951S Rebuild - Borg Warner EFR 6258 - Need Advice

[PDX-944]

So the car is a 1988 Porsche 944 Turbo S (Silver Rose)

Wolf3D V400 EMS using MAP sensor
J&S Knocksafe (tuned for 18psi on premium fuel, tunable via laptop)
B&B Header
EFR 6258 Turbo with internal recirc valve
3" Stainless downpipe (ceramic coated)
4" Lindsey Racing stainless cat-back
Custom oil cooler
Custom aluminum intake piping (larger diameter)
Aluminum flywheel
Spec Stage II clutch
Tial Wastegate
72# injectors
Aluminum fuel rail
Adjustable Lindsey "stock location" FPR

My compression numbers are not good, and I believe have been not great since the start of this project a few years ago. It accounts for the lag I deal with.
I have been racing every weekend the past few summers, and the car does very well, but is getting tired, and it's time for a rebuild.

I was going to just rebuild as-is, but I've just been offered a connection to have anything milled for me at cost. Crank. Cam. Etc.

So, my thought is to have a 3.0 crank made, and a cam. But I need specs or something to give the guy.
Any other thoughts on what I could have made that might be worthwhile?

EDIT:

Heres what I have come up with so far, based on pulling from other peoples information:

3.31L

Deck Height = 9.05”
Bore = 106mm = 4.17”
Stroke = 94mm = 3.7”
Rod Length = 145.288mm = 5.72” (Pauter 944-240-550-1454C)
Chamber Volume = 58cc?
Gasket Thickness = .04”?
Piston Dome Volume= -31
Pin Height (Compression Height) = 1.425?




if I bump down to a 104mm bore, I end up with a 3.2L, at 8.28:1CR...

Thoughts?

[nize]

if you're going to have the motor apart, you should install the piston oil squirters (like what's on the 968). there is a guy in everett who has the jig set up to do this. it's been a while and i'm not sure if he's still in business but it's definitely something i would do to improve reliability. other shops might have the ability to do this also but i don't know of any others off hand.

[333pg333]

There are differing opinions on Oil squirters. We found that a low oil pressure situation was 'fixed' by blocking up the retro fitted squirters. But probably worth a bit more investigation. Perhaps we were just unlucky.

If you're going down the 3lt path I would read this thread from Rennlist.

https://rennlist.com/forums/944-turbo-and-turbo-s-forum/796346-blown-944-hybrid-stroker-diy-guide.html

[PDX-944]

very good link, thank you!

ohhh a 2.85L sounds good to me. 3500? is that still reasonable? I can do a lot of labor myself... use my current crank assuming the guy can do an offset grind, etc.
id need to give him something to go off of though. no idea how to tell him what to do...

Also I don't see what the point in filling the water jacket is - stability of cylinders? I DO have temp issues - though no oil temp gauge. Something ill need to work on.

I also need to add a decent clutch on the list of items, and I have no idea what to go with. I wont know if the current lightweight flywheel is going to still be usable until I get it apart. but that's what like another $1200 probably for a clutch...

[333pg333]

Yes, as most of us learn, upgrading power/tq leads to many other similar requirements to deal with the extra load. I've gone down the path of very expensive motors. The reason that I point to that link is that a few guys have proven you can modify these motors relatively affordably and get great results. The Achilles heal of these motors when increasing the power is the headgaskets. So that's their method of reducing the amount of cylinder wobble with an open deck block. There are other ways like a bespoke deckplate but not many people can make these and they're not super cheap. Having said that, how many changed headgaskets equal building in protection (future proofing) these motors in time? Either way, I'd switch to a Cometic MLS metal headgasket as these can 're-seal' and at least let you drive home from an event. ie if you are running extra boost on the track and have a headgasket leak, you can generally get away with turning the boost down and still driving home. When an OEM gasket fails, that's it. Tow it.

Difference between the 2.8 or 3+ litre isn't much in terms of cost. I think if I were you and competing in Xcross and hillclimbs I'd go for the larger capacity with greater torque. It would be my advice to find someone that has done a stroker crank before rather than handing it to your machinist and saying 'Go for it'. I'd reach out to Shawn (aka refresh951) if you can't get all the info you need in that thread.

[PDX-944]

Originally Posted by 333pg333

Yes, as most of us learn, upgrading power/tq leads to many other similar requirements to deal with the extra load. I've gone down the path of very expensive motors. The reason that I point to that link is that a few guys have proven you can modify these motors relatively affordably and get great results. The Achilles heal of these motors when increasing the power is the headgaskets. So that's their method of reducing the amount of cylinder wobble with an open deck block. There are other ways like a bespoke deckplate but not many people can make these and they're not super cheap. Having said that, how many changed headgaskets equal building in protection (future proofing) these motors in time? Either way, I'd switch to a Cometic MLS metal headgasket as these can 're-seal' and at least let you drive home from an event. ie if you are running extra boost on the track and have a headgasket leak, you can generally get away with turning the boost down and still driving home. When an OEM gasket fails, that's it. Tow it.

