It looks like that maximum boost on a stock LB7 is about 22 psi. The wastegate begins to open at about 30 psi (according to the service manual). Why did they bother to have it there?

Ever heard of Juicegrips? ;)

Ever heard of Juicegrips? ;)
;) :eek: :mad: ):h :help:


Turbochargers are wastegated for a number of reasons.
1. Wastegates improve transient response time over a turbo with a non wastegated housing

2. Wastegates Enable Designers to make a turbo small/large enough to be responsive at a given fuelling/ displacement property providing good emissions charecteristics and favorable EGT's over a larger non wastegated turbo that would be a lag pig without one (exh hsg size/exducer)

3 Wastegates Keep your turbo from Blowing the FCensored up!):h
Turbochargers, like engines have a finite engineered maximum RPM before they either :Aerodynamically Stall : Disintegrate : Fail at Thrust Bearing.

Our IHI Turbos are fantastic out of the box. Which is why we have been able to overfuel and keep up to other diesels out there.

BUT at a 2.4:1 Pressure ratio we are spinning said turbo at 110,000 RPMS.
And that is right at the 'sweet spot' or 'on the map' of the turbocharger.
We maintain that high adiabatic efficiency and flow from 95000 RPMS to roughly 135000 RPMS.

Pushing higher boost will approach Surge (or stall) faster and we are also running out of volumetric capacity and adiabatic efficiency after 35 PSIGA

This turbo WILL come apart when pushed past this pressure. BUT other factors will also dictate the max boost you can run on an adjustable gate.

For example if 37 PSIGA Stalls and blows up your turbo at sea level, and 35 PSIGA is safe at sea level.. what is safe at 5000' ASL?
A good rule of thumb is to DROP 1.5 PSIG for every 1000' ASL of altitude you encounter.
Likewise Humidity as it relates to air density also has this effect. More humidity, you can run more boost. Less humidity... less boost.

This is very general information. Not Gospel by any means.

So what good is a boost gauge? Almost none. It only tells you your turbo is operating and can help identify problems with high EGT's (boost leak etc)

For example, I modded my cylinder heads.... not much, but enough so that i actually 'lost boost' on my gauge. I hadn't touched my wastegate or my fuelling, so where did the lost pressure go? It went into my engine thanks to better flow on the heads. Unfortunately , Stupid me forgot that little tidbit that boost is never 'lost'.... i cranked my wastegate up to compensate for this percieved loss.... Made good power.... and promptly fragged my turbo.

There is a thread dealing with this in more in depth terms. Steve Cole Provides some very good information there.

Search for 550.5 It is a long thread... some 25 pages IIRC..... the turbo stuff is on page 13 I think.

Oh, BTW.... I am on turbo #5....... but this one's gonna last a long long time at 9 PSIG:D

Holly Crap Juice that is a long answer to a simple question.

The wastegate opens to avoid to much pressure which otherwise would result in damage.

Thanks for all good information, but I don't think I made my point. It looks to me that on a stock LB7 the wastegate will NEVER open. With the GM mindset of removing underhood lights and door lock cylinders, I'm wondering why they have something more expensive that is never used?

[QUOTE=Wayne Dohnal]Thanks for all good information, but I don't think I made my point. It looks to me that on a stock LB7 the wastegate will NEVER open. QUOTE]

I can get mine to open quite easily and then some...:muahaha: With the right power you can do anything....

Thanks for all good information, but I don't think I made my point. It looks to me that on a stock LB7 the wastegate will NEVER open. With the GM mindset of removing underhood lights and door lock cylinders, I'm wondering why they have something more expensive that is never used?
Under the right circumstances you might open that wastegate.

If you alter your vehicle the chances are even greater.

You can always salle yours on Ebay if you think you do not need it. LOL.

Holly Crap Juice that is a long answer to a simple question.

