I recently has my comp upgraded to a drag comp, that along with the 80Hp injectors, witht the comp all the way up my egt gauge will peg 1600 fast, and its probably going higher cause thats where the gauge stops, I still have the stock 3" straight, I am going to order an exhaust, I want a 4" exhaust, but I am worried that it will not coll down my egt enough, and am wondering if I should get 5 instead. I would rather get a 4", but if I need a 5 for egts, ill get that. I am only thinking about scavanging with 5". Anyone have any input as to how much 4" will cool it down?

 

A good 4" system will buy you about 150°F drop in EGT's. IMHO, unless you are running Twins and need the 5", its a waste of money. Most dyno reports I saw show no gain and mostly loss from having a 5" system. Bigger isn't always better as the exhaust doesn't flow as well and doesn't cool any more than a good 4" system would..

Honestly, the stock turbo is giving you the most grief.. Exhaust isn't going to fix the fact that the turbo is the biggest restriction.. Any of the boost you make over the 38 psi mark is causing the exhaust back pressure in the manifold to skyrocket. I would guess that the drive pressure to the turbo in your case is close to 60 psi with 46 psi boost. Which isn't good for scavenging (clean air in) and is increasing EGT's..

 

Ok, great thanks for reply, exactly the info I was looking for. I am probably going to order one of the exhaust systems of ebay, I think they are about 210 with 65 shipping, so under 300 aint bad, Anyone here had any experience with them? A lot of guys buy them from this guy, so I think it will bo ok, I dont drive in the winter and I plan on spraying it with high heat to prevent any rust.

 

I didnt have any problem ordering a 4" from ebay. it was for more '02PSD before I saw the light and got the Cummins. Just remeber that they are aluminized steel and wont last as long as the stainless. if you can find one with 14gauge steel instead on the 16gauge that would be better. I the 4" for my Cummins from RPM outlet and didnt have any problem with it. I've had it for about a year and its been great. Before I just had stock exhaust with out the muff. When I put the 4" on it did lower the egt about 100F but what I noticed more is it took alot more time to egt up there.

 

I would go with 5". Well I guess you can say I did. I can still peg out my EGT'S at 1600 but it takes a lot longer. My motto, "GO BIG OR GO HOME". Then if you ever go to twins you will already be set up in that dept.

 

5" only cools maybe 50* better and cost more. Also, a lot more trouble to install, in most cases. 4" will take you to 550-600 hp with no problem.

After having done it.... only reason I see for a 5" exhaust is sound!

RJ

 

I got the 4" off ebay. It has been on for 2yrs with no problems. I did not like the way the muffler sounded so I took it off. Straight pipe now. I love it and my neighbors hate it. I guess they will have to move.

 

5 inch looks great an should in theory prove to put less back pressure on the engine. Less back pressure means the engne can scavenge heat faster and use less power to push exhaust out. I have to believe, and everything I have read confirms that a 4 inch exhaust will support what this little engine will build HP wise. 5 inch looks better though, I think.

 

Check out Markoidaho on ebay. Oh and get a 5".

 

It's more about the velocity of exhaust gasses leaving the pipe. If you go too big it'll slow the gasses down too much and would then have to be "pushed" out; hence, loss of power. 4" is all you really need. But 5" looks and sounds cool. They're all about the same though...

 

There are alot of guys on here past the 700hp mark with a 4" exhaust still.
5" looks cool, but you dont necassarily need it. But then again who really needs a 11-13 sec. 1/4 mile 8000lb. truck?

ME!!!!!!!!!!!!!

 

I understand the theory... and I'm certainly no engineer, but standing in front of my 5" exhaust on a 100* day, I will say "I don't buy it"
Also, no change in TIP (drive pressures) between 4" & 5" tells me there is virtually no difference in back pressure.

RJ

 

My truck is at 700hp through a full 4" exhaust with a muffler. So is 5" nesecary? I would say no. But on the other hand, its not going to hurt you.

 

If you have 14.7psi atmospheric pressure, then the backpressure is 14.7psi-- maybe more.

The cooling aspect of oversized pipe is way overhyped.

The one important thing that I think is relevant is to avoid drastic transitions-- like from 3" to 5" instantly. Better to gradually change from 3" to 4" to 5".

Now you MIGHT see a loss of power with a 6" pipe or something, but that's a much larger increase than from 4" to 5". (think square inches)

Excessively large pipe is a HUGE no-non with a NA engine, but with a turbodiesel, it's not nearly as big an issue.


I still prefer 4", unless you have a big turbo with a 5" outlet.

jh