Has anyone that has blown a motor actually seen the AF ratio 'required' to do so?

I continually hear about the 'no leaner than 12.5:1' for supercharged motors and I can only assume that that means AT ANY TIME.

Those that do not have AF ratio monitoring rely on the AF gauge when they dyno. My dyno AF ratio seems to be very rich compared to my actual track datalogging - only the order of .25 to .5 leaner in 'real life'. It is easily understandable that a dyno, especially without the eddy brake, cannot simulate real world and is to be used as only a guide. The dyno also only addresses third gear with no view of the affect or RPM swings at shift points.

In my case, my dyno AF was around 11.8 and I am seeing around 12.2 on the track with blips above 12.5 and I'm at 13:1 through most of first gear. I have my warning light set to show when I am leaner than 12.5 with at least 75% throttle and at least 4200 RPM. I see this little red light several times in each run.

As a further curiousity, what is the slowest running truck tp blown rods with a pulley and a chip?

Thanks,
Herb

 

On the dyno are you using a tailpipe sniffer or your own wideband?

 

Herb101, that is a reasonable question. It's good to see guys digging to find out what causes what.

It comes down to simple science. Too many folks think that the "A/F ratio" is only way to determine the engines state of tune. It IS a very good clue... but not the end all.

Stress that typically breaks the rods in a *bolt on* 5.4L S/C ford modular motor is detonation. Detonation is cause by more factors than just how fat the burn is. Timing being the number one thing to look at.

BTW: Your description of your A/F throughout your run does'nt sound unreasonable to me. A little lean maybe... what does your EGTs look like? What about the plugs condition?

Rich

 

One reason for the difference is that a dyno is static ( fresh air). On the track you are forcing air into the intake. Dyno fans cannot duplicate the amount of air a 100+ mph pass creates. At tip in you will always show very lean. 13.0 at tip does not sound that bad. Running high rpm's at part throttle will also produce lean A/F & high EGT's.

 

FLA-SVT - I used both the dyno's tailpipe and my own WB O2 (Dynojet commander). I datalogged the run and compared the two sets of readings and outlined it in this post:

https://www.f150online.com/forums/sh...10#post1446210

My WBO2 reads a bit leaner than the tailpipe sensor, by around .25.

Rich - thanks for the good words. The LAST thing I need to do right now is pick up rod pieces off the track and figure out how to get to work the next day!

When I had the EGT connected, I could not get data consistant with what I would have expected. At the track, the EGT would peg at 1600 and stay throughout the run. I brought up these concerns in an earlier post:

https://www.f150online.com/forums/sh...hreadid=163790

When I installed the WBO2, I pulled out the EGT, so I've not seen them simultaneously. The probe is still in place - I just need another spot to put a 2-1/16 gauge.

I've got the datalog of three runs overlayed from the other night. They are real consistant and all three have some weird 'blips' in them. I'll transfer the file from my laptop and try to get the plots posted tonight.

Thanks,
Herb

 

Where is your EGT bung located? If it's in the collector it's too far from the cylinder to be accurate. Basic rule of thumb is that it should be located within the first 4" after it exits the head. Also the quality of gage will make all the difference in the world. Autometer's are notorisly inaccurate. Do yourself a big favor and invest in a top quality gage system. I am currently running the DEFI 60mm BF series and love them. I have cross checked their accuracy and they are dead on. However they are not cheap. 3 gage setup with controller runs about $800.

 

Herb, under a load at the track with your truck in open loop full throttle low 13's for A/F above 4K in 2 or 3 should be grounds for a retune wouldnt you agree., did it ping at the track that night ?

 

Red,

I would think that over 13:1 near the top of 2nd or 3rd would CERTAINLY be a good reason for a re-tune!

I don't hear any pinging on my runs but there is a weild smell at the top end.?>

The datalog of my three runs is shown below - I sync'ed the time at the 1-2 shift and you can see how cleanly the three runs overlay. The questions I've got about it are:

1 - what's up with the dogleg in the middle of 2nd?
2 - what's up with the lean condition through most of first?
3 - what's up with the jogs above 12.5:1 through the run?
4 - is that dataplot a sign of danger?
5 - am I too damn ****?

My main concern is to find out how, comparing this with my Dyno data, I can make real-world sense of the danger threshold.



Thanks,
Herb

 

A/F is one thing, but high timing and a pegged MAF's have probably blow more motors than being 12.1 A/F as opposed to say 11.7

 

Casey - do you datalog in conjunction with the SCT Pro RAcer tuning?

Is there any way to easily determine the timing and MAF voltage?

I have looked at the SCT Raptor and will be purchasing one (one day). I have also looked at teh Auto-Tap a bit.

What other options are there for determining this info?

What experiences do others have with the Auto-Tap and/or Raptor?

Thanks,
Herb

 

I've got the Raptor, but havn't got a chance to use it very much yet since I just got it. Before I was using my old Predator to read MAF voltage, and check timing; but the resolution rate was kindof slow, spaced out, and hard to read.