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[Deacon]

Unbalanced brought up an interesting point in another thread.

"The 255 cam in the 110 runs out at about 4200 if someone is riding the bike and not shifting till say 5k or 5500 then they are shifting to late and you will need to learn to short shift at 4200 - 4500 latest to stay in the power."

I dug out my dyno sheet to look over the HP and TQ figures.
TQ   
100ftlbs TQ @ 2200 rpms, peaks @ 111 ftlbs around 3800 and starts falling off and by 4700 rpms is back down to 100ftlbs.

HP
doesn't hit 80hp till 3700 rpms then peaks @ 5250 with 92hp and holds that till about 5500rpms.

So in a drag race will short shifting @ 4000 actually be better than holding her out till the HP starts to drop @ around 5500?
It still feels like it's pulling real strong but I have never timed my bike short shifting.
What ya think?
Anybody ever tired it at the drags and compared results or is it all theory?

[Unbalanced]

Deacon,

I can only tell you what happened with Rhino and ex site member here and myself.  We tried it short shifting and we tried it with running it out.  Running it out didn't work, he could stay closer short shifting.

[Deacon]

Well, I am going to give it a try.
 Grudge II is coming soon with my buddy and his Street Rod. He bought some kinda electric LED Gizmo shift light and is looking for a win this time. By all rights if he drives that bike right he should blow by me, or so he says.
He makes fun of my potato tractor motor. I would like to put on a good show for him.
He said he couldn't  read the tach last race.
Those H2O Harley-Porche bikes are supposed to be running mid 11's stock with a good rider.
If I get a hole shot on him and short shift @ 4000 and he drives his bike right I would be real happy beating him to 60mph.
We will see.
Grudge II comming to you local highway soon.
Current count. Tractor motor 1
                     Porche motor 0

[grc]

If you want to determine optimum shift points, you have to do some calculating after obtaining detailed torque curve data.  What you have to do is come up with a curve for each gear ratio (torque X gear ratio) over the normal rpm range.  If you then plot all of the curves on the same chart, you will note that they intersect each other at some point.  Where the 1st gear curve intersects the 2nd gear curve is your shift point, where the 2nd gear curve intersects the 3rd gear curve is that shift point, etc.  Unless you have a gearbox with the exact same rpm drop between every gear, your optimum shift rpm will vary by gear.  Normally 1-2 will be the highest rpm, and each succeeding shift will come at a lower rpm.

The typical but wrong assumption is to shift at redline.  Redline has nothing to do with the torque curve; it is a mechanical safety and reliability indicator.

Jerry

[erniezap]

Keep in mind the difference between torque and horsepower:

Torque gets you there, horsepower keeps you there.  For a drag race, torque is more important than horsepower.

BTW, great explanation GRC!

[Deacon]

Thanks for the replies. Good information there.

[SPIDERMAN]

Here's my take. When you're running side by side with your bros and one of em pulls ahead by shifting up a gear, you're shifting too late.

B B

[rednectum]

well, i have to interject about the hp/tq thing when racing. at the track-------------tq gets you off the line, too much too early and you break the tire and drive toward the ambulance. enuff about that, okay------two good riders, one on bike with 80 tq 140 hp, the other on bike with 130 tq, 120 hp.

here we go, the 80 tq guy will be leaving slowly, but constant. the 130 tq will be peddlin, prayin, thinking how huch power he has----

now after the 60 ft, tq guy starts pulling a little, everytime he bumps a gear ( you only get a couple in a real dragrace) he feels he is pulling ahead.

the hp guy is watching mr tq get bigger and bigger, till he blows by him like mr tq stomped the brakes. on the track, you can see this all happening in slow motion!!!!! on strret, you are a baddass, on the track, after half track, you swear something is wrong with your bike. hehehe why did it just stop accelerating? why did mr hp blow by me?

oh, as to the statement the vrod runs 11's stock------------i will argue that too. i got a bunch of little vrods carved intomy belt. im proud of the ones that say SE. hahahahahahahahaha

[Dan_Lockwood]

Keep in mind the difference between torque and horsepower:

Torque gets you there, horsepower keeps you there.  For a drag race, torque is more important than horsepower.

