Boost Arguement

[Alexxs]

Me and my friend were having a argument about boost, and he told me to post on here to find out who was right so here goes.

He says - Adding an aftermarket free flowing exhaust will increase ur boost...

I say - Go f**k ur self, the boost controller controls the boost way before the exhaust flow has anything to do with it.

Thoughts... and please only people that know something about this as yeah.... Neither of us are adimiting to being wrong! THIS IS SRS BUSINESS!

So help me SAU prove me right!

[mad082]

theoretically speaking you are correct. theoretically you shouldn't see any boost increase from changing the exhaust as the pessure in the intercooler piping is what determines the boost level and you could remove the exhaust all together and it shouldn't alter the boost level. this doesn't always happen in the real world though. sometimes turbulence, etc from aftermarket exhausts can actually restrict the wastegate gases and cause them to have to flow throught the compressor wheel and give you an inceased boost pressure

that said, i never saw a boost increase when adding a turbo back exhaust or intercooler, but others have. i still had 7psi all the time using the wastegate and solenoid only with a 3" turbo to cat and 3.5" catback.

[R31Nismoid]

You're wrong. He is right.

Exhausts that "choke" turbo cars, restrict them.

Restriction causes backpressure, backpressure is the enemy of turbocharhing in many ways.

You put a free flowing exhaust (vs stock) on a R33, you'll see a psi or two increase right away.

[astrotristan]

oh zing

[STATUS]

change the cat back on just about any early mazda (familia gtr) and the boost raises to the point of boost cut, changing exhaust definatley can have an effect on boost, it all depends on how restrictive it is to begin with, subaru's are also prone to overboosting with str8 through turbo back exhausts.

[joeyjoejoejuniorshabadoo]

hardcore boost increase on the mazda gtr's!

but they are strangled HARD from factory...

my mate has one and he is keeping it stock... FTL

[GTRNUR]

Stock 2jz supra twin turbo's use a restrictor in the exhaust to reduce exhaust flow. Once thats removed boost climbs to 15-18 from memory.

I put an 80mm nismo catback on my R34 gtr and it went up to 1 bar with the stock ecu, now though with the power fc (and no boost controller kit) its back to 0.8 bar max.

[Alexxs]

You're wrong. He is right.

Exhausts that "choke" turbo cars, restrict them.

Restriction causes backpressure, backpressure is the enemy of turbocharhing in many ways.

You put a free flowing exhaust (vs stock) on a R33, you'll see a psi or two increase right away.

how so, i had a 3inch turbo back, with high flow cat. and it didnt change at all on my boost gauge, was still running 7psi.. from stock exhaust to 3inch turbo back...???

how does the exhaust over right the boost controller i get that it might spike over 7psi because there are less restrictions in the way etc... but how will it flow over what the boost controller will let it?

***EDIT***

im not looking to argue on here, im just looking for an explanation

Edited January 8, 2010 by Alexxs

[astrotristan]

stock or aftermarket boost gauge?

[Lithium]

Pass, most people I know have had a bit of a gain when changing exhaust. From memory, stock R33s I have been in run 5psi stepping up to 7psi with stock exhaust and 7psi stepping up to 9psi with full exhaust. 7psi flat if the boost solenoid is eliminated...

[sneki81]

when i changed the full exhaust system in my 33 the boost went up 2psi.

it ran with stock exhaust- 5psi until 4500rpm, then jumped to 7psi.

with aftermarket turbo back system- 7psi until 4500rpm, then jumps to 9psi.

so yes it does change.

[skylinecouple]

Everybody is right as this is the basics of turbo understanding. If this is a standard R33 then boost will increase a little if exhaust is changed yet other cars might not gain anything. How many times have we had a problem with rich and retard due to exhaust and intercooler being changed to a far more efficient type. An EBC will control that boost but that boost will still come on earlier due to less restriction. Lets face it, most manufactures use exhausts to limit boost or to pass EPA laws.

[rtune]

a free flow exhaust makes boost come on sooner (ramp up faster) but as you say, EBC should set desired PSI. Once set psi is reached, it is the same between the two cars (although the one with the open exhaust is making a bit more power at that psi due to less back pressure).

However if you look at the dyno graphs which show PSI, you'll frequently see roll off at the top end. This is where a free flowing exhaust might help, after fitting, it should stay at the target psi for longer and therefore make more peak power due to the higher psi at 8000 rpm.

[JonnoHR31]

most ebc's work with a duty cycle, if you leave the duty the same the boost will go up as the maximum possible boost is higher with a bigger exhaust

[mosquitocoils]

Without adding a boost controller, and just by adding zorst + intercooler, it's possible to get from 7psi (stock max) to around 8-9 psi.

That's what I hear from trolling these forums as if my life depended on it, however have no factual evidence to back it up!

[tigermm]

You're both right!

It depends if you have a proper closed loop boost controller which actually measures boost pressure, or a factory type setup which is made to give a certain pressure when the stock restrictions like exhaust and IC are in place.

So on a factory car he is right, removing restrictions makes the whole system work better and you get a boost increase.

On a car with a proper EBC you are right, the boost is being measured and digitally controlled without any regard to restrictions, so it should stay pegged at whatever its set to no matter what you change around it.

[boostn0199]

a intercooler and good exhust will see it raise up to about 9psi from 7

[l_uk3y]

Before I did exhaust and cooler, I had previously changed my 33 to 7psi all the way through the factory boost solenoid.

This was confirmed by an A/M boost gauge. When I added the Catback exhaust and Front mount IC (front half of exhaust came later), my boost increased upto roughly 9psi. However didn't notice any change when I completed front half of the exhaust.

Luke