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  #16 (permalink)  
Old 10-17-2005, 12:18 AM
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Let's see. This really helps, Thanks.
Now we're getting somewhere.
Here's your numbers.

60 ft = .048 quicker
1/8 = .242 quicker
1/4 = .217 quicker
1/4 = 1.12 mph faster

This is not that far out of line with the outline in # 4.

You're falling off just a little in the last half of the quarter... .025 =That tells us something.

Let's see if you can get your 60 ft down from 2.24 to 1.99... As is that would put you into the 14.60 range and maybe 93.3 mph. You said you are hooking up well..... mmmmm??? Is it spinning at all? Is the suspension unloading at 15-20 feet?

If you can help that top end pull just a little.... maybe 14.55 @ 93.6.

What kind of Ford is it?

Last edited by xntrik; 10-17-2005 at 12:25 AM.
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  #17 (permalink)  
Old 10-17-2005, 06:03 AM
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Doesn't anyone have any performance software to help our friend with his problem? (I've changed operating systems and can no longer run the program I had written in BASIC. Have to write another one, I guess.) Just adjust to get his old performance and then change axle ratio.

And, the memory has faded in 4 years. You were turning 3900 at that speed. (It happens to all of us.)
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  #18 (permalink)  
Old 10-17-2005, 06:41 AM
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thanks to everyone again, oops I guess my memory did slip a bit on that part haha. the car is a 70 mercury montego that weighs 3660 with me in it.
http://members.cox.net/70montego/car...inal/index.htm
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Old 10-17-2005, 09:47 PM
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You indicated that you did not remember the rpm. So I ignored it. The numbers you gave do not compute.
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Old 10-18-2005, 12:30 AM
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Quote:
Originally Posted by voodoosurfer
thanks to everyone again, oops I guess my memory did slip a bit on that part haha. the car is a 70 mercury montego that weighs 3660 with me in it.
http://members.cox.net/70montego/car...inal/index.htm
Shane,
That's a nice car. I like yellow.
It is unusual in the "hotrod" world. Thanks for doing it well.

When you get ready to try some things, give me a shout.

thanks,
Ford Guy
x

www.readershotrods.com drag cars/georges
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  #21 (permalink)  
Old 10-18-2005, 07:39 AM
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Quote:
Originally Posted by xntrik
You indicated that you did not remember the rpm. So I ignored it. The numbers you gave do not compute.
Which numbers dont compute? everything I typed is on my time slips and the only number I dont remember definitely is my rpm from my first run. maybe if something isnt computing right thats my problem?? please let me know, thanks
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  #22 (permalink)  
Old 10-18-2005, 11:26 AM
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Quote:
Originally Posted by voodoosurfer
Which numbers dont compute? everything I typed is on my time slips and the only number I dont remember definitely is my rpm from my first run. maybe if something isnt computing right thats my problem?? please let me know, thanks
Quote:
Originally Posted by xntrik
You indicated that you did not remember the rpm. So I ignored it. The numbers you gave do not compute.
As Billy indicated
RPMs ....... 4600 then and 5000 now

3.00 divided by 3.80 = 79 %

5000 times 79 % = 3950 rpm

If we conclude that 5000 now is accurate:

Just taking your old and new numbers at face value (ignoring all the variables I listed previously), your new combination is "falling off" in the last half of the quarter mile.

Using your figures= your eighth is .242 quicker. But your second (eighth) half of the quarter is now slower than before by .025 sec. So you actually had less acceleration than before and actually lost some of the time you gained in the first half.

Meaning that between 4000 and 5000 rpm you are not pulling as hard.

You either need more power in that rpm range or less gear.

Some might suggest taller tires to crutch the gear ratio, but taller tires are heavier and have more rolling resistence. A futile exercise.
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  #23 (permalink)  
Old 10-18-2005, 01:46 PM
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Good work, xntrik! I picked up on the rpm problem, but I missed the slower second furlong. (Not used to having all that data. Back in the fifties, we were lucky to get our speed and e.t..) Yeah, we might be dealing with an ignition problem that shows up only on long pulls in a gear. Or, possibly, a fuel pressure problem.

But, I'll point out that less gear (lower numerical axle ratio) is never a fix (unless you're way past the power peak before you hit the traps in the final gear).

A neat way to visualize this is to consider a plot of car speed (horizontal axis) versus acceleration (vertical axis). If you plot on this an acceleration curve equal to:

12075 (available horsepower)/((effective car weight)(car speed))

where weight is in pounds and car speed is in mph, you'll have a curve which goes to an infinite acceleration at zero speed and zero acceleration at infinite speed. The "effective car weight" is the actual car weight plus effective weight of the rotating inertia in the drive train. (The latter can become quite significant with a "granny" first gear and a very high numerical axle ratio, which is why you don't have to worry about achieving infinite acceleration.) The value for "available horsepower" is the peak engine horsepower less the horsepower necessary to overcome air resistance and friction at the car speed under consideration. The acceleration curves for each gear must all be under this curve, but each gear's curve will rise up and "kiss" this limiting curve at the speed corresponding to the maximum horsepower in that gear. So, it becomes obvious that, to keep those gear curves up as close as possible to the limiting curve, it's necessary to have a lot of gears and as low (high numerical) an axle ratio as possible (subject to the previously mentioned limit).

