Pistons For 4.1

[boostmaster]

Looking to do a rebuild on a 4.1 production block. My question is I know it is recommended that you overbore to 0.35 to take advantage of the 4.00" bore but what I need to know is can I use chevy pistons or do I have to get custom pieces.

Thanks, Pete

 

[bruce]

I just finished one.
All I can say is DON'T use BRC's.
They don't know the difference from a -45 to -35 reverse dome'd piston.
Then they made NO attempt to correct the situation, all in all after using them for many years, they've lost me as a customer, forever.
Not to mention all 6 were the same instead of 4 and 2. The valve reliefs should differ, and the builder had to renotch 2 to get the necessary valve clearance.

 

[Whitettype86]

I have venolia pistons and look top notch, but I have 8.9cr with a 50cc head. U can go with Venolias or J&Es.

If u go with a chevy piston u will need 3.1 or 3.0 chevy rods if i remember right.

What are your plans

 

[Nick Micale]

Buick did not make a turbo 4.1 so the good pistons for these motors are custom built. Don't think SBC pistons in a 4.1 turbo application would be a good idea unless it is destined for "easy" street duty.

 

[KendallF]

I was planning one with early 3.0 (80-85) rods and 383 SBC pistons from Keith Black. The early 3.0s were tall deck motors and used a 6.35" rod, which works out well with a 383 piston designed for a stroker small block with a 5.7" rod. Keith Black has some fairly inexpensive ones with a big dish that are aimed at boosted 383s.

I did not finish the build as that was about the time I went nuts and started buying stage parts..heh. It might work out nicely..or it might blow up.

Mike Savino has had pretty good luck so far with some very cheap hypereutectic pistons in the 4.1 in his Mazda RX-7. He has around 10k miles on it and some 125+ mph passes at the track. www.misred.com or www.turbobuicks.com, try the hybrid section for info.

 

[Intercooler]

Originally posted by Nick Micale
Buick did not make a turbo 4.1 so the good pistons for these motors are custom built. Don't think SBC pistons in a 4.1 turbo application would be a good idea unless it is destined for "easy" street duty.

I think they did. I think it was 82. Reason I remember is because I had tried to locate the pistons used in that motor but come up empty. Discontinued.

 

[Intercooler]

It was an Indy Pace Car. Twins!

 

[KendallF]

Originally posted by Intercooler
It was an Indy Pace Car. Twins!

There are some pics of an early twin setup in the Power Source book and elsewhere. That was a one-off built by a race shop, however. Nick is correct; Buick never built a 4.1 turbo production motor.

On a totally unrelated note, why the heck am I reading this stuff at 1:45 AM?!

 

[turbo buicks]

why would you need new rods? cant they fit the stock ones on?

http://www.turbobuicks.com/ubb/ultimatebb.php?ubb=get_topic;f=9;t=003609#000000

 

[KendallF]

Originally posted by turbo buicks
why would you need new rods? cant they fit the stock ones on?

http://www.turbobuicks.com/ubb/ultimatebb.php?ubb=get_topic;f=9;t=003609#000000

The original poster asked about boring it for a 4.000" piston. This would require a custom piston or some finagling such as I described. There are some cheap hyper replacement pistons available that will work with the stock rods; I believe the only available oversize is .040" (4.005" bore).

 

[fuzzyGN]

Originally posted by KendallF
I was planning one with early 3.0 (80-85) rods and 383 SBC pistons from Keith Black. The early 3.0s were tall deck motors and used a 6.35" rod, which works out well with a 383 piston designed for a stroker small block with a 5.7" rod. Keith Black has some fairly inexpensive ones with a big dish that are aimed at boosted 383s.

Kendall, did you actually buy the parts for this? I am thinking of doing the same but in a N/A version for my Vega. I was looking for a CR closer to 10 to 1 though. Do they make 383 stroker pistons in a standard bore? According to my calc, a 383 piston for use with a 6" rod would have the proper compression height not the one with a 5.7" rod. I may have messed that up but the rod takes up another .335" which would really shorten up the piston. Any help apprciated. Direct email me if you want. Thanks.

 

[turbo buicks]

Originally posted by KendallF
I was planning one with early 3.0 (80-85) rods and 383 SBC pistons from Keith Black. The early 3.0s were tall deck motors and used a 6.35" rod, which works out well with a 383 piston designed for a stroker small block with a 5.7" rod. Keith Black has some fairly inexpensive ones with a big dish that are aimed at boosted 383s.

I did not finish the build as that was about the time I went nuts and started buying stage parts..heh. It might work out nicely..or it might blow up.

Mike Savino has had pretty good luck so far with some very cheap hypereutectic pistons in the 4.1 in his Mazda RX-7. He has around 10k miles on it and some 125+ mph passes at the track. www.misred.com or www.turbobuicks.com, try the hybrid section for info.

WOULDNT 383 PISTONS BE TOO LARGE? STOCK SBC BORE IS 4.000 AND A 383 IS 4.030. AND IF YOU CAN TAKE A 4.1 TO 4.000 MAX I DONT SEE HOW 383 PISTONS CAN WORK.


NICK, ARE SBC PISTONS NOT A GOOD IDEA B/C OF THE PLACEMENT OF THE RINGS? IVE READ TURBO PISTONS NEED THICKER RING LANDS OR SOMETHING TO THAT EFFECT

 

[KendallF]

Originally posted by fuzzyGN

Kendall, did you actually buy the parts for this? I am thinking of doing the same but in a N/A version for my Vega. I was looking for a CR closer to 10 to 1 though. Do they make 383 stroker pistons in a standard bore? According to my calc, a 383 piston for use with a 6" rod would have the proper compression height not the one with a 5.7" rod. I may have messed that up but the rod takes up another .335" which would really shorten up the piston. Any help apprciated. Direct email me if you want. Thanks.

Erik, I had the rods and trial fitted a couple of pistons. There are a number of dish sizes and/or flat-tops available. You might be able to find a cheap forged flat-top for this; the only problem might be finding it in a std (4.000") bore.

Stock rods are 5.95" so the 6.35" rods are actually .400" longer. For a 9.535" deck height the compression height should be 1.485". The KB 135s (18cc dish) are 1.433" which would put them down in the hole .052". These are 383 pistons for a 5.7 rod. After the block is cleaned up and decked, it would be less, of course.

The stock replacement pistons are generally about .030" in the hole anyway and with an open chamber head, another .020" shouldn't matter as long as you take it into account when figuring compression ratio.

Originally posted by Homer

WOULDNT 383 PISTONS BE TOO LARGE? STOCK SBC BORE IS 4.000 AND A 383 IS 4.030. AND IF YOU CAN TAKE A 4.1 TO 4.000 MAX I DONT SEE HOW 383 PISTONS CAN WORK.


NICK, ARE SBC PISTONS NOT A GOOD IDEA B/C OF THE PLACEMENT OF THE RINGS? IVE READ TURBO PISTONS NEED THICKER RING LANDS OR SOMETHING TO THAT EFFECT

Homer, you're giving me a headache.. I referred to them as "383" pistons because that's a rather generic term for a stroker 350 Chevy using a 3.750 crank. I had actually selected the KB pistons because they were available in a suitable dish and in a standard (4.000") bore. For the anal retents out there, this would be a 377" motor.

Turbo pistons should have a top ring further down on the piston than a NA piston and should be thicker in general. The KB pistons actually have a top ring located about .300" down and reasonable thickness under the dish. They will of course suffer from the same weaknesses as any other hyper piston.