Downpipe Choices
29 May 2002, 02:42 PM
#1
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I've been offered a new HKS Downpipe for an amazing price its a 3" bore, will it mate up to my standard centre section ok? How does this compare to a Scoobysport?
Cheers
Ian
[Edited by IanW - 5/29/2002 6:56:40 PM]
Cheers
Ian
[Edited by IanW - 5/29/2002 6:56:40 PM]
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30 May 2002, 10:50 AM
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Pete the one Tony bought is better because Tony bought it 
at Tony 
You'll need to sell me something so I can get my handbag out and tell Tony the one I bought is better than the one he bought because I bought it. Funny thing brand loyalty - we all do it. No offence Tony.
at Tony You'll need to sell me something so I can get my handbag out and tell Tony the one I bought is better than the one he bought because I bought it. Funny thing brand loyalty - we all do it. No offence Tony.
30 May 2002, 11:18 AM
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Matt,
You are going to be posting in the muppets by tomorrow lunch!
Someone mentioned something to me about a closed wastegate?
means nothing to me, but apparantly the Scoobysport has an open one? Does that make much difference?
You are going to be posting in the muppets by tomorrow lunch!
Someone mentioned something to me about a closed wastegate?
means nothing to me, but apparantly the Scoobysport has an open one? Does that make much difference?
30 May 2002, 11:38 AM
#13
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HKS downpipe indeed does have a 'closed' flange that blocks the path of the turbo's wastegate opening, just like the stock downpipe.
Scoobysport downpipe I believe has a wide bell-mouth opening which collects both wastegate and exhaust gases.
It's easy to theorize that the SS design is better, but I have yet to see a quantifiable/repeatable test that shows such design IS better.
BTW the BEST design supposedly runs a different pipe altogether for the wastegate exhaust. The pipe will then join the main pipe much further down to minimize gas turbulence caused by 'collision' of exhaust and wastegate exhaust flows.
If I were you, the HKS has to be a really really good deal for me to take it.
Even so, 5-6 months down the road, wouldn't you start wondering if you could accelerate a tenth of a second faster by having a "better"-designed downpipe?
Scoobysport downpipe I believe has a wide bell-mouth opening which collects both wastegate and exhaust gases.
It's easy to theorize that the SS design is better, but I have yet to see a quantifiable/repeatable test that shows such design IS better.
BTW the BEST design supposedly runs a different pipe altogether for the wastegate exhaust. The pipe will then join the main pipe much further down to minimize gas turbulence caused by 'collision' of exhaust and wastegate exhaust flows.
If I were you, the HKS has to be a really really good deal for me to take it.
Even so, 5-6 months down the road, wouldn't you start wondering if you could accelerate a tenth of a second faster by having a "better"-designed downpipe?
30 May 2002, 12:21 PM
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GDB,
Well, the debate continues on that one but most people seem to be agreed that any open neck/twin dump design is better and freer flowing than a closed w/g type design.
Ian, I would go for a SS/Magnex/TSL/BPM over an HKS/PE
Matt
BTW the BEST design supposedly runs a different pipe altogether for the wastegate exhaust
Ian, I would go for a SS/Magnex/TSL/BPM over an HKS/PE
Matt
30 May 2002, 12:26 PM
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Ian,
Been this way myself when going from standard DP to catless one.
Was looking at HKS one, Scoobysport, BPM, and others, in other words, had a look at normal type necks (HKS) open neck (Scoobysport) and Twin dump (BPM).
Bottom line was that I was told that for the system I had, Apexi N1 center and backbox, as it was 3" I should go for a 3" downpipe, and the BPM Twindump came recommened by a few people who I trust, and one happened to come up at the right price, so I nabbed it!
As said, was originally looking at HKS, and if it's a bargin go for it.
Oh, and I am NOT knocking the Scoobysport DP, i've seen and heard them and they are rather good, though at the time I think they did not have a 3" one, though i never actually asked them direct, so if I wrong please correct me Pete.
No matter what, you'll get rid of the DP cat, which is always a good thing (well, apart from round MOT time, but we'll ignore that for the moment!
)
Been this way myself when going from standard DP to catless one.
Was looking at HKS one, Scoobysport, BPM, and others, in other words, had a look at normal type necks (HKS) open neck (Scoobysport) and Twin dump (BPM).
Bottom line was that I was told that for the system I had, Apexi N1 center and backbox, as it was 3" I should go for a 3" downpipe, and the BPM Twindump came recommened by a few people who I trust, and one happened to come up at the right price, so I nabbed it!
As said, was originally looking at HKS, and if it's a bargin go for it.
Oh, and I am NOT knocking the Scoobysport DP, i've seen and heard them and they are rather good, though at the time I think they did not have a 3" one, though i never actually asked them direct, so if I wrong please correct me Pete.
No matter what, you'll get rid of the DP cat, which is always a good thing (well, apart from round MOT time, but we'll ignore that for the moment!
