use a small hit of nitrous. So if I can pull out the pistons, get the rods checked and shot peened, add arp rod bolts, and hang some TRW forged pistons, I'll be set. I'm definitely going to take your advice about the bearings, and I'll do the head gaskets too while I have the motor out.

 

...or telescope gauges and a large 3-4" mic or 6" digital caliper. You'll have to practice for a while to get accurate with the telescoping gauges, but you can get into places you'd never reach with an inside mic, like lifter bores...

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Later,
Vader
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"I'm gonna talk about some freaky sheet now..."
Adobe Acrobat Reader 4.0
KaleCo Auto Parts

 

if you haven't already bought them, trw pistons suck. they are heavier than crap and you can definately feel it when you rev the motor up. i had these in a 406 that lost a rod and those heavy pistons were probably one of the causes. get keith black hypers. they do require a tighter bore clearance, though. about 2-3 thousanths maybe, whereas a forged is like 3.5-5. i could be a little off on these specs, but i'm close. the keith blacks can take the little hit of nitrous you refered to and they weigh less than those trws.

if you have extra cash around, get JE SRPs. they are sweet. The pistons for my 406 weigh 540 grams with the pin. a buddy of mine has trws for a 460 ford that weigh 960 grams with the pin. granted, his 460 pistons are bigger in diameter, but 400 grams is a lot and you would definately feel it. only prob is SRPs cost about 475 bucks a set, expensive, but not bad for a set of top quality pistons.

other than the trws, i would go ahead and hone the bores and put it back together with new bearings and oil pump. should be cheap fun.

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88 S10
Dropped 3/4
Dart equipped 406
12.20 @ 115.25 mph

 

I wasn't going to get into it but 406 S10 brought up a good point. Don't forged pistons require different clearences?

My take on it: Spend the extra 125 or so and bore the block. Do it once, Do it right. I'm not saying go with the full rebuild just the boring

406, 960 grams = 2.11 LBS, Damn!

[This message has been edited by 87RS402 (edited January 25, 2001).]

 

87rs402 forged pistons do take differance clearances, but it's built into the piston, not the bore. that way no matter what you run the bore stays the same.

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ICON Motorsports

1st & 3rd

 

it is possible to build a motor that way and have it last; it depends on the measurements. Definitely get the right gauges and use them carefully before you make a decision.

The 400 in my car right now is std bore. It came to me when my brother bought a 69 Chevelle SS396. After he'd had it for a couple of days, he decided to open the trunk. Lo and behold, there's an extra engine block, improperly installed of course. He called the guy and asked him if he wanted it. The guy said "Is it a big block or a small block?" When we told him it was a small block he said he wasn't interested, we could keep it. Upon inspection it turned out to be a std bore 400 block with about .002" of ring wear and no particular taper.

I built it with TRW forged pistons using lightweight pins. BTW that's where the weight is, 406, not the pistons themselves: the TRW pin weighs more than the piston and the other pin combined. It ran 110,000 miles then blew a head gasket; I figured it was time for a refresh anyway, so I tore it down and re-used the pistons even though a couple of them had cracked skirts. Then the cam committed suicide 10,000 miles later, taking the crank with it due to metal shed into the oil, and I rebuilt it again, using the same pistons except replacing the 2 broken ones. I have about 12,000 miles on this build. No ring problems whatsoever. In fact a couple of months ago it pulled a trailer from Memphis to Denver, then drove here (So Cal).

So it can be done, if everything is just right; but I sure as hell wouldn't buy any pistons until I had mic'ed everything. And as far as the bearings, if you disturb them, replace them. Don't bother Plastigaging a bunch of used bearings, that's about a waste of perfectly good time and materials. I'd do as ede says and put a new oil pump in while I was at it, a Melling M55 with the Mr Gasket spring is my choice.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Another thing to consider when using any aftermarket piston is to get the engine balanced. When I got the machine work done to my big block last fall I had new pistons, balancer and flexplate. Reused the crank and rods. Everything was rebalanced and you can see under the pistons where weight was removed.

Balancing will add life to the engine.

Don't forget a set of good rod bolts for the new engine. That 2 pound piston doesn't hurt the crank going down but pulls really hard on the rod bolts when it reaches the top of the cylinder.

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
454 Big Block almost ready for the 2001 racing season

Best results before the 383 blew up
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Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

I still think trws suck. this is from personal experience. they are heavy. it is not all from the pin. the 960 grams for the 460 ford pistons had the weight written on the bottom from when they were balanced, yes that is damn heavy. i used them in my first 406 because they were cheap, well, you get what you pay for. i didn't know how heavy they were until i held a piston from my uncle's 555 big block. it was an SRP with a 4.560 diameter and it weighed considerably less than the trw that was going in my 406.

the guy building the motor in question wants to go fast, which generally requires a higher rpm than a towing motor. a heavy piston spinning at a high rpm creates a lot of inertia. overcoming this inertia at the top and bottom of the stroke will result in less overall power and a slower rate of acceleration.

i do not see a problem if the block comes out with the proper bore clearance for a forged piston. that is why i had to use forged pistons in mine, the block was 30 over when i got it and it was bored for use with forged pistons, i.e. a couple extra thousandths to allow for the extra growth of a forged pistons. some of the extra clearance is built into the pistons, some is not. that is why you are supposed to have the pistons when you have the block bored. half assed engine rebuilds don't work as the last poster found out. nothing personal, i did it myself, that is how i know.

i don't think there will be a problem with putting new pistons in a block with a decent bore.

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88 S10
Dropped 3/4
Dart equipped 406
12.20 @ 115.25 mph

 

I really appreciate all the input. What I really think its going to come down to is the budget. If I can afford to do it right, I'll rebuild the motor the right way and use a big hit of nitrous. If I can't afford it, I'll use the motor as is, maybe with some arp rod bolts and new bearings, and keep the nitrous hit at 125hp. Does anyone know what the stock compression ratio is on the vortec 350's?

 

The TRW forged piston has always been a good performance piston for the money. I myself have used them and they've been performed with out any problems. It's definitely a favorite with alot of turbo Buick guys.
I've compared the wieght of the Keith Black pistons flat top 406 pistons to flat top TRW 406 and surprisingly they're are very close. 406 S10 if you've ever looked in the Keith Black catalog, most of their 406 flat top pistons average around 540 - 560 grams (with out pin). That's not much off the 540 grams of the TRW's you're talking about 406 S10. Keith Black does sell 406 pistons that are in the 430 to 470 gram weight, but these are for use with 6" rods which means that they are at a shorter overall height compared to a 5.7" rod and that means less material there. Even Lingenfelter uses the Sealed Power pistons (same company as TRW which is Federal Mogul) with much success. TRW pistons aren't really a liability because of there weight.


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N/A 406, TPIS Miniram, 58mm TB, 30lbs injectors, Custom Ground Elgin Cam, Ported TFS heads, SLP 1-3/4", & DFI computer.
11.70@117mph

 

FastLife,
Ditto on your TRW comments!