Turbo Torque Curve

How does one go about flattening and extending the torque curve on a 3.3 C2 Turbo? I'm trying to sort through some options for the next 911 in my life. I guess my question is, how does one go about modifying a 91-92 Turbo to effectively emulate a powerful normally aspirated (or supercharged for that matter) engine? Are there turbo/intercooler combinations that spool quickly enough to do this (i.e., substantially full torque by 3000 RPM)?

The C2 isn't much different than the 930, I think they made small improvements to the exhaust, intercooler and cams. I haven't seen any dyno charts of a stock C2 turbo but here is a comparison of my 79 3.3 turbo motor. It's comparing stock to a setup with B&B exhaust, larger intercooler, intake and larger turbo. If I put a smaller turbo on it should spool up quicker. An HKS boost control will also get to full boost quicker.

If you really want to cut the lag though you might think about increasing compression and or the displacement. These of course cost big/bigger $$$.

BTW, these dyno runs were done with a splipping clutch, it shaved off about 20lbs of peak torque.



Chuck
83 911 turbo cab

Yes, the C2 Turbo engine is similar to, although not exactly the same as, the earlier 930 engine. Bruce Anderson's 911 Performance Handbook has the details, but modification wisdom from the 930 is certainly transferable to the C2 Turbo.

You say you want maximum torque at 3000 rpm. That is very hard to do with a single turbo that has any top end at all. But you can do this: My 930 develops around 300 ft lbs at the crank at just over 3000 rpm, and that's a lot of torque (stock, it was just over 100 at the wheels--dog city). Now, it goes on to develop about 500 at 5000, but I'm not particularly bothered by that .

This happens at .83 bar on pump gas. But my turbo is big enough to pump out enough air for 650 hp at 1.3 bar, so I didn't get the good torque improvements by downsizing the turbo. Instead, I went with Mahle 8.0:1 98 mm pistons and a 3.6 crank from a 993 (had to cut straight chamfers into the heads for this because of the longer stroke). Gives you a 3.45 displacement and one point higher compression. This combination helped significantly with raising torque down low. The line is not flat, like you can get with a twin turbo set-up, but it starts getting pretty high a heckuva lot earlier than it did before.

Originally posted by Bruce M.:


Instead, I went with Mahle 8.0:1 98 mm pistons and a 3.6 crank from a 993 (had to cut straight chamfers into the heads for this because of the longer stroke). Gives you a 3.45 displacement and one point higher compression.

Bruce,

Does this mean that you have a 9.0:1 CR (8.0:1 pistons + higher comp from longer stroke)? The 996 tt runs 9.4:1 CR with 0.7bar of boost. Ahh, the wonders of modern engine management and knock control.....

I really appreciate the responses!

Bruce,

Your set-up sounds excellent. What I didn't want was the 100 ft lb at 3000 rpm scenario, then sudden boost through to 5500, as this will be my daily and DE/autocross driver. Is engine longevity significantly reduced with a higher CR at .8 boost and 500 ft lb set-up such as yours?

930 fan--You're right. I looked back at all my spec sheets and it turns out I have 7.5:1 Mahle pistons. With the longer stroke, the EFFECTIVE compression ratio is 8.0:1, according to the engine builder (Bob Holcombe of Motorsport Design). And yes, engine management is a must at these levels of compression, horsepower and torque. I've got a Motec 48 Pro engine management system.

tcampbell--as to reliablity, with good gas, and IF I stay at .83 bar, this thing should should have zero reliabilty issues. Time will tell. So far, the only problem I've run into is when I had 110 gas in the tank, had the boost set at 1.3 bar, drilled the throttle for about 30 minutes of crazinesss, then looked at my boost gauge (a 935 tell-tale gauge in place of the clock), and saw that it registered 1.7 bar! Cracked a piston, warped the ring lands on the others. Saw God, though .

Engine had been programmed at 2000 feet above sea level and at ambient temperature of 107 Farenheit. In Seattle, I'm at sealevel and a lot colder, so I made a bunch more boost at the same setting.

One new set of pistons later, I'm poorer but wiser. And, frankly, I have no need to feel the kind of power I felt at 1.7 bar again. It was a traction disaster, and when the tires finally hooked up it was literally a feeling that I was about to die. Things were happening too damn fast. At 25, that's cool. At 41, that's crazy. And I was just stupid enough to keep doing it (the theory being that I needed to get the 110 out of the tank to refill it with 92 unleaded for smogging purposes). Heart didn't settle down for a week.

I've done some quarter mileing in the past, although almost all in Japanese cars when I was younger. Running on the .8 bar wastegate spring (instead of electronic wastegate control with the Motec), and starting from idle, my car ran a 12.05 at 125 on pump gas and Dunlop street tires. I know what that feels like. But the power I felt at 1.7 bar with the Motec, given traction (which is a huge given), was definitely in the 10s. Too crazy, at least for me. I'm sticking to 1 bar or lower, with a default setting of .83 bar with Motec boost control.

