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Brando
 
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911sc turbo boost limits

I am looking into wastegates. I wonder what the boost limits with 92 octane and race gas would be with the sc engine and 930 fuel meter. Will be using an intercooler as well.
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Old 08-22-2007, 10:10 AM
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Since you make no mention if you have the stock pistons in the SC motor or not, I will assume that you have the stock pistons. With that assumption, I would say race fuel or street gas, it doesnt matter, you should not run hardly any boost at all. With this being an air cooled motor, the C/R, not twin plugged, and the fact that you will not be running any type of aftermarket enigne management system ( MoTec, Link EFi, Fast, etc), I would say that the C/R will be your limiting factor, not what gas you run. IMHO, I would say anything more than 5 PSi of boost would be pushing it... and Porsche motors are a little more expensive than your average domestic or import motor if things go wrong.
Why not swap out the stock P&C's for some stock 930 ones?? It would be a cheap way to go, and you could then run about one bar of boost (14.5PSi). that is assuming that you have the other parts in place, good I/C, Euro fuel head, WUR mod.
BTW, I know where there is a good set of P&C's for a 3.3L 930 motor for cheap! and they include the cooling tin around the cyl as well......
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Old 08-22-2007, 10:22 AM
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Brando
 
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Good advise. It's what I expected. I plan to run about 5.9psi as I am waiting for this engine to loose compression or something before I go into it. I figure adding boost will help to quicken this process. Then, I will go with lower compression and maybe even go with tbitz efi (cheep).
I know others have used higher boost with the higher compression and had years use with no issues at all?
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Old 08-22-2007, 10:53 AM
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with stock 9.3:1 I smoked the pistons at default of the waste gate. But was running perfect at 5.8 psi=.4bar.. Infact still run that with lower compression but larger bore and works great.. I will go higher boost levels when I get bigger injectors but my goal this year was to not break anything..
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Old 08-22-2007, 01:25 PM
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Ben,
Do you still use the sc compression ratio? Or did you go lower?
I know you did some work to build the engine up.
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Old 08-22-2007, 01:41 PM
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I ran my 79 SC 3.0 at 8lbs with a 6BTM MSD boost retard ignition system and a 7th injector that fired off a Hobbs pressure switch at 4lbs without an intercooler and SC fuel dizzy. 8.51 compression, I had no problems. The pistons are the weak link, I wouldnt go over 8lbs, and with the higher compression you will still be laying down some good horsepower.
I rebuilt using full fin 3.3 pistons and cylinders with the rod bushing modification, twin plugged it, 930 oil pump, and added a 86 930 Euro fuel dizzy an intercooler and still have a 7th injector hooked up to an adjustable pressure switch just incase i need it at 14lbs..
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Old 08-22-2007, 02:13 PM
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Here's a chart from "Forced Induction Performance Tuning" by A. Graham Bell



98 RON is about what our 93 is.

The chart shows with a 60% efficient intercooler and 9.3 compression you could get away with about 9psi, but I'd knock off another point or two or three since it's an aircooled 2-valve motor. Be sure to data log your lambda numbers as you ease the engine up to speed.
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Old 08-22-2007, 04:00 PM
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Quote:
Originally Posted by quattrorunner View Post
Ben,
Do you still use the sc compression ratio? Or did you go lower?
I know you did some work to build the engine up.

I run 8.5:1 now
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Old 08-22-2007, 05:37 PM
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I have early SC pistons in my 3.0. I think they're 8.5:1 CR. I have run 8 PSI boost, currently run 5 PSI, with CIS. No extra injector, stock SC fuel pump, but I have an IA fuel head, Brian Leask WUR, and water injection. The water injection allows me to approach virtually 100% intercooler efficiency, as well as being an anti-detonant. I also have DC-15 cams, which seem to work well.

With an SC engine running low to moderate boost, I see no advantage to using 7.xx:1 CR pistons. The car would be undriveable until the boost comes on. I start making positive manifold pressure at 2100 RPM, and the engine pulls pretty hard up to 7000.

