Turbo Experts: Waking up the Roadmaster

[convert2diesel]

Hi guys:

Just when I figured the 6.2 conversion was doing all I had expected, we decided to purchase a new trailer. Nice trailer but it is over a ton heavier then the old one, which means I should try to squeak out a few more ponies out of the old 6.2.

I have 6.5 (bad heads, probably craked webs) sitting on the bench awaiting another conversion and I started to do some mock ups to see if I could shoe horn a turbo into the Buick. My question lies in the cast 90 degree down pipe at the exhaust side of the Bosch turbo (probably a GM 4). Upon inspection I have found that my job would be considerably easier if that outlet didn't make that 90 degree bend immediately after the turbo.

My thought was to make up a 1/4 inch plate and weld on a 3 inch pipe with the needed flange to allow the down pipe to exit the turbo straight back. My question is, is the shape of the OEM flange engineered to effect the performance of the turbo? My gut feeling is that if it was straight through it could only help things. There is a wild flattening in the pipe as it exits the turbo and then turns 90 degrees down. Does this have any adverse effects on the backpressure? I would think so but it may have been engineered into the design of the unit, or as we have all experienced, is this just another example of accountants trying to be engineers?.

Am I seeing ghosts in the closet or is it that I am just over thinking this problem?

Any input or observations into this would be greatly appreciated.

Bill

[gmctd]

That is a Borg-Warner\IHI GM-4 turbo, and your proposed modification would help - that scrunched-up exh-elbow was one reason for the upgrade to the -5\-8 series - the flange form\dimension is to clear the cartridge-mounted wastegate flapper, so the straight exit would improve exhaust flow - go fer it, dude............

[arveetek]

Yep, that would work just fine. Here's a couple of pics of my home-made turbo downpipe that I built just like you're saying. My turbo isn't a GM-4, but it's the same concepts.

http://rides.webshots.com/photo/1153305262029465272jCXrKi

http://rides.webshots.com/photo/1153307015029465272ubSFoy

Casey

[convert2diesel]

Thanks guys:

I didn't think that 90 degree turn could in any way help things but you never know. Have seen flow venturis used in the aircraft game that actually improved gas flow but when you looked at it it seems that exactly the opposite would occur.

It is at times like this that I envy you guys with all that room to work with. Originally considered the first Banks set-up for these engines but after doing some priliminary measurements found that it would impact the upper control arm on the passenger side. As it stands I have only about 1/2 inch of clearance to get the 3 inch downpipe around the back of the head, thus my need to decrease the angle coming out of the turbo.

Oh the joys of stuffing an engine into a space that was never designed to accomodate it. Going to have to win a lottery so I can build up a complete fab shop to do all this stuff.

Thanks again.

Bill

[j_k_auto]

Yea if you look at the gm 4 vrs the gm 8 you would not be thinking of this.
I have both turbos in my garage. The gm 4 looks to be square/recangle shape vrs the gm 8 which is almost completly round. I was:eek: of how different the elbows are.