GT3 crank on 3.2/3.4
 

Folks

Wondering if anyone is running a gt3 crank on their 3.2/3.4 and can detail what changes were made to accommodate the crank? I'm in touch with William Knight (great guy) but keen to hear from anyone else whose done this. Guessing most people won't change the crank isolation so difficult to gauge benefits of the crank change on its own?

Cheers peeps

Talk to Henry from Supertec. I bet he has done a few, and he might have a super crank to sell you too.

Happens all the time. There are a few different flavors of GT3 cranks, and dependent on stroke, there are different challenges. Especially with the latest GT3 cranks and their very long strokes, there are some clearance issues around the oil pump. Generally, you have to run custom rods and pistons, but the increased displacement is a pretty nice benefit.

Thanks chaps - yes I've just read about the stroke differences between early and late cranks. The 2003 on cranks are reasonably priced, especially if I can sell on the 3.2 crank and rods.

Just bear in mind that an increase in stroke will necessitate a decrease in compression height of the piston and or rod length. All easy to calculate and the results in stroke are really good compared to just making the bore larger.

regards

Hello - I thought the GT3 crank only fit in the 3.6 engine and not the 3.2. I could be wrong on this.

Are there super cranks that feature increased stroke that would fin in the 3.2 case?

Regards,
Steve

Yes the GT3 will fit in a 3.2 and yes you could have a 3.2 stroked.

Thanks - was speaking to William Knight last night, he concurred that stroke is king, and if he can source at the price he's been quoted i may consider a 4.0 crank. May require a new oil pump, definitely new rods, but with my 98mm mahles should make a healthy torque laden 3.7.

I'm not a professional engine builder but I've been searching details to build this configuration in an SC case using a GT3 crank (76.4mm stroke) and 98.0mm bore. While a slightly different starting point from a 3.2 the configuration to get the end result is fairly the same.

As others pointed out the longer stroke has to be accounted for in the build to ensure proper piston deck height, clearances, and parts alignment during assembly. I have not found where anyone has documented building this engine or which dimensions to alter for the best overall results.

Following what Porsche did when the 3.0L was replaced by the 3.2L they accounted for 4.0mm increase in stroke (+2mm each direction up/down) by moving the piston wrist pin higher by 1.2mm and shortening the connecting rod by 0.8mm. One possible downside was it also lowered the Rod Length to Stroke ratio (RLSR) from 1.82 (SC) to 1.71 (Carrera).

Taking a similiar theoretical approach to fit a GT3 crank in a 3.0/3.2 case this is (in simplified form) what I'm considering...

Connecting Rods:
Using a rod with SC dimensions could provide several benefits. 1) the big end is properly sized for the GT3 journals 2) the length 127.8mm (SC) vs 127.0mm (Carrera) helps maintain RLSR ~1.67 3) the smaller piston pin diameter 22.0mm (SC) vs 23.0mm (Carrera) could save an extra .5mm to move piston pin higher.

Custom Pistons:
Given the 127.8mm connecting rod length, the piston pin location would need to be moved 3mm higher in comparison to stock (SC) pin location. I spoke to someone at JE and they believed it was possible with a custom piston order but I couldnt say it was definitive since I haven't requested an order.

Perhaps one of the professional builders on this site has actually built this configuration and can comment if this is the best approach to maintain required assy dimensions or not...

Yes I built one with a 3.2 case 76.4 X 98 with a 22 pin and a 130 ti rod from a Cup Car, CP piston with
1.113" piston compression height and a 106 L/C cam. The Cam is important to keep the top center timing out of the pockets.

Here is how you do it
1. find the deck of your case
2. length of rod
3. 1/2 stroke
4. length of barrel
5. figure 1 mm of deck clearance so subtract that
6. the remaining dimension is going to be piston compression height which is center line of piston pin to piston periphery.
7. give the dimension to CP contact Jerry Roche he will reassure youand he knows what to do.
Regards

Just wanted to see what kind of safety factor with ARP rod bolts. Rod bolt stress for above come's out to about 126 Kpsi assuming the 9800 lbs is per bolt. ARP 2000 are supposed to be good for 220 Kpsi.

This was a Ti rod with ARP bolt

Regards

Given what you've shown in calculations I've assumed you were able to assemble this build without need of custom spacers for the cylinders and chain boxes to accomodate the stroke...

I really like that you used a 130mm rod for this build. For this rod length (etc...) your build required a piston pin compression height of 1.113" (28.27mm). Did this Compression height require the wrist pin bore to be so high as it encroaches into the oil ring groove on the piston?

