Boost control
Turbo Mini Forums

Sorry to impose my ignorance/inexperience again.
I have fitted a new engine with a head by Turbophil and a cam from Kent stated to be turbo specific.The intercooler is now in a cold airstream and it performs way beyond expectation, showing 15 lbs boost on WOT.
I have a -31 actuator, which is unchanged, and this actuator only gave me 12 lbs with the old engine,although with a bleed valve I did run 15lbs occasionally.How has the boost been increased,without changing the actuator/bleed valve ?Is there any way I can reduce the boost with the present components, as I dont feel that 15lbs will ensure any kind of reliability?
(One thing has changed - the actuator is now actuated from the feed from the compressor housing, whereas previously I fed it direct from the inlet manifold)

plug it back to compressor housing, boost signal is stronger there.
From inlet manifold, it has been smoothed by pipes, interccoler, plenum and carb, in your case this seem a 3 psi restriction.

I agree entirely with what fab says, but tadge's last sentence says he has made the opposite move so pressure should have gone down, not up...

Are you still measuring boost pressure from the same place ???

Another thought, are you now using the original brass "Tee" connector on the compressor housing (assuming it's a Metro T3)... they are quite small so you may have a restricted signal, esp. for a larger actuator.

Also, if it was on the inlet manifold before, how could it have worked reliably/consistently under closed (or closing) throttle conditions ???

Schrödinger's cat - so which one am I ???

(One thing has changed - the actuator is now actuated from the feed from the compressor housing, whereas previously I fed it direct from the inlet manifold)


fab , i think tadge is sayings its NOW on the housing ,not before ?
thats strange ,normally if you take the pressure take off to the wastegate at the plenum youd get a higher psi ,unless where it was at the plenum was a dynamic take off ...tadge ,id put it back on the plenum and see .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Thanks guys for the quick response.
Dont understand your comment,Rod, re the poss. unreliability of taking the signal from the inlet manifold, as it gave me no problems of which I was aware. Can you expand, please ?.The boost guage was previously fed from the lean off connection on the carb flange, as covered in an earlier thread(I had run a 1/8 drill through it to remove what seemed to be a small spring and one way valve)It gave what I thought were representative boost readings AND showed the normal manifold depression on idle or closed throttle, despite what was said in the earlier thread !.The guage is now connected to a tee off the inlet manifold which also feeds the closed loop dump valve.Whether the boost guage readings are now inconsistent with each other is open to conjecture, but it sure as hell reaches for the horizon a LOT quicker than it ever did. Robert, will try what you suggest when I can get the silly grin off my face every time I gas it.I think we live quite close, I,m near H/Wycombe -maybe you could look at it sometime ?.

Oh, and no one has suggested how I might actually be able to control(reduce) the boost without changing components ,yet.

Would it not be a simple test to put the boost gauge back to its old feed point, just to see?

I agree with the above, I would expect the boost pressure to go down rather than up by changeing the actuator feed from the plenum to the compressor.

I really can't see how it would be higher, have you increased the pre-load on the actuator at all?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Schrödinger's cat - so which one am I ???

I think a -31 actuator should have an adjustable rod so lengthen it a few turns and see how much the boost drops by.

Thanks guys.
I am more confused than ever now Rod,as you seem to have interpreted what I have been saying as if I am feeding the actuator from the manifold whereas I am feeding it direct from the brass T on the compresor housing, as I said originally. I am now going to go away and boil my head for a while to try and work out what I am doing wrong.I shall try the simple expedient of switching the boost guage back,but the boost is clearly much higher ,going by the power.I am beginning to suspect a leak somewhere between the brass T and the actuator but my installation is so cramped I cant get in there without stripping away a lot of stuff.If I do, then I will also try lengthening the rod.May take a while - dont like testing on wet roads and we got a new grandson 48 hours ago, which is a bit of a distraction.

Congratulations!Another TM grandad.No doubt the higher authority is in great excite,requiring much of your time.
15psi rear wheel drive wet roads=very scary!

'Where does the engine go?'

Edited by Rod S on 18th Feb, 2009.

Schrödinger's cat - so which one am I ???

the other thing i can thing ok mate, is that as you have changed the engine a little the flow of it all has changed and that might be why there is a difference in pressue, so you might have to adjust things to suit your new set up

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

http://www.mattwoodsphotography.com

yes i agree mat , a much better flowing intercooler could have eased the flow ,so instead of losing ,say 3 psi ,through it your losing next to nothing so you get a 3 psi gain at the carb .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

i think something must have happened to your bleed valve. maybe it has been adjusted by accident in the instalation for example. or it was last on 15psi but you had forgotten?

is the bleed valve fully closed and giving 15psi? can you adjust it at all?

is your actuator set to 12psi or are you bleeding off to 12?

without either the bleed vlave being adjusted or the wastegate actuator being touched i cannot see how the opening pressure has changed. if the actuator is set to open at 12psi it should always open at 15psi (provided there is no signal being bled off!) if nothing is amiss with the set-up then there much be a leak in the pipe that runs from the compressor to the actuator.

if you change it and there is no difference then adjust the actuaor back to the desired level.

Bleed valve fully closed.I needed to open it to get 15 psi with the old engine etc.This is becoming a bit of an epic and I do appreciate the ideas.Give me time to sort out a few and I will report progress, if any.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Wrong -its the same intercooler, just placed in a cool airstream whereas before it was badly positioned and pretty ineffective.

AND the signal hase been moved from plenum to compressor.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Could you have had a slight leak from one of the boost hoses previously? Then by moving the cooler and re plumbing the pipework you have fixed the leak?

Either way, you need to adjust the actuator pre-load or (if this is not possible) fit a different actuator.

In the 13's at last!.. Just

I,ve sorted it !! Now running a nice steady 12lbs without the bleed valve,measured at the manifold(I now understand that the -31 actuator usually opens at 15 lbs which is consistent with the apparent pressure loss through the I/C) In the workshop by 7.30 to get something done before we dash off to see grandsprog and bit the bullet by stripping out all the pipework tp see whats happening.It was so simple even I realised what it was - a clip on the line from compressor to actuator was too big and had not closed down properly, also the bleed valve, previously shut right down, was slightly open, probably because the locking grubscrew had fallen out.Re assembled with all clips done up properly - road tested -big grin all round.
The possibility of a leak had been suggested and I was reluctant to set about stripping so much (you have not seen how cramped the engine bay is ) but the best answers are often the simplest.
Big thanks all round to everyone for putting up with my inexperience - hopefully it can only get better.

WWW.TURBO-MINI.COM

glad you have sorted it mate.

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

http://www.mattwoodsphotography.com