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How will you go faster?

General engine tech -- Drag Racing to Circle Track

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skinny z
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Re: How will you go faster?

Post by skinny z »

Stan Weiss wrote: Wed Nov 23, 2022 4:34 pm
skinny z wrote: Wed Nov 23, 2022 4:14 pm So many sims Stan I've lost track.
Was that one the 470HP@6000 as an answer in another thread?
Kevin,
I believe that is the one I used see below. Note these graphs are for illustration purposes only as there are factor which can / will change these curve somewhat. One would need information about the car to get closer, but it still comes down to what runs best at the track.

Stan

G_Force_vs_Time_Input.gif
That would be it Stan.
Now, my question is, even without the vehicle info, what is the reasoning behind carrying the 1-2 to 7500 when peak is at 6k?
I've understood carrying another 500-1000 RPM, but 1500 is a long way.
Kevin
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Re: How will you go faster?

Post by rebelrouser »

Ken_Parkman wrote: Wed Nov 23, 2022 1:26 pm This is actually the point, and how you optimize. That input shows a rpm drops of 21, 33, and 38% and the point is the curves do not cross. So it is not optimized and cannot be with this data.

You should run the engine high enough to understand how it drops off, and knowing the characteristics you can also then begin to optimize torque converter, ratios for rpm drop, and clutch if applicable. Then pick reasonable gears and shift points, factored for the rates of acceleration.

I always have an idea about the power characteristics above peak, and use that to optimize drivetrain, perhaps limited by a mechanical redline. The better the converter or the smaller the ratio drop the less you have to overrev the engine to go fast. This is why a CVT is perfect, but with a good converter you can get closer.

I have gone mid 10's in my bracket car with a taxicab junk parts engine; maybe 400 hp. The torque converter was worth more than the engine and allowed the engine operated in an 600 rpm band. Very much the curves crossed so you also have to include or at least understand the converter in your simulation. The actual engine torque peak rpm should never be seen in performance use unless you have drivetrain limitations, and if you can it is much preferred to fix the drivetrain.
I totally agree with your observation. Just curious how did you arrive at a torque converter suited to your engine? My experience with getting a good converter built is hit and miss.
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Re: How will you go faster?

Post by Ken_Parkman »

It is a long way, and might be a good way to get a slap in the face with a connecting rod. Shows the problem of a wide gear ratio and a big rpm drop. If you had a usable power curve to that rpm it may be possible. But it also shows why closer ratios and more speeds with a stick is faster.

The good news is there is a better solution.

So approach it from the other direction. Converter the car so the rpm drop back to stall is a much smaller drop. On top of that you get torque multiplication through the converter with a delta in input and output speed, depending on how good the converter is. So you keep the engine in its maximum power band, and bracket the peak power with the operating rpm range.

Problem to simulate is a converter is a variable ratio and I have never been able to find a good graph for that.

Took one guys car to the chassis dyno. It had an 8" converter and we got good data with that. Prior to this he was convinced he had to spin it to 6200 and was making a lot of effort to do so, which was a problem with that hydraulic cam which was nosing over. So with the data we could show shifting at at 5800 with the 5400 stall narrowed up the operating range and kept the average power higher in his operating range. Car went faster.
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Re: How will you go faster?

Post by Ken_Parkman »

rebelrouser wrote: Wed Nov 23, 2022 5:09 pm
Ken_Parkman wrote: Wed Nov 23, 2022 1:26 pm This is actually the point, and how you optimize. That input shows a rpm drops of 21, 33, and 38% and the point is the curves do not cross. So it is not optimized and cannot be with this data.

You should run the engine high enough to understand how it drops off, and knowing the characteristics you can also then begin to optimize torque converter, ratios for rpm drop, and clutch if applicable. Then pick reasonable gears and shift points, factored for the rates of acceleration.

I always have an idea about the power characteristics above peak, and use that to optimize drivetrain, perhaps limited by a mechanical redline. The better the converter or the smaller the ratio drop the less you have to overrev the engine to go fast. This is why a CVT is perfect, but with a good converter you can get closer.

