Shift Point / Above or Below Max Horsepower RPM ?

[Mike Gaines]

If your dyno sheet shows maximum horsepower, let's say, at 6000RPM should you actually shift at 5800 (or so) so that the shift goes thru at 6000 or should you actually shift at 6000 and then the shift would not complete until about 6200.

(Note: I am not questioning how long it takes your tranny to execute the shift just if you should have the motor shifted into the next gear right at the Max Horsepower RPM OR go past the Max Horsepower RPM and then shift)

In other words, should you run your motor just up to the Max Horsepower RPM and then shift OR should you go OVER the Max Horsepower RPM and then shift.

This is, of course, for the 1-2 shift and the 2-3 shift...nothing to do with high gear.

But...some people tell me it is good to get into high gear as soon as reasonably possible to have it start building RPM to go thru the lights and a higher MPH.

Please weigh in on this...thanks.

 

[hangn0ut]

Shift past peak hp. Ideally you want to shift at a point past peak hp so that when the shift is complete you are at the same hp below peak hp. Ya want to be at the average highest hp through out the run. You have a dyno sheet. With the percentage of rpm drop between gears you can figure mathmatically when to shift. Personally, i shift where it feels fastest.

- - - Updated - - -

As far as getting into high asap ya must have been talking to them diesel racers. Or an A/Fuel guy.

 

[HT413]

I'm not a racer, but I've studied this in college and according to my professor, you should start with a shift point that maximizes your area under the horsepower curve. This is really just another way of saying what hangnout said up above. So basically, say your peak is 6000 hp and shifting from 1st to 2nd gear drops your rpm by 800. Then your best ET will be somewhere around a 6400 rpm shift point.

Keep in mind that this technique 'theoretically' maximizes your horsepower at any point on the track but there are a lot of real world issues that need to be accounted for, such as

a! can your engine actually live in that rpm?
b) most hp curves drop off steeply as carb / head max cfm are approached, so this shifts the ideal shift point down.

 

[66Satellite47]

Mike, take a look at what RPM the peak torque is. Try shifting at the RPM that drops you back to the peak torque RPM. But if the torque curve is really flat (which I think may be the case for you, if I remember your dyno sheet correctly), then go past peak HP to maximize that area under the curve like HT413 said. However keep in mind what your desired max RPM is for durability sake. After doing the benchtop analysis some trial & error testing will let you fine tune the real world conditions.

 

[Cranky]

Track testing is your best dyno too. And wouldn't you also figure in gear multiplication for each gear to optimize torque to the rear wheels? I've read that shifting at slightly different rpm in each gear can also improve ET's....

 

[HT413]

Because of the converter, i think I have to change my answer. Question for ya, I see you have a 5000 stall converter, but when you make the 1-2 shift, what is the actual rpm that motor settles into in 2nd gear?

Also, i saw in your motor thread that were shifting at 6200, is that where the motor really shifted, or was that where you shifted and the motor wound past it by a few hundred rpm?

Because the converter keeps the motor at that stall rpm (until you basically exceed the stall), shifting at the hp peak will just drop it into the stall rpm and the converter does the rest. So i think converter stall has a lot more to do with how much hp you are putting to the ground down the track than shift point. So basically, after fooling with the shift point and maximizing your ET, i think tuning your converter to settle into just the right rpm would have a greater effect, since you are into the stall for far greater time than out of it.

 

[uwss]

AT!!!!!!

 

[lewtot184]

ideally i think you want to stay around the peak torque rpm when up shifting and rpms drop. don't confuse engine dyno peak horsepower with peak horsepower that the chassis sees. back in the day the used to say shift at 10% above peak horsepower rpm. i think that's way too high. in reality only track testing will give the true answer. with an automatic trans i've tried doing the 1-2 shift at a little higher rpm than the 2-3. i've done this because the gear spread of 1 and 2 is greater than 2 and 3.

 

[Tex013]

Mike ,
I am of the group that feels you should be shifting 2-500 above peak HP . The motor should be able to carry past this peak number before falling off so on the shift you don't drop too far from the fat of your TQ and HP
I chassis dyno my motors so at least I can see what the wheels are seeing .
Now some of this is impacted by your converter stall because often on shift the motor will pull down to this number .
Short shifting I have found will slow my ET, 1 or 2 hundreds , but often pick up MPH , runs longer in top gear . This was with a 500RPM lower shift , 300RPM made no difference
My motor makes peak HP at around 5500/5600 . I shift at 6000 , stall is 5000/5100 trap at 6300/6400. In car video shows RPM fall back to the stall no lower .
Have you tried in car video to see what is happening on your tacho , I see you have a read back unit .?
Testing is the only way to know for sure what your motor likes

Tex

 

[lewtot184]

anybody remember the "G-meters"?

