How much boost should a 1990 hdt 80 make?

[cruisernerd]

I recently bought an 80, they are new to me. I am get around 10 psi boost, is this an acceptable amount of boost for this engine? At highway speed it is already spooled up to 10 psi, there isn't anymore if you stroke the skinny pedal. It sometimes hits 12 psi. I don't know if it's relevant but it also has a thirsty fuel pin installed. Makes almost an obnoxious amount of smoke when the turbo isn't spooled up. Pretty sweet actually...
Thanks,
Eric.

 

[Tapage]

FSM said about 8 - 9 PSI so due to amount of fuel you are seen probably more .. keep an eye on those EGT's .. and adjust ( if possible now ) your boost compensator ..

 

[mudgudgeon]

FSM said about 8 - 9 PSI so due to amount of fuel you are seen probably more .. keep an eye on those EGT's .. and adjust ( if possible now ) your boost compensator ..

Actually, it should produce around 12-13psi, max of 15. FSM testing procedure is stationary, with no load on the engine, so you won't see full boost.

And yeah, if its smokey, check EGTs, it should only be smokey as you hit the throttle off idle, and then only a short puff of smoke

 

[Tapage]

your FSM said 12 - 13 ..?

and yes Overboost light comes 14 - 15 PSI ..

 

[mudgudgeon]

No, FSM says 8-9psi, but this test is done revving the engine while stationary. You won't produce full boost with no load on the engine. 8-9psi is a test only to test the turbo is operating correctly, not indicative of full boost under load whilst driving.

 

[Tapage]

It's my understanding that FSM said this coz that what you suppose to see under all conditions .. and also there is safe room to go up to 14 - 15 when overboost light comes on ..

 

[ForealBoreal]

don't boost that stock turbo over 14.5lbs.
Its the safe limit for the stock turbo....

 

[Enigma]

Well I guess I'll be seeing how long mine lasts at 18.

 

[Tapage]

I never seen more than 10 - 11 ( for very few segs under severe fueling / load conditions ) when I was stock .. ( stock all that does not means had the spec IP fueling )

 

[mudgudgeon]

Mine tested at more or less what FSM said, but on road saw around 12-13psi under load before mods. You won't see full boost without a load on the engine.

adding a bleed valve on the waste gate and more fuel increased boost.


Enigma, I hope you have an intercooler to catch the shrapnel. Mine went pop at 18-ish psi (was seeing 22 at times)

 

[IanB]

It's my understanding that FSM said this coz that what you suppose to see under all conditions .. and also there is safe room to go up to 14 - 15 when overboost light comes on ..

I don't have gauges yet to see what mine does stock, but this has always been my understanding as well.

 

[mudgudgeon]

Boost is a produced through the expansion of exhaust gases. The hotter the combustion gas the more energy/gas expansion, the more drive pressure available as the expanding gases try to force their way past the turbine.
A resting vehicle being revved while stationary with no load on the engine will require very little fuel to be burnt to reach 2500rpm for the FSM testtest, maybe 1/8 throttle. The air fuel ratio will be very lean producing relatively low exhaust gas temperatures.
With a diesel, the higher the fuel to air ratio, the hotter the combustion gases will be.
Under load, to achieve the same RPM, you pump in more fuel with no increase in air into the engine eg, a hill climb, full wide open throttle, same 2500RPM, EGTs rise, turbine drive pressure goes up, so does boost pressure.

the FSM test is just simply a test, not an absolute reading on the boost your engine will always produce. Boost varies constantly depending on engine load, rpm and throttle position

 

[Tapage]

We all know that .. ( at least me ) my point here it's FSM put a number that should be the boost you see .. under which conditions, FSM didn't specify.

