I have an early '99 with stock turbo and installed a 4" turbo back MBRP kit with no issues. I can not give a comparison to a 3.5" DP as I never ran one on this truck, but I can tell you I didn't notice any change in HP or TQ over the stock DP. And as far as changing the TQ curve, it really doesn't change that much. I attended a local dyno day last year and compaired my run with another guy that had an early 99 with stock exhaust and the TQ curve was pretty close to each other. We both ran stock programming and my peak TQ was only higher than his in RPM by about 100 RPM's. To me, the change isn't even noticable when towing. But I will tell you my EGT's drop alot with my chip while towing. I can run a higher tow setting and stay in it longer before having to back out of it and most times I don't have to back out at all now. I usually run it up to 1200 (pre-turbo pyro) towing in my area with the hills. There have only been a few occasions where it started to climb higher than that and I would have to back out of it. I do know I couldn't do that with the stock DP and I honestly don't know if I could do that with a 3.5", but my primary concern when I made my choice was to get the lowest EGT's possible while towing and for the area I tow in.

I look at it this way, I am not driving a race car nor do I rarely run it at WOT, but what I do most is tow in an area with a lot of hills. I usually leave it on Jody's 60T and never have issues with EGT's with my setup. As far as weight for towing it all varies on the load. Somedays it's hay, horse, cattle, tractors, etc. My point is, if you tow alot, spending the extra $120 to me was worth it when I can stay in it on hills and maintain my spend versus having to back out of it, causing me to slow down while towing. If you don't tow much or your area is mostly flat then I don't think it would be much of an issue as I don't come close to going over 1200 on flat ground. So I think you need to consider how you use your truck, where you drive it and how you drive it before you make your choice.

Maybe I could get away with the same thing in my area with a 3.5" DP, but I have never ran one so I can't tell you how it compares to a 4".

-Mike

 

Well said, Zwalters..... Pipe length is yet one more vairable here.

Danny... if I came across as a "Professor", please forgive my approach. That was not intentional, and I am well aware that there are plenty of folks in here who can engineer circles around me.

My 31% was meant to represent a simple "area calculation" and its associated relationship to gas velocity... that's all. My wording of "the same percentage gain" was badly done, and reading over it again now I see that it sounded like I was saying that there would be a 31% reduction in temps... even though that is not what I was trying to say. I had typed much more information and then removed a lot of it, and didn't re-read before posting. My bad.

My only point is that there would be a temperature reduction, even if it is too small to "make much difference" in the big scheme of things.

I probably should not have chimed in at all. Sorry for any confusion.

 

I am glad you chimed in as I learned a little bit as to why it lowers the EGT. Before I just knew that it did, but really didn't know the why behind it. But what you said makes sense.

-Mike

 

Thanks, Mike. Sometimes my words get run over by my thoughts and everything doesn't get said very clearly. Trying to work more at thinking before speaking instead of while speaking.

 

Pete- please feel no offense!! LOL, I was just being a smarty pants hehe. Believe me, I appreciate any and all repsonses to a question I have. Unless you try to respond that a jap truck can do it better then the gloves come off

 

The turbo housing is a little over 3", nice transition to 3.5"..But a good jump to 4", creating a void or low pressure area..The exhaust gassers are going to change velocity in there.

Most people wont feel or notice a torque curve shift, because the addition of the exhaust system gives a noticeable difference in performance then the stock system.

I have had some 4 different exhaust systems and have had the oppurtunity to go from 4" to a 3.5", you can tell the difference going back, and you will notice the difference not at WOT, but just cruising around. I manage the EGT's through the programming(by Jody) rather then by the DP size. I also have my 3.5 DP wrapped with thermal wrap, which works great driving the turbo with the retained heat. Its the heat that drives the turbo not the velocity of the exhaust gasses...

The Magnaflow is the best exhaust system out there..

 

Once again I am not trying to start an arguement, but clarify. The turbo runs off of gas pushed through it. Heat retained creates hotter gas, which in a closed environment creates pressure. The created pressure is constantly released through the turbine via flow over the vanes. Due to the shape of the vanes it causes the turbine to spin because of the gradual turn the the direction of the vane transfering the flow of the hot gasses energy into mechanical energy. Without the heat, you wouldn't get the compounding effect to create boost and you would simply be wasting energy and adding restriction. The idea of the turbo is to utilized wasted energy in normal combustion and create more power. The velocity of the gasses is relavent to the speed of the turbo which translates into more boost on the other side. Without the heat of those gasses (E.G. - Inlet temp equaled outlet temp of the engine) the turbo would cause loss of power. You guys are both wrong for disagreeing with eachother because you are both equally right. One hand washed the other. Have a nice day.

