nom

Thought that this might be interesting to a few of you.

This is a fairly direct comparison of two exhaust systems, run within an hour of each other on the same car with the only thing varied being the centre section and the back-box.
The downpipe (the same in both tests) is the full 3" BPM one; the 2.5" system is the TSL 'original' backbox & straight-through centre (don't think it's TSL but it's just a tube, whatever), and the 3" is the H&S/Scoobyworld 'Afterburner' one. The Afterburner is serionsly loud in comparison to the TSL one, in case anyone was wondering
The map was adjusted for fueling between the two (beforehand so the runs could be in as similar as possible conditions), but that was all. The eventual AFR was as similar as possible in each case.

The information was evaluated by DataLogLab over a run in 3rd - both on exactly the same bit of road, from the same point and repeated twice to withing 1bhp.
I've probably got the weight of the car wrong so pay attention to the differences rather than the actual numbers although they should be 'ball park'
And yes, it's a UK, so it doesn't rev that high & I don't rev the pants off it either



Ignore the very bottom bit of the graph. Kludging gears is a great plan

So, peak power is up by 18bhp (ATW), torque by 17 lbft from just changing to a less restrictive system. The peak torque is also almost 1,000 rpm higher up on the 3".
Noticeable as well is the HKS headers which come 'on song' at around 4k4rpm (look at the torque curves - maybe a bit of a guess that this is what's going on here, but Merv(PE) & I both hqve noticed the HKS doing this on different set-ups) - not noticeable with the 2.5" system which is obviously causing a restriction, but the tubular headers are showing what they can do (and I might put the oem headers back on again to do another run, just to see what difference they make. I'll see how busy I am...)

It's a shame I kludged the gears on the 3" system - I had a plan here to see if a system that's more restrictive behind the turbo brings torque in earlier on or not, as is being discussed at the moment here & there... I'll see if I can find something more
useful on another graph (I took a few! )

I don't intend to make the TSL look bad (it isn't) or the Afterburner look good (although it does ), just show the restriction of a 2.5" system over a 3" in a medium- powered car. I'd just like an exhaust with the 2.5" noise levels & the 3" flow... roll on the new PatTech exhaust

Anyone else got direct comparisons between two bits of kit?

[Edited by nom - 2/18/2003 10:42:22 PM]

john banks

Thanks Nom. Pat's system sounds promising. Waiting to hear his impressions of the sound on an Impreza with OEM headers before I go for it. Noise is an issue for me as well. Have T-uk's Blitz Nur Spec BB on it at present and it makes the whole thing feel like a 3" - which it is until each end of the centre section.

[Edited by john banks - 2/18/2003 10:28:52 PM]

Beastie

iTrader: (2)

I think that also adequately serves to demonstrate the effect of exhaust on low down torque.
Beastie

nom

Except, check the run - the one with the 2.5" starts at ~1,500rpm, the 3" 2,400rpm. And the turbo takes its time to get going.
I wouldn't put too much into the low rpm - it wasn't particularly what the run was for!
I should have another to compare it to somewhere that starts of low down, I just need to gather the enthusiasm to pull it out

Beastie

iTrader: (2)

Nom
yes, thats what I meant, a slightly more restrictive exhaust seems to give more torque down the rev range according to your graph.

I found with my PPP exhaust back box I had more low down torque, whilst with my scoobysport backbox the low down had gone, replaced by more top end power. However, just based on "feeling" no results to back it up.

Many other people have reported similar findings though and I thought that maybe your graph was some proof of this.

I am now looking for 3" exhaust system to fit after your results!

I look forward to seeing your other graph.

Beastie

Gussie Cup

When I put a 3" Mongoose system on, I immediatly noticed that the torque lower down the rev range wasn't so available - felt like it came in much later - didn't feel like there was much before 3800 rpm.

But, its a lot less restrictive and as the turbo spools up (and the revs rise), it really pulls and both torque and power 'overtake' the standard setup.

A re-map should replace some of that torque and it feels so much better at the top end that I think its worth doing.

On the subject of noise, the Mongoose isn't too loud at all - even without any cats, although you can hear its noticeably louder than standard, it wont set off any car alarms as you go past!

A good compromise - incidentally on a RR with standard exhaust the car was putting out 244bhp (can't remember the torque off-hand)

After fitting the Mongoose full system and an HKS Induction kit it read 285bhp. This was on the same day just an hour or so later so I was quite impressed with its abilities.

Wish I still had the graphs but this was a couple of years ago now...

