I think it'll be way low. MPH doesn't change much because you don't pick up much speed at 100mph in a half second, which is what seperates a good run from a bad one. You simply won't have enough acceleration to get there.


It takes about 50 feet to pick up 1mph at that speed.


If you could keep the tires spinning and hold it in 4th, then I'd say mph would be close.

I'm getting about 80 mph.... with a "hook" rpm of 500 or 100rpm. You can't figure it with no clutch or tire slip, since the engine never turns 0rpm, nor can the car accellerate instantaneously to engine llaunch/stall rpm.

 

It isn't going to be even in the same time zone.

Your maximum speed is directly related to the power that you produced over the length of the quarter mile. After you have hooked up in fourth you are at low rev's. Even tho you are making torque, you aren't making any power, (remember power is torque X rpm / 5250) so your acceleration is much slower, not only time wise, but in terms of speed at a given distance.

Another way to look at is if that velocity over time is the derivative of acceleration. If the acceleration is down (since you have less rear wheel torque in the taller gear), so is the velocity.

 

I was assuming an auto first, then the MPH will be silmlar i the 1/4 mile.

Starting on forth with a manual is too slow to get the same MPH in the quarter. A standing mile is a different story. Then MPH will be similar again when starting in fourth with a stick. ET will be way different.

 

Absolutely true.......

 

Being another altered driver i would have to say that running a 3200lb car from the start in 4th with a single disk clutch will result in a lower mph as well as needing a new disk and maybe fly wheel at the end of the run, i agree that a tubo 350 will beat a powerglide simply because of the gear spread( i used to run a clutch turbo 400 that only dropped 100 rpm between shifts, a real good test of your bottom end!). Now if you had the power and ran a multi disk slider that would produce differante results, and if you ran nos or a turbo you could adjust the slider and get better mph. ... just a thought,...lots of variables in that question.

 

Dont call mythbusters. Remember what happened last time they got there hands on a C4?

 

Figure I would chime in here:

There are some people mis-interpreting what I think you asked.

Correct me if I am wrong, but I believe you were asking what would happen if you started out in 4th gear and ran it through the 1/4.

More specifically, 4th gear in a MANUAL (for 1:1 gear ratio)
This would be 3rd gear for an AUTO.

I can almost assure you the car would run very close to your normal MPH, the ET would SUCK, and your trans would be severely stressed (manual or auto) by doing it, but setting aside any damage or severe slippage on the clutch do to heat, it should run the same MPH.

Now understand that same MPH means within a few like if your usually running 125MPH, it will come in at +/-2MPH of the same.

For myself I used to have troubles with shifting from 1st into 3rd on occastion with the stock shifter, very easy to do if your not careful. When this would happen, EVERY time, the car would lugg through the gear and still pull the same MPH, but the ET would be much slower ~.2-.3sec less. So that is very close to what your trying to ask, just not as bad, but when you look at our cars, first gear is only a split second and only out maybe a litte past the 60' mark. So from that point on she was pulling in 3rd gear the ENTIRE way down the track. VERY eery feeling since I am used to shifting.

You have to assume some things to make the connection, like no damage being done, and you could actually get the car going. Obviously in both transmissions there is going to be quite a bit of heat generated, which is going to effect the performace and the coupling effects of the fluid in the AUTO and adhesion of a clutch. But neglecting those effects it should run very close.

Spinning off the line as some mentioned can and will give a higher MPH, but its still within 1 or 2 MPH usually and for this situation close enough to call it the same.

1 or two MPH difference when trying to figure out your HP from your MPH and weight will put you within 30 hp assuming a power level of 600 and less HP. As close as anything else is going to get you.

Putting an auto in 4th gear, would cause a MUCH less MPH due to less gearing.

Again its not an easy thing for people to comprehend - but thats the way it works out. Do it at the track next time. Take out and roll out about 100 ft them only get into the car, if you run it through the 1/4 then, it will still MPH about the same. I will pull a video of my car when I changed my exhaust and the WB drowned the motor with fuel from seeing the outside air, the car rolled out a little ways, I rolled onto the throttle real slow, and got things going and it still pulled a very good MPH. Et I think was in the 11s, but it did the MPH with much less track than it normally sees.

 

My 92 corvette went consistent 108's on street tires, and 110-111 on ET streets.

The ET street's were on 16 inch Camaro wheels though, so maybe they are a bit lighter. 3 MPH is a bunch to pick up from wheel weight savings. My car definietly traped higher when I didn't spin through all of first gear.

 

It was interesting reading about one guys comparison to bicycles. Did anyone watch the Tour de France? Lance used a smaller gear to climb than the German did. The German was probably stronger, but couldn't attain the speed Lance did on the climb. The German had more horsepower, but not the speed. I know, it has nothing to do with the original post, but I thought I'd throw this in there. BTW, I'd hate to launch in 4th, I don't like the smell of clutches burning.

