The V8 Owners Forum -

Hope this helps a few of you out on working out you air fuel ratios,

Cheers Coops!!

I've been scouring the net for AFR targets for my 4.6 RV8. Found a few but this is the best I've seen. Comments?




the only adjustment I've made is at 45kpa-50kpa/ 500-800 richer to 13.5AFR as the RV8 likes to be rich at idle. My closed loop is only engaged above 1100rpm anyway.

adamnreeves wrote:I've been scouring the net for AFR targets for my 4.6 RV8. Found a few but this is the best I've seen. Comments?




the only adjustment I've made is at 45kpa-50kpa/ 500-800 richer to 13.5AFR as the RV8 likes to be rich at idle. My closed loop is only engaged above 1100rpm anyway.

Looks as good starting point - and as you note, you will probably find it wants it richer than 14.7 around idle.
Probably dont need as much as 12.5 on a n/a engine though - but 12.5 is on the safe side, so you wont go far wrong.

My lump and Muscle Manta's are both stage III 4.6's running Eddy 500 carbs and similar 285 cams. Both need the AFR around 12.2:1 in order to get a good idle. MM's idle was a fraction leaner than mine but not much. I think the long exhaust pipes that he has causes a bit more back pressure and that it good for getting a stable idle, I run large primaries going into sidepipes. I've watched the idle on my car go unstable just by turning the pilot screws in 1/4 of a turn, the AFR was around 13:1. My mates 3.5 with a mild cam will run leaner at idle. (I can't remember the figure).

Both the 4.6 lumps will cruise at 14.5:1, the setup was an 86 primary jet and a 69 needle. We then tried a 70 needle in MM's car and the cruise went down the pan showing 15:1, the car was not drivable! This was just a 1 thou increase in the rod size! The 69 rods are home made. The power step at the moment is 52 but we might try 55. With EFI I'm sure that leaner cruise figures can be used successfully.

Both the 4.6 lumps run 12:1 during 1/2 throttle acceleration (The 55 step might get this up to around 12.5:1). The WOT is 12.5-12.8:1. I have to run a 77 secondary jet, MM's runs an 83 secondary!!

Thanks Elliot for the reply. My next step is to do some autotuning in Tunerstudio, wish me luck

sidecar, sorry most of that went over my head.

As a note, the 12.5 comment was in the wide open throttle area not the idle area.
Idle will need whatever it needs - it would be as rich as 12, but you risk plug fowling when its cold - try to get into the 13's

Eliot wrote:As a note, the 12.5 comment was in the wide open throttle area not the idle area.
Idle will need whatever it needs - it would be as rich as 12, but you risk plug fowling when its cold - try to get into the 13's

The factory setting for the 3.5 EFI is 1.5-2% CO, and I find I get a good reliable idle at 14.1 and 600 RPM. On a bog standard 3.5 with MS 2 V3 and IDIS.

DaveEFI wrote:

Eliot wrote:As a note, the 12.5 comment was in the wide open throttle area not the idle area.
Idle will need whatever it needs - it would be as rich as 12, but you risk plug fowling when its cold - try to get into the 13's

The factory setting for the 3.5 EFI is 1.5-2% CO, and I find I get a good reliable idle at 14.1 and 600 RPM. On a bog standard 3.5 with MS 2 V3 and IDIS.

I think that you have hit the nail on the head, a bog stock engine will run leaner on tickover than one that has large bore primaries, gas flowed heads and a longer duration cam. On top of that EFI must help too.

sidecar wrote:

DaveEFI wrote:

Eliot wrote:As a note, the 12.5 comment was in the wide open throttle area not the idle area.
Idle will need whatever it needs - it would be as rich as 12, but you risk plug fowling when its cold - try to get into the 13's

The factory setting for the 3.5 EFI is 1.5-2% CO, and I find I get a good reliable idle at 14.1 and 600 RPM. On a bog standard 3.5 with MS 2 V3 and IDIS.

I think that you have hit the nail on the head, a bog stock engine will run leaner on tickover than one that has large bore primaries, gas flowed heads and a longer duration cam. On top of that EFI must help too.

Yup. Once you modify an engine in any way, the stock settings for ignition and fuelling go out the window.

When I was running the standard flapper injection on my 3.5, I bought a 'better' cam said to be suitable for the standard EFI system. Never got it to run properly, as there are no adjustments to the fuelling on that system, other than for idle.

On my twin turbo rover 3.5 what should I be looking for? I'm installing my wideband kits tonight

im using it on my road car, a rover sd1. if you go to the post on pre-cut lexan the company web site is there and they do all makes of cars. Smile rich
rectangular dining table