Jump to content
carrpet

AFR target ranges

Recommended Posts

Posted (edited)

Hi All,

Just installed an AEM X-series wideband AFR gauge and 0-100psi fuel pressure gauge in place of the old ash tray ! They seem to work really well. Very stable.

My fuel pressure at 5C this morning was 14 psi cold and 55psi with a warm engine (66 engine model).

I have the car warm idling happily at 950 rpm with an AFR of 14.3. Is that too lean ? The Americans seem to target 13.0 - 13.50 but they use a different WUR to Europe.

Would welcome thoughts.

Peter

 

Edited by carrpet
missing information

Share this post


Link to post
Share on other sites

What engine and fuelling?

Is this K Jetronic or .........?

Share this post


Link to post
Share on other sites
25 minutes ago, topcarrera said:

What engine and fuelling?

Is this K Jetronic or .........?

K-Jetronic on an '89 930 with a 66 engine

Share this post


Link to post
Share on other sites

From a warm idle only point of view then I really cant see that this AFR level by itself is anything to worry about - instinctively I would have thought something nearer to 14 or just below  (14.0 / 13.8).   Stating the obvious then of course of more real importance is that the various controls (WUR / Pressure Reg / Air Meter etc..) are all working as they should to ensure that mixture adjusts correctly as engine speed and load change.

Will your gauge respond fast enough and show reading during driving at different load situations?

If I had a 930 and wanted to be sure that things were running correctly then I would probably invest in a session on a rolling road with someone familiar with what should be expected    

Share this post


Link to post
Share on other sites
4 minutes ago, topcarrera said:

From a warm idle only point of view then I really cant see that this AFR level by itself is anything to worry about - instinctively I would have thought something nearer to 14 or just below  (14.0 / 13.8).   Stating the obvious then of course of more real importance is that the various controls (WUR / Pressure Reg / Air Meter etc..) are all working as they should to ensure that mixture adjusts correctly as engine speed and load change.

Will your gauge respond fast enough and show reading during driving at different load situations?

If I had a 930 and wanted to be sure that things were running correctly then I would probably invest in a session on a rolling road with someone familiar with what should be expected    

Thanks for the input.

Share this post


Link to post
Share on other sites

Sounds like you're measuring the fuel pressure post warm-up regulator? That's useful for seeing if the WUR is working properly but I'm thinking once you've confirmed that you want to measure the system pressure to confirm the pressure doesn't drop under heavy loads?

Your wideband lambda sensor should be as accurate as anything used on a rolling road. You can try adjusting the idle mixture but what's really important is the mixture under load.

Share this post


Link to post
Share on other sites

Hi 

25 minutes ago, sopor said:

Sounds like you're measuring the fuel pressure post warm-up regulator? That's useful for seeing if the WUR is working properly but I'm thinking once you've confirmed that you want to measure the system pressure to confirm the pressure doesn't drop under heavy loads?

Your wideband lambda sensor should be as accurate as anything used on a rolling road. You can try adjusting the idle mixture but what's really important is the mixture under load.

System pressure is spot on at 93 psi so the WUR is within specification for cold pressure, warm pressure and system pressure.

That was my next question. What should the AFR's look like under each of these conditions ?

Cold idle on start

Warm idle

3000 rpm gentle load

Under boost (WOT) 

Input welcome !

Share this post


Link to post
Share on other sites

This is a US view of target AFR ranges ?

Cold start idle = 11.5-12

Idle warm 14

Cruising 1500-2000 rpm cold = 12-13

Cruising after 10 minutes = 13-14

Cruising warm = 13.5-14.5

Light Acceleration warm (2000-2500 rpm) = 13-14

WOT On Boost 12

Share this post


Link to post
Share on other sites

For 100% efficient burn the optimum ratio for petrol is 14.7:1.

However the best burn doesn't necessarily yield the most bhp.

Share this post


Link to post
Share on other sites

I run an Innovate LM2 to log data and I see an AFR of about 13.4 at idle dropping to 11.4 at WOT and full boost. It around 14 when tootling along off boost on part throttle. 

At idle the motor is under no load so mixture isn’t going to matter much. What does matter is where your AFR is at under  boost and it’s this that you really need to understand. Logging boost, AFR and rpm allows you to plot this properly but you should be able to see roughly where you are just logging AFR. It’s better to record this rather than look at your gauge though as the world seems to accelerates on boost! 

