loscooby

Hi!
I'm about to tune my STI8, going for a TEK3.
Most tuners say a full exhaust or a backbox change at the same time will give the best/safest gains due to overboosting-problems with the original exhaust.
I want to stay legal in terms of emissions so I would like to avoid fitting a decat. So I guess a system with one or 2 sports-cat could keep the emissions safe and give a good flow...
How much of a difference is there between a decat-system and a system with sports-cat?

hades

Depends how much power you want to run. Power Engineering reckon on no difference at all with their sports catted centre section up to something like 350bhp IIRC. My MY02 WRX has an APS sports cat downpipe, running 284bhp/272lbft, which is at least as good as most people with a similar set-up and full de-cat. However, if you wanted say 400bhp or more, I think the cat would restrict you.

I don't know off hand of anyone ever having run two sports cats, although it could be done. Cost would be higher, and if you can pass emmissions with one cat, why bother with two?

All IMHO, hope it helps!

loscooby

Thanks,

sounds good, that is what I have thought since I used to run a full APS system(Club spe kit from APS) on my old MY00 impreza which got me 285HP on the rollers.

My only problem is that the APS-stuff is fairly expensive and since I also will do ECUTEK my budget is suffering...

Does anybody know of any other brand of sports-cat-downpipe(I might want to mix and match exhaust parts from several )

sorry for hi-jacking the thread....

/L-O

loscooby

Also, does the diameter of the downpipe come into consideration when opting for 330 HP , 2.5 or 3" or will a 2.5" be ok?
/L-O

hades

Graham Goode, MRT, Milltek are other sports cat downpipes, also think Scoobyworld do one now. Also, several american brands - check nasioc.com. That's off the top of my head, there are bound to be others.

nom

I think you might find that the APS one is one of the cheapest out there! Most DPs with a sports cat are £500ish, i think the PE centre cat is £450 or around there. For the £500 DP, add on the mid section (£80) & back-box (could go as low as £250?) & you're up to the same price as the APS anyway - so they're all much the same!
And with the sti8, doesn't it have a cat in the up-pipe as well, which also should be swapped out...?

nom

Oo, just got the 2.5" or 3" bit - depends what you're after noise level-wise with that sort of power - 330 is sort of on the border of a 3" making more sense, flow-wise, unless you don't like too much noise, in which case 2.5" is a good idea (or the 3" APS!).
I'd go for the 3" myself (and don't like the noise but would prefer the possibility of the option of going to more power without shelling out for another exhaust system), but that's just me

hades

3" systems with sports cat and quiet, MRT or APS have to win; I believe the MRT is a little quieter than the APS. Both will flow fine for 330bhp. Several people have had good results with the Milltek on STi 7 - similar power/torque to STi PPP IIRC - but not sure what size that is off-hand.

hades

Nom, the STi7 was not a catted up-pipe, don't think the STi8 is either. Up-pipe cat is reserved for us "lucky" WRX owners!

loscooby

You are right about the up-pipe, nocat on sti8!

Are there any reasons having the sports-cat either in the downpipe or in the center section(I so not know if this is a stupid Q. but I will risk it)?

/L-O

hades

No really big differences, where you put it, IMHO. PE reckon that having the centre section catted is slightly less restrictive. Centre section is further from turbo so will take longer to warm up therefore worse emmissions from a cold start. Having a downpipe cat allows a resonator in the centre section, so will tend to be quieter - personally I found the PE system quite boomy around town on a test drive, and much prefer the sound of the APS, but that may have been their backbox. On the other hand, some people prefer the sound of the PE pipe.

Don't know if that helps?

nom

Ta for the info on the sti7/8 - can never remember the details!

With the positioning of the cat, basically as Hades says - the further down the exhaust system it is, the better for flow, but the longer it takes to heat up. Hence a cat where the backbox is quite possibly would barely be noticed flow-wise, but would never get up to temps (so would be useless). Likewise, I have heard bad things about the MRT catted DP - the cat is so close to the turbo that it seriously restricts flow. Although it probably heats up nice & quick
APS & PE put the cats in pretty much the same place - APS right at the back of the DP, PE right at the front of the centre. Seems that's the best compromise point!

