4.1 pistons

[boosted]

i was wondering..i have a buddy whose fixing to build 4.1 gas motor and wondering why you cant run the stock pistons of the 4.1 or ones from a 3.8 in the 4.1 block. why do you have to buy the expensive replacements to make the motor work..thanks

 

[Ormand]

You could run the pistons out of a 3.8, but since there is a 0.20" difference in bore, you would burn a lot of oil, make a lot of noise, and generate no power. In other words, they are the wrong size. The stock 4.1 pistons are designed for about 150 horspower. If you want to limit the engine to that kind of power, then the stock pistons will work fine. But they don't have much margin for absorbing detonation, some may run them with a turbo, but I wouldn't expect them to last very long. If the 4.1 is not going to be a turbo, then the stock pistons would be a more reasonable choice, but still not designed for high performance.

 

[boosted]

ok i see now...well i forgot to post he was converting it to run a turbo and put it in an 87 tr. now everyone we talked to has said that hes goin to run these high dollar custom pistons and we were wondering why..the 3.8 and 4.1 have the same crank and stroke whats the big difference in pistons why do we have to order custom pistons

 

[trbodon21]

the 4.1 is not as common as the 3.8, which is the main reason pistons will cost more.the standard bore on a 4.1 is 3.985, which usually needs to be cutom made when (including oversize) getting forged pistons. i believe speed pro still makes hyper pistons for the 4.1, which are much cheaper, but i would stay with the forged.

 

[Whitettype86]

Correct 4.1 have the same stroke and crank but bore is bigger then the 3.8. The 4.1 motors are natural aspirated motors and u will need custom pistons due to u will need lower compression say from 8:1 or 8:5:1. U can get Hypy pistons for about $225 just make sure u don't detonate or you'll burn the piston up. U can get J&E or Veniola and other forged pistons from $450 to $600.
So yes you'll need custom pistons for a turbo 4.1 motor. U can also bore the motor out to .015 to achieve a 4 inch bore and run chevy pistons and you'll need chevy 3.0 rods but buy that time or price its almost the same price. How much horse power does your friend plan on running with his 4.1?

 

[boosted]

ahh i see...that makes sense...well as far as muich power im not sure...i do know hes bought 50lb injectors, a turbo in the te60 area and a cam in the 212/212 range...so i know hes not exactly goin back stock..lol

 

[trbodon21]

If I were you I would just go with the forged pistons. Save yourself the hassel of finishing a motor, detonation, and then broken hypers. Some guys may dissagree and say they have no problems with hypers, but that is with no detonation. If you get severe enough detonation the hypers will crack. Where as with the forged you will usually only have to replace the headgaskets.