ACB10 & Aeroscreen advantage ???

[RESOLVIWOLF]

Just drove brands and donnington in my SLR. Top speeds are pretty poor... getting much more speed out of the corners but less top speed than in previous cars. Was wondering just how much difference th aeroscreen makes past 100mph ? ANyone done a comparison of top speeds on a track with and without ?

 

Also, will ACB10's improve cornering speeds much over CR500's ?

[julians]

Cant really give you any hard or fast figures, but I've just changed from windscreen to aeroscreen, and there is a definate (ie you WILL notice an improvement) increase in acceleration in the upper ends of the speed range (say from 80mph +), whether or not this will actually give you an appreciably higher top end I dont know.

 

I was at Donington as well (in the bar ali/black nosecone/wings car), and was seeing 120mph (dont know if thats actually fast or not, in terms of what an experienced donington'er could acheive, as it was my first time there) on the last straight before the sharp right/left onto the start/finish straight.

 

I've not done donnington before so I cant really comment on what speed was like with windscreens.

 

I guess I should qualify this by saying the car has somewhere around 200bhp.

 

Edited by - julians on 3 May 2002 14:15:47

[ashaughnessy]

In line with the thread about measuring power, how much consistency and accuracy is there between the speedometers in different cars?

 

Also, is your speedometer accurately calibrated to the rolling radius of your tyres and your gearbox/final drive ratio? And was that the case in your last car?

 

Anthony

[robmar]

I believe the perceived wisdom is that removing the screen gives you aprox +10 mph top speed on a 1.6 SL, although I am not sure of any empirical evidence. However the windscreen is not the most aerodynamic feature on a 7

 

top speeds on a 7 are not always that high when compared to other cars, mainly due to the lack of aerodynamics

 

 

[julians]

My 120mph is from a GPS, so should be accurate.

[Gary G]

I'm not technical and nor is this post, but if you take your sidescreens off and stick your head out from behind the windscreen at 80mph+, you will certainly feel the kind of force the the windscreen is battling against. I therefore reckon the aeroscreen would give a huge advantage.

 

C7 GARid=red>

[Alex Wong1697456877]

Rich,

 

ACB10's are much better than CR500's in the dry. I tried a set of CR500's and wouldn't get another set. I've found the difference between ACB10's and full slicks of the same compound to be marginal. The only downside is that ACB10's are no good with standing water and on they road, they tramline alot - but you soon get used to this. They are also expensive and don't last long.

 

Alex Wong

www.alexwong.net

www.slipstream-trackdays.co.uk

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[RESOLVIWOLF]

julian,

 

guess its hard to tell but judging by my speedo, i wasn't hitting 120 down the back straight. Maybe 115-117. My car is an SLR so similar to yours and i dont think my top speed was compromised by Coppice exit speed or early braking - i was putting in what i consider some reasonbly repectable times. The straight at brands was the same. Used to see 120mph plus in my evo6 & 340r but didn't get to 120 in the SLR. So looks as though aeroscreen could play a substantial role here.

 

BTW: what gps/data logging system do you use ?

[julians]

Just a cheapo handheld GPS designed for sailing, so no fancy datalogging or anything.

[dino ferrana]

ACB10s good tyres in the dry much used in racing ****e in the wet.

 

Aeroscreen does make quite a difference to top speed and high (100mph+) acceleration.

 

Plus Aeroscreen really intensifies the experience!

[scooby dooby doo]

I did a few back of the envelope calculations and reckon its worth 20 bhp at 100 mph ish. This is backed up by my own expriences and speaking to others that have had engine upgrades and changed to aeroscreens and vice versa.

 

In simple terms with my 1.6 K SS 76 speed it meant that 4th gear had useful acceleration wheras before i'd be halfway down the straight before needing 5th.

 

Dave Hooper - North London

dmch2@lineone.net

[ian crocker]

If you work out the power required to push a flat plate the size of a windscreen through the air at 100mph then it is indeed around 20HP. However the windscreen is not square on to the airflow and it is not open to the airflow on all 4 sides. Add to that the fact that whatever replaces the screen has some drag (aeroscreen and maybe the top part of your head depending on seating position) and I think the likely gain is going to be somewhat less than 20HP.

