A Question of Exhausts

[Snikty]

My question has sort of been touched on already a while back in this thread..

http://www.micra.org.uk/showthread.php?t=21401

But I just wanted to bring it up for discussion again coz I really feel like there is two solid schools of thought on this subject.

My aim with the performance of my car will be for doing qtr mile runs (I'm too scared to put it in circuit due to damaging body parts). I did some playing around with getting used to my take offs with the car etc and on 175 tyres with 98.6bhp, I found that getting revs up to about the 5.5k mark was giving me my smoothest take offs without loosing too much traction.

Having said that, it would appear I am running the car entirely in turbo range and it would stand to reason that a bigger exhaust would be optimal for my turbo usage.

However, if I got the appropriate supporting mods to be running figures like baz and Ed (say 150-180bhp) would it stand to reason that you could better utilise the sc? Then set up the exhaust so that it had a decent amount of back pressure (like you would on a car that was only sc) to allow better takes off through 1st gear and then just make sure you didn't have too much back pressure to be damaging your turbo so that you could then drive it like a standard turbo car through the rest of the gears.

I'm just spouting half-educated theory for now but thought it was worth discussing. I am thinking that with the exhaust I get now I will go for a bit of back pressure as it is only going to be used as a run around car for the next few years and I rarely need to use the turbo.

I'd be interested in hearing what you all think

 

[Baz]

My question has sort of been touched on already a while back in this thread..

http://www.micra.org.uk/showthread.php?t=21401

But I just wanted to bring it up for discussion again coz I really feel like there is two solid schools of thought on this subject.

My aim with the performance of my car will be for doing qtr mile runs (I'm too scared to put it in circuit due to damaging body parts). I did some playing around with getting used to my take offs with the car etc and on 175 tyres with 98.6bhp, I found that getting revs up to about the 5.5k mark was giving me my smoothest take offs without loosing too much traction.

Having said that, it would appear I am running the car entirely in turbo range and it would stand to reason that a bigger exhaust would be optimal for my turbo usage.

However, if I got the appropriate supporting mods to be running figures like baz and Ed (say 150-180bhp) would it stand to reason that you could better utilise the sc? Then set up the exhaust so that it had a decent amount of back pressure (like you would on a car that was only sc) to allow better takes off through 1st gear and then just make sure you didn't have too much back pressure to be damaging your turbo so that you could then drive it like a standard turbo car through the rest of the gears.

I'm just spouting half-educated theory for now but thought it was worth discussing. I am thinking that with the exhaust I get now I will go for a bit of back pressure as it is only going to be used as a run around car for the next few years and I rarely need to use the turbo.

I'd be interested in hearing what you all think

I'm pretty sure back pressure is not that important in these cars?I'm running no cat,2 1/4" pipe wit two small silencer boxes one in the middle and a back box.I use to have no middle box but the car sounded like a tractor:grinning: on s/c and low rpm

 

[Ed]

First of all back pressure = bad ALWAYS.

Its simply a misconception, secondly. You want to use power so you will always be in turbo on a 1/4 mile. You want at least a 2 inch system. Idealy from the turbo back. The standard down pipe inc cat is pretty horrid.



Above shows one I experimented with, it seems to work fine.

There are so so many areas to improve on the ST its pretty strained as standard. Be warned however, above 150-180+ it seems only a matter of time until headgaskets will start to fail.

 

[Snikty]

OK cheers for that lads, that all makes a lot of sense. Thanks for the pic too Ed, that is a very neat job.

Unfortunately we cant get rid of cats over here, but I'll see if I can try and get it done from turbo back. From what I can see the down pipe is the part that's currently in the wost shape so I assume my mechanic is planning to do the lot. I'll let yas know how it goes.

 

[Ed]

Can you not remove the cat from the oem location and fit a new high flow cat further down the pipe?

How strict are they on emissions over there? Is there anything to say the car had a cat in the first place?

 

[Snikty]

Yup I think I can put a high flow in further down, and will definitely be looking into that.

I'm not entirely sure how strict they are but am pretty sure that if it didn't have a cat on it when it came over I'd be forced to put one on it to register it...its pretty lame...

 

[smidge]

the rules are a little vague for a car thats this rare... i've still got the crappy down pipe i believe and was about to post a thread asking about if but you've saved me the trouble, i might change mine out when i fit a different (and locally available) turbo

my exhaust is 2 & 1/4 inch, straight off the down pipe, into a small straight through muffler (not a crappy hot dog, proper packed muffler) then into a HKS dragger big muffler on the back, nice not and not too annoying when cruising

 

[Ed]

That will do the job, I have a 2.5 inch system with muffler at the back. Its loud possibly a bit too much, but it suits the car and its intended purpose fine.

 

[Snikty]

I just checked it out and it appears that all cars in oz manufactured after 1986 must have a cat fitted, so we got no choice smidge

Thanks for that guys I've a very good idea of what I want now but may have to delay it for a month or two to afford it...but I'd rather wait and get exactly what I want...hopefully i wont have to tho

 

[smidge]

yeah sounds like the go, i'm definately going to throw a different turbo on, i want to be able to blow them, walk down the road and get a new one and fit it in an hour, probly a decent T25 or something close to the same size, i only wanna run about 15-16 psi absolute max so as long as it can do that efficiently then i'm happy as

will get a new dump pipe made up then and put a high flow cat in there instead of the stock dump, i'd run a cat even if we didn't have to