[Cliff R]

Fun stuff Darby, but it all goes right out the window if you start changing jets at the track on both ends of the carb, which even today seems to be a common practice for quite a few folks at just about every race I've ever went to.

I see folks doing this in the pits between runs, searching in vane for that additional half a second ET and 4-5 mph they think they are missing.

I've tuned carbs (Holley's and Q-jets) from "pig" rich to so lean the engine was surging a bit in high gear, and to date have never seen much over a tenth and 2mph for all runs. As long as none of the tuning killed off the 60' and short times, the car still runs about the same overall.....FWIW.....Cliff

[grandville455]

Why Would I change jets at the track?,LOL.. That is what my meter is for if its saying i am close to 12.6 especially when I make a pass at the track,and plugs look good I don't care if i slow down some in the summer cause of being rich. Its bracket racing not heads up. I agree never seen much with a jetting change unless its far off to begine with! Case in point freind of mine has a TA close to same setup only stock KRE heads and a flat tappet, well the thing picked up big when he went to a different larger carb like 4 tenths i think? I think he only had a 650 or something and I told him man u need a 850, think he bought a 750 hp?

[Cliff R]

We did some carb testing a few years ago on two different cars, at the track, at a track rental, so we could make just about as many runs as we wanted to.

Testing 8 carbs total, 5 q-jets, 2 Holley's and one Edelbrock AVS 800, we saw less than .2 between ALL of them, regardless which vehicle they were installed on. About 90 percent of the runs were no more than .03-.05 seconds and less than 2mph. If we would have left the AVS out of the testing, the spread of ET was less than .12 seconds for all the other carbs.

Seeing .4 seconds between two carbs tells me one of them was WAY, WAY off the mark just about everyplace.

FWIW, I don't tune at the track, I just run it like we brung it. For most of the year I'll run just a tad rich, then lean it up about .008" on the secondary metering rods for really hot/humid weather. Don't touch anything, anyplace, otherwise, aside from adding fuel and checking tire pressure.....Cliff

[grandville455]

Yes I told him all along that 650 was not cutting it with what he had! It was close to 3-4 tenths i know that! I like you don't touch my car at the track,once i get it worked out either on a test day or street testing I don't touch a thing,But I ALWAYS looking for ways to improve it in hot weather cause then it just runs that much better in good air! On race days it is left alone! Ask anyone at the Rock How consistent my car is! Last race with the gov issue I got no time trials put a 11.60 on and ran a 62.2 and 62.8, then a 61. My car is just making rounds rarely do u see me working on it unless there is a issue!

[Cliff R]

3-4 tenths, a mud dabber must have built a nest in one of the float bowls to see than much difference!

Seriously, I've back to back tested 750, vs 828, vs 850, and only saw .12 seconds spread between the 3, and the 828 ran within .02 of the 850 and .30mph slower. That was on my old engine at 514hp/587tq.

On the dyno, the smaller 750cfm carb was even in power production to apprx 4400rpm's, and only gaveup 11hp to the 850 at 5600rpm's (peak HP).

That testing was done on a 455, with Edelbrock heads, making 505hp/551tq.

Darby, best to get your good runs in now, while the air is 400' below sea level. It's going to slow down nearly a .1 for every ten degrees till we are up in 90's and "pea soup" humidity.....LOL.....Cliff

[grandville455]

Don't know wasn't my carb or my tune, all I know is what i saw when he switched carbs from the last time he was out.

[Skip Fix]

Cliff we gained almost 0.4 seconds on my car with the first 455 E head motor by air cleaner removal, jetting, float level/jet extension and timing changes first time out -it wasn't dyno tuned. When we first pulled the air cleaner off after a decent run with it on it lean popped out the Shaker at night during a dry hop! Quite impressive in your face at night. Same carb and same jetting made 695 HP on the 500 IA2. Sometimes little changes all add up.

[Cliff R]

Skip, exactly why I started dynoing the engines we build here, before installing them and going to the track. I keep hearing that we "don't race dyno's", but it sure helps "cut to the chase" BEFORE you get to the track.

The dragstrip, is, and always has been the best place to tune, as real vehicle performance is what we are after anyhow.

Even so, there are a LOT of inconsistancies associated with the track, and testing parts, finding the best tune, etc. The worst thing about track tuning, is that you may only get a few good runs in, even sitting there most of the day waiting your turn. You might not hook up consistantly for every run either. Might as well toss out the runs where you spun hard off the line vs the ones where you hooked up hard. The weather can change some during the day and into the evening as well.

The reason we only see a few hundreths difference testing parts, carburetors (for example), is because we've already got them "dialed in" based on previous experiences with them.

Intake manifold testing was the most educational for me, as we could see at every point on the run where the intake "shifted" the power curve, and where the car slowed down, and picked up, etc.

I still to this day can't believe that a ported iron intake with no spacer outran every aftermarket intake we could fit under the hood. Even more suprising, is that some of the intakes "felt" much stronger when evaluated "by the seat of your pants". As strong as they felt on top end, with the tight converter and conservative gearing we were using, they still ran slower in ET, even when we saw more MPH with them.

Anyhow, we're still waiting for good weather here. Ohio is sending all the water that's been dumped on us South. I guess folks are in real trouble along some of the rivers and low areas.....Cliff

[Skip Fix]

"Even so, there are a LOT of inconsistancies associated with the track, and testing parts, finding the best tune, etc. The worst thing about track tuning, is that you may only get a few good runs in, even sitting there most of the day waiting your turn."

I agree maybe because I'm older sitting all day to get a few runs isn't as fun as it used to be. Normally I like to dyno first to find leaks and dial them in better. That motor also developed a pan leak we had to fix in the car! Real fun-that darned 3 prong seal.