GM-8 comparo notes

[patrick m.]

after a few weeks of runnin the GM-8, the verdict is in. This 6.5 wont make more low end power. Even with 10psi at ~1500-1700 rpm.
The only advantage is slight, at that range. the dissadvantage is big. Major power loss above 2400 rpm when compared to the others i have run (exceptin the 4 of course). I even experimented with different methods of operating the wastegate. no amount of boost makes more power over 2500 rpm than the other Garretts i have. Pick your poison folks a tad more power down low, or plenty more power up top.

So im done....... the the TC...what ever Garrett will go back on, i will keep one of the others for a spare. This 6.5l will stay the way it is untill the day it dies. at 206k and counting, decission time must be nearing.

[DA BIG ONE]

Guess, we are looking at turbine housing back pressure so it takes a dump at those rpms, or?

[patrick m.]

its like JK said some time ago, " the small turbo will outrun the big one on take-off, but the big one comes back fast".
all of the larger turbos i have used make more power at less boost than the two GM units. (after 2000rpm that is).

[Dvldog 8793]

Howdy
Patrick-
What is drivability like at highway cruising RPMs of 185-2000 like with the big turbos? I've always thought my GM 8 seemed pretty good at those speeds/rpms. BUT when I pull a big load it seems to lack a little when the RPMs get up there. Almost like running into a wall.
L8r
Conley

[patrick m.]

that is the rpm range where the larger turbos start to shine!
cruising at 65 and up, in 4th tc locked, power is MUCH better.
With the last Garrett, i can pull away from a 2000 model 1500 standard cab/ short bed with a 5.3L gas at 70mph. I dont stand a chance with the GM-8

[jspringator]

What max boost are you running with that Garrett?

[grape]

Originally posted by Patrick m.:

all of the larger turbos i have used make more power at less boost than the two GM units. (after 2000rpm that is). That just can't be true, we need RJ to the rescue.... smile.gif Please save our demented minds and set us straight.

[GMC Hauler]

C'mon now, Let Ron try a different turbo. You can't bust on him about the turbo and not expect him to give you crap about the crossover/water flow issue. If it doesn't work, we've lost nothing, but if it works, we all win. tongue.gif

[grape]

blind leading the blind

[patrick m.]

James, max boost on the two Garretts is 15psi. The non-wastegated one, and the onw with. I havent found an acuator for the latter one that will hold past 15 psi (originally meant to run about 10psi)


Grape: my results are from the turbos i have used, on my truck, not knowing how to calculate flow rates, and the effects of compressor wheel pitch, stall speeds .....etc I am unable to "pick" a better suited turbo. But i know how to interperet my but dyno ;)

[john8662]

Originally posted by grape:
blind leading the blind Another one of Grape's famous one line statements!

I know this will go unanswered, but what would YOU recommend for a replacement turbo for the SIX POINT FIVE engine? Of course, this opinion/advice will have to take into account:

Mountability to Stock exhaust manifold, intake, and the exhaust downpipe.

Oh, I almost forgot, we all keep hearing about the some magic 6.5 engine you're assembling, but never any pics or evidence to back it, but some RED already assembled 6.5 engine sitting on an engine stand for years now...

[rjschoolcraft]

Originally posted by GMC Hauler:
C'mon now, Let Ron try a different turbo. You can't bust on him about the turbo and not expect him to give you crap about the crossover/water flow issue. If it doesn't work, we've lost nothing, but if it works, we all win. tongue.gif
Originally posted by john8662:
</font><blockquote>quote:</font><hr />Originally posted by grape:
blind leading the blind Another one of Grape's famous one line statements!

I know this will go unanswered, but what would YOU recommend for a replacement turbo for the SIX POINT FIVE engine? Of course, this opinion/advice will have to take into account:

Mountability to Stock exhaust manifold, intake, and the exhaust downpipe.

Oh, I almost forgot, we all keep hearing about the some magic 6.5 engine you're assembling, but never any pics or evidence to back it, but some RED already assembled 6.5 engine sitting on an engine stand for years now... </font>[/QUOTE]Thanks, both of you. However, let him be. He's not hurting me any and I'm flattered to be considered his best friend. I had no idea that I mattered that much to him. ;)

[grape]

1 person out of 18,000 regestered members in a 10 year time span questioned a vendor who had printed matrial that showed an engine making 100 hp at 1000 rpm and proved somebody was lying. Unless the said engine was making 530 ft lbs of torque at 1000 rpm.................