Last edited by BillyShope; 10-18-2005 at 01:53 PM.
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  #24 (permalink)  
Old 10-18-2005, 02:25 PM
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Ok, I will say that you are probably correct on the rpms for my run 4 years ago (I failed to write that down) but 3950 sounds about right. but you say that my 1/8th mile time is slower by .25 its actually .25 faster. all my times are quicker now than my previous run. just not near as substantial as I think they should be with what I changed. I did just order a new fuel pump and filter, because the very last run it started bogging near the end of the track. could a failing alternator cause this?? I think my alternator or my regulator might be going out.
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  #25 (permalink)  
Old 10-18-2005, 11:59 PM
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Quote:
Originally Posted by voodoosurfer
Ok, I will say that you are probably correct on the rpms for my run 4 years ago (I failed to write that down) but 3950 sounds about right. but you say that my 1/8th mile time is slower by .25 its actually .25 faster. all my times are quicker now than my previous run. just not near as substantial as I think they should be with what I changed. I did just order a new fuel pump and filter, because the very last run it started bogging near the end of the track. could a failing alternator cause this?? I think my alternator or my regulator might be going out.

I apologize for not being more clear. Please allow me to go over this in more detail.

The first 1/8 of the quarter you are quicker.
The second 1/8 of the quarter you are covering it slower than you were 4 yrs ago.

15.073 - 9.753 = 5.320 for the old second half
14.856 - 9.511 = 5.3454 for the new second half

It has taken you longer to cover the second half of the quarter now than it did 4 years ago. 5.345 - 5.320= .025 ... You are .025 slower now.

So all the 1/4 et reduction you got was in the first 1/8 = .242, and you are slower now and lost .025 in the second 1/8, so your overall 1/4 reduction was only .217.

Theoretically if you were ON the power peak, your gaining .242 in the first half, you might be .121 quicker in the second half (instead of losing .025), your quarter could have been 14.710 . So theoretically speaking your car is .146 too slow for you to be on your power peak.

So whatever the reason, according to your numbers, you are over your power peak with that gear.

Whatever it takes to fix the power peak..... who knows? timing, dragging brakes, tire pressure, etc. It doesn't take much of an undetectable transmission slip to make that much difference.

So how much is that really????
If you were racing your theoretical self...... You would be dead even from the line to the 1/8 mark and then you fall back in the second half = 20 feet at the end of the quarter. You would lose by 20 feet. One looooong car length.. All in the last half.

This is why all those numbers are so important to professional racers. They can interpret what they see and decide what they need to adjust. Think about doing the quarter in 4.6 sec and 330 mph....... wow. If the driver burps the car slows down. lol

Now if you could fix that AND get that 60 ft time down to 1.99 like I said earlier...... you could be looking at 14.5xx

Think about it.

Last edited by xntrik; 10-19-2005 at 01:15 AM.
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  #26 (permalink)  
Old 10-19-2005, 06:02 AM
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Rather than edit my previous post, I'll use this post to correct a small error in my description of the limiting acceleration-speed curve.

For expediency, this curve is often calculated using the total maximum horsepower, in which case the acceleration does go to zero as the speed goes to infinity, just as I described. However, since I chose to use the available horsepower, the acceleration would go to zero at the maximum possible car speed.

It's a small matter, but I tend to be very tough on myself regarding accuracy.
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Old 10-19-2005, 09:48 PM
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WOW

You guys are laying down some real usefull information here.

Why are you thinking its an ignition problem or fuel pressure? I am no racer but did have a simular 351 cleavland but with 4v heads on it that was starved for fuel with the small carb it came stock with.
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Old 10-19-2005, 09:53 PM
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Quote:
Originally Posted by voodoosurfer
my alternator or my regulator might be going out.
Eather its charging or its not charging,If the alternator is not charging you running off of the reserve of the battery,as the battery charge drops so does you ignition out put.


Ps I like the color of the car and it sure does looks slipperely,How is it so lite.The tube frammed vette I built come in at 3195 with me in the car.
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Old 10-19-2005, 10:18 PM
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All the information here has been heela usefull, thanks to all. I have so much different things to look at now, I did put a 750 on tonight so hopefull friday I can get it out and test it. it sounds throatier to me, or I could be imagining things. the regulators on these old fords go out alot, where it will charge and then not charge so im gonna replace that and see if that makes any difference in my electrical. I know that when I put on my lights the voltage regultor was reading 12.5 not 14 and my blinkers would make it dance real pretty like. LOL. I think the reason my car is so lite is maybe the uniframe? I know when I hit a bump in the road you really feel and hear it. thanks again to all. I hope to figure some stuff out this weekend.
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  #30 (permalink)  
Old 10-20-2005, 05:11 AM
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Quote:
Originally Posted by ih2lose
Why are you thinking its...fuel pressure?
Just happen to have a very good example:

Had a '56 Chevy with the 265 engine and the factory dual quads. Loaned the manifold and carbs to a friend with a '57 with the 265 engine (the "economy" package in '57; you might not have even heard of it) while I rebuilt my engine. His car ran strong in first gear with the dual quads, but, towards the end of second gear, it went flat. The smaller fuel pump just couldn't keep up with the increased demand.

In this case, I would be more inclined to suspect a restriction or an internal leak.
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