Exhaust sizing? b18c turbo.

[Codeman]

Have seen many many people go for 3" on stock b18c turbo's with the likes of a To4e and turbo's a bit bigger than my GT28,

I have been told that while going to 3" is good for outright power, A 2.5" can support up to 600hp (proven) and will be much better for spooling around the street. So why go for 3"?

Will it be more responsive on the 2.5" round the streets compered to the bigger? But Will a 3" make more power?

[b16a2]

how will a smaller exchaust make a turbos pool quiker... maybe you could support 600 whp on a 2.5" system.. but u show me a 600hp car with a 2.5" system that would be stupid, you would have unbelieveable gains by just changing to 3"

BIG IS BETTER" hell go 4" your not going to see any loses in anything

and im still failing to see how if you think critically about how a turbo system works that you can say a smaller exhaust will improove respeonsiveness on a fi car??

[Codeman]

Originally Posted by b16a2

how will a smaller exchaust make a turbos pool quiker... maybe you could support 600 whp on a 2.5" system.. but u show me a 600hp car with a 2.5" system that would be stupid, you would have unbelieveable gains by just changing to 3"

BIG IS BETTER" hell go 4" your not going to see any loses in anything

and im still failing to see how if you think critically about how a turbo system works that you can say a smaller exhaust will improove respeonsiveness on a fi car??

Its on a ca18det, went slower down the quarter by changing to a 3", said he had more responsivness with the 2.5" and had more down low.

I have not really thought about it to be honest. just wondering what others think. Even the back pressure is important on a N/A, to some extent would it not still be the same for turbo?

[b16a2]

on a turbo car from the turbo back... BIGGER IS BETTER

given all things equal.. a larger exhaust/dp will produce more power THROUGH OUT THE REV RANGE

i challenge that person who said it felt better down low.. show me dyno results... bum dyno mean shit

and if you undertood what the term "back pressure" referred to and its purpose on an na car, then you would know it has no use on a turbo car

[Locust2000]

I'm usually on the bigger is better after the turbo for the exhaust. However, I had a book from the library late last year I read through about performance tuning FI engines and there were things to be gained from a properly sized exhaust system all the way to the muffler including having the correct diameter meant better spool etc. To actually have those gains though you had to have it all pretty much spot on which means a full custom exhaust. They were also going to the level of having these extra lips on the inside of the headers just after the motor to help cancel reversion.

So yes it can give better spool etc, but it'd be marginal and would have to be thoroughly designed.

[DSCRET]

I gained 10kw from to 2.5 to 3 inch

[Horny_Devil]

ull spool quicker with a smaller exhast but it will limit outright power

unless ur chassing massive numbers go with whats cheaper and what fits

[nemesisteg]

personally i wouldnt put anything less then 3" exhaust on something with moderate boost levels, 2.5" would be fine for stock motor 7psi but heck why would you want to restrict the output of the turbo with a smaller exhaust, exhaust design is key, im sure you dont really need me to point out that a well designed 2.5" could flow better then a 3" with hundy bends etc

[Locust2000]

Originally Posted by nemesisteg

im sure you dont really need me to point out that a well designed 2.5" could flow better then a 3" with hundy bends etc

I'm not talking about that. I'm talking about an exhaust designed to run the same route with the same bends, using the right diameter exhaust will improve flow. So using a smaller diameter, if it's not restricting, will improve spool.

[b16a2]

Originally Posted by Horny_Devil

ull spool quicker with a smaller exhast but it will limit outright power

unless ur chassing massive numbers go with whats cheaper and what fits

u got anyhting to back this up?? dyno plots etc etc.. or you just speaking your opinion???

Originally Posted by Locust2000

I'm usually on the bigger is better after the turbo for the exhaust. However, I had a book from the library late last year I read through about performance tuning FI engines and there were things to be gained from a properly sized exhaust system all the way to the muffler including having the correct diameter meant better spool etc. To actually have those gains though you had to have it all pretty much spot on which means a full custom exhaust. They were also going to the level of having these extra lips on the inside of the headers just after the motor to help cancel reversion.

So yes it can give better spool etc, but it'd be marginal and would have to be thoroughly designed.

books name and author please

to the two above not trying to be a smart ass, but would genuinely like to see some proof of claims a smaller exhaustw ill increase spool,

[Horny_Devil]

just rember luke we can ask for proof from you on ur theory too.

if ur down pipe is already 2.5in then do u need to go any bigger?

as long as there arent any more restrictions in the exhaust system this should help spool the turbo faster.

if your running a recerc dump then run a 3in exhaust as u need to compensate for wastegate gas being put back into the exhaust, (reserc dump also causes u to loose power)

i would have thought it would have been simular to the old throttle body discussion, the smaller the pipe the faster the velosity, this will add a back pressure though which could be detriemental

[b16a2]

Originally Posted by Horny_Devil

if ur down pipe is already 2.5in then do u need to go any bigger?

as long as there arent any more restrictions in the exhaust system this should help spool the turbo faster.

if your running a recerc dump then run a 3in exhaust as u need to compensate for wastegate gas being put back into the exhaust, (reserc dump also causes u to loose power)

why.. why do you say this..
where are you getting your info from.. your opinion..
are you just regurgutating what everyone else says...

