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What makes the factory IHI turbo so "bad"?

G

great white

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Looking for turbine doc or someone similar to chime in here:

So, the ATT is apparently the choice of upgrade/replacement.

I've read a bit here and there about the stock GM-X turbo's and vague references to what's the problem with them.

The most "popular" issue seems to be around 10-15 PSI they become a restriction in the exhaust flow.

Why is this?

Wastegate design?

Turbine design?

housing design?

Sizing?

Inquiring minds want to know....

Is it a result of the "quick spool" characteristics of the IHI design?

Personally, it'll be a long time before I go over stock HP or turbo pressures. Probably never enough to warrant a replacement for the sake of replacement, but I may dial it up a couple PSI from time to time.

I spend most of my time in "off idle" situations, so low end "snap" is more of a concern for me than winding the P out of it....

Here's another question:

I've seen it written here the -8 turbo is "better" than the -4, etc. What makes it "better"?
 
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great white said:
Looking for turbine doc or someone similar to chime in here:

So, the ATT is apparently the choice of upgrade/replacement.


The most "popular" issue seems to be around 10-15 PSI they become a restriction in the exhaust flow.

My GM-8 is a great turbo. I can get well over 23 pounds of boost with it but I don't. I like my engine the way it is. BUT the GM- 8 is coming off and my ATT is going back on in the few days. With it I can get more air charge in the system but have less boost pressure.
Click to expand...
 
Its quite simple. Turbine is much larger on ATT. It is more efficient at 10-20psi boost, meaning it requires less engine backpressure for the amount of boost pressure. This is explained in a couple really long threads.

There is nothing wrong with the factory turbos, just that if you want 15+ psi boost becaue you need it, its not efficient and a turbo is PARASITIC, it takes engine power to build boost. In your question, the answer for this would be sizing. It has a small turbine and housing to put as much drive pressure to the turbine and spool it quickly.

I can get 20psi out of my GM4 easy, but it drives IATs really high and engine backpressure, so I'm losing power with its inefficiencies. An intercooler or water injection could counter the IATs, but you cant change the turbo's efficiency so it will still be taking more engine power away to make boost.

The ATT can essentially help you tow, or it can enable you to tow more.
 
Buddy's on it ..

The Law of Diminishing Returns affects all turbos, really ... the higher the output IAT, the less ovygen present (density decreases). For turbos that are inefficient (like the GMx), the parasitic loss is compounded by the higher IATs.

You can get lots of boost pressure out of a GMx, but at the expense of really high backpressure and really high IATs ... small, incremental improvements in design (mostly a shift in how the elbow was cast) made it possible for the GM8 to be more efficient than the GM4, but the basic design inefficiencies are still there.

More efficient turbos can maintain higher pressures/airflows, along with significantly more dense air at the same backpressures.

That there is where the ATT really shines. Sometimes, bigger is better. There are trade-offs with that, too - but it is a better compromise for a working (towing) 6.5TD... the cool part is, those same efficiencies also lead to better mileage and general performance when not towing, too!
 
Here's my comparison.

'95 Suburban 2500 4x4, GM-4 with vac pump, Heath cooling upgrades, no ECM flash, crossover, downpipe, no kitty, otherwise essentially stock.

'99 Suburban 2500 4x4 w/ ATT, Heath Flash, crossover, downpipe, punched out kitty.

Acceleration from a dead stop, the '99 just blows the '95 away, not even close. Conclusion, you lose nothing on the low end with the bigger ATT.

Higher speeds/rpms, the '95 hits the wall like it has a potato stuffed in the exhaust. The '99 keeps on charging.

Towing, well just add weight to the '95 with the potato in the exhaust and you can imagine. The '99 just keeps accelerating and pulling like a fiend AND it stays cooler.

Anyone worried thinking they're giving up the low end acceleration or quickness off the line is simply kidding themselves.

Now the increased mileage claims......I know, LET IT GO!):h
 
Big T said:
Here's my comparison.

'95 Suburban 2500 4x4, GM-4 with vac pump, Heath cooling upgrades, no ECM flash, crossover, downpipe, no kitty, otherwise essentially stock.

'99 Suburban 2500 4x4 w/ ATT, Heath Flash, crossover, downpipe, punched out kitty.

Acceleration from a dead stop, the '99 just blows the '95 away, not even close. Conclusion, you lose nothing on the low end with the bigger ATT.

Higher speeds/rpms, the '95 hits the wall like it has a potato stuffed in the exhaust. The '99 keeps on charging.

Towing, well just add weight to the '95 with the potato in the exhaust and you can imagine. The '99 just keeps accelerating and pulling like a fiend AND it stays cooler.

Anyone worried thinking they're giving up the low end acceleration or quickness off the line is simply kidding themselves.

Now the increased mileage claims......I know, LET IT GO!):h
Click to expand...

Thanks for the input, but I wasn't asking about the ATT.

I was wondering what the design limitations are on the stock IHI unit.

The more i dig into "turbo studies" (been a long tme since I dabbled in this stuff), the more I'm coming to realize it's not so much about PSI as it is CFM.

Same old rules, just a different game.....):h
 
I'm serious, T... you really need to take all kinds of measurements, timings, real-world tests.

