boost spiking
Turbo Mini Forums

took my car for an RR check-up on saturday as i've been running minimum boost for a while now cos the settings have all been to cock.

while we were upping the boost it was peaking to 10psi then levelling out at 7psi around 4500rpm. is this down to me just using a stock actuator with a bleed valve? Would it hold boost better with a billet 10psi actuator or maybe even a boost controller so that i could run 10 & 15psi as and when needed?



was a decent trip to the rollers anyway, got the car running safely and highlighted a few problems. need to get a restrictor before my reg and rebuild the carb. The bloke was really sound, i dont think he's done much with turbo's but he's a mini specialist and wasn't one of these rag it up to 7500rpm and see what happens types.

car made 120 banana's & 138lb/ft, these were both at around 4500rpm aswell due to the boost spiking.

Nick :)

What spec is your engine Nick?

Alex

AlexF

its not a great deal over std really.

1293cc,
21253 pistons machined to 11cc,
ph2 cam,
st2 mspd head,
8:1 CR,
full SC box & drops, minispares diff,
stock t3 for now,
2wd cossie cooler

nic you would be better to fit a stronger actuator say 10 psi and then you can bleed the signal off from there!

you could try shortening the actuator rod by 5m or 6mm to give a touch more crack off pressure

if this does not get you what you want then go for the above i would also place a shade more preload on the actuator this stops boost spike!

cool, i think i need to look at my actuator pre-load anyway. at the minute with the bleed valve shut i'm only getting 1psi of boost so i think the arm may be a fair bit too long as it is...

cheers :)

Bud where did you go im looking for a RR for when mines sorted out im over by the NEC

i went to a chap in erdington, about 2 mins off J6 on the A38. i think his website is http://www.mini-specialist.co.uk there's a dodgy pic of me on there under the minifinity club RR day

Cheers Bud nice figures ill be running similar set up minus the 11cc pistons but ill have 30cc chambers in the head don't know what CR that works out to. I'll be buying an up rated actuator then added to me shopping list

Nick - the boost spike is definately because you have a weak or incorrectly adjusted actuator arm. However - I also had a similar issue in the past. The cure is to fit a restrictor in the line before bleed valve - OR to take the boost signal from the plenum chamber. Jimster did this and it held the boost beautifully. Very, very smooth.

as dave said, I connect my actuator to my plenum, my boost does peak slightly, but not as much as it use to. This was a graph was done back on 2003

Team Racing

cheers dudes. i'll have a play with the actuator arm first off then. if i get no joy there then i'll start messsing with the piping :)

i'm guessing there isn't a standard length on the arm? just a bit of trial and error?

aim for about 4mm preload on the acuator to start with and see how you get on. (e.g. need to pull on spring in actuator by 4mm for it to reach wastegate linkage)

cheers tom :)

i get this aswell but i do have a avonbar billet 10 psi act.

but jimster do you reon its because mine is piped from the inlet housing.

pehaps i will plumb it from my plenum as well to see if that fixes the prob

always looking for them bigger bunches of bannanas

hogy, give it a go, it worked well for me

Team Racing

Where else are you connecting the wastegate line too (other than the plenum?)

Alex

AlexF

the turbo...

oh!

I run mine off the plenum as its generally considered better.

You want to control the boost at the plenum, not the turbo outlet.

Alex

AlexF

6274 rpm @95 mph, what diff is that? a 3.6 or a 3.9

3.7 on 13"s

Team Racing

As a bit of an aside, I personally quite like a bit of boost spike, e.g. the wastegate being slow to react. Makes the car in question very driveable, e.g. when overtaking you get a good initial surge of torque to get you past whatever it is before the boost reaches steady state........

Wasn't saying it was the best way just how the mettys originally ran

Got me car re-insured yesterday and after having set about 6mm pre-load on the actuator took it out for a spin and it holds 10psi without dropping at all.

Cheers dudes

Edited by wil_h on 1st Mar, 2006.

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