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Discussion Starter #1
Hi can anyone tell me the boost pressures of the brooklands LPT and the pressures of the turbo R
Both intro and flying list the same turbo and part number ? So was wondering what the different boost pressures are if anyone knows
 

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I know that the earlier Turbo R's and the LPT are the same. The later Turbo R's got a little more boost as well as a liquid inter cooler that increased horse power to 400+
I'm pretty sure the boost was .7 bar. Later cars that had Transient Boost would give you up to 1 bar for several seconds. I would love to increase my boost.
 

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Hi its best to first check you are getting the boost you should be getting.
Mine is still a bit low so further things to look at.
Mike
 

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Discussion Starter #4
Hi thanks for both answers but the trouble is I don't know what boost I should be getting to check it's correct!
Also there is no waste gate on these turbos so don't know how to increase it if it is low !
 

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Hi Blue
Read this as a staring place ok ( copy & paste link in your browser)
Australian RR Forums » Spirit Series » Boost Control – Turbocharged Cars – Bring It Back Up to Scratch
Mike
 

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Hi!
Sorry for resurrecting an old thread, but I suspect that I might not have full boost either!
I've read the threads on the Australian forum, but I'm not sure I've understood everything....

My car is a 91 Turbo R, and it's got 2 solenoids attached to the right cylinder head. I gather the front plastic one is the boost solenoid that controls the pressure in the manifold, and the rear one (metal) is the one that controls the wastegate. Correct?

28435


What's the easiest way to check? Disconnect the hoses from the boost solenoid?

Where would you fit an external boost gauge?

I've been looking for the solid-state Hella relay mentioned in the Australian article, but can't find it in Germany. Are there any alternatives?

Cheers

Es
 

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Thanks!
I checked the front solenid:
With ignition on, it clicks, and also clicks when the brake is applied. I'm getting about 11,8V with the solenoid connected, so I gather the electrical connections are OK?!
I disconnected the hoses and tried blowing and sucking through it with ignition on and off, but it doesn't appear to seal completely - am I missing something?

How do I test the rear solenoid?

Cheers

Es
 

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Hi ES,

Just remember you have a Low Pressure Turbo. Like you I was expecting when I bought my Turbo R with very low mileage a serious boost in the back, which was not the case. I was indeed disappointed. FInally, the double kick in the back came with the next generation in 96 when they put an intercooler, Zytec power management and 400 HP.

But frankly, having both, yours is the best and most simple to maintain. The intercooler cars from 96 are very difficult to work on becaus ehtere is no place , no room, and you need to take all this intercooler factory out to work on the engine, and it really a pain.
Yes much more power, but much more complication and torubles, British style.

You may have a trouble but not so sure,.
 

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Hi Jean,

I'm not expecting supercar performance, but just want what's there in theory :)
I do have the impression that it's a bit livelier after I cleaned all the contacts, but that may be wishful thinking indeed.

By the way, mine would appear to have an intercooler fitted: there's what's looks like an intercooler under the right headlamp, and the hose from the turbo also disappears fown there!

Cheers

Es
 

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Its a radiator, for either transmission, either air for Turbo, because your turbo is air / air. On later car its air / water, with a second expansion tank, a huge intercooler aboive the engien, an electric pump , coolant just for turbo, a radiator front raidator.
Its possible you have a lack of power, because this Turbo is ondeed efficient. Check indeed air filter, fuel filter, spark plugs, distributors completely and wires.
Drive it with premium gas, you may wake her up if she was sat for some time, always wait car is warm, minium 20 km , before sollicitating turbo.
 

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Hi Mike and Jean,
I think I've understood the workings now: a pressure line from the compressor goes to the boost solenoid. When a certain level of boost is reached, the solenoid opens, sending the pressure to the wastegate, which in turn opens. I still have to trace where the piping goes - it all disappears under the turbo!

I was trying to find the boost sensors, or APT as Bentley likes calling them.
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IETIS says they're located adjacent to the ECU compartment. Maybe I'm blind, but when I look in that area, I'm finding my two ignition coils and two stacked modules with a green wire and a 4-pole plug. Am I looking in the wrong place?

Cheers

Es
 

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Hi Guys,

I just had another fiddle (working in the engine bay when it's 30 degrees outside is wonderful 🥵), and rigged up a manometer to the pressure line from the compressor side of the turbo.
Flooring it, I'm getting maybe 200mbar or so.
I then went naughty, and blocked the pressure line downstream of the manometer, hence bypassing both solenoids. I'm now getting 400-500mbar, and the Fat Lady really gets long legs!
28468


Is the plumbing correct?

I checked the solenoids too:
1. Front solenoid, above the "E" in Bentley: When blowing into the line with the T-junction an no voltage applied to the solenoid, it vents to the connection above the "Y". When voltage is applied it vents to the open connection above the "N". The solenoid doesn't seem "airtight" even with voltage applied.....
2. Rear solenoid: with no voltage applied, it vents to the open connection towards the bulkhead. This one is "airtight", an im sure the hose I'm holding with my finger goes to the wastegate.

What next?

Cheers

Es
 

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very interested in your progress, and will apply to my 90 Turbo R

I think in psi, so 200 mbar is only roughly 2.9 pounds of boost, barely worthwhile. 500 mbar is roughly 7 pounds of boost, which is still less than the boost pressure I use on my 1979 Honda CBX 1000 air cooled six cylinder motorcycle that I turbocharged with a plain bearing Rajay turbo and a draw through Mikuni flat slide carb. The motorcycle engine finally blew up at 28 pounds of boost, but now that I have rebuilt it I routinely run 12 pounds of boost on the air cooled motorcycle in regular street use. If it blows up, I will rebuild the motorcycle engine yet again, but don't want to deal with rebuilding a Bentley motor damaged from too much boost

does anyone here have experience on "safe" boost pressures on the 6.75 motor? Obviously the factory on later engines went with higher boost using an intercooler etc., and eventually had head gasket issues apparently. What levels of boost do the later motors run?

I don't know anything about Bentley engine management. Do the knock sensors still work with the disconnect done by The_Nuge???? If so, why doesn't everyone do the disconnect and enjoy the 7 pound's of boost???? Alternatively, I wonder if an aftermarket adjustable waste gate solenoid could be adapted to allow boost to be easily adjusted?

Paul LeClair
 

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Hi Paul,
Is there any chance you could:
1. Take a picture(s) of your boost pressure plumbing? I'd like to see if it's the same as one mine!
2. Test the plastic solenoid by blowing air through with and without voltage applied to it. Mine doesn't close entirely as described above, which seems weird to me.

I'm also still convinced that the metal solenoid is for the wastegate and the plastic one for the dump valve, but I'd love to be corrected if wrong 😉

Cheers

Es
 

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Test the plastic solenoid by blowing air through with and without voltage applied to it. Mine doesn't close entirely as described above, which seems weird to me
The plastic valve is the same part as used on the early Saab 900 "APC" Turbo.

Part # 7517477
The entire boost regulation system was produced by the same company that supplied Saab

My valve leaks under pressure between the tan/yellow top cap and the brown body.

Plastic valve dIagnostic tips can be found on Saab forums

I plan on replacing mine with an all-metal aftermarket part in September.

 

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And the transient boost solenoid appears to be the same as CBC4269.
My car was not fitted with this metal valve and I have no way to compare if it flows the same
 
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