leaky dv causing inconsisten afr?

[Corty]

bit of a strange one
i have twin grp a dumpers on my 5
i have been dialing in my carb and got the afrs nice - 12.5 - 12.8 on full chat @ 18psi
i noticed that the dump valves were sucking in air on idle
i have swapped them out to an old bailey one from my rs turbo ,which dosent leak (well it does on 20psi but not idle )

and now my afr reading have gone to poo
boosting in 13s -

do the 5s leak pressure on idle through the dumpvalves?
or do i need to get a new twinpiston bailey ?

also can someone post a cup mod pipe work as i have about a million pipes comming off the vac pipe to ecu and this cant be doing the advance /retard of the ecu any favours

Carb-
130 main - could be 135?
130 second stage
standard first stage
100 a/c jet

Ktec lobster
ktec 180 turbo
ktec front mount
ktec full twin exhaust
ktec ktec ktec.....l..

[scratcher]

Just do away with the dump valves - problem solved

Here's a link to the cup mod for the vacuum lines. There shouldn't really be anything else in the AEI reference line. Maybe a boost gauge but that's about it.

https://rtoc.org/boards/showthread.php?t=4756

There's easy to follow diagrams to the right of that page

Here's a photo from when I done it to my own car. The blue hose from the carb to the actuator is now the only part of the circuit.

The two ports on the lobster plenum just need to be looped together.

An old wheel bolt in the exhaust elbow cut off and welded to seal to replace the part from there and you're good to go.



And you'll be doing away with these bits.

[Corty]

thanks buddy
is the turbo gona be ok with 20psi surging back through it?
ill drop the dumpers off and try it i guess ?

[scratcher]

The air doesn't go back through the turbo
A lot of people have run pretty high pressure with no DV. I ran 24psi on my old Evo without one with no problems
As long as you turbo is on good condition and your oil supply is good there shouldn't be any issues.

[R5MJH]

also it will sound better as the wastegate will chatter more

[Trevhib]

Of the DVs I've seen, they only close up under throttle. So it sounds like there may not have been anything wrong with your original set-up. Why you would need two DVs though is anyone's guess. Some say one is one too many!

Also, if it's a Bailey piston type DV you swapped in then ditch it, they are no good for the GTT.

My advice would be, if you like DV's (and I do, at times), to put one of your originals back on, along with doing the cup mod.

[Alex]

As above. Your original AFR's are too lean also. Aim for 11.5-12 @ WOT