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3,050 RPM is 70 MPH on mine...

When I bought this car, the previous owner[s] stated that I had a 915 ring and pinion... Don't know exactly what that meant, but my guess is it had something to do with the final gear ratio????

I'm just checking to make sure I have the same gearing as the stock 930 with 4-speed. I'm running 3,050 rpm at 70 mph. By my calculation, the theoretical top speed [at 6k rpm] would be less than 140 mph.

What say you?

Also, I make about .2 bar boost cruising at 70 mph. Is this normal?
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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 11-11-2008, 07:07 PM
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My 1978 60mph 2,000 rpm + or - never checked at 70mph
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Old 11-11-2008, 07:21 PM
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A 915 R&P will not fit a 930 case. Typical 915 R&P is 8:31, sounds like you have a 8:39.
My 915 with 8:31 sits at 3400RPM @ 70mph.
Yes, a stock 930 engine cruising at 70mph @ 3000rpm could very well be making 0.2bar all of the time. That will suck gas.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 11-11-2008, 07:22 PM
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Sounds like a short ring and pinion...
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Old 11-11-2008, 07:23 PM
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Quote:
Originally Posted by mooney265 View Post
When I bought this car, the previous owner[s] stated that I had a 915 ring and pinion... Don't know exactly what that meant, but my guess is it had something to do with the final gear ratio????

I'm just checking to make sure I have the same gearing as the stock 930 with 4-speed. I'm running 3,050 rpm at 70 mph. By my calculation, the theoretical top speed [at 6k rpm] would be less than 140 mph.

What say you?

Also, I make about .2 bar boost cruising at 70 mph. Is this normal?
Since the red line is 6800 the top speed is closer to 160. Sounds like you have a 8.41. With a stock 930 gearing it is almost best to drive in 3rd at most legal speed limits. The gearing you have is close to ideal for the anemic 70-75 legal speed limits in most US states. The boost level problem is related to something other than your gears. I have had many 930 over the years and at cruise 3000 rpm the boost Gage is not raised. So check your motors ancillary gadgets as something is malfunctioning.

Last edited by voitureltd; 11-11-2008 at 07:59 PM..
Old 11-11-2008, 07:35 PM
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I just saw your mod list. You have a problem if the engine is making boost at 3K cruise. A stock engine might do that but a modified one should not. Is the K27 a 7200?
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 11-11-2008, 07:50 PM
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Quote:
Originally Posted by mooney265 View Post
When I bought this car, the previous owner[s] stated that I had a 915 ring and pinion... Don't know exactly what that meant, but my guess is it had something to do with the final gear ratio????

I'm just checking to make sure I have the same gearing as the stock 930 with 4-speed. I'm running 3,050 rpm at 70 mph. By my calculation, the theoretical top speed [at 6k rpm] would be less than 140 mph.

What say you?

Also, I make about .2 bar boost cruising at 70 mph. Is this normal?
I have a 8:41 R&P w/17" 25.7"OD Tires, turning about 3100RPM at 70MPH. Are you reading boost from the factory boost gauge or another type?

My mods are similar to yours w/B&B exhaust system, K27-7006 turbo, SC cams, Kokeln IC, twin plug crank-fire. I do see .2 bar at 70MPH when cruising and going up very slight incline, but on flat level surface, 0 bar. With this gearing, exhaust setup, spool-up is very fast, feeling initially like a normally aspirated 993. Once the turbo hits it's sweet spot, lord, hang on!
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Old 11-12-2008, 09:14 AM
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Right at 90 at 3100rpm's. Stock gearing.
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Old 11-12-2008, 10:58 AM
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Brian: What's the issue if you're running a K 27 7200....like I am with stock internals, 16 inch Fuchs, and stock R & P? Is there a significance here? You know what else I'm running....so I'm naturally curious about your statement.
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Old 11-12-2008, 11:20 AM
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Les-Paul & Waynesco1: That' what i figured it should be...

Werk: Your gearing sounds like mine... I have a 934 boost gauge and it's very touchy... it bounces between 0 and .2 at 70mph. It's the trying to maintain 70mph that causes the boost issues. As the boost kicks in, I accelerate past 70, then ever so slightly release the go-pedal, then the boost drops to 0. Once this occurs, the car rapidly slows, thus the need to push the gas pedal, again... It's like walking a tight rope...

Turbo: I believe it's a k-27 [it's got KKK on it, too]. Not too sure how to VERIFY. Maybe some help here...

