Cosworth boost problems

[enginearin]

Hello all,

Having some problems getting the right amount of boost on my Dax cosworth.

The symptoms :

The car appears to generate different amount of boost depending on the load on the engine i.e. what gear you are in

in 2nd i get approx 15psi
in 3rd i get approx 16-17psi
in 4th i get approx 18psi
in 5th i get approx 19-20psi

After realising this was happening i held the car back on the brakes in 2nd gear and the car produces 20psi boost until you release the brakes and it drops back to about 16psi.

I am baffled... anyone shed some light on what's going on?

Cheers

Tim

[andys2]

Is there something in the ECU that limits boost in the lower gears?
I've heard of this being done to limit wheelspin, don't know if this is a feature on the Cosworth engine though.

[enginearin]

Errr.. i don't think so. i used to get the same boost in all gears.

Funny though, when i was trying to see the funny side of the problem i thought that gear related boost level was quite a good feature to have, especially when you've put the engine in a Dax! LOL!

Any more ideas?

[annodomini2]

You got an induction kit? ducted intake?

Higher velocity the air is force into the intake compressing it? an idea!

wastegate malfunctioning?

[Munter]

[pratchettmodeon]Just tell the imp working the boost controller to stop fing around........[pratchettmodeoff]

[andygtt]

are you talking peek... or is this what its leveling out to.

in lower gears the engine will level off much quicker than it will in higher gears due to the loading... your car is also much lighter than a normal cossie.

I can't get a peek of 25psi in first gear as it just breaks traction, second I can just manage it briefly..... its only in 3rd upwards that I can see its real peek (it levels out a little slower).

What you really need to check is that its leveling out at the same psi in each gear... about a year ago I had a problem were it wouldn't hit boost in low gears then build to much in high gears.
It turned out to be an air leak around the intercooler.... result was it overspan the brand new turbo and damaged it badly (needed a full re-build).

Andy

[enginearin]

Thanks guys,

I think that andygtt is closest to the mark here. Although i've jetted the amal valve so that there is no peak boost (it just settles straight away without surging)

I've checked all the hoses many times but i'm going to get a compression test done on the intake side of the system (pump it full of air and see if it holds!!)

I just hope and pray that my new turbo hasn't gone the same way as yours andy!!

Will post up the results of the test as soon as its done.

Cheers

Tim