at what point does a silent hi power become restrictive?????

[DeanS15]

i'm in a bit of a pickle at the moment, i'm taking my car off the road for a while and while its off the road i want to get a couple of things ready before i eventually find the time and money to have steve re-map it.......

anyway, whilst the exhaust system is off the car i'm considering changing the back box on my silent hi-power for a hi-power 409 box as craig has done - the reason being the silent rear box restricts down to about 2 inch internal diameter and the 409 is 3 inch all the way.

i love the sound of the current setup on the go, but its a bit puffy and farty on tickover with the slightly lumpy idle from big injectors and cams (plug gap may be a tad wide too) - anyway without going too far off the subject is it worth having the less restrictive box fitted prior to a new map in order to make the most out of the mapping, and does anyone know whats the upshot of doing so - is less restriction going to reduce/increase spool time...is the lesser back pressure going to have any detrimental effect on torque output against horsepower?

if anyone has any answers i'd appreciate it :thumbs:

 

[pegliobaglio]

I would have thought a less restrictive box would definitely make a difference mate,end of the day a 3 inch would always produce more power than a 2.
Biggest difference on my car to other 15's I drove was the exhaust,got a nismo sports cat and a 3 inch kakimoto racing exhaust and it made ahuge difference to the way the car responds compared to standard,I am sure there would be somewhere on the web with the pro'S and con's power wise for the 2 systems.I just have to think a larger diameter pipe would make more power.as to responsiveness my car is definitely more responsive with a free flowing exhaust,don't have figures to back it up yet but am sure it would be worthwhile.

 

[DeanS15]

i'd imagine that to be true, the exhaust is all 3 inch from the turbo back with a tubular manifold....it spools very well in low gears, mental in fact, but i want to be sure there are gains to be had - otherwise i'll stick with it if not......

 

[pegliobaglio]

Yeah I see where your coming from,if there is virtually no power gain to be had from sacrificing the noise level then stick with what you have,I always thought a restrictive box would cause back pressure though and in turn reduce power ,I am sure someone will be able to prove it one wAy or the other mate.

 

[craig8585]

Haven't got a clue how much difference the boxes make but I remember you asking about the noise mine makes with no silencers.. Well, it may have got a bit louder since you last asked! Still sounds really really nice especially when your on it, but does droan on the motorway. I don't mind it at all but it does the GF's head in!

 

[TomK]

If you wanted Dean I have a HKS Hi-Power, and would like a Silent Hi-Power (im still running stock engine, turbo and boost), if your interested im sure we could come to an arragement that we'd both be happy with. PM me on here or sxoc (same user name, TomK, my usual hang out) if your interested and want to talk details.

 

[DeanS15]

i would be interested mate but i have customised my system and only want to change the rear box and stay full stainless, the 409 is a mild steel system apart from the rear box so its not really what i'm looking for, but thanks anyway

 

[LuPix_S15]

Dean - I keep thinking about this too... I was just gonna drop down to local Powerflow guys and get them to replace my Silent Hi-Power can for a more free flowing smaller back box etc.

I don't mind the extra noise but what puts me off is the 95 dB restriction at most tracks as well as Nurburgring :wack:

 

[craig8585]

You can get a bung for the Hi-Power which takes it down to 2" but makes it a lot quieter for trackdays, or at least the noise test anyway! Apex Performance sell them.