So got the car on a dyno today - down on power diagnosis...

[M@r]{]

Blyton - struggled to keep up on the straights with a factory Elise SC.  Other Exige SC seem to pull on me.  Spa last week, can run out of puff at 120 down the back straight.  Just doesn't feel as quick as my last exige (260bhp)   So took it along to CAD motorsport today, they have a Dyno and lots of experience with Lotus.  Stuck it on the dyno and.......

 

 

 

What the actual f**k.  I really did think it would get around 200bhp.  Apparently this dyno under reads compared to most (fondly nicknamed the heart-breaker)  I'm baffled, don't get it.  It definitely doesn't feel that quick out on track.  Alan stuck it on his scales, just over 900kg wet with half a tank of fuel.  So it's not weight.  Spoiler is set at max rake so could be acting as an air brake?  But that would only effect at high speed right?  Springs are quite soft, tyres show rubbing, perhaps the downforce is so high it's pushing the car on to the tyres?  But wouldn't I see plumbs of tyre smoke?  Part of me is over the moon that the car is obviously in very good health, but part of me is disappointed that I still don't know what the issue is (or is it just me?)    Someone want to give me a ride out in their Exige so I can compare? 

[russelld]

Geo, Tyre pressures and aero will all make a difference at high speed. 

Sorry can't help with the ride out, K series Elise is not really apples for apples.

At least the power is there & lots of it 

[timbo]

The obvious thing from your info, assuming there are no mechanical issues (eg. different gearing) is aero drag. Bear in mind that drag rises as the square of speed, so a doubling of speed will create 4x the drag.

So if - as you say - you have your car set up for maximum downforce, then you will be killing the straight line speed.

You might also want to look at suspension settings, which can affect aero in themselves by altering the 'stance' of the car when it's moving. If, for example, over-soft front springs increase the rake angle then that will increase the incidence of the rear wing, increasing drag further.

Suspension settings will also affect massively how fast you exit a corner onto a straight, which in turn dictates what speed you will reach on that straight.

[jonnyfox]

At over 900kg's only half full it is actually weight as well as aero Mark. In the first respect exactly the same as a slightly modified S2 maybe with lighter wheels and exhaust.

[M@r]{]

46 minutes ago, jonnyfox said:

At over 900kg's only half full it is actually weight as well as aero Mark. In the first respect exactly the same as a slightly modified S2 maybe with lighter wheels and exhaust.

I’m surprised you say that, a standard Exige is booked at over 900kg? (And I’m comparing this with my last Exige) And I imagine that Lotus quotes oem figure is without any fuel.  My car was fully wet when weighed, oil, water and half a tank of fuel.  I’m not sure when Lotus quote the oem cars weight all that is included either? 

[M@r]{]

12 hours ago, timbo said:

The obvious thing from your info, assuming there are no mechanical issues (eg. different gearing) is aero drag. Bear in mind that drag rises as the square of speed, so a doubling of speed will create 4x the drag.

So if - as you say - you have your car set up for maximum downforce, then you will be killing the straight line speed.

You might also want to look at suspension settings, which can affect aero in themselves by altering the 'stance' of the car when it's moving. If, for example, over-soft front springs increase the rake angle then that will increase the incidence of the rear wing, increasing drag further.

Suspension settings will also affect massively how fast you exit a corner onto a straight, which in turn dictates what speed you will reach on that straight.

Thanks for that input, it is looking more and more that drag is the issue.  Will definitely have a play with some settings at Rockingham on the 8th

[jonnyfox]

My NA with touring pack but wheels and a full exhaust changed was 889kg half full. I was pretty obsessive in getting weight down, it took a lot of effort and money getting it to 815 kgs. My clam's were standard size, the rear CF. Yours are GT3 replicas so a bigger surface area. I've sat in a mates garage and watched them being made, I've watched your car being modified twice. I know you can peddle Mark but your car is as heavey as the rest with much more aero. Nothing is significantly light about it. An Elise R or SC is lighter still than a standard S2 Exige and likely slightly modified to reduce it further but thats the nature of the beasties. 

Listen don't get me wrong I'm not trying to push any buttons but you said it yourself its just over 900kgs therefore similar to other S2's. 

[M@r]{]

4 hours ago, jonnyfox said:

My NA with touring pack but wheels and a full exhaust changed was 889kg half full. I was pretty obsessive in getting weight down, it took a lot of effort and money getting it to 815 kgs. My clam's were standard size, the rear CF. Yours are GT3 replicas so a bigger surface area. I've sat in a mates garage and watched them being made, I've watched your car being modified twice. I know you can peddle Mark but your car is as heavey as the rest with much more aero. Nothing is significantly light about it. An Elise R or SC is lighter still than a standard S2 Exige and likely slightly modified to reduce it further but thats the nature of the beasties. 

Listen don't get me wrong I'm not trying to push any buttons but you said it yourself its just over 900kgs therefore similar to other S2's. 

I know Jonny, your input is really appreciated.  I need people to table any ideas as I'm a bit baffled.  What I was getting at is this car is no heavier than my last Exige, that had 40bhp (actually after Hangar 111 dyno'd it seems it was more like 60bhp less) than this car.  Yet this car feels slower.  I've no doubt there are some weight savings to be had, but this particular issue I don't believe is related to weight, something else is slowing it down.  

Once I've got to the bottom of this I'd love to pick your brains sometime and get some ideas about how to get the weight down on this.

[Daveb99]

Since your first Exige, have you bought shares in McDonalds or KFC, or put your local Indian/Chinese takeaways on speed dial ?  

Just putting it out there 

Sorry, not helpful..