KB downpipe with stock headers/turbo

[canadian]

Thanks to Josh for hosting the pics. Geoshitties sucks.

It is true that the KB downpipe won't work with the stock headers and turbo the way it comes, but with a little cutting a rewelding, it'll work just fine. I bought a used KB downpipe from someboey (can't remember who) in the classified section and figured that there's gotta be a way to make it work.

First thing is that the KB downpipe comes in two sections. The upper section bolts to the turbo and the lower section slips into the cat. The joint between the two is flared so the upper portion can slip into the lower portion and away you go.

Since the KB header/turbo combo locates the turbo up and away from the motor, just bolting the DP on isn't going to happen. You can see the mismatch here:

You can see how the lower half of the downpipe comes up between the motor and the frame rail just like the stocker. Since this is the same, the portion that will need to be modified is the upper half of the downpipe.

The upper half of the downpipe is cut right behind where the 02 sensor mounts, and the portion that bolts to turbo needs to be rotated so that the bolt holes line up. The only problem with this is that it puts the 02 sensor farther away from the motor. You can either drill a hole and weld in a new 02 sensor bung, or make the 02 sensor wires longer.

You can see where the upper portion was cut and rewelded in the following picture. It's the weld right after the 02 sensor bung:

I had to trim and inch or two off of the upper half to make sure it lined up with the back of the turbo and the lower half of the downpipe. With all that said and done it wasn't that big of a deal, and now I have a downpipe with no nasty crimp bends like the stocker. Here's the comparison:

And all mounted and ready to go. Need to work on the O2 sensor wiring now. I painted it with high temp header paint. Guess I'll see how long that lasts:

 

[Ian Turgeon]

lots of not workin there warren...

oh, btw.. what did you need (email sent to me)?

 

[canadian]

what's "lots of not working"?

question is where are you registered?

 

[Ian Turgeon]

every one of those bad boys are red x's

bed bath & beyond
& home depot gift cards are workable.

 

[TheObiJuan]

have BW host the pics.
his server is always up.

also, if you copy and paste the pics hyperlinks into an internet window and view them, the next time you view this topic they all show up.
dunno, works for me.

 

[canadian]

Josh is hosting the pics now. Should work for everybody.

 

[bdubb]

can you still reach all the plugs with the DP in?

 

[0-60N4]

Question: Could you have rotated the flange 180 degrees and put the O2 sensor on the other side and have the wiring reach?

I have an extra KB downpipe if anyone is interested. It has also ben Jet Hot coated silver inside and out side.

I would recommend mounting to the turbo and making the modifications/extension to the bottom end.

 

[canadian]

you could probably cut it right after the mounting flange, and then rotate it that way to get everything to line up a bit better. since i cut the dp after the 02 sensor bung, i was kind of stuck mounting it to the back of the turbo that way so the everything lined up.

 

[E-Rue]

soooooo............ what is all the hoopla with this downpipe?

it looks like its the same size as a stocker and it has a LOT more bends in it. so im guessing any gains made by the mandrel bends are negated by all the additional bends?

i just dont see why its any better?

e

 

[0-60N4]

It's slightly larger in diameter than the stock DP. In my opinion, it's a comprimise between stock vs. buying or fabricating a full 3" DP since there are several KB DP's available from people that have gone to big turbo's and custom DP's over the years.

 

[canadian]

the only "extra" bend (and it's not reall extra) is a the top of the downpipe near the 02 sensor. then look at how crimped the stock downpipe is at each of the bends (especially at the bottom portion where it bends to go under the truck).

find the smallest opening on your downpipe (typically where the crimp bends are) and measure the actual area inside the downpipe available for flow. that will be your limiting factor. the kb downpipe is mandrel bent all the way through so you're going to have 2.5" of downpipe the whole way.

let's say (for shits and giggles) that at the worst kink bend in the stock downpipe limits the flow area to 2.25". the area of a circle is pi r^2, so:

2.25" = 3.14159 * 2.25^2 = 15.904 sq in. (approx)
2.5" = 3.14159 * 2.5^2 = 19.635 sq in. (approx)
3.0" = 3.14159 * 3.0^2 = 28.274 sq in. (approx)

(is this right?)

so going to a mandrel bent 2.5" downpipe will allow more flow than the stock downpipe. since an atr 3" downpipe is assloads more expensive than an old used kb downpipe i figured wtf, why not try it. i also have a te44 with the atr 3" sitting in the garage as well so i might not even use this one.

can anybody out there in syty land tell me if i'm waaay off here? i'm just pulling numbers and theory out of my ass at this point, but it sounded good to me.

