Query about gearing...

[andrew34ruby]

Duncan let's make it Wednesday morning. I will phone you before 10am. 07885 543453 Strangely I never drink anything hot.

[Duncan Grimmond]

Ok, see you then, but I won't offer you a beer at that time of day!

[Malcolm Parker]

The second Wednesday of the month is our little gathering at Lakeside Garden Centre, Ellerton, Near Catterick.  All being well I will be giving the Pytchley a run out after sorting a few minor teething troubles.  The road that runs alongside the A1 would be perfect for working out your gear ratio!
According to the speed tables in the back of Bill Williams book, a 5.25 axle with 19 x 3.50 tyres should give you a top gear road speed of 14.75mph per 1000rpm.
So 45mph equates to about 3000rpm.   In top gear in my modern that would be almost 100mph.

[andrew34ruby]

Ellerton, about a 70 mile round trip. Interesting Malcolm, what time do you meet each month please? Looking on googlemaps I can see Lakeside car park, is the garden centre near there? I might pop up next month.

[Malcolm Parker]

Hi Andrew
The Garden Centre is next to the Lakeside car park.   A group of us meet up from about 10.00am on the second Wednesday and have a coffee and scone or whatever.   I always enjoy the trip from Thirsk as the back road between Northallerton and Richmond is wonderful.
We talk about all sorts of things, sometimes even old cars, and usually have a good laugh.

[Bob Culver]

At least with this topic it seems we will learn the outcome. Over the last decade there have been several which simply petered out. One had a vdeo of a drive shaft clonk. Many dutifully listened and relistened to it and expressed thoughtful ideas but I dont think we ever learned the explanation!

[andrew34ruby]

Outcome so far. We went a few miles in Duncan's special, around roundabouts, then on open road, and return. Some of the route is flat and some is a slight gradient. Then we repeated the route in my Ruby.

Mine is 5.25 axle ratio. 17" wheels, LC head. Zenith sidedraught. max speed 49mph
Duncan's is 5.25 axle, 19" wheels, HC head, Solex downraught. max speed about 45mph

Both speeds were measured with the same sat nav device.

To keep mine at top speed needed full throttle.
Approaching top speed in the special it seemed to make little different whether the pedal was to the floor or a bit less.

In both cars I don't think the engine was running out of revs, but the engine wasn't developing enough power to overcome the increasing air resistance. Air resistance is proportional to the square of the speed. The 19" wheels will make the special slightly higher geared, so slightly less revs at a given speed. Power is torque multiplied by revs so the power might be less at less revs, or if the higher revs are getting beyond the engine's peak, then the less revs can mean more power.

To some extent guessing, but i think the special suffers from a non-standard exhaust system, and also the body might be quite high air resistance. It might be interesting to try the ruby again with all the windows closed - it can make a difference.

[Malcolm Parker]

That sounds like fun!  If you look back at period road tests of the box saloon and the open two seater, the saloon had the higher top speed.
For all its boxy appearance. a smooth box is probably more aerodynamic than an open car.
Did you factor in the extra drag due to Duncan's mouchtache?

[Bob Culver]

Get that effect with carbs too large but top speed not actually reduced. Would expect a Reliant carb to be OK. Acceleration in the gears reduces the obscuring effect of wind. As before the engine should still feel to be accelerating at the equiv of 50 in 3rd (30 mph). (Should pull steadily to valve bounce around 40 mph!)
Many things can make an engine flat in a saloon, including pocketed valves with very wide seats but would not expect to dampen a light special to such an extent. And the hc head should add considerably.
Did the car sound normal or "flat"? Is the cam standarrd? For a stock cam it is not dificult to verify valve timing to the accuracy likely to affect performance.
On my car certain exh leaks seriously sapped power. i dunno if there are layouts whch seriously detract.

[andrew34ruby]

Did the car sound normal or "flat"? 

To me, in the passenger seat of the open top special, the exhaust did not sound normal. It sounded loud and muffled. Exhaust drowned out any sound of the engine. In contrast to my Ruby with all the windows open (or closed) where you here nothing from the exhaust but here every tick rumble and rattle from the engine!