AFR numbers on dual fuel setup/300A tuning tip?

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gottago
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by gottago » Sun Jun 18, 2017 4:11 pm

I also went two steps heavier on the advance springs that on paper have everything in (with the black bush) at around 2500 rpm. However this does move the start point of the centrifugal well after idle.

The issue you have is you still get a slow curve rate with the bush.. go to using stops as I described above, and light springs.. basically you go as light as possible but not light enough for the springs to bounce at idle or fast(choked) idle. If you do, the advance increases, the rpms increase to a point the idle mixture circuits cant supply the required fuel, the rpms drop and repeats. you will find that usually cent all in at 2500 rpms will bounce the weights.. 2600 pushing it, 2700 good.



So timing aside I reckon I still have something a little weird going on (some sort of restriction?).


If was a 425 I would say remove the centre piston and check it and the bore for the most tiny of machining burrs.. a very light rub with around 1600or 1800 wet dry . Many yrs since messed with a 300...I would guess a similar situation inside that.
Q..Have you tried to run an impco 425 ? It may work better on a 400 cu in engine.

In regard your timing issues, the msd is a bit tougher to get to work with a low idle fast curve but there are ways around. An adjustable vacuum pot helps. I have used the heaviest and lightest spring in combination with a slightly higher initial. Heavy spring held off the curve a bit longer then went all in quickly due the light spring at about 2800. Vacuum filled in the middle. It worked for me but I was at much higher compression. Does your engine run well with a higher or lower initial?

Otherwise to get the low initial fast curve, an hei style distributer is much easier to tailor.


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Steptoe
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by Steptoe » Sun Jun 18, 2017 7:33 pm

I have been messing with LPG, classic, vintage compressions, re designing old engines, compressions , custom cam designes to run on modern fuels since the early 70s.
All I can say it I get damn good results.... for the last 30 odd yrs, and with technology and data loggers etc becoming affordable in the last 20 yrs...even better results.
If Im that wrong it would not be happening.
eg.. the thought of stopping a clutch fan can not be a prerequisite to coming to the conclusion it uses more power...crunch a few numbers.. eg load on alternators, and calc the momentum force of steel blades, then calc the force required to create that momentum...and that not all that force is from the engine but also the speed of the air while the car is moving...

Same basic reasons HEI / high voltage dizzies introduced...crunch the numbers, read the factory service manuals of the day...sections on points/ coil issues, and the bulletins.
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storm
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by storm » Sun Jun 18, 2017 9:20 pm

I had a big post written up in reply but it's not worth it. You obviously don't like being corrected so I'll stop correcting you and I'll just leave others to do their own research to see how some of the things you post are just wrong. Lastly don't get upset that someone corrects you. I don't get upset when I am corrected and being an Aussie I appreciate it that someone with more knowledge has taken the time to share so I can learn even more. Life is to short to be so uptight. I hope that's not "harsh" but I'm over the whole PC thing.
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Billhilly
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by Billhilly » Mon Jun 19, 2017 5:51 am

storm wrote: Converting Lambda back to AFRs for LPG will give you 1 Lambda = 15.5 AFR, 0.89 Lambda = 13.8:1 AFR, 0.85 Lambda = 13.2:1 AFR.

Going by these numbers your WOT could be left alone or slightly richened up but your cruise after 2200rpm is way to rich. I'd also Richen your idle back to 15.5. Now I have 1 question for you, how often do you mildly accelerate? 13:1 is to rich and wont provide you with more power than 13.5:1 or even 14:1

Download this file and check the part numbers in your 300A to the part numbers in the file, specifically what model 300A you have and what gas metering valve is in it.
I drove to a job today and richened the idle up a bit. Idle numbers are probably a bit rich now, but it's idling smoother. Cruise to 2200 rpm is probably still about the same. Yeah, maybe I'm not articulating this well enough, but cruise after 2200 rpm is way to rich. If I lean it out on the power mixture I get into a situation where it actually leans even more on acceleration.... Comes across as restricted.....
You lost me here -
how often do you mildly accelerate? 13:1 is to rich and wont provide you with more power than 13.5:1 or even 14:1
Where were you heading with that? Oh, and good spotting on the gas metering valve. The guy I spoke to in the States talked about that as well. I will dismantle it and check, but my (poor) memory says I replaced the valve when I rebuilt it like for like. The -49 has the three slots and that's what I had.

gottago wrote: Q..Have you tried to run an impco 425 ? It may work better on a 400 cu in engine.

