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

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

Post by storm » Mon Jun 12, 2017 12:49 am

BigBlockMopar wrote:This is where a programmable digital ignition system can be of great help to visualise what's happening at what rpm and vacuumrange, and also find out what your engine likes best.
Yes, programmable ignition systems are the best of all the options. No need for any mechanical or vacuum advance systems because the ignition computer takes it all into account. Having said that it still needs to be tuned properly.
BigBlockMopar wrote:Just for fun, I tried out the 14+14+14 timing map today to compare it to my current ignition map.
During regular steady state driving there was no obvious difference to be noticed.
Only during accelerations I noticed the 3x14 timing map felt a tad slower then my regular timing table.
I'd be interested to see how you actually had that setup in a spreadsheet.
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by BigBlockMopar » Mon Jun 12, 2017 6:22 am

EDIT:
I started a new topic with the ignition tables here -> viewtopic.php?f=5&t=1720
Last edited by BigBlockMopar on Tue Jun 13, 2017 6:10 pm, edited 1 time in total.
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by storm » Mon Jun 12, 2017 6:59 am

What's your normal kpa and rpm at various cruising speeds?

I wonder if this thread should be split into 2 topics?
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by BigBlockMopar » Mon Jun 12, 2017 2:51 pm

Highway rpm is around 2200-2400rpm.
kPa at those rpms and steady speeds is usually between 40 and 50.

To not further hijack this topic I started a new topic here: -> viewtopic.php?f=5&t=1720
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'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by kikkegek » Wed Jun 14, 2017 8:38 am

interesting topic...have battled this myself too

I hardly ever improved mileage with timing. Only driveability improvements.

The two things that really made a difference for me were:
- electric cooling fans: gave me about 10-15% improvement in mileage and better throttle response from less drag on engine

and

- swapping the TH400 in my K2500 for a TH700R overdrive transmission: improved my mileage only on highways, but by about 20-25% from the .7 last gear ratio....rpms went from 2900 at 100kph to about 1900 with the lockup engaged
daily: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.1 end gears - IMPCO425 mixer - IMPCO model E vaporizer
project: 1977 GMC C15 Suburban - 454 big block - TH400 - gasoline
sold: 1986 Chevrolet Suburban K20 Silverado

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

Post by Steptoe » Wed Jun 14, 2017 4:53 pm

Changing timing AND AFRs makes a huge difference in economy and power. Simply changing one or the other may only be slight, depending how far the other is out.
Any timing change.. be it at idle or in the rpm range will require a a change in mixture....unless the timing is over advanced... and visa versa.
Doing a slight turn on the dizzy, and a slight turn on the idle mixture screw is required, maybe also the idle speed...no difference to any where in the overall rpm range.
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by storm » Wed Jun 14, 2017 6:07 pm

kikkegek wrote:interesting topic...have battled this myself too

I hardly ever improved mileage with timing. Only driveability improvements.

The two things that really made a difference for me were:
- electric cooling fans: gave me about 10-15% improvement in mileage and better throttle response from less drag on engine

and

- swapping the TH400 in my K2500 for a TH700R overdrive transmission: improved my mileage only on highways, but by about 20-25% from the .7 last gear ratio....rpms went from 2900 at 100kph to about 1900 with the lockup engaged
You have hit the nail on the head right there. Anything running directly off the engine (fan, water pump, a/c, p/s) all use engine power and alot more than people realise. Also the higher the engine rpm at the desired cruising speed the more fuel will be used. One reason we got overdrive automatics was because the US was mandating better fuel economy numbers each year and one of the only ways to lower fuel usage on a big carburettored v8 was to lower engine rpm at cruising speed.
Steptoe wrote:Changing timing AND AFRs makes a huge difference in economy and power. Simply changing one or the other may only be slight, depending how far the other is out.
Any timing change.. be it at idle or in the rpm range will require a a change in mixture....unless the timing is over advanced... and visa versa.
Doing a slight turn on the dizzy, and a slight turn on the idle mixture screw is required, maybe also the idle speed...no difference to any where in the overall rpm range.
Most people don't have the tools to be able to see this though so they play with one and leave the other alone. OEM spends hundreds of hours setting things up, home mechanics spend 15 minutes and think they've got it spot on. Look at the effort BigBlockMopar has put into his car, 99.9999999999999% of people wouldn't take that much care and effort.
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by BigBlockMopar » Wed Jun 14, 2017 6:20 pm

Eventhough, after everything I've done to my car, I still can't produce any MPG's to be proud off, as I'm currently only netting around 12mpg.

