Interesting boost issues

[A7NTY]

Ok here is a perplexing problem that has me utterly confused.

On the Janspeed turbo.

The turbo has an external wastegate and is intercooled. The intercooler pipes appear to be sealing and ok.

With everything connected under full load in 4th or 5th gear she will make about  7 psi from around 3-4000 rpm, after 4000 rpm it starts to tail off, by about 6000 rpm its barely making 3 psi.

Now we would like to raise the boost as it now has a low compression engine, if I completely disconnect the vacuum pipe from the carb to the wastegate NOTHING changes its boosts in exactly the same manner.

Now I am utterly confused, with that pipe disconnected it should boost its head off, up to a ludicrous amount but it does not do anything.

I have looked over as Matt Maclennan thought it might have a pop off valve (a primitive form of boost control) unless I am having a Stevie Wonder day I cannot see one anywhere.

We have taken the wastegate off, and it may not be working properly but with the pipe off it should definetely not do anything.

I cant see that the turbo just wont make more boost, even on my old bluebird turbo I got the boost to about 2 bar with the pipe disconnected.... ..I am so confused and me and my dad have probably confused the hell out of Tim and Matt at RX motors too?

So the question is what the hell is regulating boost!!!!!!!!!!! :Hammer :Hammer  :2Confused

[Prof]

With the wastegate off, are you not now venting exhaust straight to atmosphere all the time ?  If you suspect the wastegate is maybe stuck open, then you need to blank off the pipe it was stuck to, then all the exhaust gas can hit the turbo and spin it with no loss, but eventually the turbo will be overwhelmed and fail to produce more boost.

[A7NTY]

Wastegate is definetely not stuck open, if anything its jammed shut.

Ant.

[kbareham]

Ant
It might be worth checking the diaphram in the wastegate. I have a Janspeed manifold and wastegate on my old Opel. With age the diaphram split and therefore offered no control at all.  The diaphram is replaceble.

Keith

[A7NTY]

My point is even with the wastegate disconnected its NOT over boosting.... I am certain the wastegate has seen better days but thats not at issue here.

[BlitzBoy]

The Problem is your wastegage Ant, even with the signal hose disconnected if the diaphram is split inside it will be leaking exhaust gases into the exhaust pipe via the wastegate rather suppling gasses into the exhaust housing of the turbo.
Take the wastegate apart and check the diaphram

[A7NTY]

I dont think it is the wastegate. The wastegate is external and gets its gas straight from the manifold, the spring is stiff as fduk, it wont budge at all, it also seems to be sealing well. Ian at RX motors seems to think it is a pop off valve, or a big boost leak, I will have to do some more searching another day.

Ant.

[BlitzBoy]

yes I realise your wastegate is external, it doesnt matter if your spring is stiff if the diaphram is split it will cause your symptoms, But if you say you have taken it off and checked it then the only other causes like Ian had said is boost leak or leaky pop off valve

[RE:Worx]

if your spring is weak you need to put boost prssure to the otherside of the wastegate to stop it opening. external ones don\'t work like poppet/flap ones. that\'s why external gates have two pipes into them.  You got a bleed valve yet?

Geff

[A7NTY]

All this talk of springs and stuff is giving me a headache. Ill have another look when I get a chance. Thanks for all the advice everyone.

Geff as it is a bleed off valve wont increase the boost - disconnecting the wastegate pipe did nothing so putting a bleed in that pipe want do sweet FA, I tried to ring you today to say I would like to change the booking to another day so I can get this sorted before I bring it over, not a lot of point as it is.
If I get too stuck ill just take it over to Tims and give him the headache I want the car to be right as its so damn cool.

Ant.

[Timrxmotors]

I think the wastegate is jammed slightly open.I say that because you should be able to push the valve back with your fingers.Unseize it ,and try again.

[A7NTY]

Fduk it im fitting a mazda 323 engine!

The trouble is I have this wastegate infront of me, I have to use my little brain to try and understand it, my dad is telling me one thing, and everyone else something else. Who\'d work with their father eh

Still we put it back together as is, running a pathetic amount of boost and he happily drove it home humming about its virtues.

Ill have another crack at the waste gate next week when I have some more time. Right now I have a promise to keep to the captain some pictures of some \'track beasts\' comin right up

[RE:Worx]

get a bleed valve bring it down and It will boost you are not understanding how an external wategate works, don\'t bother phoning me. have found it is a lot more cost effective to ignore the phone and get work done rather than spend all day on the phone giving out free advice.

Geff

[Glenn Butcher]

Ant, what size exhaust does it have on it?  is it a standard exhaust - and have you checked to see it isn\'t a blocked cat./collapsed baffle in a muffler or similar?

Does it do it in all gears? or does it boost properly say in 2nd gear all the way to the redline?

[A7NTY]

Its the standard Janspeed exhaust Glen (quite a big one) I am sure its not blocked, thanks for the tip though.

Yes all gears, but unless you REALLY put it under load (full throttle 2000rpm in 4th for example) you wont see more than 4-5psi max.