Turbo and exhaust bends question

[Freewheel]

So I've had an AXT Turbo on my 2H for about 4 years, and after having 4 exhaust systems rot out in the 9 years I've had my truck, I decided to make up a stainless steel exhaust. When I first put the turbo on (4 years ago) , I made a 2.5" steel pipe exhaust (no muffler) that worked quite nicely. When I made up the new stainless exhaust, I matched everything to the original exhaust I had made, except for one thing. The down pipe from the Turbo in the original install has 2 mandrel bends in it that are probably about 60°. The new one I made up has 2 mandrel bends of 90°. These are the first two bends off the turbo, the first one being 3 inches from the turbo outlet and the next one being a foot below the first.

It feels like I've got considerably less power than I did before, and I'm wondering whether the tighter bends could possibly be the problem. The other possibility is that the engine was just breathing better before because the entire exhaust was so rotten (broken off completely in front of the rear wheel), but I'm curious what people think. Most threads I have seen agree that a 2.5" exhaust works pretty well on a turbo'd 2H, but something has definitely cut my power in the changeover from a rotten 2.5" exhaust (with two 60° bends) to the nice new one (with two 90°bends).

 

[IanB]

Sharp bends right off the turbo are definitely going to kill your exhaust velocity and add restriction to the system worse than if they were further back in the system (after the exhaust has cooled and lost some volume, where your flow needs are less), and worse than a routing with less sharp bends obviously. As far as bottlenecks go, you've added one at the very beginning of your exhaust, limiting the potential for all areas behind it in the system.

If you're able to, try disconnecting the exhaust after the downpipe and run that to see if the power comes back. Then you'll know the issue is exhaust flow, but you won't yet know for sure if your problem is in the downpipe or the exhaust system that attaches. From what you've described, I'd agree that downpipe design is most likely the culprit.

 

[Dougal]

If the exhaust was restricted then boost would be delayed. Is this happening?

 

[Freewheel]

Hey Ian and Dougal, thanks for the replies. The exhaust has been clamped together in a few spots so I can easy pull it apart for some experimentation. I'll also check to see whether boost is delayed, wasn't watching for that when i was driving yesterday.

 

[Freewheel]

Hi Dougal, i've never really watched my boost too carefully before in how it kicks in. I was just playing with it and from standing still and flooring the accelerator, it takes about 3 seconds to get up to 8 PSI. If I'm already moving but not under load and then floor its a bit faster.

How would you suggest I best test whether boost seems to be delayed or not?

 

[dousty]

You'd need to change the exhaust back to how is was previously and compare.

 

[Eric Winkworth]

I just got pieces like this and every 3 feet or so put a 3 bolt flange and gasket, when a section rots just take it out, and replace... ended up with a really nice exhaust. for super cheap....

EXDALMJ

 

[Freewheel]

Hi Dousty, Can't really return to what i had since it was rotten and ended to be cut out in parts.

And Erik, what you did is pretty much what I did, except I got tired of how often pieces needed replacing and didn't really like the look of a rusty exhaust pipe...so, stainless is where I went... but using your theory of easy replaceability with 3 bolt flanges and clamps. Changing the exhaust won't be to much of a pain work wise, but replacing the brand new stainless that I just bought will be a little bitter...

 

[Freewheel]

Near my home, there's a mountain highway that I am very familiar with, and requires very specific gear ranges as one climbs it. When I first put my turbo on, the gear ranges dropped by a full 2 gears from when the engine was naturally aspirated. Which instantly made the new turbo the best purchase ever.
To get back to this thread and the feeling that I had lost power after putting the new exhaust on- I was driving unfamiliar roads right after the install and my perception was that the truck didn't have the same power. After getting back to the roads that I'm familiar with, I'm feeling better. The hill climb gearing is the same as it used to be and the EGTs and water temperatures may be a tiny bit higher, but not by very much. Internet research says that a 2.5" exhaust pipe should be fine for a 250 Hp truck and the 2H with an AXT turbo should max out at less than 180 Hp.

So I'm going to relax and move on to my other land cruiser projects...
Thanks to all who gave advice.