One reason why GT3 engine makes power
 

Factory CNC machined ports.

http://forums.pelicanparts.com/uploa...1257384501.jpg


http://forums.pelicanparts.com/uploa...1257384534.jpg

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.

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

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.

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

http://forums.pelicanparts.com/uploa...1257542707.jpg

Damn sexy machining...

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.

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

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:

http://forums.pelicanparts.com/uploa...1257970717.jpg

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.

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.

Is it a secret?
 

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...

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.

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.

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

regards

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.

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
http://forums.pelicanparts.com/uploa...1258494118.jpg

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 .

That jibes w/ Geoffrey's info 80-85lb from 3k up at B which is before the top case oil galley

What's the ballpark price for a set of these rods? Carillo and Pauter are "reasonably" priced but if these can be had for just a few bucks more... Mmmmm titanium!

Check with Porsche dealer, they used to be around $5000 a set a couple of years ago. Probably more now.

Yikes, that's triple the price of the others. It seems the old saying is true, "if you have to ask how much".....

I thought Pauter Ti rods were around $5000.

996.103.012.93 is only $1700 per rod. OUCH. A complete set of chromoly Pauters for our old cars is the cost of one GT3 rod. :eek:

GT3 Rod Cost Via Pelican

What book has that level of data. The owner/tech manual is pretty basic?

Can a Ti rod be run 150k miles, resized, and run another 150k miles? Or does Ti fatigue more rapidly than a steel rod making it one-use-only?

Are the GT3 cranks much lighter? Do they have better oiling? Are all 3.6L cranks way heavier than say a 3.0SC crank?

Ti rods are made to higher quality now than the first ones and can be designed to have a fatigue life long enough for a street car, but Ti alloys do not exhibit a fatigue endurance limit like Ferrous alloys do. Steel rods can still be made light enough that they fatigue due to being stressed beyond the "infinite life" fatigue endurance limit, however.

I've heard that the GT3 rods can be reconditioned. But most who race the GT3 engine really hard (endurance races) choose to junk them and replace.

Notice how the GT3 crank isn't even knife-edged? That in my mind demonstrates that the 911 engine doesn't benefit a whole lot from that racer's trick. That said, knife edging reduces weight, aside from typical windage losses in wet sump engines. So i'm not saying that knifing doesn't have it's benefits.

Also looks like the counterweights on the GT3 crank are smaller (thinner?) than the 964.

The GT3 crank is lighter than the 964 crank. It's rod journals are smaller (SC size). Oilling is basically the same- no cross-drilling on the GT3 crank from factory.

The 3.0 crank is lighter than the 964 crank because it has smaller journals and the stroke is shorter- 70.4mm stroke for SC, 76.4mm stroke for 964.

That 964 crank pictured looks like it had a rod bearing problem on #6?

Over on 911uk.com, I remember reading a couple of articles on the GT3 engine when I had my 996 GT3 Mk2

https://techinfo.porsche.com/techinfo/sit/en/996Carrera/2004/1_2004_996_gt3.pdf

And one on the RS variant:
https://techinfo.porsche.com/techinfo/sit/en/996Carrera/2004/1_2004_911gt3rs.pdf

That is opposite to what I have long understood (and what is printed in one of my university textbooks). A quick Google calls up numerous sources that confirm that titanium and ferrous alloys both have distinct fatigue limits.

GT3s use a mondo oil pump to partially evacuate the crankcase of air, using a special main seal to hold it. No air means that windage mods are completely unneccessary.

I was told differently, but I could be wrong. I am not a materials engineer, just mechanical.

I was under the impression that the mechanism of the fatigue endurance limit had to do with interstitial alloy atoms such as carbon in iron arresting crack growth. With Aluminum alloys it is usually a substitutional alloy since the Al ions are smaller than the Fe ones and therefore there is no endurance limit.

I don't believe the intent of the oil pump is also to expel air from the case.... Isn't the case breather housing there to address the air/positive crankcase pressure issue? Air-entrained oil is the enemy to oil cooling. So I can't imagine the intent is to use the pump to evac air and introduce it into the scavenged oil?

Typical windage loss in wet sump engines is related to the crank counterweights slinging through the oil. I'm not saying there is not a loss caused by the crank parting the air in the case. Just saying that the viscosity of oil is much higher than air (both are considered fluids) and the air effect is much less of a concern than oil. So what you're saying is in the dry sump condition, there's no worry about oil losses and therefore the next loss to tackle is the air effect on the crank?

All Porsche dry sump engines run a partial vacuum in the crankcase, the GT3 just enhanced it w/ special crank seals and and breather valves. It's speculated that this contributes to the rear main leaks that these cars are notorious for. The seals work fine dynamically but tend to leak when they sit, causing no end of consternation in the owners minds.

Yes, the pumping of the piston pushing air more than the crank I believe.

Air in oil is common in high rpm dry sump engines from what I read. That is what the air-oil separator (baffles in a 911 oil tank) is for. I can't remember where I read about the oil pump being used for crankase vacuum. I think it might have actually been a Toyota F1 engine. They had to open a tiny hole in the case however. I guess to prevent cavitation or something? Anyway, they had to have some small amount of airflow. But the benefits of lower pressure drop off like most everything as the pressure becomes closer and closer to a vacuum. So that last little bit of air did not matter.

Take a look at the new Suzuki GSX-R engines. The engineers even designed an optimal shape for the holes connecting the crankcase sections (holes through the main bearing saddles). This allowed the air to be pushed around rather than compressed and expanded which would normally also happen on a boxer engine. They made pentagons for some reason. I guess resonance.

While it's true that the bigger the piston the more air it pushes around, the source of the cc vac is the oil pump, more specifically the scavenge section.
the scavenge side of a 993 pump moves 120l/min
scavenge side of a GT3 pump moves 135 l/min
the competition pumps used in LeMans GT1 move 160 l/min on the scavenge side

these pumps leave the cc under vacuum, increasingly so as the revs go up.

Yes, I was talking about the bike engine because it still has some meaningful air pressure in the crank case and so they put the ports in the bearing webs. I was just giving evidence that the air pumping losses are significant enough for KTL.