What do you do when your exhaust is too JDM? Too JDM for 56k even?

[White Comet]

We can go into more detail later about WC's idiot friend, but his situation was a combination of the above, coupled with the fact that old V8's have competing exhaust pulses from opposite banks (reasoning behind dual exhausts, and crossover / X-pipes).

how do you explain it on a 4 cylinder though? i had to drive an integra to an exhaust shop with an open header. the response was terrible and had no acceleration.

[AZhitman]

Quite possibly the same thing.

Read my post again.

It's NOT backpressure that's helping.

Unless you're gonna study this stuff on your own, you're gonna have to take our word for it.

[Hooked on 240]

All i have to say is BRM FTW!

I <3 my 2.5in catback with the dual tips

[White Comet]

Quite possibly the same thing.

Read my post again.

It's NOT backpressure that's helping.

Unless you're gonna study this stuff on your own, you're gonna have to take our word for it.

i'm not trying to challenge or disagree with you, just asking for clarification on the subject since the reason you gave for my last example didn't apply to a 4 cyl

[Salem240]

OP... that looks to be a S14 exhaust. Find some douche that will buy it and put the money toward a BRM exhaust

[Hooked on 240]

Greg vs jeff

annnnnd GO!

OP... that looks to be a S14 exhaust. Find some douche that will buy it and put the money toward a BRM exhaust

YESSSSSSSSS

[AZhitman]

i'm not trying to challenge or disagree with you, just asking for clarification on the subject since the reason you gave for my last example didn't apply to a 4 cyl

I know. I'm just lazy and my head hurts.

Plus, contrary to popular belief, I don't know everything.

[estrada42]

Quote »by any chance you have a side pic of your car?[/quote]Any particular side? I'm going out tomorrow with a real camera that's not my G1 and taking some (hopefully) nicer shots. Is there something your looking for in particular?

I'm going to sell it once I replace it. It seems there's definitely a market for it.

Also, for clarification, I have a KA24DE powered 92 S13 coupe. No need for an SR20DET 3" piped, 5" tipped exhaust.

[iRides13]

well, i have an sr20 im lookin at right now that my buddy hasjust the motor, so the exhaust sounds like a great asset i wouldnt mind haveinso hook me up, ill pay the shippin.how much you want.and it dont madder, you cars hella sexy, imm loookin for a front end tooim not new on here, i just forgot my password so i had to make a new account.i just wanna see the side

[freakyjason]

There's simply no NEED for 3" piping on a 2-liter engine, unless you're running insane amounts of boost. It's unnecessary.

So let's say I'm running 24 psi on my sr. Is 3 inch piping too much? Will I gain response in switching to 2.5 inch but loose overall power somehow? When should you be running the big pipes? Sorry, just don't really understand where the cutoff would be.

Plus, contrary to popular belief, I don't know everything.

[PyR0NiAk]

This thread needs to keep going...

[spolitte]

So let's say I'm running 24 psi on my sr. Is 3 inch piping too much? Will I gain response in switching to 2.5 inch but loose overall power somehow? When should you be running the big pipes? Sorry, just don't really understand where the cutoff would be.

Unfortunately, I don't believe there is one definate answer to your question jason, but this is due to the many variables involved ranging from whether the engine is modded or stock to how you prefer to drive your car (conservatively vs driving to the grocery store and making sure the engine doesnt drop below 4k rpm's). However, from all the hours I spent researching this topic I have picked a few websites that I like in particular. Check this one out...

http://www.tercelreference.com....html

Please keep in mind this is all theory as stated at the top of the link and has not been proven. Furthermore, there are countless theories that say and 'prove' the opposite. Basically what I am trying to say is that no one has definatively proven their theory on exhaust and backpressure and that in the real world there are SOO many variables to consider that it is truly a matter of opinion still (albeit some opinions and theories are more substantiated than others) but everyone is just going to have to go out, do some research, and decide for themselves what the correct answer to the infamous exhaust question of 'how big to get!?!.

[AZhitman]

^ This.

Well-said. And that article is good, I have it bookmarked (from its original source back in the day).

I am working on a huge exhaust article, but its a long process... I need 3 of me.

[Jdmstyles]

Plus, contrary to popular belief, I don't know everything.

That's a lie! You do know everything.

