Boost problem

[cover]

Hi everyone

I just installed Rarly L8 headers and muffler on my otherwise stock 1976 930.
It is a very nice "plug and play" fit and it sounds great.

In the meantime I have another problem:

Appearently I have no boost and the car wonīt rev beyond 4000 rpm.

It runs nicely below 3000 rpm but it has a hard time reving from 3000 - 4000 rpm.

The engine has been on the floor for about 3 months while the car was repainted
and I have adjusted the valves, renewed the plugs and plug cables.
I did a compression test also and it showed nice compression.


I have tried following witout solving the problem:

- Checked that the turbo was spinning freely before I installed the muffler.

- Adjusted the ignition. (with wacumhose connected....is that a problem?)

- Checked and tightened all hoses.

- Checked for exhaust leakes (can see no carbon residues anywhere)

- Tried two different wastegates.
I did find a small hole between the cooling ribbons on both wastegates (is that a problem)

[mooney265]

Originally Posted by cover

I did find a small hole between the cooling ribbons on both wastegates (is that a problem)

No, I have one, too - - and no problem with boost/rpm's...

Do you think you could be "overboosting," thus causing your overboost sensor to shut off the fuel pumps? Or, maybe your overboost switch is malfunctioning?

Or, maybe you're running on 1 fuel pump [instead of 2]?

[cover]

Both fuel pumps are running.

Overboost theory is worth checking........ but I feel no boost at all when driving.
There is no boost gauge in the car but shouldnīt I be able to register a signifigant boost before the sensor cuts off the fuel?

Are the overboost sensor supposed to shut off the fuel pumps completely causing the engine to stop, or will it prevent further reving only?

[infraredcalvin]

Originally Posted by cover

Both fuel pumps are running.

Overboost theory is worth checking........ but I feel no boost at all when driving.
There is no boost gauge in the car but shouldnīt I be able to register a signifigant boost before the sensor cuts off the fuel?

Are the overboost sensor supposed to shut off the fuel pumps completely causing the engine to stop, or will it prevent further reving only?

Easy to test the over boost switch, take the lead off and ground it on the case, my 76 had an empty blade already installed close to the switch. You are correct though, if the switch is failing you'll get some boost then your face will hit the steering wheel...

Sounds more like a boost leak, check your plumbing for tight seals.

[cover]

Just trawled the forum for similar issues.

One guy talks about a frozen "shutter valve" causing a 1977 930 to be restricted below 4000 rpm.

Picture of the shutter valve:
http://forums.pelicanparts.com/uploads4/83turbo1101254334.jpg

here is the thread:
Porsche Turbo Problems

Is this maybe worth checking?

[cole930]

Cover,

I was just going to suggest checking the shuttle in the recirculation assy. That would cause exactly what you are experiencing. Easy fix, take a look at that thread,

Cole

[RarlyL8]

Hey there, didn't know you were having troubles.
Things that can prevent rev/boost:
- Ignition/timing malfunction, verify timing advance.
- Exhaust occlusion, not the problem.
- Low fuel pressure/flow, check system pressure.
- BOV malfunction, shouldn't prevent reving so ???
- Intake occlusion, rag left in throttle body?
- Mechanical brake on engine such as tranny lock-up, odd but can happen such as e-brakes not releasing.
I can't think of anything else off the top and encourage others to chime in. Good to eliminate the possibilities from the list and narrow the search.

[IMONBOOST]

Since your engine was dropped for some time, were any of the vacuum lines disturbed or intercooler piping? You could be running extremely rich under boost, do you see black smoke coming out the back?

[occb2]

I think you have your fuel lines crossed. Happen on my rebuilt and the car would choke itself on boost and run like crap over 3000 rpm.

Robert

[dhg1337]

I had First hand experience with crossing the Fuel lines, vacuum leaks, and left a paper towel in the intake tube infront of the turbo. Any of those can cause it not to rev.

[cover]

Thanks guys

I will start checking

[cover]

So, Iīve been checking hoses, ignition, recirkulation valve etc......didnīt find any problem and the engine still didnīt rev very well.
Decided to run a tankfull of gasoline with "Bell Add nozzle cleaner" added.

I drove approx. 50 miles......and bang!!! Suddenly she came back from the dead.
Now she Boosts, howls and roars like never before. Donīt ask me why.

Brian Bodart :-) that exhaust delivers pure audio-porn. It sounds a bit like an old RSR when the boost kicks in and everything goes on full song.
Boost also kicks in a couple of hundred revs earlier, thanks to the exhaust.
LOVE IT LOVE IT LOVE IT :-)

I will run another tankfull of gas with cleaning additive and then put the car on a dyno to make sure everything is tuned in perfectly.

[cover]

By the way...speaking of exhaust systems.
I visited "JP Group" in Denmark last week with the local Porsche Club/forum .
This is the company behind Dansk Exhausts.
Very impressive factory and the owner is a huge Porsche fan and a very nice guy.

The company now produce original specification 930 exhaust for 3.0 l as well as 3.3 l.
They look very nice and this is as original as it gets in 2011.
(Dansk is an OEM supplier to Porsche)

But I will tell you one thing though!!
The craftmanship of the original Porsche exhaust as well as the 2011 Dansk version can not be compared to what you get from Rarly L8.
Brians work is simply in a different (higher) league.

Marry me Brian ....ha ha

[RarlyL8]

Glad you're happy and all but that's gonna be a little awkward for the kids ...