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MG MGA - SU Tuning and Exhaust Monitoring

I had these comments buried in another recent long thread..I would welcome any comments/advice on exhaust CO monitoring ..and using the gunson monitor
""I have just finished a retune of the car and found it running lean ..resetting it right now using gunson colour tune . I have only a single SU HIF 44 with the judson supercharger so tuning is relatively easy....no doubt my fuel consumption will increase ( and maybe a little more umfh) but not by much and ..
I have also just bought a Gunson Exhaust CO analyser from Amazon UK ( I had a load of gift cards for this bunch for my recent birthday ..got it for just under 100 quid delivered to Oz.. so pleased.) . It won't arrive until mid march but reports i have read are generally ( but not universally) complimentary . After reading up a load on exhaust gas I expect to be looking for about 2% CO or thereabouts...see generic chart I came across below.""


Neil Ferguson

For our cars 5% is around the mark.

A Bowie

I have just been reading Peter Burgess's "How to Power Tune MGB.." and he has precise commentary on this subject . He states (for mgb) that the best power is at 5% CO and best economy at 0.5 to 1% . He recommends about 2 to 3% as a balanced average . I also read in Vizards excellent " Tuning the A-series engine " that best power is at about 12:5 to 13 AFR. This corresponds very well with about 4.5 to 5% on the CO curve on the chart in my original post ...and Vizard recommends 14:1 for the A engine ..which is about 2% on the curve .
A reasonable correlation for similar vintage engines ..but not been able to find anything on the MGA !!!!
Looks like 2 to 3% as a starter target

Dominic..thanks for your comment re MMO and its possible CO affect on another thread. I will try with and without .
Neil Ferguson

I reckon 3% is too lean.
A Bowie

A Bowie.. I would ask upon what basis you make your very precise but short statements . I explain in some detail how I arrive at my conclusion and they are based on some detailed expertise by others.
Have you had your mga on a rolling road with exhaust emission testing ..or is it judgement??
There must be others out there in MGA land who have tested their car on rolling roads and exhausts .....advice requested?
Neil Ferguson

Neil you asked for an opinion, and 5% is mine.

To be honest a lot of my tuning experience is with 6 cylinder Jag XK engines. I have had a couple of these cars on the dyno over the years and it does seem to correlate reasonably with what I've found with plug chops, which I accept are a somewhat subjective measure. A dyno is also an artificial playing field, to a degree, when compared to real driving.

I've got both the books you mention above as well and both authors have a wealth of experience. Des Hammill also has a couple of books on tuning cars with SU carbs which are worth a look.

I'm currently fine tuning the engine I've built for my MGA. At present I'm running 5%. I have RO needles and heavier springs as the standard needles were too lean for the tune of my engine.

In essence it's all an exercise in suck it and see, as every engine is different. My view is that a bit rich does little harm and can always be corrected but too lean can cause damage. If it were me I'd start at 5% and go from there.

Cheers,

Andrew
A Bowie

Andrew..good to hear your reasoning and experience. I get my analyser in another week or so and will build up some personal experience from then . My objective is to try and get a reasonably and consistently slightly rich condition and try to maintain it over range idle up to 3000 rpm. ...luckily I have a single Su hif 44 ( combined with a Judson ) and it seems so far to be easy to adjust but I am sure I will have to change or hone the needle to get the range ....looking forward to it.
Neil Ferguson

Neil are you an MG Car Club member in Victoria?

One of my mates in Melbourne is going through the same process with a supercharged Pre War MG at the moment.

I'm sure he'd be happy to discuss this with you.

Let me know.

Andrew
A Bowie

Andrew..just rejoined last week . I have been living on NSW south coast but returning to Victoria in April ....with car. Would appreciate talking to someone with a similar set up....by the time I get to vic and the club I hope to have generally climbed on top of the co monitoring and tune ....
Neil Ferguson

Flick me an email and I'll send you his contact details.
A Bowie

Just got the gunson CO analyser ( ordered 27 Th February ) ..7 days early . It also was dispatched fron Denmark for some strange reason and I live way away from the big cities here in oz. how do they get a box from a warehouse in Denmark to a house in the oz bush in 11 days ..amazing !!!
I rushed to try it out ....took car for a spin to warm it up. Read the bumf, Calibrated the analyser and inserted to sampler......3.7% CO or about 13 afr ..too rich ...at 900 idle. Adjusted the mix ..and every quarter turn reduced CO by about 0.2% . Reduced it to 2.8% and then wound the engine up to about 2000 and held. CO reading at 3.4% .....wound the mix back to get 3% and went back to idle and CO was 2.6% and afr about 13.8 .
Very pleased with the kit ...will be playing more in very near future .....can tune the needle with this.
Neil Ferguson

This thread was discussed between 02/03/2016 and 09/03/2016

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This thread is from the archive. The Live MG MGA BBS is active now.