Boost dropping off

[Brigsy]

Just fitted a new turbo to the van whilst in bits - its the typical .42ar comp .49ex t28

The problem i have is the boost is coming in strong and peaking at maybe 1.6bar and dropping off to 1.3-1.4 bar at higher rpms.

Here is a vid of the problem http://m.youtube.com/watch?v=lC5G_SgQYA0

The current actuator setup is a fair whack of preload on a -34 with a small bleed off for current boost - was ok on old blower and previous blower

Have messed about changing actuator brackets - thought it was flexing - made no difference

No leaks as far as im aware on the boost circuit - all in good nick

I did have a problem with loosing 0.2bar boost after a long pull in 5th last year - never got to bottom of it and wound the bleed valve out more.

From reading old posts could the inlet/ex gasket be knackered? The engine is running sweet.

[westy94]

I have the same problem brigsy mine boosts to 22psi then drops back to about 20psi, but if I set my bleed valve to say 15psi it will stay there throughout the boost:scratch:

[GTphil]

have you tried back off the actuator to say 1bar then trying a bleed valve as above to see if it's any different?

[Brigsy]

I have the actuator preloaded at 1 bar with a bleed off to set desired boost. May take some preload off although i usually run loads more with no probs?

[GT Josh]

Possibly a tired actuator mate?? Or maybe a slight boost leak at the higher levels?? :scratch:

[GTphil]

strange one, spikes like a weak actuator would, so i can see why you have tried different brackets, do you have another actuator to try?

[Tony Walker]

You'd think an actuator working at 18psi at 4000rpm would be the same at 6-7k or is there increased pressure in the exhaust housing forcing the gate open?

[Brigsy]

Only got this actuator, the spring still seems brutally strong though? Might try more preload lol

[Mart]

More exhaust gas flow at 6-7k rpm than at 4k for sure.

Jon, just to eliminate what we were texting about yesterday, try feeding the actuator from the carb top instead, and see if that makes a difference.

[Brigsy]

I will have a play about with the ref location mate:agree: not a lot has changed apart from using the base of the scroll..saying that i may have used a -31 on my last t28 cant remember exactly now.

Going to do a leak test today if poss. Anybody local got a -31 that i can borrow for a few hours?

[SCHWARTZ]

I brought a -31 actuator off you maybe a year and half ago ish brigsy if that helps at all. Also I found that those ball and spring mumby development bleed valves to be a lot mote stable as was getting creep due to the ****e bleed valve I had before.

[Brigsy]

Ah yeah i remember selling it now lol.

I have preloaded the actuator more (which is only approx 10mm) and less of a bleed off is required. It seems better but still drops a couple of psi. Possibly tired actuator?

Done a leak test on boost cct, had it holding 3bar so all is ok there. Infact it must be **** hot as the cap decided to blow out of the airfilter leaving a small dent in the wing:laugh: absolutely poo'd me pants when it came out. Old gaffer who was watching me do it down my mates garage nearly had a heart attack!