Ben

Pavlo

What nom is saying is the power run with the 3" exhaust was bolloxed up, and that it would normally show MORE low down grunt, not less.

paul

Beastie

iTrader: (2)

Pavlo
aah, I see what you mean. 3" it is then!
Beastie

Gussie Cup

But Pavlo, with a 3" exhaust, isn't there less backpressure therefore causing it to take longer for the turbo to spool up?

Wouldn't this mean the torque comes in later?

Ben

john banks

High EGBP results in less pressure differential across the turbine = poor spool. That is why an exhaust often makes a car overboost.

Gussie Cup

John - EGBP? Assuming this is to do with backpressure?

Are you saying that a more restrictive exhaust is more likely to overboost than a less restrictive one or vice versa?

From my own experience, once I had the Mongoose on I regularly suffered from overboost and spent my time 'driving around it'

Ben

nom

Before everyone gets carried away reading stuff into the low rpm bit, as I've pointed out 3 times and Pavlo once, the run - low down - was different in both cases & below 3,500rpm should largely be ignored.
I shall try to pull out another run - from low rpm - for a real comparison down there!

tato_dc

Nom,

What turbo are you using??

Tato

nom

MD254
It's the 'BR developments' jobbie.

carlos_hiraoka

hummmmmmmmmmmmmmmm ..........................

Is that a P20 exhaust housing with some sort of Garrett compressor wheel and ? compressor housing

nom

That's about as much as I know, yes...
I'm pretty sure it's a very hybrid hybrid as opposed to a hybrid that is, say, a VF23 with a different compressor wheel.
Who cares? I think it works pretty nicely, which is good enough for me!

carlos_hiraoka

well 280whp sure must be nice

nom

Aren't you running standard (ported) headers? Could they be the restriction? The above graph does of course show a lot more than just the post-turbo exhaust system, and there is the 'bump' where the HKS headers are known to improve performance... all your numbers are higher than mine () but you're running rather higher boost than I am so the restirction would be 'seen' higher up.
Well, it's a thought!

Pavlo

Well, my headwork has been cheap so far, cheaper than the headers will be anyway!

Put the headers on, you know it makes sense.

paul

john banks

Been there before with headers and largely unimpressed. Maybe these Ion ones would be good.

nom

Fiddly things, headers.
They were 'equal length' last time you tried, weren't they? Even more tricky to match, aren't they?
Presumably, just like an exhaust, the headers only make a difference at higher power levels. Which, I think, you might have these days...

EMS

John,

The Supersprint manifold is worth trying! It did bring about 20 wheel BHP at unchanged boost in 2 cars I tried. (one STi7 and one MY99 with VF23) It has also a nice wide range in which it is effective. (from 3.500 - 6.500 RPM)

I have to remap a MY99 in the near future with this manifold and TD05, I can compare it to the standard manifold then.

I only have experience with the PE manifold and the Supersprint, the PE is a little more effective between 4.000 and 5.000 RPM but is worse above that. Spool up is about the same with little advantage for the Supersprint.

Tim W

iTrader: (1)

Just thought I'd share some pics that I took of my new 'Pat Spec' exhaust before it goes on the car

It's not pretty:


Quite Big as well:


But by God is it free flowing

nom

It's meant to be quite for what it is ... We'll see!

Dxx

Quick querry for John Banks - Just wanting to clarify...
About the Revolution system - it's a 3" straight through system - but do you think that despite the lower noise levels, it still provides the same or better flow (and power) as the other systems on the market ie. SS / Blitz etc?

Haven't actually seen full system off the car - is it straight through??

Dxx

john banks

I think my heads and cams are starting to limit rather than the exhaust. No one has gone over 400 BHP with UK heads AFAIK. I like the Revolution, can't really say if it will do the job yet because I think it is held back elsewhere.

Pete Croney

John

You can't just go telling people that you got 320bhp at the wheels on 2.5" pipework and you certainly can't tell them that a 3" system didn't give you any more

john banks

LOL. I had convinced myself that the 2.5" centre was the blockage. But it is elsewhere for now. It was only the centre and its flanges that were 2.5" though I suppose... I am sure at some point the 3" extra flow will be useful Am I saying that UK cams will top out before a 2.5" centre? I don't honestly know. More work to be done. What do you think?

Pavlo

check out Andy Tang's dyno plots.

PE1818 is similar to a MD304/9 with P18 exhaust housing as far as I can tell.

Paul

Razor2001

Hi guys,

I see that Pat's zorst does not have the normal 'S bend' behind the back box. I thought it was shown that this S-Bend really helps with torque ? I guess that this system with its straight through design is less torquey but better for huge BHP engines and big top end power ?

Cheers,
Ray