The wastegate opens to avoid to much pressure which otherwise would result in damage.
Thanks Bronco):h

Because the subject was so near and dear to my wallet i figured that more information was better than 'Because' or 'Do a Search';)

Which reminds me i did forget to mention why you would want to drop your pressures when at high altitude.

When at higher altitudes, the air is less dense (unlike me:eek: ) the turbine must spin faster to maintain the boost level you have set your wastegate to.

Which explains people who frag their turbo at higher elevations that only saw '35 PSIGA' of boost at 5000' ASL
The turbo has approached its critical RPM and is overspeeding...... and presto... another convert to Ebay Turbo shopping.

When shopping on Ebay, look for a turbo that has low carboning levels on the exducer side, as well check the housing colour. Reddish colour indicated high heat in the nodular cast iron base, while a natural cast iron appearance indicates stock fuelling. This however does not garantee the center section is in ok shape.
Buyer Beware.

I have bought several off of Ebay. The most pristine turbo i ever got I paid the grand sum of 50.00 for.

Yeah I wish my turbo had it's own RPM guage. I am sure it spins pretty fast with the Quad set on 70, 4000 LB on the bumper, OD lockout, 3300 RPM, up Georgetown hill and through the Eisonhower tunnel ( 11,000 feet). :eek: :eek: :eek:

If it makes you feel any better I passed every vehicle on the road.

Can you say 125,000 +++++++++

Compressor surge is some serious s**t. I haven't seen first hand the damage to our trucks but have on centrifugal compressors. Later! Frank

What is Juicegrips?

What is Juicegrips?
Sort of a true urban legend that goes like this:
Canadians are a different breed....rather than use conventional thinking for some things, such as the quest for more power, they use....well....whatever is handy....in this case, our hero (Got Juice?) used a vice-grip to block-off the wastegate hose, thus creating higher boost..(and, unknowingly created a need for more IHI turbo chargers on e-bay)
The good thing about this is he taught us what not to do...We also get a good laugh out of it ):h
Unfortuneately, he's got a different set-up now, so we are now waiting on his next reach-into-the-toolbox idea that will create problems for him and amusement for us.....
We're patiently waiting, buddy....

Sort of a true urban legend that goes like this:
Canadians are a different breed....rather than use conventional thinking for some things, such as the quest for more power, they use....well....whatever is handy....in this case, our hero (Got Juice?) used a vice-grip to block-off the wastegate hose, thus creating higher boost..(and, unknowingly created a need for more IHI turbo chargers on e-bay)
The good thing about this is he taught us what not to do...We also get a good laugh out of it ):h
Unfortuneately, he's got a different set-up now, so we are now waiting on his next reach-into-the-toolbox idea that will create problems for him and amusement for us.....
We're patiently waiting, buddy....
I think the grips were used on the actuator rod, thereby keeping excessive exh. back pressure from blowing open the waste gate. In effect he pretty well bypassed all aspects of having a wastegate and answered the question of why we have a wastegate very well. Also I do not know what the book say's the wastegate opens at 30 psi. I'm pretty sure it opens at around 23psi. Maybe it's not fully open until 30 psi?

If you have a service manual look at the diagnostic procedure for DTC P0234, overboost. It starts on page 6-2617 of my 2003 manual. Diagnostic step 6 says that the wastegate should begin to open near 30 psi and fully open at 45 psi, which led to my question, since the wastegate begins to open well past the maximum boost produced by a stock engine.

The manual also says that the fully-open actuator stroke is 2-tenths of an inch. This has got to be wrong, which made me think maybe the pressures are wrong, but when I tested mine with compressed air it didn't start opening until above 30 psi.

I think the grips were used on the actuator rod, thereby keeping excessive exh. back pressure from blowing open the waste gate. In effect he pretty well bypassed all aspects of having a wastegate and answered the question of why we have a wastegate very well. Also I do not know what the book say's the wastegate opens at 30 psi. I'm pretty sure it opens at around 23psi. Maybe it's not fully open until 30 psi?
Not on the actuator Rod... that is too low tech.


