One reason why GT3 engine makes power

[Cupcar]

Factory CNC machined ports.

[Don Settergren]

The Porsche GT3 equivalent of Breathe Right Strips. Open her up for a deap breath. Impressive!

Please keep the photos coming. Most of us will never see the inside of a GT3 engine.

[JFairman]

Nice how the valve guides are recessed and shrouded by the port wall.

[colescrogham]

The latest RSR heads are even zoomier, with smaller stems and just beautiful valve seat work. Like jewelry. The X51 street heads are CNC too.

[Bill Verburg]

another is the crank shown above here(964 on bottom), can you say 8800+rpm?

[sc_rufctr]

Damn sexy machining...

[Cupcar]

Originally Posted by Don Settergren

The Porsche GT3 equivalent of Breathe Right Strips. Open her up for a deap breath. Impressive!

Please keep the photos coming. Most of us will never see the inside of a GT3 engine.

I will do from time to time. I will not be really into it for a bit since I am in the slow process of redoing my garage shop- new floor, some cabinetry and shelves, etc.- and don't want the engine "really" apart yet.

The real "inside" of the GT3 pretty much looks the same as the air-cooled except the Ti rods.

[Beetspeed]

Originally Posted by Cupcar

The real "inside" of the GT3 pretty much looks the same as the air-cooled except the Ti rods.

Speaking of the Ti rods...in which engines were these?

And: are the Ti rods the same length as the normal steel rods or longer??

Thanks a lot to whoever can answer these,
Walter

[kenikh]

The Titanium rods are a bit special in dimension. The are 130mm length, just like the early 2 and 2.2L rods, except they have the same rod journal diameter as the 70.4mm crank on the 2.4, 2.7 and 3L cars.

This makes them quite the hot upgrade for an early car - just send your crank in for a rod journal regrind to SC journal spec @ 66mm stroke (or any custom stroke for that matter) and you have something very special!

[Cupcar]

Originally Posted by kenikh

The Titanium rods are a bit special in dimension. The are 130mm length, just like the early 2 and 2.2L rods, except they have the same rod journal diameter as the 70.4mm crank on the 2.4, 2.7 and 3L cars.

This makes them quite the hot upgrade for an early car - just send your crank in for a rod journal regrind to SC journal spec @ 66mm stroke (or any custom stroke for that matter) and you have something very special!

Hey, we did that!!

Ti 130 mm GT3 rods, 89 mm Mahle pistons, 66 mm regound, Early 2.0 case, 40 mm Webers, GE80's

241 HP @ 7300 RPM on dyno so it worked OK, insides below:

[kenikh]

SWEET! I love the Pankl Ti rods, but had some R&R chromoly rods made to GT3 spec instead. They were about half the price of used Ti rods and a third the price of new ones.

With the Pankl rods coming in at 418g, the moly rods are heavier by 122g (@540g/ea), but still 160g lighter than stockers (@700g/ea). I am curious to see what the big end weights are of a Pankl rod - I have never seen a number to compare the really important numbers of end-weight vs. end-weight.

[blue72s]

Originally Posted by Cupcar

Hey, we did that!!

Ti 130 mm GT3 rods, 89 mm Mahle pistons, 66 mm regound, Early 2.0 case,

Nice. What bearings? Who did the work on the crank?

[Cupcar]

Originally Posted by blue72s

Nice. What bearings? Who did the work on the crank?

Marine Crankshaft in Santa Ana, Ca. Crankshaft repair, outboard marine, motorcycles, circle track, quarter mile and imports, billet crankshaft - We Fix Crankshafts - Marine Crankshaft, Inc.

Crank was polished on its standard size main bearings, reground to 53mm rod bearings, center main drilled & grooved, counterweights lightened, re-hardened and re-nitride with balance and plug R&R for cleaning (they send out nitride to someone and re-plug job sent to Ollie's machine by Marine).

Bearings were Glyco standard mains and Porsche Motorsport GT3 standard rods.

[tadd]

Pardon me for tipping a boat that should not be tipped, but shouldn't that motor do 8.5k on GE80 cams easy? I would assume that you have heads to match... wouldn't 270-280 would be a more fair number??

If I could, why did you choose the GE80 over the RSR sprint (or 906 cam)? I'm trying to make that decision now...

[Cupcar]

We were looking for drivability and throttle response more than peak power in a 2.5 liter.

The headers were 1 1/2", only 35 mm exhaust and 37 mm intake ports, single plug, 10.2:1 C.R. and carbs with 36 mm venturis, so a lot of peak power was left on the table and I am sure 270-280 is certainly possible.

The good news was we got a broad torque curve of around 190 lb.ft. from 5000 to 6500 and great throttle response.

Since we wanted to keep RPM below 7600 in service, an engine with around a 7300 RPM power peak seemed right and the GE80 had done this for us in the past, so we used one again, and got what we wanted, maybe a GE60 would have been fine.

[tadd]

Thanks for background. I've often wondered about the general 'rule' of under camming vs over. I have always wanted to overlay an S with say a 906 cam. Just from eyeballing them side by
side it seems like very little is given away for a lot more on top. Same jist as the early 'rally' spec using 906 cams and pistons with S heads.
What would be interesting is if the extra lift 'makes up' for the smaller ports given that the GE80 has 0.51" vs 0.46" lift on the RSR sprint.

[racing97]

Why doesn't the RSR or Supercup crank shown in Bill's picture need all the case and crank mods for oiling.

regards

[Cupcar]

I asked the guys at PMNA about the lack of extra crank oiling and they said Porsche never uses it on their race engines...

On thing of interest on the GT3 engine is the oil pressure relief valve parts package is very different than we are used to. The retention plug has a 36 mm deep recess in it and the spring is different with a different spindle within the spring. The safety valve parts package is the same as usual.

I think this set of parts along with a big pump regulates the oil pressure at 90 PSI over a broad range and that may help. This is speculation on my part.

[Bill Verburg]

I think Geoffrey said it was 85psi, Unfortunately Rennlist is down again so I can't check. It also makes a difference where oil pressure is measured. The 964/993 cases have 2 different taps

JoeMag posted this one w/ the 2 ports labled

[Cupcar]

My factory book says the GT3 oil pressure relief valve opens at 5.3 bar or 77 PSI, not 90, so I was wrong in memory here, and the safety valve opens at 7 Bar or 102 PSI .