Classic cars forum & vehicle restoration.
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Norseman
Joined: 09 Jan 2019 Posts: 78 Location: Essex UK
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Posted: Sat Feb 09, 2019 11:07 pm Post subject: one or two? |
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Hi folks, here's one for enthusiasts (such as myself) of Rover classic.
Q1: why did the P6 2000/2200 in automatic spec. only have one SU when the manual versions had two ?
Q2: why was the P5 (auto or manual) only fitted with a single SU at a time when rivals such as BMC, Rootes & Triumph all fitted twin carbs to their straight six's of the same cyl. capacity. Although Ford used downdraft carbs the six pots were usually of the twin-choke variety.
nb: out of interest, the automatic P4 105R DID have twin SU's !
I have James Taylors's 1934-77 collectors guide, but cannot find an explanation for the P6 difference in spec. _________________ 1987 classic Range Rover Vouge
1998 E39 523i SE sedan
A great many models have served me well since the 'sixties, all of them old & some even older than me. |
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Rick Site Admin
Joined: 27 Apr 2005 Posts: 22446 Location: UK
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47Jag
Joined: 26 Jun 2008 Posts: 1480 Location: Bothwell, Scotland
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Posted: Sat Feb 09, 2019 11:36 pm Post subject: |
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Norseman
A possible answer to your question could be the autos used the Borg Warner type 35 which probably couldn’t handle the increased torque of the twin carb engines? The older Rover 105 would have used the older DG gearbox which was stronger.
Art |
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Ray White
Joined: 02 Dec 2014 Posts: 6310 Location: Derby
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Posted: Sun Feb 10, 2019 1:17 am Post subject: |
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I thought it was due to fuel consumption. The automatic is thirsty enough with just one carb. ! |
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roverdriver
Joined: 18 Oct 2008 Posts: 1210 Location: 100 miles from Melbourne, Victoria, Australia
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Posted: Sun Feb 10, 2019 6:37 am Post subject: |
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The standard Rover 2000 had only a single SU. The more powerful 2000 TC had twin SU's as a more 'sporty' version of the car. You are right the 2000 automatic had a single SU. In my experience the standard 2000 had very performance that I would describe as more than adequate for the circumstances for which is was made.
The first of the P4's, the Rover 75 had twin SU's as it was considered that the engine was a little underpowered with a single carburettor. The later P4 engines with a bigger capacity reverted to a single carby, but twins were used later on certain models.
I cannot speak for the P5 as I have never owned one. _________________ Dane- roverdriver but not a Viking. |
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mikeC
Joined: 31 Jul 2009 Posts: 1774 Location: Market Warsop, Nottinghamshire
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Posted: Sun Feb 10, 2019 9:24 am Post subject: |
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The fitting of a larger carburettor, or in this case fitting twin carbs, usually results in more power, but produced at higher revs. A small carburettor, or a single in place of twins, will produce greater low-speed power and torque. The automatic gearbox of the period was usually a 3-speed (and in some cases only a 2-speed), so the greater flexibility of the single-carb engine was needed to mask the limitations of the transmission. _________________ in the garage: 1938 Talbot Ten Airline
Recently departed: 1953 Lancia Appia, 1931 Austin Seven, 1967 Singer Chamois, 1914 Saxon, 1930 Morris Cowley, 1936 BSA Scout, 1958 Lancia Appia coupe, 1922 Star 11.9 ... the list goes on!
Last edited by mikeC on Sun Feb 10, 2019 1:13 pm; edited 1 time in total |
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alastairq
Joined: 14 Oct 2016 Posts: 1952 Location: East Yorkshire
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Posted: Sun Feb 10, 2019 10:47 am Post subject: |
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I agree with mikeC....Also, was the final drive ratio on automatics raised at all? [To compensate for loss of performance due to fewer gear ratios?] _________________ Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces. |
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alanb
Joined: 10 Sep 2012 Posts: 516 Location: Berkshire.
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Posted: Sun Feb 10, 2019 2:16 pm Post subject: |
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Spot on MikeC, the single carb produced a more flexible engine and better torque at Lower engine speeds _________________ old tourer
Morris 8 two seater |
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Penman
Joined: 23 Nov 2007 Posts: 4756 Location: Swindon, Wilts.
