[Stan Weiss]

Originally Posted by PontGuy

Remember HP is not a function of gear ratio so calculating it like you are doing is not correct. Hence the 700+ HP numbers which are way more than your engine makes. Just read the HP right off the dyno chart. So for 1-2 your car will be making 320 HP at a 5300 RPM shift which matches nicely with the 320 HP at 3950 after the shift. And so on for the other shift points. Doing it this way is a lot easier than calculating wheel torque and you end up with the same results.

The curves in your dyno chart are very flat which would mean that the shift points should not be that critical at the track. But then again with carb/fuel flow issues resolved the curves may look a lot different. And real world never works out quite like theoretical due to other factors in play.

X1000

I do not know anything about Adam's car or setup but playing with a computer simulated run shifting at 5300 5200 5200 and saying that this is the best then 5000 5000 5000 and 5500 5500 5500 are both only about .03 worse. You would be much better off working on getting good 60 foot times than playing with getting the perfect shift rpm.

Stan

[i82much]

I don't think there is any getting around the fact that you should go faster if you maximize the average power under the curve. Physics won't let you get away from that. However, as has been suggested elsewhere in this thread, a lot of these Pontiac builds have really flat power curves. For my money, if I could run 11 flat shifting at 6300 RPM or 11.1 shifting at 5500 RPM, I'd lose the tenth and keep my engine together for a long time and enjoy racing. So as I see it, you can probably shift a good bit earlier than would be theoretically optimal, still run really close to your theoretically optimum et/MPH, and have an engine that lives a lot longer. Not to mention it will help keep the rest of your drivetrain intact.

[Cliff R]

For the big 455 street/strip engines most woln't care all that much about rear gear used or exactly where you shift them at. This assumes you've done your homework and built a pretty stout one that makes peak power past 5000rpms and has a broad/flat torque curve.

For my engine I can shift anywhere from 5000rpm's to 5800rpm's and it will only vary about .04 seconds for the entire spread. For this reason I short shift at 5000rpm's for most runs vs "grinding" up the engine more just to put up a little better time slip.

Many years ago I owned and raced a 1965 Nova SS with a high-winding SBC in it. I shifted it around 7000rpms and went thru lights around 7500rpm's. If you short shifted that little bugger you'd get your BUTT handed to you in a bracket race.......FWIW.......Cliff

[AdamIsAdam]

Stan,
You are correct. I was just enjoying learning about the intricacies of bench racing, partly because I will likely have limited track time when I go so I'd like to at least start off with a theoretical baseline good shift points.

As for the 60' times, I've experimented with different launch techniques by timing 0-60 runs with a phone app that seems accurate. I've gotten three bests of 3.6 (in a row actually). Not sure how that converts to 60' times, but when I search all other cars' 0-60 times, cars with times of 3.6 seconds are running about 11.90 ET. And the car pulls strong up top, so who knows what it'll do!

[AdamIsAdam]

Originally Posted by i82much

I don't think there is any getting around the fact that you should go faster if you maximize the average power under the curve. Physics won't let you get away from that. However, as has been suggested elsewhere in this thread, a lot of these Pontiac builds have really flat power curves. For my money, if I could run 11 flat shifting at 6300 RPM or 11.1 shifting at 5500 RPM, I'd lose the tenth and keep my engine together for a long time and enjoy racing. So as I see it, you can probably shift a good bit earlier than would be theoretically optimal, still run really close to your theoretically optimum et/MPH, and have an engine that lives a lot longer. Not to mention it will help keep the rest of your drivetrain intact.

AGREED 100%! See goals #1 & 2 above. LOL

[TedRamAirII]

Adam. What phone app do you use?

[AdamIsAdam]

Originally Posted by TedRamAirII

Adam. What phone app do you use?

Tapatalk. Why do you ask?

[TedRamAirII]

Originally Posted by AdamIsAdam

Tapatalk. Why do you ask?

I thought you had a phone app for measuring your car performance? Maybe I misread that.

[AdamIsAdam]

DUH! Sorry about that. Yes, you read correctly - it was me who read incorrectly when you asked -- I do have a phone app for measuring the following: 0-60, 1/4 mile, as well as a rolling time from any starting to any stopping speeds. (ie, 5-60 MPH).

It's called CT Speedometer Systems PRO. This is an Android app but I'm sure there are Apple versions or similar models. I find it to be accurate AFAIK. But I've only done 0-60 because I'm not very comfortable taking my 64 to 110MPH or more screaming on the streets of LI. Too risky. 0-60 is as I get onto the highway is practically legal.

[54nomore]

Here's the results of my experimenting at the track just yesterday. The first timeslip is me shifting manually at 5000. The second is with the trans. in DRIVE shifting it's self at 43-4400. My car is on the right on both slips. The pics aren't super clear, but they read 15.301 and 15.328

[70GS455]

Stan has the right answer as shown in his graphs. And you can use either driveshaft torque or driveshaft hp, the math works out the same and will give you the same answer. The idea is to maximize the available power (or torque, you get same answer) delivered during the run as the engine changes rpm and the gears change. Simple. Just follow the tops of the curves and shift where they cross


Sent from my SM-T817V using Tapatalk

[Formulajones]

Originally Posted by 54nomore

Here's the results of my experimenting at the track just yesterday. The first timeslip is me shifting manually at 5000. The second is with the trans. in DRIVE shifting it's self at 43-4400. My car is on the right on both slips. The pics aren't super clear, but they read 15.301 and 15.328

Better 60 foot by a tenth on the second pass should have equated to close to 2 tenths quicker ET, but you slowed down. That tells me that short shifting the car on your second pass hurt your ET, likely by more than your slips are showing.

