O2 readings at idle Options

[yeahmag]

Just an idiot check here... I got Evan's old header on the car and all fixed up. It now clears my tuna can, has leak free collector/slip joints, mounts to the stock trans location, and has an O2 bung welded just past the collector.

Now my question is simple. I wanted to idiot check that I should be gunning for 12.5:1 or so at all points; idle, transition, at WOT. I leaned out on idle to the point that I think I'll need a 65 idle jet on my 40 Dell's (34mm vent). I took an extra full turn on the idle volume screws to get it around 13.5:1.

I must say though I picked up more than a few HP with it. It's a 4-1 in somewhat of a KH design with a Phase9 style muffler with an extra 360 degree SS loop between the collector and muffler to add some length to the secondaries.

Pictures coming...

[Mark Henry]

12.5 to 13.5 is fine.
Idle has no load so it can be off.

[yeahmag]

Put in a 65 idle and it seems OK if not a bit soggy. 12.5-13.0:1 at idle and in transition. I think I'm going a bit rich from transition on to the mains now though...

I'll need to graph it I guess as watching the LM-1 is pointless as it changes too fast. I need to make or buy a cheap gauge that I can dampen the output...

[brant]

Idle really doesn't matter
it will hurt your emmisions.. and the motor isn't harmed by a leaner mixture at idle.

we often end up at 14:1 or around there (some times even more lean)

what matters is the numbers under load
and what really matters are the higher rpms.

your just hurting your transition and poor tip in performance
brant

[yeahmag]

Sounds like I should go back to the 62 idle then... Under load I was 13:1 or so on that jet. I'm richer than that now...

[brant]

I'm not expert.. but in my opinion that would be fine
just make it transition well from stop lights and not bog too bad.

then use the innovate for load testing on the road

I used an innovate to jet my carb'd street car
I did a part throttle average
and a redline average
(you can also watch for anomolys... or weird numbers in between)

the redline is really the more important number. If you have to sacrifice your part throttle in order to not go lean at redline then that is the sacrifice to make. You can change emulsion tubes (or venturi's if you have too) to get your part throttle numbers back.

Redline should drive your jetting and work backwards from there

I also used an innovate to tune an MPS on a street car and it was much the same process.

I also use an innovate to tune my race car, and I could care less about anything below 4,000rpm... so its the same process with all of the attention given to the range of 4k - 7.5k

in my opinion... idle jets aren't about fuel ratio adjustments. They are a way to fine-tune the main jets and also to tweek your low throttle response.

brant

[yeahmag]

I ended up with a 62 idle jet with my stock HE's and a bursch due to a lean part throttle (under load) condition at mid RPM's. With the short tires on a 15" rim I cruise at a fairly high RPM (3500-4000). This produced a lean condition going up hills of the like.

I was (and am) always fine at full throttle. Since I'll put the 62 back in and drive around a bit. Tip in right now seems a bit boggy with the 65. Seemed cleaner with the 62 even though I was showing lean conditions.

[Mark Henry]

You need to open up the main jets.

WOT and going up a hill are a full load and you should be 12.5 to 13.5:1
Same for going highway speed on level ground, you might be a hair higher say at the 13.5:1 mark.

You notice it goes crazy downhill and leans way out, that's normal and OK as there is no load.

[yeahmag]

Hmm... I thought I'd be on the idles at part throttle. I'm talking less than 1/4, but more than "cracked". Opening the mains is easy as I have a ton of them...