CW & P ratios

[Nick Mayne]

Some years ago when starting my 1932 A7 RN style van I had two back axle/torque tube assemblies. One was from the van and the other from a later (year unknown) scrapped Ruby. I find the the CW & P ratios are both 8/42 ie. 6.25
Looking in the source book page it says the CW & P ratio is 8/45. I thought I would get up hills better with the 8/45 but don't have much choice without spending a lot of money. Out of interest can anyone shed any light on this anomaly?
In any case would the change in ratio really make any noticeable difference?

[Jack in the Box]

Nick,

May be a typo but 8/42 is 5.25 not 6.25.

Alan

[Parazine]

Most A7's were 8/42 or 5.25:1 from 1932 onwards. Late in the production run, the ratio was unified with the Big 7 at 5.125:1 (8/41).

Vans and the early Sports 65/Nippy were 5.625:1 or 8/45. The last Nippy and Speedy models were 5.25:1 I believe.

Over the years, these ratios may have changed about as axles were swopped between cars and CWP sets were changed/upgraded. A friend bought a Ruby in 1978 with a 5.625 CWP and it was awful! 45mph flat out but went up hills well. The change in ratio made a dramatic difference.

So your van axle may have started life on a car or had its internals replaced in 1952 or another myriad of reasons as to why it's apparently incorrect now.

[JonE]

the value of not over-gearing (mentioned a lot on here) was brought home when talking to a taxi driver Prius owner who had plainly been experimenting to find a sustainable solution for a huge annual mileage. He found that on raising the profile of standard wheels from 45 section to 50 then 55 (increasing diameter in order to give better ride height on rural roads) the average mpg decreased from 65 to 58 to 52. Remarkable. Presumably mostly torque-related and also rising drag as it gets less near the road.

[Nick Mayne]

So Parazine do you think I would have a big difference if I changed to 8/45 CW & P? The pepped up engine should be ok revving a bit higher.

[dickie65]

That odd my EB65 will do 45 mph in third gear and 65mph + in fourth ( best recorded against GPS is 72 MPH )

[Bob Culver]

From old road tests and many on here the original 4.9:1 is/was considered overgeared and despite faster running today several have converted early cars to the common 5.25:1. To the occupants 5.25 Sevens seem high revving but are no more and less so than many older cars (1950s Minx, A40 A30 ect) and much less than commercials (Fordson A40 pick up etc). Revs do not prolong the crank. It is a bit surprising that the higher speed sports models were lower geared, but the wind drowns out the din.
Economy not a consideration for most owners but generally improves as the gear revs are lowered. Unless on more sophisticated carbs the engine is more often prodded into enrichment territory, possibky the action of the Prius computer. I assume he corrected for the greater distance run. Peak power on pre 1936 is about 3200 rpm, admittedly a speed hard to maintain in top on any hill. Lowering the gearing further reduces the reasonable speed in 3rd, already modest at prudent  revs.

[Parazine]

That odd my EB65 will do 45 mph in third gear and 65mph + in fourth ( best recorded against GPS is 72 MPH )

That's because your engine will rev happily! The poor old standard Ruby in 1978 couldn't, hence ran out of puff at 45MPH.

Nick, if your engine has been gasflowed a little and is able to pull more RPM than a standard 7 then a lower axle ratio is the way to go. I'm running a 5.375 Regent CWP in my Chummy with a mildly tuned engine and the performance is very good. Acceleration is great and top speed is about 60 but best not to hold it for too long without ear defenders!

[Nick Mayne]

Thank you Parazine, you sound as if you are an expert. When I rebuilt (re constructed!!) the van I wanted it to be more useable so went for a bit more more power but things went a bit over the top. I ended up with a new John Barlow crank and CNC con-rods with appropriate pistons, sporty cam and followers with increased flow oil pump and oil filter from Pigsty, and an HC head from John Sutton (whom some may have known). Also a speedy exhaust manifold from Pigsty and inlet manifold from John Barlow. A bit of gas flowing from me and oversize inlet valves. Of course rebore and balance check (but it already had good balance) and an SU carb. New auto distributor and 12V system. All good fun but it did not seem to make much difference at all. Pigsty then checked it over and pointed out that I needed a non standard carb needle as everything else was changed. They modified one with emery on a lathe and now the engine starts at a touch and revs freely fine but does not seem to have much power on the road!! Yes it is very noisy and a good job I am rather deaf.
So I will look for a half decent 8/45 CW & P.

For interest I used John Sutton's concept for fully floating front brakes and Girling (adjustable) back brakes which again has not seemed to make much difference although not many miles done to run in. I also have the twin front damper assembly. However I cannot really brake well or steer well!!!  Perhaps when the CW & P is sorted some expert could look over the whole car and advise for a modest fee! Any suggestions?

   

[Parazine]

Well Nick, that engine should fly! 

Whereabouts in the country are you?