Bruce,

When I was at a Porsche repair shop recently, I came across an old VW&Porsche magazine with an article about a Motorsport Design customer that had a street driven 930 that ran 9.8@153mph on street tyres. What was amazing was that this was in 1987!!The car was also geared to do a record (for a stock bodied prod. car) 225+mph at Bonneville. That's what you get with 901bhp.

As for your experience at 1.7bar - Ouch! It's amazing that nothing else broke. It's funny that my rings broke due to overboost whereas you cracked your piston - do you know what would explain why we broke different things?

You may want to go with a separate electronic boost controller - all the latest ones have altitude and temperature compensation so what you experienced cannot happen with this set up. My overboost was a result of a similar situation - I got one of those 1 bar springs which is 1 bar with a stock engine. I had the headers, big i/c, big turbo so it became a 1.15 bar spring and then Boom! Damn I hate it when I learn through experience - it costs too much

Holcombe is an evil genius with 930s, I'll tell you that. He's not the most instantly friendly guy around, but he's actually a pretty good guy, and he knows what he's doing. He's also used to working with people to whom money is little or no object, though, so he needs a reality check every now and them. And what he thinks of as "good" power and torque is waaaaaay out there.

But, damn, he's completely changed my car from a proud relic to a modern beast (or at least the engine--can't retrofit pms, abs, etc., and wouldn't want to--only thing I put in was a limited slip, which is vital). The Motec is something else--there are so many sensors, and such precision available to a tuner, that it can remake your car, especially if your car has a distributor and CIS.

I have no idea why I cracked a piston (right at the top, near the valve relief) and not the rings. Wish I had "just" busted the rings instead, like you. As it was, I'm glad the cylinders were still o.k.

Good thought on a Greddy or HKS controller, and the altitude and temperature compensation business. I would have thought that the Motec would do that, too. I'll check with their techs.

Are you still modding, or done for awhile? If you're still at it, and are thinking of any particular mod, I'd be happy to share whatever experience I have had. I've definitely had a few. Among the coolest things about these cars is how great a platform they are for carefully planned mods.

That, and they have the best automotive asses this planet has ever seen .

Mind if I interject a question since you have performed some of the mods I am in the process of doing.

I am changing the turbo and exhaust to free flow. I have an electronic boost control and will be installing that after the other mods are finished.

My question: If you have a stock wastegate, does the electronic control over ride the the .8 bar spring (I may be thick...but I don't see how it can). Do you have to upgrade the spring to the max bar rate you want to achieve.

Any info would be of interest.

Thanks, Todd

I feel your pain about Motorsport and money, I brought mine to Powerhause which is right next store to Motorsport and has them do all the wrench work. I took my car for a test drive after they did some upgrades and couldn't believe the difference in power and range. Then I looked at the bill, holy crap, I just sold my Rx7 for that much. Solid work though, they really now all the little things to check and fix up.

930fan, when you broke a ring at 1.15 bar were you running in hot weather or with bad gas? I was thinking of adding that spring and I'm at 0.9bar right now. Going to 1.1 bar should put me at 450 engine hp which will be the max for my 915 tranny and the CIS.

As for the electronic boost control I thought it replaced the spring and controlled the wastegate diaphram with additional hardware, not sure though.

Chuck

As to an electronic boost controller, I'm not sure about the ones you're talking about, because I control boost through the Motec, alhtough I don't know much about that eiter, I'm embarrassed to say. I believe the Motec keeps the wastegate snapped shut until a predetermined boost level, regardless of the spring used, but how it does that without additional hardware I do not know (maybe it doesn't, and there is additional hardware). From what I understand, the aftermarket boost controllers do the same thing.

Powerhaus is a solid shop. I started out with them, but before they could start on my engine, their wrench quit, so they had to sub the job out to Holcombe. He's a whole different ball game. He did everything, including building the loom for the Motec, installing the sensors, programming the system on his engine dyno, tweeking it on a laptop in the car, rebuilding my tranny with a limited slip, twin-plugging the heads, machining them to accept the pistons with the longer crank, valve springs, retainers, building me a full stainless exhaust with the prettiest headers you'd ever want to see, etc.

Man was I an idiot. But at least it's done.

Bruce I am soon to be in the market for a 930 and your setup sounds interesting!.
If you have any pics, the gallery would benefit from them as well as me
Thanks
Ben
Gallery address:
http://www.cheaterswayside.com/911/

[This message has been edited by 86ragtop (edited 01-31-2001).]

Originally posted by 86ragtop:
Bruce I am soon to be in the market for a 930 and your setup sounds interesting!.
If you have any pics, the gallery would benefit from them as well as me
Thanks
Ben
Gallery address:
http://www.cheaterswayside.com/911/

[This message has been edited by 86ragtop (edited 01-31-2001).]

Well, I've got a few pics, but I have no clue how to post them on a site, the Gallery or otherwise. They're sitting in my e-mail as we speak.

Chuck450,

Electronic boost controllers work with the standard wastegate and spring so you cannot preset a boost lower than what the spring is rated for as what the controllers essentially do is bleed away air to the control section of the w/g, delaying the opening of the spring thereby increasing boost.

