SDIF

I had my car chassis dynoed and it showed a 14:1 air fuel mixture. Dyno man said this is too lean.

From what I have read in my Dave Visard Books 13:1 makes more power because the extra fuel helps to cool the intake charge.

Car is very rich at idle 1200rpms
Timing is locked at 34 degrees


Here are the engine specs.

zz4 short block
afr 195 with 62 cc chamber
Felpro 1003 head gaskets
comp cams XR294HR .540 / .562 lift 242 /248 duration at .050
Edlebrock RPM airgap
holley 750 dp / no air horn / factory jetting / 71 /80 jets
1 3/4 headers open exhaust, boom tube

4 speed
3.25 rear end in 9 inch ford

3rd gear Car made 397 rwhp and 343 ft / lbs tq
4th gear Car made 405 rwhp and 379 ft /lbs tq

Dyno did not record any rpms. I believe the machine had problems with the pick up. It only showed MPH of 145.

I did not have time to


Please make some initial jet change recomendations.

Any comments on the validity of the dyno numbers. Do they seem too high?

jamon8

iTrader: (3)

what kind of ign are you running

burn all that fuel with a tri-spark diggy ign

SDIF

MSD 6al is the ignition with an msd dist

305sbc

iTrader: (3)

What I would do is work on the idle & low RPM first to get rid of any rich condition, then make sure you have a good set of sparkplugs in there (old plugs could be partially rich fouled), make sure there are no exhaust leaks and test the AFR again with another WBO2 sensor to verify.
There are some engines that like to run at 14.0:1 AFR and others that would cause a lean misfire - which you'd know by the power loss.
Install your WBO2 in the header collector area and make sure there are no exhaust leaks to get an accurate reading.

Pending the results of that you may consider rejetting for WOT.
What type of racing do you do? short sprints like drag racing or endurance racing?
Endurance engines do need to run a bit richer to keep temps down.

SDIF

OK I will be scientific and go up two jets sizes. I thought someone would have played with AFRs before and would know a good recommendation.

The car is for road racing.

305sbc

iTrader: (3)

Sure lots of people have, but not on your engine.

Quasi-Traction

12.6-13.0 is a good ballpark for you WOT Air/Fuel. You can get away with being richer if your quench distance is within .005-007" or so of ideal (.040").

I would go up from #80 on the secondary side to an #83-84 and get a Wide band readout from there.

where do you have your mixture screws set at? play with those first, and take vaccum readings.

what size PV do you have in it?

If none of those work, double check the float level, check and see how much of your transfer slot is exposed.

5678TA

why is your idle so high and rich with so little jet? whats your fuel pressure?

i run an annular mighty demon and i use 71 jets up front to get me 13.0-13.5 at a 750rpm idle. not to mention i have a 260/260 flat tappet cam which bleeds compression like crazy.