AFR check after new turbo

[JFairman]

Just want to add 14.7 was a target back in the days when we had real gasoline with no ethanol mixed in. I don't know what kind of gas you're using but if it's E10 gas with around 10% ethanol mixed in the target will be somewhere around 14.1
That's because the ethanol molecule has oxygen in it so you have to run a little richer AFR to make up for that or it will run a little lean.

When I had a good running '87 911 turbo with idle speed timing around 10 degrees before TDC, 964 cams set at 1.25mm intake valve lift at TDC before the intake stroke, and a CIS flowtech 007 fuel head it ran best with idle AFR around 12.8:1 and 65mph steady speed cruise AFR on flat roads was around 15:1
CIS without a frequency valve controlled by an O2 sensor in the exhaust header is never perfectly consistant all the time and never will be but it can run very well within it's limits when everything is set up right

In the end maybe it's best to forget about all the numbers and just set it by ear where it runs best. That said not everybody can do that but if you have experience adjusting carburetors by ear you may be able to do that with CIS if it's not too far off.

[Jeff NJ]

And to back up what Jim is saying, I found that when my cruise AFR was a bit too lean, I could feel surging while driving at a constant speed. Slightly richening WCP from there got me to about 14 as my cruise AFR where my car is happy.

[flightlead404]

Originally Posted by Rawknees'Turbo

^^^

Theoretic perfect AFR for cruising is 14.7 (stoichiometric ratio), so you are actually on the rich side and sending a bit more than necessary unburnt fuel out of the tailpipe. I say "theoretic" as not all engines are going to run smoothly at that AFR - mine does and my steady highway cruising is even a few tenths higher depending on weather conditions, etc.

Best power is at around 100 deg f rich of peak egt, best econ around 35-50 deg lean of peak egt. You may need to be even richer than that to provide additional protection esp under boost or running long periods at high power.

modern cars in steady state cruise are at the ragged edge of lean misfire, but that's because we can do that with a modern ecu with sequential ignition and injection.

stoich is neither best power nor best economy.

[1979-930]

Originally Posted by Rawknees'Turbo

^^^

Theoretic perfect AFR for cruising is 14.7 (stoichiometric ratio), so you are actually on the rich side and sending a bit more than necessary unburnt fuel out of the tailpipe. I say "theoretic" as not all engines are going to run smoothly at that AFR - mine does and my steady highway cruising is even a few tenths higher depending on weather conditions, etc.

You need to factor in all that TexAZZ humidity helping slow the burn rate and reducing the chance of detonation.

[Rawknees'Turbo]

Good info Jim F. (different than "Effff Jim!" ) and FlyingFlamer!


Deez, I'm reminded of the TexASS humidity each time I stop the car and so much water is pouring out of the evap box that it looks like there's a radiator leak. Hmmmmm, maybe that could be a ready source for water injection (just need to use some of the meth from my pipe to mix with it!!!).

[flightlead404]

Originally Posted by Rawknees'Turbo

Good info Jim F. (different than "Effff Jim!" ) and FlyingFlamer!


Deez, I'm reminded of the TexASS humidity each time I stop the car and so much water is pouring out of the evap box that it looks like there's a radiator leak. Hmmmmm, maybe that could be a ready source for water injection (just need to use some of the meth from my pipe to mix with it!!!).

Lol I tried to insert a super excellent graph that I have that shows the relationship between AFR, EGT, CHT, power, and specific fuel consumption. Actually on this plot it's FAR nor AFR so its inverted, but still clear to see the relationship. I guess it didn't work.

I'm at 34,000 heading to TEXASSS as I type this (Allen/Dallas for a couple of days), so I'll try and re link it later.

[1979-930]

Question about the cold pressure. It wasn't mentioned in the thread.
My warm idle is good but when moving the car last night I noticed the car was drowning during warm up 9.8 - 10.1 when first started. I could hear it was too rich. So I'm going to raise the cold pressure a little tonight.

What should the AFR be during warm up? I would think 13.0 but thought I would ask.

And about how much BAR pressure would raise it 2 AFR points?

[Jeff NJ]

Every car is a bit different, but mine likes around 12 at cold start, maybe a hair less, which then slowly rises as the WUR warms up. I actually have to tweak mine again since it seems to be starting at around 13-13.3, which it just doesn't like. PITA, since each adjustment seems to have a slight effect on the other adjustments, so after richening ccp, my wcp will probably be a bit richer too and require adjustment.

[puddy]

My Cold pressure is set at 1.4 bar, it starts and idles nice so i'm not messing with it, I can't recall what my cold AFR is, probably 13-14ish.

I think the Cold pressure adjustment is one of the easier ones to make so may be worth tinkering with.

[puddy]

Minor update - just flogged my car at Mosport and the AFR gauge shows me dipping into mid 11's and back up into 12's before redline. I ran my best laps ever and the car was great. It's a hot day too. Oil Temperature never going above 190. I don't think I'll bother making any further adjustments.

I suppose if I were to adjust anything maybe it would be the enrichment threshold but I'm not sure what that'll really gain me? Other than changing the point at which the AFR start heading towards lean. I'm not sure if raising the enrichment threshold would lower the point at which the AFRs start leaning out, allowing me to have 6500+ rpm going into 13's from current mid 12's. Any comments?

[Jeff NJ]

I don't believe changing the enrichment threshold will have any effect on the AFR at higher RPM
All the threshold adjustment does is determine the RPM at which the boost dump will take place, and then it stays that way until the rpms drop from letting off the gas. So you should get the exact same amount of fuel at 6500rpm whether the threshold is at 4200 or 4800 rpm, for instance. Going higher with the threshold is only necessary if the AFR dips too low at the point of enrichment. The thinking is that at higher rpm, it is using more fuel, so it will be leaner than it would be at a lower rpm. Just be sure that you aren't going too lean just prior to enrichment if you raise it. Each car has its sweet spot for when to enrich and the datalogging either while driving or dyno tuning really helps to figure that out.

[JFairman]

I never felt much performance change when I fiddled with those 3 Brian Leask threshhold adjustment screws he puts in the bottom of the WUR.

If you take the thing apart you can see that the largest diameter spring seats against those adjustment screws so screwing them in will compress that spring a little. If I remember correctly there's 2 or 3 springs in there of different diameters.

Try adjusting them. Can't hurt unless you screw them in too far and they fall inside or something.
Count how many turns you make so you can go bck to where they were if you want.

[1979-930]

I’m good at idle and cruising. I even leaned it out more at cruising so the AFRs are mid to upper 14’s. The disc is all the way in and I have a 4800 rpm pill and I can’t get out of the 11’s on boost.
Any suggestions?
I feel like moving the disc in changed nothing. Could something be stuck inside the WUR?


Sent from my iPhone using Tapatalk

[puddy]

Originally Posted by 1979-930

I’m good at idle and cruising. I even leaned it out more at cruising so the AFRs are mid to upper 14’s. The disc is all the way in and I have a 4800 rpm pill and I can’t get out of the 11’s on boost.
Any suggestions?
I feel like moving the disc in changed nothing. Could something be stuck inside the WUR?

Sent from my iPhone using Tapatalk

I think it's strange your disk is pushed so far in. Mine is probably 1/8" in at most. I wonder why yours is so far off?

[JFairman]

When I had one the disc wasn't in all the way either.
I think some people go too far with one WUR control pressure adjustment and because they don't know what they're doing they try to compensate for that by adjusting the CO adjustment too far one way or the other.
Then CIS can become a miserable frustrating mess that never runs right all the time.
and...
EFI becomes much more attractive if you can afford it.