Regards 

David 

 

143DA21B-D73E-40D0-8F04-2D315E0CF294.png

Share this post


Link to post
Share on other sites
2 minutes ago, Leicestershire said:

For 100% efficient burn the optimum ratio for petrol is 14.7:1.

However the best burn doesn't necessarily yield the most bhp.

And to get 14.7 across all conditions with a high tech WUR is a big ask !

Share this post


Link to post
Share on other sites
4 minutes ago, flatsix777 said:

I run an Innovate LM2 to log data and I see an AFR of about 13.4 at idle dropping to 11.4 at WOT and full boost. It around 14 when tootling along off boost on part throttle. 

At idle the motor is under no load so mixture isn’t going to matter much. What does matter is where your AFR is at under  boost and it’s this that you really need to understand. Logging boost, AFR and rpm allows you to plot this properly but you should be able to see roughly where you are just logging AFR. It’s better to record this rather than look at your gauge though as the world seems to accelerates on boost! 

Regards 

David 

 

143DA21B-D73E-40D0-8F04-2D315E0CF294.png

David,

That is very helpful thanks !

Have you set up your idle around an AFR target, a CO target or increasing the mixture until you get hunting then backing off a tad, until it stops or a combination of these ?

Peter

Share this post


Link to post
Share on other sites

Hi Peter, 

My only real target was an AFR less than 12 when on WOT and full boost, which is 0.8 bar on mine. I concluded that above 12 on a CIS 930 was too lean - just my own view. 

I normally set my CO at around 3-3.5%, which I consider fine for these motors (without air pump). When I logged this I had it about 2.9%. Yours is down at 0.5% which I think maybe a bit lean (without air pump), although it’s what your mixture is at full boost & load that matters.

I did all this as I was tracking the car so was on boost for relatively long periods so wanted to know it had a safe margin. On the road you barely get on boost so it matters less, which is why most 930s happily pootle about with fueling all over the place. Here is my LM2 install thread. 

Regards 

David 

Share this post


Link to post
Share on other sites
3 minutes ago, flatsix777 said:

Hi Peter, 

My only real target was an AFR less than 12 when on WOT and full boost, which is 0.8 bar on mine. I concluded that above 12 on a CIS 930 was too lean - just my own view. 

I normally set my CO at around 3-3.5%, which I consider fine for these motors (without air pump). When I logged this I had it about 2.9%. Yours is down at 0.5% which I think maybe a bit lean (without air pump), although it’s what your mixture is at full boost & load that matters.

I did all this as I was tracking the car so was on boost for relatively long periods so wanted to know it had a safe margin. On the road you barely get on boost so it matters less, which is why most 930s happily pootle about with fueling all over the place. Here is my LM2 install thread. 

Regards 

David 

David, 

I will take a look at your thread.

Are you able to convert my AFR of 14.3 to an 0.5% CO level. Is this where you got the 0.5% from ?

My 66 engine specification is 1.5 to 2.5% CO.

Peter

Share this post


Link to post
Share on other sites
16 minutes ago, carrpet said:

David, 

I will take a look at your thread.

Are you able to convert my AFR of 14.3 to an 0.5% CO level. Is this where you got the 0.5% from ?

My 66 engine specification is 1.5 to 2.5% CO.

Peter

I have found the conversion table for AFR to CO% 

AFR to CO% table.JPG

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


Gatherings organised via IB

Anyone attending a meet or event organised via ImpactBumpers.com does so at their own risk. ImpactBumpers.com is not responsible in any way for damage or personal injury sustained while attending any such gatherings. Please behave responsibly.

IB & Mighty Motor Media

ImpactBumpers.com is part of Mighty Motor Media Limited: UK company 07983578. The Impact Bumpers name and all logos are ©Mighty Motor Media Ltd. We have no connection to DR. ING. H.C. F. PORSCHE AG or any of its subsidiaries.

Respect Creative Copyright

We do not endorse the sharing of copyrighted images. Individual users are responsible for all content they post. It is impossible for admin to check every upload but we will remove disputed images swiftly to support copyright holders. Contact us anytime.

More JG websites

Using The Sheriff's other websites supports the IB forum! Please share my valuation services with anyone needing assistance.

×
×
  • Create New...