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-   -   Over Boost Troubleshooting (http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/381188-over-boost-troubleshooting.html)

MT930 12-06-2007 07:56 PM

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

BReyes 12-07-2007 12:07 AM

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,

beepbeep 12-07-2007 01:45 AM

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).

dean 12-07-2007 04:52 AM

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.

MT930 12-07-2007 02:45 PM

Quote:

Originally Posted by dean (Post 3630949)
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.

BReyes 12-10-2007 08:13 PM

What about the gauge? Are they rebuildable?

NathanUK 12-11-2007 01:48 PM

I bet NHS could rebuild them.

North Hollywood Speedo

930gt-40r 12-12-2007 07:10 AM

I would go with an autometer boost gauge- they are a little tacky but mine is right on everytime and it was cheap -$40

les_garten 12-12-2007 07:34 AM

Quote:

Originally Posted by MT930 (Post 3630620)
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

fredmeister 12-12-2007 02:40 PM

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.

MT930 12-12-2007 03:46 PM

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.
http://forums.pelicanparts.com/uploa...1197503206.jpg

NathanUK 12-12-2007 04:00 PM

NOT stock.

Nice though, if it is accurate.

This is mine, stock. With a twist :)

http://farm1.static.flickr.com/145/3...4d324cf6_o.jpg

OSI930 12-12-2007 04:04 PM

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?

MT930 12-12-2007 04:15 PM

It may not be calibrated for the non stock tach face the needle swing may be stock. Can they be adjusted if so how?

h20cooled7 12-12-2007 04:22 PM

whats the biggest spring you can get for the wastegate?

OSI930 12-12-2007 05:18 PM

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.

wmunchovie 12-12-2007 05:56 PM

Quote:

Originally Posted by h20cooled7 (Post 3641554)
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

beepbeep 12-13-2007 01:50 AM

Quote:

Originally Posted by wmunchovie (Post 3641750)
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.

cl8ton 01-16-2008 08:51 AM

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?
http://forums.pelicanparts.com/uploa...1200502246.jpg

fredmeister 01-17-2008 04:46 PM

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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