I am very curious about sequential gearboxes like the cup cars have, and their use. I have heard they cannot be driven on the street, or are very difficult to drive on the street. Can one of you smart race-car-drivers/mechanics/experts explain the issues of driving a sequential gearbox off the race track. Is it a traffic issue with stop and go?

I have also heard the maintenance is frequent and expensive. Is this another "street" issue?

 

Interested in hearing more on this. Subscribed.

 

In cup cars you do not use the clutch for up shifting. 99.9% of the time you are at full throttle. The ECU is programmed to lower the rpm for a millisecond that allows the shift.
On down shifts you use the clutch and blip the throttle.
Both shifts are pretty violent and has to be done forcefully.
The street conversions I have seen are really not sequential.
I would suggest anyone wanting a full explanation should contact Matt at Guard Transmissions. he is incredibly knowledgeable about these boxes.
If you have not done so, search for videos of cup cars on the track and you will see what I mean.

 

There is 100+ ways to spend $30k on your car than putting in a sequential for the street..

Have you ever heard a cup car in the pits or start from a stop.. not a pretty sound.. sounds like the gearbox is going to blow up!

The cost of a sequential box is really to save 1-2 seconds a lap on the race track..it does not belong on the street

 

I have no intention of putting a sequential gearbox in my car. I just want to know about them, because it is interesting.

Anyone else that wants to elaborate, please...

 

Sequential shifter maybe, sequential crash box on a street car, no way.

-Troy

 

I considered about getting a Quaife sequential gearbox for GT3 RS.
I have used Quaife in the past in my rally days and still remember the rawness of the shift and the sensation it gives.

If one is going to use it solely on track, there is nothing compared to it it terms of feeling and pleasure you get from shifting.
Maybe Scuderia's shifts can be compared in thump (meh) but nothing can match it on physical sensation.

But on street/traffic driving, the mechanical sound is unbearable and the shifts are too raw, you can not drive smoothly unless you stay on the same gear for a long time.
And you have to pull another lever to engage reverse which can be frustrating in city.
Plus, you have to rebuild the box every 50hrs or so in hard use.
Don't know how long it will take in street use but i'm thinking not much longer because of constant start stop, 1st gear.

Considering all of the above and the price (€16k only for quaife sqg +vat+service etc) I gave up on the idea for a road car.

But I think it might be best mod you can do to get the best from a dedicated track car in terms of enjoyment and race car feel.

In terms of improving seconds, well for 1/10 of that price you can be a master driver with hours of tutoring and track miles under your belt and draw circles around a beginner with sequential gearbox.

Thats my $0.5.

cheers..

 

Well said, case closed.

Despite our willingness to try, not everything in racing translates to the street.

 

The problem with driving Porsche's sequential gearbox is not so much the shifting mechanism itself as the fact that it's a dog box. As such it has no synchronizers in it. The slowing and speeding of gears between shifts is normally done by the synchros. With a dog box it's done with a bang as you quickly pull it into gear and the teeth slap against each other and engage.

Can you drive a dog box, any sort of dog box on the street? Sure. If you were to do that, unlike in racing, you would use the clutch on upshift. You would also learn your rpm drops by feel and shift at a point where the differential of speed in the shafts is similar to the engine speed as it drops and mimimize the shockload for maximum durability.

The downshift is a bit more tricky on the sequential. The reason for this is that there's not really any neutral. On an H-pattern dogbox on the street you double clutch and rev match to mimimize the hit. Can't really do that without a neutral phase. The best you can do is clutch in, select the gear and let it hit, rev the engine to minimize the second shock load of the clutch, and let it out.

Now if all of this sounds like a lot of work and brain damage, you're right. And that's your answer. You don't see many people driving a sequential on the street because it requires 100% attention at all times. You can't be complacement. You've got to be on top of it and interacting with the gearbox. The sequential gearbox punishes laziness, and it punishes it with a big rebuild bill.

 

THANK YOU!! THAT was the kind of explanation I was looking for, not "don't do it." ....no offense meant.

 

Thanks, Matt! I appreciate the explanation. I've never really gotten a concise answer about it until this thread, which is the beauty of 6speed.com and the great folks who frequent it.

 

It's not a simple answer. There are multiple things that go into a "sequential gearbox".

1. shift pattern.
This is what actually makes a gearbox sequential.
Obviously it's not ideal for the street to have to go down to 1st to select neutral. This is just a matter of how gears get selected. Some gearboxes can be converted between H-pattern and sequential.

None of the rest of this is specific to being "sequential". All of these features are found on H-pattern race gearboxes, and some of these can be missing from sequential pattern gearboxes depending on the design and usage.

2. gear angle.
Race gearboxes have straight cut gears. Street gearboxes have helical cut gears. Straight gears are stronger and lighter but are NOISY and WEAR.

3. gear engagement.
Race gearboxes use dog ring engagement. Street gearboxes use syncros. Dogs require FAST gear changes and should be well timed with throttle lift to avoid dog wear. Dogs have slop between accel and decel as part of the design; this makes cruising clunky (hard to avoid bucking) and noisy as you butt up against the up and down sides of the dogs alternately. Shifting at low throttle load is more difficult and more likely to cause wear because the timing of the torque release / gear shift is less exact. Dogs require you to come to a complete stop to change direction (forward/reverse).

4. maintenance.
Because the dogs and gears wear, the gearbox needs frequent inspection. It's normal to inspect the gearbox after every race weekend, maybe every other depending on how good you are at shifting and how beefy the gearbox is relative to the engine output and tire grip.

PDK/DCT is a great sequential technology for the street. Traditional sequentials are NOT.

 

Great thread and great forum to host this kind of information. I was just discussing this same topic with my father the other day.

 

GREAT info! Thanks!

 

The sound of straight cut gears and an open exhaust is hard to beat.