Rarely8 & Voitureltd: I guess I don't have a 915 pinion gear... But, obviously have a lower final ratio - - looks like maybe a 8.41

Q: What's are my ancillary gadgets???? Sorry that's above my pay grade!
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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 11-12-2008, 01:42 PM
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Chuck - the 7200 has a typical boost threshold of ~2600rpm dependant upon other engine components. Turbos such as the 7006 boost later, others such as the 27S boost sooner.
I was guessing that the turbo being used was likely a 7200 or maybe a 7006.

There is a "sweet spot" that you need to find and stay in vacuum all of the time while cruising, at any speed. Anything else will waste fuel and leads to a touchy throttle. This involves tuning your cam timing, ignition timing, and AFRs.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 11-12-2008, 02:59 PM
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Brian: Thanx for the explanation. I went out and ran it up to 3000 rpm...and the speedo needle was just resting on 80....the problelm is I don't know how accurate the needle is. Next time I'll put in the GPS unit and check it against the speedo. I have no idea where the sweet spot might be, but I do know that it does start spooling at around 2600-2800whereas before it would have to get to 4000 before the turbo lit up. Much more linear and sophisticated acceleration now. Most likely due to that RarlyL8 exhaust system you made up for me!!

I know that the local cops were trying to get close enough to get a clock on me, but I spotted them back there in time and slowed it down.....then they pulled up next to me at the next light and gave me the thumbs up!! I smiled and went happily on my way....much slower of course.
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Old 11-12-2008, 03:09 PM
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Quote:
Originally Posted by mooney265 View Post
Werk: Your gearing sounds like mine... I have a 934 boost gauge and it's very touchy... it bounces between 0 and .2 at 70mph. It's the trying to maintain 70mph that causes the boost issues. As the boost kicks in, I accelerate past 70, then ever so slightly release the go-pedal, then the boost drops to 0. Once this occurs, the car rapidly slows, thus the need to push the gas pedal, again... It's like walking a tight rope...

Turbo: I believe it's a k-27 [it's got KKK on it, too]. Not too sure how to VERIFY. Maybe some help here...
What kind of IC do you have? Is it a long neck or does it mount onto the existing recirculating valve/plenum like the factory's? Does it have the C2 turbo divert valve mounted on the rubber elbow by the CIS metering housing? Mine does not exhibit the problems maintaining steady speed at 70.

The data plate for the turbo is mounted on the cold side (compressor) of the turbocharger. You will need a light to look up at the plate (it's blue and silver). Write down the three lines on the plate and we can tell you what type you have.
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Old 11-12-2008, 04:08 PM
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As far as the boost gage is concerned, you need to determine if the gage is accurate first. If you're using the gage in the tach forget about it. If you use the typical VDO in the clock location as you should be, then ok. Secondly determine how the gage is getting the input signal. If it is tapped into the brake booster line up front then you are reading vacuum and boost after the throttle plate. If you are tapped into the intake before the throttle plate then you could still be seeing boost pressure with your modded turbo but still seeing vacuum at the intake after the thottle body. I have one gage in either location and notice this alot.
If your cruising along at 70mph with no load on the car, you should be seeing a vacuum after the throttle plate because your engine is barely loaded (probably using 20h.p.). Soon as you start climbing a hill or accelerating and load the engine then boost will develop.
Your final drive gear is very low it appears.
Look into your turbo owners manual to get the gearing chart info, but you should be around 2500-2550rpm at 70mph, give or take with stock 16 inch rims and tires.
Be happy, cause the stock 4 speed is geared way too low, where are you gonna see 180mph at redline in the US anyway?
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---"When you're racing it's life! Anything else either before or after, is just waiting"

Last edited by fredmeister; 11-12-2008 at 04:47 PM..
Old 11-12-2008, 04:42 PM
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I've got some pics of the turbo. Also, I noticed a pinhole in the wastegate. Is this serious/common?

Hopefully, someone can give me a definitive answer as to what turbo I have...

Thanks!
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Old 11-12-2008, 07:07 PM
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I've got some pics of the turbo. Also, I noticed a pinhole in the wastegate. Is this serious/common?

Hopefully, someone can give me a definitive answer as to what turbo I have...

Thanks!
mooney,
Sorry, those weren't the numbers we needed. They're on a plate that's riveted to the cold side of the turbo. The plate is higher up from the pic shown.

The pinhole on the wastegate casting probably is giving you a "tic" when the engine is running, but won't really effect the boost.
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'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
Old 11-12-2008, 07:16 PM
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I'll get a mirror and look above tomorrow night.
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Old 11-12-2008, 07:26 PM
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That pin hole may not even break into the flow passage. See if any smoke comes out of it or if you feel any hot gas coming out with your finger when starting the car cold. No biggie either way, just watch that a crack does not develop there.
Fred
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Old 11-13-2008, 09:45 AM
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