I have gone mid 10's in my bracket car with a taxicab junk parts engine; maybe 400 hp. The torque converter was worth more than the engine and allowed the engine operated in an 600 rpm band. Very much the curves crossed so you also have to include or at least understand the converter in your simulation. The actual engine torque peak rpm should never be seen in performance use unless you have drivetrain limitations, and if you can it is much preferred to fix the drivetrain.
I totally agree with your observation. Just curious how did you arrive at a torque converter suited to your engine? My experience with getting a good converter built is hit and miss.
After learning the hard way with cheap crap purchased on an incomplete understanding of this stuff resulting in blown up transmissions and a slow car I had enough. Picked a converter manufacturer with a very good reputation and a lot of records in class racing. The car went 8 tenths faster the next weekend with a good converter from a good manufacturer specifically built to my combination. Never looked back, and will never cheap out on a converter.

Was also very educational when the car goes 8 tenths by keeping the engine in it's powerband.
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Re: How will you go faster?

Post by BobbyB »

skinny z wrote: Wed Nov 23, 2022 4:36 pm
Stan Weiss wrote: Wed Nov 23, 2022 4:34 pm
skinny z wrote: Wed Nov 23, 2022 4:14 pm So many sims Stan I've lost track.
Was that one the 470HP@6000 as an answer in another thread?
Kevin,
I believe that is the one I used see below. Note these graphs are for illustration purposes only as there are factor which can / will change these curve somewhat. One would need information about the car to get closer, but it still comes down to what runs best at the track.

Stan

G_Force_vs_Time_Input.gif
That would be it Stan.
Now, my question is, even without the vehicle info, what is the reasoning behind carrying the 1-2 to 7500 when peak is at 6k?
I've understood carrying another 500-1000 RPM, but 1500 is a long way.
The acceleration is the product of the engine torque times the gear multiplication.
In this case you show 283 ft lbs at 7500 rpm. In first gear your driveshaft sees 283 ft lbs x 2.5=707.5 ft lbs
After the 1-2 shift engine speed drops to 4500 rpm, because 7500 x 1.5/2.5=4500.
At 4500 rpm you make 464 ft lbs at the flywheel, but, in second gear it only gets multiplied by 1.5 to 696 ft lbs.
Does this make sense?
skinny z
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Re: How will you go faster?

Post by skinny z »

BobbyB wrote: Wed Nov 23, 2022 7:45 pm
skinny z wrote: Wed Nov 23, 2022 4:36 pm
Stan Weiss wrote: Wed Nov 23, 2022 4:34 pm

Kevin,
I believe that is the one I used see below. Note these graphs are for illustration purposes only as there are factor which can / will change these curve somewhat. One would need information about the car to get closer, but it still comes down to what runs best at the track.

Stan

G_Force_vs_Time_Input.gif
That would be it Stan.
Now, my question is, even without the vehicle info, what is the reasoning behind carrying the 1-2 to 7500 when peak is at 6k?
I've understood carrying another 500-1000 RPM, but 1500 is a long way.
The acceleration is the product of the engine torque times the gear multiplication.
In this case you show 283 ft lbs at 7500 rpm. In first gear your driveshaft sees 283 ft lbs x 2.5=707.5 ft lbs
After the 1-2 shift engine speed drops to 4500 rpm, because 7500 x 1.5/2.5=4500.
At 4500 rpm you make 464 ft lbs at the flywheel, but, in second gear it only gets multiplied by 1.5 to 696 ft lbs.
Does this make sense?
Actually, it makes a lot of sense.
What had escaped me, despite the discussion of gearing, et al, was thinking about it in terms of drive shaft TQ or to extend that further, what's seen at the tires. I've concentrated on engine speed and working on the drop between shifts. (In my case it's a 3.06, 1.63, 1). Generally converter related.

Thanks for that BobbyB. Sometimes a guy needs a smack upside the head to re-register.
Kevin
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Re: How will you go faster?

Post by 289nate »

The proper drag racing clutch properly set up can help keep an engine in a narrow power band going down the track. Especially when you start talking more than a four-speed and clutchless.

There is a reason why in so many forms of class racing manual transmissions have carried a significant weight penalty. So we should talk about Clutches as much as torque converters when it comes to wanting to go quicker.
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Re: How will you go faster?

