Hi Tone,Cobratone wrote:Pete, I did a lot of work on my Rover engine with regards to power and afr targets (easier with megasquirt) and found the best for my engine was 14:1 at idle, 15.5:1 at cruise, 13.5:1 on acceleration and 13.1:1 at WOT. I know we had similar engine outputs albeit with different induction and wondered whether you had tried the above figures and what your opinions were? Just for everyone else's info Pete is on carbs and I had tb injection.sidecar wrote:My AFR figures are 14.5:1 on cruise, 12.5:1 during acceleration and around 12.5 -13:1 at WOT.
I have tried lots of different AFR's for each part of the carb's circuit and the figures that I now use do seem to suit my engine. That does not mean that they suit other engines!
For example if I lean off the idle AFR the tickover quality really starts to go down the pan! One difference between my engine and yours (apart from the EFI) is the camshaft, I guess my cam is making my engine quite 'dirty' in terms of the exhaust gases. I sure that your EFI is helping too.
All the other carb circuits seem to react the same way, I can feel the cruise quality going all 'flat' as soon as the AFR for this mode gets to around 15:1.
One circuit that I was running too lean for a long time was the WOT, I was running it around 13.5:1 but a while a go I was messing with my NOS system, I had a small fuel jet in it and I was firing the system whilst the NOS bottle was turned off so the system could only dump fuel into the engine. I found that the engine pulled much harder above 5000 RPM when the extra fuel was being dumped in!
I then read Vizards book on carbs and manifolds, he explained how the WOT ratio must be between 12.7 -13:1 and going any leaner will harm the max BHP whilst going richer has a much less damaging effect on BHP. He also give a good reason why a carb will lose out to EFI in terms of max BHP! Basically a 4 barrel carb needs 1.5 inches of mercury pressure drop in order to work, this is about 5% of the available atmospheric pressure required to push the fresh charge into the cylinder. So in theory I've got a 5% penalty right from the start! (There are other reasons too!)
As you know I do like to take the pi55 out of you EFI boys on the Cob forum but really I know that in order to 'max my engine out' I would really need EFI.
I have some across a guy that has a dyno that bolts onto the hubs not too far way from me, at some point I may have another go at tweaking the carb and the ignition. (It would be good to fire the NOS and see what BHP it is adding). I've not been that impressed with rolling road dynos round here.
Cheers,
Pete
