How much boost should I expect- '90 740ft

  • Thread starter Thread starter jimb
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jimb

Good day,

Recently purchased a '90 740 turbo.

How much boost (by the gauge) should I see?

Needle gets about halfway into the yellow.

I don't suspect a problem, just checking.

TIA

jimB
 
Should go WAY into the red.

Something isn't right.

Of course, you DO understand that you only get boost while
accelerating under load?

No boost will occur when the car is sitting still and you rev the
motor.
 
jimb said:
Good day,

Recently purchased a '90 740 turbo.

How much boost (by the gauge) should I see?

Needle gets about halfway into the yellow.

I don't suspect a problem, just checking.

TIA

jimB
Click to expand...


That sounds about right. You could hook up a calibrated pressure gauge
and should see 7-8 psi at full boost. You can crank it up a bit if you
want more power, but longevity will suffer some.
 
James said:
That sounds about right. You could hook up a calibrated pressure gauge
and should see 7-8 psi at full boost. You can crank it up a bit if you
want more power, but longevity will suffer some.
Click to expand...

Not at all, if you put in premium and make it a modest increase.
Remember that the 780 Bertone Turbos made more horsepower (188hp vs.
165hp) by bumping the boost and requiring premium, no internal
modifications at all.

Bill
 
Bill said:
Not at all, if you put in premium and make it a modest increase.
Remember that the 780 Bertone Turbos made more horsepower (188hp vs.
165hp) by bumping the boost and requiring premium, no internal
modifications at all.

Bill
Click to expand...


The more power a given engine produces, the faster it will wear out, end
of story. I didn't say longevity will be unacceptable, but increased
boost creates more horsepower which puts more wear on engine and
drivetrain components, period. That said, these motors are legendary in
durability, so even with modestly higher boost they will probably
outlast the car.

I've run 16 psi in my 240T for years, the motor has held up so far but
I've broken a transmission, clutch, u-joints, and several engine mounts.
 
Should go WAY into the red.

Something isn't right.

Of course, you DO understand that you only get boost while
accelerating under load?
Click to expand...

yes

Car is new to me.

When I bought it, there was NO boost.

Searched around a bit and found that the waste gate was disconnected
from actuator <read: always open>.

Hooked it up, viola! We have boost.

jimB
 
jimb said:
yes

Car is new to me.

When I bought it, there was NO boost.

Searched around a bit and found that the waste gate was disconnected
from actuator <read: always open>.

Hooked it up, viola! We have boost.

jimB
Click to expand...


It should never go into the red, unless you've fiddled with it. Cars
made past '86 don't have red anyway, just yellow and in those full boost
is about halfway into the yellow. You really need to hook up a
calibrated gauge to have any useful information, no need to leave it
installed, just tee it in and go for a drive, then you'll have an idea
of what the needle position on the factory gauge represents.
 
This is very accurate information but I use synthetic oil so as to off set
the wear and heat as well I rarely use the full boost but its nice to know
its there if you need it .Make sure all your pipe and hoses are up to the
task ...
 
It should never go into the red, unless you've fiddled with it.
Click to expand...

Never say "never."

Mine goes into the red.

In fact, after reading your dismissive post I went out and WATCHED it
go well into the red.

Not toward the end, but about half way in.

And I wasn't really thrashing it as hard as I could.

No detonation, either.

As for having fiddled with it: upgraded turbo, some head work, and a
wider exhaust.

My 740 goes into the red, too.

I spot a trend.
 
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