2.5i sport - optimal/max/healthy rpm?

S

schpikster

Member
 Banstead, Surrey
Hi all,

Been lurking on the forum for some time whilst planning my purchase and finally due to be picking up my 2007 2.5i sport tomorrow, exciting! I've got a fairly nice drive home to look forward to and want to make the most of it. However, I dont want to destroy the engine on day one so I'm wary of overrevving the engine.

I test drove a wide range of zeds before I settled on this (inc 2.0i, 3.0i, 3.0si and 3.2m) and have varying advice from the dealers and owners, so nothing consistent, plus I recognise that different engines will have different limits.

So to all you 2.5i owners out there, how much can I rev the engine without killing it? and what would be a recommended healthy limit, as i dont want to even be close, though obviously i want to enjoy it. I love the engine noise especially at high revs and want to know how to optimise the acceleration, even though im sure 90% of the time I'll be crusing at 70 in 6th at 2000rpm or atuck in neutral in m25 traffic.
 
I had a 2.5i sport and it was a great car, however been an auto I didn't notice the the revs.

I've got an m now and I'm not sure when I change now, it's just instinct I guess. Make sure you warm her up and I'm sure you will find your way through the gears I'm no time.

Can I ask why you chose that 2.5i over all the others you have taken out?
 
If you're cruising 90% of the time then maxing it out every so often is not going to hurt it - it'll probably love you a little more for it. I have an auto and if I stick it in Sport then floor it, the car will red line every gear. As Popey says, it's your style that determines the change points, but I defy you to let her run to 6k+ revs and not fall instantly for the noise :evil:

One point worth making - I try not to bang it around when cold, so I keep it below about 3-3.5k revs until the temp gauge is in it's normal position.
 
Not sure about a healthy limit but I would say:

- For efficiency, stay in the highest gear you can without the engine getting bogged down or knocking, and drive as smoothly as possible. All of the Z4 6 cyls should be able to hold a steady 40mph in 6th without trouble (and you should get silly mpg at that speed in that gear)
- For max acceleration, go all the way to the red line and change as fast as you can (theoretically, it's probably possible to optimise use of the torque curve by shifting a little earlier but there's a trade-off because you need to maintain drive as well, i.e. shift as little and as fast as you can)
- Don't go above 3k RPM until the engine has warmed up fully - can use the temp gauge for this but I've heard it's a bit unreliable. The handbook gives some guidance re. the approximate mileage you should aim for before ragging it, IIRC (although it doesn't use the phrase "ragging it", of course)

Doubt you will be harming the engine much by taking it close to the red line quite often. Given the amount of care that goes into the cars on here, for example, I would happily pick something up second hand that had been round a track quite often, assuming it had been looked after by its owner. It's a bit of a shame not to - think of it as a waste of money if you don't. :D Especially in the 2.5 which (assuming it's similar to the 2.5si), surges forward quite gloriously between 5k and 6k RPM.
 
I've been told a good old "Italian tune up" is good for it every so often - especially with the N52 - getting oil into the tappets!

I think from the top of my head the torque/ bhp crossed on my dyno at around 5.3K rpm - so on my 3.0 that would be the best shift point - i'd imagine your's would be similar.
 
Surely you want to change a little above the crossover point, so that when the car picks up the next gear you're not far off the next crossover point, i.e. using the max torque ? I dunno though, not a scientist :D
 
The torque curve on a 2.5 N52 is pretty flat, so for max acceleration rev the nuts off it :D For efficiency it's a pretty flexible old lump and will pull from down the rev range. Max torque arrives at 2750

 
wow, really comprehensive responses, thanks all. I love this forum!

will take all on board and let you know how i get on this evening!
 
ps forgot to mention, I went for the 2.5 as couldn't find a 3.0 with the right spec (age, condition, mileage, etc) for the right price. I did find a couple but they sold before I could get to them! I should probably have waited but wanted to grab one before the summer has completely gone.

I would have loved an M but just couldn't afford it. the 2.5 will be enough for me I think, though I loved the 3.0si. the 2.0 didnt have the right sound and quite enough oomph. to be fair though anything is an upgrade from my current 1.2 fiesta!
 
Based on that graph I see no reason to ever change before 6.5k again. Except for perhaps speed limits :evil:
 
aquazi said:
I think from the top of my head the torque/ bhp crossed on my dyno at around 5.3K rpm
Click to expand...
Warning, nerdy maths and physics ahead!
All imperial hp/torque curves cross at 5252, it is a function of how horse power is calculated (HP=Torque x rpm/5252). It has nothing to do with the optimal shift point. In E85/6s this is pretty much redline in every gear. The optimal point is determined by the decrease in torque due to changing up (gear ratios) and how fast the top end torque curve falls off. Relatively flat torque and typical street gearing usually means shift at redline.
 
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