The AFR's are 'fairly' in the ballpark, except for idling. Probably still a tiny leak in the vaporiser I suspect.
Timing is pretty much as good as I can get it as of yet with streettuning (although I want to add vapour injection EFI soon, to be able to play with that too).

The few things I'm suspecting of what are holding back the MPG's are the;
- 3.55:1 rear gears
- 'Heavy' late 90s dodge-pickup overdrive-transmission, with large 12" '60s stall convertor. Lot of mass.
- Small, stock cam in fairly low CR mid-1980s 318 engine. Although engine vacuum is great and all, I'm on the fence if this is really hurting MPGs.

I want to go back to 3.23 gears soon, and also plan to rebuild another Overdrive-transmission I have with a 1" smaller convertor, and it has Lock-up as well.
(Besides installing a high cr 360 engine.)
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'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

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

Post by Steptoe » Thu Jun 15, 2017 5:41 pm

Eventhough, after everything I've done to my car, I still can't produce any MPG's to be proud off, as I'm currently only netting around 12mpg.
Im between 15 and 16 mpg
Also musty go right back to basics..
The amount of mixture used per mile is directly related to the volume moved by the engine per mile. This can be by a smaller engine or a large engine at lower rpms. Ball park you need to know the amount of hp at the back wheels/ prop to move the vehicle (be it a boat, tractor, truck , car whatever) at a given speed There are std formula / constants one can use( eg crouches for a plaining hull boat) You also need to allow around 15 to 20% this for acceleration, small hills and maintain speed without a gear change , and for boats , chop, wakes , bar crossings.
Match those curves to your rpm/ hp curves.. and bang you have economy and power.
After working out some yrs ago the above, have since applied these principles to our boat...was 'professionally ' propped for cruise economy.. applied the 'camaro lpg' principles and found the 'professionals ' dont know the difference or even understand these principles...The prop I wanted did not exist, the next best thing... overall 47% increase in economy (overall mpg not gal/ hr), 4 mph increase in cruise, WoT 3 mph.
But the numbers indicated the boat was min powered for weight to meet expectations, so replaced the 115 hp with 150 hp.
Pulled another 12% economy at same cruising general speeds, and able to cruise another 5mph faster at the same economy as the 115 simply due to slightly less engine volume per mile even thu going from a V4 to larger V6 engine.
Also bonus, the hull performs like a totally different boat in every thing from flat water thru to heavy seas .

Basically this is how modern muscle cars can be so damn fact yet also economical.. all to do with final gearing to a matched hp/ torque/ rpms curves to meet the expectations of the vehicle with min volume of engine per mile.
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by Billhilly » Fri Jun 16, 2017 5:03 am

Thanks for all the information guys.
I've reduced initial to around 9 degrees, installed the 'black' advance stop bush, and that has dropped the initial/centrifugal from 36 degrees to around 28 degrees. Tomorrow I will make up some vacuum advance stops and drop that from 16 down to 12-14 degrees. 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. I'll get some help tomorrow and get some rpm readings to go with the advance curve. I talked to a guy in the States and he said a large percentage of vehicles running 300A's had their power mixture adjuster just on the rich side of middle. I was on the lean side of middle so took it up to the middle. Driving around over the last couple of days I've currently got AFR's of around 15.5 -16 right up to 2200rpm (about 80 kph) than as I accelerate away moderately they drop to 13 (as you'd expect) but never lean out again.
So timing aside I reakon I still have something a little weird going on (some sort of restriction?). Or do you think things will continue to improve as I work with timing/AFR's?
I'll let you know how I get on tomorrow.

