4" or 3.5" exhaust?

[Bluebird]

I know it's been covered many times, just looking for input before I spend $$$. I plan to keep the rest of my truck stock (accept for guages later) from this point, and I would like to know if 3. 5" straight pipe/muffer would be a good choice or just go with the 4". I'm planning to go from the downpipe back mandrel bent, aluminized steel, (the 4" will cost $375. 00 I think the 3. 5" is $275. 00)

Thanks to anyone who replys, Patrick.

 

[Lock93]

Lots of opinions on this topic, and some facts quoted also. I listened to everything and went 4" the entire way just in case I wanted to modify the truck later. I always believe in doing something once.



I belive I was told no need for anything larger than 3. 5" on a first gen, especially a stock first gen.

 

[Greenleaf]

I dunno.

I have had both. I like both. I made them myself, so cost wasn't so much a factor. I upgraded to 4" cause I wanted to git that hot air outta there. Think I will try the Monster 6" now. The township is replacing some culvert pipe... ... ... . hummmmmm



Oh, speaking of hot air... ... ... ... .



-S

 

[JLEONARD]

I will try the Monster 6" now

That should suck a few extra PSI of boost thru the engine!!



I went 4 inch because I didn't want to wonder down the road if I had a restriction... . just do it once and be done was my thinking.

With 3 1/2 I would have saved, but would also be wondering... . would 4 inch be better?



The 3 1/2 would probably be a nice upgrade for a stock engine..... but would 4 be better? I was told I would see no difference from stock to 4 inch because of my meager hp level..... I saw some pretty significant gains.

So the answer is a definate "I don't know it's your call".

Jay

 

[Bob Beauchaine]

I went turbo back 4" and could feel the difference in performance plus a drop in EGT's. Check my sig for numbers.



Bob

 

[dpuckett]

I went with a 4" and noticed a BIG difference in performance over the stock barely 3". I know, I know, there is no difference on a dyno, but who spends their lives driving on a dyno? I know my boost increased by about 3-4psi, and the gauge is about 35% faster getting there than before. Dropped EGT by about 75deg across the board. SOuNDS a lot better- the exhaust flows out better and isnt crammed up by that kink over the axle; has a much mellower rumble. Cant say about a 3. 5" as the Freighliner dealer only had 4" and 5" pipe.



I'd go the extra $75 or so for 4". We ALL intend to stay at current power levels, :-laf only to need injectors, or a new pump, etc, etc. And why not upgrade? You may need a H2E or HX40, and be glad you have the 4" pipe to start with. I dont know of ANYONE who cant use a little extra power now and then.



Daniel

 

[Bluebird]

Exhaust - Done...

Excellent input from everyone, TDR First Gen forum is the best!

I had a 3" straight-pipe mandrel bent with a 14" Flow Master muffler installed. A great, clean, custom job done by Jim's Mufflers in Rialto CA (pm me if you want details on location or phone #). The first thing I noticed is that the auto shifted seamlessly, (does less back pressure affect engine trans performance?), and more go with less pedal. I don't have gauges so I don't know about EGT, or boost. Sure drives better The whole job materials, labor, and tax=$236. 00. Done in one hour .

Thanks again for all the informative replys, Patrick. Oo.

 

[tugboatphil]

Is there a 4" downpipe available for us? Does it have the heat shield, or is a firewall mod required?

 

[BushWakr - RIP]

We normally use an HX40 downpipe that is modded to fit the turbo. There is an adapter that makes the transition from the normal HX35 outlet to the 4" downpipe.

Remember, the 4" system is a real bear to get past the crossmember on the 4X4 models.

On some it will JUST make it with nearly zero clearance, on others it hits the crossmember and needs to be heated up and kinda "tuned" a bit. On others, it also contacts the/a floor pan seal and that needs some tweakin too... .

Just go into this knowing you'll need to do some custom fiddling.



IMO, a 3 1/2" mandrell bent exhaust system will have the capacity to handle the exhaust volume of an engine pushing around 350-400 RWHP.



pb...

 

[Greenleaf]

The 4" DP on a two wheeler fits great. I have never tried one on a four by four.



You have to obtain a 3 to 4 adapter to weld onto the turbo flange. This adapter must be cut extremely short to provide clearance between the back edge of exhaust elbow and the firewall.



I leave the fire-wall-protector in place, which covers the blower motor and duct work. I use the heat shield from the original DP and transfer it to the new 4".



The other mod required is the bell-housing mounting brace for the DP. It to requires a bit of reworking.



-S

 

[Lock93]

Stans Headers in Auburn (ad in TDR) fabbed a 4" downtube for my system, and made a couple models so they could begin offering it to the public. They are local for me, so it was an easy decision, but I read that others exist (PDR, Rip's, others?). Stan's was the only shop locally that could custom mandral bend anything bigger than 3". I have no clearance issues as a result.

 

[sparks57]

I got all my parts from Rip Rook. The guy is AWESOME! I did the whole system by my lonesome, and had to do a lot of fabrication (nobody sells a dualed out system like mine) but it was worth it.



There is absolutely NO WAY you're going to just add gauges... :-laf so go 4" turbo back to prepare, just in case...

 

[JStraw]

I had to change over to a 2nd gen transmission dip stick and tube assy when I put in the 4" DP.