optimal exhaust size

[fastvicar]

The exit port on a K14 turbo (92 Eco) is about 2.25 in. diameter. I guess I don't see the advantage of going to a larger ID downstream of the port. I run 2.25 in. I.D. pipe.

I am no expert, but my understanding is that tapered exhausts are used on NA engines because the velocity of the hot gases slows down as they cool off.  Therefore, you will need a larger container to move the slower gases away at the same rate as the hotter gases.  Whether the exhaust gases have cooled down enough on the exit port of a K14 for a taper to make any difference, I don't know.  I do believe that a larger pipe will give a more pleasing tone to the sound though.

[spencebm]

i say if you are going to put a downpipe on it should be at least 2.5, you want to eliminate any possibility of back pressure, i would love to go 3" with my k14 if it is possible!  i just have the stock downpipe and it is a little small i think, even with 2.5 exhaust pipe.

[rabbit gti guy]

what size is the outlet on the turbo...i know on mine the 2.5" tubing was bigger already than the outlet.   is there any benefit in going even bigger than that?   i know u get more flow but if the tubing is already bigger than the port...than whats the sence

[MJF]

In my experience 2,5" is perfect up to 170hp. I could measure a little backpressure, not much but little. Dumped the exhaust, drove with only 3" downpipe and got 0,1 seconds off 1/4mile time with gtech Now I have all 3"

[burn_your_money]

i say if you are going to put a downpipe on it should be at least 2.5, you want to eliminate any possibility of back pressure[/i], i would love to go 3" with my k14 if it is possible!  i just have the stock downpipe and it is a little small i think, even with 2.5 exhaust pipe.

From what I've read I don't agree with the bolded part of your statement. If you have no back pressure post turbo you will over spin the turbo or your wastegate will constantly be open. The post turbo restriction slows the rate that the exhaust gases can pass the turbine.

I believe Dave said that a 3" is too big for the K14 but I'm not positive

[giulianot]

this was originally posted by 935 racer in the vendors section under 3" downpipes ". The reason is that exhaust post turbine can expell quicker than it can exit the engine due to the small turbine, the downpipe can move more volume than what is capable of being pushed though the tiny turbine and the manifold pressure increases."

[935racer]

this was originally posted by 935 racer in the vendors section under 3" downpipes ". The reason is that exhaust post turbine can expell quicker than it can exit the engine due to the small turbine, the downpipe can move more volume than what is capable of being pushed though the tiny turbine and the manifold pressure increases."

That was in regards to turbochargers that are too small for the application, like k14, t2, vnt15, etc. With larger sized turbo the reason you want to go with a bigger tube than the outlet of the turbo is that the exhaust gases are EXPANDING, hence the need for bigger tubing to help drop the pressure that you would see with tubing the same diameter of the turbines outlet.

[935racer]

In my experience 2,5" is perfect up to 170hp. I could measure a little backpressure, not much but little. Dumped the exhaust, drove with only 3" downpipe and got 0,1 seconds off 1/4mile time with gtech Now I have all 3"

Do you have any pictures of your 1.7 IDI engine bay, and some dyno sheets or other details? I'd love to build a 1.7 myself.

[giulianot]

thanks for clearing that up for us Dave :wink:

[burn_your_money]

So what would be the recommended size of a DP/exhaust for a 1.6TD that's stock but has a K14 on it?


From what you are saying you can't have too big of a downpipe regardless of turbo size?

[935racer]

So what would be the recommended size of a DP/exhaust for a 1.6TD that's stock but has a K14 on it?


From what you are saying you can't have too big of a downpipe regardless of turbo size?

No what I am saying is you can have too big of a downpipe if your turbo is too small, like a k14. If you have a larger turbo and especially if you have a really big turbo you can't have a downpipe too large.

[burn_your_money]

No what I am saying is you can have too big of a downpipe if your turbo is too small, like a k14. If you have a larger turbo and especially if you have a really big turbo you can't have a downpipe too large.

Logically I can't make sense of your answer :?

[MJF]

In my experience 2,5" is perfect up to 170hp. I could measure a little backpressure, not much but little. Dumped the exhaust, drove with only 3" downpipe and got 0,1 seconds off 1/4mile time with gtech Now I have all 3"

Do you have any pictures of your 1.7 IDI engine bay, and some dyno sheets or other details? I'd love to build a 1.7 myself.

Didnīt find any engine bay pictures. Looks like any mk1 1,6td with Vw LT intake  :lol: Dynosheet is here, unforunately without revs and torque Max hp ~4700 continues straight to ~5500 and calculated max torque ~350nm@4200

[rattler]

After the c-clamp shelf rusted off the downpipe on my 91 TD I modified the downpipe and from a newer TDI and bolted it to the turbo; it already had the flexpipe and is a much nicer setup than the original.

Just last week I backed into a frozen snowbank and broke the muffler clean off. I'm currently looking for a cost effective replacement as I travel 2 hours a day on the highway and the slight increase in noise is annoying.

Will the $50 generic mufflers that most parts stores carry work ok? Is there a desirable inlet/outlet size? I have replaceed most of the exhaust with 2" as it wears out.

Has anybody tried a Cherry Bomb? Low cost but I don't know how it would sound on the TD...

[bevboyy]

Cheery bombs work fine. I used two on my wifes Quantum. 1 as resonator, the second as muffler. Ran 2.25" mandrel bent all through, including downpipe. You could really hear the T3 spool :twisted: