Exhaust sizes

[Spyda]

Ive just bought a set of mk1 8v extractors and the end is about 1.6", i've been told that they are designed for high torque (but i wasn't told that the end was 1.6"). 1.6" on the exit doesn't seem very big considering the output from the head is not much smaller.
The plan was to fit them to my mk2, doing away with the duel down pipe and join it to a 2.25" cat less system but i'm thinking the 1.6" extractors to 2.25" exhaust doesn't work (or does it?)

So the change of plan was to fit them to a 2L Audi motor that will go in to the mk1 but i've been told the 8v extractors only fit up to 1.8L head and im thinking that the extractors are too small for the 2l exhaust flow. However if the extractors don't i have another mk3 duel downpipe and mani sitting around, would that be a better option?

I've also got a 1.6L k-jet motor in the GLi that im confident the extractors will fit to but im still thinking 1.6" is a bit small.

I'm interested in how to work out the best exhaust size for primarily a mk1 but also in general.
And whats the best choice and why?

[Peter Jones]

1.6 and 1.8 extractors are the same.

For a 2.0 you really need an extra 1cm height in the vertical section to suit the tall block but they often fit anyway. I'm running a set of 1600/1800 extractors on a 2.0 now (but it's got the 1.8 head on it.

There's no point in your extractor downpipes being bigger than your ports 1.6" sounds about right form the collector back is where you maesure your exhaust system diameter.

As to the perfect size for the MK exhaust, I'm going to run a mile from that argument.

Pete

[Spyda]

1.6 and 1.8 extractors are the same.

For a 2.0 you really need an extra 1cm height in the vertical section to suit the tall block but they often fit anyway. I'm running a set of 1600/1800 extractors on a 2.0 now (but it's got the 1.8 head on it.

There's no point in your extractor downpipes being bigger than your ports 1.6" sounds about right form the collector back is where you measure your exhaust system diameter.

As to the perfect size for the MK exhaust, I'm going to run a mile from that argument.

Pete

I didn't mean to say the downpipes should be bigger than the ports, i meant that it doesn't make a lot of scenes to me that the downpipes are about the same size the the exit on the collector.

I was told that these where custom made as well, i dunno if extractors cam stock on mk1s. I think you told me that yours came with the car.

So can the collector be changed to suit a 2.25" exhaust or should i just keep it and fit it to one of the mk1's? Are the gains worth it over a mk3 duel downpipe?

[roccodingo]

remember reading years ago that the primary pipe diameter should be about 1 5/8" ( 1.625 ") so your 1.6 is pretty well on the mark. The length of the primary will determine where in the rev range the best cylinder scavenging will occur.

My daily has a GTI 8V cast manifold ( factory) into the GTI twin tube downpipe, from there into a TT 2.25 system till it exits.

According to Darryl Vittone ( at TT ) the factory GTI cast manifold and downpipe pretty well matches the power output of a header system.

One little note is that the GTI exhaust manifold may look the same as your 8V carbed manifold, however it does have slightly larger runner diameters and the flange bolt spacing is greater...

HTH..

[gldgti]

i think spyda is saying that the collector output diameter is only 1.6".

this is OK, but the real problem will be that the mk1 extractors are a different shape to mk2/3 style ones, because of the subframe in the mk2/3 that isnt there in the mk1.

i would think your extractors will need work to fit a mk2 in any case.

opening up the collector to 2" shouldnt be a problem anyway, since part of it should be around that daimeter.

are these 4-2-1 extractors or just 4-1?

[Spyda]

i think spyda is saying that the collector output diameter is only 1.6".

this is OK, but the real problem will be that the mk1 extractors are a different shape to mk2/3 style ones, because of the subframe in the mk2/3 that isnt there in the mk1.

i would think your extractors will need work to fit a mk2 in any case.

opening up the collector to 2" shouldnt be a problem anyway, since part of it should be around that daimeter.

are these 4-2-1 extractors or just 4-1?

Yeah sorry i did mean the collector output is 1.6" but i went and took some more carefull measurements and the primary pipe is 1.6" and the collector output is a bit bigger about 1.8"

The extractors are 4-1

The output from the SS mk2 downpipe i have is 2.25" and the rest of the exhaust is 2" all the way through.

If what roccodingo is saying is the case then i think ill just stick the full catless system ive got on the mk2 and see if the mk1 extractors will fit the 2L audi motor, if not then on the GLi they go.

If i do fit it to a mk1 motor what size is recommended for the full exhaust and would i have to change the size if it was a side exit exhaust?

[gldgti]

Yeah sorry i did mean the collector output is 1.6" but i went and took some more carefull measurements and the primary pipe is 1.6" and the collector output is a bit bigger about 1.8"

The extractors are 4-1

The output from the SS mk2 downpipe i have is 2.25" and the rest of the exhaust is 2" all the way through.

If what roccodingo is saying is the case then i think ill just stick the full catless system ive got on the mk2 and see if the mk1 extractors will fit the 2L audi motor, if not then on the GLi they go.

If i do fit it to a mk1 motor what size is recommended for the full exhaust and would i have to change the size if it was a side exit exhaust?

i've found that 2" exhaust on a petrol mk1 seems to be about hte biggest to go without losing some midrange on a stock cam. i think a well tuned and high revving engine could benefit from something bigger, but it all depends what your doing... for a roadie, i'd stay to about 2".

[Spyda]

i've found that 2" exhaust on a petrol mk1 seems to be about hte biggest to go without losing some midrange on a stock cam. i think a well tuned and high revving engine could benefit from something bigger, but it all depends what your doing... for a roadie, i'd stay to about 2".

Cheers mate.

Thanks for all the info guys.

[roccodingo]

The 1.8 in my daily is running a 268 TT cam ( forgot to tell )

[dub be good to me]

Deleted as off the topic...