 

Ian

[scooby dooby doo]

Good point - the simple calc was to give a rough idea. also the screen may well be worse than a simple vertical plate: it generates a HUGE amount of turbulence. I guess we need two santa pod runs for with and without screen to compare the 1/8 to 1/4 times...

 

Dave Hooper - North London

dmch2@lineone.net

[ian crocker]

With windscreen 4.331s, putting on 21.35mph and finishing at 113.08mph. Without windscreen 4.311s, putting on 21.69mph and finishing at 113.74mph. Both runs had almost identical 60ft times so the comparison should be valid.

 

Ian

[Bilbo]

Hi all

 

I am not sure how much the Brooklands effected my acceleration/top speed as the engine was up-graded up at the same time. However just over 120, on a good day, was the max before its seen 130 + now (nearer 135) and I don't feel that is all down to the engine up-grade from 170 to 200 bhp. The formers a dyno reading the latter a coast down. Thats not the whole story as the torque a LOT more.

 

Actually I have never had it full out since the re-build...... I am sure the speedo out anyway, so its rather irrelevant. The old rear tyres were 185/60/14, with the new 205/60/13 on the 7.5" rim there is very little difference in measured diameter. If anything the 205's are bigger.

 

Brooklands are defiantly much more FUN and less buffering. As to the Clamwings, well they stop the front wheels throwing things at me. biggrin.gif At Oakington I had a car full of small stone chippings from other cars and was really glad I had them. It was er quite noticeable when other cars passed me or when I passed them. Kept clearing the stones out between runs. However nothing realy hit me or my son in the face/helmet.

 

On the track I put the Brooklands down flat, another plus point. However when the car hit 130+ they were up. However, this would make a VERY small difference in acceleration/top speed. Still any edge....

 

The Brookland do make a big difference in comfort up to down flat, my one fell down on the way back from Curborough last year, I did not re-tighten it properly, even at 60/65 mph the wind difference was enormous. I tend to check the wing nuts more often now.

 

 

 

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BDX with Brooklands and Clamshell wings Q 979 CGY

 

[Jason Plato]

having run my car in sprints with and without the windscreen , the difference on the same day wih and without screen was less than 3/10 sec over 55 sec run . This could have easily been down to my driving , plus the highest speed was only 85 mph for a short distance .

On a circuit however , I dont think the screen makes *much* difference untill you are accelarating above 90 mph , then I think the aero screen makes a huge difference - or it feels like at least , there is a much greater punch in 5th and 6th gears , and the car revs out better ....... dont forget that the screen not only hinders acelaration but also makes you slow down quicker - acting like an air brake .

 

just my 2p worth ...

 

dave

 

 

[Bilbo]

Hi Dave J

 

"acting like an air brake"

 

Well there are otherways of slowing down but I nearly posted that as well as a downside for track use. Think its a good point.

 

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BDX with Brooklands and Clamshell wings Q 979 CGY

 

[rgrigsby]

The point at which taking the screen off helps varies quite a bit depending on how much power you have. Without a screen my 155bhp Crossflow does 113 in the wet on 021r's and around 118-119 in the dry on ACB10's at the end of the straight at Brands. Those are GPS figures so pretty accurate. I think with a screen you can take around 5-8mph off both those figures.

 

The car tops out at around 125ish so that's pretty much as fast as it's ever going to go. I find without the screen anything above 75mph the acceleration is much better.

 

Cheers

 

Rob G

www.SpeedySeven.com

 

Edited by - rgrigsby on 5 May 2002 20:58:44

[scooby dooby doo]

from the closeness of those santa pod times it doesn't make that much difference then. although i am surprised by the smallness of the difference...

 

the sprinting figures of a few tyenths a minute also seem small but the top speed is lower there.

 

I agree with rob that by about 70 it *feels* a lot faster but maybe its a lesser effect than it seems then...

[Stijn LUYCK 1]

I returned from SPA yesterday where I tried out my new "retro screen". From my data logger the speed difference at a certain point near to the end of the Kemmel straight is almost 4mph (average of 7 laps with normal screen and 10 laps with retro screen, 102 versus 106mph)

I have got a 1.6SS, 6speed, 3.92 and ACB10's and in certain corners the extra few revs allowed me to shift one gear up and feel more in control.

It is not a standard Aeroscreen but a cut down version of an old screen I got so airflow over it might be a bit more turbulent ... another 1/10th of a mile maybe?