Just for fun, I tried out the 14+14+14 timing map today to compare it to my current ignition map.
During regular steady state driving there was no obvious difference to be noticed.
Only during accelerations I noticed the 3x14 timing map felt a tad slower then my regular timing table.
Interesting info BigBlock. I can't find it tonight, but in one of my Impco books it also says low compression motors are less 'fussy' about timing changes. Intersting considering the slug I have....


I do have, like kikkegek, electric fans, but an OD is not going to be an option. So moving the (up to) 3500kg brick down the road is always going to take a certain amount of BTU's!

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

Post by BigBlockMopar » Fri Jun 16, 2017 4:35 pm

My smog heap under the hood only squeezes the mixture to about 8.7:1 so that could confirm timing might indeed not be too noticable for these engines during regular driving.
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MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by Steptoe » Fri Jun 16, 2017 6:41 pm

Dont believe everything about electric fans.. If going to replace a fixed fan.. yes.. If a clutch fan.. no.. forget the marketing propaganda to sell electric fans (like the 'flexi fan bs) .. . there is no load on a clutch fan when it is not needed.. this is one of those old wives tails.. like HEI was a upgrade, in the early 70s.. it wasnt.. it was introduce will the introduction of EGR.. lean cruise burns, and lean mixture means more resistance across the spark gap that need more energy available. to meet that extra drawn

lower compression.. cylinder pressure... means less advance higher octane means more advance needed.
So taking a low compression medium range/ duration rpm cam engine engine one hand you need less because of low cylinder pressure, but since LPG has a octane (NZ, most of the world rating system) of around 100, and std petrol only 91.
Also if want to increase cylinder pressure , decrease the duration of the cam for better low end cylinder pressure.
Which as I state before, compression ratio means squat.. it is the cylinder pressure thats important at a given load and rpm to meet the octane requires of the supplied fuel.. cam duration and overlap (little simplified) is the time the both valves are open on the compression stroke..the amount of pressure that is lost before both valves have closed (time this are open is also determined by the rpms... so higher the rpms les time to leak, higher cylinder pressure... So want bottom end torque/ hp low duration low overlap.
A classic extreme example is WW2 (1936 +1954) British 'Pool" fuel had a very low octane.. to meet this octane British engines where meant to have a compression ratio around 6.8 to 7 :1.. in reality they had around 5 to 6:1 and used a 'square' cam.. ie one that had no overlap that had any 'leak' on the compression stroke.
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.
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by storm » Fri Jun 16, 2017 8:14 pm

Steptoe wrote:Dont believe everything about electric fans.. If going to replace a fixed fan.. yes.. If a clutch fan.. no.. forget the marketing propaganda to sell electric fans (like the 'flexi fan bs) .. . there is no load on a clutch fan when it is not needed.. this is one of those old wives tails..
Have to disagree with you there. Even with a clutch you are spinning a mass that is not needed and I dare anyone to be game enough to put their hand in a clutch fan with the engine running and see how much of a load it has behind it (it will mash your hand if you don't believe me try it but if you have doubts then trust what I am saying cause I have seen the damage they can do).
Steptoe wrote:like HEI was a upgrade, in the early 70s.. it wasnt.. it was introduce will the introduction of EGR.. lean cruise burns, and lean mixture means more resistance across the spark gap that need more energy available. to meet that extra drawn
That's a blanket statement. EGR was introduced in the late 60s, HEI was introduced in 1974.
Steptoe wrote:lower compression.. cylinder pressure... means less advance higher octane means more advance needed.
Um nope, engine efficiency dictates timing advance. You can have a low comp engine with less advance than a high comp engine purely because its overall design makes it more efficient. Edelbrock did alot of R&D on high comp engines using various cams and timings and found that cylinder head design has more effect on efficiency than compression ratio.
Steptoe wrote:Also if want to increase cylinder pressure , decrease the duration of the cam for better low end cylinder pressure.
If you want to increase cylinder pressure put more air/fuel mix in it. Again we go back to cylinder head design not cam duration.
Steptoe wrote:Which as I state before, compression ratio means squat..
I agree with this 100%
Steptoe wrote:it is the cylinder pressure thats important at a given load and rpm to meet the octane requires of the supplied fuel.. cam duration and overlap (little simplified) is the time the both valves are open on the compression stroke..the amount of pressure that is lost before both valves have closed (time this are open is also determined by the rpms... so higher the rpms les time to leak, higher cylinder pressure... So want bottom end torque/ hp low duration low overlap.
You have totally ignored the 1 thing that determines how much air/fuel gets into an engine. If you have a crappy head/intake you aren't going to get good pressure cause you aren't going to have good airflow. Low airflow = low pressure.
Steptoe wrote:A classic extreme example is WW2 (1936 +1954) British 'Pool" fuel had a very low octane.. to meet this octane British engines where meant to have a compression ratio around 6.8 to 7 :1.. in reality they had around 5 to 6:1 and used a 'square' cam.. ie one that had no overlap that had any 'leak' on the compression stroke.
The static vs dynamic compression discussion is totally misunderstood and, dare I say it, overblown. Static compression is a calculation of overall volume and compressed volume. Dynamic compression cannot be calculated with any reasonable accuracy if we do not know how much airflow the engine is capable of in its fully built state. As an example an engine built with 10:1 static is often said to have 8:1 dynamic if it has a high duration cam. How do we know this? we don't. If it is BBC it could have peanut heads which have really poor flow and won't allow the engine to build pressure, or it could have oval port heads which have good flow and will allow an engine to build pressure at streetable rpms, or it could have rectangular ports which have alot of flow but the flow is to slow at streetable rpms to fill the cylinder efficiently but at high rpms will fill the engine extremely well. Engines should be built for a purpose not for dynamic compression. Build it with the right parts to suit the revs and fuel it will be used and you won't have to worry about dynamic compression.
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Re: AFR numbers on dual fuel setup/300A tuning tip?

