Speed 20 SB Engine RPM

Some guidance on the following would be appreciated. All things being equal, that is a fit and healthy engine, what RPM  is it considered sensible to run at on the open road for reasonable lengths of time? Also what RPM is it considered sensible to run up too in the intermediate gears. Many thanks  Mike Wheadon Posted by Mike Wheadon 15/11/2012 08:14:55

Hello fellow Alvis Speed 20 ownwers. Dissapointed in the zero response to my query. Somebody out there must use their car!!!!!!!!!!!!!!.  Regards  Mike Wheadon Posted by Mike Wheadon 21/11/2012 15:55:32

Hi Mike, I'm not fortunate enough to have one of these fine cars, but I expect that opinions vary.   Are you just looking for a ballpark idea, or do you want a Speed 20 to compare yours with? I don't really understand why you want this info. Tick-over, maybe to indicate the state of tune, but when you're whizzing down the road, why not drive it as hard/fast as you like/dare?! Taking it easy will obviously preserve things better than driving the stones out of it.  Paul. Posted by pryantcc 21/11/2012 16:41:04

Hello Paul. Many thanks for your comments. I have driven vintage and prewar cars, to use your expression, hard and fast, for over 50 years including competively. I have a good mechanical feel for things and so far have not actually broken an engine. However some of these cars are now in their 80's and their driver is in his 70's so perhaps a little caution is called for. Hence my enquiry about RPM hoping that other drivers might relate their habbits or somebody might have original manufacturers data on this subject. I no longer have the desire to rebuid something that I might have broken and my family say that I, personally, will not be easy to rebuild!!!  Regards  Mike Posted by Mike Wheadon 22/11/2012 08:39:33

A great response Mike, it sounds like you're looking for someone to help you resist the urge to "floor it"! It also sounds like you have an appreciation for how to be kind to a machine. Everything wears out eventually,  but keep up the maintenance and drive it nicely so that it will last as long as possible. Posted by pryantcc 22/11/2012 09:14:22

Hi Mike, I have speed 20SB with a rebuilt engine which is still a bit tight. In the past I have owned a 16/80 Lagonda which is a two litre six of similar vintage to the alvis. I am always concerned about the 80 year old conn rods and also the lubrication system and so I tend to be conservative and drive at about 2500 RPM continuously,lifting my foot off the throttle occasionally to let some oil up to the top end of the cylinders. With my 4.5 final drive this gives me about 50mph which can be a bit slow on motorways but I would rather do this than repair the block if a rod breaks. Im just looking at a 4.1 ratio which has been recommended by a couple of Alvis people who have adopted this and seem to feel this is the optimum for the speed 20 with a saloon body. As a futher word of caution . A pal of mine has a 1931 Sunbeam approx 2300 cc six and he adopted the flat out on motorways approach . This ended in tears when the gudgion pin siezed with expensive results.  best regards  John Posted by speed20 06/12/2012 17:09:27

I'm sorry to be very late coming to this topic due difficulties coping with the new BB set-up.     I remember discussing with the late Nick Walker, my predecessor as 20SB model secretary, this very subject.  Nick produced an argument for the use of root 2 times the original max recommended RPM of 4,500, which equates to 3,200 as a suitable maximum.  Later he included this suggestion on page 150 of his book Alvis Speed Models in detail.  I have pretty well stuck to this max in 12 years and 30,000 miles of driving my SB, and I'd like to be able to report trouble free motoring as a consequence, but unfortunately I can't!   To date I've had two nasty valve failures, the first after a reasonably prolonged use of 3200 rpm overtaking trucks on the M6.  That one pretty well wrecked the front two cylinders and was nearly terminal.  The more recent one was, by happenstance, incredibly benign - I only had to change No1 piston! Posted by PeterSedgwick 08/12/2012 14:51:13

Correction to my last post - 4500rpm divided by root 2 equates (roughly) to 3200rpm as a NW suggested maximum. Posted by PeterSedgwick 08/12/2012 16:32:17

Hi Mike I own an SD Speed 20 and have always kept below ~3000 rpm (= 60 mph). As others have pointed out this leaves you getting mixed up with every HGV on the road. My solution was to fit a Laycock overdrive close coupled to the gearbox. This gives 75mph @ 3000rpm. I cruise at 65 / 70 mph (= 2600 / 2800rpm) &amp; everyone is happy! For photos &amp; details of overdrive E mail me: <!-- e --><a href="mailto:hugh@theoldvic.plus.com">hugh@theoldvic.plus.com</a><!-- e --> Kind regards, Hugh Westlake Posted by alvisspeed20 13/12/2012 20:09:29

Just like to say many thanks to everybody who has made a contribution to this subject.  Best regards to all members for Christmas and the New Year.  Mike Wheadon Posted by Mike Wheadon 15/12/2012 10:06:58