If so, do you just use oil ring support rails and move on, and/or any concerns using the support rails on our engines?

I don't believe it required any spacers and I know it did not require oil ring supports.
It all hinged on the length of the particular barrels I used. The wild card is the cam I shoved a (for a Porsche) farily racey cam and it required a particular Lobe Center to clear the Valve Pockets so I knew what I wanted to run as far as a cam was concerend but waited on the Pistons and missed by a few degrees so the Intake pocket need to come down by 1mm and that put the material thickness of the Piston Dome at the bare min.

regards

Great input on your build experience with this crank...

You got me wondering about the attention to the cam specs...I would think the same timing/clearance issues would occur if used a similarly aggressive cam profile with a stock 3.2 Carrera crank, assuming same heads, deck height, etc.

Or....you really did mean the valve timing/clearance issues become even more critical with the longer stroke of the GT3 crank?

This task doesn't involve off the self Porsche Pistons at least not with the 130mm rod and
the tight compression height and the type of Forging used don't leave alot of material under the Piston valve pockets so you can't just bury the valves by fly cutting the pockets for clearance, you need to kind of know what kind of valve drop you have. This is determined by the Top timing (how far the valves are off the seat at TDC overlap at your proper timing) now you can tell the Piston guys what this is but they sometimes don't pay attention that will possibley force you to change the lift of one of the cam lobes at TDC hence the widening of the L/C angle. Wider has less lift Narrower has more. These engines aren't deadly responsive to L/C so you aren't sacraficing any performance.
The only reason I mentioned it is without the change in length you can find a suitable Pistons that allready are clearnced this will be a new application and I did not want to leave you without covering this possiblity. I am sure if you mention it to the Piston guys they will at least be aware and leave you some recourse in case you have some fitment issues.
Hope I didn't make to confusing

Regards

racing97,

Ok, makes sense now....designing custom pistons to accommodate both the longer 130mm rods and longer stroke in combination doesn't leave much extra material for clearancing deep valve pockets. Hence careful planning in cam specs. Thanks!

Correct

I'm in the process of rebuilding my '87 Carrera 3.2L, and got a new 997 GT3 crank and oil pump (from William Knight), new 997 GT3 3.8L Pankl Ti pistons (130mm), 997 GT3 Cup intermediate shaft (slightly used), and 102mm P/C set from LNE. The pistons are custom made for the longer crank and rods. I'm changing the rod bolts to stronger ARP bolts, due to heavier pistons than the GT3. I got a set of "crazy" cams from Elgin, with 325 degrees inlet and 318 degrees exhaust with high (cant remember on top of my head) lift. My worry is that there might be a too tight clearance between pistons and valves... My engine builder did the math, and figured out it should be OK. However, he wants to assemble the engine and measure the valve to piston gap (and compression), and then machine out bigger valve pockets if necessary. However, if the pistons and valves collide, and there is not enough material in the pistons to be machined, would it be possible to put spacer rings on the cylinders (on the case side or the head side) to increase the gap?

Piston crowns are generally thick and machining a shallow valve relief pocket should not be a problem. The relief is not that much. The majority of the material removed is at the bottom of the radius.

I wonder how much it might lower the compression ratio machining out the pistons like that?

Fly, that sounds like it's gonna be a pretty big engine for a 3.2 case! Keep us in the loop on how it turns out.

Something else to consider is the 3.0/3.2 crank pulley in stock form is not compatible with the GT3 crank. The setup requires a custom made crank pulley for proper alignment plus a different pulley bolt.

I've also not seen it mentioned anywhere...but there are several different styles of flywheels and pilot bearings depending which engine and year you start with.

A few examples:

It seems the 78-79 3.0L w/915 trans and 87-89 3.2L w/G50 trans both use flywheels with press-in pilot bearings. I would expect these may work the same as original when used with a GT3 crank.

The 80-86 3.0/3.2 w/915 trans on the other hand uses a flywheel where the center is clearanced for a flanged pilot bearing. The pilot bearing bolts directly to the crank with (3) small socket cap screws. The GT3 crank does not have the threaded holes for attaching the pilot bearing in this case.

if you wanted to re-use the flywheel on 80-86 models I expect you could just have the (3) threaded holes added.

Any reason not to do it this way and just add the threaded holes similar to original....?

