Is 13.5-13.6 too lean at wot?? - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

xdclevo · 02-24-2005, 02:47

I made a thread a while ago about jets and 750dp's. At one of the dyno's up here i was told i had an afr of 12.4. He said it was too rich. With no changes, i went to the only other dyno up this way, which uses "shootout" mode.
They told me it was way too lean(mid 13's). They had a quick play, but said it need "further investigation". The following graph was with the 750 demon and 76 and 83 jets. Does it just need a bit more jet?

northiam · 02-24-2005, 02:57

Every man here and his dog will tell you its to lean, mine runs much harder at 13.4-13.2 with 73 - 75 jets than it did at 12.5afr . Any unburnt fuel left in the chamber will cost you HP fact!

xdclevo · 02-24-2005, 03:12

Quote:

Originally Posted by northiam

Every man here and his dog will tell you its to lean, mine runs much harder at 13.4-13.2 with 73 - 75 jets than it did at 12.5afr . Any unburnt fuel left in the chamber will cost you HP fact!

There does seem to be big differences in peoples ideas in a safe, but ideal ratio. Another guy up here that has build some "nice" motors commented if i can control the temp, and go no leaner, it is perfect for a Demon type carby.
Oviously there is a point where a lack of fuel will hurt horsepower real bad.
Where is that point

brenx · 02-24-2005, 03:23

I've ran mine @ 13.2 with no issues. Last setup ran 12.7 and I am going to ask them not to run it so rich this time. As I believe thats the reason my plugs keep fouling.

Brenden

TruBlu351 · 02-24-2005, 04:01

Speaking to a few engine builders......

COME Racing in Melbourne say that 13.2 is your magic number.........they have extensive dyno research (make their own cams/heads etc).

Too rich, won't give optimum burn. Too lean and it starts getting way too hot, pinging/burning things etc. Safer to run tad rich , than tad lean.

Make sure your dyno guy is running a WIDE BAND oxy sensor. Most should be. They use a 0-5volt gauge instead of the standard 0-1 volt vehicle types.

blackxbhardtop · 02-24-2005, 04:20

Stoich is 14.7 from memory, good idea to run a bit richer as fuel is far cheaper than pistons.

A bit leaner than stoich tends to give more power and melt motors. Check out the thread on reading plugs properly and experiment very slowly when your leaning it out however.

TruBlu351 · 02-24-2005, 04:56

Stoichiometric is 14.7:1, ie: the ideal AFR for CRUISE power only. 14.7:1 under full load/power will kill any engine quick smart.

I think some of the new EFI engines drop it even higher than (19:1??) that so they get ultra good economy when cruising, using their knock sensors to control the pinging.

TTNOS8 · 02-24-2005, 14:53

Don't try and go anywhere near 14.7:1

You'll nearly always get more power out of a 'lean' mixture than a 'rich' mixture.

If everything else is good, ie fuel pump is keeping up, not fuel issues like poor pickup under acceleration, etc, then I'd be happy with a a/f ratio of 13 to 13.4

But play around a bit on the dyno, power will drop off either way when its not happy. You may find you can go a little leaner without having to worry about pinging because your running alloys

worth a try

Let us know

Racer · 02-24-2005, 15:58

Your printout shows 13.4/13.5 at the business end. Thats only just OK, and starting to get into lean territory. I'd fatten it up a couple of numbers.

If its not pinging and its not raced, it would probably be ok as it is.

shaynet · 02-25-2005, 04:57

Is this too rich then?