Power and Torque Question

[RMC83]

Alright folks,

Given that Power = Torque x rpm, i have an interesting question for you...

I'm trying to work out the impact of a stage 2 vs 3 to the stock gearbox. It seems the general consensis is that a 'safe' stage 2 would be in the region of 750bhp / 1050Nm.

However, if we set the torque to 1050Nm & assuming redline is shifted to 7k rpm, this would give a possible 1030HP (based on the above formula) if other parts of the car can also achieve this ie, bigger turbo's and IC to deal with the heat etc.

So the question is, what is the impact to the GB between these 2nos tuning levels, given that the Torque remains the same. Afterall, torque is just the twisting force applied by the crankshaft, which stays the same on both levels on tune, so in theory the affect on the GB would be the same would it not? Difference being, the higher power figure would allow the car to 'use' the torque more efficiently & hence, the faster car compared to the 750HP tune.

I would be interested to hear some views on this & if anyone has had similar discussions with the likes of MRC or Ricky E etc. If there is a difference, in terms of stress on the GB, with 1000HP compared to 750HP with the same torque figure, i would be interested to find out what exactly causes more stress on the GB.

Cheers
Roy

[cammmy]

Apt timing as this is something that I'm looking at right now as if my turbos have to come out, then I may as well make the most of the labour.

Firstly, I'll state that I'm not an expert and that these are opinions.

I believe you are mostly correct. The gearbox is mostly concerned about torque, rather than power. When tuning my Esprit, there is a torque limit on the box that I had to keep in mind, not a power limit. That being said though, at the end of the day, you are asking the box to do more work, so it will create more heat and undergo more wear.

I believe a lot of drivetrain failures come down to shock loading. I.e. launches and kickdown or the opposite direction, sudden lift off in high gear. Again, with the Esprit, at high speed in 5th, you don't want to snap the throttle shut as the sudden shock can snap the shaft; although this is mostly down the the box being a 4 speed modified later down the line into a 5 speed and the shaft necking down where 5th is.

As for the RS6, I can see a few areas where this may cause issue.

If you are on it for long periods and the cooling can't keep up
If your trans is already marginal and the extra load takes it over the edge
if you stomp the throttle and the car kicks down to an area above peak torque on a stage 2

Would love to hear from anyone who has more experience with this.

[welwynnick]

For reference, this is the power equation:
For torque in lb/ft, power = torque x revs / 5252.
For torque in Nm, power = torque x revs / 7122.
So yes in principle, if you can maintain a flat torque curve at 1050Nm right up to 7000rpm, then you will get 1032 bhp.
Is that feasible? Well, these tunes got very close to doing exactly that:

So you're saying if a gearbox will take 1050Nm at 4000rpm, will it also manage 1050Nm at 7000rpm? Going by the first example above, yes it will. That car used a stock gearbox.

Gearboxes are generally rated by torque, not power, so if you can put the same torque at higher revs, you can in principle get the gearbox to carry more power. However, looking at lots of ZF specs, they often have dual ratings - a high torque for low revving diesels and a slightly lower torque for higher revving petrol engines. Although torque is the most important parameter, that does suggest power is still part of the equation. I don't know why that would be - maybe cooling?

Nick

[IanH755]

The gearbox is mostly concerned about torque, rather than power.

I believe a lot of drivetrain failures come down to shock loading. I.e. launches and kickdown or the opposite direction, sudden lift off in high gear.

As for the RS6, I can see a few areas where this may cause issue.

if you stomp the throttle and the car kicks down to an area above peak torque on a stage 2

I've trimmed down your quote to just the appropriate bits and agree 100% with them. From all the Stage 2 & Stage 3 cars that have had gearbox problems I haven't seen any which failed because of slipping clutch packs etc as the only failures I've seen have been from mechanical failures like sheared shafts.

I don't think the HP figure is anywhere near as important to the RS6 gearbox as the torque figure is at the power levels we're running (I mean a 1500hp+ engine maybe different!). I think that holding somewhere around the 1000nm figure is the "sweet spot" for torque vs reliability as it seems to be extremely rare for a stage 2 car to pop a gearbox despite all the kickdown changes they can go through.

Alternatively once you start raising above 1100nm that risk means you can either modify your driving slightly (not using the full kickdown down button) or just accepting the increased risk. I think driving style plays a far bigger role in keeping a healthy gearbox TBH, as a 1250+nm engine can be driven in a way which is still blisteringly fast but with enough mechanical sympathy that the gearbox will out live a lead-footed 1050nm driven gearbox.

[RMC83]

Thanks for the responses, we all seem to be generally aliigned that in principle, with the same driving style, a stock gb with a 1000hp / 1000nm tune should not really be at more risk than a 750hp / 1000nm tune.

I guess the biggest difference is that with 1000hp under your right foot, the chances of you "abusing it" are higher compared to having 750hp (either on purpose or by accident!)...so maybe this is the crux of the topic.

Interesting discussion.

Cheers
Roy

[RMC83]

I've seen that JD Engineering graph before. This is the tune level that i'm looking towards, as long as i can convince myself it will be reliable enough...which i'm still not 100% sure of, hence the reason for this discussion.

Does anyone know more about the car? Ie, is it still running fine with this tune on a stick gb?

Cheers
Riy

[cammmy]

I think the 1000nm - 1,100nm 'limit' offers a good stopping point. It seems that while it's not cheap to get there, going another 200-300 higher is VASTLY more expensive and helps resist the temptation, which I definitely need (this wasn't supposed to be a project and I'm already looking at turbo options...)

[RMC83]

I think the 1000nm - 1,100nm 'limit' offers a good stopping point. It seems that while it's not cheap to get there, going another 200-300 higher is VASTLY more expensive and helps resist the temptation, which I definitely need (this wasn't supposed to be a project and I'm already looking at turbo options...)

I am in the same boat, i had an option to buy a stage 2, but i got a great deal on a stock rs6 plus saloon with only 30k on the clock . I could get the TTE1000+ turbo's, Wagner IC, downpipes & my total spend would still be less than what the stage 2 would have cost me, but potentially getting 1000hp / 1000nm out of it.

[cammmy]

Indeed, I thought mine was stock but it's already a stage two. There's a chance it needs turbo seals though and i'm loath to put stock parts back if the engine has to be dropped to get them out.