Propane Tuning AFR and Lamda

Propane, Butane, LPG, GPL, C3H8, C4H10
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PropaneIH
Posts: 10
Joined: Wed Nov 13, 2019 12:40 pm

Propane Tuning AFR and Lamda

Post by PropaneIH »

Good Evening All,

So I am new to the group and I have been reading up on a lot and its helped on my build. Today while being quarantined at home due to the Covid scare it was time to get the data logger out and start tuning my new setup. I am running 2 used Impco 425's, 2 used model E converters, and 2 used VC shutoffs. Converters and Shutoffs have been rebuilt by myself with new Blue diaphragms and parts. My setup is 355 SBC with S475 turbo and propane. The Zetronix datalogger I am using is currently logging AFR,RPM, and EGT.

I have blocked off the front 425 and tuning the rear while 2nd gear road tuning. The Zetronix was set on Gas Scale on AFR. And I set the idle mixture at 900rpm to 14.5. The Lamda is 0.99 when I edit the scale. Now referencing the (AFR numbers on duel fuel setup/300A tuning tip) post, 1 Lamba is 15.5 propane, and 14.7 gas. But many people on here reference the gas scale even Dario. Stating he has gotten close to 14.7 and not worried about lean out. Soooooo.... When I did my 2nd gear pull I was recording 13.3 AFR (0.9 Lamda), 4654 RPM, 1341 F egt.

So should I richen it up to 0.85 Lamda NA and then add the boost and see what it does?
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storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Propane Tuning AFR and Lamda

Post by storm »

Most O2 sensors and loggers are setup to tune in the petrol AFR scale regardless of the fuel. I, personally, tune in Lambda so that when people see me tune they don't get confused.

With regards to richening up and then adding boost it isn't what I would do but I'm not a turbo expert and others who are may chime in with their hard earned wisdom.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

PropaneIH
Posts: 10
Joined: Wed Nov 13, 2019 12:40 pm

Re: Propane Tuning AFR and Lamda

Post by PropaneIH »

Well I set the idle mixture to 0.95 Lamda on both front and rear mixers @ 900rpm. Was able to get the rear mixer set to 0.85 Lamda under WOT 5200-5500rpm. Am still adjusting front mixer under WOT. How do you know that you have exceeded the airflow ability of the Impco 425? As RPM gets higher does the AFR start going lean around 6000rpm on a 350 sbc?

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Propane Tuning AFR and Lamda

Post by storm »

PropaneIH wrote:
Mon Mar 23, 2020 2:09 pm
How do you know that you have exceeded the airflow ability of the Impco 425?
As RPM gets higher does the AFR start going lean around 6000rpm on a 350 sbc?
You'll get alot of different answers to both the questions depending on who answers them.
1. I run a vacuum gauge once you see the vacuum rising at high RPM WOT you have reached the stated airflow limit of the 425.
2. In theory, unless you have a race engine, the 350 chev should be fine up to about 5000 RPM, at 5500 RPM you'll need at least 473 CFM, at 6000 RPM you will need at least 516 CFM.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

PropaneIH
Posts: 10
Joined: Wed Nov 13, 2019 12:40 pm

Re: Propane Tuning AFR and Lamda

Post by PropaneIH »

Ok I'll stop tuning at 5000rpm as my limit. Once they are both set time to see what they can do together.
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PropaneIH
Posts: 10
Joined: Wed Nov 13, 2019 12:40 pm

Re: Propane Tuning AFR and Lamda

Post by PropaneIH »

So while road tuning the other day, the #2 Propane system while WOT coughed and the engine quit at roughtly 5000rpm. Coasted to a stop and could not restart the engine. I had to swap over to #1 system, and it restarted and I was able to drive home. When I got home I was unable to get it running or keep the engine running on the #2 system, it was very lean. It had been idling just fine earlier in the day before it stalled. So what troubleshooting I have done is swap E converters between system 1 and 2 yesterday. I started it today and it still has the issue on #2 system. So the converter is ruled out. Going to swap the VCC30's next before looking at the Impco 425.

Has anyone had issues with Impco 425's just coming out of adjustment or stopping working?

PropaneIH
Posts: 10
Joined: Wed Nov 13, 2019 12:40 pm

Re: Propane Tuning AFR and Lamda

Post by PropaneIH »

Well I found that the #2 425 mixer has a blown idle diaphragm. That's causing the lean issue.

Steptoe
Posts: 1504
Joined: Fri Feb 02, 2007 8:32 pm
Location: JAFA , New Zealand

Re: Propane Tuning AFR and Lamda

Post by Steptoe »

Sold all my cars etc when retired a while back
Spent a lot time on Data logger dialing in SB chev.
With a single 425 found lean out started about 4400/4500 then got more serious around the 4900/5000.
In practice, passing a large cattle truck (they are long in NZ) maybe doing 80/90km/h , the whole maneuver is over in seconds, going past the truck cab around 90mph and already backed off..hit 5200 rpms.
The amount of time at this lean and number rpms is very little.

The other thing you must do is not just adjust the mixture at any given load/ rpms, you must also adjust the timing curve.
Timing and mixture work very close hand in hand. Cylinder pressure at point of ign changes at different loads and rpms. this effects how and how much of the the fuel burns.
And have to keep in mind the required advance at say 4000 rpms at cruise will be very different to 4000 rpms under full load. hence the use of the old vac advance units... and that curve also has to be dialed in.
My Spelling is Not Incorrect...It's 'Creative'

PropaneIH
Posts: 10
Joined: Wed Nov 13, 2019 12:40 pm

Re: Propane Tuning AFR and Lamda

Post by PropaneIH »

The timing is locked at 30deg. No mechanical or vacuum advance.

Did you modify your 425 mixer by removing the plate in the gas inlet? What's the benefit?

Tom68
Posts: 75
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Propane Tuning AFR and Lamda

Post by Tom68 »

Steptoe wrote:
Sat Apr 04, 2020 3:43 pm
Sold all my cars etc when retired a while back
Spent a lot time on Data logger dialing in SB chev.
With a single 425 found lean out started about 4400/4500 then got more serious around the 4900/5000.
In practice, passing a large cattle truck (they are long in NZ) maybe doing 80/90km/h , the whole maneuver is over in seconds, going past the truck cab around 90mph and already backed off..hit 5200 rpms.
The amount of time at this lean and number rpms is very little.

The other thing you must do is not just adjust the mixture at any given load/ rpms, you must also adjust the timing curve.
Timing and mixture work very close hand in hand. Cylinder pressure at point of ign changes at different loads and rpms. this effects how and how much of the the fuel burns.
And have to keep in mind the required advance at say 4000 rpms at cruise will be very different to 4000 rpms under full load. hence the use of the old vac advance units... and that curve also has to be dialed in.
Glad to see someone that appreciates Vac Advance.

What's with the lean out ? are the 425's to small in the gas/vapour supply plumbing ?

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Propane Tuning AFR and Lamda

Post by storm »

Tom68 wrote:
Sat Apr 04, 2020 11:53 pm
Glad to see someone that appreciates Vac Advance.
You haven't read much of this forum if this is the first you have come across this. There are literally dozens of threads on here with various discussions about it.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

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