OK, got the DE 4" exhaust in the 91.5 and my observations.
The bad:
Increased turbo lag.
A huge amount of black smoke due to lag.
An EGT spike due to lag.
The good:
Lower overall EGTs.
Uses/produces less boost to hold the same speed.
More boost. I'm going to need a different boost gage. 35 is no long enough!
Faster boost climb rate.
The ugly:
The DP is danger close to the drive shaft yoke.
Other:
No noticeable difference in noise levels in the cab.
Throughtier tone outside the cab, but no louder.

I'm going to start by cranking up the star wheel some more, then back off on the fuel screw until lag and smoke get back under control.

 

That's weird. You'd think your turbo would spool faster with a wider open exhaust.

 

Yah, that one was totally unexpected. At minimum, I was hopping it would drop my EGTs enough so I could turn the fuel screw in some more. But this situation is going to hurt me towing. I'm just hopping I can tune it out.

 

That's strange.

Maybe that muffler they include is a big restriction.

I've always liked 3" striaght pipes.

 

Sounds like the muffler is too tight to me.

 

I'm pretty sure it's NOT the muffler. I've got the DE kit for my 91....just haven't gotten it installed. There is NO restriction in the muffler.

I'm thinking the OP had his truck tuned for the old smaller exhaust. The new exhaust will require some retweaking. I would think backing OFF on the starwheel would help.

 

Not the muffler. When the turbo does catch up, it launches like a grayhound after a rabbit. It pegs my 35psi boost gage like right now. I'm going to crank the star wheel up to flush and see. Next would be backing off on the fuel screw.

 

turn it 4 turns up from bottomed out... any more than that and youre binding your spring and it could keep your fuel pin from going down all of the way.

 

OK, I cranked the star wheel up.
Lower boost, higher EGT.
No change in the amount of low end smoke and lag.
Anyone have any ideas???
My smoke screw is already all the way up. The only other thing I can think of trying is grinding the top of the fuel pin down to make it go up higher.

 

M&H has a spacer for the afc top... i havent seen/heard anyone use one personally but theres not much to mess up so id assume its good.

i machined mine... my smoke screw is 7 threads above the jam nut.. heres a pic

 

4" isn't as good as 3" as far as exhaust scavenging is concerned at lower power levels.

 

Well Guys I have 3 D/E Coming For three different trucks Mine The W250 Reg Cab 4x4 5 speed /1992W250 Reg Cab Auto 4x4/ And 1992 club cab W250 auto 4x4

Two Reg cab are straight piped now..... Club cab Is 3 inch stock Rusty . I suspect his will see the most gains

I know with mine which is basically stock i can really get going just with the muffler off Very noticeable plus mine is lifted I still have gained mileage and power (seat of the pants towing I notice climbing hills )

 

That's an idea, I have lots of aluminum laying around the shop.
The next question is how high can the fuel pin go before getting you into trouble. I have some .080" I could use.

 

the way i did it i couldnt say exactly how much because.. i tried to grind it first but couldnt do it right so i put it on a cnc mill and did it at work. as you can tell i had to mill into the center (where the smoke screw is) so the fuel pins nut had a place to recess.

if you make a spacer you should use gaskets of some sort. the boost needs to be sealed in there.

 

I just put a 4" Diamond Eye exhaust on my 92' and I was thinking the same