Ways to reduce top speed... Think i might have a problem!

[Eternal]

Soooo i did some more research into my gear ratios and have found i have a small problem....



The only real way i can think to reduce this is to tune the ecu to not go above say 6k rpm but even that will give me a top speed of 168mph..... in fairness the engine is good for it as its making around 290hp at the moment but still not a good plan. I guess in an ideal world i would be able to limit it to only 4 gears and a max rpm of 6k that would give me a top speed of 127mhp. I think i remember reading something in the IVA book about a test that involves speed in some way can anyone clarify this?

Thanks

[Hairy Santa]

change diff to a 4.25 to 1 and reduce wheel/ tyre size by 20% that should sort it

dont think they cover acceleration in the IVA so all will be fine with sub 3 secs 

[Bulldog Bri]

The only thing I can think of that referes to speed is to make sure your tyre rating is up to the top speed that you claim the car is capable of.

[bluehornetrider]

don't see where your problem is, 200mph is not a problem, if your on a large track 170 should be possible, a bit too much is better than running out of revs, don't know how stable a light kit car would be at that speed though.  Might be worth adding a HairySanta spec rear spoiler.
Nurburgring is calling

[paintman]

Don't forget to purchase some brown corduroys for your first outing!!! lol

['The Gaffer']

I'm in agreement with Santa. You will need to mess about with diff ratios. Your problem will be finding one with the right ratio. You will probably have to get the prop modified too.

You can use a ratio calculator like this one that allows you to add tyre sizes and rpm http://www.advanced-ev.com/Calculators/TireSize/index.html

I reckon the car would be very unstable at 168mph and would probably take off without serious aero mods.

[Camber Dave]

I wouldn't take too much notice of the chart as it is function of revs and gearing.
Air resistance is  a function of the square of speed (doubling the speed the air resistance Quadruples)
7's are often referred to a less aerodynamic than a brick but electrifying to 100!
A few supercars do 200 mph with 500 - 600 HP but the super slippery Veyron takes a banked oval circuit and 1200 hp to get to 250ish
When I was gearbox mech on a 550KG F3000 car we mostly geared it for 165 with a 450BHP DFV Cosworth (163 through Brands speed trap) I had a 178 top gear but couldn't find where we used it (poss Silverstone GP for testing but no race there)

Dave

[Hairy Santa]

gear it down to 145-150mph, you wont go up there very often ( should get the passengers screaming )

beef up all your drive shafts/prop/axle as much as possible, stick a bit of down force front and rear, lighten it as much as possible, widen the track ,then let Dave set it up suspension wise and there wont be much out there that will stay with you - mainly in a straight line 

what are you expecting as your all up weight ?   

[Eternal]

At a guess with the full cage, 6pot engine and chassis stretch oh and a large tank probably around 900kg.

The only problem with the diff is i would require a 3.9 - 4.02 diff from any of these not exactly easy to find with an LSD

My current diff is this one... but the other would be better i think. All are 7.5" diffs
3.64    Scorpio(Cosworth)    Lobro    LSD              91GG 4006 ADA
3.91    Sierra[DL20](May91−), Granada(Feb92−)    Lobro    LSD         6663906    91GG 4006 ABA
3.92    Sierra[DL20](Jan90−), Granada(Feb92−)    Lobro    LSD         6171465    86GG 4006 AAA, 8600 4006 AAA
4.09    Scorpio[DL20](Jan96−)    Lobro    LSD         1015626    96GG 4006 BAA
4.09    Scorpio[DL20](Jun95−Jan96)    Lobro    LSD         1013747    95GG 4006 AAA

With keeping the same diff and dropping down to 17" rims with 40mm rubber and a 6.0k redline. Will give me a top speed of 159 mph seeing as the power band drops off at 6k rpm on these rb engines that sounds ok to me!