1.6 na what should i do

[shegel]

im going to be rebuilding my 86 golf within the next month or so. i have purchased a gasser intake manifold as my valve cover wont allow me to properly clamp my na box down. and i have also purchased a dual downpipe exhaust manifold. what size exhaust should i run with this setup to see the best drivability increase. i was thinking 2 inch but i might go to a turbo later so i was thinking 2 1/4? do these little diesels need the exhaust for backpressure. (the 93 f-350 idi that i have has 2 1/2 dual exhaust all the way back with no muffler or cat or anything just strait pipe.)

thanks,
steve

[Vincent Waldon]

NA diesels don't require any backpressure for scavaging like a gasser does, so you can pretty much go as big as you can afford... although most would say the difference between 2.5 and 3 is perhaps not worth the trouble.

I've seen some discussion about how it *is* possible to go too big with a turbo... don't quite understand it yet so hopefully someone will enlighten us both !

As far as I can tell somewhere around 2.5" seems to be the sweet spot for price vs performance (haven't done side-by-sides myself) but perhaps someone has and can chime in.

[RabbitJockey]

yeah ive heard about being too big with a turbo before, my friend as a wrx with a 4 " dp and the place the dynoed it told him it's too big

[Turbinepowered]

yeah ive heard about being too big with a turbo before, my friend as a wrx with a 4 " dp and the place the dynoed it told him it's too big

I can definitely see too big on a gasser, 'cause of the whole backpressure requirement, but on a diesel?

[RabbitJockey]

i think it has more to do with how the gas flow.  yeah its gas but it has a turbo so obviously it has all the back pressure it could ever need.

[shegel]

so the final verdict is.....without turbo any size pipe can be used.


with turbo. exhaust size is limited to 2 1/2 ?

[shegel]

[riddleyo]

There seems to be a misconception about back pressure here. Back pressure is absolutely not wanted on gas or diesel engines. It is a myth.

When you size an exhaust way too big, what you are doing is reducing the exhaust gas velocity. Reduction in velocity results in a reduction of scavenging ability.

It is the same principal when porting cylinder heads. You don't want to hog out the ports way too big because your velocity will suffer.

[nokivasara]

If velocity decreases the pressure increases, at least it did back in school when I studied aerodynamics  :lol:
One just needs to find the sweet spot where the velocity, temperature and pressure is optimal, might aswell buy a lottery ticket...

What´s the dual pipe exhaust manifold you´re using, is it from a gasser?
Is it even possible to gain power with a header on a low revving diesel?
Would a free flowing manifold and pipes reduce smoke?

[dieselwagen]

gasser manifolds on diesel engines are worthwhile upgrades..theyre cheaper and easier to do compared to force induction, and engine longevity is not compromised considering this is being done on a bone stock engine internals. caution on going bigger than 2.5" exhaust system, vw dual downpipe flange diameter is 2.5". and in order to maintain proper velocity, apply the "garden hose" principle when designing your exh. system....you may also find the compression ignition "noise" to be somewhat sweeter sounding resonating against the aluminium intake compared to the n/a plastic.

[dieselwagen]

bravo shegel.!!!..you repowered a karmann ghia w/ the right engine..that was my dream car..how's that thing run.?....good luck on your '86 golf

[RabbitJockey]

i don't see the benefit of a gas intake manifold over the stock na manifold that has a larger snorkel.

[jtanguay]

i don't see the benefit of a gas intake manifold over the stock na manifold that has a larger snorkel.

plus the n/a intake has long runners.  good for torque  :wink:  not as long as some other manifolds available though...

[shegel]

well the problem i ran into is that my polo g40 valve cover is too close to the na box so i cant seal it on the front. thats why i got the gasser intake. i think i'll go with probably 2.5" but im not sure i think 2.25" might be a happy medium. i havent gotten the downpipe for my manifold yet so its still not in the car.  :roll: just waiting to get out of school to do the engine work

[nokivasara]

im going to be rebuilding my 86 golf within the next month or so. i have purchased a gasser intake manifold as my valve cover wont allow me to properly clamp my na box down. and i have also purchased a dual downpipe exhaust manifold. what size exhaust should i run with this setup to see the best drivability increase. i was thinking 2 inch but i might go to a turbo later so i was thinking 2 1/4? do these little diesels need the exhaust for backpressure. (the 93 f-350 idi that i have has 2 1/2 dual exhaust all the way back with no muffler or cat or anything just strait pipe.)

thanks,
steve

What models have the dual pipe exhaust manifold? The ones I found did not have the right bolt pattern, my manifold has 2 bolts/port.