While on the dyno on the weekend, I was told that it was running alittle lean (13:1) while wide open. It presently has 82H jets on the secondaries. Can someone suggest proper size jets to richen it up slightly?
Thanks, Will
Original Post
Replies sorted oldest to newest
13:1 is not too lean. It is actually a pretty good ratio for a street motor. You might want lower if you have a high compression race engine. If you were supercharged then you might want 12:1. Dont worry, your ratio is fine. Any richer and you can actually loose power.
I have to agree. Ideal for best MPG is 14.7. Best Power/Torque is around 12.5 to 13.1. This is considered "Rich". Over 14.7 is Lean.
You are at the point of splitting hairs. Air temp, engine temp etc could effect your mix. Going from 13:1 to 12:5 is not too much. You can increase the secondaries. Like adding just one jet a little higher number (next larger number) while keeping the other at 82.
You are at the point of splitting hairs. Air temp, engine temp etc could effect your mix. Going from 13:1 to 12:5 is not too much. You can increase the secondaries. Like adding just one jet a little higher number (next larger number) while keeping the other at 82.
Back in the good ol' days when gasoline was gasoline and men were men (and the sheep were scared), 14.7:1 A/F ratio was considered stoichiometric, and 12.6:1 best power.
However, with all the crap they put in gasoline today, I doubt those numbers still apply. In fact, here in the states, fuel formulas vary from region to region, AND season to season. I'm sure your fuel formulas in Canada vary from ours south of the border too.
You hired the dyno operator because he has expertise at his job. If he says you're lean, I would be inclined to beleive him.
What size & type of carb is that Will? 82 would be pretty rich for a 750 Holley. Why not just go up one size & see what happens?
cowboy from hell
However, with all the crap they put in gasoline today, I doubt those numbers still apply. In fact, here in the states, fuel formulas vary from region to region, AND season to season. I'm sure your fuel formulas in Canada vary from ours south of the border too.
You hired the dyno operator because he has expertise at his job. If he says you're lean, I would be inclined to beleive him.
What size & type of carb is that Will? 82 would be pretty rich for a 750 Holley. Why not just go up one size & see what happens?
cowboy from hell
If it is just at 'wide open' would a bigger power valve be the answer?
quote:Originally posted by Rapier:
If it is just at 'wide open' would a bigger power valve be the answer?
Power valve rating does not affect the flow rate.
Secondary jets are what needs to be dinked with.
Power Valve is a transitional. It reacts to the vac change. When vac drops will dump in more fuel to enrich to prevent a flat spot or lean out.
Wide open and sustained, the Power Valve plays less of a role and the secondary metering Jets determine the air fuel mix.
Wide open and sustained, the Power Valve plays less of a role and the secondary metering Jets determine the air fuel mix.
First I agree that you are pretty close.
The dyno seems to indicate that 12.8 to 12.9 at WOT is as close to perfect as you can get.
At least with NY air.
In the good old days, if u'z was runnin a Holley DP, the cool secret tip to get it perfect, this is secret now right?
Put a Holley 850 DP secondary metering block in the carb with a secondary power valve. Since you are trying to richen only at WOT you want to use a 2.5hg power valve.
If by chance you become too rich, and you might, you will have to close down the secondary powervalve orafices in the metering block, under the power valve.
It's a little bit of work but is good for another 4 or 5 mph in the 1/4 mile and unless you are certifiable really won't even come into play on the street.
This is a secret now right?
Mak sure cause I can't check back here all the time. In this institution I have to share the computer with the other...patients.
The dyno seems to indicate that 12.8 to 12.9 at WOT is as close to perfect as you can get.
At least with NY air.
In the good old days, if u'z was runnin a Holley DP, the cool secret tip to get it perfect, this is secret now right?
Put a Holley 850 DP secondary metering block in the carb with a secondary power valve. Since you are trying to richen only at WOT you want to use a 2.5hg power valve.
If by chance you become too rich, and you might, you will have to close down the secondary powervalve orafices in the metering block, under the power valve.
It's a little bit of work but is good for another 4 or 5 mph in the 1/4 mile and unless you are certifiable really won't even come into play on the street.
This is a secret now right?
Mak sure cause I can't check back here all the time. In this institution I have to share the computer with the other...patients.