How did I break my rings? I'm ashamed to admit it for fear of being admonished from the more responsible members on this board but I was (whisper it) street racing with a modified Mistubishi Lancer Evo on an empty highway at 3 am. After reading up on the subject, I have discovered that detonation is a complicated phenomena - the cool night air increases air density which is good but it also means that you have to richen your mixture if not it will go lean. Plus, boost also goes up (1.2 at night with 1 bar spring)with cool air which resulted in broken rings after 5 back to back runs from 30 to 140mph. At least I won.

For some reason, the PO of my car filed down the standard w/g spring to give less boost (0.7) so that was why I changed to the 1 bar spring. Now I use the boost controller (Blitz DSBC)with the standard spring. PH is a good shop, I bought all my parts there by mail order so get their advice as they know far more than I do. If I were you, I'd skip the higher boost unless you can get PH to set the a/f mixture up at 1 bar on their dyno. I think the 915 is marginal at this level - you already have a slipping clutch so it's telling you something. Be very careful on what you do next!!

Btw, have you done any upgrades to the 915 and is there anything that can be done to make it bulletproof at this hp level? What is the gearing (mph/1000rpm) in 5th on your tranny?

Heh 930 fan - you will have Juan after your tail with that 'whisperring' street racing!.
Hav eyou looked into G50 tranny conversions? as it is a stronger setup!
The 4 speed box is one thing that I feel lets the 930 down for day to day driving, and a reason the Carrera is hot on it's tail to 60mph (standard trim)

Bruce and all, if you set up a profile on the site. Once it has been established (you must give an e-mail address, but you can always set up a temp. free one @ yahoo/hotmail etc.)
Then you can edit your profile and uploading pics from your computer is really easy, promise, I am no computer geek
rgds Ben



[This message has been edited by 86ragtop (edited 02-01-2001).]

86ragtop,

Sure I'd love to have the g50 set up but they cost minimum 6k plus intallation with the upgraded clutch (a must). A 915 can be had for fraction of that so if it costs say 2k to upgrade it (if possible) then I get to save a packet and have 5 speeds. The Ruf 5sp is another possibility but I'll bet they are stupidly priced too.

My only problem with the 915 is the ratios. 23.2mph/1000rpm in top is too short as it means 150.8mph at 6500rpm. The 4sp 930 has 27.5mph/1000rpm so does 178.75mph at the same revs which is just nice except it becomes a pain when you get to corners. Actually, what I really need is an engine like Bruce's, then I'll have enough torque at any revs so 4sp will be fine

I believe there are many variations for gear choices if you go non standard with the 915 which may give you better rev/speed ratio's.
My only concern would be the max. torque that the standard 915 can survive.
Thanks for your info. though, I have learnt some, just reading yours and Bruce's post's.
rgds Ben

930fan,

I did upgrade the clutch and flywheel at powehaus to an RSR3.0 race clutch. My left leg is now twice as big as my right from pumping that thing. The stock 915 clutch was toast at the first set of upgrades. And you can barely see on the dyno graph that I get 53rpm/mpm in 4th. This equates to 122 at 6500rpm in 4th, I am planning on new tires that will be a higher profile so it will increase this about 5% and increase the contact patch a little for handling.

As for 915 upgrades I have had it rebuilt, lsd added and they machined the case and put a steel sleeve in the pinion bearing case. Not sure if this really beafs up the tranny or is just for normal wear and tear.

I have asked the people at Powerhaus, Zucz and several other tuners about the 915 tranny in a 930 and they all say it depends on the user. Doing something wrong in a normal 911 and it can be damaged, in a high power 930 it will just do more damage. I do admit that shifting from 2nd to 3rd full throttle is difficult, but I'm getting better. If you shift smooth I doubt if just the raw power from the engine can rip teeth off gears or damage things, but noway is it bulletproof.

Chuck



[This message has been edited by Chuck450 (edited 02-01-2001).]

Great subject!
Well heres my question.As must of all of you know i had my 3.2 carrera Turbocharge she is running.5 Bar of boost non adjustable with no internal modifications,she is doing 276RWHP,im in the process of installing a massive intercooler,but i want to go up in horsises to be able to run 1.0 Bar of boost ,so im thinking,lower the compression to7/1
change the spring in my wastegate (tial) install turbo pistons,of course all the hardware,haletech system,polish,ported bigger valves flow test heads,Msd.
I will like your opinion in this proyect any feed back welcome
REgards Juan
www.geocities.com/titos88911/MY911.HTML

Heh Juan!
I thought this thread might catch your eye!
I am learning a bunch of stuff from these guys chatting!.
I spoke to Dave of Proto Tech and I think he will hook me up with a powerfull 'ride' when I get back from the Bahamas (2 months).
I have to sell my beast, so if you hear of anyone wanting it e-mail me!.
I will try to catch up on e-mails occaisionally but where we are going is "3rd World!".
So after Sunday, I am going to reallty miss this board for a couple of months! .
Maybe I will have time to talk to the wife, or even go outdoors!...
Naaaa!