 

Copied from the other debate...

Heaven forbid someone bring a bit of rationallity to the table.

A dyno REAL purpose is a tuning tool. Its like ignition scope.. If you go around comparing raw dyno numbers with raw dyno numbers than your in for a suprize. Everyone knows the type of transmission, rear-end, and stall will affect what is reported at the wheels.. Everyone should also know that there is a definate difference between dynojet, Mustang, superflow, and dynapack....


Track times also need to be taken with the same grain of salt.. If my car is not setup for the track your not going to show the power that your actually making.. Whats the problem in understanding that? If you don't than simply go out to test and tune and watch a new Z06 run a 12.5 at 110... we know that wasn't a indication of what the car was making... right??? Hell my car is by no means setup for the track and I know I have around .3-.4 tenths and a few mph left in it without touching the engine... that doesn't mean that the car is making less horsepower than what we measured on a dynojet dyno..



Bottom line.. Take your results with a grain of salt.. Realize how your setup effects your numbers weather they be MPH, ET, or RWHP.

Damn is everyone satisfied yet?

 

What was the overall diameter of both wheel combos? I'd think perhaps if the 16 inch wheel/tire is shorter, part of your gain comes from a slightly lower drive ratio. Way back in the olden days, they used to call using shorter tires the "poor man's gear change".

 

Jessie for once I can agree with what you've got to say. Naturally you would have to consider that nothing breaks, the clutch doesn't slip etc. If the MPH worked out ot be similar then yeah I'd have to say that the MPH is a great indicator of the power regardless of "driveline variations." If the MPH was radically different then I would say that there is a point of difference where MPH isn't the best indicator. Granted it may be an EXTREME difference that is highly unlikely, but it would prove the point.

Unfortunately we may never know the answer to the experiment as I've proposed it because it involves launching a car in 4th gear. It really wouldn't matter if it was an auto or a stick, the point would be that instead of starting in 1st gear, you find a way to start out in your final gear, whatever that final gear may be. I certainly don't want to use my clutch to try it out, but it is an interesting question to ponder just the same.

Anybody want to mark this day in history as the day that Jesse and I actually agreed on something? I think that should go down in a record book somewhere.

Interesting discussion, lets keep hearing the input.

 

It's definitely the total power you are making over the time. Not just peak horsepower.

In this case you are making a radical change to the total power put down. Ordinarily the car would sweep through peak power 2-3 times, in this case you are lucky to get there at all. So an ET or Trap calculator would be quite inaccurate.

But the thing is, is those calculators are estimates. They assume certain reasonable things. Most cars run reasonably similar through the 1/4. They probably use 3-4 gears to get to the end, get close to peak horsepower within 200-300', and then stay reasonably within the vicinity of peak horsepower the rest of the distance. And they never hit a speed limiter (like if you said "make the run in 2nd" or something).

I think if you looked at something like slicks or maybe even gears, you might find they make a more significant difference to the ET than they do to trap speeds. These don't change the power the car makes at all.

You need to compare like to like. You could probably make a calculator for trap speed vs weight and horsepower for cars that make the whole run in 4th gear. It would probably be less accurate, though, as you spend less time at the peak, or possibly never reach the power peak, making it more an indicator of total power. I suspect it would still be better than a calculator based on ET.

As a sort of aside, my only time at the track with the 'vette, I could make runs anywhere from ~14 seconds due to terrible launching, down to 13.2 seconds, yet my trap speeds were within a range of about 106-108mph.

 

Unfortunately we may never know the answer to the experiment as I've proposed it because it involves launching a car in 4th gear. It really wouldn't matter if it was an auto or a stick, the point would be that instead of starting in 1st gear, you find a way to start out in your final gear, whatever that final gear may be. I certainly don't want to use my clutch to try it out, but it is an interesting question to ponder just the same.

Why not just try it? It does not have to be a full throttle launch, just a light launch to get rolling in lower gears, then shift into 4th, maybe at 20mph or so, and slowly floor it so it does not start bucking.

It really helps everyone's theory when it can be backed up with actual facts

 

Alvin I started this thread after I almost got in the arguement with Jesse in the other thread. The biggest point I was trying to make is that at some point in the modification, or world of differences between two cars, there comes a time when MPH might not be an accurate method to compare the power that two cars are making. Trying to come up with an extreme example with which to prove a point I came across this question, which the more I thought about it, the more interesting it became. It quickly grew from "just trying to prove a point" to "Damn, that's actually a fascinating question."

The truth as I see it is as follows:
A dyno is a good tuning tool that will allow you to make adjustments to your car in a controlled environment. These adjustments might not be perfectly optimized for the real world, but they will be much closer than it was before you started. Do I advocate spending hundreds of dollars dyno tuning your car every day? No, absolutely not. However if you've made extensive modifications to your car it is a great place to start and will get you headed in the right area. If you so choose to continue tweaking your tune at the racetrack, fine. You likely won't have to tweak the tune nearly as much as if you'd made all of your mods and went straight to the track, and skipped the dyno altogether.