Clewitt will make you you pulley, I also ran the Elgin cam 324,318 and I believe it was at 106 L/C you will need to measure the dome thickness as it is common practice to make the domes as thin as possible. I think I needed to cut .040 or 1mm out of the inlet pocket to get min Piston to Valve clearance and I think that number turned out to be 1.25 mm of clearance I believe the total lift of that cam to be 13mm.
It runs pretty quick you will be pleased.

Regards

Invaluable input here chaps. First stage complete - 997gt3 crank (99610202196) has arrived at the engine builders, and rods are on order.

racing97 - would you mind sharing what kind of peak hp RPM can be expected from an engine like you mention above with the Elgin 324 grind on a 3.8L or similar sized motor? Thank you.

The Engine in the data was 3.4 ltr and made 347 hp at 8,000 it was for all intents and purposes is a slide valve RSR the 3.8's I have had experience with were Factory rsr's with Plenium and the best made 380 with various modifications but essentially a different cam then Elgin.

regards

would love to see this build

yes

more details, i am doing ground work on this also, prepping for winter project.

impressive from a 3.4

@impactbumper

Just a hi level design at present:

Gt3 crank
Pauter rods (ordered by engine builder but I don't have specifics yet)
Shaftless ITBs - designed by BSMotorsport in UK
964/993 intake with WKP/rothsport t piece filter
WKP cams

All this on top of my current 98mm mahle/3.4 setup with motec/COP

Oil pump is TBC - I'm told I had a gt3 pump fitted at last build but no part numbers on the invoice

Main restriction at present is my SSIs - will use these until I find a better solution with heat

If you don't have to use late ti rods at 130mm use 127 it will make your design a little easier

regards

Many builds use a GT3 oil pump along with the GT3 crank upgrade. There is some minor clearancing to fit the oil pump to the 3.0/3.2 case which is not a big deal.

What I was wondering though...are there issues with clearance between the oil pump and connecting rods depending which rod type or rod length is used?

For example, if you used a stock 127.8mm SC rod is there a rod/oil pump clearance issue?

If stock rods have clearance issues, can it be solved by using after market Pauter rods?

I just did this test fit to a 3.0 case and the 76.4 GT3 crank. I put the stock 3.0/3.2 oil pump in and installed a set of stock 3.0 rods. #3 & #6 hit the oil pump. Then I installed a 930 Turbo oil pump. #3, #6, and #2 hit the pump. #2 & #6 would need alot of clearance mods to the 930 oil pump. With some better rods and a little clearance work this should work fine.

Pump clearance is a known issue with aftermarket rods and with original Porsche rods as Mark has indicated. I think this is one of the reasons Carillo, Pauter, R&R reverses the location of their rod bolts? These rods have the bolt threading into the rod cap and therefore they don't have nuts with the bolts.

Here's a tech bulletin from Carillo

http://forums.pelicanparts.com/uploa...1468248975.jpg

Here's a picture of clearancing the big body of a 964 pump, which is approximately the same size as a 930 or GT3 pump in terms of its shape. That's not to say the 964 pump has the same oil delivery rates as a 930 or GT3 pump

http://forums.pelicanparts.com/911-engine-rebuilding-forum/267356-another-3-6-3-8-rebuild-thread-2.html#post2929771

You can see in the above link that the pump is already clearanced (notice the "dents" where the machining was done) when manufactured and it needs to be clearanced even a little bit more for the aftermarket rods.

Good info KTL - I'm *hoping* I already have a gt3 pump fitted but won't know for certain until the cases are split.

So dismantling has begun:
https://www.dropbox.com/sh/x2x6q8zcwizn0q4/AAD-Agz9QGYlIwwoAzTpfba-a?dl=0#

Rockers are stuffed - these were refurbished items, however blocked spray bars have taken their toll. Lots of excess sealant visible in the pics, linked?
Standard 3.2 oil pump fitted, new gt3 pump procured.
William Knights cams have turned up, he's asked me not to share specs.
Staying with SSIs until I find a solution with heat. WK has no time for the 993 heat exchangers, the newly marketed Eisenmann SSI copies may be an option.

Have you identified what pistons you have there? The flat top looks like a low compression piston for a turbo engine.

98mm Mahle single plug, 10.3:1 CR

Have you determined what rod length and type you will be using for this build?

Also which pistons and pin height?

Since there are a few different ways to accommodate the increase in stroke just wondering what combination was decided here...

Have asked the question of the engine builder, nothing forthcoming just yet. Would (Pauter) rod lengths in this case be considered intellectual property ?

Anyway, bottom end together back together (inc Gt3 pump, steel IS gears), will share more pics once received.

http://forums.pelicanparts.com/uploa...1493243006.JPG