Difference between the 2.8 or 3+ litre isn't much in terms of cost. I think if I were you and competing in Xcross and hillclimbs I'd go for the larger capacity with greater torque. It would be my advice to find someone that has done a stroker crank before rather than handing it to your machinist and saying 'Go for it'. I'd reach out to Shawn (aka refresh951) if you can't get all the info you need in that thread.

thanks for the info. ive been running reliably on 3-400hp for a few years, and the car is driven hard almost exclusively. im at events every weekend and its done extremely well. the power is just getting slowly lower and lower... it had a decent clutch in there, but its feeling on its last legs.

I always wanted to find a 3.0 because of the hillclimbs, but perhaps this is an easier option to get there.
its just a matter of which place does the sleeves for a reasonable price. most threads I find on anything related to this are quite old and info is missing and/or links are broken.

[333pg333]

It's all do-able...but do your due diligence first. As in research. I wasted a Ton of money over the years making mistakes. Reach out to others that have had success and ask where they got their products / machining done.

[nize]

photo links no longer work, but here's my old thread on a 2.7 darton cylinder build with JE pistons:
2.7 darton wet sleeved motor with custom JE pistons

[v2rocket_aka944]

...so how much for a ready-made 95mm stroke crank with 45mm rod journals?

[PDX-944]

Originally Posted by v2rocket_aka944

...so how much for a ready-made 95mm stroke crank with 45mm rod journals?

from my understanding of the deal, it would be at material cost. im not sure how much material costs though lol

[PDX-944]

So im trying to piece together numbers, and struggling a bit. this is my first build of this depth. as you can see, the numbers from the post above combined with my numbers is not good lol
I can shorten the rods? im not sure where to go from here. help? =D

I saw that max bore was 108mm for 3.2, but I saw 94.75mm for a 3.1, but now that I do the math that makes a 3.472 liter motor... woops. heres how that would look, though not run...
warning: learning curve ahead.
106 bore with 94.75 would be 3.345L

so what are the magical combinations? im pretty sure 14:1 is not a good compression ratio for a turbo motor

Deck Height = 9.05”
Bore = 108mm = 4.25”
Stroke = 94.75mm = 3.73”
Rod Length = 5.9”
Chamber Volume = 56-62cc?
Gasket Thickness = .04”?
Piston Dome Volume= ??
Pin Height (Compression Height) = ??

[PDX-944]

okay, here are a few better sets of numbers - the second set is still at 8.51:1 CR though, what do you all think?

3.1L
Deck Height = 9.05”
Bore = 102.1mm = 4.02”
Stroke = 94mm = 3.7”
Rod Length = 145.288mm = 5.72” (Pauter 944-240-550-1454C)
Chamber Volume = 58cc?
Gasket Thickness = .04”?
Piston Dome Volume= -31
Pin Height (Compression Height) = 1.425?




3.31L

Deck Height = 9.05”
Bore = 106mm = 4.17”
Stroke = 94mm = 3.7”
Rod Length = 145.288mm = 5.72” (Pauter 944-240-550-1454C)
Chamber Volume = 58cc?
Gasket Thickness = .04”?
Piston Dome Volume= -31
Pin Height (Compression Height) = 1.425?




if I bump down to a 104mm bore, I end up with a 3.2L, at 8.28:1CR which seems better

[PDX-944]

which of these seems like a better option? im reading every thread I can find on this kind of build. not many out there, a lot more 2.8/85s
definitely could use some guidance through the process.

944 Enhancement responded with:
"The usual kit – you send the block (head studs removed) and I will machine it, insert sleeves, finish bore/hone to match pistons and supply Wossner custom pistons for $3350. Balance Pistons and gap rings for additional $150"

That seems like a pretty inclusive deal, no? I still am waiting to get in touch with my machine shop person to see if this is stuff they are experienced with.

as far as making a crank - better option to offset grind the 2.5 crank, or have him make a fully new one at cost? obviously he can do whatever I want, but that's the issue - how would I tell him what to make...? where could he cut down on weight etc.?

if it works out, I could probably make quite a few for people at low cost instead of having to buy 3.0 cranks and grind them etc.

[333pg333]

Personally I would ask these questions in that Rennlist thread I posted. You will get some good advice directly from people that have built these offset grind motors.