Forged SpeedPro piston question.....

[Skids]

I have a very tight spec standard bore block.........lightly honed for Molly rings. I'd like to drop a set of SpeedPro forged pistons in........would a standard bore set just drop in???

 

[jwillettgn]

It would be best to measure the pistons in the bore to make sure. You should use the clearance that is given with the pistons for best results.


Jim

 

[Skids]

To be more specific, I guess I want to know if the Std-Bore sized 3.8 Speedpro pistons are designed to go into an unmodified (read not bored) block. Thanks.

 

[jpwalt1987]

The only true way to know is to measure the pistons and then measure the bore. You need .004 clearance for the TRWs. Too tight and you will scuff the cylinder walls. I personally dont like the TRWs as they are pretty heavy. It will require a balance job. hope this helps.

 

[gossamer]

Agreed. You will have to measure the bore and the pistons. TRW's catalog calls for .0035 clearance. Measure twice, install once :smile:

 

[Skids]

I heard that the TRW's with the heavy wrist pins were a "drop-in" mod, and didn't need balancing...........if you opt fotr the lighter pins, then a balance is required............is this wrong???

 

[jpwalt1987]

I had the heavy wrist pins and it required some heavy metal to added to crank. I also had to have some additional weight added to the flywheel for the external balance. I didnt really care for it beinng set up that way so when it was rebuild time i went with an eagle crank, k1 rods and diamond pistons. I am not a machinist or engine balancer but this is what was done to make my rotating assembly balance out. hope this helps. jeremy:biggrin:

 

[gossamer]

I am using the TRW / Speed-Pro pistons with the JE light weight wrist pins in my engine. That brings the weight down to where minimum rebalancing is required. The heavy pins that come with the pistons require more reworking on the rotating assembly. The engine should be rebalanced anytime you change a part on the rotating assembly anyway unless you have the new pistons weight matched to the old set. Hope that helps you:smile:

 

[67turboCamaro]

I used std bore TRW's and didn't rebalance. I had zero problems, the motor was together for over 6 years, had thousands of street miles and ran 10.0's in the 1/4.

 

[novaderrik]

a piston for a that is designed for a standard bore will be designed so that it has the proper clearance in a standard bore block.. well, in a perfect world, anyways..

 

[Kip]

Skids, to answer your question no it is not a drop in piston. On the balance issue I have built a bunch of TRW piston engines without rebalancing and have had no problems. If money is not a concern you could do a rebalance but it not a must do.
Take care, Kip

 

[kingots2004]

dont take a chance rebalance the engine.itll be cheaper now ,then replacing the bearings again .if you change pistons and dont balance the rotating assembly and you dont have any problem....well buy lottery tickets my friend cause your lucky

 

[wickedtt]

dont take a chance rebalance the engine.itll be cheaper now ,then replacing the bearings again .if you change pistons and dont balance the rotating assembly and you dont have any problem....well buy lottery tickets my friend cause your lucky

+1

 

[gossamer]

+ 2 Rebalance it :smile:

 

[bison]

Personally i dont see any advantage replacing the OEM 86-87 piston with anything else if you are not building a crazy engine with steel mains or a girdle. The factory eutectic pistons are very strong and take a lot of abuse and are more proven than any other piston for mild engines. I dont see any advantage in putting in TRW's. They will cost you $ and the re-balance will cost you $. If you do it id go .004-.005 piston to wall. Just have the cylinders honed to the proper size and correct finish.

 

[LSJM1]

Are OEM pistons still available?