Who Stole The Boost?

[mad082]

yesterday we stuck my mates 33 on the dyno. it has a fmic, turbo back exhaust, pod and a 3076r (IW, 0.63a/r). we were tunning the boost controller at 16 psi and it made 290hp but it was bleeding off boost back to 12psi at redline. it was making max power at 14psi at about 5500 rpm.

we thought it may have been the boost controller so we disconnected the hose to the wastegate to run open boost. no real change. it went up to about 18psi but then bled off back down to 12psi and there was about 1hp difference in power.

now we know there is a restriction but we aren't sure where. we know the cat is a bit screwed, but not sure how bad and it is on the 'to do' list. i'm also thinking it may be the fmic as i don't think it flows very well. it uses the stock piping but the core doesn't seem to be that good IMO. the air comes in the top (from the side) then has to do a 90 degree turn into the core, then has to do another 90 degree turn at the bottom to exit out the same side it came in. i think a cross flowing cooler would be an improvement. we are going to put a boost line in before the cooler to measure the difference in boost pressure between the 2 sides.

we know it isn't the pod, because we took that off and lost nearly 10hp, but i think that was more to do with heatsoak.

so any ideas you have would be welcome.

[sh@un]

have you eliminated the possibility that the spring strength on the w.g actuator may not be up to it?

[mad082]

no hadn't thought of that.once we have a look at the cat we might have another run and try and restrict how far the wastegate can move to see if that makes a difference.

[sh@un]

good place to start

[tridentt150v]

split dump? I assume 3" system.

[mad082]

no it is only a bellmouth dump pipe, but i know people making just under 250kw with the same dump pipe.

[Gazee]

no hadn't thought of that.once we have a look at the cat we might have another run and try and restrict how far the wastegate can move to see if that makes a difference.

if your cats blocked, boost will continue to rise and if your wastegate can't open all the way to expell the exhaust gasses, boost will rise

the only time i've seen it taper off at redline is when i had a bleed valve, i put the ebc in and it held to redline no prob

have you thaught about a air leak or something along the lines of that?

[tridentt150v]

Then my money is on the cat, replace it [like you said]. You have to do that before you can look at anything else anyway.

[mad082]

if your cats blocked, boost will continue to rise and if your wastegate can't open all the way to expell the exhaust gasses, boost will rise

the only time i've seen it taper off at redline is when i had a bleed valve, i put the ebc in and it held to redline no prob

have you thaught about a air leak or something along the lines of that?

if the cat is blocked the boost won't continue to rise. the air in the system will back up so the turbo won't be spining as fast. that is why people get a boost increase when they put a turbo back exhaust on.

[Gazee]

hhmm fair enough...

is he running the standard bov?

[mad082]

greddy type r i think.

i don't know how stiff it is set though.

[mad082]

also, the coils are miss firing, but as the boost drops they come good again. i was thinking that may cause a bit of a drop in boost as well. i will post the dyno graph up on monday. it has the boost pressure logged on it.

[Gazee]

have a read of this marc

http://www.skylinesaustralia.com/forums/in...20cat&st=60

or maybe you already did, its pretty much the same sheit that your mates going through

but at least your mates not getting infinite boost like what i was getting

[UCD15R33]

ok well a bit of an update (it's my car that mad082 is talking about). we just took the cat off. that is looking to be our problem. the rear honeycomb had turned sideways, so the holes were flowing sideways rather than from front to back, so effectively the cat was only flowing through about a 1" x 2" hole. mad will post up a pic of it on monday, and we are putting a new cat on next week (we just punched out the rear honeycomb for now, but the front honeycomb is still intact.

we will post up our findings later on.

[mad082]

here is the pic of the guts of the cat

as you can see, the rear honeycomb is blocking most of the airflow