[AdamIsAdam]

Originally Posted by Formulajones

Better 60 foot by a tenth on the second pass should have equated to close to 2 tenths quicker ET, but you slowed down. That tells me that short shifting the car on your second pass hurt your ET, likely by more than your slips are showing.

Good catch.

[johnta1]

I took it as the 5000 RPM launch had the tires spinning some thus the slow 60' (and 1/8th).
The higher RPM helped though on the top end.
(ET and MPH)

The lower launch hooked and pulled through the 1/8th but was out of the RPM range of the engine on last half of run.



Try some slicks and see what the results would be.

[54nomore]

LOL. I posted merely to illustrate how little difference there was in ET even with my low powered 301. There was actually no detectable wheel spin on either pass, but there were definite outside temperature differences as well as possible engine temp differences between the two. Still, I think 2 hundredths isn't a lot of difference.

[Formulajones]

60 foot would have to be identical to make a decent comparison.

The issue is putting together consistent runs while only changing one variable. Tough to do.
Really need more passes with each example.

If your 60 foot was a 2.07 on the first pass instead of 2.15, the ET on the first pass would have likely been a 15.20 or better instead of a 30.

These reasons are why Adam is going to have a tough time finding his ultimate shift point. Especially with a 4-speed car. He is going to need to 60 foot consistently, and probably just experiment with that a while until he finds something that works best. Then start driving the rest of the track, and not change a darn thing he does, including how he shifts, and just play with shift points. Not even sure he would get enough runs in a days time to iron it all out. May be several trips to the track.

[54nomore]

FWIW, I have to take back part of my statement. The first time slip was my first pass of the day and I actually did have a slight bit of spin on that one. Engine wasn't fully warmed up either as they had us shut down in the water box while they worked out some computer problem with the clock. Opening day bugs and all.

[STEELCITYFIREBIRD]

Originally Posted by johnta1

Try some slicks and see what the results would be.

Agree..keep tool box, checkbook and tow vehicle ready.

[Lee]

Originally Posted by ponyakr

Since I raced a 4-speed car for a few years, I'll take a stab at this one.

You experiment with shift points, til you find those which produce the lowest ET. Without actual, on track testing, all you have are opinions. And, as we've seen on this and most every forum, opinions can differ WIDELY, on most any given subject.

There can be too many variables with engine & cam torque & power numbers, trans & rear gear ratios, etc.

I totally agree. After running a wide variety of cars at the track, and having tested several of them on a chassis dyno, the track testing is THE way to figure it out.

One variable I've not seen mentioned, is the tachometer. Not all are accurate. Not all respond as quickly as the engine rpm actually changes.

My FIRST 455 I ever totally built, was in the very early 90's. I bought the block & crank, all parts, all machine work, and rented an engine hoist for under $1,500. That was my tax refund that year, and was ALL the money I could spend. In a '79 T/A, stock torque converter, Q-jet, pre-EGR iron intake, and 2.93 gears, it was running 13.8's shifting at 5,000rpm. On a whim, I tried shifting lower - eventually ran 13.2's shifting at 4,600. Between 4,600 and 5,000 rpm, THAT car would lose a solid half-second at the track.

I had an '03 Mach 1. It had a redline around 7,000 (DOHC motor). On the chassis dyno the HP peaked a bit after 6,000rpm. While the rest of the world were shifting these cars at close to redline, I started dropping shift points and running quicker. Totally stock except for stock-size Nitto DR's, I ran several 12.9's shifting at 6200rpm.

My old Falcon wagon had a 427 inch Windsor. I probably made close to hundred dyno pulls with that car, testing various things (intake manifolds, valve lash, air cleaners, timing, jetting, etc.) and it always made peak HP right around 6,200. Now, my instincts were that this motor should perform best when shifted around 6,500, MAYBE 6,600. But it always gave best e.t. and MPH when it shifted around 6,900-7,000. I retested several times, but always got the same results.

Some combos like short-shifting, others like to be revved. Some are not very sensitive to shift point, while others are hyper-sensitive.

[PontGuy]

Been just watching along since helping to sort out the math a couple dozen posts ago. I said back then that math is math, but real world never works out quite like theoretical. Lots of posts since then agreeing with this point.

I am not a drag racer, only a very occasional test-and-tuner, and managing a strong stick car down the 1/4 without a bunch of practice is challenging. And I can speak from experience that breaking rear end parts definitely reduces the fun factor. Even with street tires launching on a prepped track is harder on things back there than a typical street launch. From the perspective of a relative rookie, a few things I focus on-

1. Don't spin the tires. Dropping the clutch is fun on the street but a mistake at the track. I try to think think "smooth application of power". A good launch makes a huge difference compared to shift points.
2. Don't over-rev before shifting. The 1-2 shift point on a stick car comes up very fast and I find it is easy to go too far with it unless I stay focused, even if I have a particular shift RPM in mind.
3. Be conservative on the first passes to get a feel for it. This takes self-control especially if a car is lined up in the other lane, but I find the difference between conservative and aggressive is usually no more than a couple of tenths or so. And smoking the tires or over-revving the shifts definitely doesn't help.

I really like driving stick cars, but an auto trans is sooo much easier..

After all this discussion Adam, really looking forward to hearing how it goes when you do get your car to the track!