Jetting Question??

[Mustang_Geezer]

Are you better off to jet rich or lean for more horsepower/performance??

I know if you jet to lean, your piston goes by-by!

Mine seems to be jetted to rich out of the box and the leaner I jet it, the better it runs.

Later,

Doug

 

[StrangeRanger]

Most engines make maximum power when they are piston-burning lean. Nobody in their right mind runs them there. That may or may not apply to those of us on this board.

 

[Mustang_Geezer]

Heres the story....

I started out with number 74's installed in the carb when it was new. You could smell that it was running rich as you drove it down the road....

Replaced the 74's with 71's. Performance seemed to improve and gas smell was not as noticeable going down the road.

Had a slight bog if you nailed it from a standing stop, so I installed another extra (.028) accelerator pump nozzle drilled out to a .031. Bog was a lot less noticeable. Redrilled it to a .034 and tried it again. Bog was gone. Drilled it again to .037. Started to feel the bog coming back so I drilled out my original nozzle to .034 and reinstalled it. No more bog at all. I did all my drilling with a Mac pin vise set...

Last weekend I installed the heat shield and got the kinks all worked out of that.

Today I replaced the jets with a set of 68's.....Runs ver good!!

Plugs are a very light tan color. I was just curious when I should leave well enough alone.....


I'm still running the water injection if that is a factor.

Thanks,

Doug

 

[StrangeRanger]

Quit just before you see the aluminum flecks on your spark plugs

If that's not a practical solution, go down one more jet size and pull the plugs after a making hot full throttle run followed instantly by a hot shutdown. Read the plugs and see if they're still tan. If you're feeling brave, go one more jet size and do the same thing. When you see white or grey plugs or worse yet shiny flecks on the electrode, go back to your last comfortable tan setting and repeat the run just to confirm.

Or just quit now. It runs good, you've sorted out the jets to a good safe mixture and have the accelerator pump where you want it. Why tamper with success?

 

[xctasy]

Yes, leave it as is. The intake set up you have is very effiecient, and it lookes like you've compensated for a very lean jet by going up in squirter size. Well done.

I've done some reconcilliation with the jet sizes to cc/min flow rates as published by Barry Grant in his manuals. It lookes like the 350 Holley can be feeding in the 155 hp zone with those jets. I'm not posting these until I get a proper easy to read chart like what RougeS has posted on the HolleyWeber metric jets.

I've done some flow curves betwwen carb cfm, jet cc per minute, and bhp levels. There lookes to be a clear valid jet selection comming through. Often, little 2 liter cars run in the 65 jet zone, and they do 130 hp easily with a 350 Holley 2-bbl. So those two 68 mains sound pretty good.

If you ever run a 500, a set of 74's would be a good start.

See what happens when you make that Ford log manifold fetch stick! Horsepower and fuel economy! You and the Schjeldahl boys have learned that the log head isn't a disadvantage, it's an asset!

 

[Mustang_Geezer]

Quit just before you see the aluminum flecks on your spark plugs

When reading plugs, (the way your explaining) Should I have a spare set on hand to change, or is just cleaning them with a air powered spark plug cleaner good enough?? Since I'm constantly dinkin with this thing, I pull the plugs occasionally just to check the color...

XE,

My bad!! I guess I should have mentioned that this is a 500 cfm Holley!!

I've always thought about changing to a 2V head, but I like to re-engineer things, so I stuck with the log head because lots of people said you couldnt make HP with it so I wanted to prove them wrong....sometimes my re-engineering works, and sometimes it dont!

Later,

Doug

 

[xctasy]

Youre kidding, a 500?

Man, that is lean with 68 jets. And it still runs with no bogging!

That's heaps less than I've seen before. Any time you can run small jets like that indicates very good intake atomisation.

I'll bet your fuel economy is pretty good.


I'll add it to my list of valid jet selctions for the 500 then.

That's brilliant. Have to tell the other boy on the formum looking at his 500 to stock conversion that he amy get way with lighter jetting if he ups the squirter size.

Are you using an 8.5 power valve?

 

[Mustang_Geezer]

Picture coming.....

I'll have to show you the picture tomorrow...homestead wont let me publish it right now :roll:

The picture was a close up of my carb mount on the intake. Instead of just a oval opening to accomadate both barrels, I choose to make 2 seperate holes....Car Craft magazine almost always mentions that they make more HP with a 4 hole carb spacer vs a open spacer on there dyno tests, so I figured it should apply to 6's also....

Anyway,

Yes no bogging at all! Floor it from a standing stop (now) and at least 50% of the time the right rear tire goes up in smoke. Fuel economy is right around 20 mpg when I can keep my foot out of it . As far as the squirter size goes, that was how my Holley book reccomended curing it. Either drilling out another squirter or having several larger sizes on hand to change to.

Not sure on the power valve....I'll look tomorrow when I replace the bowl gasket.

Later,

Doug

 

[StrangeRanger]

Just cleaningthe plugs is probably good enough but a spare set is a lot handier. Seriously though, You're probably right where you want to be. At most you're off by 1 jet size. If you're not actually racing the car, why push it?

 

[Mustang_Geezer]

I've decided that I'm going to leave well enough alone per your guy's advice!

XE,

It has a 8.5 power valve

Later,

Doug

 

[MustangSix]

My crossflow tends to be more powerful at WOT when it's running slightly richer than stoich, probably close to 12.5:1. I set the ECU to disable closed loop at low vacuum/high power settings and inject more fuel in that scenario. At extremely lean settings like SR described, the engine tends to not pull as hard, probably because a lean mix is harder to light consistently.

The engine also likes to idle slightly rich as well. Not black smoke, ey burning rich, but just a bit more fuel. Outside of those two events, it runs closed loop.

 

[Anonymous]

The guy I went to at Jan and Ablies who has had lots of experience with Holleys (came highly recommended) said the smallest he had seen run succesfully on a 250 was a 67 jet in a 500 Holley. I had 71s went to 68s then to 74s none of the changes made much difference to times but It did with fuel economy.