I have a 340 block that is .030. and I have a set of old TRW pistons that are .030 flat top, but I think are about 950 grams each. Any one have their pistons lightened ? Looking to put a cheap street engine together.
Piston lightening
- Thread starter Sterling
- Start date
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Likely be cheaper to buy new pistons... Forged Speed pros are lighter and are pretty decent.
nm9stheham
Well-Known Member
Those ought to be the same as stock weight which are 719 gr for the piston and 154 grams for the pin; 873 grams total. Rings and locks might push the total up to the 940-950 gram range.
If you lighten them any real amount, you need to re-balance the crank to match the lighter resulting bobweight. Not what I would do for a cheap rebuild; I'd just use as-is.
If you want to do this, the easiest step is to put in lighter pins. The lightest pins I am aware of that are the same 3.00" length as stock pins are from UEM (KB's) and weigh 132 grams. That is only 22 grams off of the bobweight so does not seem worth the effort for a street engine. The only real way to knock off a lot of weight IMHO is to go with other aftermarket pistons.
If you lighten them any real amount, you need to re-balance the crank to match the lighter resulting bobweight. Not what I would do for a cheap rebuild; I'd just use as-is.
If you want to do this, the easiest step is to put in lighter pins. The lightest pins I am aware of that are the same 3.00" length as stock pins are from UEM (KB's) and weigh 132 grams. That is only 22 grams off of the bobweight so does not seem worth the effort for a street engine. The only real way to knock off a lot of weight IMHO is to go with other aftermarket pistons.
nm9stheham
Well-Known Member
Lighter than the number that the OP gives but that is not the correct stock piston weight.... the Speed Pro's should be stock weight equivalent.
Inertia
Well-Known Member
I've chopped my 12 1/2 - 1 pistons 3 times thru the decades, they're prob 10.5 now.
Here's some pistons I bought off the net, 340 + 0.060.
They've been lightened too !
I'll probably use them,- maybe.
Here's some pistons I bought off the net, 340 + 0.060.
They've been lightened too !
I'll probably use them,- maybe.
I just found 13 12.5-1 trw pistons today I forgot I had . does anyone still use them ?
mderoy340
Well-Known Member
If your pistons are in good shape you can mill around .020 off or whatever is needed to zero deck. I've run those pistons with Eagle I beam rods for years to 6400-6600 with no problems. I'd use them any day vs a cheaper cast or hyper piston.
Wyrmrider
Well-Known Member
long heavy skirts
you can do some but not a lot
newer multi axis skirt designs are much better
but those pistons are strong
will take a big hit
just keep the revs down- no problem for a torque build or blower
you can do some but not a lot
newer multi axis skirt designs are much better
but those pistons are strong
will take a big hit
just keep the revs down- no problem for a torque build or blower
Thanks for the replies. When I get some of my other engines together, I will start mocking it up and see what I got. The pistons have been in 3 different engines, with 2 different part numbers. Was going to put on a set of 60 cc X heads I got with a old solid lift cam. Trying to use up some of the parts I got laying around.
jbc426
Well-Known Member
Damn, those are heavy. The lightened Ross piston in my 493" RB weighs 524 grams. It all depends on the intended use of the motor you are building.
nm9stheham
Well-Known Member
They are really around 719 grams + or -... but still a lot heavier than your Ross's.
Krooser
Building Chinese Free Engines since 1959...
Iirc the Ross pustons from my 383 are way over 700 grams. Was run at 7k hooked to 340 rods for 25 laps every week on a 1/2 mile track.
I wouldn't worry about piston weight in your build.
I wouldn't worry about piston weight in your build.
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