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Posted: Sun Feb 10, 2019 2:43 pm Post subject: |
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Hi
My father had a twin carb MG 1100.
They had 2 different performance outcomes compared with the single carb 1100s
I got places quicker, and my father used far less fuel.
Whether driving style produced those differences on other engines I can't say, but I suspect it would. _________________ Bristols should always come in pairs.
Any 2 from:-
Straight 6
V8 V10 |
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Ashley
Joined: 02 Jan 2008 Posts: 1426 Location: Near Stroud, Glos
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Posted: Tue Feb 12, 2019 3:03 pm Post subject: |
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In simple terms two Carburettors give more top end power at the expense of low end torque. How much torque depends on the capacity of the engine and size of the carburettors.
Typically the kind of cars most members on here are interested in will produce peak torque at around 2000 revs, while sports cars like TRs, MGs, Healey’s etc at nearer to 3000 because it’s assumed that owners are happy to change gear a little more often.
Big engines cars like Jaguars and Bentleys etc need two carbs because more air flows through bigger engines so are still very torquey. For example an S1 Bentley has two 2 x 2" SUs and still produces max torque at about 2000rpm.
Hope this helps. |
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alastairq
Joined: 14 Oct 2016 Posts: 1952 Location: East Yorkshire
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Posted: Tue Feb 12, 2019 5:32 pm Post subject: |
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Inline sixes work better with multiple carbs, compared to one carb, due to the distance to the end cylinders? This can lead to very uneven mixture strengths along the line of cylinders.
{US Ford inline sixes a case in point....together with the integrally-cast inlet manifold & cylinder head......Offenhauser produced [still do] a piggy-back manifold which houses 3 carbs.....and a nicely complex linkage which meant that on light throttle, only the centre carb was 'working'...floor it, and the other two came on line]
Changing to a vee cylinder formation made fuelling [and emissions] far easier to deal with.
If the choke size of the [twin] carb setup is appropriately small enough, so low down torque can be improved.
Hence, I have a twin SU set-up, which are 1 1/8th inch....for a sidevalve Ford...also, an 1 1/4 twin SU set-up, for a later[??] sidevalve Ford engine.
Camshaft shape does more to dictate how far up the rev range power comes in.....hence, modified cams can lead to rough idling [or a higher-than-normal idle speed] and a loss of low-down torque.
When I trialled a Skoda Estelle [with 1300cc engine] I had, at one time, a swan neck inlet manifold, with 40 DCOE Weber jug clamped on.....a session on a local [long screwdriver type] rolling road tuner, led to the fitment of 26mm chokes..to get the torque back up at tickover and just above.
Latest trials Skoda has 4 bike carbs.... _________________ Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces. |
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emmerson
Joined: 30 Sep 2008 Posts: 1268 Location: South East Wales
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Posted: Tue Feb 12, 2019 7:44 pm Post subject: |
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My old Dad used to say that anything which came in twos was double trouble! |
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alastairq
Joined: 14 Oct 2016 Posts: 1952 Location: East Yorkshire
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Posted: Tue Feb 12, 2019 8:02 pm Post subject: |
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Bike carbs are very reliable...don't go out of tune , unlike SU's....
After all, look at the popularity of Japanese 4 cylinder motorcycles over the decades? _________________ Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces. |
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Norseman
Joined: 09 Jan 2019 Posts: 78 Location: Essex UK
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Posted: Wed Feb 13, 2019 10:03 pm Post subject: |
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Many thanks for the very comprehensive replies, for which I will query just two.
47 jag : the BW35 was the only option on the P5B whose V8 produced greater power & torque than the Rover IOE engines.
mike C : still leaves the question as to why all Rover's main competitors chose to use twin carbs on their auto's (some of which I've owned)
Cheers to all, interesting viewpoints _________________ 1987 classic Range Rover Vouge
1998 E39 523i SE sedan
A great many models have served me well since the 'sixties, all of them old & some even older than me. |
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Mog
Joined: 30 Dec 2007 Posts: 661 Location: Sydney
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Posted: Thu Feb 14, 2019 3:58 am Post subject: |
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I remember seeing a Mini pick up with 4 Amal Mono Blocs fitted .
I think it belonged to Tony Marsh . He lived not far from me . |
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