What size exhaust system for VR4?

quote:Originally posted by MiSTER2:
Well as i mentioned sooner or later i'll be doing more serious mods to the car so i wouldn't wanna pay twice.

In terms of noise level, i picked remus 2.5inch muffler thinking it'll quiten the 3inch system before the gasses come out. Am i wrong? I don't want to put a resonator on. Do i really need one or can the car still be quiet without one? (considering 3inch all the way going down to 2.5inch after the cat converter). I've got a full 3" system from the turbo back with a ported b16g, no resinator & only a shite lukey straight through 3" muffler, it doesn't sound too loud or droney to me but different strokes for different blokes.

If I was you, I'd go 3" right to the remus seeing as you already have it, the 2.5" will quiet it down & hopefully not get you a defect - I don't really have to worry about exhaust DB testing up here in hicksville but you probably have to be a bit more worried.

 

[spoulson]

quote:Originally posted by 4orced4door:
And by opening up your exhaust, you are helping to free that air. I'm afraid DSMBalk has corrupted you...

I don't think that makes sense. If the wastegate is already being outflowed, creating less backpressure with bigger pipes is only going to make the problem worse.

My understanding: If the turbo is creeping with high backpressure from stock exhaust, then how could it be any better by putting on high-flow 3" exhaust? You're only allowing more gasses to make it through the turbine when the turbo is experiencing boost creeping.

 

[gvr4ever]

Boost creep is caused by installing a bigger turbo that out flows the wastgate flapper and 02 housing. The effect is the boost rising for your engine. You might try and set it at 16, but it will keep going up and you can't do anything about it untill the flow problem is fixed.

If you had a 20G with a stock exhaust (just a example) then I'm sure the stock exhaust would play a roll in boost creep too.

So how could putting a bigger exhaust on ever cause boost creep?!?!? It can't.

People don't just add external wast gate dumps to scare old people. Well, it's not the only reason.

 

quote:Originally posted by gvr4ever:
Boost creep is caused by installing a bigger turbo that out flows the wastgate flapper and 02 housing. The effect is the boost rising for your engine. You might try and set it at 16, but it will keep going up and you can't do anything about it untill the flow problem is fixed.

If you had a 20G with a stock exhaust (just a example) then I'm sure the stock exhaust would play a roll in boost creep too.

So how could putting a bigger exhaust on ever cause boost creep?!?!? It can't.

People don't just add external wast gate dumps to scare old people. Well, it's not the only reason. That's not correct.

Boost creep is caused by the resistance in the exhaust being LESS than the resistance going through the wastegate valve. Exhaust takes the easiest route, which is through the turbine wheel, thus making more boost.

Problem can be remedied by
A) larger WG flapper
B) proper porting

See what I'm saying? The bigger exhaust can reduce backpressure so much that exhaust doesn't want to go through the wastegate and bleed off. W

 

Howard is correct. And with larger exaust you will get more lag, untill you get that first pound of boost your motor is NA and needs tuned exaust(not to big not to small). But when your in boost the best exaust is no exaust at all.

~John

 

I'm not sure you can go wrong either way, but my argument is very simple - IMO until ~400hp, 2.5" is plenty. A 2.5" system can be tucked in nicely with no loss in ground clearance.

Shepherd ran high 11s @ ~118mph in his TEL using a BR 2.5" pressbent downpipe, HKS catback and big 16G. When he switched to 3" and 20G he dropped to low 11s @ ~123mph. So if you aren't going deep into the 12s / ~115+ mph, 3" is probably not necessary.

just my $0.02...

 

quote:Originally posted by BlackHole:
I'm not sure you can go wrong either way, but my argument is very simple - IMO until ~400hp, 2.5" is plenty. A 2.5" system can be tucked in nicely with no loss in ground clearance.

Shepherd ran high 11s @ ~118mph in his TEL using a BR 2.5" pressbent downpipe, HKS catback and big 16G. When he switched to 3" and 20G he dropped to low 11s @ ~123mph. So if you aren't going deep into the 12s / ~115+ mph, 3" is probably not necessary.

just my $0.02... I concur, I've had a 2.5" exhaust for many years, and I'm pretty sure it's finally getting close to being maxed out. I'd really like to use the FP dyno before I switch to 3" to see what happens. For anyone with a 16G or smaller, I wouldn't bother with a 3".

