Aerodynamic Data for GT40s

gt40fran said:
Fix all the problems by building a Mk4....much more slippery... and stable at speeds above 200mph with the same drivetrain as the Mk2....;)
Shhhh, Fran, then everybody will start building them, like what happened to Ron's "batmobile"
Hi Bob,
I would be extremly interested in either buying the same publications that you have tracked down or accessing the information in them, have you received your copies yet ?
Hi Iain,

I have received “The Inside Story of the Fastest Fords” and “The Ford GT: New Vehicle Engineering and Technical History of the GT-40” which I am reading now (references in prior post above). Both of these books are very interesting and include lots of historical pictures and explanation of design. I would highly recommend them to any GT40 lover. However I have found very little aerodynamic information of particular practical value. All three volumes of Style Auto are also on order and will arrive soon but I understand they may be the same articles used to create “The Inside Story of the Fastest Fords.” Once I read all the material I will post some comments.

Basically no one has come forward with hard factual aerodynamic test results, either from public information or their private data. And, the information in the books so far does not have enough details about the conditions and variable in the tests to be of much value. I am starting to believe that we will have to do the testing ourselves. If that is the case then maybe we should take up a collection to pay for someone who lives near a rent-a-wind-tunnel facility to get the data. Otherwise a few linear encoders and pressure transducers could be attached to a car and then go for a little drive.
Hi Bob,
Thanks for the feed back, I will look foreward to your review. After 5 years of racing a Cobra I am building a Roaring Forties (#117) as a dedicated race car here in Australia and plan to use any of the advantages that our rule book allows, we are allowed a front air dam or splitter and we are allowed to add a rear wing -- uh oh -- I can hear the GT40 purists groaning from here ! I will race the car in the same group as Ross Nicol however he is based in Melbourne and I'm in Sydney, we face competition from GT3 Cup cars, Ferrari F430 & F360 GT, Dodge Vipers etc etc so I need all the help I can get in terms of Aerodynamic "assistance". One of the members of our group has a son who runs the Aerodynamic department for the F1 Toyota Team, he has provided an amount of advice but without any base information he is a little constrained. He felt that the addition of a rear wing would not be necessary, however the front splitter would be required, he indicated that by far the most important factor was the underbody of the car and managing the air flow as it leaves the rear of the car. He provided some sketches of how a rear diffuser would acheive this, unfortunatley I am not allowed to do this ! The Ferraris however are allowed !


That's too bad about not being able to use a diffuser. IMHO, your buddy's son is spot on. We had a discussion in another thread that led to this one and that was pretty much how the speculation ended there as well.


Peter Delaney

GT40s Supporter
I guess that the writers of the "rule book" are Ferrari owners !!

If you can add a non-original front spoiler, why not a rear diffuser ?? After all, each GT40 replica has a different under-body scenario (both from the originals & from eachother) - so, who is to say which replica is "right" ??

Kind Regards,

Peter D.

Ross Nicol

GT40s Supporter
Yes we are supposedly adhering to a rule book that sets the maximum engine capacity to 6 litres but allows the Dodge Viper to race, Bans sequential gearboxes but allows Ferrari 360s (that have one) to race. And you are allowed a turbo but it must have the original manifold. So the car that has won our championship for the past 3 seasons is a Porsche GT2 with a single massive Turbo developing 700hp and the original manifold catered for 2 much smaller turbos.Iain's car could be a problem for him too as He has Yates heads on a 302 and a hewland transaxle.Now for his car to conform to the rule book RF would have had to have produced 10 cars with this spec and I know they haven't. With this in mind you would say to yourself oh bugger it I'll fit the damn diffuser anyway. It is likely a similar motor may be dropped in to my car soon too. we can change our log book to 2a instead of 2b but then you are at the mercy of the race promoter as an invited car and not guaranteed a start.

Pete McCluskey.

Lifetime Supporter
It seems to me that motor sport across the world is blighted by those who make the rules and then by those who enforce them according to their particular bias.

I still remember the heady days of Formula Libre' :dead:

Peter Delaney

GT40s Supporter
Ross, wow ! And I thought that dealing with government clients was a PITA in terms of dumb people making up dumb rules to suit themselves !!

I admire your tenacity in the face of such stupidity !

Hopefully, race promoters are a bit more sensible - it wouldn't take a great leap of intelligence to figure out that a GT40 in a race is a huge crowd puller - specially when it is lined up against the same old boring fleet of "squashed Volkswagens" !!

Go get 'em !

Kind Regards,

Peter D.

Ross Nicol

GT40s Supporter
Yeah your right Peter I have a promoter chasing me at the moment.He's offering television coverage but as we all know it's only going to advantage the first 3 cars and he's unlikely to force his beloved squashed volks wagons to pull the big hair dryers off and play fair when they belong to his club eh! Of course he hasn't discounted the $500 entry fee to a more normal $300 either, and I haven't forgotten his bad behaviour when I was racing the 240z.

