Best jet size, etc ?? 650 Holley 302 Ford crate

[Jerry Clayton]

650 + 28 = 678 round up to 700 sort of fits my profile, huh?

The stub stack will significantly flow more at the lower carb openings, causing the carb boosters and venturis to act like considerable bigger carb

You can put a divider in the single plane manifold plenum area that will pick up the lower ranges response

Jerry

[wtm442]

If the plugs look OK, and the only thing that is wrong is the car stumbles, I would look at the squirter size, or a different squirter cam. But it all depends if the stumble is a lean condition or an over rich condition.

Get the RPM's above 3000 RPM in any gear and mash the gas pedal. If there is NO stumble, look at the squirter and squirter cam.

[FUNFER2]

Do you have a local business that has a chassis dyno ?
That is the BEST,...way of tuning your fuel curve timing ect.. rather than in your garage or on the street. It's well worth even traveling to find one.

[wtm442]

Based on Holley's carb numerical listing

http://www.holley.com/TechService/Library.asp

that carb originally had 67 primary and 73 secondary jets with a 65 power valve.

[FUNFER2]

The great thing with a chassis dyno (if the operator know's what he's doing)
you can make a full run, read the numbers and adjust the mixture at high rpm's then do a idle adjustment through the whole rpm range and you're set. It's well worth the money.

[wtm442]

Jerry
I agree with you about seat of pants driving conditions, but a dyno will tell you if the jets are too lean or too rich. It will also tell you if a low speed stumble is because of a too lean or too rich condition. Then after the jets are OK (and the power valve), then you can play with squirter's, etc.

I find that many people make 2 or more changes to a carb at the same time. Bad decision. Only make ONE adjustment and then see if problem is better or worse.

[FUNFER2]

We had a guy come to the dyno that raced in the Pro-5 class with his Mistang. He decided just to stop by for fun before racing at Heartland Park for a national meet. He assumed his motor was dialed in. When he hit 4,000 rpm, he was already way,.....lean. We went up three jet settings, adjusted timing and he put out 900 HP. He was extremely happy for two reasons, 1- he would have melted his engine being that lean. 2- we found 32 more HP just in simple tuning. We made 5 full runs and cost him $160 (2 hrs.) for shop time. Said he has $30,000 in the motor. He kissed me on the forehead for saving his engine !

[wtm442]

Kevin
As long as the kiss was on your forehead.

I was at a dyno shop with a bunch of Cobras a couple of years ago and the owner stopped a pull on one of the Cobras at about 4000 RPM. Just cheap $ pulls on a Sat morning with no tuning provided by the dyno shop owner. He said the motor was so lean, he did not want to chance blowing the motor. He told the Cobra owner to drive home, do not floor the gas pedal, and increase the jet sizes by 4 to 6 steps on primary and secondary.

[FUNFER2]

Jerry- he is one of our sponsors on our sprint car so, $150 was cheaper for him. We don't overcharge our new customers. Because of that reason, we have four dyno nights per week. It brings in a lot of business. There is now way,......you can beat tuning on a chassis dyno ! You can even calibrate for weather conditions. If the operator can't tune your car for the street, you had better find a better one. There are some dyno shops out there that the operator is only a computer geek, not a mechanic.
Our Mustang dyno is a real world test, unlike the dynosport. The only changes after a dyno run you'll have to make is if the weather changes a great deal if you're racing or, a elevation change. We've had drag racers spend hours in the pits trying to find what the motor needs. They come to our shop for a dyno run and figure it out in one hour or less.

442- We also have a "dyno day" (the last was for all Mopars) and they were single runs for $50. It was a blast for all of us. Had pizza & soda (some had beer) Now, most want to come back to dial in their engines. That will be more $$$. We have all the jet's, spark plugs and distributer springs ect... to super tune most engines.
The dyno is good for our business as we don't over charge plus, "the word of mouth" for the dyno and our regular daily driver mechanic business is fantastic. We even put our sprint car on the dyno. Long story but, it was hilarious.