 

[Blake]

I looked some stuff up on pnuematics several years ago when the dual 2 1/2's versus single 3" pipe wars started and plugged some numbers in. Surface area isn't the only factor. The formula came out of the "Engineer's Handbook" that I picked up at my local library. I took 8' of pipe 3" in diameter and 8' of pipe 2.5" in diameter and flowed 1000cfm through it at 200 degrees F(plugging in the numbers). Results surprised the hell out of me. The one 3" pipe flowed just slightly less, I mean SLIGHTLY less, than TWO 2.5" pipes TOGETHER. The 1/2" didn't seem like squat until you start plugging things in. There are doubters out there that do not like formulas but if they weren't in the ballpark, why would they have them? 3" is the way to go, in my opinion, since I saw this. No flames, just what I saw. Now this was just straight piping. If I remember right, curves of specific degrees could be factored in. I'll go look if you guy are genuinely interested and see if I can find the book again or an updated version and run the numbers.
Blake

 

[canadian]

i don't disagree with what the numbers told you for two 2.5" pipes vs. 3" pipe. don't suppose you could run the numbers for 2.25", 2.5" and 3" single pipes and see what you come up with? in this situation we're talking single pipes when it comes to the downpipe, the rest of the exhaust is a different story though.

 

[E-Rue]

look at the pics again.

the KB looks like its doing a lot more bending.
keep in mind air flow characteristics, and how air moves more to the inside of a sharp bend than a mellow bend. there might be slight gains to be had from this upgrade, but my gut feeling tells me its not much. after all, a 3" DP only offers so much peformance over a stocker (all things being equal) and thats not anywhere near 3"

e

 

[canadian]

anybody have a flow bench they can test it on?


:new-bday: to me!

 

[Blake]

The numbers were run both ways. The 3" flowed almost as much as two 2.5" pipes(2.5" side by side running same amount of air through them). So a 3 inch flowed nearly twice as much as a single 2.5"(roughly). Been a while but pretty close.

As far as air moving one way down stream and a different at the other end....air doesn't care where it is at. In reality as air(or any gas) cools, more will fit in a fixed space. So as it approaches the tailpipe, the same pipe will flow more, kinda accellerating out as it cools. I may have misunderstood the point that you were trying to make. I'm not above that.

I don't disagree with you at all, E-RUE. There were some additional factors for degrees of bend. When I did HVAC work, I got to see first hand what would happen at a bend. Image a duct 4' wide by 2' tall and a 45 degree sweeping bend. The air tried to hold its line. You could feel where it would "cram" where it would hit the bend and really pressurise about 1/2 the opening. As you moved your hand to the other side of the opening you would suddenly have little to no air mov't. It was a little over 1/2 way across where the change happened. If bends are kept to a minimum though, 3" greatly outdoes the 2.5" or the 2.25" whatever the stock downpipe is.

What is the diameter of the KB downpipe? I thought it was advertised as a 3"?? If not, I'll definitely run the numbers. If a KB is only 2.5" diameter, I would rather have the 3" ATR. Just me though.
Blake

 

[canadian]

the kb is around the same size as the stocker if i remember correctly. the only benefit is that it's mandrel bent and not crimp bent. it would be nice to have some back to back testing, but that's not in the plan right now.

try pricing out the difference between a used kb downpipe and a used atr donwpipe and i'm pretty sure you'll save cash going with the kb, but it might not be worth the cost and effort if you plan on replacing it with a 3" downpipe down the road.

if you can pick one up cheap and do the mods yourself it might be something to test out at the track and see if you can drop the e.t a little bit or not.

 

[syclone3]

Re: KB downpipe with stock headers/turbo

I had a new KB DP left from my built truck as I made a 3 inch for its Garret. So I cut up and TIG welded the KB DP up for my stock turbo beater Syclone. Got the O2 to sit on top like the stock DP
Had to lower the small section down quite a bit as this thread shows. Also took a bit out back near where the stock DP bolts to the bracket on the side of the trans. Once done 1500 degree painted it then heat wrapped it past the trans. Wrapped the crossover pipe. Truck spools a little quicker and is quieter. Also took out the stock mufflers and used Dynomax straight through race mufflers. Old lady who had this truck had a new dealer exhaust on it and even in this dry climate they were rotting out. Rest of exhaust was fine. Truck is so quiet now with all the exhaust changes and no cat. Plus I like the stock twin tailpipe look. Not worried about the systems weight. Just trying to make max power on the stock turbo to run lower 12's.