what is the cause of boost backing off if you set your car to run 2 bar and it holds only 1.5 bar after it hits 2 .what causes that .and any way to get it to hold all the way

 

fit an -34 actuator IMO.

Jets in the amal valve are also a factor.

 

Bosch-Man
i allready have a /34 and i use a bleed valve

 

Depends if the ECU is trying to bring it back down of course, as obviously if it shuts the amal valve again thats going to cause it.

The other thing of course is the turbo may not be big enough ot manage the boost further up the rev range, as t34's do kind of run out of puff, so is that it s dropping striaght off or trailing off?

 

chip-3door
yes its a t34.48 housing and its got a rs 500 intercoler and i dont run off a amal valve it runs off a bleed valve and a /34 .but ther alot of other with the same spec and the run and hold alot more

 

Possible its something nasty and expensive thats mechanical of course, but fingers crossed it isnt!

Bleed valves arent the greatest idea TBH, they dont really control the wastegate all that well, and the wastegate creep is bad too, which means the gate may not be shut properly making it easier for the boost to force it open

Whats the boost level with the bleed valve shut?

 

Ps

What rpm does it happen at?

If you are expecting a T34.48 to hold 2 bar to 7K for example, you can forget it!

 

Bad Jetting or a shonky turbo normally.

 

wont be jetting stu, he is on a bleed valve not an amal valve.

 

Can still be the jetting using my own terminology as the bleed valve is a jet of forms, its just adjustable, but in escense your right, im just trying to squeeze may way out of a capping . In this instance, how far away from the turbo the bleed valve is positioned will affect the amount of overshoot you see.

 

But its still likely to be a shonky turbo or an air leak.. lol

 

So what is it- closer to acruator means more or less overshoot?
I got a bleedvalve coming soon for the S13 drifto shed

 

I shot but i missed

 

Closer gives more overshoot from my limited experience of bleed valves, but it may be a case of there is an optimum point so its more of an "x squared" sort of curve?

 

I thought it was the other way round, as I seem to remember an article many moons ago, where they showed you how to get a big spike by having a huge length of hose (coiled up) between the turbo and bleedvalve, by varying the length, you could dictate the overshoot .

 

Makes sense as it would take longer for it to fill the pipe, but its just not how it happened on mine, but it might be to do with the speed at which the gate is moving too?

Im sure Stu can give one of his nice definitive technical answers later

 

What mike says is to do with length of hose though.

What im asking is a set length of hose, just the positioning of the bleed valve in it.
Ie in right by actuator or right by other end of pipe, or somewhere in between.

 

Stu @ M Developments
turbo is new .its starts to creep at around 5000 rpm buy the time iam at 6500rpm its holding 1.5 bar .with the bleed valve shut totaly it will hold1.3 bar may be i need to adjust the actuator to hold the wastgate closed for longer

 

TBH 6500rpm and 1.5 bar from a T34.48 doesnt sound too bad to me at all, im not really onvinced there is a real problem there!

 

try a .63 housing then, cos as chip says that doesn't sound like a problem ?

 

.63 wont help, more to do with the compressor not being able to flow enough if there no other problems.

If anything a .63 would make the boost drop more as will make the exhaust less restrictive.

 

Although running a .48 at the top end instead of a .63 to keep the boost up is not a good idea, just means less effective emptying of the cylinders (so less power) and higher EGT's (so less reliable potentially)


People focus too much on what boost they are running and not enough on making more power on less boost IMHO (not a dig at the thread poster, just cossie owners in general)
I dont see why cossie owners cant accept that needing 2 bar of boost to not even make 400bhp on a 2.0 16v engine is a BAD thing!

 

itsmeagain;

my point was more that he could make the same power on less boost, say holding 1.5 bar all the way

 

But ford drivers down want power, they just want boost

 

may the boost be with you