Jesse, I believe I am the some that you are referring to. If in theory you start out in 4th gear vs going through the gears you are in effect changing the gear ratio. So how is this not going to affect the final mph covering the same distance of 1320 ft?

I edit the post to add Nathans question I am referring to.
Quote

What would happen if....

You launched your car in 4th gear and just left it there through the entire run? What would your MPH be at the end of the track? Would it be the same as your MPH if you raced normally?


I highlighted the parts of the post in question.

If you feel I am wrong or missing something here please explain so I and others can understand.

 

Whether you agree with Ski or not, it still isn't gonna happen. If you can slip the clutch, you can transmit enough torque to the rear to get up to your normal trap speed.

Without clutch slip, you're engine will produce far less torque at the low rpms, and you won't get all the way up to speed.

There's no trick question to it.

Part of the reason trap mph doesn't change much is because you're usually close to the top of your 1:1 gear, and acceleration is beginning to drop off. If you were halfway through 4th, you'd notice more mph difference.

Here's my last trip to the 1/8th mile: Not much difference, but definitely a trend.

 

.4s = 1mph on my car at the 660' mark. At 80 mph, .4s is about 40 feet.

 

As promised, here are the videos I said I would post of two different events. Not as "harsh" as what Nathan posted, but none the less, two incidents that caused the runs to be interupted, getting out the gas, and then back it through the rest of the run - then comparing them to the next run.

First is my fathers: First one you will see him get VERY loose off the line, completely get out of it, then run it out the back door. MPH is 132.89MPH. (you'll have to excuse my mothers filming, when he almost looses it).

And PETEK, what the hell you doing with my sister!

http://www.azzatochips.com/videos/Dad_burn1.wmv

Then here is the next run which he gets off pretty clean...still lots of spinning but you can clearly see that the MPH is still nearly dead on taking into account possible DA changes ect. 134.4MPH.

http://www.azzatochips.com/videos/Dad_clean2.wmv

There you have it, two COMPLETELY different style runs - but nearly the same MPH.

Next is my runs when my WB o2 saw the outside air on my DFI system ( it automatically corrects for A/F, and when it saw that outside air, it just POURED the fuel in.) As you can see those 30# injectors, DUMPING the fuel out the pipes the whole way down the track. Actually almost stalled the car out off the line! 127.XMPH through that run running as I said REDICULOUSLY RICH.

Then you will see the next run, slightly later in the night - and with the A/F corrected, but still not perfect. Car goes 130MPH, which the difference of MPH as previously mentioned is due to the A/F being slight better, and the change of air. Still only 3MPH difference - again it two ENTIRELY different runs.

http://www.azzatochips.com/videos/vette_too_rich.wmv

CLEARLY from those two examples you can see even giving up a good portion of the track, you can still maintain your MPH.

---------------------------

On the comment about "Gear change" what is not being understood is you need to maintain the SAME effective gear ratio when making the comparison. For example if you were to complete Nathans experiment in real life you would need to run your car through the 1/4 mile with say 3.73 gear using all the gears, but your 1:1 gear ratio total gearing would be 3.73. You get this by your 3rd gear (auto) multiplied by rear gearing = 1 x 3.73 = 3.73 gearing.

Next you would need to get the car at the starting line, get it moving out of the hole with the car in third gear, again total gearing would be 1x 3.73 = 3.73 gearing and let the dog eat. The RPMs would climb at a MUCH slower rate, but eventually it would get to the same MPH at the end of the track. The only difference you would see would be the "rate" at which the RPMs climb through 3rd gear.

NOW here is where you thinking of changing rear gears is going wrong. If you between the first normal run (remember 3.73 gears) changed the rear gearing to 3.07, your effective total gearing would be NOW 3.07. 3.73 does NOT equal 3.07, therefore your MPH would be less because you have now changed the ramp rate of the RPMs through 3rd gear.

I hope you can see the difference and I explained it clear enough. Both instances should be clear now.

And if Nathan can either confirm or deny my thought, but this experiment was not really to prove what would happen from a standing start with a car in 1:1 ratio (while creative, destructive , and a good brain teaser), but rather an exaggerated instance of what these videos clearly show. That you can either have massive wheel spin vs a dead hook and still turn the same 1/4 mile MPH.

Nathan can we agree again?

 

So the runs that were 3 mph difference... what was the difference in ET?

1.5 seconds or thereabouts?

A run starting out in 4th would probably take you 25 seconds. There's another 20 mph, give or take.

We're talking running in the powerband vs running in the bottom of a gear with less power. And it's gonna be out of the power band like that for more than half of the run. When you blow your launch, it's still a small part of the run, and you're not moving quick, so mistakes don't cost much distance there, you still have plenty of track to get your mph.

 

Not sure how else to explain it. but just like the instance where I used to go from 1st gear to 3rd gear with the stock shifter. you can see how quick I shift out of first gear in the videos, and YES the car has a little boost to get off the line, but those runs where I missed a gear, the car STILL pulls the same MPH. ET was wose of course, but MPH is the same.

