Quick tuning question?

[my95z28]

Hey guys, I have a friend that is trying to dial in a carbed big block car that he has. Has a wideband on it, he's just trying to get the Air to Fuel decent. I know that 14.7 is stoich, but you just want that for cruising right? Isn't 12 or 13:1 about what you want WOT? I honestly have no idea, so if someone could school me or show me a how to or something like that would be great. Thanks!!

[meissen]

Mine's a little rich at WOT at 12.0 but I like that Steve put it to that - the richer combustion will keep the engine cooler than a little leaner.

[JoeliusZ28]

between 12.0 and 12.5 is generally considered the best A/F range for mean best torque. The idea is that it needs to be rich enough to ensure that every air molecule is burned, and more fuel is better odds for that.

[JoeliusZ28]

another thing to keep in mind is that carbs rarely distribute fuel evenly to the various cylinders, so it might actually run better if its running even a little richer than that. play with it a little and see what happens.

[my95z28]

So other than that he should try to get it as close as possible to 14.7? For part throttle and cruising? What about idle? Thanks a bunch Joel, I'm tryin to show this guy how useful it would be if he actually go on the forums, lol.

[shawnc16]

negative.. a little lean at cruising. Say 15.5 to 1.... 12.5 to 1 is perfect for an N/A engine @ WOT. Only problem is.. its carbed. NOTHING wrong with carbs.. just hard to tune them for driveability

[meissen]

14.7 is stoich but leaner will result in better mpg and a little more HPs at cruise/partial throttle.

[shawnc16]

That and its hard as hell to see when yur eyes are watering from it being so rich!

[JoeliusZ28]

So other than that he should try to get it as close as possible to 14.7? For part throttle and cruising? What about idle? Thanks a bunch Joel, I'm tryin to show this guy how useful it would be if he actually go on the forums, lol.

stoich or leaner at cruise and light throttle, like shawn said.

Idle depends a lot on your cam. the more overlap the more unburnt fuel will be escaping and throwing off your reading. You cant really hurt much at an idle. Lean is fine but you dont want it so lean that it runs hotter.

realistically, its going to be hard to achieve all this with a carb. do what you can to make it run good.

[my95z28]

Thanks a ton for the help guys. One other thing. He said at WOT if you nail it and then let back out it will backfire bad out the carb. It is roughly 11:1 WOT. Is that rich enough to be making it backfire out the carb or is there another issue?

[JoeliusZ28]

sounds like a mechanical issue with the carb, but im no expert on that sorry.

[c0ncEpT]

Thanks a ton for the help guys. One other thing. He said at WOT if you nail it and then let back out it will backfire bad out the carb. It is roughly 11:1 WOT. Is that rich enough to be making it backfire out the carb or is there another issue?

I'm not carb guy but 11:1 is pretty damn rich at WOT... Sounds like all the fuel isnt getting burned if its backfireing

[1BADAIR]

if its a carb you want around 14.5-15 at cruise.(if it surges go a tad richer)
12.7 wot

[MP81]

Mine runs 11.5-12 at WOT, but I'm also FI.

[shawnc16]

Sounds like a timing issue to me..