Pat
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Old 08-22-2007, 06:35 PM
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Pat, what kind of power would you say you have with the 5 psi? Like seat of the pants feel?
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Old 08-22-2007, 06:40 PM
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Hard to tell. It's going on the dyno soon. It seems like a lot, like 3.6 sort of power, but not 930 type power. I just want it to stay in the mirrors of the 996 and 997's at the track. I will say, it is no comparison to the 161 RWHP it had. I will definitely post the dyno results, good or bad.

It drives pretty much like an SC on the street, which is also what I wanted.
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Old 08-22-2007, 06:50 PM
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Me too, I don't want the lag of the 930, just some more power. But I don't want to wait till 4000rpm.
Later, after the engine has given up(it has 189000 miles) I'll do more inside. But it runs well and has no signs of giving up soon.
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Old 08-22-2007, 06:57 PM
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So if I get this, quattrorunner, do you plan to do a turbo on your sc engine without any internal modifications?
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Old 01-14-2008, 02:50 AM
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Quote:
Originally Posted by 125shifter View Post
Here's a chart from "Forced Induction Performance Tuning" by A. Graham Bell



98 RON is about what our 93 is.

The chart shows with a 60% efficient intercooler and 9.3 compression you could get away with about 9psi, but I'd knock off another point or two or three since it's an aircooled 2-valve motor. Be sure to data log your lambda numbers as you ease the engine up to speed.
Hi David,
Any idea where the Garrettson IC sits on this graph?

Les
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Old 01-14-2008, 05:59 AM
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Quote:
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So if I get this, quattrorunner, do you plan to do a turbo on your sc engine without any internal modifications?
I did that but then blew it up from an overboost
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Old 01-14-2008, 06:04 AM
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Quote:
Originally Posted by mb911 View Post
I did that but then blew it up from an overboost
That is the outcome I would expect, that is why I asked. But then I am not a turbo expert....
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Old 01-14-2008, 06:33 AM
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Hi David,
Any idea where the Garrettson IC sits on this graph?

Les
The small Andial/Garrettson style unit is only around 60%, as far as I have heard from Todd at Protomotive.

There is a larger Garrettson which I would think is better than the small 7" by 14" unit.
Old 01-14-2008, 10:52 AM
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Quote:
Originally Posted by les_garten View Post
Hi David,
Any idea where the Garrettson IC sits on this graph?

Les
I would imagine the big half bay IC's are about 60-65% like DDDD wrote.

I figure my full bay Bell at about 70%, but I don't a have a pre-IC temp sensor installed to find out. I'm wired for it, so one of these days I'll get around to putting one in along with all the other sensors I wired for but haven't installed .
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Old 01-14-2008, 03:31 PM
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I have no air-air IC, but I do have water injection. I can drop the temps in the plenum secton of the airbox (after the compressor) to pretty much what ambient air is entering my air filter. And, I can do this at the track, when the boost is on for long periods of time. I have instrumentation to measure these two key temperatures. Keep in mind my pressure ratio is low in comparison to high boost 930 type applications...I run 6 PSI. Looking at the chart above, I can surmise I have an extremely high efficiency intercooler.

Here is the dyno sheet from last fall; boost was around 6 PSI steady, although I have sinced changed my old junk wastegate to a Tial Sport. I have the car sorted much better now; spike is gone (had some air leaks on the pressure side of the turbo and got the WUR/fuel delivery issues resolved). I think the area under the curve is bigger now, and may have a few extra HP also. This is basically a stock 78 SC, rebuilt, with some longevity items and DC-15 cams, and stock 8.5:1 CR pistons.

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Old 01-14-2008, 03:51 PM
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A 3.2 Carrera motor will handle 0.7bar/10psi of boost all day every day, at the stock C/R of 9.5:1 (with intercooler). I can't see why the SC motor won't handle that with the proper adjustments to fuel and ignition delivery.
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Old 01-14-2008, 04:31 PM
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