You have to completely forget about the ET part of the equation. It can and will be anything depending on where you start from on the track.

Its really no different than if tomorrow I installed a powerglide in the car. neglecting any gains from the benefits of the lower rotating mass that may be had, the cars 1:1 gear ratio if I stick with the same gears, the MPH would remain the same (assuming the converter was also exactly the same).

Again, the instance or experiment here is an exageration of what would really happen on the track. The videos above typically at the track what would happen, and even they are exaggerated. Usually you have some spin, not to the 330ft mark, but just a little off the starting line and then running out the runs.

I am going to think about this a little, I believe there is a pretty easy way to work it out with math.

 

I wasn't sure either until I graphed my timeslips. Try doing that, for runs with the same setup.

If you change anything tune/da/gears, obviously then you can't compare em.

 

Actually your comment captures the concept I was talking about and I appreciate your comments.

 

CC you get it, some folks here don't....

This is real simple, and to prove it to yourself, just go out and do a slow launch and then short shift into fourth at 15mph. Set the odometer before you start and hold your foot to the floor for .25 miles. I doubt that you will be doing 70 by the time the time you you get to the 1/4 mile... Surely you won't be anywhere near the speed that you would get using the gears.

Road racers understand that the speed at any point on the stratightaway is a direct function of how fast you left the previous corner. Same thing here. If you are at 1,500 rpm with a wide open throttle you are only making about 100 hp, and like CC said you are at pretty low power outputs for much of the run. No hp no speed... pretty simple.

 

 

An example would be if you were running a 5 speed and when you were pulling 3rd you accidently hit 5th and drove it out in 5th your MPH would be way down at the finish line. I have done this and I didn't run anywhere near the same MPH and I stayed in it through the lights...I was down over 8 mph.

 

Here is nother way to view the problem.

my stall speed is ~5000rpm. So even in 3rd gear, I slam the gas, the RPMs are going to go to 5000rpm. Again assuming the heat generation could be handled - the car would being to move forward.

Now typically when I am running the car, my RPMs run from 5800-7000 RPMs. So really I only need to overcome that 800 rpm or so differerence to get into the typical "power" band that my 3rd gear pulls it.

The only difference is the RPMs are a function of Speed, and the RPM ramp that typically takes place over the last 1/2 of the track - will now take place along the entire track, at a much slower rate.

- To add more to the topic of real world, my father and I were speaking tonight about this topic. He was quick to remind me that when his car was really having tough times hooking up, usually smoking the tires on the 1-2 shift - MANY time in the elimination runs, we would dial his car assuming a direct shift from 1 right into 3rd gear. So the other difference from what he was doing, which still yielded the same MPH, was he used first gear to get the car moving.

He is running a 100% reverse manual valve body in his Rossler T350. The thing is like a manual - you put it into 3rd, it goes into 3rd. You come to a stop in 3rd and forget to move it back, it takes out in 3rd gear. I came back one of the runs this past year after running his car down the strip, and on the return road, I forgot I needed to "downshift" the trans. Surprisingly it wasn't all that sluggish - but again he has a 5000+ stall speed converter in it. I did notice it right away, as it did feel different, but the car still moved around the turn, and down the return road. I would NOT suggest doing it from a dead stop at WOT.

I am saying this with our cars and larger flat broad torque motors, perhaps its more masked in our cars, whereas if you had a stock converter, it might cause your speed to deviate more. Although racing my car from stock form, up to where it is now, I never saw much deviation run to run in my MPH - so I have to stick with my original thoughts that is would not change.

It certainly make the brain hurt thinking about it.

Nathan, is this your new method of driving me nuts

 

Well, you'd be somewhat behind on mph, and wayyyy behind on time.

1-2-3-4 shift at 5000rpm: 13.7@100.2
1-2 to 5000rpm, then 4th gear: 13.9@99.5 mph
1st to 5000rpm, then 4th gear: 14.7@96.3 mph
1st to 3000rpm, then 4th gear: 16.7@91.9 mph


Ski, if you give me some dyno numbers in table format, and other basics, like stall speed, shift points, tire size, gears, I'll see how close this sim comes to your car. It seems good except for the launch and 60' times. The dyno torque isn't enough to move the car to the 60' mark to meet reality. I have no idea why it doesn't add up there.

 

Sam. Wouldn't that be changing the effective gear ratio though? Trans x rear gear = effective.

Again perhaps that is why we are not completely seeing this the same way. In my examples my effective gear ratio is staying the same from normal run (at the end of the track), and then in 3rd gear the whole way.

I 100% agree that if you change that effective gear ratio you will loose MPH.

More food for thought:

Another reason I believe that I am thinking about this correctly is this reason. I have severely short shifted 1-2nd gear trying to find my optimum 1-2 gear shift point, and I ALWAYS have the same 2-3rd shift point at the track. Even despite the fact that the "drop back" RPM is much lower comparing the two shift points.