Post by Billhilly » Sat Jun 17, 2017 2:01 am

As of half an hour ago this is where I'm at.
9 initial/20 centrifugal/11 vacuum = 40 degrees total advance.

Idle rpm 600 9 degrees - vacuum disconnected, in Drive
1000rpm 9
1500rpm 17.5
2000rpm 22
2500rpm 29 (all in)

AFR
Idle 16
Moderate acceleration 13
Cruise to 2200rpm 15.5
Cruise after 2200rpm 13
WOT from 2500rpm 14

Steptoe wrote: The issue you have is you still get a slow curve rate with the bush.. go to using stops as I described above

The top plate of a chevy dizzy.. be it HEI or points, has a couple holes.. tap that hole, get a grub screw, file the outside off into flats at different distances from the center. You now have an adjustable cam stop to reduce the amount of cent in the dizzy. set to your required cent amount of degs required.
While not 'adjustable' the advance stop bush on the MSD is
Steptoe wrote:stop to reduce the amount of cent in the dizzy..
is it not?

I am two steps down from the lightest springs that came with the dizzy. One step down had everything in a hair over 2000rpm. With the springs I've got you can't have 'light', 'very fast initial', and '2700 good'. You can have light, very fast initial, but you'll have all in well under 2000rpm....

So I've reduced timing a bunch, with some fine tuning to do. However I still can't get open road speed limit cruise AFR levels right. I don't believe this is a timing issue, but am open to suggestion. I need to do more miles tomorrow. Power mixture adjuster is right around the middle mark.
Can we put timing aside for a minute. I've richened the power mixture up since starting this thread, but now moderate acceleration from 2600rpm doesn't richen it up at all (because I'm already on 13) but WOT leans it to 14.....

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

Post by storm » Sat Jun 17, 2017 3:22 am

Ok back to discussing mixtures. When tuning an engine for different fuels you need to understand that different fuels require different AFRs (Air Fuel Ratios), the vast majority of "professional" tuners tune in Lambda not in AFR. Why? because Lambda doesn't change between fuels but AFR does.
So when you tune for petrol you want 14.7 AFR from about 1000 rpm (I actually do it closer to idle speed) right through to 85% of WOT. From 85%-100% WOT you need to richen it up to 13:1 or 12.5:1 AFR.

These numbers equate to 1 Lambda, 0.89 Lambda to 0.85 Lambda. Going richer than that does nothing for power unless you are using forced induction which you aren't. Furthermore going richer than required with LPG can, over time, cause valve seat recession.

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.
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