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Achieving Top End Speed @ Bonneville Salt Flats Gt6


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If not this year in 2018 I intend to field a purpose built GT6 in the GT 2Liter category for stock production imported 2 passenger vehicles. 

While the speed record is established far beyond my comfort zone,165MPH Mazda MX5, I am at least trying to establish an official, top speed for an essentially stock GT6.

The main criteria:

 

Staying naturally aspirated, as in no turbo or supercharger or EFI

Maintaining original displacement. There is an opportunity to stay in the "family" of engines but modifying to go over 165 is not in the cards.

Maintaining all original body panels, no stream lining, such as the overhang from windshield to roof alterations.

 

Interior fixments are not a concern, It can be stripped and a cage installed, weight is not a concern, more is better to keep the car in a straight line and attached to the ground via the tires.

Engine mods including cams and head work are allowed, no point in Nitrous, the final mile is averaged for speed.

Conditions are extreme, heat, thinner air and a loose resistant surface.

A few of us have been brave?foolish enough to take our street machines to the limit, at established factory limits around 107MPH

I would like to see 130MPH

Experience, suggestions to getting there?

Cheers Tim

 

 

 

 

 

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I had the Silverback at 123mph on the Nurbergring, downhill and not externally confirmed, but calculated from the revs and my gearing.

See: 

 

Sb was an aerodynamic experiment, with a rear radiator, and the intention of reducing the airflow into the under bonnet and under car area as much as possible, to reduce lift.

It had side skirts, and I had intended to fit front spoiler/air dam that Old Blue had, but never got around to it.

I'd not recommend the rear radiator, as if you had anywhere to put it in a GT6 (lots of room in a Vitesse Estate!) as it never really worked on track, but some means of stopping all the air getting under the car would be worthwhile, IMHO.

Effective bonnet vents - I'd suggest sides, not top, unless you ca put them just behind the radiator, GT40 extractor style.

 

Are there rules about ground clearance in your class?

I was never able to run less than 3" above the ground, and that is about optimum for a spoiler, but 2" maximum for sides skirts, and the lower and smoother the  underside, the better.

 

Good luck!

Please keep us up to date with the project!

John

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This an interesting little calculator

http://www.wallaceracing.com/Calculate%20HP%20For%20Speed.php

 

I reckon that is you are not allowed to mess with aero at all you are going to need another 50 bhp at the wheels to crack 130.  Do-able, though the extra resistance of the surface is an unknown, perhaps partly offset by the reduced aero drag due to altitude........

 

Stuff like lowering (reduces effective frontal area) an under tray, reduced grill aperture can all help, but maybe outside the spirit.

 

Interesting project.

 

Nick

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You have reminded me, Nick!

 

I'd better recommend Prof. Joe Katz' "Race car aerodynamics".   https://www.amazon.co.uk/d/Books/Race-Car-Aerodynamics-Designing-Technical-including-modifying/0837601428/ref=sr_1_1?s=books&ie=UTF8&qid=1488406836&sr=1-1&keywords=race+car+aerodynamics+designing+for+speed

 

Lots in there to think about, ride height, intake size (Nick's point), extractor design, spoilers etc. etc, mostly with useful numbers attached, not just concepts.

OR

For real world, years-of-experience-distilled, rather than pro-aero academia, Alan Staniforth's "Race & Rally Car Sourcebook" :https://www.amazon.co.uk/d/Books/Source-Anniversary-building-modifying-competition/0857333488/ref=sr_1_1?s=books&ie=UTF8&qid=1488407043&sr=1-1&keywords=race+rally+car+source+book  Chapter 4, Aero

 

John

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Stuff like lowering (reduces effective frontal area) an under tray, reduced grill aperture can all help, but maybe outside the spirit.

 

 

 

I fitted a very small under tray on the Vitesse last year, actually a result of trying 13" wheels and finding that I almost ripped the exhaust off putting on the trailer afterwards (it is a trifle lowered).  By small I actually mean I cut an aluminium sheet to box in between the chassis rails from the bell housing backwards for about a meter, in effect making a sledge to ride over the trailer edges rather than the exhaust catching on them.

 

But anyway whilst doing it and looking around underneath I did ponder that if you wanted to smooth up the bottom side of the Vitesse (GT6 being similar) that a few big sheets of aluminium that went from the front outriggers out to the sills and back to rear could be easily fitted with self tappers and would make a significant difference to what is a turbulence generating nightmare underneath as standard.

 

Alan

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Some very interesting stuff to peruse, thanks guys.

There really aren't many restrictions other than engine size, maintaining original body panels and chassis dimensions and stating naturally aspirated.

Air dams of some sort would be needed to hold it down, lowering is fine, pushing it with another vehicle to start is ok. The exterior cant be altered for streamlining, as in removing the visor like airdam above the windshield. Underbody streamlining is okay, anything that increases safety is encouraged.

It isn't so much a class of vehicle other than being a 2 seat import that is basically stock, class G/G GT( 2000CC / Gas 2 seat grand touring). At El Mirage the class is set at 138MPH for the time being, not many people bother with it. El mirage has plenty of dates to compete in, not quite the prestige of Bonneville but the same end result,

Both are a long haul, in the 2000 Mile range one way, don't want to forget anything and have to go back to retrieve it. A car set up for those conditions would be difficult to drive on the street regardless of Brownie points,125 gallons of diesel, one way @ $3 per gallon for my tow vehicle

Fuel for the car must be purchased on site but high octane @100 is available.

If only I had a friend like Steve Smith nearby, or just borrow one of his GT6s.

Cheers Tim

That highly modified altered is scary, maintains an original back half but anything else goes, 287MPH IIRC.

No, just No, too fast, 150MPH is too fast for me in a stock GT6.

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