How to achieve best acceleration ?

[welwynnick]

With traction control off, will a stage 2 car spin it's wheels from launch?

Yes it's only a torque converter automatic, but then so is the C7.

The stall speed might be low, but surely it's high enough for the turbo to generate some boost?

Even the ZF 6HP gearbox has the advantage of torque multiplication from standstill - I think that gives about 1.6x multiplication.

Nick

[IanH755]

The TC stall speed is around 2300rpm so, if the ground is dry and you have "good" tyres then a stage 2 car won't spin them on the road - I tried a few times

However if you have worn/cheap tyres and/or damp/wet conditions or you are doing it when the car isn't straight (so pulling out onto a road) then you will, but at that point it's "accidental" rather than deliberate.

I'd think that raising the TC stall speed to 4000rpm would help a lot but also break quite a few things like driveshafts

[welwynnick]

Thanks Ian.

I assume that it doesn't do a rolling burnout when it comes on boost in first gear, which would mean a lot of the torque is being used just to accelerate the engine, so the net torque into the gearbox is a lot lower than the dyno measurements.

From what you say, it sounds like bigger turbos will actually make the initial launch slower because the boost comes in later.

The C7 seems to launch well, so maybe an 8 speed box with a lower first gear would help.

Nick

[cammmy]

I have fairly new and decent tyres on mine (Eagle F1's I believe) and it will spin them in 1st, even from a rolling start.

Question is, how long and how often can you hold the car on the converter before you break something? I've done it maybe 3 times and never for more than maybe 1.5 seconds.

[welwynnick]

It sounds like the irresistible force meets the immovable object to me.

Will the stock car allow you to hold full throttle against full brakes, or is that something you need a re-map for?

You only get full TC multiplication at standstill, but I get the impression that wheel hop, or shock loading on kickdown, are the worst case events.

Nick

[cammmy]

I've got no idea, I've heard the standard car will sense what you are doing and tell you off but mine's an MRC stage 2 with gearbox remap.

Yeah, I'm not worried about shock loading as holding it on the brakes takes up any backlash. Same as holding a manual on the handbrake and dragging the clutch slightly. It's more that you are building significant energy that has nowhere to go other than as heat. I also don't know what load on the internals is like when holding the throttle and the brake Vs at full chat when that load has somewhere to go.

[welwynnick]

I also don't know what load on the internals is like when holding the throttle and the brake Vs at full chat when that load has somewhere to go.

When you hold it on the brake and the wheels are stationary, you get the torque converter multiplication, so the torque going into the gearbox internals is a lot more than the output of the engine.

Once you're up and rolling there's virtually no TC multiplication, just the engine output. However, once the engine reaches near half revs, the turbos are spooled and the engine torque output is much higher than at launch / stall.

I don't know which scenario puts the most load on the gearbox internals, they might even be the same.

Some other factors:

When you accelerate in first gear, the engine revs increase very fast, and a significant proportion of the engine is power is needed just to accelerate the engine itself, because of the moment of inertia of the rotating and reciprocating parts. Therefore in first gear the torque output will be lower than in high gears.

When you accelerate in first gear you will suffer more turbo lag because the turbos are continually catching up with the engine, so that will reduce the torque somewhat.

When you accelerate in first gear there is more mechanical multiplication and more torque will be applied to the final gearset of the gearbox, and the drive shafts and differentials.

However, in high gears there's less multiplication (reduction in top gear), so it's just the gearbox input shaft that bears the brunt of the engine output.

Nick