Top Speed

[Mark Cowling]

Hi all what top speeds have people achieved a on sprints & b on track days, trying to work out some gearing options Regards Mark.

[SUSIT]

Hi Mark,
If I remember correctly you run a honda V6? What options do you have?
I reckon for rallying and sprinting 120 mph would be more than adequate but with the Alfa there is no way to get the final drive ratio that low (numericaly high) the best I can acheive is 3.7:1 when on the tyres i think I will be using I would really like a 4.5:1
the problem then would be first gear would be almost useless. Only way out is to spend large sums getting custom gears made. Out of my leauge i am afraid
Stephen

[Sando]

Hi Mark
Never had time to look! :eek: I'm not in the big boys club yet so doesn't really apply, but probably did get up over the ton / ton ten at Abingdon I would have thought in the afternoon. With a third more horsepower I think I would have got there a lot sooner and kept going some more mind :D........................maybe next year ;)

Rob

[Stratos]

Mark,

Fastest section of an event I have ever done was during a rally at Colerne airfield.

There is a long very wide runway, which turns 90right onto another very wide runway. Depends which way round they run it as to what top speed you achieve.

When they run the shorter section onto the longer section you go very fast :eek: - we saw 5700 in 5th. I don't know what that equates to in mph cos my speedo doesn't work - in fact, I don't want it to work or I'd frighten myself.

(P.S. You should ask Andrew about trying to overtake cars on the corner when it's run long to short :rolleyes: :rolleyes: )

Anyway, if I could I would gear my car for about 120mph tops, but I can't get gearing that low, as Stephen pointed out.

[Martin K]

Did you end up owning my 'special' diff Mark?

From my records I believe that in the PG2 gearbox, 1st is 2.923:1 and 2nd is 1.789:1, 3rd is 1.222:1, 4th .909:1 and 5th 0.702:1 Standard final drive is 4.2:1 My tricky one was 5.214:1.

As Susit says it does make 1st gear very low if you raise final drive ratio (lower the gearing), but my intention was to avoid 1st gear once rolling and only use 2nd gear for slow corners, which was a nice distance from 3rd, rather than waste time changing down to 1st for a second or two only to have to change up to 2nd again. And, boy, does it go off the line! Changing from 1st to second at 6500 the revs drop to 3978 rpm - horrible. At 7000 rpm the revs drop to 4284 which is only marginally better!

Changing from 2nd to 3rd the revs drop to 4781 if you can change at 7000 rpm or 4400 if you change at 6500 rpm. Much nicer!

Without that diff, my Honda was geared to do 151 mph at 6500 rpm on the 15" tyres I was running which were 878 revs per mile. With the tricky diff it was 121 mph at 6500, 131 mph at 7000 rpm, which the engine would pull to with that gearing even though we were past peak bhp, which was great for long airfield straights and downhill sections at Millbrook! But my main reason for changing final drive was, as I said above, to avoid using the useless 1st gear wherever possible.

At 6500 rpm speeds in the gears were:

1st 29 mph
2nd 48 mph
3rd 70 mph
4th 94 mph
5th 121 mph.

Martin

[Jerry B]

Hi Mark
Thanks for the help at Abingdon, pity it didn't last longer.
Gear your car as low as you can, 100-110 mph is plenty fast enough for 99% of sprints and rallies I certainly didn't use 5th gear at Abingdon. Lower gearing will give you much better acceleration and closer gear ratios and as Martin says you can use 2nd gear for tight corners.
I have seen 140mph on my speedo around Thruxton but the car was getting decidedly `floaty` at the time and that sort of gearing is only needed for circuits.

Jerry
Jerry

[David May]

I suggest you keep away from Italian race tracks. I have to use my (overdrive) 5th at Monza, Imola and Mugello (4th running out at a mere 230kmh = 144mph.) 1970's aerodynamics do nothing for the stability at those speeds (luckily both tracks are very wide) and the brakes never cool enough to give me much confidence!

[rutthenut]

If you go to Goodwood, that will want a taller top gear.

I need to use fifth there, but nowhere else when sprinting.

Top speed on the back straight there is over 130mph with my Strat.

Elsewhere, 110 probably more like it.

[Mark Cowling]

Hi all thanks for all the answers very informative, nothing like real exsperience to compare the calculations too, a real good responce, Martin thanks for the revs dropped per gear, the gear ratios you state are 825 (c3p4) the 827 ratios are different for 3rd 4th & 5th (g3u4) thanks again to you all, PS has anybody got a 825 box for sale code (c3p4) regards Mark.

[stratos_lover]

i was reading your message and i found that the lancia startos only has a top speed of only 143mph it could hit 144mph but the v6 engine is only designed for acceleration

[SUSIT]

i was reading your message and i found that the lancia startos only has a top speed of only 143mph it could hit 144mph but the v6 engine is only designed for acceleration

Think you miss the point here, we are talking about replica's fitted with different engines not the Dino V6. and top speed is not just about power gearing plays a large part. As a rally car the original stratos had quick change drop gears in the gearbox and top speed could be altered between stages. Most Stratos on rallies would have been geared between 110 and 130 mph.

[GaryFitz]

Mark, on the original motor you can change the top gear ratios reasonably easily. I have not calculated it but I am reliably told you can vary the top speed gearing from 180kph to around 240kph. So top speed will depend upon the gear ratios used. Cheers Gary