Attention: TDR Forum Junkies 
Hello everyone,
I've been coming to this site for advice since before I bought my truck, and was convinced that every answer was one that could be found with enough searching. But I finally found a problem I just cant wrap my head around and finally made an account because I need some help. I have a 1993 W250, 4x4, 5spd that I bought completely stock. Its beat up, but I want it to be a reliable workhorse, mostly just carrying stuff around in the bed, driving down the highway, but occasionally towing a car trailer, or a trip up the mountains in the snow. My goals for it are eventually around 300HP and 700ft/lbs of torque, which seems like a good place to keep it relatively cheap, make it a lot more fun, but without throwing utility and reliability out the window. I know fuel mileage will be poor, but I still want to do everything I can to keep it as high as possible. I really havent done too much to it yet, since chasing down oil leaks has been my biggest job, but so far I have a boost guage, and a 4" SS Diamond Eye exhaust, with a lot more changing before I'm finished.
With my stock 18mm H1C, and a crushed stock exhaust I was able to build 15PSI at WOT just driving down the freeway. After installing the 4" exhaust, that number jumped to 22PSI, and my fuel mileage went up by about 1 MPG (Which could still be better with a lighter foot...) My problem comes because I was still hoping for a little more power at the low end, without just installing bigger injectors and throwing fuel at it, and have heard nothing but praise about the HX35W for its quick spooling and power limits still well above my goals. I bought a brand new cummins remanufactured unit off CL with a 12cm exhaust housing, and finally got a chance to install it yesterday, minus a few hiccups. The wastegate actuator interfered with the oil return line, so I removed it, and mounted a plate which holds the WG lever completely closed at all times. I know people weld the flappers shut, so I didnt think this was anything unusual, I just knew to keep an eye on my guage to make sure it didnt get anywhere close to the 35PSI mark when I didnt expect it to. Besides that, everything went in as expected, so I took the truck for a test drive and hated every second of it. The truck never made more than 15PSI, and only after I had been laying on the throttle for a long time. The truck felt significantly slower, and when I upshifted, I just got to watch my boost guage slowly droop lower and lower until I got to 1800-2200RPM when it would finally start picking up pressure again. The strangest thing of all was that driving almost felt like the turbo was surging, but the gauge showed none of it. Just kind of a constant rolling sputter until I got high enough in the revs to make it really sing, but by that point I had to shift, and I was still making less pressure than my H1C was anyways.
I'm really at a loss, because the results I have are almost exactly the opposite of what I expected. Looking around, it seems like most people who talk about using an HX35W already have a fuel pin and 3200k rpm governor spring, which I dont have yet. But as of right now, I feel like I will have better luck just ditching the HX35W all together to go back to my H1C. Are the fuel pin and gov. Spring required to run an HX35W? Is the wastegate supposed to help at the bottom end, or just prevent runaway at the top? Is my stock airbox limiting me, but if so, why wasnt it a problem with the H1C? Am I having fueling issues, air restriction issues, exhaust backpressure issues? If I just have to dump more fuel into the mix to get more power at the bottom end, is there really any difference between the HX35W and my H1C?
I wouldnt be surprised if I'm just missing something basic, but I really dont even know where to start, so any help would be seriously appreciated.
TL;DR: I replaced an 18cm H1C with an 12CM HX35 on an otherwise stock truck and lost power and boost, not gained. Why?
I've been coming to this site for advice since before I bought my truck, and was convinced that every answer was one that could be found with enough searching. But I finally found a problem I just cant wrap my head around and finally made an account because I need some help. I have a 1993 W250, 4x4, 5spd that I bought completely stock. Its beat up, but I want it to be a reliable workhorse, mostly just carrying stuff around in the bed, driving down the highway, but occasionally towing a car trailer, or a trip up the mountains in the snow. My goals for it are eventually around 300HP and 700ft/lbs of torque, which seems like a good place to keep it relatively cheap, make it a lot more fun, but without throwing utility and reliability out the window. I know fuel mileage will be poor, but I still want to do everything I can to keep it as high as possible. I really havent done too much to it yet, since chasing down oil leaks has been my biggest job, but so far I have a boost guage, and a 4" SS Diamond Eye exhaust, with a lot more changing before I'm finished.
With my stock 18mm H1C, and a crushed stock exhaust I was able to build 15PSI at WOT just driving down the freeway. After installing the 4" exhaust, that number jumped to 22PSI, and my fuel mileage went up by about 1 MPG (Which could still be better with a lighter foot...) My problem comes because I was still hoping for a little more power at the low end, without just installing bigger injectors and throwing fuel at it, and have heard nothing but praise about the HX35W for its quick spooling and power limits still well above my goals. I bought a brand new cummins remanufactured unit off CL with a 12cm exhaust housing, and finally got a chance to install it yesterday, minus a few hiccups. The wastegate actuator interfered with the oil return line, so I removed it, and mounted a plate which holds the WG lever completely closed at all times. I know people weld the flappers shut, so I didnt think this was anything unusual, I just knew to keep an eye on my guage to make sure it didnt get anywhere close to the 35PSI mark when I didnt expect it to. Besides that, everything went in as expected, so I took the truck for a test drive and hated every second of it. The truck never made more than 15PSI, and only after I had been laying on the throttle for a long time. The truck felt significantly slower, and when I upshifted, I just got to watch my boost guage slowly droop lower and lower until I got to 1800-2200RPM when it would finally start picking up pressure again. The strangest thing of all was that driving almost felt like the turbo was surging, but the gauge showed none of it. Just kind of a constant rolling sputter until I got high enough in the revs to make it really sing, but by that point I had to shift, and I was still making less pressure than my H1C was anyways.
I'm really at a loss, because the results I have are almost exactly the opposite of what I expected. Looking around, it seems like most people who talk about using an HX35W already have a fuel pin and 3200k rpm governor spring, which I dont have yet. But as of right now, I feel like I will have better luck just ditching the HX35W all together to go back to my H1C. Are the fuel pin and gov. Spring required to run an HX35W? Is the wastegate supposed to help at the bottom end, or just prevent runaway at the top? Is my stock airbox limiting me, but if so, why wasnt it a problem with the H1C? Am I having fueling issues, air restriction issues, exhaust backpressure issues? If I just have to dump more fuel into the mix to get more power at the bottom end, is there really any difference between the HX35W and my H1C?
I wouldnt be surprised if I'm just missing something basic, but I really dont even know where to start, so any help would be seriously appreciated.
TL;DR: I replaced an 18cm H1C with an 12CM HX35 on an otherwise stock truck and lost power and boost, not gained. Why?