With the 1-2 drop point being lower than normal, and causing a slower ramp rate on the RPMs it takes longer for those rpms to reach 2-3rd shift point. Since its slower, and I shifted sooner on the track I achieve 2-3rd shifts at the same phyiscal reference point on the track.

Not sure if I explained that OK.

 

Jesse, I think there is another side of this that may be worth thinking about.

#1.
Actually what it does is pull your engine rpm down way early below its sweet spot and you are not making the same power to the ground for the same period of time. Kinda like having an engine that makes 600 horsepower between 5500 rpm and 7500 rpm but on your single gear run you never get the engine over 5,000 rpm and the car never sees the sweet spot of the engine during the run. That run will never MPH the same as a run that utilizes all the gears and is able to put the 5500 rpm to 7500 power rpm through all gears.

#2.
If your car runs the same MPH in both examples there are at least two issues you would want to look at. One, you may be running a converter that is way loose or you may be running out of gearing. This is pretty simple. Consider if you ran your car 1/2 mile would the car keep picking up speed or would it still run roughly the same MPH? I am not being an AZZ about this but this is a valid question because if the car would continue gaining speed then the car would run a faster MPH on a full power blast over a single gear run. If it is pretty much done picking up speed you have a converter, gearing or RPM issue with your engine.

Short shifting is entirely different than starting out in 4th gear and running the exact same MPH. I would agree if you short shift you will not see as much of a dropoff in a higher torque engine like yours because your engine has the grunt to pull the gear. Short shift a car with 300 horsepower and pull the engine 1500 rpm where it makes any power and that car will never pull the same MPH. That is fact. If it does you are not running enough gear or way too much stall in your converter.

I would say in your car you are keeping the engine under load and utilizing it's torque to pull the car. Again, Do it in a LT4 engine and get it below it's ideal operating range and the car will bog down and rev slower and not pull the same MPH.

This is a good discussion.

 

As I read and think about this, I really think the engine configuration has alot to do with the results, this was alluded to before.

Jesse's 406 was shifted at 5150RPM and likely made a very high % of its torque peak by 1800-2000RPM (if not even sooner)so the effect of missing the gear, or even starting off in 1:1 gear is negligable. Think of it this way, if you put your current heads, cam, intake on the old 406, do you think you would still get a good MPH on a missed shift run? I think you end up so far out of its operating range that you would have to slow down. I certainly could be wrong, what do you think?

However, a motor that needs to see 2500, 3000 or more,to be at the same % of torque will take too long to get there and require a lot of throttle and clutch manipulation. This, in effect, means making much of the run at less than WOT. This however does not disprove the MPH/HP correlation. The MPH would simply reflect a % of HP, relative to what was used. Similar to a dyno run at say 75% throttle. SO, the correlation remains between HP and MPH but certain engines will perform better than others in such an extreme test.

Something that would likely perform well in this test would be a motor with variable valve timing. You could go WOT without slipping the clutch from 1500-7000RPM.

 

Hey look at it this way. Nobody is arguing, they're actually discussing reasonably! IMHO that's a lot more fun when you sit down and try to reason through things from different points of view without getting into all the name calling / mud slinging.

 

Exactly. The point of the question requires that you maintain the same FINAL gear ratio. The only difference being if you start off using that gear ratio vs building up to that gear ratio.

Somebody mentioned the bycycle example and that's a fantastic point. I have a road which I can ride my bike on that is plenty long. If I start the bike in a lower gear I will most certain accelerate from a stop faster than if I start out in top gear. At the end of the road though it doesn't matter, I'll be going the same speed because I can only pedal so fast.

Ultimately I'll go faster E.T. if I start in a low gear, but my MPH would be the same. The reason being that I have a relatively slow top speed comparitavely so the length of the road is excessively long. If you were to have an unlimited length of road there is no doubt that the car would reach the same top speed, that isn't the question. The question is that if you constrain it to a quarter mile distance, do you have the length of road required to overcome the slower acceleration and still obtain the same speed?

EVENTUALLY you'll end up at the same speed, that is of absolutely no doubt. The question is, will it happen in the quarter mile?

Personally I believe that a lot of this is going to have to do with the nature of your car's power curve. The more power you make, the faster you accelerate and therefore the less time it is going to take to overcome the difference.

 

my friend has a blown bbc 68 camaro with a pro control. It ****s the motor off instead of studdering it like a rev limiter. I guess blowers don't like that ? Anyway on 3 passes when he first started racing he would over rev 1st gear and shut the motor off, reach down reset the box, restart the car and still run 120 MPH trap speed. I never knew why but alwys thought that was kind of neat. Of course it would be like a 14 sec run @120.

Mike

 

Don't think about the long ET giving you more time to accelerate. Slower acceleration will use more length of track to get to a certain mph.

The track is a fixed length.


Your motor doesn't make constant power across the powerband, and that's why the mph will be lower. Because your rate of acceleration will be lower in the rpms below the powerband.