Jump to content
SAU Community

Recommended Posts

OK every base has been covered with the car, no leaks in the piping, HKS actuator set at 15psi (and 11psi)

This is what I'm faced with (see below)....initial comments on my car was it's very quiet for a 3" turbo back system.

I'm convinced it's too much back-pressure slowing the turbine down and boost dropping off.

Comments please :thumbsup:

post-1182-1185141113_thumb.jpg

Link to comment
https://www.sau.com.au/forums/topic/177679-confirm-my-exhaust-restriction/
Share on other sites

  • Replies 81
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Posted Images

Do you have an EBC? And what sort of exhaust do you have?

Have a look at the exhaust, do you have a hi-flow cat, mandrel bends, how many and what kind of mufflers (design and diameter). Dropping boost usually means a restriction somewhere, my exhaust is pretty loud but holds 12psi all the way to redline. My rotor has a fairly muffled 3" system with some crush bends, and it can't hold onto the boost to redline.

Fixxxer

Has a CES split dump, mandrel 3" the CAT should be a 3" highflow (installed by CES) doesn't have a hotdog it's a proper baffel toward the rear but the magnaflow twin tip is where I think I'm coming unstuck.

One run was done with EBC another with purely HKS actuator setting, also displayed the same behaviour with a turbotech bleedvalve, the stock actuator and trying an RB20 actuator.

I've got a nice free-flowing exhaust with cannon as a loaner to put on to confirm my suspicions.

seems awefully similar to mine

190rwkw 14psi dropping to 12psi

manifold was cracked and replaced, rear Fujitsubo was causing a restricition - added a highflow 3inch Kakimoto muffler and all is fine now. Just got to retune it, soon hopefully.

Hey Dan

One important thing that we need to know first. What turbo are you running?

I remember you telling me that its the slide highflow, but which one (rb25, rb25 oversize, vg, vg oversize).

Even the smallest one on 15 psi should make a fair amount more than that. On 15 psi, a car we did got around 225 rwkw (after tune).

Best way to find out, to just crack the catback off (including the cat) and see HOW restrictive it is

It's the VG30 oversize, it pretty much looks like as the engine is starting to get going then the exhaust is restricting like hell.

I'd be expecting over 200rwkw at 11psi

A mate is giving me his system to try on the car, should answer the question instantly.

Whoever has heard my car would agree it's spookily quiet for 3" system :cool:

Whoever has heard my car would agree it's spookily quiet for 3" system :cool:

so was mine.... centre to offset muffle, muffled big time. very quiet.

got a 2ndhand Kakimoto 3inch centre to centre straight thru muffler off a GTR. niiiiice. $65 delivered from WA.

welded it on, nice sound, restriction gone. set at 14psi but seen 15psi in a cold valley with foot down mashn the pedal.

stage1 slide rb25 highflow turbo

For what it's worth Dan, Me thinks it's not the exhaust...... With my stocka, and almost identical exhaust to yours I am getting 176rwkw.

OK every base has been covered with the car, no leaks in the piping, HKS actuator set at 15psi (and 11psi)

This is what I'm faced with (see below)....initial comments on my car was it's very quiet for a 3" turbo back system.

I'm convinced it's too much back-pressure slowing the turbine down and boost dropping off.

Comments please :cool:

post-1182-1185141113_thumb.jpg

Mine does this too

boosts to 12psi and tapers off to 9psi (got 195.5rwkws)

also a r34 gtt and also very quiet for a 3" turbo back exhaust

I thought maybe my cat had shit itself

im going to make a new cat section and try that out

For what it's worth Dan, Me thinks it's not the exhaust...... With my stocka, and almost identical exhaust to yours I am getting 176rwkw.

It's not identical Pete, we've got different mufflers...yours is bigger. You've always had a better flowing exhaust than my one. You'r boost went through the roof after installing it, my stock turbo never really budged.

This is 100% exhaust restriction, I just wanted a few others to confirm.

Nothing else on the car can account for what's happening.

I suspect that it is exhaust restriction, but I don't think anyone can really say for certain.

When you knock the exhaust off and swap it with your friends, make sure you do the cat too. Some 'high flow' cats are not really high flow at all.

Your car is quite a bit down on power in terms of what it 'should' be making. After swapping exhausts, if you feel a lot more power, and response, then that means it was the exhaust :cool:

umm .. not sure why nobody has commented on this before

why dont you just disconnect your Exhaust from where it bolts onto the dump from the turbo ?

its going to be loud as hell .. and *might* run a bit lean .. but if the restriction is as massive as your leading it on to be .. a quick run on the dyno should be able to confirm if its pumping out much more horsepower. Even the " seat of the pants " dyno will tell you pretty quickly.

just support the remaining portions of the exhaust if your going to road test it and be careful and you should be ok ..

