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

[Jerry Clayton]

Cobra Ed

I disagree---the main jets are Carb 101, the rest is the advanced studies

Jerry

[Jerry Clayton]

One other thing that these days effect tuning----the gasoline being used, we have had guys show up with 100+ race gas for the dyno and later try to run street pump gas

Uh oh golly gee

What ever happened

Jerry

[CobraEd]

Originally Posted by Jerry Clayton

Cobra Ed

I disagree---the main jets are Carb 101, the rest is the advanced studies

Jerry

Jerry,

All that stuff can be done with the car sitting parked in the garage with absolutely no tools or analysis. Selecting the right main jets requires the car to be at idle, . . . and under full load, . . . .and everything in between while being monitered with an oxygen sensor to measure fuel/air ratio, all while under load on a dyno. Also plugs must be analyzed. This is the essence of carb tuning for performance. What you stated is for grandpa to ensure that the care drives "nice" and will idle. It has nothing to do with maximizing performance.

Ed

.

[Jerry Clayton]

Two things Ed

The carb will idle without any jets in it

This was about idling and driving nice

An dyno is not an O2 sensor

Jerry

[FUNFER2]

Jerry- The o2 sensor is all a part of the dyno's computer. It WILL.........tell you if it's rich or lean !!!
It can give you so much information, the book is 3" thick. Suggest you read one and go over it with a computer/mechanic/dyno expert.
My intent is not to start a war over backyard tuning vs a dyno but, with today's technology, a dyno and it's computer is the best way of tuning any engine. Even on a engine dyno, it can tell you if you're lean or rich.

[Jerry Clayton]

Kevin

we use O2 sensors and EGT sensors----the point is ----separate what the dyno is (load ) and the attachments ( O2, rpm, etc)---A dyno's computer and software only draw you a very crude chart of the run---I can moniter and record data in a vehicle on the road with a much greater accuricy and greater rate than any of the dynos I've seen
We sometimes go to dyno facilities 2 or 3 times a week in addition to what we do in house and on the road.
The popularity of dynos is where its at because the check writers want to brag about how much power they have. As far as I know a dyno has never won a race. Engine dynos are great for developement work, but you should have several extra parts so you can do a-b-a testing.
The run on a chassis dyno is risky at best as if you don't get the power and get too aggressive with tuning you will probably hurt something- on the otherhand if you don't hurt something every now and then you haven't explored the maximun. Where does a dyno operator draw the line? quick tie down, warmup,pull , print graph, untie car collect money? Or is it sign waiver, pay in advance, etc?

The best use of the chassis dyno that I have seen is for bolt on stuff---make run, change air intake, muffler, etc make run how much gain?/

I'm not arguing dyno, I'm only trying to make the point that it isn't the answer to everything, in fact very little for a driven car---a race car is a different scene---where you need to establish a tuning baseline because of limited track time, etc---and maybe more performance gain could be had with tire therometer than a dyno sheet

Where in Ne are you?

Jerry

[FUNFER2]

Well, I guess we disagree & that's fine. I live near Lincoln.

[rdorman]

Originally Posted by CobraEd

Uhhh how about the main jets???? They are the key element of performance tuning. All this other stuff is just carburators 101.

Uhhh which is exactly what he needs to start with.

[CobraEd]

There was NO MENTION of main jets at all in what he wrote.


.

[rdorman]

Absolutely there was. But, he is starting in the wrong place. Carbs out of the box are generally very close on main jets. Some one else led him to the oem setting for jets for which he should return to if they have been changed. Jets are more dependent on the carb itself and atmospheric conditions then what is setting under it. He complained about drivability problems, said the plugs where a good color (althought reading plugs is an art so he probably is not seeing many things) and said that it had been a long time and he was rusty. Hence, as you put it, carb 101. What carbs and crate motors for that matter generally have against them out of the box is proper adjustment. Which is where I think he should start before trying some magical modifications only to see no improvement, run out and by another carb, and continue to be frustrated because the initial setup was still not done. Eliminate the simple and free stuff before he starts looking for a problem that may not exist.

You did bring up a very good point though. Once he does try and set up the main jets, he can't do it sitting in the driveway. Even the carb 101 that I gave him will need to be tested on the road and final adjustments made. But assuming the carb is not defective or in need of repair, if he carefully sets it up, I would be willing to bet he will be much happier then he is now.