Big Tdi Horsepower

[dimcon]

I know there has been several threads on tdi power, but I wanted to run some of my recently gained knowledge by the diesel guys. I'm in the process of having the 14 liter cummins in my haul truck rebuilt to gain some power, and have been told that in order to have any real gains that the compression has to be dropped to safely increase fuel pressure and turbo boost. Currently its running 15.5:1, about 18 psi boost and about 50 psi fuel pressure. The new pistons are 14:1, new fuel pump up to 150 psi and new turbo about 50 psi. All this will take the 300 hp, 1050 lb ft to 700 + hp and 2600+ lb ft. I guess what I'm getting at is this cummins is an old design mechincal engine very similar to the 200 tdi and I was wondering if the same principal would apply.
I know some people will say that there is no need for major power or that the fuel economy will go away or even that the drive train can't handle the power, so go ahead and bring it on. Cause there ain't nothing like diesel power.

[Buckon37s]

I have never personally heard that there is a big issue with lowering the compression in order to add fuel or air. It seems to me like it would not be necessary but I am not sure. What you have is an awesome project and I LOVE this type of thing.

A few tips, run as big an intercooler and you can possibly demensionally fit. Also, run at least 4in pipe, 5in is better with a very free flowing muffler or no muffler. Also fit an EGT auto kill in order to keep your heads from lollipopping. Finally, add nitrous, seriously. Adding nitro to the system as a safety measure will lean out your fuel mixture and allow you to keep your egt's down when your dumping on it.

Thats it, you didn't post what your transmission is or anything else so there is no way of knowing whether it will handle what you plan to do. That being said, I have seen a 12 second Dodge used as a daily driver so I know that it can be done safely. Good luck.

[dimcon]

I got the information on compression by looking at cummins engines specs. Just to clarify the engine I'm talking about is a big-rig motor. But by looking at the specs I noticed that the higher the horsepower the lower the compression and more boost and fuel psi. Example, the engine I have is a NTC 300 ( 300 hp) 15.5:1 com. the 350 runs 15:1, the 400 14.5:1 and the 475 14:1. Of course the fuel pressure and turbo boost increase by about the same factor. I really found all this out because I turned the fuel pump on my engine to make about 400 hp and it burned holes in my pistons. Running about the same pressure as a factory 400 hp engine. And to specify these engines are exactly the same (block, crank, cubic inches, heads, valves, everything, expect for compression ratio and the fuel, boost settings).

It just kind of stood out to me and figured it may be worth looking into. Maybe when I've got a little more disposable money, I'll see if I can lower the compression and crank the fuel and boost all the way up. Just using the factor above lowering the compression by 1.5:1 and increasing boost and fuel pressure net a gain of about 50% more horsepower imagine then if you add a larger intercooler, nitrous, or propane. And as far as the transmission holding up I'd say you didn't punch it in the low gears and progressive shifted I believe it would hold up just fine. I've learned a lot of this from driving semi's on and off for the past 9 years, with plenty of high power motors that well exceed the torque ratings of the tranny.

But I guess we learn the best lessons from trying and the dents it puts in the wallet huh?

[Buckon37s]

Ouch! I would bet, once again just guessing, that the burnt pistons had less to do with the compression and more to do with the fact that you did not offset the higher egt's. If you just dump lots of fuel, you get more power, and way higher egt's. You hit 1400, and you melt!

[dimcon]

I absolutely agree that high EGT's will kill a motor, but that's just my point that the exact same motor using the same amount fuel pressure that I created in mine, but with lower compression can run a million miles with no ill effects. Just seems a little odd to me.

[headdamage]

The relation between boost, fueling, and compression is why the rover TDI motors have much lower compresion than the 2.5na and 2.5TD.

[snuffer]

I got the information on compression by looking at cummins engines specs. Just to clarify the engine I'm talking about is a big-rig motor. But by looking at the specs I noticed that the higher the horsepower the lower the compression and more boost and fuel psi. Example, the engine I have is a NTC 300 ( 300 hp) 15.5:1 com. the 350 runs 15:1, the 400 14.5:1 and the 475 14:1. Of course the fuel pressure and turbo boost increase by about the same factor. I really found all this out because I turned the fuel pump on my engine to make about 400 hp and it burned holes in my pistons. Running about the same pressure as a factory 400 hp engine. And to specify these engines are exactly the same (block, crank, cubic inches, heads, valves, everything, expect for compression ratio and the fuel, boost settings).

It just kind of stood out to me and figured it may be worth looking into. Maybe when I've got a little more disposable money, I'll see if I can lower the compression and crank the fuel and boost all the way up. Just using the factor above lowering the compression by 1.5:1 and increasing boost and fuel pressure net a gain of about 50% more horsepower imagine then if you add a larger intercooler, nitrous, or propane. And as far as the transmission holding up I'd say you didn't punch it in the low gears and progressive shifted I believe it would hold up just fine. I've learned a lot of this from driving semi's on and off for the past 9 years, with plenty of high power motors that well exceed the torque ratings of the tranny.

But I guess we learn the best lessons from trying and the dents it puts in the wallet huh?


If your running an auto transmission anything like my 2000 Dodge has it won't last long. Dodge autos are known to be crap behind the diesel even if the engine is stock.

[dimcon]

No autos for me. I run an Eaton 9spd and looking for a good used 18spd.