Optimal A/F ratio for max HP

[z ya]

For max hp what do you guys feel is the optimal

a/f ratio for a n/a motor? Is it the standard 14.7

or is 13 or 13.5 better? The local dyno guy told me to look for around 13. Whats your opinion?

[Guest Anonymous]

This is somewhat a complicated question, and it certainly varies. Umm.. if I'm not mistaken , based on a chemical combustion equation.. any hydrocarbon will create the most energy when undergone full/ideal combustion.

Take octane

(x)C8H18 + (x)O2= (x)CO2 + (x)H20 + ENERGY!

ugh.. balancing equations...

Well, 2/25/16/18 (correct?)

Now remember, that's for PERFECT combustion, where the only reacting elements are fuel and oxygen.. alright now throw in nitrogen and all that crap and you get some change in emissions and you will never have a car tuned so perfect, you will always get CO, NOx emissions and whatnot, now perfect combustion results in the most energy release. Alright, now examine the actual properties of burning fuel, now since perfect combustion is on the leaner side, the burning of all this leads to higher tempuratures in chamber. These tempuratures can actually untimely expload the fuel/air mixture and [KNOCK!]- ahem.. less power because less piston able to commit to the upcoming compression stroke

So by richening one can prevent this sort of thing, keeping things safe to increase more pressure, etc (as in high comp or FI motors).

Now what I said above is just my knowledge, a physics-enthused college boy .. its probably wrong and there's always someone willing to get all scientific on yo @$$ on this board, its great too; I have the most respect for engineers and those of the sort. Anyway, this I KNOW is true: the factors involved are probably too hard to pin down an answer, and since all motors are different, all fuels are different, all AIR is different (at least in different elevations), so your best bet is to tune your car to however works best and makes the most power for you. Dyno, track, wherever. There's a huge line between writing equations down on paper and what will actually get your arse to the traps faster, I'd say go with whatever darn ratio works best for you. I'll probably run around ~12:1 for power, with my turbo, put race gas in it and I might be able to lean it out a little bit.. but I'd rather just turn up the boost (isn't that what race gas is for?)

-980mak

 

PS. smart fellers, please don't jump down my throat, I wrote this at like midnight, I've been awake for 21 hours..

-980mak

[johnc]

Ultimately each cylinder requires a slightly different a/f ratio for optimum performance. A lot depends on compression ratio (both static and dynamic), intake and exhaust flow, cam design, spark plug position, heat loss, etc.

 

And if each cylinder wants a different a/f ratio, then it stands to reason that each engine also wants a different a/f ratio. Dyno or track testing are the only ways to come up with the best number for your engine.

 

A simple way is to use EGT to tune the engine. Try for 1,325 degrees at WOT throughout the rpm range. You'll need fast acting probes and, ideally, you'll want at least two - one for each side of the engine mounted as close to the exhaust port as possible. Weld bungs on each primary - down by the collector is too far away.

[Guest Anonymous]

Keep in mind also to maintain anything close to ideal would require fuel injection. Carbs are to course and have no feedback to change the mixture to anything close to ideal. They're statically set devices so ideal mixtures are somewhat of a oxymoron on a carb.

Anyone know where the earliest form of carburation was invented? A automizer. (little bottle with a bulb and you squeeze for like perfumes and other liquids you wanted to spray in a mist back then).

 

Regards,

 

Lone

[PaulR]

Edelbrock's carburetor manual implies you should tune their carbs for about 12.5 at Wide Open Throttle, around 14.0 for part throttle acceleration and 15 - 15.5 for part throttle cruise.

 

 

You can see their full explanation here:

http://www.edelbrock.com/automotive/eps_sect1.html#requirements

[z ya]

Paul, Thanks a bunch! I will use this for my guide

when doing future tuning. I am curious how much

power I will pick up going from 10.0's across the

board to 12.5 to 13.0 at WOT.