Don Terrill’s Speed-Talk

It might be very interesting to examine what makes a drag car perform quicker and by how much.

Obviously, the engine size and state of tune is a starting point.
But several other factors will influence strip times.
Torque curve
Ambient air temperature
Ambient barometer
Humidity
Fuel energy
Air/Fuel ratio
Tire diameter
Tire traction
Rear end ratio
Gear set ratios
Torque converter
Weight
Frontal area
Drag Coefficient

How much does each factor contribute to ET?
Suppose we were to change each parameter by +-5%.

Which will produce the best bang for the buck?

Do you have a car in the works David?

I’ll start

Traction (tires and suspension)
Power to weight (torque curve is part of this)
Gearing (includes tire diameter)
Converter

I would ask Vortecpro, he seems to be able to squeeze a lot of extra ET out of his combos.

For what it is worth I have been drag racing since 1974. I have always done everything to my car. and tuned several other's cars. On your list select a gear so the car crosses the finish line at max HP and select a converter that flashes right before max torque output. Select the tallest tire that will fit under the car, for every revolution of the tire the car goes further with a taller tire. So select a gear after you have picked a tire. Depending on the weight of the car you can fine tune the trans with different gear ratio's heavy car with a small engine usually will like a lower 1st gear, light car with big engine usually likes a higher low gear. On the converter, that is still a black art, just ask several converter companies to spec a converter, you will get as many answers as companies in my experience, and nothing on your list will kill or make a car more than a converter. I know lots of guys you try 3 or 4 before finding one that really works. One trend I see is that they no longer really use OEM units to modify, they buy and assemble components. The torque multiplication of the stator is really a big deal on how it launches. And two converter guys told me the trend is to use high torque multiplication stators now.
As long as the air fuel ration is between 12.5 to 13 I don't see much difference, and between mine shaft air conditions and a 100-degree humid day is about 3 tenths on my car. I track it with an old moon air density gauge, guess I should buy a modern weather station.
On the weight, when I raced slower heavier cars, the 100 lbs equals 1/10 of a second held pretty true. As my car got into the 9's and less than 3,000 lbs not so much. I race NSS on index's and one time I was too fast for the index, so I added 100 lbs, it went faster. 60 foots were similar, so it had to be down track.
Traction is not just the starting line, you can launch hard and still spin tires down track, found that out this summer. Again got a different converter had to change a bunch of suspension settings, but it was faster after that.
Do a burn out until tires are 10 degrees hotter than the track, that is as good as the tire will hook. Use an infer-red temp gun.
All the mopars I raced were bricks, can't speak to aerodynamics much.

Once all the variables are worked out, it's all about low drag.

Low drag trans, third members, ceramic bearings, LW grease. All the stuff that cost high dollar.

I was floored at the low drag of my new metric TH200.m

David Redszus wrote: ↑Tue Nov 15, 2022 12:33 pm It might be very interesting to examine what makes a drag car perform quicker and by how much.

Obviously, the engine size and state of tune is a starting point.
But several other factors will influence strip times.
Torque curve
Ambient air temperature
Ambient barometer
Humidity
Fuel energy
Air/Fuel ratio
Tire diameter
Tire traction
Rear end ratio
Gear set ratios
Torque converter
Weight
Frontal area
Drag Coefficient

How much does each factor contribute to ET?
Suppose we were to change each parameter by +-5%.

Which will produce the best bang for the buck?

%5...Relating to my experiences.
Some of that may be difficult to quantify. How do you figure 5% better traction? Improved 60' by the same percentage?
Converter stall. 4000 RPM with a 5% increase in stall speed? An additional 200 RPM. If the stall was too low, a couple hundred should yield something but I'd bet not a lot.
I can see weight being easy though. Take my 3600 lb porker. Pull a couple of hundred pounds out of it (180 to be precise) and if the old racer's saying is true, that's a couple of tenth's quicker and a couple of MPH faster.
Frontal area and drag coefficient would have the greatest impact for the faster cars. But even at my performance level, my small and low to the crowd 3rd gen Camaro has it over the fleet's 67 Chevelle. And especially over the 69 C10. But how much from time slips and estimated HP/TQ is difficult to cypher. I'd prefer the flying mile for that metric.
Combining the ambient air temperature, ambient barometer and humidity (isn't that DA without the altitude?) I know has a significant impact but I've only worked in the DA sense. The change from sea level to 3500' is monstrous. But that's a significant jump over 5%.

skinny z wrote: ↑Tue Nov 15, 2022 7:47 pm

David Redszus wrote: ↑Tue Nov 15, 2022 12:33 pm It might be very interesting to examine what makes a drag car perform quicker and by how much.

Obviously, the engine size and state of tune is a starting point.
But several other factors will influence strip times.
Torque curve
Ambient air temperature
Ambient barometer
Humidity
Fuel energy
Air/Fuel ratio
Tire diameter
Tire traction
Rear end ratio
Gear set ratios
Torque converter
Weight
Frontal area
Drag Coefficient

How much does each factor contribute to ET?
Suppose we were to change each parameter by +-5%.

Which will produce the best bang for the buck?

%5...Relating to my experiences.
Some of that may be difficult to quantify. How do you figure 5% better traction? Improved 60' by the same percentage?
Converter stall. 4000 RPM with a 5% increase in stall speed? An additional 200 RPM. If the stall was too low, a couple hundred should yield something but I'd bet not a lot.
I can see weight being easy though. Take my 3600 lb porker. Pull a couple of hundred pounds out of it (180 to be precise) and if the old racer's saying is true, that's a couple of tenth's quicker and a couple of MPH faster.
Frontal area and drag coefficient would have the greatest impact for the faster cars. But even at my performance level, my small and low to the crowd 3rd gen Camaro has it over the fleet's 67 Chevelle. And especially over the 69 C10. But how much from time slips and estimated HP/TQ is difficult to cypher. I'd prefer the flying mile for that metric.
Combining the ambient air temperature, ambient barometer and humidity (isn't that DA without the altitude?) I know has a significant impact but I've only worked in the DA sense. The change from sea level to 3500' is monstrous. But that's a significant jump over 5%.

I am still out to lunch on the weight deal. One year I had to have stents put in my arteries and after that I lost 60lbs. and thought I am going to pick up a 1/2 tenth next time out. Sure as heck, I picked up nothing, natta, none. Made me want to eat more junk food after that, but the $71K bill we got changed my mind so I keep the weight off and will find other ways to lighten up my car.

1980RS wrote: ↑Tue Nov 15, 2022 10:14 pm

skinny z wrote: ↑Tue Nov 15, 2022 7:47 pm

David Redszus wrote: ↑Tue Nov 15, 2022 12:33 pm It might be very interesting to examine what makes a drag car perform quicker and by how much.

Obviously, the engine size and state of tune is a starting point.
But several other factors will influence strip times.
Torque curve
Ambient air temperature
Ambient barometer
Humidity
Fuel energy
Air/Fuel ratio
Tire diameter
Tire traction
Rear end ratio
Gear set ratios
Torque converter
Weight
Frontal area
Drag Coefficient

How much does each factor contribute to ET?
Suppose we were to change each parameter by +-5%.

Which will produce the best bang for the buck?

%5...Relating to my experiences.
Some of that may be difficult to quantify. How do you figure 5% better traction? Improved 60' by the same percentage?
Converter stall. 4000 RPM with a 5% increase in stall speed? An additional 200 RPM. If the stall was too low, a couple hundred should yield something but I'd bet not a lot.
I can see weight being easy though. Take my 3600 lb porker. Pull a couple of hundred pounds out of it (180 to be precise) and if the old racer's saying is true, that's a couple of tenth's quicker and a couple of MPH faster.
Frontal area and drag coefficient would have the greatest impact for the faster cars. But even at my performance level, my small and low to the crowd 3rd gen Camaro has it over the fleet's 67 Chevelle. And especially over the 69 C10. But how much from time slips and estimated HP/TQ is difficult to cypher. I'd prefer the flying mile for that metric.
Combining the ambient air temperature, ambient barometer and humidity (isn't that DA without the altitude?) I know has a significant impact but I've only worked in the DA sense. The change from sea level to 3500' is monstrous. But that's a significant jump over 5%.

I am still out to lunch on the weight deal. One year I had to have stents put in my arteries and after that I lost 60lbs. and thought I am going to pick up a 1/2 tenth next time out. Sure as heck, I picked up nothing, natta, none. Made me want to eat more junk food after that, but the $71K bill we got changed my mind so I keep the weight off and will find other ways to lighten up my car.

60 lbs! Good job. Let's say that'll add a few years of racing to your life.
As for lighter is faster...60 lbs for you is great. For the car, it's one of those things that would be hard to judge from an ET point of view. We've all picked up or lost a tenth form one day to the next with no other changes other than the air and track prep.

Best place to gain 5% will normally be weight reduction depends on the type of car though

I vote converter first,
I have track tested alot between 9" 4200 converter
8" 5600 converter
The 8" wins every time and it is all in the 60ft.
I have used it in several combinations even only turning engine to 6000rpm.
Stall speed and the flare off the launch changes as well depending on how much power your engine makes.
My current 383 makes peak torque at 5300rpm and peak power at 6600rpm.
At the hit the converter will flare to 6000rpm off the footbrake and won't drop below 6000rpm on the gearshift.
I vote for stall speed above peak torque.
Rear gear and tyre size would be my next choice.
Got to rev past peak in my opinion.
If you can't 60ft you probably won't make it up at the big end.

steve cowan wrote: ↑Wed Nov 16, 2022 2:14 am I vote converter first,
I have track tested alot between 9" 4200 converter
8" 5600 converter
The 8" wins every time and it is all in the 60ft.
I have used it in several combinations even only turning engine to 6000rpm.
Stall speed and the flare off the launch changes as well depending on how much power your engine makes.
My current 383 makes peak torque at 5300rpm and peak power at 6600rpm.
At the hit the converter will flare to 6000rpm off the footbrake and won't drop below 6000rpm on the gearshift.
I vote for stall speed above peak torque.
Rear gear and tyre size would be my next choice.
Got to rev past peak in my opinion.
If you can't 60ft you probably won't make it up at the big end.

