How fast can an E89 go? Part Deux!

[B21]

Inspired by the discussion of the orginal post, I've been ruminating away to try and bottom out the question in the absence of a (at least) 3 mile flat straight road.

There is a web site that gives a pretty good crack at it for non modified cars.

https://www.automobile-catalog.com/car/2015/1861385/bmw_z4_sdrive35is.html

Also from a purely theoretical viewpoint I was intrigued to see how re-mapping and/or re-turbo-ing a car would affect its performance.

Sadly I've not been able to find (maybe I'm not so hot on Google after all) a program /website that allows you to answer this question.

The problem is complicated by several factors..

Most modern turbo cars run out of puff before they hit the redline

Several cars have overdrive higher gears.

So I took data from published sources for the drag factors, used a wheel horse power to drag calculator to determine the bhp required for a certain speed and plotted it all out..enjoy!

Here's a dropbox link for anyone wishing to look at the workings.. and a better copy of the image

https://www.dropbox.com/s/x1dq3f3au8ggdv2/35is%20top%20speed%20predictor.jpg?dl=0

https://www.dropbox.com/s/u8uwwos0xqisgtd/35is%20speed%20calculator.xlsx?dl=0

 

[Smartbear]

How does that extrapolate to a 28i with 240 odd bhp reaching 155mph? :?

Rob

 

[B21]

Approx (weight is less so has a small improving effect)

240 bhp buys you about 157-160 mph...as you can see from the graph you are entering the zone where it's taking a lot more BHP to get anywhere..at the change from 59-61 mph takes 2 bhp, from 154 to 157 takes 7 bhp

That's assuming the gearing and BHP shape work for you..

 

[Pondrew]

There are other factors to consider, though, young Peter.
For instance; I know the maximum speed of my Z4 on anything other than a billiard table, is 72mph, as the 326s will shatter if they come into contact with any unfortunate insect crossing my path at a higher velocity.
I checked and this information can be verified by most MOT testers

 

[B21]

There are other factors to consider, though, young Peter.
For instance; I know the maximum speed of my Z4 on anything other than a billiard table, is 72mph, as the 326s will shatter if they come into contact with any unfortunate insect crossing my path at a higher velocity.
I checked and this information can be verified by most MOT testers

Quite so, sounds like a 'fact'..more interesting is that say at 155 mph the wind shifts for 10 mph tail to 10 mph head wind (nobody ever checks the wind strength and direction on these high speed runs) then you needed 163 rear wheel horsepower and now you need 228 of those ponies..

All these numbers are superalitives..wing mirrors in, tape over the door seals etc...

 

[Pondrew]

All these numbers are superalitives..wing mirrors in, tape over the door seals etc...

Roof up or down? :lol: :lol:

 

[Scubaregs]

Wasaaay too much time on your hands.

 

[B21]

All these numbers are superalitives..wing mirrors in, tape over the door seals etc...

Roof up or down? :lol: :lol:

Sadly to keep life 'simple' roof up..I'm working on the rood down version..would imagine 176 mph roof down would be a bit blowy...

 

[Pondrew]

I'm working on the rood down version..would imagine 176 mph roof down would be a bit blowy...

I thought that was why we have wind deflectors :lol:

Sorry Peter for trivialising your very scientific research.....carry on

 

[ronk]

I do know that the wind noise (top down) at 130/140mph is bad.
Couple that with the yelling from the speed limiter in the passenger seat!

 

[tiglon]

Forgive me if I've misinterpreted the graph, but is that estimating top speed, for your output, of 185-190mph?

 

[flybobbie]

Basic physics if it takes 100hp to hit 100mph, it will take 400hp to hit 200mph.
So 350hp won't hit 200mph.
My 23i i believe limited to 155mph, be surprised it would go that fast, perhaps heading south with a tailwind it might.

 

[B21]

Forgive me if I've misinterpreted the graph, but is that estimating top speed, for your output, of 185-190mph?

In this model 183-185 mph is the prediction based on the declining power curve past peak versus increasing drag curve

 

[B21]

Basic physics if it takes 100hp to hit 100mph, it will take 400hp to hit 200mph.
So 350hp won't hit 200mph.
My 23i i believe limited to 155mph, be surprised it would go that fast, perhaps heading south with a tailwind it might.

This model shows circa 58 BHP for 100 and 420 BHP for 200 mph (at the wheels)…unlike an aircraft you have a rolling resistance component as well..

Your 23i BMW says 151mph ..this model says about 151 mph…

 

[flybobbie]

I think you need more HP for 100mph. My diesel Peugeot was 80hp, flat out do 90mph. Was ovetaken by 2CV!
Piper Tomahawk aircraft, flat out 112hp will do 115mph.

 

[Smartbear]

I think you need more HP for 100mph. My diesel Peugeot was 80hp, flat out do 90mph. Was ovetaken by 2CV!
Piper Tomahawk aircraft, flat out 112hp will do 115mph.

Was the Peugeot particularly un-aerodynamic compared to an E89?
Rob

 

[Pondrew]

Was the Peugeot particularly terrible compared to the majority of cars?

There fixed that for you Roberto. No thanks required

 

[B21]

I think you need more HP for 100mph. My diesel Peugeot was 80hp, flat out do 90mph. Was ovetaken by 2CV!
Piper Tomahawk aircraft, flat out 112hp will do 115mph.

I suspect that:

Frog ponies are piss poor

The marriage of BHP curve vs gearing probably would mean it would only do 100mph in free fall..

The total aerodynamic drag of the pug is vastly worse than an E89

Best not to upset you on my views on PA38s.

PS just seen SmartBear with his finger on the aerodynamics

 

[flybobbie]

106 is about half the weight per horsepower than Z4. Below 100 don't think drag would have much effect.

PA38 great aircraft, but don't spin them, learnt my lesson.

 

[flybobbie]

Thrust ssc had 102,000 brake horsepower to achieve 760mph.
Pretty much a square rule.