Juicegrips(TM) must be installed on the boost line!

I do offer a Certification course for 29.95.
Includes Shirt, Diploma and Handshake.

Does not cover the costs of consumables though (read: bring spare Turbo)):h

I don't know about this 30 psi stock thing. With my stock wastegate I get around 23psi max even with my TST comp box. By only changing the sense line and adding a "calibrated" leak that will not allow the wastegate to see the real boost, I can crank the boost beyond 32 psi. I stopped at 32 psi for alas I'm not independately wealthy and cannot afford extra turbos. Remove the "calibrated" leak and I'm back to around 23 psi. Now of course that's with my truck and maybe there is something wrong with it.

Don't have an answer about why we have a wastegate just an observation. My truck (sig) is bone stock. I actually plugged my boost tube for a short while. I saw a sustained 25psi while pulling a 7400lb trailer in 4th (TH engaged) turning 3000rpms. I have since put the boost tube back to original configuration. Coming back from Inks Lake State Park, I saw a max of 23 only for a split second after down shifting then it settled at 22psi while pulling some steep hills on 281 back to Hwy 46. This was with the same trailer after a camping trip. I'm sure we were closer to 8000lbs. I know I said the truck is stock and some are wondering, "Why does he have guages if it's stock?" A friend had an a-pillar setup that was to good to pass up. Seems to me the wastegate comes into play earlier than 30psi.

If you have a service manual look at the diagnostic procedure for DTC P0234, overboost. It starts on page 6-2617 of my 2003 manual. Diagnostic step 6 says that the wastegate should begin to open near 30 psi and fully open at 45 psi, which led to my question, since the wastegate begins to open well past the maximum boost produced by a stock engine.

The manual also says that the fully-open actuator stroke is 2-tenths of an inch. This has got to be wrong, which made me think maybe the pressures are wrong, but when I tested mine with compressed air it didn't start opening until above 30 psi.This thread really had me scratching the old noodle because you have air tested the gate actuator in accordance with the manual. But the last post turned on the old lightbulb! The air test on the actuator is done with the ENGINE OFF! When the engine is running, there is a positive exhaust pressure and flow in the turbo snail inlet and it provides additional opening force on the underside of the flapper of the wastegate! The wastegate opens upward against spring tension on the actuator which is overcome by the COMBINED action of turbo outlet pressure in the actuator diaphragm AND internal snail inlet plenum pressure on the suface area of the wastegate. Therefore, the wastgate is opening in the 20 psi range when both forces are combined!;)

Yes, the difference between lbs per square inch as per gauge
and lbs per sq inch absolute!

Sort of a true urban legend that goes like this:
Canadians are a different breed....rather than use conventional thinking for some things, such as the quest for more power, they use....well....whatever is handy....in this case, our hero (Got Juice?) used a vice-grip to block-off the wastegate hose, thus creating higher boost..(and, unknowingly created a need for more IHI turbo chargers on e-bay)
The good thing about this is he taught us what not to do...We also get a good laugh out of it ):h
Unfortuneately, he's got a different set-up now, so we are now waiting on his next reach-into-the-toolbox idea that will create problems for him and amusement for us.....
We're patiently waiting, buddy....

:rotflmao:
Too funny

Yes, the difference between lbs per square inch as per gauge
and lbs per sq inch absolute!
Didn't think about that, too. The Baro and Boost sensors both are rated in psia, aren't they?

Didn't think about that, too. The Baro and Boost sensors both are rated in psia, aren't they?Ah, the plot thickens. Problem is there is about 15 psi diff between psig and psia. Ever heard the joke where you ask the Norm type the difference between psi,psia,psig,and pepsi? It's really not obvious when you hear it a letter at a time and don't see it in print.

