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Over Boost Troubleshooting

I am sure that in the last week before I put the car away for the winter I was getting a slight over boost condition. I do have the 0-1.5 Bar speedo gage indicator (I know they are not as accurate as the clock mount gage) last drive it's pegging 1.5 Bar a couple times. I have a 1.0 Bar Spring installed. I think I am going to look at the waste gate first, I hope I just need a new diaphragm/ membrane . If not give me a idea of what to check next. It's the original waste gate.

Mod's include Turbo (k27 Hi flow) complete B&B exhaust system/headers,Kokeln IC, SCCams, AI flowed fuel head, 1 bar boost spring,

Help
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Old 12-06-2007, 07:56 PM
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So your bottom end is running great. A little run through the top of fourth, uh I mean first huh . Wonder if your gears are the same as mine (G50).

Reasoning based on what you have done the stock waste gate unit is defintely not preventing boost. I can only imagine what you are going through on a Montana road.

Would it be your right foot is sticking to the floor.

When did you do the top end? How many miles?

Regards,
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Old 12-07-2007, 12:07 AM
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There is a vent on the top of the wastegate bell. If you can blow air trough it, wastegate membrane is ruptured and needs to be replaced.

You pegged boost at 1.5 bar? Hmm, is your overboost switch in working order? It's there to prevent exactly that sort of things. It should cut ignition at roughly 1.1 bar.

If you peg your boost at 1.5 bar couple of more times you might need little more than wastegate membrane. You'll need new piston compression rings to begin with (frankly, you might need them already).
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Old 12-07-2007, 01:45 AM
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I would test your gauge to see how accurate it is. I would also bench test your wastegate to see when it is opening. When bench testing your wastegate don't put more than @ 20 lbs into it cause that might damage the diaphram.
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Old 12-07-2007, 04:52 AM
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Quote:
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I would test your gage to see how accurate it is. I would also bench test your waste gate to see when it is opening. When bench testing your waste gate don't put more than @ 20 lbs into it cause that might damage the diaphragm.

I am suspect of the gage, can they be that inaccurate? the engine during the needle deflection was not making any more power than before. I did not notice anything un-normal when it happened. I will bench test the waste gate.
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1987 930 - Gone but not forgotten
A man with priorities so far out of whack doesn't deserve such a fine automobile.
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Old 12-07-2007, 02:45 PM
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What about the gauge? Are they rebuildable?
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Old 12-10-2007, 08:13 PM
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I bet NHS could rebuild them.

North Hollywood Speedo
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
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Old 12-11-2007, 01:48 PM
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I would go with an autometer boost gauge- they are a little tacky but mine is right on everytime and it was cheap -$40
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Old 12-12-2007, 07:10 AM
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Quote:
Originally Posted by MT930 View Post
I am sure that in the last week before I put the car away for the winter I was getting a slight over boost condition. I do have the 0-1.5 Bar speedo gage indicator (I know they are not as accurate as the clock mount gage) last drive it's pegging 1.5 Bar a couple times. I have a 1.0 Bar Spring installed. I think I am going to look at the waste gate first, I hope I just need a new diaphragm/ membrane . If not give me a idea of what to check next. It's the original waste gate.

Mod's include Turbo (k27 Hi flow) complete B&B exhaust system/headers,Kokeln IC, SCCams, AI flowed fuel head, 1 bar boost spring,

Help
My Speedo Boost gauge only goes to 1 Bar??

Les
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Old 12-12-2007, 07:34 AM
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Buy a clock boost gage and forget the tach gage. It is useless.
After you buy the clock boost gage then see what boost readings you get and write back.
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Old 12-12-2007, 02:40 PM
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Here is what I have. Based other comments this may not be stock. The service records show that the PO sent the tach out for repair could they they have put a new face on it that goes up to 1.5 bar (no description on the exact work performed). and can it be calibrated? I plan on getting a clock mount anyway. Can anyone tell me if this is a stock tach face?
I appreciate your help.
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Old 12-12-2007, 03:46 PM
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NOT stock.

Nice though, if it is accurate.

This is mine, stock. With a twist

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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 12-12-2007, 04:00 PM
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I have never seen a gauge face on a factory tach that goes to 1.5 before. Mine goes to 1.0 and actually pretty accurate but I always look at my clock opening mounted VDO gauge. It is so much easier to see and it has the resettable needle. I wonder how your gauge was calibrated?
Old 12-12-2007, 04:04 PM
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It may not be calibrated for the non stock tach face the needle swing may be stock. Can they be adjusted if so how?
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Old 12-12-2007, 04:15 PM
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whats the biggest spring you can get for the wastegate?
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Old 12-12-2007, 04:22 PM
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I would contact North Hollywood Speedometer , 818-761-5136 about calibration. I sent them my VDO boost gauge and they repaired the clutch in the telltale needle assembly and checked the calibration. Maybe they can test and recalibrate, if required, your gauge as well.
Old 12-12-2007, 05:18 PM
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Quote:
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whats the biggest spring you can get for the wastegate?
what would happen if you restricted the wastegate outlet port size by 50% instead

munchovie
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Last edited by wmunchovie; 12-12-2007 at 05:59 PM.. Reason: wastegate instead of turbo
Old 12-12-2007, 05:56 PM
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what would happen if you restricted the wastegate outlet port size by 50% instead

munchovie
It would regulate the boost until it reached certain point where mass flow would be restricted and boost would start to raise again regardless of spring.
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Old 12-13-2007, 01:50 AM
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Have an issue with the stock boost gauge pegging all the way to 1.0 when under boost.
The PO told me it was stock, but the gauge and the lack of wastegate wooosh tells me otherwise.

The stock boost gauge appears accurate and predictable under all acceleration conditions; engine is stock with a Borla exhaust

Tore down the wastegate and the diaphragm looks fine along with the valve/piston.

Can anyone identify this spring as a stock .8 spring?
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Old 01-16-2008, 08:51 AM
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Measure the spring height from end to end and then measure the actual wire diameter. These 2 factors will determine the stiffness of the spring and therefore what boost level it will be for. Post you results on the forum and hopefully someone will chime in on which spring it is.
I may be able to respond next week as I have a 1.0 bar spring in my garage that I can try to measure for you this weekend and compare to your measurements.
Good luck,
Fred
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Old 01-17-2008, 04:46 PM
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