AFR Tech Question

General engine tech -- Drag Racing to Circle Track

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AFR Tech Question

Post by Mike Laws »

Guys:

A hypothetical/tech question for comparing intake systems.

Given the same engine, same atmospheric conditions, same fuel, same inlet size (area), same dyno/race car, etc. (In other words – an ideal scenario for performance comparison of intake systems).

If this engine produces the same air fuel ratio value & trend from beginning rpm to ending rpm – does it matter what the induction system is as far as power is concerned? [Carburetor(s), carb location, EFI, MFI, inlet location, injector location, # of injectors…]

Note: Posting this on a few sites...
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Re: AFR Tech Question

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Mike Laws wrote: Thu Jun 28, 2018 11:35 am Guys:

A hypothetical/tech question for comparing intake systems.

Given the same engine, same atmospheric conditions, same fuel, same inlet size (area), same dyno/race car, etc. (In other words – an ideal scenario for performance comparison of intake systems).

If this engine produces the same air fuel ratio value & trend from beginning rpm to ending rpm – does it matter what the induction system is as far as power is concerned? [Carburetor(s), carb location, EFI, MFI, inlet location, injector location, # of injectors…]

Note: Posting this on a few sites...
Hey Mike,
Is there any difference in fuel droplet size produced by the different systems?

Stan
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Re: AFR Tech Question

Post by bigfoot584 »

Driving on the street, Yes.
Driving at the track, No.
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Re: AFR Tech Question

Post by user-30257 »

Did they burn the same amount of fuel to make the same hp?

If it's delivered equally homogenized between type into the combustion chamber, it may not matter the means of introduction.
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Re: AFR Tech Question

Post by Dragsinger »

Mike,

it seems to me, in simple layman's knowledge, there is no way to arrive at a "perfect world answer" [maybe in engineering theory, but in practical application, something always is a fly in the ointment.] You know from talking with me and watching videos of my work that my packages run well and win races. Yet, I never consider anything fully developed, always think something is beyond where I am now.

I have raced your old BLP carbs, other carbs, Ron's injection and find all of them to excel in one way over the other.

I do want to test one of the twin blade deals at some point.
Larry Woodfin - Team Woodfin Racing - Owner, Woodfin Automotive
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AFR Tech Question

Post by Mike Laws »

Stan Weiss wrote: Thu Jun 28, 2018 1:59 pm
Mike Laws wrote: Thu Jun 28, 2018 11:35 am Guys:

A hypothetical/tech question for comparing intake systems.

Given the same engine, same atmospheric conditions, same fuel, same inlet size (area), same dyno/race car, etc. (In other words – an ideal scenario for performance comparison of intake systems).

If this engine produces the same air fuel ratio value & trend from beginning rpm to ending rpm – does it matter what the induction system is as far as power is concerned? [Carburetor(s), carb location, EFI, MFI, inlet location, injector location, # of injectors…]

Note: Posting this on a few sites...
Hey Mike,
Is there any difference in fuel droplet size produced by the different systems?

Stan
Hey Stan!

There are no constraints or restrictions in mind. Pls feel free to think outside the box...

Mike
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Re: AFR Tech Question

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bigfoot584 wrote: Thu Jun 28, 2018 2:06 pm Driving on the street, Yes.
Driving at the track, No.
I'm interested. Please expound...
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Re: AFR Tech Question

Post by Mike Laws »

Headguy wrote: Thu Jun 28, 2018 3:30 pm Did they burn the same amount of fuel to make the same hp?

If it's delivered equally homogenized between type into the combustion chamber, it may not matter the means of introduction.
Great question! This is not a 'focused' real-world test (yet), so I cannot answer your question about consumption or bsfc. It would be a good follow-up...

Homogenization is definitely involved. I'm trying to figure out how involved it is and looking for ideas and practical experience to prove/disprove...
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Re: AFR Tech Question

Post by groberts101 »

Mike Laws wrote: Thu Jun 28, 2018 11:35 am Guys:

A hypothetical/tech question for comparing intake systems.

Given the same engine, same atmospheric conditions, same fuel, same inlet size (area), same dyno/race car, etc. (In other words – an ideal scenario for performance comparison of intake systems).

If this engine produces the same air fuel ratio value & trend from beginning rpm to ending rpm – does it matter what the induction system is as far as power is concerned? [Carburetor(s), carb location, EFI, MFI, inlet location, injector location, # of injectors…]

Note: Posting this on a few sites...
Based on your wording.. most definitely. Charge cooling and pulse strength(density), pressure stacking, etc. Just injector placement along can aid charge cooling and make life easier with more latitude in manifold design. Think dry manifold vs wet.. dry is more forgiving and allows larger csa without as many low piston speed fuel suspension related negatives.
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Re: AFR Tech Question

Post by Mike Laws »

Dragsinger wrote: Thu Jun 28, 2018 4:52 pm Mike,

it seems to me, in simple layman's knowledge, there is no way to arrive at a "perfect world answer" [maybe in engineering theory, but in practical application, something always is a fly in the ointment.] You know from talking with me and watching videos of my work that my packages run well and win races. Yet, I never consider anything fully developed, always think something is beyond where I am now.