)
30 May 2002, 02:02 PM
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Pete, not knocking the scoobysport pipe but 3inch over 2.5inch.... would go for the 3 and the fact that i also wanted a twin dump pipe which im very happy with and scoobysport dont do one... It is in the end brand loyalty but as i love my SCOOBYMANIA D/P to bits and the fact that i wanted to be different (and its not too intrusive and sounds great from outside the car ) this is what i went for But even you must have to admit for that price its one bargain of a D/P
John just wanted bigger one matey and if everyone got a scoobysport downpipe all scoobs would sound roughtly the same, so had to do something about it
Tony
PS, buy that HKS, definately worth it!
and the fact that i also wanted a twin dump pipe which im very happy with and scoobysport dont do one... It is in the end brand loyalty but as i love my SCOOBYMANIA D/P to bits and the fact that i wanted to be different (and its not too intrusive and sounds great from outside the car ) this is what i went for But even you must have to admit for that price its one bargain of a D/P John
just wanted bigger one matey and if everyone got a scoobysport downpipe all scoobs would sound roughtly the same, so had to do something about it Tony
PS, buy that HKS, definately worth it!
30 May 2002, 04:01 PM
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There is much mis-information about our downpipe.
It is 3".
At the end of the pipe, it tapers (smoothly) to 2.5". Tis is because virtually every centre section, 2.5" or 3" has been designed to mate with the standard downpipe, which is also 2.5".
By the time the gas reaches the bottom of the downpipe, it has already lost around 200 degC. The volume of gas is reducing all the way along the pipe, as it cools.
There are a couple of centre sections that are available without a 2.5" connection and for customers with these, we also make a downpipe that doesn't taper, remaining 3" all the way through.
As for the restriction created by the taper... Andy Tang had one of these on his monster 357bhp UK car and Top Cat also has one. Trout and Steve Mc have the non taper version.
The main advantage of open neck, over closed neck or twin dump is the lack of restriction for gas leaving the wastegate. On big power cars, this makes it much easier to accurately map. The reason for this is that accurate wastegate control means a chosen boost level can be achieved, and held, accurately and reliably so the map for this boost level can also be accurate. If boost fluctuates, you must map for the worst case to avoid det. If want 1.40 but have to map for 1.45 bar fluctautions, the average boost of 1.40 will be overfuelled, resulting in less efficiency/power.
If you aren't going to be running a remapped ECU/high boost levels, then the cheapest 3" mandrel bent downpipe, that doesn't choke too suddenly at the bottom, will be fine.
It is 3".
At the end of the pipe, it tapers (smoothly) to 2.5". Tis is because virtually every centre section, 2.5" or 3" has been designed to mate with the standard downpipe, which is also 2.5".
By the time the gas reaches the bottom of the downpipe, it has already lost around 200 degC. The volume of gas is reducing all the way along the pipe, as it cools.
There are a couple of centre sections that are available without a 2.5" connection and for customers with these, we also make a downpipe that doesn't taper, remaining 3" all the way through.
As for the restriction created by the taper... Andy Tang had one of these on his monster 357bhp UK car and Top Cat also has one. Trout and Steve Mc have the non taper version.
The main advantage of open neck, over closed neck or twin dump is the lack of restriction for gas leaving the wastegate. On big power cars, this makes it much easier to accurately map. The reason for this is that accurate wastegate control means a chosen boost level can be achieved, and held, accurately and reliably so the map for this boost level can also be accurate. If boost fluctuates, you must map for the worst case to avoid det. If want 1.40 but have to map for 1.45 bar fluctautions, the average boost of 1.40 will be overfuelled, resulting in less efficiency/power.
If you aren't going to be running a remapped ECU/high boost levels, then the cheapest 3" mandrel bent downpipe, that doesn't choke too suddenly at the bottom, will be fine.
30 May 2002, 04:06 PM
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just fitted my scooby sport d/p (to kakimoto racing system)it has gave a noticed power increase and sounds the great too.
the open end of the d/p is a much better design than the twin dump IMHO.
that said,both are better than a cat
the open end of the d/p is a much better design than the twin dump IMHO.
that said,both are better than a cat
30 May 2002, 06:13 PM
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Interesting points Pete.
Regarding ECUs, if you remap the JECS you set not only boost targets but also duty cycles by RPM and closed loop dynamic adjustments which helps with stability, and I have had no boost control issues with the right map with a twin dump pipe, but I am not saying it doesn't happen. The other advantage of high resolution MAF based mapping is that the fuelling values are not absolute like the sounds of the system you describe, but calculated air fuel ratios with full interpolation and scaling maps, so you can map sensible values around the area of the map you will hit with a fine degree of control. Shame it uses brittle MAF sensors though.
Regarding ECUs, if you remap the JECS you set not only boost targets but also duty cycles by RPM and closed loop dynamic adjustments which helps with stability, and I have had no boost control issues with the right map with a twin dump pipe, but I am not saying it doesn't happen. The other advantage of high resolution MAF based mapping is that the fuelling values are not absolute like the sounds of the system you describe, but calculated air fuel ratios with full interpolation and scaling maps, so you can map sensible values around the area of the map you will hit with a fine degree of control. Shame it uses brittle MAF sensors though.
31 May 2002, 10:57 AM
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Johm
Its only very recently that JECS mapping has been possible.
Link and Motec (not sure about GEMS) don't use MAF and you must specify how much fuel goes in.
Although the sensors are fragile, MAF fuel metering is incredibly safe.
Its only very recently that JECS mapping has been possible.
Link and Motec (not sure about GEMS) don't use MAF and you must specify how much fuel goes in.
Although the sensors are fragile, MAF fuel metering is incredibly safe.
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