Today I fitted a Stack AFR Gauge to see for myself if my car would run lean following recent addition of a 2bular 4/1 + decat+chambered silencer.
here it is …
I ran the car and did around 8 Full Power Pulls…
result??
AT NO TIME DID THE AFR GO ABOVE 13.5 on WOT …
Mostly was between 11-13
The car goes like a train, no flat spots ,no holes in delivery etc.etc.
All I can say is that the Lotus 260 Map is well able to accomodate a 2bular 4/1.
Maybe Sincs “could” squeeze a couple more ponies out of it … who knows?
But here at last is proof that with a proper Lotus 260 map there is no need.
Car is going on CN’s dyno in a couple of weeks to see what “difference” the exhaust setup has made. There have been no other changes since it was last there so it will be a golden opportunity to dispel any myths good or bad.
It says I’d better get some driver training in quick !!!
Answer to Boothy (below) … Yes m8 , it does !
If I were to stick my neck out I’d say 10%
If it is that will show over 300 bhp on CN,s dyno ,but let’s wait and see !!!
Well 14.7 is the magic figure for complete burn of petrol .
Anything higher than 14.7 is termed lean , likewise anything lower than 14.7 is termed rich .
For “high load acceleration” rich is best … ie lower than 14.7 … how much lower is the issue I think Frank raises .
The 14 green segments on the stack cover values from about 12.5 -15.5 .
Slightly rich is good news for protecting engines , lean is not so good for piston crown temps ,(although I think the pudding has been over egged in the Lotus community) .
I have not heard of any holed pistons in a 2zz Exige ??
For sure this thread will attract comments suggesting remap and tunes … of course it will . But for me I’ve achieved all I wanted from my little Orange project and if others benefit from my findings that’s cool .
Ps Frank … Fook me ! how rich should I be on wot ?
Us brits have to actually pay for our petrol whereas you yanks simply own the oil fields !!
If recall some of my basic engine knowledge and as Frank has alluded to, a naturally aspirated engine should run an air/fuel ratio of around 12 - 14:1 at peak torque.
The exact air/fuel ratio can be determined by dyno testing, with the ratio selected on the basis of the one that gives best torque. Rich air/fuel ratios can be used to control detonation, and this is a strategy normally employed in forced induction engines. Thus, on a forced induction engine, the mixture should be substantially richer: 11.6 - 12.3:1 on a boosted turbo car and as rich as 11:1 on an engine converted to forced aspiration without being decompressed. As is also the case for ignition timing, the air/fuel ratio should vary with torque, rather than with power.
Most factory forced induction cars run very rich full load mixtures, with 10:1 being common. This is done for engine and cat converter safety reasons - in case an injector becomes slightly blocked, or the intake air temperature rises to very high levels. These cars will normally develop more power if leaned out. Note that emissions testing does not normally take place at full throttle, so full load emissions can be high without legal problems.
In the engine operating range from peak torque to peak power, a naturally aspirated engine should be slightly leaner at about 13:1, with the forced induction factory engine about 12:1 and an aftermarket supercharged engine staying at about 11:1.
Now that you have read all that, it’s not me!!! It’s from a google about AFR’s for Supercharged engines!
The 2zz makes its best power in the 12-12.4 range anything lower loses power anything higher eats pistons… Don’t believe everything on the internet since the volumetric efficiency is not the same for every engine…
When I spoke to Jim, he mentioned that the car wouldn’t sound much louder, but it’s more the pitch of the noise that changes…apparently it’s more of a metallic sound?
I’d love to see some video of the car if you have time to record some! I bet it goes like an absolute train now.
I think this will be my next mod after my mounts because I need more power. Especially after a MK2 Golf pulled away easily from me on the M25 yesterday…although I don’t think it was standard!
Im with Frank here. The ideal when cruising is 14.7 for economy etc, but under load, high 11’s to low 12’s is where you want it. Slightly richer doesn’t seem to loose me any power at all, just builds in a margin of safety. I run my car at around 11.5 - 11.7 under any kind of decent boost.
However it isn’t as easy as simply the fueling, the ignition is a factor also. Power is all about the ignition timing. The more advance you run the more power it will make (obviously to a point) once advanced too far the power will drop off or you will get pre ignition. Also the more ignition you run the hotter the cylinder temps get and this can be countered by running more fuel.
So without knowing what ignition is being run we cant make an accurate assumption as to what a safe AFR is. Now Frank probably does know what ignition is being run, so is probably best placed to make the call.
