small displacement turbos

[TimT]

369 lb-ft @5700 rpm is nothing to sneeze at....

at 2000 rpm its probably got a higher torque output than a NA 2.0...at 3000 rpm its probably got more torque than a 2.0 911S...at 4000 its probably got.... etc..

Choose a proper cam, time the cam approprialtely, combine with some of the new efficient turbos and you could have a wicked small displacement turbo engine.

Ive been squireling away parts to buil a similar engine for years.. I have a set of iconel 935 header, TWM throttle bodies, GT3 oil pump etc...

I think ill stick it in my 914, instead of my 911

[Henry Schmidt]

[QUOTE]Originally posted by beepbeep
problems with 911 engines with high boost are twofold:
They have individual heads which is worse when it comes to keeping "lid" shut when combustion occurs. Watercooled cars have one head per cylinder bank which means that there are many studs keeping it in the place. When combustion occurs (and it's almost always only one cylinder at a time per cylinder bank), head will be kept in place not just by head-studs surrounding that particular cylinder but by the adjacent ones too. Being single-piece cast object, that head will tolerate more boost before it starts leaking. 930 head, for example, is kept there by only four studs and will start "walking" when subjected to high boost. [QUOTE]

Supertec Head studs will reduce and under certain circumstance eliminate head movement. One customer is running our head studs at 45 ft/lb of torque. Although we don't recommend head torque in this range it seems to work with his 700+ hp.
Watch for the SUPERTEC HEAD STUD KIT on the pages of Pelican parts soon.

[beepbeep]

Originally posted by KobaltBlau
First of all, Goran, you and I have similar interests, although you are taking more action. Since I first drove a car with ~1 bar at 2000 rpm, I have been very impressed with this type of engine.

According to my calculations, our engine will pass the boost treshold @ 2600 RPM and reach 1 bar @ 3200 RPM.
Full boost won't be achieved until 4400 RPM though :-) That's the price you have to pay when using big turbocharger. We'll see how good my estimate works in practice.

due to piston shape? chamber in head should be relatively knock-resistant with twin plug. (I have no data)

Flame-front has finite speed that is pretty constant regardless of RPM. With two plugs, you "lighten" the mixture from two sides so whole mixture is combusted faster, which leeds to more distinct pressure peak in cylinder. It means that more of that pressure can be used to push the piston downwards and you don't need to lighten it too early. Twin-plugs won't make the chamber less knock-prone directly but will allow you to achieve same power with less boost or more power with same boost (as more of cylinder pressure is converted to work)

Speaking about chamber design, domed pistons are usually big no-no when it comes to knock resistance. You want your combustion chamber free of sharp edges and slightly spherical. This is little easier to achieve when you have four small valves instead of two big ones.

Agreed. However, is this really a problem at 1 bar and 8.5-9:1, if preignition is avoided, with quality steel studs? I'm not sure if anyone can give a definitive answer, but I tend to think it wouldn't be. As you probably know, combustion pressures increase radically when preignition occurs, and many owners of tuned turbocharged cars are not very careful about this. More care can ensure a longer lasting engine in many ways.

Unfortunately, i believe that it happends even on stock 930's, given enough time/miles. Many are modified which only hastens the process. It's not immediate failure but slow cumulative process that progressively gets worse. It is also speeded up by the fact that head/cylinder temperature is fluctuating all the time on aircooled engines which means they will sustain many more thermal cycles (with moderate delta T though), compared to watercooled engine which effectivly only gets one per drive. Different thermal properties of heads and cylinder, however slight, will eventually lead to leaky seals after prolonged "grinding"...refered as "uneven mating surface".

True, but the engines they were using those techniques on were running very high boost.

Not so terribly high, actually. Around 1.2 to 1.4 bar, with C/R ranging from 6.5:1 to 7.0:1. Note that those boost figures are nowadays used on cars with C/R of 9.0:1 and higher, thanx to advances in combustion-shape geometry and knock-detection.

My main concern here is that I like the (original) 911, and I like the engine it has. I don't like the kind of crap most people who convert their cars to water cooled engines have to do for cooling plumbing and radiators. If you are able to complete your conversion without running front radiators, I will be very impressed (I'm not doubting, I just think that is a much nicer solution, like the guy with the geo metro engine did)

Yepp, that is going to be our biggest challenge. I'm against cutting out the front trunk and spoiler and spoiling (sic) the air-flow underneath. My initial idea is to use a radiator adjacent to engine, on the cold side. If that's not enough, we'll run additional small cooler in front lip. Third way is mounting radiator high up in the wing, but it will raise CG so it's last resort.

In practice, it would probably be easier to just do this on an SC motor. No longer small displacement, but strong and very nice. I would not consider single plug, and would try for 9:1. (heck, my engine has 9.3:1, and it probably isn't quite that high in practice, hmmm.) I'm not sure if a turbo small enough to provide 12psi say by 2500rpm could flow out to 7000 rpm, but that would be very nice. But you could build the hardware on this type of motor to go 8000.

You can get a pretty decent idea of where your boost treshold will be by calculating mass flow at certain RPM's and plotting it on compressor map. My guess (without really calculating) is that Garrett GT32 would fit the bill quite nicely. It might blow hot air at 7000 RPM but it's not a showstopper, just a price you pay for low-end grunt.

interesting idea. But if you try to put that engine in an air-cooled body, you probably have more of a cooling challenge than you guys have with the SAAB engine.

Hehe. No, I was thinking of turbo-converting a existing Porsche Boxter (2.7 "the hairdresser edition"). It's light and has middle-engine. Very good platform. I understand that PAG doesn't want to develop it too much, it would start eating into bread-and-butter 911 segment ;-)

Thanks for the interesting feedback Goran,

My pleasure Andy!
Cheers!

[KobaltBlau]

Originally posted by TimT
369 lb-ft @5700 rpm is nothing to sneeze at....

at 2000 rpm its probably got a higher torque output than a NA 2.0...at 3000 rpm its probably got more torque than a 2.0 911S...at 4000 its probably got.... etc..

Definitely True! I'm just curious about a turbo 911 based engine that reaches peak boost (and first reaches high torque) at 2000-2500 rpm. More a street engine than a track engine, certainly not a race engine like that one. That engine is very interesting in its own right, I've just been thinking about something different

PS Goran I don't have time to respond now but I will later, your reponses are again very interesting.