Boost issues

Gareth · Post by **Gareth** » Mon Mar 05, 2007 9:33 pm

Hi guys,

Obviously a question directed at the turbo peeps.

I have a -31 actuator controlling the boost on my Maestro Turbo, the Turbo itself is straight off a Cossie, running a 2.5 inch system from turbo back.

The problem i have is this - Inconsistant boost. I've noticed it more since i reverted back to a standard air filter housing.

Bascially my boost in 1st and 2nd is no more than 14psi, less with heat soak. In 3rd i might see 16 but then it drops back to 15psi +- 0.5psi, in 4th and 5th i can see 17psi without a problem.

Now i can cope with some small boost differences in the gears but a 3 psi difference is quite large IMO and it didnt used to be as bad as this.

The question is, will an uprated actuator with a stronger spring create some sort of solution to my problem? I've been on the look out for a -34 which is a 14psi spring, ideal for my needs as the -31 is a 7psi spring.

Gareth

stockcar · Post by **stockcar** » Tue Mar 06, 2007 8:30 am

sounds perfectly normal for most cars, all turbo's work in basically the same way in that the more work you give them (higher gears) the more effort they will return...................

how are you actually controlling the boost??

Gareth · Post by **Gareth** » Tue Mar 06, 2007 2:42 pm

As said, it runs directly off actuator boost, no electronic control, or a manual boost controller. I find i get excessive boost spiking with the MBC's. I understand the concept of more load = more boost, but still feel the boost should be stronger than what it is. Running the 7psi actuator means no matter how much i shorten the arm, it still actuates at 7psi, possibly lower, which reduces the boost build in the lower gears. With a 14psi actuator the wastegate stays shut for longer and therefore gives me more boost... in theory!

Also, because the arm is so short, the actuator doesnt open the wastegate enough in the higher gears, not enough to prevent the boost creeping anyway despite the cosworth exhaust housing which is very well designed.

Gareth

BenTaylor · Post by **BenTaylor** » Tue Mar 06, 2007 4:36 pm

I think an actuator with a stronger spring would only really help if the boost was dropping off at the top end.

Gareth · Post by **Gareth** » Tue Mar 06, 2007 11:49 pm

I've always found boost dropping off to be more related to things such as leaks under pressure, at least in my experience.

I guess it depends on the state of tune a particular engine is in. I used to have the boost dropping before i had a bigger exhaust but this was a long time ago.

The actuator would have to be really weak or not have enough pre-load to have the wastegate flapper open under boost and high engine load, something that is unlikely to happen on mine because of the amount of pre-load on the actuator.

stockcar · Post by **stockcar** » Wed Mar 07, 2007 8:19 am

if you use a proper manual boost controller (not a bleed type!!) then i would think you woukld have far more control over the boost than relying on the actuator to do it for you??

Gareth · Post by **Gareth** » Wed Mar 07, 2007 9:27 am

stockcar wrote:if you use a proper manual boost controller (not a bleed type!!) then i would think you woukld have far more control over the boost than relying on the actuator to do it for you??

A proper manual boost controller (i.e) a Dawes type device of which i have used many in the past do give quicker spool up.

I would not touch a bleed valves mainly because on my car its use would also mean bleeding off pressure which would go to the fuel pressure regulator causing it to lean out in 4th and 5th, this has killed many an O series engine.

The ball and spring type controller has its uses, but it still causes too much spiking no matter where i place the valve ( the closest i can get it is about six inches away from the actuator)

Unfortunatly due to financial circumstances i had to sell my last MBC, just like my Apexi air filter, my autometer AFR gauge and next on the list is my dump valve. I can make do without.

In the mean time i may add an external spring like the Vauxhall boys have done. I've tried this in the past and did find it made a difference and may keep me going until i can afford a better actuator as funds could not justify

Gareth · Post by **Gareth** » Wed Mar 07, 2007 9:48 pm

An update.

I removed a throttle pedal spring from a spare Maestro i had laying about and fitted one end to the wastegate arm, and the other end over the top of the actuator inlet, then refitted the actuator hose.

Result? Job done. I now have stronger boost in the lower gears, now seeing 16psi. In the higher gears the boost has not actually increased, im seeing a peak of 17psi and it hovers between 16 and 17psi on the gauge. So i have the results of a stronger actuator with zero expense and hassle

Rnash2002 · Post by **Rnash2002** » Wed Mar 07, 2007 11:50 pm

Glad you got it sorted