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Aero Advantage of Full-Bodied Kits...
scootz - 16/9/11 at 05:57 PM

We al know that the Seven-styled cars have horrendous aerodynamic properties. But what are the real-world differences when pitted against the full-bodied cars (Phoenix, Fulcrum, J15, etc.).

For example...

1. On a twisty track?
2. On a long flowing track?
3. On a quarter-mile strip?
4. On a top-speed run?

Is there any one of the above that would show a significant difference?

(Assuming that both cars had the same power, weighed the same and were both properly set-up... the only difference is the body-shape).

stevebubs - 16/9/11 at 06:07 PM

Top Speed run is more noticeable - supposedly to the tune of 5-10mph...

JoelP - 16/9/11 at 07:50 PM

Fully body must add up to 100kgs including bracing, so there is a downside as well.

A compromise would be to do a few simple changes to smooth out the 7 shape. Ie modified rear arches and front nose, partially enclosed cockpit etc.

matt_gsxr - 16/9/11 at 08:27 PM

Depends on whether there are lower weight limits in the race series.
Full body adds some weight, but adds some top speed. The Phoenix body adds maybe 30kg to a striker maybe less as I have never had to hoik around Striker bodywork. (definitely not 100kg in this case!!!).

Not many strikers winning in RGB, but Phoenix and Fury do okay.

Strikers seem popular and successful in hill-climbs.

I guess this is all the obvious stuff.

Matt

Sam_68 - 16/9/11 at 08:37 PM

quote:
Originally posted by stevebubs Top Speed run is more noticeable - supposedly to the tune of 5-10mph...


I'd say that was conservative. My Sylva Phoenix could hit 135mph (on GPS), if you were brave enough. The Caterham I had previously was flat out at about 120mph, on pretty much identical engine (circa 145-150bhp Crossflow) and gearing.

IMO, there's enough difference in drag for it to become noticeable at anything above about 70mph.

The ultimate example must be the original 'single seater' version of the Lotus Eleven, whcih could do a (verified) 133mph with a Climax 1100 engine that couldn't be producing much above 85bhp.

quote:
JoelP Fully body must add up to 100kgs including bracing, so there is a downside as well.


Nothing like, if you're talking about something like a Sylva Phoenix or Westfield Eleven. I never weighed it, but I'd say the whole front bodywork of the Sylva maybe weighed 5-7 kilos more than the bonnet and front wings of a Westfield; the rear bodywork (upper bodywork from scuttle to tail; a one-piece moulding) was probably lighter, and the cills would have weighed maybe 10 kilos.

Whatever, the car with a cast iron crossflow, iron bellhousing and cast iron diff. nose was corner weighted at 510 kilos or thereabouts.... I doubt you could build a conventional 'Seven' style Sylva Striker with that running gear at more than 15-20 kilos less weight.

[Edited on 16/9/11 by Sam_68]

Antnicuk - 16/9/11 at 09:06 PM

i have no problem reaching 140 at the end of the back straight at woodbridge and i can still see. The curved windscreens that the stylus has from a lotus elan makes a huge difference for driver comfort with no buffeting, the 7's i have had with flat screens had massive buffeting which would also mean a poor drag efficiency i would imagine. The people to ask would be the high powered, 300 - 500 bhp westy's and the like where power is definitely not lacking and and top speed restriction must be down the drag.

In the drag racing case, i suppose it depends on how much power you have as if you have a 140 hp, then you are only looking at 80 - 90 mph terminal speeds so aero isnt so much of an issue but if you have 400 hp and should be getting in the region of 120 - 130 mph terminal in a tin top then the aero may make a significant difference. When i was running 300 bhp i managed 120 mph terminal at the pod.

jeffw - 16/9/11 at 09:09 PM

I've Sprinted my Phoenix this year against a number of Sevens (mainly R400 & R500 caterhams). At Lydden or Crystal Palace I'm about 1-2secs down. At Goodwood I won it by 6.5secs

Really too many variables to draw a real conclusion but it does seem that the high speed circuits hold an advantage for the full bodied cars.

bi22le - 16/9/11 at 09:21 PM

Interesting topic this because i love the focused se7en look but would would consider a full body at a later date if it made a big difference.

lucky i love driving tight and twisties and have no intension in doing silverstone any time soon!!

ashg - 16/9/11 at 09:35 PM

my roadster will do 135 flat out given the space but its proper brutal without a windscreen. it hits a bit of a brick wall at around 120ish but still pulls ok ish until its flat out. if i actually wanted to go any faster i either need to up the rev limit or change the diff ratio but to be honest im happy how it is.


so in my opinion aero does come into play a bit but you need to be going pretty quick for it to be a problem worth sorting out.

stevebubs - 16/9/11 at 10:21 PM

My 1340 crossflow fury would run out of revs @ 100mph+ before it ran into aero problems. With the zetec, I've not been brave enough on public roads to take it to Vmax....