In regard your timing issues, the msd is a bit tougher to get to work with a low idle fast curve but there are ways around. An adjustable vacuum pot helps. I have used the heaviest and lightest spring in combination with a slightly higher initial. Heavy spring held off the curve a bit longer then went all in quickly due the light spring at about 2800. Vacuum filled in the middle. It worked for me but I was at much higher compression. Does your engine run well with a higher or lower initial?
No, haven't tried a 425, but again, a good thought. I'd actually thought about twin 225's..... but that's another story. The 400cid motor is right on the limit of the 300 according to the Impco data. Again, after talking to guys who have installed alot of these over the decades they were reasonably happy and told me to install it and see how I got on. Time will tell. The 425 has only a 6% higher hp rating than the 300 -70, so that's why I went off on the twin 225 tangent!
Good info on the MSD. I need to get a better timing light, and an adjustable pot, and play some more.
Does your engine run well with a higher or lower initial?
That is a great question, that I don't have an answer to. To many variables for my tiny little man brain at the moment! I will have to give the one heavy/one light deal a try though.

gottago
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by gottago » Mon Jun 19, 2017 2:00 pm

A good timing light is a must. MSD has the triple firing mechanism below 3000 rpm and some of the newer digital timing dial back lights don't work properly with it. I have run locked out timing with the msd just to test what timing the engine likes at various rpms. At times it has produced surprising results. You slowly up the locked timing then interpret all your recorded results and find a spring set that replicates what the engine liked best at all those rpms. Forgot to mention that I purchased an entire set of aftermarket distributer springs so the heavy light spring combo that I used may not be whats included with the msd.

ps.. I have used the 300 before and it leaned out on me at higher rpm in larger cu in engines. (You had to over richen early to get it to hang on later.) Not sure you are running into the same but if you have access to a 425, I think its worth a try.

storm
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by storm » Mon Jun 19, 2017 4:00 pm

Billhilly wrote:You lost me here -
how often do you mildly accelerate? 13:1 is to rich and wont provide you with more power than 13.5:1 or even 14:1
Where were you heading with that? Oh, and good spotting on the gas metering valve. The guy I spoke to in the States talked about that as well. I will dismantle it and check, but my (poor) memory says I replaced the valve when I rebuilt it like for like. The -49 has the three slots and that's what I had.
The more you "mildly accelerate" the higher your fuel consumption will be because the afrs you quoted for mild acceleration are way to rich. I was initially thinking the 300a was to restrictive so it was going full rich on mild acceleration. But then I was thinking if your WOT runs are leaner than your mild acceleration it may be the wrong gas valve. Anyway what model 300a do you have? If you have the 1-20 you wont get many rpm out of it because its airflow is lower than the 50-70.
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storm
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by storm » Mon Jun 19, 2017 9:03 pm

If your 300A is a 1 & 20 you've got 348 cfm to play with which equates to a maximum of 3500 rpm. If it is a 50 & 70 you've got 432 cfm which gives you an approximate max of 4200 rpm. I am wondering if you've got a 1 & 20 and it's behaving like a restriction when you load it up.
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Billhilly
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by Billhilly » Mon Jun 19, 2017 9:06 pm

The aftermarket springs/adjustable vacuum pot/timing tape need to be on my shopping list! No 425's around down here. Have only ever seen one listed on the local 'Ebay' deal. I feel like it's not tooo far off, but it certainly isn't right yet...

Storm, I should have said, I have the 50-70 so that's not the problem. (Just saw your second post there). I wonder if my terrible heads are compounding the problem, beyond 'they just don't breathe that well'?

Where about's in BC are you gottago?

storm
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by storm » Mon Jun 19, 2017 9:33 pm

If you had a BBC (396 or 402) with peanut heads I'd think they wouldn't be helping but modern (post 1967) SBC heads (even the bad ones) shouldn't be a problem.

