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Home > Technical Chat > what CO setting to aim for on a turbo setup?

All-agroA+

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When setting up a base tune with a gas analyser what should I aim for CO wise? I looked at the Metro turbo spec and it says between 0.5 -1.0 CO. Seems a bit lean to me, what do you turbo peeps recommend or are running In your cars? Using a BDD needle.


Brett

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What year is your car?

Yes i moved to the darkside *happy*

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All-agroA+

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W reg 1980.


stevieturbo

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For MOT purposes your car only needs to be below 4.5% CO and 1200ppm HCC

And I'm sure it will idle much happier richer than it will around 0.5-1.0% CO

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will


All-agroA+

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I noticed when I adjusted the CO it seems to stumble and possibly pink too on load, wich it didn't before I adjusted it. Was at 2.5 - 3 when checked it. Wernt a bad guess when set it up from sound and smell lol
Think I should go bsck to that.


metroturbo

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0.5 - 1% doesn't sound like the recommended CO. I'm sure it is more like 3%


Shauna

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Swansea boyo!

Sure my standard 998 was about 2.5-3.5% on the last MOT which is a 79/80 mini. If you want an exact figure (well what mines running at now) I can borrow a gas analyser from work and stick it up my zorst for you tomorrow

Edited by Shauna on 23rd Nov, 2014.

They don't die, they just get faster!


All-agroA+

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i think 2.5 3.5 % sounds more realistic than what the book says, richer the better on a turbo motor i guess? is the Standard needle only rated to 7 psi boost, or can you run a little more before a needle change?


Brett

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CO at idle is CO at IDLE, it is no indication of the fueling for the rest of the needle you seem to be confusing this with running


On 23rd Nov, 2014 All-agroA+ said:
I noticed when I adjusted the CO it seems to stumble and possibly pink too on load,


this is too lean, see above

On 23rd Nov, 2014 All-agroA+ said:
i think 2.5 3.5 % sounds more realistic than what the book says, richer the better on a turbo motor i guess?

the higher the CO the more fuel you are wasting and penguins you are killing
no richer is not better, correct is perfect, imo the lower the CO at idle the better

On 23rd Nov, 2014 All-agroA+ said:
is the Standard needle only rated to 7 psi boost, or can you run a little more before a needle change?


you should be asking what AFR is to lean on boost or a question along those lines, a wild stab in the dark will end in tears, also if you have an intercooler you maybe should be running less boost on the same needle

Edited by Brett on 23rd Nov, 2014.

Yes i moved to the darkside *happy*

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All-agroA+

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surely if the CO is 3.5% at idle, you would have a slightly richer mixture throughout the rev range regardless of the needle profile, than what you would if the CO was set a lot less like 0.5% because the jet is physically sat lower in the carb and thus further down the needle to start with to get 3.5%.

on my set up, it pinged at actuator boost pressure when it was set at 1-1.5% CO. i've wound it back up to where it was before i adjusted it, so now roughly 2.5-3.5 % CO and it does not ping any more.

on a turbo motor under boost safe AFR is 12-13:1, yes running richer can be wasting fuel, but in high boost it also helps cool the valves and pistons from what ive read and been told. id rather run richer and cooler than leaner and hotter.

at 4 psi i don't think that really applies until i get into higher boost pressure as a standard needle would surely over fuel on 4 psi.

im not running an intercooler at present but intend to do this.

if i wanted to run 10 psi with an intercooler at 8.8:1 CR what needle would i need to start with?

would i expect with the lower CR than the standard metro turbo lump i would need a little more boost to get the same power but would have increase the torque over standard?

i've seen "high boost" needles on ebay but they don't say what boost they're good for.


Shauna

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Swansea boyo!

I'm confused! Why are you trying to tune your car by co? Surely you should be looking at the aft gauge just to get you going before the rolling road like Brett has said? Mines got the bdd needle and runs okay on boost at 8psi, it's just too rich off it.

Edited by Shauna on 23rd Nov, 2014.

They don't die, they just get faster!


Sprocket

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Preston On The Brook

In the not too distant past, you tuned the fueling using an exhaust gas analyser. Tuning for full power you would aim for around 6% CO at full load full throttle (obviously on a dyno) with ~3% at idle.


Edited by Sprocket on 23rd Nov, 2014.

On 26th Oct, 2004 TurboDave16v said:
Is it A-Series only? I think it should be...
So when some joey comes on here about how his 16v turbo vauxhall is great compared to ours, he can be given the 'bird'...


On 26th Oct, 2004 Tom Fenton said:
Yep I agree with TD........


Shauna

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Swansea boyo!

Makes sense back in the day where nobody had afr gauges *tongue*. I'd be willing to stick one in to see the idle but I'm not driving around with a probe stuck in there haha!

They don't die, they just get faster!


stevieturbo

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Northern Ireland



On 23rd Nov, 2014 Shauna said:
I'm confused! Why are you trying to tune your car by co? Surely you should be looking at the aft gauge just to get you going before the rolling road like Brett has said? Mines got the bdd needle and runs okay on boost at 8psi, it's just too rich off it.


Idle mixture WILL have a direct link to mixture under all operating conditions, simply because it's the same needle and jet used for all loads.

If it's richer at idle, it will be richer at full load. And visa versa.

Obviously most CO monitors are far too slow to be of any use on the road, but there are expensive versions that read fast, and a proper gas analyser is far superior for tuning/diagnostics than any cheap AFR gauge....but you'd be close to 5 figures for that unit. Which makes them rather impractical for anyone but OEM testing etc.

And you tune idle by CO because that's the legal requirement you need to pass for MOT.
Lambda sensor based AFR gauges cannot be relied upon for this. Yes more often they may be fine and give a good indication of AFR which should relate to a specific CO, but in no way whatsoever does a Lambda sensor measure or know CO, likewise with hydrocarbons.

Both have their uses and their place and are valid ways keeping an eye on how the engine is running

Many cars of old were set via CO at idle, and this was the baseline to ensure mixtures were good throughout. Whether carb cars, early fuel injection like The Bosch Jetronic stuff, or Even Marelli Cossie stuff etc
All their generic chip upgrades were sold, plug it in and baseline to a specified CO level at idle via the idle adjustment screw.

Edited by stevieturbo on 24th Nov, 2014.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

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