 

Why do I hear a lot of "Magnaflow is the best" ? Don't get me wrong- I'm glad to have it for that reason, but since I don't have a cat or a muffler on my exhaust, what differentiates Magnaflow from Banks or anyone else out there?

 

not a whole lot other than price

 

Walters the turbo is driven by HEAT...Not gas velocities..

Magnaflow and Banks are the only ones made in the USA..Banks is a little proud of their exhaust sytem, price wise. I have installed the silverline, Banks, Magnaflow, MBRP, Bassiani, HOG,and some others I dont care to mention. Overal install, Product quality, Use of OEM hangers, is top considerations.

The Magnaflow, retains use of the stock hangers, they are welded SS hangers, Auto-machine Mandrel bent, The turbo flange is premuin quality, Fit beats all the rest. And the price, I dont even install Aluminumized for the difference of $30...SS all the way and a 3.5" DP.

 

the only exhaust i've ever installed on my diesel is my home brew stack kit so i can't really comment but i have helpd put on a bully dog 4" turbo back and that went fairly smooth on my truck with the 4" downpipe i had to cut some of it and there was a few choice words said to get the darn thing to slide up to the turbo it's a tight fit

 

I don't want to argue, but I have to point out something here.

Mach1, even though I am not a turbine designer, I do know a few things about thermodynamics, gas flow, and mechanical movements. It is the exhaust gas FLOW that drives the turbine, not the heat. If it were the heat alone, there would be no need for the hot exhaust gasses to go through it, as it would simply be driven by the heat alone.

To prove this, you can put a torch on the turbine housing and it will not cause the turbine to spool up. If the vanes do manage to move at all, it will be due to the expansion of gases caused by the external heat source, hence, it will be the FLOW of gas, not the termperature of the gas.

I would propose that the reason you see a relationship between the hotter gases and mroe turbine performance is that the hotter gases have more volume (or, pressure in a closed system). Since the volume of our pipes cannot change as the gases expand, the gas velocities increase, which in turn drives the turbine vanes more agressively, which is what I believe Walters was trying to say as well.

 

250, I wont debate the heat Vs. velocities driving the turbo, cause I understand why it drives and it is from the heat of the engine..No heat No turbo boost. Diagnose one of the engines that is not making boost and it becomes apparent real quick, that if you are not delivering the fuel you will not make boost.

You also have it right that the gas velocities change at the flange because of the larger area the velocities will slow, therefore a low pressure area is developed which will change the exhaust flow. Here again, moving the torque curve up because of the larger low pressure area created after the turbo housing into the exhaust pipe flange because of the 4" area Vs. the smaller 3.5 DP area.

 

Mach1, I expect that you have more "in engine" experience than I, and you're right... there is not much to be gained in debating over "chickens" and "eggs". There is no doubt that the fuel has to be there for either heat or velocity to be present, and I can live with that the way it is. I sometimes run into similar issues in my own Christian faith where I don't understand every "why", "why not", and/or "how", and end up satisfying myself in knowing that I don't really have to understand it anyway in order for things to be either the way they are or the way they were.

That said, I appreciate your demeaner and in-depth explanations.

 

well, you guys are both on the money, the Turbo is driven by Hot gas and its Velocities,
the gas is driving the turbo Turbine when there is no big boost condition, like going 40mph, so heat at this point wont change anything, once you put your foot down and start making 20-30 or more # of boost thats where heat night help to drive he turbine, cause hot gases while compressed will heat up more , and gas when it heats up it expends , so in other words makes more volume, which drives the turbine faster and you making more boost, this applies to certain point of any turbo , once you reach the turbo efficiency than heat is what will kill you , you not making more boost cause the design of the housing and vanes, and you just heatng the gases more and more thats how you Bake you berrings, or cause a meltdown,

just to prove the point get a bottle of FREEZE its a cold gas that when you press te nozzle it changes temp from 0-to ambient in split second which causes expension, take the same can and hold it in the freezer for a day and you wont be geting anything from it,
so what i think is, Heat mostly is needed for the motor to run, Combustion, and gas velocities are needed to drive the turbo
the gases from the block are allready compressed, when they enter UP pipes, than they start to expend in the turbo, causing it to spin,


well im just rumbling here , sorry

i might be totally wrong here, just taking a stab at it,reading it its a one big blah blah