Max Engine Speed - Standard 38 Ruby

[fatcatvera]

There will obviously be a maximum engine speed limited by valve bounce, but I'm not entirely sure my engine is running correctly at higher engine speed....

In the absence of a rev counter, what should be the maximum achievable road speed in each gear?

Car is standard (as far as I know) 1938 Ruby 3bearing/twin valve spring engine/4 speed 'box.

Thanks

Ray

[Chris KC]

Ray, I feel you may be asking the wrong question, a comparison of road speeds isn't likely to help you much.

If your engine isn't running cleanly at speed the first thing I'd do is check your ignition points and gap them, clean or replace as necessary. Hitting valve bounce is generally quite noticeable and I don't think you'd mistake it.

[Reckless Rat]

The term "performance" in relation to Austin Sevens is relative. Don't expect any and you won't be disappointed. A reasonably well set up standard car should be OK for 45mph on the flat (after a reasonable build up of speed) and possibly a bit more if the wind and/or gradient is favourable. Just don't expect it to be able to keep up with modern day traffic. The factory quoted maximum speed of the RP saloon was 48mph. The later Rubies were slightly more powerful especially those with the 37 head (13bhp), but the cars were a little heavier. My RP will show 55mph on the flat absolutely "banzai" flat out but running at that speed is asking for trouble. It will run at 40-45mph all day long no bother, no stress.(as long as there's no hills)

The Austin Seven is a (quote) "Dependable car". It will get you there.








Eventually.

[Bob Culver]

If a standard crank (and a 3 bearing will be) a pity to stress, but my RP with standard valve springs bounced at over 40 mph in 3rd, or equivalent. You can work out the equivalnts from the ratio of the gear ratios. In the gears the car should  accelerate continuously.  It is difficult to find a really flat road with no wind and degree of warm up, temp, engine oil, makes a difference. Most cars are now oversize which also raise cr; the later slightly rounded car should certainly exceed a true 50 mph. (I think RRs car above is not pure RP engine) 30 in 3rd, a prudent limit, same revs as 50 in top.

[Colin Morgan]

Austin themselves recommend changing up at 8mph, 18mph and 25mph on '36 to '39 cars.  However, maximum power is quoted as 17 bhp at 3800 rpm.  Using the figure of 800 revs per mile for 4.00 x 17 tyres (17" rims) quoted in the back of Bill William's book, this equates to 1st 13mph, 2nd 21 mph, 3rd 33mph and 4th 56 mph for the 5.125 axle ratio.  When driving my Ruby, I sometimes reach 30 in third (about 3400 rpm, apparently), but generally do not tend to exceed the Austin figures.  (And there is no chance of attaining 56 mph in my car.)  As already suggested, if the engine is not running smoothly at higher revs, it is best to look for the cause directly.  

Colin

[Bob Culver]

My car was used in city traffic and main road and always run to 30 mph in 3rd except downhill. The revs about the same as 30 mph in 2nd in standard swb 3 speed cars.
The Austin change up speeds are conservative but somewhere I found an Austin recommended change down figure which was not quite so. Seven owners learn lightning double declutch but I suppose a generous allowance was made for speed loss for others.
In their day few mature owners would have ever exceeded 45 mph and many never saw that! My father used to say that at 45 mph on our only "'motorway"' just post war, was the fast lane! He found 45 mph on long trips (200 miles) on roads of time too tiring and later settled for 40.

[Bob Culver]

Further to the above, just found my copy of Nicholson. One  apparent error but generally as per the Austin recommendations, although he does change to 2nd (4 speed) up hills at a daring 20 mph!

[Robert Leigh]

There will obviously be a maximum engine speed limited by valve bounce, but I'm not entirely sure my engine is running correctly at higher engine speed....

In the absence of a rev counter, what should be the maximum achievable road speed in each gear?

Car is standard (as far as I know) 1938 Ruby 3bearing/twin valve spring engine/4 speed 'box.

Thanks

Ray

You use the words 'standard' and 'twin valve spring' (I presume you mean double valve springs). Double springs are not standard, and are only useful if you want to exceed the original standard maximum revs, which I believe were 4400. On the late Ruby I used for a Jogle we were showing above 70 mph on the speedo on some of the downhill motorway stretches, this with single valve springs but with a 1" SU carburettor. The fact that an off load engine may achieve 4400 rpm does not mean it will achieve this when it is on the road under load. In the early 1960s I regularly reached valve bounce on my RP, but not in top gear. It was so reliable that I naively assumed nothing would go wrong! The late Ray Walker did not understand why I did not break crankshafts, but he also agreed that they usually broke when running at the speeds which encouraged resonant frequency vibration; I think he quoted 28 and 56 mph, but I can't remember which model and rear axle ratio were involved.

[fatcatvera]

I'm assuming the engine is 'standard' however it's definitely been rebuilt (or replaced?) in the last 80 years - crank is 30thou u/s on bigends and block has been sleeved).

There a double valve springs fitted - I had no idea if this is standard for a 38 Ruby engine or not.

Either way I now have a good idea of whether it's achieving roughly the expected engine speed under load, so will go and test it.

Ray

[Chris KC]

The thing you must appreciate Ray is that A7's are very over-geared, so the speed you will reach on the road has more to do with air resistance, weight, gradients and wind direction than it has to do with engine performance. When comparing speeds then look at cars of similar size and weight, and with similar overall gearing. Based on replies above you ought to be able to hold 45 or 50 on a decent road; but this alone is a doubtful barometer of engine health.