Post by 289nate »

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Re: How will you go faster?

Post by 289nate »

Clutches for the average man.
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Re: How will you go faster?

Post by weedburner »

From my stick shift drag racing point of view, taking a torque@rpm number from a dyno session and multiplying it by gear ratio and tire diameter to get accel force only makes sense for a CVT. Because that method ignores the inertia effects of different engine acceleration rates on the engine's net torque output, it doesn't work with a conventional multi-speed transmission where the engine does not operate at a constant rpm.

A torque converter does act somewhat like a CVT, which in my mind makes a multi-speed automatic trans somewhat of a hybrid. The converter smooths out engine rpm swings as the car works its way thru the gears, but rpm swings are still there due to the mechanical ratio changes.

Here's a couple links to my clutch tuning pages, they help explain my stick shift approach to quantifying the effects of rotating assy inertia on accel rate...
https://grannys.tripod.com/clutchtuning.html
https://grannys.tripod.com/clutchtuning3.html

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Re: How will you go faster?

Post by Stan Weiss »

The G graph I produced earlier used the gear ratios from a Turbo 350. I now see it looks like Kevin / Skinny Z has a 700R.

Take my calculations with a gain of salt. lol I have been told that they seem high.

What this graph shows is the acceleration rate in each gear for both a 700R (higher lines) and Turbo 350 (lower lines).

Stan
RPS_vs_Time.gif
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skinny z
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Re: How will you go faster?

Post by skinny z »

Stan Weiss wrote: Fri Nov 25, 2022 8:06 am The G graph I produced earlier used the gear ratios from a Turbo 350. I now see it looks like Kevin / Skinny Z has a 700R.

Take my calculations with a gain of salt. lol I have been told that they seem high.

What this graph shows is the acceleration rate in each gear for both a 700R (higher lines) and Turbo 350 (lower lines).

Stan

RPS_vs_Time.gif
It may seem obvious but am I seeing the 700R4 has better acceleration overall? Which makes sense given the gear ratios.
Kevin
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Re: How will you go faster?

Post by Ken_Parkman »

Probably not, depending on the converter. I'm a believer in the more converter less gear theory. A very important point is a good converter that properly torque multiplies, or more correctly does not waste power. With the 3.06 (?) low, 2 or more ratio through the converter, and rear axle you might (should) end up with too much for the tires. As well a high numerically low gear means the engine will accelerate through the converter faster losing the multiplication quickly.

So you will end up with a big spike of torque and tire spin, then dropping off quickly.

With less gear and a better converter the initial spike is less, helping with traction; the converter keeps the engine in it's power band, and you get a better average power or torque to the wheels throughout low. And the phenomena repeats on the gear shift.

Lots of gear is much more important with a stick or street converter, but that forces you to badly over rev the engine to optimize the powerband if you have a wide gear spread. A good converter is so much easier on the engine.

In my old bracket car I went to a 1.82 low glide to get away from the big torque spike. Then the car was "on the converter" for a much longer time, and on the converter again on the high gear shift. Turned it into a deadly consistent bracket car and does a much better job of getting closer to a CVT. Went faster too.

I also completely agree with the statements on clutches (except I'm not keen on centerforce). A friend runs a pretty high end stick car, and I find it amazing how little the amount of time where the clutch is actually locked. Definitely keeps the engine in a high rpm narrow powerband, and you have to factor the combo for the acceleration rates.
skinny z
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Re: How will you go faster?

Post by skinny z »

Definitely. The converter can make all the difference.
Between what we had (off the shelf TCI 10") to what we have (spec'd 9.5" Yank) we cut a couple tenths off of the 60' and an equal amount at the top end. The transmission was the same with the wide gear split but revs never dropped below 5k. It was obvious we were on the converter for much longer.
For this project, another converter is on the wish list but it'll be testing with a pile of new parts before that happens.
Further experimenting with shift points is high on the list.
Kevin
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Re: How will you go faster?

Post by F-BIRD'88 »

"we cut a couple tenths off of the 60' and an equal amount at the top end"

Somebody was trying to tell me this does not happen.
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