3.0L with 130mm GT3 Cup Pankle rods, what pistons to use?

Evan Fullerton · 10:23 AM

So a set of Pankl rods found their way home with me for an unbelievable price with 45 hours on them out of an '07 Cup motor that was converted to a 4.0L. I have been contemplating using them in a 3.0L engine that I have but have been starting to wonder if there is an off the shelf piston option out there. Possibly a very high compression 3.2L application piston could be used to net a pump gas friendly compression ratio? Short of pulling the heads and CCing them, I am thinking someone on here must have figured it out already and have the answer if they would be so kind as to share it.

Thanks,
Evan Fullerton

kenikh · 06-21-2013, 10:42 PM

My approach would be to shim the cylinders 2.5mm then flycut the cam towers the same.

PFM · 06-23-2013, 07:20 AM

Evan,

If that does not work I could take the rods off your hands, for a really good price... Just kidding.

YTNUKLR · YTNUKLR's Garage

The standard 964/993 set up would work w/ no mods. Why don't you put your 3.0 crank, GT3 rods into a 964/993 case with some Mahle 102's (3.8RSR)? 930/964 cam towers & stock 993 vario heads, would be awesome. 3.45L short stroke.

Your compression will be off about 0.8 points compared to any spec. 964/993 RSR sets due to the shorter stroke (one of the issues with the short stroke designs). So if you get a true 11.3:1 3.8RSR set-up you will end up around 10.5:1

Evan Fullerton · 06-23-2013, 02:08 PM

Now that would be an engine I would love to build but it isn't in the budget right now. Trying to build a hot rod on a budget that won't be too much for the 915 gear box I have. As much as I would like tons of power in this car, for the planned usage I have of it, I would want to put a G50 in and that really blows the budget.

These rods weren't part of the original plan for the motor but when I was given them, some further project creep seemed necessary.

Proposed specs for the rest of the motor are a stock large port 3.0L with a 3.2L oil pump, 993 Vario-Ram intake, Pectel ECU with LS1 coils, triple stepped headers, and an AASCO/Tilton 5.5" twin plate clutch. Depending on how I go about solving the piston question and if I end up using these rods in this motor, twin plug heads and some hotter cams are being considered as well.

The goal is a reliable, broad powerband engine that revs extremely quickly, is tolerant of over revs and will run on pump gas. The chassis it will go into isn't is my '75 tub that hasn't really been built for any specific race class, just a hot rod that can be club raced or the ultimate goal of taking it to Targa Newfoundland.

winders · 06-23-2013, 02:47 PM

Sell the rods and get some Pauter rods instead. You will be ahead financially and won't notice any difference in the motor until you don't have replace the Pankles because they timed out....

Scott

Evan Fullerton · 06-23-2013, 05:19 PM

I have yet to hear of someone with a Cup motor have a rod fail due to age and know of several run past 300hours. With 6mm less stroke and 1000+ less revs I am not all that concerned with long term longevity. If guys are getting 200k+ street miles out of S2000 Ti rods without failure, I think I should be ok for a very long time.

But what is a used set worth anyways, $1500?

Flieger · Flieger's Garage

What is the maximum (at redline) mean piston speed in the S2000 and GT3 motors compared to your proposed motor?

Evan Fullerton · 10:32 PM

3.0L at 7500 17.6 m/s
GT3 3.6L/3.8L at 8500 21.65 m/s
GT3 4.0L at 8500 22.78 m/s
LS7 Z06 7.0L at 7100 24.05 m/s
S2000 2.0L at 9000 25.2 m/s

Flieger · Flieger's Garage

Quote:

Originally Posted by Evan Fullerton

3.0L at 7500 17.6 m/s
GT3 3.6L/3.8L at 8500 21.65 m/s
GT3 4.0L at 8500 22.78 m/s
LS7 Z06 7.0L at 7100 24.05 m/s
S2000 2.0L at 9000 25.2 m/s

Cool. I agree with you that longevity shouldn't be a problem based on those numbers. I assume the S2000 rods are a similar alloy.

Unless Honda figured people wouldn't spend much time at redline...

Steve@Rennsport · 06-23-2013, 10:58 PM

Quote:

Originally Posted by winders

Sell the rods and get some Pauter rods instead. You will be ahead financially and won't notice any difference in the motor until you don't have replace the Pankles because they timed out....

Scott

Superb advice!!!

At 45 hours, they are almost halfway there.

YTNUKLR · YTNUKLR's Garage

The S2000 did not use Ti rods

Mr9146 · 07-14-2013, 05:01 PM

Quote:

Originally Posted by Steve@Rennsport

Superb advice!!!

At 45 hours, they are almost halfway there.

This....

tadd · 07-15-2013, 06:26 AM

Titanium fatigue in recproating parts is a surface problem. There are shot peen treatments that can return timed out parts to almost full service. These were developed for the avaitation industry... so they work... cause people don't like planes falling out of the sky

.

This last bit is just my 2 cents as a chemist not a porsche expert so YMMV... Pankel will (does and has) refurbish(ed) ti rods. Although the 906 motor wasn't 'common' it also wasn't a 917. There are lots of those running around with with 40 year old ti rods.

I would check out Supertec. They make shims that go between the cam tray and the heads. That would tweak out the shorting of the cylinders.

t

PS It was the acura NSX that had commerical Ti rods and there are a bunch of those still running around...