Ross Nicol

GT40s Supporter
Getting back to aerodynamics I will most likely fit the Gurney flap to the rear of my car. Can't bring myself to fit a wing, just doesn't look right and as Iain says the aerodynamic guru from Toyota F1 doesn't think the car needs it. I like the front splitter but there's a bump in the dummy grid at Sandown thats attacked my front clip without the splitter so knowing my luck the splitter would be off before entering the track.My car feels quite stable at high speed so I'm not rushing to increase the drag either.
Ray was able to make a reasonably effective splitter from flat 3/4" plywood bolted right under the nose. It will take some abuse and with a little creativity in the mounting you can keep your ground clearance. As I recall it gave about a 6 or 7 inch flat surface in front of the rad opening. Unfortunately you have to remove it to open the front panel.
Firstly a qualifier: I'm no aero expert!

In all this discussion, I agree with the main points
1. Rear spoiler of car works fine as is (data suggests this).
2. Front needs a splitter as the std Mk 1b front end does very little (by looking at it) to minimise air going under the car (bad).

However, I don't recall seeing any thoughts regarding airflow getting under car from the sides. When you look at the tank covers, it almost seems they are purpose designed to maximise air spilling under the car! I recall reading somewhere with the the design of the new Ford GT one of the main aero improvements made was installing the lower sideskirts, which look much like a front splitter and work in a similar way.

If one were to add relatively discreet front splitter and sideskirts (coloured black in the new GT?), plus undertray/diffuser the rear of the car best as possible, you'd not mess too much with the shape of the car, which we all can agree is important. But you would likely get a decent aero improvement.

This is all not that important except at high speeds however, and for those chasing the last few 10ths around a track. Given that in WA we don't have tracks with high speed corners comparable to Phillip Island or Eastern Creek turn 1, don't think I'll bother adding any extra aero aids which just add weight and detract a little from the shape. Which brings me to my next point!

Ross - I'm getting close (a few months now till rego) to getting my DRB going and I'm going to get onto CAMS soon about getting a 2B log book (Marque Sports). Not sure how I'll go with that since they are not listed yet, despite GT40 Aust submitting all the details some time ago. Also not sure if my planned Alloy heads will be permissible, but I'm sure GT40 Aust would have 'made' the 10 required with Alloy heads. In any case, car will primarily be used for supersprint/hillclimb/motorkhana/road rally type use so a 2B logbook is not essential, but sure would be nice! We'll see.

Anyways, better go and get back to wiring up my dashboard!
Peter - For pics of car see AlbanyGT40 thread in builders forum. Mine is the other car in some of the pics. Basically the same as Daves, but different wheels, brakes and seats.

Regarding the earlier comment on testing. Well, I've just been fooling around with some low pressure transducers (1 psi) for work, and we also have linear transducers to measure suspension travel. Plus we have all the data logging gear. Simpler sloution for those without all this gear (99% of people) is to get a little 'lipstick' type camera recording front suspension movement, against a fixed type scale under the front guard. Bit fiddly, but should be doable. Mythbusters style, but without the hole puched through the top of the mudguard!

So, if someone gave me a nice long test track.... May get around to it one day, but not till next year at earliest. Would be interesting to see the effects of adding splitters etc on lift, drag etc. Thing is with a GT40 is that adding rear diffusers, splitters etc should be quite useful compare to a normal car, due to flat underside of GT. Even so, don't think I'll add any aero devices though.

Easy enough to measure drag by either measuring TPS or MAP outputs (measuring engine load - you can get/log this data straight from ECU) at a constant fairly high speed or doing coast down testing (measuring how long to slow from a high to low speed in neutral and no braking). You'd just need to change over aero devices quickly so atmospheric condition changes don't affect results.
Hi everyone. Sorry I've been quite busy and Lynn was nice enough to let me know there was an aero discussion going on.

Last winter I attached linear potentiometers to each corner of my suspension. Using a controlled power source and my LM-1 lambda gauge I gathered ride height data from zero to 160 mph and kept that speed for a half mile.

Yes that nasty Beast got to 160 inside a half mile with half throttle in first, half throttle through half of second then WOT the rest of the gears.

Maxton AFB is very bumpy. I did a lot of averaging to get the median data. With my series 1 splitter and side sill extensions I got about 300 lbs down force in the front and 150 lift still at the rear. I've redone the side sills and affixed a small tab (ala 2005 GT) and I'm headed for the wind tunnel.

If I have rid the car of lift I have the Series 3 stuff in mind to remove drag. It's been a lot of fun. You need to pick up the video of my 162 mph run and take a close look at the rear part of the nostril section. THAT needs to stop.

So I'm really close to being able to test the car's real top speed. But I seemed to have run out of the gobs of cash it took to get this far so I've come up with a side venture. (Obvious commercial plug here) Six Minute Tutor - Home Anyone making quality videos you think might fetch a price, I host them for free. Go live at end of March.

Cough, cough. Did I say that?

So all I'm waiting on now is a single radiator exhaust opening nose piece and I'm off for some wind tunnel testing.

The splitter works perfectly but there is still some lift at the rear. And that's the MkI ERA.

One major caveat here is each manufacturer's GT40 nose is different so no one splitter will work for all cars. I have molds for the ERA and for the tube frame CAV which is also..... brain fade. Anyway gotta run. Filming Tae Kwon Do forms tonight. Hiiii Yaaaaa!