 

this topic is getting ridiculous. a lot of people are saying the same thing just in different ways. i think that everyone realizes that exhaust will take the easiest rout out, which means bypassing the very restrictive wasgate. that being said, please don't say it again. its pretty basic.

so i think that you have a good chance of getting boost creep, but if so many others haven't gotten it, then maybe you won't either.

because i'm making my own exhaust i'm also going to make my own o2 housing.

and i'm going to be attaching the downpipe to the block, people who don't usually end up regretting it later on. so for me its 2.5 from turbo to flex section, and then 3 from there on. i think that will be a very nice system once i get it done

 

[scooter]

i guess nobody wanted to take my word for what boost creep is. im glad some people think the same way i do.

 

[scooter]

i think a few people had the wrong idea completly. thats why other people kept bringing it back up.

 

[gvr4ever]

quote:Originally posted by howard:
quote:Originally posted by gvr4ever:
Boost creep is caused by installing a bigger turbo that out flows the wastgate flapper and 02 housing. The effect is the boost rising for your engine. You might try and set it at 16, but it will keep going up and you can't do anything about it untill the flow problem is fixed.

If you had a 20G with a stock exhaust (just a example) then I'm sure the stock exhaust would play a roll in boost creep too.

So how could putting a bigger exhaust on ever cause boost creep?!?!? It can't.

People don't just add external wast gate dumps to scare old people. Well, it's not the only reason. That's not correct.

Boost creep is caused by the resistance in the exhaust being LESS than the resistance going through the wastegate valve. Exhaust takes the easiest route, which is through the turbine wheel, thus making more boost.

Problem can be remedied by
A) larger WG flapper
B) proper porting

See what I'm saying? The bigger exhaust can reduce backpressure so much that exhaust doesn't want to go through the wastegate and bleed off. W I don't want to start a fight, but I've ran with no exhaust before and I didn't get boost creep at all with a big 16G. So if what you are saying is true about no back pressure = exhaust bypassing the wastgage and going out the exhaust, then why wouldn't I get boost creep running without a exhaust at all?

I've never heard anyone suggest that a bigger exhaust will cause boost creep and I've never had that problem with a stock turbo or upgraded turbo.

 

Can anybody tell me the logic behind idea of starting the system 2.5inch and going 3 inch after or just before the cat? Isn't the right way to start 3inch and then going down to 2.5inch as exhaust gas volume decreases towards the end?

A 2.5inch might be more responsive in city driving conditions but a 3inch system will definitely perform better in highway racing.

p.s. Highways of Sydney are beautiful

 

[4orced4door]

quote:Originally posted by MiSTER2:
Can anybody tell me the logic behind idea of starting the system 2.5inch and going 3 inch after or just before the cat? Isn't the right way to start 3inch and then going down to 2.5inch as exhaust gas volume decreases towards the end?
If that were true, then after-market catbacks would be smaller than stock, no?

The point of opening up your exhaust is to get rid of restriction. By putting 2.5" back there after you've had it opened up to 3" through the downpipe, you are adding in another restriction. Either go full 2.5", full 3", or 2.5" to 3", but don't go 3" to 2.5" The exhaust expands as it travels through the system. When the exhaust gasses are hot, they flow better. As the gasses cool, bigger helps.

 

quote:Originally posted by gvr4ever:
I don't want to start a fight, but I've ran with no exhaust before and I didn't get boost creep at all with a big 16G. So if what you are saying is true about no back pressure = exhaust bypassing the wastgage and going out the exhaust, then why wouldn't I get boost creep running without a exhaust at all?
I'll tell you why, because the variables are too different between cars to make a broad generalization that 3" exhaust ALWAYS equals boost creep. There are way more factors than just the size of the exhaust. I don't think anyone is saying that big exhaust will cause boost creep in every situation.

 

[gvr4ever]

quote:Originally posted by howard:
quote:Originally posted by gvr4ever:
I don't want to start a fight, but I've ran with no exhaust before and I didn't get boost creep at all with a big 16G. So if what you are saying is true about no back pressure = exhaust bypassing the wastgage and going out the exhaust, then why wouldn't I get boost creep running without a exhaust at all?
I'll tell you why, because the variables are too different between cars to make a broad generalization that 3" exhaust ALWAYS equals boost creep. There are way more factors than just the size of the exhaust. I don't think anyone is saying that big exhaust will cause boost creep in every situation. In your own words try explaining how any exhaust (larger then stock)in any variable could ever cause boost creep.