Lemmy

Loscooby

I have the PE sports cat system on my STi7 and am very pleased with the sound level and quality. It does not boom at all and is quiet on the motorway. However, noise levels are very subjective and other people might find it too lound or too quiet. The system is slightly more expensive than Milltek's and others at around £1200 including VAT, but then it is of reputedly higher quality than other systems. PE claim that the sports cat is gas flow rated to 400 hp, which is sufficient for most of us!

I went for this system because I had PE do a Ecutek remap and thought I would get the best results if I used their own exhaust system.

Hope this helps.

Alan

Judge

Don't bother with a cat at all!Even a sports cat is restrictive to a painfull degree.The law is fairly relaxed about emissions and you are only likely to get caught if you are subjected to a roadside emissions test by the DOT and when was the last time you saw that. As for the Plod they willonly give you a VDRS (Vehicle Defect Rectification Scheme) notice which any modifying garage with MOT testing capabilty will stamp for you without much "Work" required. This is the same come MOT time (Trust me!) So sod cats,you dont need them!

hades

Restrictive to a "painful" degree? As in PE detecting no difference in power by using theirs? As in my car giving as good or slightly better power than other similar set ups with a decat? Care to back up your statement up with any facts? Also, do we trust you that VRDS's work in Sweden, as that is where the original poster originates from?

IMHO, not convinced the PE system is better quality than the APS, which is top draw and just under £1k for the full system. That is the big problem with sports cats - cost.

Edit to add - not saying the exhaust isn't great quality, just that the APS is too.

[Edited by hades - 5/24/2003 10:05:50 PM]

Judge

PE detect no difference with the sports cat?Well that is a surprise,dont they also sell the sports cat? And at £450 it isnt exactly cheap is it?Considering I got myfull decat fitted for less! How can a cat possibly work as well as a pipe with no cat at all,the exhaust gases go through it to lower the emmissions and that must be restrictive!How else is it done?Witchcraft?

hades

How does it work? If you'd like me to go into the details at a molecular level of how a catalyst works, I could.

Not saying it has no effect, but I still maintain that a well designed and implemented sports cat will have less restriction than a less good de-cat. The cat will produce limited back-pressure up to a certain flow (and therefore power) level - beyond that power, it will restrict things. Below that flow level, other restrictions will be more significant, and the cat may cost eg 1-2bhp i.e. not "painflly restrictive"

The APS exhaust with sports cat has been shown to produce less than 1/3 of the back-pressure of the OEM system. No system will have zero back-pressure.

I'll repeat - care to back up your statement with any facts?

I haven't once suggested it was a cheap option, in fact my previous post quite clearly says otherwise.

Pavlo

Quite right, if you have no system there will be zero back pressure!

Pat's 3.5/3.25 system had no measurable back pressure on the janspeed flowbench don't think that included the downpipe though.


Paul

lucky_strike

Hades, interested in your APS sports cat - who sell's them and did they fit it for you? Does it include the up pipe as well?

You might not know this but any problems coupling the APS sports cat downpipe to a PPP system (WRX)?

Thanks
Richard.

swaussie

My STi7 runs the MRT 3" system with sport cat with centre resonator. The difference this made to the car compared with the OEM pipe was VERY noticable. Like Lemmy says the noise is subjective and at idle mine sounds very similar to the OEM but has a nice sound when under throttle but it is never intrusive. I went this route because I was told the police here often make spot checks on cars ( especially EVO's and Scoobs ) to test for emissions and if they see you run without a cat then the fine would easily buy every member on scoobynet a beer at the pub

hades

Thought this might be relevant here. Prodrive suggesting that they were actually getting more power with a sports cat . . .

I guess Paul's suggestion of no exhaust for zero backpressure might be fun. Could be a little loud, and melt a few things around the bottom of the engine bay, but that's a small price to pay for a few more bhp!

Edcase

Interesting about the spot checks on decats in switzerland. What about foreign cars? We are planning to drive s. francs / switzerland / germany in summer so what if they stop my car and its decatted?