1998chev65td
New Member
Hey sorry no I do not we do live tuning at our shop on our Dyno sorry
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98 Chevy 6.5 what new turbo setup should I use
- Thread starter 1998chev65td
- Start date
Hey sorry no I do not we do live tuning at our shop on our Dyno sorry
The GM turbo was setup for low RPM. That is spool up when the starter is spinning the engine. The downside to the undersized turbo is it's an asthma attack over 2200 RPM.
Many do not understand that a turbo needs a specific RPM range. Below the RPM range and a big turbo will not light off period. Over a RPM range and a small turbo with the WG wide open is still a restriction: heating up the engine and costing you MPG due to extreme backpressure.
Backpressure differences can get you the same HP and TQ on the dyno but with different boost numbers. For example a ATT and HX40II gave me nearly the same numbers, but, the HX40II boost was ~10 PSI higher at 24 PSI.
IMO neither turbo is spooled up enough to matter under 2000 RPM. This is ok for light load cruise when you don't need the power robbing 6 PSI boost the GMx turbo gives you from 2500 RPM alone with the fuel off. Leaving the light without boost is what most dislike about the bigger turbo's. Other than live with it and learning your power band is over 2000 RPM where the big turbo's light off and pull like a freight train to redline there be a couple other solutions.
A BD Spool valve is one solution. Takes 2psi of boost at 2000 RPM and makes it 10 PSI of boost.
A Yank High Stall converter is another solution that keeps the engine in the spoolable RPM range of the turbo. Romp throttle in reverse with the front wheels hung up on a curb. RPM flairs up over 2000, ATT turbo lights off. This is followed by the rear wheels coming loose and smoking. Real fun with a loaded trailer holding the rear wheels down esp. when it wants to step sideways.
Then there is @n8in8or and the no stone left unturned build where a turbo is part of a complete build from porting to better manifolds.
With the offroading a GMx turbo is fine. The towing you do makes a better turbo worth it. IMO you should Yank stall a better turbo to get both towing power and off road performance. Unless you are going with an all out build or matching the wheels of a turbo: something I haven't yet attempted.
Many do not understand that a turbo needs a specific RPM range. Below the RPM range and a big turbo will not light off period. Over a RPM range and a small turbo with the WG wide open is still a restriction: heating up the engine and costing you MPG due to extreme backpressure.
Backpressure differences can get you the same HP and TQ on the dyno but with different boost numbers. For example a ATT and HX40II gave me nearly the same numbers, but, the HX40II boost was ~10 PSI higher at 24 PSI.
IMO neither turbo is spooled up enough to matter under 2000 RPM. This is ok for light load cruise when you don't need the power robbing 6 PSI boost the GMx turbo gives you from 2500 RPM alone with the fuel off. Leaving the light without boost is what most dislike about the bigger turbo's. Other than live with it and learning your power band is over 2000 RPM where the big turbo's light off and pull like a freight train to redline there be a couple other solutions.
A BD Spool valve is one solution. Takes 2psi of boost at 2000 RPM and makes it 10 PSI of boost.
A Yank High Stall converter is another solution that keeps the engine in the spoolable RPM range of the turbo. Romp throttle in reverse with the front wheels hung up on a curb. RPM flairs up over 2000, ATT turbo lights off. This is followed by the rear wheels coming loose and smoking. Real fun with a loaded trailer holding the rear wheels down esp. when it wants to step sideways.
Then there is @n8in8or and the no stone left unturned build where a turbo is part of a complete build from porting to better manifolds.
With the offroading a GMx turbo is fine. The towing you do makes a better turbo worth it. IMO you should Yank stall a better turbo to get both towing power and off road performance. Unless you are going with an all out build or matching the wheels of a turbo: something I haven't yet attempted.
Last edited:
Will L.
Well-Known Member
Call Leroy about a tune. He sells tunes by Kojo- mega respected tuner for the 6.5 world. I have never heard of anyone unhappy with his tunes.
GM Guy
Manual Trans. 2WD Enthusiast
I am curious as to the condition of your turbo? is the shaft play getting bad, or what was the failure symptom?
1998chev65td
New Member
Shaft snapped right beside turbine wheel no clue why looking into it but won't be fixable unless you just get all new internals. But thank you War Wagon I've actually been looking at the high stall converter il probably end up buying it as I have lockers front and rear that stall will help lots with that especially with my 35s on it
ak diesel driver
6.5 driver
Wow talk about leaving out the details of your truck. That'll make a difference lol
1998chev65td
New Member
Lockers don't make a difference for a turbo ? tires do but don't worry about that il have that part figured out Unless you can manage to find turbo operated lockers
Will L.
Well-Known Member
Haha, no I think he means the bigger tire size.
1998chev65td
New Member
Ya I know I said tires to but the weight of my new tires and rims are lighter then stock wheels and tires so there is no worries I worked at a tire shop for 6 years when I was in school
Will L.
