Not actually asking for help. More of a brag.

 

MOT time and the twin Dellorto DHLA 40's passed with no tweaks.

Nice and steady 900rpm idle.

 

0.668% CO which is ~14.22:1 AFR according to

https://www.mgexp.com/article/co-to-air-fuel-ratio-afr-table.149

 

The AEM wideband unhelpfully displays about 14.8 AFR for that.

 

This is 44 idles in .3 holders in 31mm chokes using the idle air bleed circuit for balance. I had to go richer idle holder because of E5 petrol.

 

The HC (unburnt) is tolerable with low vacuum from twin carbs and electronic ignition advanced a lot.

 

 

In other news, the floor pan needs some welding, so a Fail.

 

Could almost fit a cat.

https://jetex.co.uk/classic-car-converters/

 

Just put a 2F one on, it'll fit and have somewhere to screw the wideband into!

noticed my wideband doesnt read same as mot station...bit crap if its that far off 

I have a 4-2-1 stainless manifold so not sure about a 2F cat.

But I also found this inline cat from Eberspacher.

 

https://www.bestpartstore.co.uk/974296-eberspacher-retrofit-kit-catalytic-converter

 

I did once ask a VW dealer in Germany if a GK fitted Polo GT with Pierburg 2e3 carb could be converted to catalytic when leadfree petrol was introduced (tax advantages) but was told no. Super Verbleit 98 was still recommended for the high compression engine.

 

Though I'm fairly sure it's worse emissions starting with the choke or when the accelerator pump squirts at high load and I'm seeing 12.6:1 AFR whatever that really is. I wonder if the AEM/garage difference is because of the 5% ethanol?

This table seems to suggest that ~14.4 A/F ratio stoich would match 5% ethanol E5 petrol (linear interpolating between 0 and 10% rows) and max power for wide open throttle would be at 12.4:1 AFR.

 

Think the wideband measures only O2 and then calculates. While a 4 or 5 gas analyzer senses all the gases so knows exactly the CO% (after calibration in free air).

 

It does confirm my seat of the pants feeling that the mixture was a tad lean for gentle driving (above flat road cruise, like leaving a roundabout) which is why I upped the idle jets to 44, and then also a richer idle holder.

 

 

 

Hm, why are 20% and 30% rows the same?

Table taken from here.

https://board.moparts.org/ubbthreads/ubbthreads.php/topics/1947400/re-e50-air-fuel-ratio.html#Post1947400

Surely for 80% Petrol, 20% Ethanol blend,

it would be same as (80/100)x14.7 + (20/100)x9.0

= 13.56 parts of air to 1 part of fuel for stoichometric AFR.

 

And for max power same

(80/100)x12.6 + (20/100)x7.7 = 11.62 AFR

 

Edited 12 November, 20223 yr by dvderlm