I'm at a stage where it is getting hard to offer suggestions. Without seeing the vehicle and the LPG setup and being able to see what is going on it is difficult to diagnose things. People like Franz, Frank, and C3H8 are a wealth of knowledge and experience and will hopefully be able to offer something based on the information you have provided.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

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Billhilly
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by Billhilly » Mon Jun 19, 2017 9:36 pm

Thanks for your time/thoughts Storm. I'll keep working away at it. Hopefully one of those guys will stop by as well.

gottago
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by gottago » Tue Jun 20, 2017 9:58 pm

The stock heads are quite limited but should still run you up near 4500 rpm with half decent numbers. I'd just keep working it and set it up best you can for now. I'm a long ways of, Okanagan valley B.C. Too bad, I have somewhere around 30 spare 425 impcos in various conditions.

Billhilly
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by Billhilly » Tue Jun 20, 2017 11:22 pm

gottago wrote:The stock heads are quite limited but should still run you up near 4500 rpm with half decent numbers. I'd just keep working it and set it up best you can for now. I'm a long ways of, Okanagan valley B.C. Too bad, I have somewhere around 30 spare 425 impcos in various conditions.
Yeah, all the numbers say it 'should' work. I will keep at it.
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by C3H8 » Fri Jun 23, 2017 5:54 pm

I've been tied up for a while and it took quite a bit of reading for me to catch up on this one. I'm a very basic person and so I'm going to start with the basics of a 300 mixer. It is unique in the fact that adjusting the fuel mixture at idle also changes the mixtures for most light load and cruise conditions. It is also unique in that it can be used with almost any negative pressure regulator even if the negative pressures are different. This is due to the fact that you can change the position of the gas valve to compensate for different negative pressure.

The thing it cannot do is tell if an engine is stock or has different cams or has a different timing curve. The 300AM4 and 20 series has a different gas valve then the 300 50/70 series. The AM4 and 20 series has a gas valve marked V2-11 An alternate was the V2-49 for feedback use. The 50/70 series has a gas valve marked V2-39. An alternate gas valve for feedback use is marked V2-50.

The issue with the 300 is that if the Idle mixtures have to be richened due to an engine modification that changes the stock airflow this means the light load and cruise mixtures will be richened also. If the mixtures have to be leaned for any reason the light load and cruise mixtures are also affected. This is because the location required for the valve on stock engines is changed. This is the only mixer in the IMPCO line that moves the gas valve to change the mixtures. All other models route either air or fuel around the gas valve. An example is the 125 mixer redirect air from the air on top of the mixer to the area just below the gas valve. The 425 redirects fuel.

The only way to change the AFR ratio on a modified engine is to change the contouring of the valve. The V2-50 is the best example of this. When the engineering experts at IMPCO (Don Bass and friends) decided to design a feed back system they took the V2-49 and V2-50 and filed the vertical grooves bigger but the results were not achieved that they wanted. So the filed/machined the mid portion of the valve smaller to deliberately richen the area off idle to about the 80% load mark. The idle area was also richened this way slightly but the power area was left as it was.

The bottom line is that if a modified or even a stock engine is not right in a preferred area such as light load or cruise on a 300 system changing the valve position to suit that area will also affect the idle mixtures or vice versa. There is no way around it other than going to a feedback system or re-contouring the valve if possible.

Personally I like feedback systems. I have seen them used as great emission devices on vehicles with catalytic convertors. I have also seen feedback controllers used to smooth out the rich areas of a poor fuel curve on older vehicles, without cats, when the ideal fuel curve cannot be achieved. Simple Feedback systems can be used with the standard or rich valves even if it is not to achieve the ultimate emission control. Simple feedback systems only require the addition of an Oxygen sensor. One dealer I know liked them because it allowed even some control of the full load mixtures. He felt the 300 richened too much during medium and full throttle so he used a feedback controller with the standard valve. The controller flattened the curve during medium loads and he adjusted the power valve to specific levels with the controller keeping the mixture from going too rich.

Back to the bottom line. The mixer is what it is (Hate that expression). Some tinkering can make it better but it was engineered during a time that precise mixture control was not considered critical. With the poor design of stock manifolds decades ago the only important consideration was to ensure the fuel reaching all cylinders was adequate. Old engines with carbs were notorious for having poor fuel distribution to the outlying cylinders.

Sorry to be so wordy.

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