i need some Pepto-bismol

[patrick m.]

since this great thread is now gone, maybe we can bring it back to life.
GMCTD, and Kennedy, would you guys mind comparing the GM8 turbo and the GM4 to the non-wastegated turbo upgrade.
what the GM8 has to offer over the GM4,
and what the non-wastegated has to offer over both

My GM4 needs to take up space on my shelf, and i need help in which replacement to get :D

[Kennedy]

If you want boost from the bottom, that peters out up top, thenthe GM4-8 series.

If you can wait for the boost to build from say 1800-2k on up, then the larger non wastegated turbo.

If we had 2 equally prepped trucks with the only difference being the turbos, The one with the GM4-8 would get up and leave the non wastegated one, BUT the non wastegated one would catch and pass it never looking back...

[gmctd]

As John states, you do have a choice.
Brittanic's threads in the 6.2 forum on the Mitsubishi TE06H wastegated turbo for the Banks Ford kit are also excellent info.
Would help if a comparo could be done on the GM-8 vs the TE06h for off-the-line torque and sustained higher rpm power.

I'm in the process of converting the '95 electronic injection in my truck to 4911 mechanical - a simple task if not for removing the electronic harness, PCM, and all the assorted jew-jaws and bric-a-bracs involved.

After adding a charge air cooler, the turbo 'problem' is next. I need and like the instant torque response of the GM-8,
but freeing up the exhaust thru the turbo lowers EGT and coolant temps, and lowers required boost.

Dr. Lee's 6.5 NA engine and Dogdiesel's new non-wastegated turbo are excellent examples power gains thru low-restriction intake and exhaust flow.

jd

[CareyWeber]

Are there any other turbine (exhaust) housing avaliable for the GM 4-8 turbos like there are for the Garret T-3 turbos?

Has anyone tried porting the exhaust side of the GM 8 turbo?

What about getting the turbine housing extruded (SP) honed? IIRC that is where they push a paste kinda like valve lapping compound through them to open them up and smooth the passages.

Carey

[grape]

How about an external wastegate.... www.turbonetics.com (http://www.turbonetics.com)

[patrick m.]

so with the non-wastegated turbo, spool-up would be fast while running down the highway, but one may have to wait a few seconds for boost from a stop.
i dont need to boil the tires (although i sometimes do :D ), i need power at 30 mph and up to say 75.

JK, this turbo you speak of, is it a direct bolt on replacement, and i dont need my soon-to-fail vac pump?

[gmctd]

IHI (Isuzu) makes many wastegated turbos, as does MHI (Mistubishi). Check out their sites for info.

Extrude honing and turbine trimming are offered by several companies, but result in only incremental improvement.

The 6.5 flows about 400 cubic feet per minute at 3500rpm and atmospheric 15psi, normally aspirated.
Turbo charge it to 15psi, and the flow rate (roughly estimated) doubles. I know, I know - my math is atrocious, but increase the input, increase the output.

More than incremental exhaust flow improvement is required.

External wastegate - that has been done, but not with this street engine in a single turbo configuration.

jd

[rjschoolcraft]

With all the talk of exhaust back pressure and lack of data, how many of you would be interested in being able to measure back pressure? I have been toying with an idea and means of doing just that (safely, with a transducer) and have begun discussions with an aerospace supplier. At present, cost is a HUGE issue, but if there were enough interest, cost could come down.

The real issue with back pressure is ensuring that EBP does not increase above boost pressure causing poor scavenging of the cylinder. This type of instrumentation could answer a lot of questions.

[Kennedy]

Originally posted by ronniejoe:
With all the talk of exhaust back pressure and lack of data, how many of you would be interested in being able to measure back pressure? I have been toying with an idea and means of doing just that (safely, with a transducer) and have begun discussions with an aerospace supplier. At present, cost is a HUGE issue, but if there were enough interest, cost could come down.

The real issue with back pressure is ensuring that EBP does not increase above boost pressure causing poor scavenging of the cylinder. This type of instrumentation could answer a lot of questions. I guess I shoulda reached into my console and shown you the gauge I have plumbed!

I have a Hewitt 50 psi twin tube unit in my 2002. Both needles are on same axis etc...

[patrick m.]

gmctd, i checked out both websites, and discovered IHI, and Borg-Warner used to be a partnership in Shelbyville IL.
The GM-4 on my rig has a label that displays "Borg-Warner", and "made in the USA Shelbyville IL". But, none of the model numbers match.
The website also gives great information about about size, compression ratio, turbine rpm, airflow. These specifications mean a great deal to someone with education in this area, as for me, my education about turbochargers is this forum and TDP. (aside from my buddy's Buick GN. But that is an entirely different beast).
I just need enough information to make a decision i will be happy with.
Im really leaning toward JK's turbo.

Question for JK, will your chip add enough fuel with your turbo upgrade to get full benefit of the added boost up top?
right now, boost drops at WOT above 2500rpm (to about 10psi) with NO smoke and max EGT 900F
If you dont feel comfortable "selling" here, i understand and will call you next week. ;)

[rjschoolcraft]

Plumbing 1300 - 1700F air into the cab is a bit of a fire hazard me thinks. I remember seeing 1700F+ on your Duramax after one of those runs.

[gmctd]

Would only experience those temps at the gage if tubing were open-ended at gage, allowing flow - main worry is carbon monoxide fumes into the cabin from minor leaks.

Here, TexDOT frowns on plumbing any exhaust directly into passenger compartment, even via 1\8" stainless tubing and Swagelock fittings.
Had to remove mine to pass state inspection.

Tanker has his BD exhaust brake egp monitored via mech pressure gage, IIRC, but his Sub is probably not subject to spot Highway Patrol inspection, as is my 3500 drw.

jd

[rjschoolcraft]

Correct on the temp at the gage...however, if a leak were to develop (not a remote possibility), extreme fire danger would result because a positive flow of exhaust gas would allow the temperature of that gas flowing through the leak to approach the temps in the manifold...1300-1700F. Most materials in the cab are easily ignited when exposed to that level of temperature.

[rjschoolcraft]

So...

Anyone interested in being able to measure exhaust back pressure safely without concern for carbon monoxide poisoning or fire hazard?

[Kennedy]

Originally posted by Patrick m.:

Question for JK, will your chip add enough fuel with your turbo upgrade to get full benefit of the added boost up top?
right now, boost drops at WOT above 2500rpm (to about 10psi) with NO smoke and max EGT 900F
If you dont feel comfortable "selling" here, i understand and will call you next week. ;) I can put 76-80mm3 fuel rate in no problem. I can allow about 14 or so psi to be seen by the boost sensor at sea level. Haven't tested the threshold to see if it will set a code, but you MAY need to do some boost fooling to keep from coding...

[More Power]

Bill Heath says he has done quite a bit of turbo investigation. Says he has compressor maps and turbine backpressure curves for these GM turbos.

His data is what we base max desired boost pressures on.... 10 psi non-intercooled and 12-14 psi intercooled.

He's also investigated the relationship between boost pressure and IAT temperature. Some of that info will appear here in the DP in a future article on water injection.

MP

[CareyWeber]

What is the cause of the excess backpressure that DieselDog talks about?

Is it that the exhaust side of the turbo is to small (might be because the 6.5 turbo spools up fast)?

Another thought is the outlet of the exhaust side of the turbo causing the restriction?

Carey