It is my also my firm belief that the same brand of dyno, with a competent operator at every site produces very consistent results. A variation of 10hp give or take might show up based on the condition of the dyno, how the car is strapped, etc, but ultimately the results should be similar. As such provided that you have the same car, or an identical car, IE same drivetrain, and the same type of dyno, a certain modification on one car should make approximately the same amount of power on the other one, especially if the cars made approximately the same power on a base line run performed before modifications. Considering these constraints it can be fairly safe to say that if one car gets 100 dyno horsepower out of a certain set of heads and a cam, and the other car gets 20, you need to at least consider the possibility that something might be wrong with the second car. This doesn't necessarily mean that you should rip the motor back apart by any means, what it means is that you need to find some other way to validate the lack of power. Hook the car up to a scan tool, see what it does. How does the seat of the pants feel? Take it to the track, see what it runs.

The same could be said for the track. If two identical cars are modded identically and one of them runs significantly slower track times, it's a good indicator that there may be a problem. You could then use the dyno as a tool to see if the car is actually making the power it is supposed to. My car was a perfect example of this with a slipping clutch. The dyno showed that I had gained 44 HP with a series of modifications but I only picked up about 2 tenths and a couple of MPH. Since the dyno chart was clean, I knew where NOT to waste my time looking. I replaced the clutch and immediately dropped my E.T. by 8 tenths and my MPH raised by an additional 3 MPH.

Dyno's are tools and damn useful tools if you know how to use them. They are not required, but they can save you a lot of time and effort if you know what you are doing. They may not be the best tools for comparing two different cars, but by that matter neither is the track because there are simply more than two ways to judge a car's performance.

As far as I'm concerned, that's the end of the story. There's no need to argue it any further because as we're all aware, it gets nowhere.

 

Personally two reasons, regardless of how you do it, there is the potential to damage something. And I hate the owner of our local drag strip, he's a crook that I refuse to give any money to.

Don't be silly, nobody here uses facts in their arguments!

 

Nathan.. You said everything I did..



As for the orginal question I'm damn sure your results will be skewed because My 93 and my 00 both picked up heavy on both the ET and the MPH.. Because my 93 is a blower car it picked up an obsered amount of MPH by keeping it in the power band.

 

Nathan, back around 2000 there used to be a forum member (Nickd) on here who had a 94 auto with a 2.59 gear. He switched to a 3.54 and reported a gain of .5 seconds and 4mph.
I agree there is really no practiacle way to test this theory at a drag strip, but, could it be done on a deserted highway? My proposal would be to mark off a section of the road, then slow your car down in 4th gear to about 750-850 rpms, cross that line then accelerate. Look at your speedometer when you cross the finishline. I may be wrong, but I cant imagine the speed would be the same if you turn around, run it again, but use your gears. The reason being you are going to be out of your torque band for a good portion of the run, so you are not going to have the same length of track when you are making power.
I may not be making sense with what I am trying to say, but think about this. If on a rolling start in 4th gear you are running 20mph at 750 rpms when you cross the first line. Now you accelerate say 320 feet down the track, what do you think your speed will be since you were in 4th at 750 rpms. Now go back, cross the same line at 20mph in first, nail it, shift gears and do you not think at that same 320 ft line you will be going faster due to the motor being in its power band and gear multiplacation? Assuming I am correct, and just for arguments sake, you crossed the first 320 ft at 30mph then the second time using gears you crossed at 60mph. This would be a rolling start for the next 1000 ft, one starting at 30 mph and the other starting at 60mph. I believe in that case we would all agree which would cross first.

 

Nathan,

mark it down again that I 100% agree with your last couple of post.

It should be said thou that some are STILL mistaking rear gear changes with what we are talking about here. Changing the effective gear ratio the test is done in - will effect the testing. Whether its 3 (auto) or 4th (manual).

Back to Nathan, as you used your example of your car, you could also refer to corky and my 406/434 combos. They are different cars, but we built the motors at first identially. They both turned nearly the same MPH - why one might ask....cause they were making the same amount of power.

Never know Nathan - we might wind up being allies afterall.

We are both pationate about our cars and learning and wanting more. Therefore we tend to step on one anothers toes. Never wanted to offend you - and I have never taken anything really to heart. Perhaps at Carlisle this coming year if I head down there you can stop over with Corky, Jim, and I and have a brew on me!

 

Ah, but you forget that your time (ET) has increased, so you have more time to accelerate, thus a similar MPH.

I think I have enough info to do the calculation for my car (1st-4th normal run MPH vs. 4th only), I'll do the math if anyone is interested. I can't promise that I'll get a good answer, but I'll post everything so you can look for mistakes...

Anyone interested?