[corey240]

You should sell your car because your a whinny dumbass who doesnt know what hes looking at. Its a Nismo exhaust dude. If your do oblivious to the fact you have a rare item on your car for free then sell the rest seriously. I have an s13 nismo power sport muffler just chilling at my house and I will probly never use it. But il be damned if I sell it. Ive had it for 2 years with no intention of installing it on my track car.

Btw, the only reason to open the exhaust more then 2.5 really is if your going to jump over what like 300+ hp? Ive had 3" on my car and have driven other sr powered cars and it makes a big difference. I had a custom stock exhaust made for a ticket and it really sucked. Unless your going for a serious hp goal up there 2.5 should suit most people fine.
Modified by corey240 at 10:51 PM 10/19/2009

[PyR0NiAk]

Greg, I'm looking very forward to this article..

Just thought I'd quote something that caught my attention.

As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side.”

[PyR0NiAk]

There's this, as well..

"Here's a worked example (simplified) of how larger exhausts help turbo cars:

Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:

(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure

o here, the turbine contributed 19.6 psig of backpressure to the total.

Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case).

So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.

This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.

As you can see, the backpressure penalty of running a too-small exhaust (like 2.5" for 350 hp) will vary depending on the match. At a given power level, a smaller turbo will generally be operating at a higher turbine pressure ratio and so will actually make the engine more sensitive to the backpressure downstream of the turbine than a larger turbine/turbo would.

[mattblancarte]

You should sell your car because your a whinny dumbass who doesnt know what hes looking at. Its a Nismo exhaust dude. If your do oblivious to the fact you have a rare item on your car for free then sell the rest seriously. I have an s13 nismo power sport muffler just chilling at my house and I will probly never use it. But il be damned if I sell it. Ive had it for 2 years with no intention of installing it on my track car.

Uh, I believe you may have overreacted. A rare muffler... oooohhhhh it gives me goosebumps.

Sell the exhaust to someone who wants it (in its incredibly beautiful condition), and replace it with one that fits.

Good luck with the new ride, OP! Hope the little surprise finds are all positive from this point in.
Modified by mattblancarte at 11:06 PM 10/19/2009

[AZhitman]

I disagree 100% with this:

As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side.�

Horsepower is not even CLOSE to an indicator of required exhaust size... that's just elementary.

I'm still at 2.5", near 400hp, and switching to a full 3" actually decreased torque down low.

[PyR0NiAk]

I think the SR may be an exception. When I was researching what turbo I wanted to use for my build, Ben at JWT tried to tell me I'd need at LEAST a top-mount 3071R to make 400whp yet I've been seeing quite a few people make it with bottom-mount 2871Rs, and there was 1 NICO member who did it with a .64 AR 2871R... Maybe, our cars respond better to the smaller numbers than others do. That post was made on a WRX forum if I read everything correctly.

[rustest86]

man i hate to get into this, but i havent seen 1 person even mention this....... all motors need some kind of backpressure, if you dont have any you will risk melting valves...... thats right the exhaust gas cools the valves!!! that is why NA cars with no exhaust have poo for throttle response and run like crap. there is a thing called valve overlap that lets just a little bit of exhaust gas back in so that the valves get cooled, help prevent pinging and promote a full even fuel mixture burn. now on a turbo car it doesnt matter what exhaust you have and what backpressure it creates....... this ranges from no exhaust to stock, as long as the there isnt as much pressure behind the turbo as in front of it thats all that is needed, the turbo creates all the backpressure needed by the motor itself. and as far as what would make the most power on any given turbo system, the bigger the better relative to the amount of exhaust flow needed.

on a stock turbo'ed SR a 3.0" wouldnt make any more power than a 2.5". but say a SR with a GT3071r WOULD make more power on the 3" than the 2.5" at the same boost levels because it will flow more air into the complete combustion system and thus need a higher flowing exhaust.

real life, i had a 2.5" pacesetter on my car and a greddy 18g running 11psi, now at 11psi my 370cc injectors are MAXED!!! the t25 would have to run about 14.5-15.5 to match that amount of flow. when i upgraded to my a-pexi' noir exhaust, which starts at 3" and ends up 3.3" before the 4" tip, i noticed a huge difference in power in the upper rev range, along with cooler egt's. which is the point of going bigger on a turbo motor.

that is the explination everyone is asking for.

also to OP im with you on the exhaust i dont like the gawdy sidways loud exhausts either thats why i went with the a-pexi, it accually quiter than the pacesetter that it replaced at idle with a deeper tone, and is only loud at the upper revs. oh and it black too .