Ah, the plot thickens. Problem is there is about 15 psi diff between psig and psia. Ever heard the joke where you ask the Norm type the difference between psi,psia,psig,and pepsi? It's really not obvious when you hear it a letter at a time and don't see it in print.
Yes, The difference must be accounted for when cranking things up, like wastegates for example:o:

But it is never a mistake if you learn your lesson from the experience that failure can teach you.

Way back when (in the 550.5 hp thread) these issues were breifly touched upon.

It would be nice to expound turbocharger theory here, but there are several well written books on the subject... by people much more knowledgeable than myself.

Mind you, I will not blow another stock turbo, the settings on it in the compounded configuration make it not worth the tradeoff in drive pressure/ volume/ adiabatic efficiency to run it higher than 9 PSIG

So what good does replaceing stock wastegate with a big head? Is it going to help any, and what will it do for me?

So what good does replaceing stock wastegate with a big head? Is it going to help any, and what will it do for me?
It help to maintain a given level of boost over a longer period of time before the gate opens and dumps boost pressure.

It will help to lower your EGT's by about 50-100F depending on your modification level.

It is a fairly easy procedure to set it up correctly, myself and others have set it up, if you get one and need help it is only a phone call away.

The Banks Gate is a good mild BOMB. If you are set on running stock turbo only, I wouldn't hesitate to recommend it.

The Banks Gate is a good mild BOMB. If you are set on running stock turbo only, I wouldn't hesitate to recommend it.

What exactly do you mean?<!-- / message --><!-- sig -->

The Banks Gate is a good mild BOMB. If you are set on running stock turbo only, I wouldn't hesitate to recommend it.

What exactly do you mean?<!-- / message --><!-- sig -->
If you don't plan on running Twin Turbos, then by all means it is a worthwhile modification.

With the Twins installed, I have a different arrangement for the gate on my truck.

But i am not selling my Banks Gate.... it will go to my Brother instead!

BOMB=Better Off Modified Baby:ro)

GOT IT! I wasn't sure of the BOMB thing. What exactly will I gain with the big head? Better acceleration?

GOT IT! I wasn't sure of the BOMB thing. What exactly will I gain with the big head? Better acceleration?
You will maintain your set peak boost PSI for a longer period of time before the wategate opens and bypasses the exducer (exhaust side of the turbine) which limits boost.

For example, a stock wastegate usually opens at 23 PSIG even if it was set to open at 25.

The Banks gate by nature of its larger diaphragm area and higher tension spring will maintain 25 PSIG longer before opening to bypass.

you get to keep the 2 PSIG and the benefits of lower EGT's from it.

of course, you CAN get too much of a good thing and blow stuff up.

If running a large program I would qualify your mean operating altitude, and what kind of load you are towing before i would suggest a setting on the banks gate.

This thread really had me scratching the old noodle because you have air tested the gate actuator in accordance with the manual. But the last post turned on the old lightbulb! The air test on the actuator is done with the ENGINE OFF! When the engine is running, there is a positive exhaust pressure and flow in the turbo snail inlet and it provides additional opening force on the underside of the flapper of the wastegate! The wastegate opens upward against spring tension on the actuator which is overcome by the COMBINED action of turbo outlet pressure in the actuator diaphragm AND internal snail inlet plenum pressure on the suface area of the wastegate. Therefore, the wastgate is opening in the 20 psi range when both forces are combined!;) I think you've found the answer here, and now that I know the explanation, it seems obvious. This would also explain the seemingly excessive spring pressure that holds the wastegate closed when the engine is off. It's darn hard to open the wastegate by hand. It could also explain the service manual saying the stroke is only 2/10 of an inch when pressure testing at 45 psi. Looks like most of the opeing force is coming from the wastegate itself, with an assist from the actuator.

I wish the service manual would describe some of the turbocharger's workings, but it's treated as a magic mystery black box. Either everything checks out or you just replace the whole unit. Nothing in-between.

THANK YOU for solving the mystery.