4" turbo-back?

[sparks57]

Ok guys, I've got some super secret EDM's comming REALLY soon, and I want to up my airflow to match the extra fuel.



I have a question:



Would I see any benefit of puting a 4" downpipe on? Does anyone make a 4" downpipe for an hx-35 exhaust housing? (mine is a 35/40)



And if the 4" downpipe is a no go, is the stock 3" pipe good or should I look into a improved 3" downpipe?



I'm going to run up to Missoula here pretty soon to a truck shop and pick up some 4" pipe and bends... and some 5" tips.



I'm going to duplicate my current dual exhaust. I don't know how hard it is to tackle the section by the t-case, but I know that Rip Rook has the piece that goes there...

 

[Bob Beauchaine]

C B



I've got an HX35, a BD exhaust brake and a 4" down pipe on mine - work done by the master himself - Rip Rook. You can see my setup on May 15th - I will be in Idaho that weekend.



Bob

 

[dpuckett]

Bob, I dont think the kid can WAIT that long. :-laf



CB- it is possible. I have half a 4" downpipe- I have the stock elbow (first 90deg bend after the turbo, not especially and elbow per se), then have the 3-4 adaptor, and a 4" 90 by the transmission belhousing. Kind of ugly, but it fits the truck and driver. If you get creative, you probably could make a true 4" DP- start with the adaptor right after the turbo flange. I can email you a pic if you still are unclear as to what I mean.



Daniel

 

[sparks57]

I sent RR a PM over the NWB site asking about a 4" downpipe and the section by the t-case... that's all I'd need... along with the 5" tips... I could fill in the rest.



I would really like to go true 4"... but I'm not sure it's worth it?



Just curiouse if the downpipe would make any difference considering the size of the e/h outlet.

 

[JLEONARD]

curiouse if the downpipe would make any difference considering the size of the e/h outlet

I think in theory it would make a difference... . the elbows/bends are where the restrictions would be... .

So even though the turbo outlet is 3 inches, the extra size of the 4 inch would eliminate the restrictions in the bend areas... .

Since you are in the quest for high HP I would think the 4 inch is the way to go..... somewhere down the line you may need it.

There..... now you got some encouragement...



Jay

 

[Jonesy]

Just had a 4 inch turbo back system put in. Can't really see that much improvement, but I'm not doing as much BOMBING as you at this time. I guess when i turn things up a bit I'll be glad I did it

 

[cerberusiam]

Its all a matter of preference I guess but everything I see tells me a 4" downpipe is overkill unless you are going to push way over 400 hp. You can probably achieve the same results by wrapping the turbo and 3" down pipe to the flare to 4" with header wrap and save the $$ for other goodies. Exactly where the break is to need a 4" exhaust is hard to justify and in some cases the big exhaust will hurt performance.

 

[Lock93]

I have 4" from the turbo back, but I had it all done at once so I can't say if the downpipe helped. SOP dyno says I picked up some power, and it spools much faster than before! Beyond that, I needed to repair the exhaust, so I went 4" so I shouldn't need to do it again later after the mods start...

 

[sparks57]

Ok, still not sure if I should go 4" downpipe or not!!!



Also, what about exhaust tone... would it change much between downpipes? I like my exhaust to be as deep as possible... even thinkin' of a resonator to make it sound more like an 8. 3.



BUT that hasn't hit the market yet... still waiting!



So far these trucks can make 500hp... is a 4" downpipe required for such numbers?

 

[dpuckett]

I dont think the DP would affect your tone that much. That, in my experience, has been more related to how long the system is, and where it dumps, what restrictions are in it, etc. The 93 Flatbed I had (I think 163" WB) had a deeper tone than the 92 W250 I had at the same time.



WIth your intentions, you might want to look into a 4" DP with a HX35/40 adaptor. THink I saw them on the PDR site. You will need it; get it once, and be done with it.



-DP

 

[Bob Beauchaine]

After I added the 4" system to my truck I saw a decrease in egt's and an increase in noise. The egt decrease ran about 75 to 100 degrees. When towing I can feel the difference. I was running a 3. 5" system with a 2nd gen 3" down pipe.



Bob