Modified by rustest86 at 1:22 PM 10/20/2009
Modified by rustest86 at 1:36 PM 10/20/2009

[mattblancarte]

Not that I want to get into a lengthy debate... but valve burning is not a direct result of a lack in back pressure. Valve burning occurs when you run your AFR super lean.

It is fair to say that a lack of back pressure could lead to the by-product of running lean, which would burn valves, but that middle step is required. Running lean from no back pressure is a result of a fuel delivery issues.

If you build and tune a motor to run open headers, it'll be just fine.

[mattblancarte]

An example of an exhaust system with a complete lack of back pressure:



Don't we all wish...

[sean@z1]

BTW the 80F25 part number makes it a S chassis part and you should give it to me and all will be forgiven

[rustest86]

but in the real world most people dont retune to run open headers and end up burning valves from, like you said leaning out, most stock valves arnt desighned for that and will burn or warp and will not reseat. i have seen it a many of times on chevy truck and honda's where they "think it sound cool". absolutly no backpressure will damage a motor. any form of pressure in an exhaust system is backpressure regardless if it right at the head or the tailpipe. a properly built/proprtioned exhaust will yeild more power and engine life than a open header will any day.

also your example of a dragster with open headers....... those things are super charged alcohol drinking monsters that that may run 5min at a time, and get rebuilt after every race....... IF they make it that long. soooooo not a good example.

[mattblancarte]

Re-read my post, and decide whether or not I'm in disagreement over whether a dude with a Honda or Chevy that runs open headers without tuning will potentially burn valves. I believe I backed you up on that one, as I said that such a configuration requires tuning...

Top Fuel doesn't run alcohol, they run 90% nitromethane and 10% methanol. How is that not a good example of a motor that was built to run open headers?

I was simply clarifying some of your statements, which were incomplete or were missing detail. Sorry mang.

[rustest86]

sorry if it seemed like i was busting chops, i wasnt been an a** or anything. after rereading im with you now. theres just so much bad info on the net thats all. but like you and i where saying the lack of backpressure will directly damage the engine unless it is retuned rich to provide cooling for the exhaust valves, and still the motor wont last as long as if it had a proper exhaust.

um a dragster isnt a good example because they dont run long enough to show what damage that can and will happen if your running open headers. and those things get rebuilt more than my kids get her diaper changed so.......... but yes if tune on engine to run open header, it will run correctly just not for very long, in a DD/street prepped situation. and for the life of me i cant think of a good example either. i can think of another one that goes with what im saying....... back when i raced gocarts with 5hp briggs we use to take the mufflers off and they ran like spotted a** apes but the exhaust valve would start over heating and we have to let them cool down or tear into them and change them.

yea i couldnt think of the kind of fuel and alcohol popped in there. thanks for clarifing that. i never once said i was completely right...... i just know more than enough to keep my fleet running.

[rustest86]

but anyway most of us are running turbo cars so we dont have to worry about backpressure...... its there at all times right before turbo.

the only way to fix it would be to remove the turbo..... and who wants to do that???

we just need proportioned exhausts for the amount of flow we need. thats all.

[PyR0NiAk]

I'm learning a lot in this thread... I just hope all the info is accurate...

[mattblancarte]

No worries, I wasn't taking your responses personally.

You an I are in agreement on the general direction the average DD car should go, which is to buy a sensibly-sized exhaust that fits.

I wasn't suggesting that people should run open headers (even on the vast majority of track cars). I simply wanted to articulate what would cause a valve to burn.

If you head to a vintage race, you'll see tons of cars making tons of HP on open headers. I could never forget the sound of big-blocks with open headers cruising by me in the hot pits at Pacific Raceways. hehe

Your example of the go-karts is a perfect example of causing the motor to deliver an improper amount of fuel, thus causing the AFR to run lean to produce excessively hot EGT. Removing the exhaust caused the tuning to go awry, thus causing the bad fuel delivery.
Modified by mattblancarte at 2:10 PM 10/20/2009