What factors dictate if an exhaust gives a gain?
06-20-2005, 11:38 AM
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What factors dictate if an exhaust gives a gain?
On a turbo generally the less restrictive an exhaust system is the more power you can get given that there is no pressure backin up into the turbo. Seems simple enough.
What factors dictate whether you see a gain on a n/a engine like (shock, horror) the S2000 engine? Why does the HKS lose a few bhp over stock and the amuse gain? Why do the single exits gain even more in general? What are the factors that make the difference between the performance of the HKS and an amuse or other bhp increasing twin exits? Is exhaust material a factor, straightness of the pipe, restiction, etc?
Where I'm going with this is there a number of companies that will do custom exhausts and if I can satisfy myself that their design has the characteristics of an exhaust that will at least match stock for bhp then I'd consider going for it.
What factors dictate whether you see a gain on a n/a engine like (shock, horror) the S2000 engine? Why does the HKS lose a few bhp over stock and the amuse gain? Why do the single exits gain even more in general? What are the factors that make the difference between the performance of the HKS and an amuse or other bhp increasing twin exits? Is exhaust material a factor, straightness of the pipe, restiction, etc?
Where I'm going with this is there a number of companies that will do custom exhausts and if I can satisfy myself that their design has the characteristics of an exhaust that will at least match stock for bhp then I'd consider going for it.
06-20-2005, 11:47 AM
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I don't think it is something you can design by rules of thumb if you want top performance.. for example, how does rpm impact exhaust performance... probably important on a 9000rpm engine.
06-20-2005, 11:49 AM
#3
Phew!
If you need to ask, you probably won't be able to evaluate which looks the best system!
That's not a flame, it's a very complex calculation.
Briefly, the less restriction, the more throughput the more power. Hence big bore, non-cat guns.
But torque characteristics are probably more important than a few extra BHP at 9000.
That's where a 4-2-1 manifold is useful, whereas a 4-1 or 4-2 tends to give top end.
Likewise, straightening the curves improves flow, but back-pressure control helps torque.
Best look at a design that truly works, buy the manifold, get your ehhaust people to plagiarise the exhaust.
PS- the standard system is notoriously efficient and hard to improve upon!
If you need to ask, you probably won't be able to evaluate which looks the best system!
That's not a flame, it's a very complex calculation.
Briefly, the less restriction, the more throughput the more power. Hence big bore, non-cat guns.
But torque characteristics are probably more important than a few extra BHP at 9000.
That's where a 4-2-1 manifold is useful, whereas a 4-1 or 4-2 tends to give top end.
Likewise, straightening the curves improves flow, but back-pressure control helps torque.
Best look at a design that truly works, buy the manifold, get your ehhaust people to plagiarise the exhaust.
PS- the standard system is notoriously efficient and hard to improve upon!
)
06-20-2005, 12:09 PM
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If you need to ask, you probably won't be able to evaluate which looks the best system!
I guess I kind of hoped someone might say 'It must have A, B and C and that will give excellent power in vtec but probably with a loss off-vtec (which I could have lived with).
06-20-2005, 12:11 PM
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and AE has a lot more power now after his cleaning session as he must have sweated at least 1 stone and only had 1 mars bar and 4 cans of diet coke during the morning! 
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06-20-2005, 12:13 PM
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8 bhp gain means diddly squat in reality. Most after market exhausts aim to improve power for those all important metal shifting figures but by sacrificing mid end torque. Those exhausts may result in higher torque at high rpm (and hence giving higher power figures) but in reality may actually result in a slower car on the road. This is immediately apparent in many after market car and motorcycle exhausts and is a constant source of amusement to the more intelligent vehicle modder.
If I was to even consider purchasing an aftermarket exhaust (which I wouldn't, since I trust that Honda know more about tuning the exhaust to the S2000 than an aftermarket "specialist") there are a few areas I'd consider critical to give me confidence that they know what they're talking about.
Firstly I would expect them to ask me which S2000 I've got as the VTEC system changes over the years. I would expect them to know this and how it affects exhaust tuning.
Secondly I would expect them to have graphs of torque and power output from a variety of S2000 engines over the different years. I would expect these graphs to tally with my own dyno figures or dyno graphs acquired by other S2000 owners.
Thirdly I would only be interested in exhausts which give significant increases in torque in the midrange. I wouldn't give a flying monkey for an exhaust which only increases high end power.
Fourthly I would expect some kind of guarantee that if I dyno'd the car with their exhaust that I'd gain their prescribed outputs. I would expect them to be fine with a financial guarantee of their claims. If they weren't prepared to guarantee it then I wouldn't be convinced that they'd done enough research to be confident in their claims and hence be worth spending the money.
If I was to even consider purchasing an aftermarket exhaust (which I wouldn't, since I trust that Honda know more about tuning the exhaust to the S2000 than an aftermarket "specialist") there are a few areas I'd consider critical to give me confidence that they know what they're talking about.
Firstly I would expect them to ask me which S2000 I've got as the VTEC system changes over the years. I would expect them to know this and how it affects exhaust tuning.
Secondly I would expect them to have graphs of torque and power output from a variety of S2000 engines over the different years. I would expect these graphs to tally with my own dyno figures or dyno graphs acquired by other S2000 owners.
Thirdly I would only be interested in exhausts which give significant increases in torque in the midrange. I wouldn't give a flying monkey for an exhaust which only increases high end power.
Fourthly I would expect some kind of guarantee that if I dyno'd the car with their exhaust that I'd gain their prescribed outputs. I would expect them to be fine with a financial guarantee of their claims. If they weren't prepared to guarantee it then I wouldn't be convinced that they'd done enough research to be confident in their claims and hence be worth spending the money.
06-20-2005, 12:20 PM
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Originally Posted by StuartL,Jun 20 2005, 09:13 PM
If I was to even consider purchasing an aftermarket exhaust (which I wouldn't, since I trust that Honda know more about tuning the exhaust to the S2000 than an aftermarket "specialist")
Enjoy your stock exhaust, Stuart - there's not a cat in hell's chance of getting an aftermarket supplier to jump through all those hoops you've listed!