The rest of you 17,999 guys keep up the good work, and be good customers. I've got some magic beans for sale to put in your fuel tank if you guys are interested. smile.gif

[Kennedy]

Originally posted by grape:
1 person out of 18,000 regestered members in a 10 year time span questioned a vendor who had printed matrial that showed an engine making 100 hp at 1000 rpm and proved somebody was lying. Unless the said engine was making 530 ft lbs of torque at 1000 rpm.................

The rest of you 17,999 guys keep up the good work, and be good customers. I've got some magic beans for sale to put in your fuel tank if you guys are interested. smile.gif I must have been asleep when that claim was made. Please enlighten us...

[JoeyD]

The great OZ has spoken, what wishes will grape award to someone who comes up with a question he acually answers

[grape]

Originally posted by kennedy:
</font><blockquote>quote:</font><hr />Originally posted by grape:
1 person out of 18,000 regestered members in a 10 year time span questioned a vendor who had printed matrial that showed an engine making 100 hp at 1000 rpm and proved somebody was lying. Unless the said engine was making 530 ft lbs of torque at 1000 rpm.................

The rest of you 17,999 guys keep up the good work, and be good customers. I've got some magic beans for sale to put in your fuel tank if you guys are interested. smile.gif I must have been asleep when that claim was made. Please enlighten us... </font>[/QUOTE]check peninsular's dyno sheets.
http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=006455

[grape]

Originally posted by Joey D:
The great OZ has spoken, what wishes will grape award to someone who comes up with a question he acually answers if you ask me how to spell "actually", I might tell you. :rolleyes:

[JoeyD]

Doubtfull. You would just dance around the fire making claims then answer nothing. Thanks though

[patrick m.]

Grape does what he does, RJ does what he does. and i do what i do, who gives a flip?

its all opinion...... i'll wait and see what RJ comes up with for a solution to the turbo issue.

as far as spelling, this is liesure, not an english class. If it where, i would suggest Grape not start a sentence with a preposition (if you are goimg to call someone else on thier spelling). ;)

[hayesash]

Aoccdrnig to a rscheearch at an Elingh uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod,the olny iprmoetnt tihng is taht frist and lsat ltteer is at the rghit pclae. The rsetcan be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae we do not raed ervey lteter by itself but the wrod as a wlohe.

Cheers

[rjschoolcraft]

:D

[nvmtnlion]

LMAO!

[DA BIG ONE]

Ok, I run the GM-8 & been tinkering with boost levels and can't run the suggested 13/14 +- boost because egt's climb. However, I can run higher boost w/o egt climbing but if I keep it down for more than 6 or 7 seconds the aircharge IAT starts to get superheated shortly thereafter (crappy IC).

Anyone of you even know what cfm the GM-8 flows at say 15psi, 75%VE, and 3,000rpms?

So, if I'm correct, I need more air flow "cfm" instead of higher boost levels to keep the egt's and aircharge in check, then what choice do I have over the GM-8?

Flow charts I find on net for turbos seem to be only for gas motors that rev 6k+ rpms. 400cid GM TD diesel looks to need lots of cfm over what the GM-8 can deliver at lower operating rpms.

[patrick m.]

the last one i got is for a mid 90's powerstroke, and i made wastegate housing to work with our exhaust. I also had to get some solicone hose adapters for the compressor end, as the inlet and outlet are diferent size from the GM series.

I bet RJ is nearing a conclusion for this dilema

[DA BIG ONE]

Originally posted by Patrick m.:
the last one i got is for a mid 90's powerstroke, and i made wastegate housing to work with our exhaust. I also had to get some solicone hose adapters for the compressor end, as the inlet and outlet are diferent size from the GM series.

I bet RJ is nearing a conclusion for this dilema I just looked a friends 2000 7.3 powerstroke the turbo compressor is at least twice the size of the GM-8.

How come there are no specs to be had on these GM-8's?

[jdmetcalf57]

Have any of you guys been monitoring back pressure also? I have on my stock turbo. I am most interested in fuel economy. The way I run my truck at 2000 rpm and about 40% throttle (according to my scangage) my back pressure runs about 8-10 psi while my boost is about 5-6 psi. Theoretically the lower the back pressure relatively to the boost the more efficient the total engine.

[Barry Nave]

jdmetcalf57

Where did you tap to get back PSI?

[jdmetcalf57]

In the crossover pipe.
You have to add a small chamber and a reasonably small orifice between the chamber and the cross over. This snubs the pulsations from the cylinder exhaust so the gage will last. I have had mine on now for over a year. At first my orifice was too small and it would plug up with soot, but i kept making it bigger untill it provided the snubbing but didn't plug.