Obviously doing this on the dyno where you can keep an eye on mixtures etc will be the better way of doing it .

I suspect that it is exhaust restriction, but I don't think anyone can really say for certain.

When you knock the exhaust off and swap it with your friends, make sure you do the cat too. Some 'high flow' cats are not really high flow at all.

Your car is quite a bit down on power in terms of what it 'should' be making. After swapping exhausts, if you feel a lot more power, and response, then that means it was the exhaust :)

x2 'hi flow' cat is too much of general term everyone seems to be classifying their cats as, when most probably flow a lot less in comparison with quality hi flow metal cats that cost $350+

umm .. not sure why nobody has commented on this before

why dont you just disconnect your Exhaust from where it bolts onto the dump from the turbo ?

its going to be loud as hell .. and *might* run a bit lean .. but if the restriction is as massive as your leading it on to be .. a quick run on the dyno should be able to confirm if its pumping out much more horsepower. Even the " seat of the pants " dyno will tell you pretty quickly.

just support the remaining portions of the exhaust if your going to road test it and be careful and you should be ok ..

Obviously doing this on the dyno where you can keep an eye on mixtures etc will be the better way of doing it .

I said that above in my first reply.

I always do that even if the power is where I expect it to be.

Every exhaust IS a restriction. What matters is whether it is a restriction at that power level. e.g. your quite 3" exhaust shoudl flow more than the standard exhaust. At standard pwoer levels, it is most likely that it won't pose much restriction at all. But then, at 200 rwkw, 250 rwkw, or 300 rwkw, the restriction will become evident

That's why I always take it off and do a back to back run just to see how much restriction there is.

ok. you need to unsrew your cat converter heat sensor and scre in a suitible fitting to mesure actual back pressure. also is it an apexi boost controler? cos they do that, it is electronic?

if its a bleed valve then thats normal. and all the vac lines to come from the inlet manifold or it will do that to.

ok.. try setting the boost controler to 4 pound higher. iff it still drops off the same amouint, then its the boost controler setting.

also adjust the gain to max, then adjust the boost setting. always the gain has to be max to stop the boost dropping off.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • For once a good news  It needed to be adjusted by that one nut and it is ok  At least something was easy But thank you very much for help. But a small issue is now(gearbox) that when the car is stationary you can hear "clinking" from gearbox so some of the bearing is 100% not that happy... It goes away once you push clutch so it is 100% gearbox. Just if you know...what that bearing could be? It sounding like "spun bearing" but it is louder.
    • Yeah, that's fine**. But the numbers you came up with are just wrong. Try it for yourself. Put in any voltage from the possible range and see what result you get. You get nonsense. ** When I say "fine", I mean, it's still shit. The very simple linear formula (slope & intercept) is shit for a sensor with a non-linear response. This is the curve, from your data above. Look at the CURVE! It's only really linear between about 30 and 90 °C. And if you used only that range to define a curve, it would be great. But you would go more and more wrong as you went to higher temps. And that is why the slope & intercept found when you use 50 and 150 as the end points is so bad halfway between those points. The real curve is a long way below the linear curve which just zips straight between the end points, like this one. You could probably use the same slope and a lower intercept, to move that straight line down, and spread the error out. But you would 5-10°C off in a lot of places. You'd need to say what temperature range you really wanted to be most right - say, 100 to 130, and plop the line closest to teh real curve in that region, which would make it quite wrong down at the lower temperatures. Let me just say that HPTuners are not being realistic in only allowing for a simple linear curve. 
    • I feel I should re-iterate. The above picture is the only option available in the software and the blurb from HP Tuners I quoted earlier is the only way to add data to it and that's the description they offer as to how to figure it out. The only fields available is the blank box after (Input/ ) and the box right before = Output. Those are the only numbers that can be entered.
    • No, your formula is arse backwards. Mine is totally different to yours, and is the one I said was bang on at 50 and 150. I'll put your data into Excel (actually it already is, chart it and fit a linear fit to it, aiming to make it evenly wrong across the whole span. But not now. Other things to do first.
    • God damnit. The only option I actually have in the software is the one that is screenshotted. I am glad that I at least got it right... for those two points. Would it actually change anything if I chose/used 80C and 120C as the two points instead? My brain wants to imagine the formula put into HPtuners would be the same equation, otherwise none of this makes sense to me, unless: 1) The formula you put into VCM Scanner/HPTuners is always linear 2) The two points/input pairs are only arbitrary to choose (as the documentation implies) IF the actual scaling of the sensor is linear. then 3) If the scaling is not linear, the two points you choose matter a great deal, because the formula will draw a line between those two points only.
×
×
  • Create New...