Do a google search. Boost creep is due to not having enough flow out of the wastgate. The only way the exhaust can play a roll is if the exhaust can't flow enough for the wastgate and engine exhaust. That's when a external dump is used. It is also used to scare old people to death.

 

when gas gets hot, it moves around faster. think back to highschool physics. as the gas cools it slows down (it gets mellow, haha). so thats my reasoning.

a counter claim would be "all i know is that when i get cold i get closer to my wife" or was it cat. who said that? i think it was ken in

anyway, i'm also going 2.5 to the flex for fitment/ clearance reasons. (i just hope i can get it to be tucked in around the rear diff. i'm not looking forward to trying to squeeze 3 inches of ss pipe there.

by the way anyone looking for some stainless steel pipe?

 

[scooter]

for those of you that think exhaust size has nothing to do with boost creep, this came straight from ddynopower.com on the exhaust page.
If a FULL 3 inch exhaust system is used, in most cases, to control the boost level, an external wastegate is needed. Keep that in mind when getting a 3 inch downpipe.

ok thats one lets try another. this is coming straight from the pages of buschurracing.com
A 3" downpipe without sufficient port work (see below), and external wastegate can cause boost creep.

so i guess david buschur and dougs dynopower have no idea what they're talking about. some of you peeps need to research before you make yourself look dumb.

 

[Romanova]

I have nothing but praise for my 3" SS Certified system with Magnaflow muffler. Insane quiet at idle, and very moderate at WOT. Crusing at 70 is pleasant... no buzzing or droning. This is also with the test pipe.

 

[gvr4ever]

You know what, I'm going to admit that I left out a variable( one that I've never seen happen with any DSM), but I still don't think you guys understand why you accually get boost creep. It has nothing to do with

"Boost creep is caused by the resistance in the exhaust being LESS than the resistance going through the wastegate valve. Exhaust takes the easiest route, which is through the turbine wheel, thus making more boost."

the exhaust not going out the wastgate. It is because the turbo makes more boost then the wastgate can control. A 3" could cause the turbo to spin too much because it flows that well, however without major intake and IC upgrades with a stock turbo and 02, wastgate flapper, that probably isn't going to happen. I think we all know that our stock IC don't flow crap.

I asked you guys to explain why a biger exhaust would cause boost creep and all you can do is post links to what someone else wrote. Do you really understand why?!?!?!? I do, but there was a factor I wasn't looking at. And really a problem I've never known anyone to have. I've been a 1G person for a long time though, so maybe the garret t too small would spin out of control with a 3" who knows.

So before you call me dumb, do you really understand, or just post links that others wrote?

 

[spoulson]

quote:Originally posted by gvr4ever:
In your own words try explaining how any exhaust (larger then stock)in any variable could ever cause boost creep.

Do a google search. Boost creep is due to not having enough flow out of the wastgate. The only way the exhaust can play a roll is if the exhaust can't flow enough for the wastgate and engine exhaust. That's when a external dump is used. It is also used to scare old people to death. Come on, now you're being naive. You're comparing apples to oranges. You're assuming car A with turbo X is comparable to car B with turbo X. You know what they say about assuming...

I think you and scooter have a false view that no one understands the idea. I understand it perfectly and a few others have concurred with me and you. The general idea of this argument is whether or not freer flowing exhaust helps or hurts the possibility of boost creep. There is no absolute.

quote:I asked you guys to explain why a biger exhaust would cause boost creep and all you can do is post links to what someone else wrote. Do you really understand why?!?!?!? I do, but there was a factor I wasn't looking at. And really a problem I've never known anyone to have. I've been a 1G person for a long time though, so maybe the garret t too small would spin out of control with a 3" who knows.Heh. I'll still trying to figure out what the issue is that you have. What is this 'factor'? The reason a t25 doesn't boost creep is because it just doesn't flow worth a crap. A 14B flows more, but I've never heard of creeping on that. The big 16G on my 2G creeped and I went for the 34mm valve and it was fixed. In the old days, they said a 20G required an external because an internal gate would creep. Now there are 20G's with internal gates that work.

So is there still a question whether or not anyone 'understands' you?