Correct Air Fuel Ratios ? - dyno chart attached

[jezzrrr]

Can you gurus have a look at the attached dyno chart and give any comments on the AFR i.e. is it too rich ?

[Jay95R33]

I wouldn't say it was too rich. It's on the safer side (11.5:1), but I wouldn't say it's too rich. The power gains made by pulling 0.5 out of it to bring it too 12:1 wouldn't be worth it.

If you think your lacking power, then maybe have a close look at the ignition map.

J

[Sydneykid]

Can you gurus have a look at the attached dyno chart and give any comments on the AFR i.e. is it too rich ?

Hi Jezzrr, let me start off by saying Steve knows his stuff, so the first thing I would do is ask him about the AFR's.

So to answer your question, for cars that we tune I would be aiming for slightly leaner ratios. I very rarely aim for less than 12 to 1 and I notice yours gets under 11.5 from 6,000 rpm onwards. Safety is an issue and there may be a valid reason why it is tuned that rich. It also may be a matter of tuning limitations, sensor out of resolution etc

Bottom line, ask Steve.

[jezzrrr]

Hi Jezzrr, let me start off by saying Steve knows his stuff, so the first thing I would do is ask him about the AFR's.

So to answer your question, for cars that we tune I would be aiming for slightly leaner ratios.   I very rarely aim for less than 12 to 1 and I notice yours gets under 11.5 from 6,000 rpm onwards.  Safety is an issue and there may be a valid reason why it is tuned that rich.  It also may be a matter of tuning limitations, sensor out of resolution etc

Bottom line, ask Steve.

Sydney Kid,

Cheers for the reply, you rarely aim for less than 12 to 1, what do you aim for exactly 12/12.5/13 to 1 ?

Jeremy

[Sydneykid]

Sydney Kid,

Cheers for the reply, you rarely aim for less than 12 to 1, what do you aim for exactly 12/12.5/13 to 1 ?

Jeremy

Hi Jeremy, a bit of philosophy first, otherwise my response might not make much sense. I use A/F ratios for safety not ignition timing, this is because I like to keep the response as fast as I can. Others may prefer to use ignition timing as the safety and sacrifice a bit a response so they can run higher A/F ratios.

Having said that, for a race car, I aim for 12.5, but it really depends on how close the detonation is. Some engines handle 12.5 easily, no knock at all, others are in the 30 to 40 range all the time. It is to do with the preparation of the engine, particularly combustion chamber size, shape and polish, with squish also being important. There is also the question of fuel, we can run 13 with Turbo Max but Optimax doesn't show as much gain up there. LMS is in between.

Plus we use a lambda sensor for each cylinder when tuning, this gives us a reliable A/F ratio for each cylinder. If you use a single lambda sensor then you get an average of all 6 cylinders, and some may be richer and some leaner than the average. Obviously all of the race cars have a lambda sensor fitting welded in each primary exhaust pipe.

For a road car, around 12 to 1 is my target, but again it very much depends on how close the detonation is. I check the individual A/F ratios with a pyrometer, but this is not as accurate as using lambda sensors. So on some cars you end up with an average of 11.5 as the best you can achieve. Often we find that the rear cylinders are lean and the front rich, so you have to tune to the leanest cylinder.

So it's not so straight forward, that's why I suggested you check with Steve, I am confident he will have sound reasoning.

[RNS11Z]

My car made 320rwkw with the fuel ratio going as low as 10.9 when on full boost. Off boost a/f ratio very similar to yours but mainly between 11.5 & 11.0.

[jezzrrr]

The difficulty in Perth is that we dont get Optimax we can only get BP Ultimate 98 so that may explain why its run a little richer ?

[Sydneykid]

The difficulty in Perth is that we dont get Optimax we can only get BP Ultimate 98 so that may explain why its run a little richer ?

That's OK, in Sydney we get Optimax sold as Ultimate.

[Steve]

To give you a different perspective again, I was told by a D1 Driver that they tune 11:1, and use timing to get good repsonse. This is how they tune their (Signal and Tinker drift club at least - that's who he drove for) cars.

[Steve]

BTW, nice dyno, nice fat power curve. Must be fun to drive.

[Guest INASNT]

WHat does RH stand for in the shootout mode settings? (As displayed on the bottom of the graph)

[Steve]

Relative Humidity?

[Guest INASNT]

Sorry i meant IT. Something to do with temperature?

[Sydneykid]

To give you a different perspective again, I was told by a D1 Driver that they tune 11:1, and use timing to get good response.  This is how they tune their (Signal and Tinker drift club at least - that's who he drove for) cars.

I can understand that, for drifting, they need ultimate throttle response. Plus drift is very harsh on the engine, free spinning wheels, high rpm for long periods, rev limiter incursions, low airflow for radiator and oil cooler etc etc. They can't afford to be blowing engines all the time, so a bit of safety is essential. By "afford" I mean a blown engine in competition means you loose, plus the cost of fixing it, of course. You also need to remember that, in drifting, a few horsepower either way is not going to make any difference to the result, but poor throttle response sure is.

This is quite different to a drag car where every horsepower counts. It is not so different to circuit racing where throttle response is very import, but you can't afford to give away a horsepower advantage to the opposition either. You need to tune it for the intended purpose, that's why I always ask "and what are you going to use the car for?"

Horses for courses as they say.

[BOOSTD]

That's OK, in Sydney we get Optimax sold as Ultimate.

:confused: is that the exception or the norm ? I have increased detenation with optimax compared to bp98(15-20points on PFC) Looks very different to me. btw optimax being the worse of the two.

[Sydneykid]

Hi Boostd, we have had a change of control fuel in Production Car Racing this year to BP Ultimate. Previously the control fuel was the same batch of Shell Optimax used by the V8Dinosaurs. I have asked a number of times for access to Ultimate direct from BP and have been told that only WA and SA have Ultimate sourced from Kwinana and it is not economical to ship it from Perth to Sydney. So the Ultimate sold here is actually sourced from a "local refinery". Since only the Shell refinery has 98 capability "locally" then all the Ultimate sold in Sydney must be Shell.

I can tell you that the Shell refinery is very old technology and the batches can be quite different. Hence the reason why they made one batch and used that same batch for the whole season of dinosaur racing. This has been happening for a number of seasons now and they stick it in a tanker and send it to the races all over the country. It even goes to NZ for the race there. If (as a registered team) you want to do engine tuning or practise then you have to go direct to Shell and get a drum from this batch.

Maybe you have been a victim of the "different batches" problem.

[BOOSTD]

Thankyou for that information Sydneykid. I will have to give optimax another go from another servo. Does seem to be cheaper in Shell form rather than bp from my local outlets. Even more reason to tune safetly if batches are going to vary that much =(