Rootes 1725 engines : the differences ?

Currently running some type of alloy headed high comp 1724cc engine. I have gone with a +40 rebore and am also running an electric fan, electric fuel pump and electric dizzy, so in theory better spark and more horses. She goes well!!! :) The weak link for me is the gearbox, we are still on the 4 speed box. The engine is the bog standard one. I do have another 1725 engine which I picked up from ebay last year for "just in case" this has the alloy sump, and alloy rocker cover, and could be a Holbay unit as it has the tubular rather than solid pushrods.
For carburation I am on the twin strombergs, but I did try twin SU's and do believe with fettling this could be a good way to go. With regards to air filter I have a sort of plenum set up with a big old K&N.
In my (2 rebuilds in a year) experience the engine is easy enough to recondition, just take your time and be methodical.
With the set up above, we can do motorway journeys quite comfortably, overtaking lorries, darksiders and Sunday drivers with ease lol.

 
http://forum.commervanfan.co.uk/topic.asp?TOPIC_ID=5483&whichpage=19
Mk1 version of air filter solution. No mods to engine bay here.

 
http://forum.commervanfan.co.uk/topic.asp?TOPIC_ID=5483&whichpage=12
Twin hif 38s on a standard alloy head manifold. Next time I will try the 44's

 
Great, thanks for the info guys! Looks like a fairly straight forward swap. I like the look of your air filter setup Nick, gotta wonder why the factory didn't drop those engines in if it fits so well.
 
And the best thing is, apart from the extra performance, I get far better fuel economy with the Rapier engine and a big SU

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Harvey & Bonnie
 
I used twin Stromberg 150 sidedrafts which work well. A trial fitment of twin webers showed they were taking up too much seat space

Cheers
Jules

RatSport: www.ratsport.co.uk

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An alloy head with one or two SU's or Stromberg's seems to be the way forward. Now - thinking sideways - if I got hold of an alloy head and manifolds, what would I need to do to put the alloy head onto my old iron-headed block? I've read that I need to change the cam. Is that all? Just the cam? Are the studs the same? Pushrods, etc? Or is it too much of a mission to swap heads? The shared knowledge on this forum is really useful - thanks everyone!
 
I think they share the same block. ..all 1725's have the same crank I think. I have two 1725's one has solid pushrods...the other tubular. I think the big difference is the cam, but you would sort of expect the higher spec engines to have better parts. Lol

 
I think it would be an idea to put a matching set if head, cam, timing gear and pushrods into your existing block if you can get them - even better swap the whole thing if you can get hold of a decent engine:)

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Harvey & Bonnie
 
My first car (in about 1985) was a 1972 Humber Sceptre with 1725cc twin strombmergs, manual/overdrive. Walnut dashboard. Vinyl roof. Phwooaaar!
As I remember it the car was really quite quick, but awful on fuel. Maybe 20-25 mpg ? I never measured it but it was nowhere near the 30 mpg my friends were getting from contemporary jap cars. It's not exactly a big car so I always wondered how Humber got so little out of that setup.
Other people who had hunters etc said the same thing about theirs : good power, lousy economy.


A couple of questions:
1) I was wondering why that engine (or the cast iron head version) is so poor on fuel, when it's not too different to say an MGB engine (1800) or triumph spitfire which will give more like 30pmpg or more.
Is it the carbs ? I saw that Panky has used a single SU which helps- Triumphs used a combination of Strombergs and SUs. My current 2500s saloon engine (straight 6) gets about 25-30mpg on twin SUs so I'm tempted to think it's the carbs. Any thoughts?

2) My Sceptre blew its head gasket for fun (alloy head prone to this, I believe). