Alright Veeky Forums, explain drag racing transmissions to me. Am I correct in thinking that they work like this: >Go to start line >Apply brake & throttle untill you hit the point where your car starts to stall (convertor stall point, let's say 3000RPM) >Release brake >Engine stays at 3000 RPM but increases wheel speed >When wheel speed catches up, RPM increases untill shift point >Automatic valvebody then shift the planetary gearset into high >Repeat Unless of course it's a manual valvebody, in which case you need to make the planetary gears shift up.
Now, why would you use a torque convertor automatic for this? They have huge internal losses, you might as well use a dogbox sequential manual instead.
Auto shifts faster, trans brake starts with an auto are much more repeatable/consistent.
Ayden Rivera
Drag racing trannies are generally dry clutches which are pneumatically actuated, driving a planetary set like a normal automatic. The takeup of the clutch can be adjusted to suit conditions to prevent tyre shake, excessive traction loss etc.
Evan Bennett
>Auto shifts faster, A dogbox sequential is instant-shift. Once the shifter fork comes off one gear, it is rammed onto the next. Especially if you use a pneumatic shifter, it should be quicker than on a planetary gearset.
> trans brake starts with an auto are much more repeatable/consistent. Those work something like this, right: >Hold transmission in forward and reverse untill desired launch RPM >Release reverse >Car launches, RPM drops to between launch RPM and convertor stall RPM >Wheel speed catches up, RPM increases >Shift Now, why can't you do the same by dropping a clutch? Something like a Lenco/Jerico can still be consistent.
Jordan Johnson
Then how does this work in Top Fuel? I don't think a generic dry clutch will take 7000hp during a start.
Leo Cook
Planetaries can be just as fast, they're only slow in normal boxes to make the shift smooth.
Hudson Lee
Why not? The clutch gets used once in all likeliness and the ability to hold the flywheel comes down to clamp pressure, when the clutch is actuated pneumatically you can run massive clamp force.
John Richardson
So Lenco's work something like this? >Go to start line >Hold handbrake, throttle and clutch >Light goes green >Drop handbrake and clutch >No slip, unlike TC automatic >Clutchless shift into 2nd/3rd/4th (if you need to) >Clutchless shifting just rams a single planetary gearset into high gear >More gearsets = more gears
Alexander Harris
Clutch is handled automatically afaik, set by the team before the driver even gets in the car, so if they get it wrong you get things like funnies turning over or slow times.
Nicholas Kelly
So if preset clutches are more consistent and reliable, why do people still bother using TH400's/Powerglides with a torque convertor and maybe a transbrake?
Nathan Cooper
They don't in the fast stuff, the quickest fluid flywheel rail I've seen ran 6's and that was a 2J from memory.
Thomas Nelson
Also they do have slip, generally they aren't locked up till past half track with the fuel cars.
Henry Howard
Didn't larry Larson run a 5.95 in that S10 of his? That definitely uses a (modified) TH400, with torque convertor.
Bentley Green
Not sure desu user, I'm from Ausfagland.
Ian Wright
High stall Tc automatics won't slip if they're holding revs, they actually get a torque boost for at least 60ft.
Juan Brooks
>Wheel speed is zero >RPM goes up That is the very definition of slip.
How do they get that torque boost? There's still X amount of hp being produced by the engine, and you're not getting any more. Is this where a TC automatic with a loose convertor sort of behaves like a CVT, keeping it in the powerband using slippage in the convertor?
Pic related, my understanding of conventional automatic transmissions.
Jose Kelly
Aye, it's also the reason they produce tons of heat, high stall converters are fun but they can be a real hassle on the street unless you have your cooling nailed down.
Yeah it's interesting how much cooling can be ignored when you're talking a ~4s burnout and a ~6s run.
Brandon Stewart
Yea they slip while stand but They won't slip off the line, all the power you need is there immediately+ a few more extra foot lbs, whereas on a clutch it slips until lock up.
So basically you have more torque available at start.
Jaxson Nguyen
They do slip user, a torque converter is a fluid labyrinth clutch, just like a hydraulic clutch fan in basic principal.
Christopher Myers
>They won't slip off the line But they do. RPM on those torque convertor drag cars stays almost constant untill wheel speed finally catches up. The really good ones are instantly at peak power, and stay there throughout the entire run.
en.m.wikipedia.org/wiki/Torque_converter >The key characteristic of a torque converter is its ability to multiply torque when the output rotational speed is so low that it allows the fluid coming off the curved vanes of the turbine to be deflected off the stator while it is locked against its one-way clutch, thus providing the equivalent of a reduction gear.
Adrian Martin
So it multiplies torque at the cost of RPM. It does not change the power that is going in, if anything, it is inefficient and therefore loses power. It's just a ''fluid gearing'' that acts as a CVT during acceleration untill it locks up.
So, how does it create more power? It doesn't. It changes the ratio between torque and RPM, that is all.
Oliver Sullivan
Transbrake has nothing to do with the footbrake, it engages reverse and first and the same time so the transmission is locked internally.
Brandon Jenkins
Notice I said torque not power, that's why it's a torque boost off the line, not a power boost.
Parker Richardson
Torque is meaningless, you need power to accelerate.
Isaac Parker
>Now, why can't you do the same by dropping a clutch? >1000+ ft/lbs clutch launch >no torque boost >2-speed manual
Good luck with that
Luis White
Top fuelers do use a clutch, or were you referring to a pedal operated clutch?
Easton Miller
I was, because you're talking about transmissions. Top Fuel doesn't.
Charles Bennett
Yeah, they do. I'm not other user, was just pointing out that 6-7000hp cars use a dry clutch, just not a manually operated one.
Brody Jackson
Sorry, I meant to type "Top Fuel doesn't use a transmission."
Lincoln Gray
try again.
Dominic Wright
Ohh got ya.
Asher Mitchell
Power is not torque and torque is not power. A torque converter is almost analogous to a CVT in that it provides a variable gear ratio effect. The power loss of a torque converter is generally overestimated as most of the time it is above 90%, particularly if you are using a CVT transmission that can keep RPMs up.
Camden Gutierrez
It's a real shame that GM gave up on the Turboglide.
Ian Gomez
>the point where your car starts to stall Torque converter stall speed is the speed at which the impeller can go no faster while the turbine is held stationary
Robert Jackson
yeah but a computer has faster reaction times than a human.
Liam Hughes
Torque convertor automatics like the TH400 or powerglide don't use computers, and it's not about reaction time when every run is basically the same.
Jayden Hall
Drag racing transmissions aside lenco and other exotic transmissions are usually variants of the TH400 or powerglide, and use a device called a transbrake to lock the transmission in your drive gear and reverse at the same time
you do your burnout to heat up tire and prep the launch surface, pre stage by rolling up to the light, hold down your transbrake button and floor it - this forces your engine to rev up to whatever your torque converter's stall RPM is, which is dependent on the platform you selected (always different based on if youre running whatever power adder and displacement you have)
once youre prestaged, some cars have a tool called a bump box, which allows you to keep the transbrake on and "bump" the car forward into your full stage
once both cars are fully staged, the tree will light and off you go
Andrew Reed
Uhm: > P = M x n
Lincoln Reed
a converter has less than fuck-all to do with gear ratios
its job is to either slip or not slip
Landon Thomas
When a torque converter slips, engine power is converted to lower RPM and higher torque, just like a gear, dingus.
Nathaniel Williams
Torque is power times RPM. Without a torque converter, the torque on the output side of a clutch pack is still going to be less than or equal to the current torque that the engine is making.
With a torque converter, the output torque can be higher than engine input torque, up until the input and output speeds roughly match. It's like having a CVT stuck to the engine with a limited gear range, something like 2.5:1 to 1:1.
The torque doesn't appear out of thin air, it's just the torque converter doing a better job of converting "slip" into power, unlike a clutch where it's all wasted in the form of heat.
Justin Bailey
It's all managed by a Engine Management System. There are many ways to do it.
>go to the line >press the clutch >two-step kicks in and turbo starts filling >hold a two-step button on the streering wheel/shifter so you can let the clutch pedal go a little so you can move to pre-stage >let the button go and keep pressing the clutch, which is the main "button" of the two-step >green light, release the clutch >fly away
In my car i don't have the button that holds the two-step.
Angel Brooks
>6-7000hp Try 11,000. The clutches weld together within 700ft typically, they're absolute monsters
Sebastian Thompson
Fuelers use dry clutches with multiple engagement points, they can last up to three passes although some actually weld together during a run. They work more like CVTs in a snowmobile than autos since there's no actual transmission.
