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Old 09-26-2008, 10:13 PM   #1 (permalink)
67_C-30
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My remedy for the restrictive exhaust housing on GM-X Turbos.

It has been covered on here before that the factory exhaust housing on the rear of the GM-X turbos is restrictive and could be the cause of some of the back pressure associated with them. After some measuring, I found that the inside of the casting measures a touch under 2.600" at the outlet and is more restricted than that on the inside the where the 90 degree bend is. It seems to me that this would have no choice but limit the effect of bigger exhaust. I decided to build a custom system that will be 4" from the turbine housing back. I machined the flange at work on the CNC, and I'm building the pipe from pre-bent 90 and 45 degree pipes that I will have to cut and butt-weld to the straight lengths. I am going to have to run outside of the frame rail due to the position of the turbo and the narrower frame on these year trucks vs the newer ones that the 6.5TD were designed for. I'm planning on turning it out right before the rear wheels on the passenger side. I know this style turbo is small and is still not going to be as efficient as a bigger one. However, maybe this will make it a little more efficient and lower EGT's a little. Either way, it should sound good! I'm just hoping it won't cause any significant lag, but I'm think as small as it is, it won't be much if any.


Here's a few mock-up shots.









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Proud member #214 of the 3500 Dually Club!!

1967 C-30 Dually Pickup

Engine and Drivetrain:
6.2L Turbo, NP435 close 4 ratio speed , 14 bolt Posi Rear
Mods:
'93 GM-3 Turbo, DSG Stud Girdle, Bosch Duraterms glow plugs, 6.5TD Marine injectors, Non-EGR J code dual plane 6.2L intake with custom pressure chamber, custom 4" turbo discharge housing and exhaust, K&N Filter

1984 M1009 CUCV Blazer - Fresh out the military, 46,000 miles. Banks Sidewinder turbo

My build thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=254096
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Old 09-26-2008, 10:29 PM   #2 (permalink)
weik
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I hope you have a egt guage on now so you can tell us a before and after mod to see if it really makes a difference and by how much. I think it sounds like a good idea!

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Old 09-26-2008, 10:48 PM   #3 (permalink)
RCpullerdude
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I was thinking of trying this on my truck. Only problem I foresee on my truck is fitment. Also, this will only work on the earlier GM-X. The later ones have the wastegate in the elbow.
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Old 09-26-2008, 10:49 PM   #4 (permalink)
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once you get that on and show that it works consider makeing that adapter, I would buy one if I could get my hands on it. I have thought of doing this my self but with no access to anything as nice as a CNC I have yet to fab something up. any way keep us posted on any improvements!
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Old 09-27-2008, 12:31 AM   #5 (permalink)
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That surely has to make an improvement. Please report how it works, I am very interested in making the most out of my little GM4 that I'm running the legs off of.

My biggest issue right now is backpressure. I know there's only so much a guy can do, -considering the turbine housing also contributes, -but that flange and pipe should help out for sure.

I like it!
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Old 09-27-2008, 12:37 AM   #6 (permalink)
DieselPro
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Check out my S.E.D.

https://www.dieselplace.com/forum/sho...&highlight=sed
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Old 09-27-2008, 12:38 AM   #7 (permalink)
DieselPro
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Open pipe is not going to cause lag
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Old 09-27-2008, 09:32 AM   #8 (permalink)
67_C-30
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Quote:
Originally Posted by DieselPro View Post
Open pipe is not going to cause lag
That's good to hear. When I get it all plumbed, I'm going to cut it near the turbo and weld in a V band ring that I bought off ebay. I will be able to compare them factory rear housing and a piece of the factory downpipe against my 4" set-up. I may even put a probe in the pipe and try to check the back pressure between the 2.

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Proud member #214 of the 3500 Dually Club!!

1967 C-30 Dually Pickup

Engine and Drivetrain:
6.2L Turbo, NP435 close 4 ratio speed , 14 bolt Posi Rear
Mods:
'93 GM-3 Turbo, DSG Stud Girdle, Bosch Duraterms glow plugs, 6.5TD Marine injectors, Non-EGR J code dual plane 6.2L intake with custom pressure chamber, custom 4" turbo discharge housing and exhaust, K&N Filter

1984 M1009 CUCV Blazer - Fresh out the military, 46,000 miles. Banks Sidewinder turbo

My build thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=254096
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Old 09-27-2008, 09:34 AM   #9 (permalink)
67_C-30
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Quote:
Originally Posted by DieselPro View Post
That is very cool!!
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Proud member #214 of the 3500 Dually Club!!

1967 C-30 Dually Pickup

Engine and Drivetrain:
6.2L Turbo, NP435 close 4 ratio speed , 14 bolt Posi Rear
Mods:
'93 GM-3 Turbo, DSG Stud Girdle, Bosch Duraterms glow plugs, 6.5TD Marine injectors, Non-EGR J code dual plane 6.2L intake with custom pressure chamber, custom 4" turbo discharge housing and exhaust, K&N Filter

1984 M1009 CUCV Blazer - Fresh out the military, 46,000 miles. Banks Sidewinder turbo

My build thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=254096
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Old 10-06-2008, 07:27 PM   #10 (permalink)
67_C-30
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I got the pipe fitted and welded top the flange. It took quite a bit of persuasion to make it fit all the way around due to odd shape of rear exit of the turbo. The opening is slightly bigger than the factory opening so there is no overhang. The ended up being a little over 4.5" at it widest point and around 3.5" at its smallest. It is still WAY bigger than the inside of the cast. The last shot shows how wide open the exit is. It makes a nice smooth transistion down for a 90 degree turn.












__________________
Proud member #214 of the 3500 Dually Club!!

1967 C-30 Dually Pickup

Engine and Drivetrain:
6.2L Turbo, NP435 close 4 ratio speed , 14 bolt Posi Rear
Mods:
'93 GM-3 Turbo, DSG Stud Girdle, Bosch Duraterms glow plugs, 6.5TD Marine injectors, Non-EGR J code dual plane 6.2L intake with custom pressure chamber, custom 4" turbo discharge housing and exhaust, K&N Filter

1984 M1009 CUCV Blazer - Fresh out the military, 46,000 miles. Banks Sidewinder turbo

My build thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=254096
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