BTW, great explanation GRC!

Right or wrong, I've had the assumption that the difference between torque and hp is this....

Torque is the power/muscle you have and hp is how fast you get the work done.

On a dyno the only measurement it reads is torque.  Hp is a calculation based on rpms, hears that speed thing again, and torque.  So really hp is a made up number that looks at power in a length of time.

So by your standards a farm tractor with 150#ft of torque and 35 hp should beat the same weight vehicle but with 60#ft torque and 90 hp.  It ain't going to happen.  The time is too long and the guy that can get the work done faster, albeit with less torque will still win the race, again depending on the length of the race.

Also if you have two like bikes with the same hp but the cams are different, in that one develops the peak torque at 1,000 rpms higher than the other, the one with the higher torque rpm will win the race every time.

There are some great websites out there dealing with this very question, but here's a site that I've used many times for my streetrod days.  Yes, it's automotive related, but there are some very good formulas listed and lots of information.

http://www.users.interport.net/s/r/srweiss/

Enjoy the website.

[rednectum]

Right or wrong, I've had the assumption that the difference between torque and hp is this....

Torque is the power/muscle you have and hp is how fast you get the work done.

On a dyno the only measurement it reads is torque.  Hp is a calculation based on rpms, hears that speed thing again, and torque.  So really hp is a made up number that looks at power in a length of time.

So by your standards a farm tractor with 150#ft of torque and 35 hp should beat the same weight vehicle but with 60#ft torque and 90 hp.  It ain't going to happen.  The time is too long and the guy that can get the work done faster, albeit with less torque will still win the race, again depending on the length of the race.

Also if you have two like bikes with the same hp but the cams are different, in that one develops the peak torque at 1,000 rpms higher than the other, the one with the higher torque rpm will win the race every time.

There are some great websites out there dealing with this very question, but here's a site that I've used many times for my streetrod days.  Yes, it's automotive related, but there are some very good formulas listed and lots of information.

http://www.users.interport.net/s/r/srweiss/

Enjoy the website.

yep, dyno will show it! look at the 255 cam , it goes up quick, hangs around a short time, falls on its face.

now look at tw55, takes time to go up, hangs around longer, and takes its sweet time to drop,


the tw55 made hp! and held the tq from 3500 to over 7000 rpm. although the dyno software converted it mathmatically to hp after 5252( 5225) (5259)im on my fourth beer. its piston speed anyway for those that know.. anyway, the 255 wouldnt hold tq long enough for the software to even bother with the hp conversion, it fell asleep. LOLOLOLOLOLOLOLOL

[Unbalanced]

Well, I am going to give it a try.
 Grudge II is coming soon with my buddy and his Street Rod. He bought some kinda electric LED Gizmo shift light and is looking for a win this time. By all rights if he drives that bike right he should blow by me, or so he says.
He makes fun of my potato tractor motor. I would like to put on a good show for him.
He said he couldn't  read the tach last race.
Those H2O Harley-Porche bikes are supposed to be running mid 11's stock with a good rider.
If I get a hole shot on him and short shift @ 4000 and he drives his bike right I would be real happy beating him to 60mph.
We will see.
Grudge II comming to you local highway soon.
Current count. Tractor motor 1
                     Porche motor 0

Well Deacon have you had a chance to settle the grudge match yet?       

[Deacon]

We are shooting for next weekend. One of us has to make a 65 mile ride to the other guys house and it just too damn hot this weekend. Goina find somebody with a pool and drink beer instead.
I want to go to the drags again after it cools down some with him and ride his bike for him at the track. Just see what it will do. My motor has loosened up now (5000mi) and it is faster than it was when I turned the 12.5. I know how to launch it better and won't be winding it ti 6200rpms
This is what being 57 years young is all about!