I would really like to see some proof, or at least some evidence backing why u say this,

sick of all the BS and missconceptions and false info online that everyone just regurgitates... so if you dont have a decent argument with some sort of evidence/proof then dont go spreading shit on the net

[Horny_Devil]

I would really like to see some proof, or at least some evidence backing why u say this,

same for you luke, can u provide proof too?

im not saying im the law on this or anything im just saying y do u need to go that big if its not needed?

if ur running a wastegate to atomosphere then isnt a lot of ur exhaust gas not going to go down the exhaust? and at the lower RPM there isnt going to be that much exhaust gas to really make much of a differance?

[turbozxi]

Recirculating the wastegate gas lower down the downpipe definitely gives you gains over combining the exhuast gases straight out the back of the turbine.. Running a open external W/G is illegal. The best exhaust for F/I is the least exhaust, shorter and larger the better.

Having said that I have gone through various setups and you do get better off boost response with smaller piping and it does make a noticeable difference before you get used to it unlike most mods.

[nemesisteg]

pretty common knowledge that an n/a motor like a bit of back pressure where as an FI motor like to flow its ass off, to a certain extent. im not saying locust2000 is wrong either with his findings in said book, but do you ever see turbo cars going in for new exhaust systems and coming out with a nice 2.5" exhaust?? in fact if you can find an exhaust specialist that would sell a guy with a turbo car looking for maximum performance a 2.5" exhaust over a 3" i'll sell my 3" exhaust and get me a mint new 2.5" one.

OP: end of the day mate 3" is ideal if your going to be putting out decent amount of power, if your on a budget and already have a 2.5" exhaust system im sure it will be suffice

[Locust2000]

Originally Posted by b16a2

books name and author please

to the two above not trying to be a smart ass, but would genuinely like to see some proof of claims a smaller exhaustw ill increase spool,

Sure i'll head into the dinsdale library when i'm passing by next couple days and get it out again.

BTW, until i'd read that book, I always used to say "bigger is always better after the turbo" also. The book is about optimal design, not necessarily what's practical on a street car.

[nemesisteg]

dinsdale has a library? wtf?!

[Hayce]

After the turbo bigger is better.

You can run 3" on a low powered/boost car, it won't hurt it but you won't gain much either over a 2.5" as there comes a point where it's out of gas.

Running 2.5" on a high hp car will adversely effect performance.


I know this because I have seen dyno sheets, been told by people cleverer than myself have read it in books/online and experienced it myself on my own cars.

[DSCRET]

When I put my 3inch on there was no difference in spool time it just made more power on my old car with low boost set up. I have the dyno plot some where.
But in saying that it made over 200kw atw with a 60mm exshuast.

[Bazda]

I find with my car when I put my silencer in the exhaust (2") its def alot more responsive down low.

If I disconnect my entire exhaust system so it exits just under the cross member it seems to feel like it spools slower.

So I just run my full length 3" system.

I think what you are all trying to say is smaller feels like it spools faster because off boost its better.

[turboteg]

i'd like to see this 600hp "proven" on a 2.5 inch full exhaust, i have a 3 inch exhaust of the turbo (wastegate plumbed back in) and the exhaust is what limited me to 550hp@wheels!

bigger is better in my eyes, maybe not at lower boost levels but you can be sure you'll want to upgrade the setup later on and then you're up for another exhaust.

[bumpd-EG]

I personally went with 2.5 because that was what was recommended for my set up by ronnie lim. my downpipe is 3 inch but the flange at the end of it fits 2.5 inch so yea?

[Naturally Aspirated]

sick of all the BS and missconceptions and false info online that everyone just regurgitates... so if you dont have a decent argument with some sort of evidence/proof then dont go spreading shit on the net

A bit hostile there, anyway after the turbo bigger is better... On Fi cars, bigger is definately better, you shouldnt need proof to understand this theory, really.

i also fail to see how a smaller exhaust, being after the turbo would make the turbo spool quicker? I can agree with you guys if you say larger IC/charge piping will decrease the spool of the turbine and cause lag........but exhaust???

Have a look on Honda-tech for the high powered h22a thread (FI)
Guys from (300-400) whp are using 3" turbo back systems and guys making (400-900whp) are on 4" and bigger turbo back systems.
[/quote]

[[UZNPSI]]

Originally Posted by bumpd-EG

I personally went with 2.5 because that was what was recommended for my set up by ronnie lim. my downpipe is 3 inch but the flange at the end of it fits 2.5 inch so yea?

I honestly have no idea personly my self but its funny u say that "ronnie" recomended it... some one who def knows what he is on about... evan from speed factor also recomends a 2.5" over a 3" for a turbo honda setup and points out there 300kw+ turbo civic also ran a 2.5".... so i dunno what back ground all you "experts" come from but having 2 guys who def know what they are on about say 2.5" is the way to go makes me think the same

just pointing out what i have been told... i walked in there asking if i should upgrade to a 3" and was told not to bother

[Hayce]

^ A bit of context is a wonderful thing aye...

If a customer walks in to a shop asking what size exhaust for n build they are (hopefully) going to give the customer the cheapest option to do the job. Which could be why Ronnie suggested 2.5" for the OP. As stated that will be fine for what he wants.

And theres no reason you can't run a 2.5" exhaust on a 300kw setup, it's just more likely to run higher hp with a larger exhaust.