GT3 engine core vs. 996 vs. 996TT

[MIK911]

A post a few months ago (by Wayne, i believe) mentioned that the stock 996 engine is different (inferior) to the 996 Turbo engine. Besides the turbo itself, i recall that the Turbo's engine is based upon a race engine core.

What about the new GT3's??? Is this engine core based on the Turbo's engine or the lesser stock 996 engine ?

Mike
'86 coupe

[ZAMIRZ]

The new 911 GT3s engine is based on the turbo's superior dry-sump engine.

[beepbeep]

Gt2, GT3 and 996TT have old-style 964 core, 996 have just baffled wet-sump.

[Paul Thomas]

Aren't the GT-2, GT-3 and 996TT based on the GT-1 motor?

Paul

[Bill Verburg]

Thet are are all based on the .5R version of this case. The one pictured is a 964.******.0R

[CamB]

Which raises the semi-obvious question.

Water pumping issues aside, does this mean they would sorta fit back there.

[beepbeep]

Originally posted by P-THOMAS
Aren't the GT-2, GT-3 and 996TT based on the GT-1 motor?

Paul

Yes. Heads are the same...case is carried over from 964...so you can say that 996TT engine has GT1 heads and cylinders and 964 case.

[beepbeep]

Originally posted by CamB
Which raises the semi-obvious question.

Water pumping issues aside, does this mean they would sorta fit back there.

No, it's just the case that is from 964. Everything else is water-pumper. Case has been used beacuse it's pretty strong. It's also expensive to produce so plain-vanilla Carreras use less sophisticated and cheaper design.

[CamB]

So the flywheel etc, and general dimension, are very different?

[NYSCAR]

Wow GT1 heads, no wonder those things respond so well to modifications...

Brad

[beepbeep]

Not so much wow...heads are heads. There are many well-designed heads around.

One thing should be considered: Porsche had two-valve heads for eons beacuse there are certain thermic consideration with air-cooled heads which means that you cannot make aircooled four-valve heads that won't overheat. Problem with aircooling is also that thermal fluctuations are much bigger as there is no "moderator media" flowing around and no thermostat (except oil-thermostat) to keep temps at bay. That's why all really fast Porsche engines had either watercooled heads or watercooled engines. With watercooling, temp goes quickly up to desired (and thermostat-regulated) value and stays there. Aircooled cannot do it as quickly, as there is a fan always blowing (which you cannot stop), different air-temperatures (which you cannot control), and cool-air flow considerations (air has very low specific temperature coeficient compared to water) which are hard to engineer away. Four-valve 935's had watercooled heads, 962's had watercooled engines alltogether, GT1 had watercooled engines etc.

It's impossible to fullfill emmision and power criteria with two-valved heads and it's impossible to make aircooled four-valve heads, hence move to watercooled engines.

[MFAFF]

From memory.. always suspect I know, the GT-1 based GT3 motor is a pukka dry sumped motor rather than the hybrid 996 wet sump with baffles and remote tank unit.

This advantage is mainly highlighted on the race track, for which the GT3 was designed.

[NYSCAR]

Nice information beepbeep!

You mean most porsche heads are capable of flowing 600+ hp out of the box?

[beepbeep]

NYSCAR: Porsche 2-valve heads have always been "optimal" in such way that they were hard to improve by porting. Unfortunately this has been widely misunderstood as "porsche heads flow really good" which isn't the case. They flow almost as good as two-valve heads can be made to flow, but still worse than 4-valve heads which cannot be used on aircooled engines....get my point? Porsche had to make those 2v heads near damn perfect to be able to achieve desired power-outputs and still be in the game, but within limitis imposed by antique aircooled design.

Answer about most Porsche heads beaing capapable of 600+ hp out of box is:

Yes, as long as you use newer-style 996 watercooled 4-valve heads or 3.6 aircooled heads and turbocharging, there shouldn't be flow problems even with stock heads. But if you are already tuning to such numbers, it's little aditional cost to have them ported little more, freeing additional 10-30hp. Actually, a friend of mine uses stock N/A 3.6 heads on his dual turbo engine and he definately pushed trough 600hp barrier (with lot's of boost) :-)

That being said, i prefere this much more than six separate, leaky, rocker-operated, aircooled two-valve heads :

[NYSCAR]

Now that's a thing of beauty...

[RickM]

In the early 90's there was a tuner/machinist in Canada that made 4 valve heads for '84-'89 911's....think they cost about $8k at the time. Wonder what happened to him and his product.

[beepbeep]

Originally posted by RickM
In the early 90's there was a tuner/machinist in Canada that made 4 valve heads for '84-'89 911's....think they cost about $8k at the time. Wonder what happened to him and his product.

As i said, Porsche tried to make 4-v aircooled heads but they failed. Problem was that there wasn't enough metal there to take away the heat, so certain spots in it got too hot.

When i was at our local Porsche tuner (expert on N/A track 911's) he showed me a prototype CNC billet-machined 2v D-port shaped 911 cylinder head and said that it also flopped.

The sad truth is that 3.6 2v heads are as good as it gets, minus some minor port-job, result of decades of development.

NYSCAR:

"thing of beauty" is nothing else but plain-vanilla SAAB B234 shortblock head, polished somewhat You can pick one of those at any junkyard for peanuts...it's exactly same head as used on Pikes Peak car with 700hp...so yeah, those modern 4v head designs can flow pretty good allright

I'm a little confused now. Have 964s got 6 seperate cylinder heads like older 911s or 2 big ones?

Are you sure that 962s were watercooled? I always thought they had aircooled cylinders and water cooled cylinder heads?

[beepbeep]

964:s and 993:s have all separate cylinder heads, just like any other 911.

When it comes to 962 engines , there seem to be two sort of them. Original one that is completly watercooled (actually finned cylinders with water-casing around) and one with flat fan for cylinders only. Wayne has picture of 962 watercooled P&C's somewhere from his Bruce Andresson engine rebuild class picture-album. Heads are electron-beam welded to cylinders so gaskets are unnecessary.

959 has also watercooled heads made in one piece.

I understand why Porsche went to watercooled heads. Every time engine heats up, cylinders and heads heat up differently and thus increase in size non-uniformly so there is "grinding" between heads and cylinders.

In watercooled cars this only happends twice, once you start driving and once you stop the engine. Watercooled cars heat up quickly beacuse thermostat shuts down water-flow trough radiator, and when desired temperature is reached it stays there and changes very slowly as water has excellent thermal coeficient and can absorb lot's of heat.

When you drive aircooled car, it heats up slowly beacuse you always have a fan that tries to cool it down, and it isn't augumented (which it is on aircooled aircraft-engines , for example) so temp goes up slowly (and engine wears more during that period). Also, head-temperatures are never stable as air is bad at absorbing heat so they heat up-and-down all the time as you drive, depending on engines load. What happends is that there are always "grinding" movements between heads and pistons while you drive instead of only two cycles in watercooled engines...after a while, you end up with "uneven mating surface" between two and those tell-tale oil leaks under engine, 911's "territorial markings".

These inherent problems forced Porsche to over-engineer their engines, which led to Porsche myth. Nowdays, water-coooled heads can be cast in one piece which is much cheaper than assembling separate cast heads. They also have more stable temperatures, can be casted with 4v/cylinder and can stand up to more boost. Also, single central plug is better than side-mounted plug beacuse of symetrical movement of flame-front.

[NYSCAR]

I happen to think SAAB is a very fine automobile.....