[jdmetcalf57]

I used about 3 feet of coper tubing set up so it could take the flex of the motor moving then connected to the orifice then the chamber then the plastic tube leading to the gage. I used a hex key 1/8 npt pipe plug in the middle of a fully threaded nipple and drilled a hole in it for the orifice.

[Barry Nave]

my orifice
Being?

[Barry Nave]

small chamber
I take it than this was done with pipe removed.
Just thinking in my head how you made this work.
I would like to see how this work. I take it that the EX. system does not come into play and it deals with just the back psi feading into the turbo with the amount of boost being added. Wounder,just thinking if after the turbo if theres any back psi. As in my system it a stright through system.

[G. Gearloose]

Alternatively, a liquid-filled guage would similarly smooth out the display.

[Barry Nave]

Than I could just tap into the crossover with 1/4 tubing or should it be smaller?

[DA BIG ONE]

The turbine housing outlet can be ported to reduce backpressure forward of it, both exhaust manifolds and crossover pipe.

I'm thinking the crossover pipe any diameter having to handle only 4 cylinders (200 ci) at 3,000 rpms or less would not be a real issue. Even if it "x-over pipe" is changed to larger diameter the exhaust still has to get past the turbine outlet "the bottle neck", and back pressure would measure the same w/different diam x-over if turbine housing is not changed, or ported.

[DA BIG ONE]

I'm also wondering how different the backpressure readings would be at x-over pipe, and after turbo?

I see most of you herein this forum are leaps and bounds ahead of me on this diesel turbo issue, that's good because others and I learn.

Hopefully, a good turbo upgrade can be found that can solve some of my issues.

[jdmetcalf57]

I have already worked on the exhaust to get low back pressure from the turbo out. To check it I disconnected the wastegate vacuum and checked the backpressure at similar conditions. It was well under 1/2 psi (barely readable on the gage) which is insignificant compared to the 10 psi it runs under my normal operating conditions.

A liquid filled gage may take care of the pressure pulsations but they are quite large and I really doubt that the liquid filled gage would not vibrate.

[toyboxrv]

If a separate waste gate could be plumbed in between the crossover and a 4" exhaust that would reduce the bottle neck from trying to push all the exhaust through the 3" outlet from the turbo. It might be possible to then get higher boost without the much higher EGTs from the stock setup. With a GM8 on my 94 and a small IC I can get a steady 14.5 without high EGTs. Above 2500 it does drop to around 13.

[DA BIG ONE]

Originally posted by toyboxrv:
If a separate waste gate could be plumbed in between the crossover and a 4" exhaust that would reduce the bottle neck from trying to push all the exhaust through the 3" outlet from the turbo. It might be possible to then get higher boost without the much higher EGTs from the stock setup. With a GM8 on my 94 and a small IC I can get a steady 14.5 without high EGTs. Above 2500 it does drop to around 13. A great idea to bypass the bottle neck, discontinue using the stock turbo gate (block, or wire it shut) then plumb in another like you suggest. This idea of yours would work, I'm going to look into this for my rig.

[ 01-16-2006, 02:55 AM: Message edited by: DA BIG ONE ]

[dieseldummy]

The limiting factor is still the inefficient stock compressor wheel. It just can't move enough air to support big power efficiently.

[DA BIG ONE]

Originally posted by dieseldummy:
The limiting factor is still the inefficient stock compressor wheel. It just can't move enough air to support big power efficiently. Think the bypass would work to limit egt's, or?

[dieseldummy]

I don't beleive that with the stock compressor it would do anything that the stock wastegate can't do. If you utilized a bigger compressor on the stock GM turbo then yes I do beleive the secondary wastegate would be benificial. To make very much boost with the stock turbo the wastegate has to be held shut most all of the time. If it opens or a secondary unit was added and opens then it will dump boost and cause EGT's to skyrocket. Remember, the only way to drop backpressure and still maintain high boost is to create more efficient compressor and turbine wheels.

[toyboxrv]

You may have a valid point about the GM-8 turbo. If the small exhaust exit from the turbo is too restrictive, then running the waste gate closed to put all the exhaust through the turbine will limit speed of the turbine. Dumping some of the exhaust elsewhere may allow an increase in exhaust velocity that lets the compressor spin a little faster. Cutting back on backpressure will possibly result in less boost with the same airflow. Anyone who's been around supercharged gas engines knows how spinning the blower faster can give higher boost pressures with an actual loss of power since the crank is trying to drive the blower against the resistance of poor head flow or exhaust back pressure. Even if bypassing the bottleneck of the 3" exhaust outlet from the turbo doesn't create more boost, it may create more air