I have raced your old BLP carbs, other carbs, Ron's injection and find all of them to excel in one way over the other.

I do want to test one of the twin blade deals at some point.
Hey Larry. Big fan here!

We agree. Nothing is fully developed, so there is always room for improvement.

You'll like the twin blades. "It's physics..."
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Re: AFR Tech Question

Post by Mike Laws »

groberts101 wrote: Thu Jun 28, 2018 5:45 pm
Mike Laws wrote: Thu Jun 28, 2018 11:35 am Guys:

A hypothetical/tech question for comparing intake systems.

Given the same engine, same atmospheric conditions, same fuel, same inlet size (area), same dyno/race car, etc. (In other words – an ideal scenario for performance comparison of intake systems).

If this engine produces the same air fuel ratio value & trend from beginning rpm to ending rpm – does it matter what the induction system is as far as power is concerned? [Carburetor(s), carb location, EFI, MFI, inlet location, injector location, # of injectors…]

Note: Posting this on a few sites...
Based on your wording.. most definitely. Charge cooling and pulse strength(density), pressure stacking, etc. Just injector placement along can aid charge cooling and make life easier with more latitude in manifold design. Think dry manifold vs wet.. dry is more forgiving and allows larger csa without as many low piston speed fuel suspension related negatives.
I'm thinking out loud so bear w/me. Are you saying that you can affect power by using any combination of the above systems all-the-while keeping the same afr's?
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Re: AFR Tech Question

Post by groberts101 »

Mike Laws wrote: Thu Jun 28, 2018 6:06 pm
groberts101 wrote: Thu Jun 28, 2018 5:45 pm
Mike Laws wrote: Thu Jun 28, 2018 11:35 am Guys:

A hypothetical/tech question for comparing intake systems.

Given the same engine, same atmospheric conditions, same fuel, same inlet size (area), same dyno/race car, etc. (In other words – an ideal scenario for performance comparison of intake systems).

If this engine produces the same air fuel ratio value & trend from beginning rpm to ending rpm – does it matter what the induction system is as far as power is concerned? [Carburetor(s), carb location, EFI, MFI, inlet location, injector location, # of injectors…]

Note: Posting this on a few sites...
Based on your wording.. most definitely. Charge cooling and pulse strength(density), pressure stacking, etc. Just injector placement along can aid charge cooling and make life easier with more latitude in manifold design. Think dry manifold vs wet.. dry is more forgiving and allows larger csa without as many low piston speed fuel suspension related negatives.
I'm thinking out loud so bear w/me. Are you saying that you can affect power by using any combination of the above systems all-the-while keeping the same afr's?
Sure either separate or combined induction design philosophies. High OR low injector placement(OEM's are doing it both ways, ie; direct injected) and high AND low injector placement(OEM's again).. plenum mounted(via F1), common plenum or split plenum, cross rams, IR in both short and long designs depending on desired torque/engine speed range emphasis. Shorter runners with bigger taper.. longer runners with smaller taper having same inlet sizing.

Seems obvious that some/many of those combo's may require specific AFR's for best power output that may not be identical to one another, but in that same token there may be some similarities for some combinations of parts despite not having identical style induction systems. Fuel efficiency be damned one combination may make best power when spitting flames out the collectors while another may have far superior combustion chamber/space design and require far less ignition lead to make similar power numbers. Just far too many variables and seems entirely feasible that even just a plenum change(design and/or volume) alone could add power without throwing a major wrench in the AFR between two otherwise identical engines.
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Re: AFR Tech Question

Post by MadBill »

The first question could be "are we referencing AFR as measured by air and fuel turbines or via accurate wide band sensors?" If the former, large unburned droplets might be present, so equal indicated AFRs could result in quite different combusted values, with a marked effect on power. Poor mixture preparation might also result in a slow burn that reduced power regardless of spark adjustments.
Also, depending on the fuel distillation curve, inlet air and engine temperature, etc., a fine-atomizing carb might produce max power at the same 'combusted' AFR as a coarse one, but due to the conflicting effects of evaporative cooling and charge displacement by fuel vapor, the power could be substantially higher or lower.
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Re: AFR Tech Question

Post by user-30257 »

MadBill wrote: Thu Jun 28, 2018 10:33 pm The first question could be "are we referencing AFR as measured by air and fuel turbines or via accurate wide band sensors?" If the former, large unburned droplets might be present, so equal indicated AFRs could result in quite different combusted values, with a marked effect on power. Poor mixture preparation might also result in a slow burn that reduced power regardless of spark adjustments.
Also, depending on the fuel distillation curve, inlet air and engine temperature, etc., a fine-atomizing carb might produce max power at the same 'combusted' AFR as a coarse one, but due to the conflicting effects of evaporative cooling and charge displacement by fuel vapor, the power could be substantially higher or lower.
Exactly. Ingestion value? Or digestion value?
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Re: AFR Tech Question

Post by cab0154 »

Not sure why anyone would target a given AFR. Its just a number. If you went from a junk carb to a carb with great emulsion and atomization you could theoretically get the same AF from both with the great carb using less fuel volume but making more power; due to far greater combustable surface area of the mixture.
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