Good point Steve. There are aspects of the car we can improve for et but what part of the track is that improvement targeted at? A focus on 60’ pays dividends at the stripe.

steve cowan wrote: ↑Wed Nov 16, 2022 2:14 am I vote converter first,
I have track tested alot between 9" 4200 converter
8" 5600 converter
The 8" wins every time and it is all in the 60ft.
I have used it in several combinations even only turning engine to 6000rpm.
Stall speed and the flare off the launch changes as well depending on how much power your engine makes.
My current 383 makes peak torque at 5300rpm and peak power at 6600rpm.
At the hit the converter will flare to 6000rpm off the footbrake and won't drop below 6000rpm on the gearshift.
I vote for stall speed above peak torque.
Rear gear and tyre size would be my next choice.
Got to rev past peak in my opinion.
If you can't 60ft you probably won't make it up at the big end.

Ideally the converter shouldn't be inflating rpm after launch, if the converter is letting the motor rpm more than the gearing etc would that means the converter is not "locked up" & is wasting power in heat production - it's inefficient when it's working like that.
So Ideally your rpm after the shift should not drop below flash stall speed.
Depending on how the motor hold power past peak shifting 2-300rpm past peak hp should show the track the most average hp.
Motor should be turning 3-500rpm past peak through the traps unless it falls on its face past peak.

steve cowan wrote: ↑Wed Nov 16, 2022 2:14 am I vote converter first,
I have track tested alot between 9" 4200 converter
8" 5600 converter
The 8" wins every time and it is all in the 60ft.
I have used it in several combinations even only turning engine to 6000rpm.
Stall speed and the flare off the launch changes as well depending on how much power your engine makes.
My current 383 makes peak torque at 5300rpm and peak power at 6600rpm.
At the hit the converter will flare to 6000rpm off the footbrake and won't drop below 6000rpm on the gearshift.
I vote for stall speed above peak torque.
Rear gear and tyre size would be my next choice.
Got to rev past peak in my opinion.
If you can't 60ft you probably won't make it up at the big end.

Steve.
How would you quantify the % change in converter stall?
While I agree, a converter is a game changer, I was trying to keep it in the context of 5%+/-.
4200 to 5600 is a big jump and no doubt there'll be an improvement.
Taking my previous converter which arguably flash stalls to 4000.
The next unit, already in play last couple of years before the engine blew up, stalls to 4500.
I expect something (still not track tested) a but probably not a lot. Unlike you, these converters don't have the best shift recovery as others I've been witness to. RPM drop between shifts is excessive and obviously hurting the ET.

KnightEngines wrote: ↑Wed Nov 16, 2022 3:40 am

steve cowan wrote: ↑Wed Nov 16, 2022 2:14 am I vote converter first,
I have track tested alot between 9" 4200 converter
8" 5600 converter
The 8" wins every time and it is all in the 60ft.
I have used it in several combinations even only turning engine to 6000rpm.
Stall speed and the flare off the launch changes as well depending on how much power your engine makes.
My current 383 makes peak torque at 5300rpm and peak power at 6600rpm.
At the hit the converter will flare to 6000rpm off the footbrake and won't drop below 6000rpm on the gearshift.
I vote for stall speed above peak torque.
Rear gear and tyre size would be my next choice.
Got to rev past peak in my opinion.
If you can't 60ft you probably won't make it up at the big end.

Ideally the converter shouldn't be inflating rpm after launch, if the converter is letting the motor rpm more than the gearing etc would that means the converter is not "locked up" & is wasting power in heat production - it's inefficient when it's working like that.
So Ideally your rpm after the shift should not drop below flash stall speed.
Depending on how the motor hold power past peak shifting 2-300rpm past peak hp should show the track the most average hp.
Motor should be turning 3-500rpm past peak through the traps unless it falls on its face past peak.

Yep the reason I replaced my last converter was after a rebuild of the engine and a few improvements it made enough more torque that the shift light never went off during the run. Also it started pushing fluid out the vent.

David Redszus wrote: ↑Tue Nov 15, 2022 12:33 pm It might be very interesting to examine what makes a drag car perform quicker and by how much.

Obviously, the engine size and state of tune is a starting point.
But several other factors will influence strip times.
Torque curve
Ambient air temperature
Ambient barometer
Humidity
Fuel energy
Air/Fuel ratio
Tire diameter
Tire traction
Rear end ratio
Gear set ratios
Torque converter
Weight
Frontal area
Drag Coefficient

How much does each factor contribute to ET?
Suppose we were to change each parameter by +-5%.

Which will produce the best bang for the buck?

David,
I would also include: aero, particularly aft-aero (especially if racing 1/4 mile) and MOI of all rotating parts because - if it moves it matters. Internal friction too.