boost with pod filter and exhaust

[ricsvtr]

hello ppl

ive heard somewhere that boost will increase slightly with a pod filter and exhaust upgrade. is this true? how is this possible? wouldnt the wastegate stop the boost from going over the standard boost level?

[32vspecII]

a turbo back exhaust will give you a couple of psi but the filter does nothing .im running a pod with stock exhaust and no boost increase is noticable

the wastegate is not "active" . it is set to a mechanical level which equals a certain amount of boost . if you remove the restriction the turbo will produce more boost at the original set actuator level . if you had an active electronic boost controller which was constantly monitoring the actual manifold pressure and adjusting accordingly then it would stop the boost going over a certain level , which is what hey do to stop spiking .

i probably didnt explain that well but hopefully you get the idea

[ricsvtr]

what do u mean by active? doesnt the wastegate only open when boost reaches a preset level eg. 7psi? can someone give me a clearer explanation please.

[MerlinTheHapyPig]

i read about 0.7-0.8kg/cm2 with pod & exhaust on a 32gtst

(which is about 10-11psi). No other engine mods.

If wastegate is fully open, on a stock system this equals 7psi. So if you remove restriction, the turbo produces more boost, so the amount of boost you'll read with wastegate fully open will be more.

I think that's right... someone correct me if im wrong.

[R31Nismoid]

pretty much on the money.

the restirction causes un-due backpressure.

Backpressure is the enemy of boost

[benl1981]

I still find this hard to understand as the pressure the actuator sees is tapped into compressor outlet (Or on most turbos anyway). If it's configured to hold boost at 7psi...then it should do this no matter what - that's what it is there for. Obviously the turbo will be more efficeint with less back pressure but really if you have a 5psi actuator thats what it should be fully open at - and open before to maintain that as a maximum.

This is the first turbo car I've had and I haven't played with boost so I don't know the practical side of what happens when you free up the exhaust. I would have thought that the wastegate should just open earlier with a better exhaust to maintain the same psi. It just may get to peak boost earlier.

[32vspecII]

the wastegate cant vent any more exhaust , the actuator is set to certain point . if that was 7psi and now the turbo is more efficient and producing 10 the wastegate can not do anything about it , its already at its set level . If you had an adjustable actuator you could open it more assuming it wasnt all the way open already and vent more gas out the wastegate producing less boost .

thats my understanding of it anyway .

[Birnie]

This is fantastic!

I asked the same question about 1 yr ago and i don't thik i got a very satisfactory explanation.

But the 'mechanical' bit makes alot of sense to me.

I can get my head around that.

I would love someone to get a camera under the hood wacthing the actuator arm with another camera watching the revs/boost, put the images side by side and watch a full dyno run and actually see it work and what really happens.

[brett33]

pretty much on the money.

the restirction causes un-due backpressure.

Backpressure is the enemy of boost

I can understand how backpressure is the enemy of response and gas flow.

But you explain to us how it can effect the spring tension in the actuator.

Which after all is acted on directly by the inlet manifold pressure.

[benl1981]

A lot of magazines and on forums people say - fit bigger exhaust and you

will gain a psi or 2 but I still can't understand based on what I wrote

above. Most factory actuators will open slightly before the 5psi or

whatever boost they are designed to hold boost at. This is so that there

will be no boost spikes etc.

....Ok listen to this:

The wastegate will always dump enough boost before it gets to the desired

level so that it vever exceeds this figure.

With the new exhaust it may make the boost easier and with greater flow.

however the peak boost should be the sameI think if the actuator is left

unchanged.

[fresh]

with the backpressure posing a restriction with the stocko exhaust on, the most the turbo can produce will be 7 psi but when you remove the backpressure the actuator won't have changed, truth be known the actuator is prolly set for 10psi but due the restrctive exhaust etc... it only flow 7 psi

[benl1981]

I don't believe that. a 5psi actuator is a 5psi actuator. They are tapped into the inlet pressure to control the wastegate flap to maintain this level of boost. The difference that an exhaust would make would be similar to the differnece between eg. High load and low revs in 4th…this allows boost to grow quicker, compared with say flooring it in 1st from low revs…there is less load so boost doesn't reach its maximum till a little later in the rev range. The actuator still maanages to maintain boost at the predetermined level no matter what the scenario.

[32vspecII]

mine doesnt , its spike city . Theres about a 3psi varience using the stock actuator depending on the conditions , ie gear load etc . the stock boost guage doesnt show these but good aftermarket guage will.

[brett33]

mine doesnt , its spike city . Theres about a 3psi varience using the stock actuator depending on the conditions , ie gear load etc . the stock boost guage doesnt show these but good aftermarket guage will.

You do realise that the stock actuator on an RB25 is 5psi. If you're getting spiking

it would be more to do with the 7psi factory boost control solenoid.

[R31Nismoid]

I can understand how backpressure is the enemy of response and gas flow.

But you explain to us how it can effect the spring tension in the actuator.

Which after all is acted on directly by the inlet manifold pressure.

i dont know.

Same happened in a few turbo cars ive had.

My stock RB20... went from 7psi to 9psi with a 3" exhaust.

backpressure was less, car was more responsive, boost came on earlier.

Its in the practice that it works.

[32vspecII]

You do realise that the stock actuator on an RB25 is 5psi. If you're getting spiking

it would be more to do with the 7psi factory boost control solenoid.

hmm

the factory boost control solenoid is not plummed in . An ebc solenoid is in its place but that it switched off cause the ebc is not working so it just passes thru . so the only thing controlling boost should be the stock actuator

[RellikZephyr]

disbelieve it all you want but the facts are bigger exhaust means slight boost increase

not sure why...

i have a R32 GTR 3" dumps and 3" straight thu exhaust (and apexi pods) after removing boost restrictor

i am running 14 psi NO ebc or bleed valves or anything of that nature

but i am installing EBC this week to stop boost spiking (luckly never had, would destroy my stockers)

RellikZephyr

[justin911]

its generaly just the people that havnt actualy tried it that tend to argue....

seems to be the case with most things on the forums on the internet

[ruffryder]

i have a 3" cat back apexi exhaust, fmic... and it runs 11psi... and its an r32... so i dunno wtf is up with that... how can two simple mods bring it up 4psi?

[lordsnipe]

im the same. i got a 3" exhaust, fmic and solenoid mod (so it's always in high boost mode) and in a R33, i get 11psi from my gauge. does fmic and exhaust make 3 psi?

i'm a bit hesitant as i don't have the cash to replace the turbo if it blows, and i hear it here all the time about overboosting the stock turbs.