Then take a weekend and sway turbos. JUST the turbos.

Then do all the same measurements and tests again.

Until you do that, you got nothin', pal... it's just like the guys claiming one chip is better than another ... stuff like that is SO truck-specific it ain't funny.

You're about the only guy around here that can do that swap - and you're the only guy whose data you will believe. Give it a shot... maybe you can make a day of it and some of the guys can give you a hand (if they live sort of nearby)... lots of people would like to see this one explored, rather than just debated.
 
JiFaire said:
I'm serious, T... you really need to take all kinds of measurements, timings, real-world tests.

Then take a weekend and sway turbos. JUST the turbos.

Then do all the same measurements and tests again.

Until you do that, you got nothin', pal... it's just like the guys claiming one chip is better than another ... stuff like that is SO truck-specific it ain't funny.

You're about the only guy around here that can do that swap - and you're the only guy whose data you will believe. Give it a shot... maybe you can make a day of it and some of the guys can give you a hand (if they live sort of nearby)... lots of people would like to see this one explored, rather than just debated.
Click to expand...

Jif, the only problem is that I'd have run at least one controlled tank of fuel in each configuration. That's like 640 miles on the highway. I'd have to pick out some fly fishing locations to justify it.):h Who knows, it might happen after we get an ATT for the '95, keeping the GM-4 as a back-up in case the '99 fails future smog checks.
 
great white said:
Thanks for the input, but I wasn't asking about the ATT.

I was wondering what the design limitations are on the stock IHI unit.

The more i dig into "turbo studies" (been a long tme since I dabbled in this stuff), the more I'm coming to realize it's not so much about PSI as it is CFM.

Same old rules, just a different game.....):h
Click to expand...

I gave you real world comparisions to highlight the inefficiency of the GM-4: exhaust back pressure. Makes it run like there's a potato jammed in the exhaust.
 
just posting random stuff so I can find, review or delete it later:

Turbine wheel Exducer is @2.12", the major is @2.41

So, that's real close to the size of a stage II T3 wheel. Not the stage III like I originally thought.
Click to expand...

http://www.ihi-turbo.com/turbo_RHE-RHF.htm

Both sides AR is .70 with a 3" inlet and 2.5" outlet. Apparently it flows at 625cfm max flow. Undivided T3 Housing. 52 trim etc...

I've also heard the wheel is very similar to the GT30 wheel.
Click to expand...

the turbos came on the 6.5 liter GM diesels...
they're roughly equivalent to a .50-E compressor...
the turbine wheel is between a stage II and stage III
turbine wheel in diameter, but it's got a tighter
pitch for quicker spool... BUT, unlike the garrett
integral wastegate orifice, these have a LARGE
wastegate hole and puck to prevent boost creep and
choking the engine off...
Click to expand...

My IHI/Borg Warner RHC6 GM-1 has a 51mm inducer and a 70mm exducer on the compressor side. I was told the exhaust wheel was similar in size to a gt30 wheel. Both housings are .70a/r with the compressor being 3"inlet, 2.5" outlet and the turbine housing is undivided t3. I believe that all the gm series turbos are alike.
Click to expand...

Borgwarner/ISHI RHC6 turbocharger.

Very high quality turbo featuring T3 compatible oil drain and turbine flange, polished Compressor housing, bigger shaft than equivalent garrett turbos, double compressor seal and sturdy internals such as bolted-Down 360deg. Thrust plate and an integrated backplate.

Compressor wheel: 50.3 / 70 mm 52 trim
compressor housing: 0.7 a/r

center section: oil cooled journal bearings

Turbine wheel: 64.6 /62.1 mm 77 trim
Turbine housing: 0.7 a/r
Click to expand...

http://www.turbointernational.com/images/catalog-pdf/Catalog-IHI.pdf
 
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Big T said:
I gave you real world comparisions to highlight the inefficiency of the GM-4: exhaust back pressure. Makes it run like there's a potato jammed in the exhaust.
Click to expand...

Your power comparisons are unfortunately worth less than 2 cents, because you are using two different trucks and one of them has a reflashed PCM and one doesnt. I could send you a chip for that there 95 with the GM4 and youd be eating that potato

Please dont compare the two on power.
 
And GW CFM through the engine is a fixed by displacement and RPM. The CFM through the turbo is exactly the same for any turbo at the same pressure. The only CFM differentiation is with temperature. The lower the temperature on the IATs the more dense the air is, so the more air you pulled from the outside and crammed on the inside. The hotter the air in the intake the less of the outer air you can cram into the same pressure. The only way a turbo flows more air at the same pressure as any other turbo is if it transfers less heat from the turbine to the compressor. The larger turbines do this because they are more efficient at higher boost and build less heat in general. You also have gains because you use less drive energy into the turbine, which means less work for the piston to push the exhaust out of the cylinder.
 
great white said:
Guys, please start another thread about fishing and do it there please....
Click to expand...

The issues/deficiencies with GM-X Turbo have been beaten to death here on these here boards. Please do a search next time.:nono:

Now back to fishing......):h
 
One word.

"Restriction."

One photo.

Have a great weekend everyone!

Lots of cool goodies coming your way!
 

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