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Discussion Starter · #1 ·
ok i bought a manual boost controller and a boost guage. i installed both turned the controller all the way down. it will boost to about 11psi then a couple seconds later it feels like the car starts fighting itself(like its missing or bogging) and drops to about 6-7 psi which was about what it was stock. then when it shifts it will boost up to 10 and drop again.

any ideas whats going on
 

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firstly, manual boost controllers are the seed of the devil.

second you have wound it all in. this is wrong, you will blow your engine up. too much boost will cause incorrect fueling and cutting out, like you are experiencing.

if you are going to run high boost you have to get colder plugs, higher octane fuel, a better intercooler, hybrid turbo and bigger capacity fuel injectors if your going the whole hog something like megasquirt engine management.

if it stock pressure at 6/7psi then you probably have the LPT. wind the boost controlller (bleed valve in essence) till your seeing about 8 or 9 psi, and i wouldnt do it any higher than that.

Matt
 

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i found this, you might want to get an induction kit and some silicone pipe work to place the intake at the very front of the car with cold air, it does help a lot!
 

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tbh the max depends on what injectors you have and what octane fuel you are running, aswell as the engine internals.

on a stock engine i wouldnt push any more than 14psi on stock gas, and you'll be lucky if the engine doesnt cut out or pre-detonate and blow your head up.

usually the hpt's are aroudn 10psi. you are also looking at a restriction on the intercooler too because it has plastic walls nd they will blow off hhahaha i have done that!

if you want more power then look at bigger injectors, better turbo better intercooler. the intercooler will help more as it will be more free-flowing and more efficient.

also you have to look at your ambient temperatures which will also affect your levels.

Matt
 

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Discussion Starter · #7 ·
ok so where can i get bigger injectors that are compatible. my intercooler is aftermarket and can take 25 max. and it only seems to hold 15lbs for a few seconds then it drops to ten. if it held at ten and didnt drop to 6 id have it set to ten.
 

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have you got an after market dump valve or are you still using the the built in CBV on the turbo itself? if so its probably that as the little membrane inside and spring cant cope with the pressure so lets out and equals the pressure.

Bigger injectors will cost a fortune mate (about £150 each here and you need 4), raising the boost of the car has lots of other things to do aswell. you will find a new camshaft, the likes of the ipd vx3 turbo camshaft will do a great job, i would recommend that, you'll loose a bit of bottom end but when it gets going it'll kick you in the bottom quite hard.

main point, what are you trying to do by raising the boost pressure? gain more acceleration, more top speed?

Matt
 

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Discussion Starter · #9 ·
wasnt volvo owned by ford at that time? if so cant i find like an svo for bigger injectors.
the acceleration is nice but it seems to not accelerate so well after 70 mph.

cbv? wastegate or bypass valve?
 

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no i think they bought volvo in like 1999 or somewhere round there.

Compressor bypass valve (cbv) is the same as a dump valve or blow off valve. It works in the principle of the larger pressure on the throttle body pushes it open against the pressure of the atmosphere and either feeds it back into the turbo's air inlet or to the atmosphere. This keeps the turbo spinning and stops the pressurized air from ripping your throttle to pieces.

A Wastegate is what controls the pressure on the exhaust side. when the engine is running, the ehxaust pressure and heat turns the turbine in the turbo. when the engine is running at speed the pressure is greater and the gasses are flowing faster, therefore making the turbo spin faster and compress more air, therefore higher pressure. To control this pressure, the wastegate opens on the exhaust side and lets some of the exhaust gasses bypass the turbo completely, stabilizing the pressure output on the cold side of the turbo.

Some wastegates are built into the turbo (not really particularly good ones) and others are external, and the external ones are for the really hard core turbo modders as they are for hybrids, for example garret gt25/35 series.

What you can do is by a new fuel pressure regulator. An adjustable one where you can raise the fuel pressure, but you have to be careful not to run it too high as your fuel pump will not cope and you'll knacker the injectors. Be warned though, the injectors are probably running at about 70-80% of they're capacity atm. I wouldnt raise it too much above stock otherwise you will have big problems.

I would also advise you to start doing some research into turbocharging, how it works, why it works, whats involved. get to know the basics first and it will help endlessly, especially with the fueling and knowing where to start when modifying a turbo'd car.

Matt
 

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QUOTE(helps @ Aug 9 2008, 12:37 AM)wasnt volvo owned by ford at that time? if so cant i find like an svo for bigger injectors.
the acceleration is nice but it seems to not accelerate so well after 70 mph.

cbv? wastegate or bypass valve?
[snapback]88686[/snapback]​


This was before Ford bought them, but in the '80s it looks like Ford and Volvo both were buying their injectors from Bosch. The SVO injectors are the same (physical) size from what Volvo was using, and injectors that fit the SVO should fit.
 

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This is my experience with my 89 760 Turbo. Manual Boost controller, waste gate adjusted (4) turns out, blow off valve. I initially installed my boost controller backwards and the car would run great until 3000 rpm. I then figured out my error. I adjusted the controller to run at a maximum of 9.5 psi and now the car pulls through 6500.

The condition that you're experiencing with it essentially falling on it's face at 14 lbs is the Knock Sensor. It basically is the engines fail safe against detonation. Soooo, my suggestion is to run a maximum of 10 psi. Also, buy an aftermarket blow off valve as 9-10 psi will give you compressor surge. That surge will trash your turbo.

Have fun. These are cheap sleepers.
 

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no i think they bought volvo in like 1999 or somewhere round there.

Compressor bypass valve (cbv) is the same as a dump valve or blow off valve. It works in the principle of the larger pressure on the throttle body pushes it open against the pressure of the atmosphere and either feeds it back into the turbo's air inlet or to the atmosphere. This keeps the turbo spinning and stops the pressurized air from ripping your throttle to pieces.

A Wastegate is what controls the pressure on the exhaust side. when the engine is running, the ehxaust pressure and heat turns the turbine in the turbo. when the engine is running at speed the pressure is greater and the gasses are flowing faster, therefore making the turbo spin faster and compress more air, therefore higher pressure. To control this pressure, the wastegate opens on the exhaust side and lets some of the exhaust gasses bypass the turbo completely, stabilizing the pressure output on the cold side of the turbo.

Some wastegates are built into the turbo (not really particularly good ones) and others are external, and the external ones are for the really hard core turbo modders as they are for hybrids, for example garret gt25/35 series.

What you can do is by a new fuel pressure regulator. An adjustable one where you can raise the fuel pressure, but you have to be careful not to run it too high as your fuel pump will not cope and you'll knacker the injectors. Be warned though, the injectors are probably running at about 70-80% of they're capacity atm. I wouldnt raise it too much above stock otherwise you will have big problems.

I would also advise you to start doing some research into turbocharging, how it works, why it works, whats involved. get to know the basics first and it will help endlessly, especially with the fueling and knowing where to start when modifying a turbo'd car.

Matt
Where can I buy a new, or replacement CBP valve? Mine has hole in diaphragm. 1985 740T, 307,000+ loving miles. Not ready to give up my car!!!!!
 
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