[Edited on 16/9/11 by stevebubs]

procomp - 16/9/11 at 10:29 PM

Hi

Take the 750Mc Kits championship Zetec class. All tuned to within 5 Hp off each other all running very similar gear box ratios Tyres and diff ratios. quite simply there is no advantage. Which ever is in front will be drafted and passed. Where a seven is not so clever on the aero the Phoenix / Furry is simply pushing more surface area through the air, as proved in the wind tunnel at MIRA.

If there was a 5-10 MPH difference then a striker / Westfield / Gold would never have won a single race.

Cheers Matt

D Beddows - 16/9/11 at 10:50 PM

Steady on there Matt - the Pistonheads 'legend' that is Sam68 thinks otherwise so you must be wrong - because HE never is apparently.........

Anyway Sam, what are you doing slumming it on here anyway?, I thought Locosts were horrible amateur built pieces of cr*p according to your many posts on the subject on Pistonheads?? or have you identified an idiot shortage you're hoping to fill??

Too much???..... hmmmmmm










[Edited on 17/9/11 by D Beddows]

Sam_68 - 17/9/11 at 01:00 AM

quote:
Originally posted by procomp Where a seven is not so clever on the aero the Phoenix / Furry is simply pushing more surface area through the air, as proved in the wind tunnel at MIRA.

quote:
Originally posted by D Beddows Steady on there Matt - the Pistonheads 'legend' that is Sam68 thinks otherwise so you must be wrong - because he never is apparently.........

Very well, Mr B (or procomp, if he wishes to expand on his wind tunnel experience)... here's your chance to prove you know better than the 'legend' that is me.

Explain to me how a Lotus Eleven can do 133mph (or 143mph with a bubble canopy and a few other tweaks) on circa 85bhp, when a Seven with a virtually identical chassis and (allegedly) equally good aero would struggle to crack 110mph on the same power?

Certainly there are other factors on the race track and a particularly well-driven and/or well set-up brick will occasionally beat an 'aero' car, and a 15mph advantage in peak speed will never translate into a 15mph advantage in lap speeds, but never the less I think the results speak for themselves:

http://www.750mc.co.uk/RaceResults-rgb.php

Have a look down the list of actual, real, timed lap speeds for the fastest 'traditional' Seven-type brick versus the fastest full bodied 'aerodynamic' cars. Then explain to me why it is typically 5-8mph per lap slower when it is (allegedly) just as effective aerodynamically?

The plain fact is that Strikers/Westfields/LA Golds rarely do win a circuit race these days, if they have to compete with more aerodynamically efficient cars...



Procomp: I'm genuinely interested in your MIRA wind tunnel results. What were the respective Cd's and CdA's of the cars tested?

Were coefficients of lift also measured?


[Edited on 17/9/11 by Sam_68]

matt_gsxr - 17/9/11 at 07:55 AM

I don't know about Procomps details, but here were some details from the new guys at RawStriker.

http://www.jpsc-online.co.uk/viewtopic.php?f=4&t=594&hilit=mira#p3721

Phoenix Pictures Aero
Phoenix Pictures Aero

I built a Phoenix because I thought it looked nice and I still do.

Matt

(Edited to sort out a picture 'cause we all like pictures)

[Edited on 17/9/11 by matt_gsxr]

jeffw - 17/9/11 at 08:02 AM

Certainly RAW, who have actually done MIRA Windtunnel testing on the Striker/Phoenix & Fulcrum, tell a different story to Procomp so I'll be interested in Procomp's MIRA results for full bodied verses 7 style cars.

[Edited on 17/9/11 by jeffw]

matt_gsxr - 17/9/11 at 08:15 AM

quote:
Originally posted by jeffw
Certainly RAW, who have actually done MIRA Windtunnel testing on the Striker/Phoenix & Fulcrum, tell a different story to Procomp so I'll be interested in Procomp's MIRA results for full bodied verses 7 style cars.

[Edited on 17/9/11 by jeffw]


RAW are unbiased too as they have both Phoenix and Striker, which is always nice.

Ivan - 17/9/11 at 09:23 AM

Running the figures for a Locost through Performance Trends Drag Analyser with a 20V Blacktop Toyota motor I get 13.72 with a 0.7 Coefficient of drag and 13.34 sec 1/4 mile times with a 0.35 coefficient of drag keeping everything else the same (including frontal area) - so even at reasonably low terminal speeds aerodynamic drag plays a big factor. Of course if the low cf body was heavier it would lose much of that advantage.

[Edited on 17/9/11 by Ivan]