So, as i've posted elsewhere, my plans are to do my auto to manual trans swap by this spring at the latest. with the new year just about here (and more importantly, the finished basement for the kids almost complete), i'm starting to plan a little more in earnest and ready to pull the trigger on buying the needed parts (and gathering from junk yards, of course).

i'm planning to replace my stock downpipe while i have the tranny out, and was looking for some advice on size. it seems that a 3" downpipe is the standard on these trucks, but that a 4" is possible and obviously better for flow. i don't have any real performance mods on my truck now, but i'm a big fan of not doing work twice, so i'd rather just do the 4" DP now if i can, and leave the exhaust system headroom for increased performance down the road - so to speak.

Since the 3" DP requires some bending of the firewall seam to make it fit, it only stands to reason that the 4" DP will require more 'persuasion' to fit (what with the extra 1/2" on the radius). it seems that some folks have made it work, though and i'm just wondering how?

is a body lift required? i'm not a big fan of body lifts, but i do plan to replace my body mounts at the same time as the tranny swap - so, blocking the cab up an extra 1" wouldn't really be any extra effort. (and yes, i plan to swap my bed with the better one from my other truck soon, so i'll block that up as well if i go this route).

just wondering if there are any other considerations i'm overlooking and if anyone out there with a 4" DP on an OBS has any advice. would a 1" body lift be enough? is there a better way about it?

Thanks.

 

I dont think it would do you any good unless your running big injectors, a good intercooler, and a larger turbo. IMOP

 

The size of the EVPB is 3" diameter, so the 4" DP is overkill and you have to make more mods (lift, more massage over the fire wall, etc), the best thing is go with a DP that goes from 3 to 3 1/2 to 4" at the end. IMO

 

Agree with Jose. I have a tymar 3-4" dp, fits great. Unless you're going for MUCHO horsepower, that 4 inch dp won't gain you anything but a major headache..

 

Like other have said. The turbo outlet is only 3" so just stick with the 3" DP. 4" will get you Nothing other than headaches

 

Unless you do a s366 ,maybe like the irate kit glenn,gabe just are doing.that turbo outlet I believe is 4" .....plenty of guys with mucho power not running 4"dp.

 

There are plenty trucks making 500+hp with a 3dp

 

Its possible the guys didn't understand your post ...
I realize you didn't come here for opinions on if you should or not .. If you want a 4" DP go for it .. Worst case , you can loosen the body bolts (6) & move the cab back if you wish .. It will fit ...

 

4" DP will NOT fit without MAJOR modification to the fire wall or at least a 2" body lift

 

thanks for all the feedback, guys. definitely a good point made by many that the turbo outlet is 3". i like the compromise option as quoted above. didnt know that a gradually expanding DP existed. can anyone recommend where to buy one? i'm guessing its a few bucks more than ~$90 3" diamond-eye i've been looking at, but i'll be saving a few bucks on adapters i'd otherwise need to go from 3" to 4", so hopefully its a wash in the end.

someone posted about an 'irate' downpipe. is that the brand of the expanding DP?

 

I know that Dale at TYMAR sells them, google Tymar and call him.

 

emailed him yesterday (couldnt call from work), and he wrote right back. he carries the hypermax line of downpipes and his prices are fair. he has a 3" to 3.5" DP so that you can keep the stock exhaust system - or at least the cat, and also has a 3" to 4" DP that would obviously need a rework of exhaust system behind it. i think i'll take the gamble at go with the 3 to 4" system, lose the cat and determine whether i want a 4" muffler once i have the truck running again.

my local PA inspection station let me go without a muffler this past year - i might as well push it a little further and go without the cat as well this year. with the pre-98 (?) diesel exception in PA, there's no emmissions insepection other than a visual one that the exhaust system is 'in tact and not altered from factory configuration' or something like that. i've heard this interpreted that if your truck had a cat and muffler when shipped from the factory, you can't remove it. clearly not the case with the muffler - or at least not enforced with me last year... anyone out there from PA have any experience with this?

 

I havent had personal experience with smog of any sort cuz IL doenst do that (about the only law others states have that IL doesnt have) but I have heard from friends in states that do that they typically are strict with the 'visual' inspection, so my recommendation would be to at least leave the Cat on there, but gut it so its really a straight pipe.

Your experience clearly shows they can go easy on you, but I wouldn't risk having my truck taken off the rode cuz of it.
You can gut a muffler and a cat and just weld it into your straight 4" pipe and it can look factory.

Just a little larger..

 

Also you could order a coated DP from him as I did, ask for the price now, I recomend it.

 

good point. maybe i'll go with the no-cat, no-muffler, fingers crossed approach first - as long as it doesnt sound too ridiculously loud to me. then, if they call me on it, i'll put the gutted/4" in/out welded cat back on. i'll only be off the road as long as it takes me to gut and mount the "cat". if the straight pipe config is too loud for my liking, i'll be going with a straight through muffler and no cat, so hopefully that would pass the visual inspection...

he did quote me the coated version, but its about $100 more. since i don't tow and don't make huge amounts of power, i didnt think it'd be worth it for me. i was thinking of wrapping the DP in some fiberglass tape, though to accomplish something similar.