Exhaust sizes - what works?

[Glenn 'Stinky' Stankevicius]

that was my understanding too, i guess if you wanted to you could weld the back doors shut, and then you could dump it out the side
seen it done but not a big fan of it.

Yeah, it'd make it hard for the passengers to get in and out 

[smithy]

Yeah, it'd make it hard for the passengers to get in and out 

easy fix, put a roll cage and wheel tubs= no beckseat passengers
seems like a long way around for an exhaust though

[Revhead_Fc]

yeh but a good way and hey if your going to do that why not put something decent under the bonnet too

[Spinner]

You'd also have to fix the windows shut.

[NO NAME]

I think from memory the exhaust has to finish 100mm past the last passenger door opening to be legal, that was why Ute's and Van's were allowed side pipes but not sedans and wagons .....FC427.....

i think its more like 50mm past the last welded seam and some distance past the nearest opening window.
 i think there is a rta error, or maybe its only in ACT that allows sedans to run side pipes without the rules but wagons, utes and vans have to comply.

[smithy]

no we are pretty much the same here leon, im pretty sure its 100mm past the last opening door.

[Ol_Girl_58]

Hi again guys,

Thanks again for your input.

I'm leaning towards a twin system, mostly because the car had a twin system long before I had it back in the 70's/80's - and I like the sense of nostalgia harking the car back to its roots. Plus it will keep everyone guessing when I'm stopped at traffic lights 

So, two questions follow:

* What set up/exhaust size etc. is best with a twin system so that it won't sound raspy/sound horrid at idle or full noise?

* Where is the best place to split the exhaust?

Thanks again,

Ol_Girl_58

[FC427]

Hi Josh cut the collector off the extractors and start your twin system right from the front as for size of pipes twin 2''pipes would be large enough for a 350hp engine with no problems but I like the look of 2.5'' exhausts .......FC427......

[waynos]

i've been told i shouldn't go  bigger than 2 1/4 for my 186 cause i will lose bottom end power.is this somewhat true?

[NO NAME]

ive heard of it but you never seem to dyno evidence, A bigger pipe gives most of its advantage when rpm is high but why would a restriction give more power down low?
 

[waynos]

i guess you lose bottom end torque  i meant to say
guess it depends if ya wanna drive it or race it or both(then its just a compromise)

[NO NAME]

i am not a exhuast expert but afaik there is no advantage of a small pipe, the only disadvantages of a big pipe is they are harder to weave through all the other stuff under the car and they are louder, more expensive pipe and less ground clearance.
 has anyone really seen a dyno improvement down low when a smaller exhaust is fitted, what do the exhaust systems look like were low down torque is needed, what do they look like on tractor racers or those 4wd comps were they pull loads, do they fit a smaller pipe, what do they do on ski race boats were there is no db limit and they can have what ever size pipe they want.
 a lot of exhaust shops say big pipes loose out down low but were is the proof, i think its a mix up from hearing big pipes give more high up, i am sure big pipes give just the same down low.

[2door350]

Ahhhh... This is a topic that interests me greatly, I have tried many pipe length/diameter combinations based on research on exhaust scavenging\pulse tuning.  There is a book called "the scientific design of intake and exhaust manifolds"  that was written some time ago and contains heaps of great info and formula's.  In a nutshell A primary header pipe 1 size too big can produce roughly  a 20% decrease in torque!!! You are better of one size too small than one size too big...

Diameter of pipe determines how hard your engine will scavenge (come on pipe) and the length will determine when scavenging will occur...Its a complicated and often miss understood science.  Have a look at the "Headers by ED" website for some more insight..

All my work has been done with x2/xu1 style headers...i have tried different combo's on the dyno with different engines....

so here goes.....

For a 202 the best street/torque combo is 1" 3/4 mandrel or 1" 7/8 crush bent and sixty inches long from header flange to muffler.  Your 2 pipes must enter a very large volume hollow design muffler immediately at their union and must be same length (1" difference is acceptable). Muffler to be at least 2 1/4 inlet and pipe afterwards doesn't matter as long as it is 2 1/4 or bigger.   I like the sound of 2.5"... This will produce  great power/torque  from 3000 to 6000 rpm

For a 186 you need same setup but with pipes 45" long for a sweet spot of 3500-7000....

An old timer speedway mechanic, since dissapeared, got me hooked on this about 10 years ago and it's taken a long time figure out.....

I was hesitant at first to share this info but i know it can be put to great use....

My current 186 produces 117rw/kw and runs a standard port head,a monster 308 duration solid cam and a 465 Holley.   Its entirely streetable idles at 800rpm and pulls hard from 3300-7000rpm and happily revs to nearly 8000rpm. I run a 2.92 diff and it will still pull in top gear from 1200rpm

hope you find this interesting/helpful

2door350

[Ol_Girl_58]

Thanks 2Door350.

This info is both interesting and helpful! 

Cheers,

Ol_Girl_58

[2door350]

In my opinion ,whatever you decide, go see shane at City Car Centre on brisbane street, he does the neatest systems by far....good luck, have fun

[waynos]

Sorry to get back to this topic but i believe a smaller pipe which obviously is hotter, somehow draws the gasses out better than a too large diameter pipe or whatever.cold air somehow minimises the flow.perhaps at low revs the bigger pipe ican't create this vacuum effect aswell(i'm no physicist)

[ratbox]

all i can say is just drove my car basically stock 202 with open extractors, then had a muffler 2" conected, but from muffler back is standard size 1.1/4"-1.1/2" exhaust and the difference was noticable

[waynos]

ratbox,were you towing ?haha this is what i'm curious about not that i am going to  what i always have been told is this bottom end stuff,which never bothers me cause i love the revs .can see how a smaller pipe works better in a towing situation you're not speeding off from the mark.i wanna go 2 1/2 but everyone tells me otherwise.heard also ya need a huge cam for a huge exhaust .