 

[IanB]

Boost is a produced through the expansion of exhaust gases. The hotter the combustion gas the more energy/gas expansion, the more drive pressure available as the expanding gases try to force their way past the turbine.
A resting vehicle being revved while stationary with no load on the engine will require very little fuel to be burnt to reach 2500rpm for the FSM testtest, maybe 1/8 throttle. The air fuel ratio will be very lean producing relatively low exhaust gas temperatures.
With a diesel, the higher the fuel to air ratio, the hotter the combustion gases will be.
Under load, to achieve the same RPM, you pump in more fuel with no increase in air into the engine eg, a hill climb, full wide open throttle, same 2500RPM, EGTs rise, turbine drive pressure goes up, so does boost pressure.

the FSM test is just simply a test, not an absolute reading on the boost your engine will always produce. Boost varies constantly depending on engine load, rpm and throttle position

So you're saying the wastegate setting from factory exceeds what the turbo is able to produce without load?

 

[Douglas S]

I never saw more than 10 before I installed a manual boost controller.

The factory isn't specifying a boost number because they tested the engine, they're specifying the wastegate crack pressure like Ian mentioned. If you saw 12-13 there was an issue with your wastegate or some sort of blockage in the signal line.

 

[mudgudgeon]

So you're saying the wastegate setting from factory exceeds what the turbo is able to produce without load?

Not really, but you are right.

Waste gates open progressively, they don't "snap" open at a set psi.
My experience was that with no mods, peak boost was approx 13psi, fiddling with fuel settings increased it to 14-15psi when overboost light came on, and fuel pump reduced fuel supply.

Interestingly, at one point I wired the wastegate shut, boost peaked at around 15psi, until I increased fuel settings a lot.

The OP asked if 10psi is an acceptable level of boost from his 1hd-t.
IMO, no, I would expect to see more like 13ish in standard trim in the conditions described.

The FSM test simply shows that the turbo is functioning correctly, but not necessarily that the engine/IP has been given an optimal tune.

I'd be disappointed in 10psi frtom a 1hd-t.

 

[mudgudgeon]

[QUOTE="Douglas S, post: 9855352, member: 53866", they're specifying the wastegate crack pressure like Ian mentioned. If you saw 12-13 there was an issue with your wastegate or some sort of blockage in the signal line.[/QUOTE]

Disagree. A wastegate doesn't "crack", it opens gradually as boost pressure against a diaphragm gradually overcomes spring pressure

 

[IanB]

My experience was that with no mods, peak boost was approx 13psi, fiddling with fuel settings increased it to 14-15psi when overboost light came on, and fuel pump reduced fuel supply.

The overboost light is triggered by a pressure sensor, there's no feedback loop on a 1HD-T with a fully mechanical injection pump to reduce fuel supply when you've exceeded the threshold (about 14.5psi I understand). It's just a warning light, nothing more. Unless I misunderstood what you were saying here.

 

[Enigma]

I increased mine to 18 (from about 15 I think it was) to reduce egt. With my current version of fuel rod I was seeing 1200 too quickly too easily. Seems to to be working well. An intercooler is on the wish list though.

 

[mudgudgeon]

The overboost light is triggered by a pressure sensor, there's no feedback loop on a 1HD-T with a fully mechanical injection puamp to reduce fuel supply when you've exceeded the threshold (about 14.5psi I understand). It's just a warning light, nothing more. Unless I misunderstood what you were saying here.

The overboost light is triggered by a pressure sensor, there's no feedback loop on a 1HD-T with a fully mechanical injection pump to reduce fuel supply when you've exceeded the threshold (about 14.5psi I understand). It's just a warning light, nothing more. Unless I misunderstood what you were saying here.

Yes, sensor is a simple electric switch and has no effect on fuel.
The stock boost compensator fuel metering rod is designed/ground in such away that once the boost exceeds spring rate on the diaphragm spring, fuel delivery is reduced. unless you custom grind a fuel rod, or add spacers to limit the fuel rod travel, maximum boost is limited to about 15psi.

Bit off topic. The "official tuning thread" covers all this