 

[dvw]

A few notes: The engine will always fall back to true stall, or fall back on the shift. This will generally be 300 rpm or so higher than converter flash. Best ET will be when the shift is made right at the peak G-force . This is usually accomplished by shifting past peak HP rpm. A graph line drawn through the fall back rpm point and shift rpm point on a graph should be level. If the line tips down towards shift rpm point, the shift is to high. If the line tips down towards the flash/fall back the shift was to low. Higher torque engines will be less sensitive to shift points.
Doug

 

[shag766]

Track testing is your best dyno too. And wouldn't you also figure in gear multiplication for each gear to optimize torque to the rear wheels? I've read that shifting at slightly different rpm in each gear can also improve ET's....

i am in the school that it is torque that moves your car also. x2 on the track testing.

 

[dvw]

Track testing is your best dyno too. And wouldn't you also figure in gear multiplication for each gear to optimize torque to the rear wheels? I've read that shifting at slightly different rpm in each gear can also improve ET's....

For sure this is the best. We have tested with G-meters. It will get you to the correct spot.
Doug

 

[Budnicks]

A dyno sheet is just a guide line the car & track set-up needs to be in the equation

like he said above,

You need to get a feel for your specific car & specific track combo

Shift when it starts to fall off, just before that point, don't float the valves or lean it,
just needlessly spinning it, to spin it to a specific RPM on a graph doesn't help,
it needs to be, "still pulling & not falling off" regardless of the Max HP RPM...

IME seems the short shift from 1st to 2nd doesn't hurt as bad as a short shift from 2nd to 3rd

I've had cars that ran better when {Short shifting} shifting earlier too, not at the peak RPM
running it longer in second, than winding it to the moon in 1st...

I'd go testing & actually see what your 60ft & 330ft & 660ft & 100ft times are,
doing it a couple different ways, different RPMS shift points, different RPM launches etc.
log it & keep track of track conditions, engine & oil temps, ambient heat/temp.,
starting line conditions, weather conditions, altitude, cloud cover or sunny, even burnout style & length, all these types of things can & will effect the times/runs variables/consistancy...

You need to actually make alike runs, in alike conditions, as close as possible or
your just spinning your proverbial wheels...

stuff like;
RPM left at ?, what ignition timing ?, what tune/jetting ?, what plugs & readings ?
whether it spun ?, whether it bogged ?, if it fell off ?, if so at what RPM ?,
did it pull hard in 2nd but fell off in third ?, did it run like a raped ape ?...LOL
I could go on & on, etc. etc. etc.

IMO it's all far more than just a specific shift point,
allot of variables, try to eliminate as many as possible,
try to do the same length burnouts same engine & oil temp etc...

I'd also do a leak-down test after a few runs,
read the plugs {lean or rich}, check valve-spring pressures etc.,
that stuff will all effect the #'s too

my $0.02 cents


BUT again IME it really depends on your specific combo,
what works for my stuff, may not be ideal for your stuff...

 

[Cranky]

Another question.....are you ET bracket racing? I like to see what the best ET I can get from my car but past history says it's not going to always be consistent doing that especially when the weather changes. Several years back, I ran a car that would run 10.50's but it wasn't consistent but once I slowed it down, it became very consistent even when the weather changed a bit. Just sayin. I like running a car that runs the number week after week. Gives me time to socialize and etc :grin: but never was much on seeing every last ounce I could squeeze from my car.

 

[Mike Gaines]

Another question.....are you ET bracket racing? I like to see what the best ET I can get from my car but past history says it's not going to always be consistent doing that especially when the weather changes. Several years back, I ran a car that would run 10.50's but it wasn't consistent but once I slowed it down, it became very consistent even when the weather changed a bit. Just sayin. I like running a car that runs the number week after week. Gives me time to socialize and etc :grin: but never was much on seeing every last ounce I could squeeze from my car.

The car is a bracket racer and I will be running E Gas at my home track which is an 11.60 dial in heads up racing...it's not fast enuf for D Gas which is 10.60 dial but.....before all that I want to see just how good of an ET and mph it will do when everything is tuned in correctly. I am pretty sure I can wring 10.80 out of it and that is my goal...make sense ?

 

[383man]

I rarely use the tach when racing. I look at it on the starting line when I come up on the converter some and I look at it in the traps. But I shift by the feel of the eng as I always have and I have had good results driving like that. It seems easy to me to drive like that as I can tell when the eng is peaking and I should shift. Sometimes I will try it sooner or higher but it seems to run the best by shifting like I always do. Ron

 

[hangn0ut]

To really test as mentioned above,you gotta rent the track. For two days. In SoCal tnt gets crowded. Maybe 4 passes a night if you make changes. And we might lose 1 of the 2 tracks in the LA area any time now. Pomona dont count. You guys with uncrowded tracks,how lucky!