Hey guys i wanna do a custom exhaust on my infiniti j30 which basically has the same motor as a 300zx n/a the vg30de v6 but i was wondering should i go with 2.25 or 2.5 piping? I dont have any other mods on the car and dont really plan on adding anymore i just want to put a exhaust system on it for now but i dont wanna go with the wrong size and cause problems.
2.25 or 2.5" Exhaust?
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Keep in mind also that there are numerous engines out there that are tuned to run best with a little back-pressure. On one of these engines, if you make the exhaust bigger, or flow better, that can effect the back-pressure and result in an engine that doesn't run quite as well.
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Go on a Z32 forum and see what exhaust systems they're using. That'll give you some good ideas.
I would stay with stock pipe size especially if u are not modifying anything else.
Originally Posted By: boostedtsiawd
Hey guys i wanna do a custom exhaust on my infiniti j30 which basically has the same motor as a 300zx n/a the vg30de v6 but i was wondering should i go with 2.25 or 2.5 piping? I dont have any other mods on the car and dont really plan on adding anymore i just want to put a exhaust system on it for now but i dont wanna go with the wrong size and cause problems.
Tell me, what PROBLEMS will be caused????
Hey guys i wanna do a custom exhaust on my infiniti j30 which basically has the same motor as a 300zx n/a the vg30de v6 but i was wondering should i go with 2.25 or 2.5 piping? I dont have any other mods on the car and dont really plan on adding anymore i just want to put a exhaust system on it for now but i dont wanna go with the wrong size and cause problems.
Tell me, what PROBLEMS will be caused????
Originally Posted By: SirTanon
Keep in mind also that there are numerous engines out there that are tuned to run best with a little back-pressure.
I like to ask people when they say this, how much back pressure? Back pressure CAN be measured.
Keep in mind also that there are numerous engines out there that are tuned to run best with a little back-pressure.
I like to ask people when they say this, how much back pressure? Back pressure CAN be measured.
How much back pressure is a number that is unique to that engine. Too many variables enter into this to give a general answer. Ed
What RPM range do your run the car at? If it's less than halfway to redline, go with the smaller diameter. If you routinely run between halfway and full redline, and by that I mean you are actually running at that RPM, not just goosing it from time to time, you *might* be able to use the extra diameter. Or maybe not.
#4234389 -> Forums » Lubrication and General Automotive » Mechanical /Maintenance Forum » 2.25 or 2.5" Exhaust?
#4234403 - > Forums » Lubrication and General Automotive » Automotive General Topics » 2.25 or 2.5" Exhaust?
Why are you posting the same question in two different forum categories? Didn't anyone tell you that is VERY BAD forum etiquette? The people who are the most experienced and can offer the best answers will probably ignore you because of that.
Don't do it again.
#4234403 - > Forums » Lubrication and General Automotive » Automotive General Topics » 2.25 or 2.5" Exhaust?
Why are you posting the same question in two different forum categories? Didn't anyone tell you that is VERY BAD forum etiquette? The people who are the most experienced and can offer the best answers will probably ignore you because of that.
Don't do it again.
Look up optionsauto.com and see what they are selling.I buy my goodies there and customer support is helpful too. IF...it was my car and you just want a good combo I would get 2.25" and find replacement mufflers that are high flow.My suggestion to do that is look up walker exhaust website and enter all your info and it will show you all the pictures of piping,mufflers and so on.Get the info of your muffler dimensions and call up borla,magnaflow,remus and see if they have a muffler in same dimensions. Sounds like finding a catback is gonna be tough. You could just have them replace mufflers for better sounding/flow. I'd also get a AEM Dryflow filter as intake/exhaust combos work well.
Originally Posted By: daves66nova
Originally Posted By: boostedtsiawd
Hey guys i wanna do a custom exhaust on my infiniti j30 which basically has the same motor as a 300zx n/a the vg30de v6 but i was wondering should i go with 2.25 or 2.5 piping? I dont have any other mods on the car and dont really plan on adding anymore i just want to put a exhaust system on it for now but i dont wanna go with the wrong size and cause problems.
Tell me, what PROBLEMS will be caused????
Reduction in torque in the lower end of the tach.
-m
Originally Posted By: boostedtsiawd
Hey guys i wanna do a custom exhaust on my infiniti j30 which basically has the same motor as a 300zx n/a the vg30de v6 but i was wondering should i go with 2.25 or 2.5 piping? I dont have any other mods on the car and dont really plan on adding anymore i just want to put a exhaust system on it for now but i dont wanna go with the wrong size and cause problems.
Tell me, what PROBLEMS will be caused????
Reduction in torque in the lower end of the tach.
-m
I'd like to say that no engine needs exhaust backpressure. "Backpressure" is a misnomer of the concept of fluid velocity. Narrower exhaust ports and smaller diameter primary header runs increase velocity which increases inertia, which when combined with camshaft overlap, can increase the scavenging effect at the exhaust port, which in turn further clears the cylinder of exhaust gasses and draws intake charge in, all during the overlap event. On some older naturally aspirated engines with more overlap (10+ degrees), the small port and tubes allowed the scavenging effect to be greatest at low and mid RPMs, but choked torque/HP in the high RPM range.
Backpressure for backpressure's sake is always bad, always. Smaller ports and primaries only still exist today on newer engines for emissions purposes in that the faster exhaust gas can leave the port, the less time it has to cool down and the hotter it arrives at the catalyst. The only benefit to small ports on a turbo engine are about the same as the emissions case, but also means hotter faster exhaust gasses at the turbine for quick spool.
That said, 2.5" is about right if you want to support the most peak HP without oversizing. 2.25" is ideal if you don't always use the top end of your RPM range (I suspect this is you). Of course system design is very important in enabling inertial flow through the exhaust, like 'straight through' muffling devices, rather than baffled, S and U shaped turns.
Backpressure for backpressure's sake is always bad, always. Smaller ports and primaries only still exist today on newer engines for emissions purposes in that the faster exhaust gas can leave the port, the less time it has to cool down and the hotter it arrives at the catalyst. The only benefit to small ports on a turbo engine are about the same as the emissions case, but also means hotter faster exhaust gasses at the turbine for quick spool.
That said, 2.5" is about right if you want to support the most peak HP without oversizing. 2.25" is ideal if you don't always use the top end of your RPM range (I suspect this is you). Of course system design is very important in enabling inertial flow through the exhaust, like 'straight through' muffling devices, rather than baffled, S and U shaped turns.
I'm not sure what size to use. However, I read in the May 1998 issue of Sport Compact Car that having an X-shaped crossover improves performance. They wanted to get 450HP from a 300ZXTT, and having the x-shaped crossover did help.
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