Well-Known Member
Your tires are 6" taller than stock. That makes a decent difference in gearing and how the turbo spools up by the load implied and the rpm down the hiway.
Then planning on going to a higher stall tc on top of it.
That has a bearing on a turbo spooling and where it lives in the rpm band.
Then planning on going to a higher stall tc on top of it.
That has a bearing on a turbo spooling and where it lives in the rpm band.
1998chev65td
New Member
Well of course it would don't worry about gearing I didint ask for that
Husker6.5
135' diagonal 16:9HD, 25KW sound!
That’s a pretty damned arrogant comment coming from somebody who is asking for advice. You're damn right that things like your tire size, gearing, transmission and GVW are important information to know right off the bat when trying to fit a turbo for an intended application/result.
I couldn't care less if you have six years experience as a wrench monkey in a tire shop, it obviously hasn't made you an expert on the 6.2/6.5 platform nor taught you any manners. There are people on here trying to help you with over 30 years experience on the 6.2/6.5 platform, hell, Will has done things never thought possible with a drag racing 6.5 and experimental fuels, and you come in here with a shit load of an attitude? That takes either a set of brass ones or a lack of brains, and I vote for the latter.
There is a reason why it is requested that you either fill in your profile with, or state from the beginning in your question, how your vehicle is equiped and any modifications made so that we can address your question without having to make guesses or ask redundant questions that waste time and space.
Now, maybe you should eat a slice of humble pie and try again, this time first telling us your year, model, transmission, body configuration (CCLB, RCSB, ECLB, etc) tire size, gearing and any mods already done (4" exhaust, intake, FTB, etc) to it and what your intended use/results you seek. We all are here to share our knowledge and expertise with these beasties, but leaving attitudes at the door is one of our few rules on this forum.
JayTheCPA
Well-Known Member
Easy now . . .
The OP had a targeted question. The down side-of a targeted question is that the rest of us can only respond based on the information at hand. If the OP wants to limit the amount of details in the discussion, that is the OP's right. Naturally, we are free to offer a more holistic answer and prod for more detail, but again, if the OP wants to limit the boundary, we need to respect that.
Toward the discussion at hand, it does appear that our new member does have a fairly good grasp of the 6.5 platform, appreciation for the details, and no apparent intent to disrespect others by asking to limit the focus of discussion.
Just say-in
The OP had a targeted question. The down side-of a targeted question is that the rest of us can only respond based on the information at hand. If the OP wants to limit the amount of details in the discussion, that is the OP's right. Naturally, we are free to offer a more holistic answer and prod for more detail, but again, if the OP wants to limit the boundary, we need to respect that.
Toward the discussion at hand, it does appear that our new member does have a fairly good grasp of the 6.5 platform, appreciation for the details, and no apparent intent to disrespect others by asking to limit the focus of discussion.
Just say-in
What is a quick spool valve? I'm not familiar with this. Does it make the ATT work better at lower RPM?
ak diesel driver
6.5 driver
Quick spool valve only works on twin scroll turbos. Diverts all the exhaust gases to one side and helps it spool faster.
pacificdrumma
Well-Known Member
Most turbos that you will run into are going to be twin scroll. A Team is, Holsets are, a lot of Borgs are. GMx isn't. Essentially shrinks the exhaust housing temporarily to get it spooling, then opens to allow the entire exhaust housing to be used. Poor man's VGT. Stone-age VGT. But it works.
@pacificdrumma explained it. @Burning oil Leroy Diesel sells em.
ATT's 2 PSI at 2000 RPM becomes 10 PSI with the BD Spool valve. 2 known examples below. last link has video.
http://www.thetruckstop.us/forum/threads/bd-quick-spool-valve-install-with-pics.36278/
http://www.thetruckstop.us/forum/threads/another-bd-quick-spool-valve-install-with-a-c.39716/
http://www.thetruckstop.us/forum/threads/att-videos.39789/
I'm thinking the ATT would probly be even more advantageous with a 5 sp like mine, better control of RPM to keep turbo in the power band. I had come up with a gear venders overdrive that I had planned to install but am wondering how this might work with the ATT. AS gear ratio gets taller with overdrive rpm drops and boost falls off because ATT will drop out of it's power band?
Split the gears with the GV for the ultimate RPM control 10 speed. I run a NV5600 behind the 5.9 (And simply run out of RPM thinking the 5.9 should spin to 3600 and it doesn't) and understand the big RPM difference on the NV4500 between some gears is not ideal. @6.5L would be the expert at MT's behind the 6.5 with an ATT. @GM Guy is the undisputed handshaker collector around here.
For towing maybe as you hold the same gear a long time. Every time you shift the MT the turbo winds down and then has to spool back up. If you drop the RPM too low or when starting off you don't have any boost at the lower RPM. Again this is the biggest thing I see people have trouble getting used to. However when you are pulling the grade the upper RPM power makes up for that trade off.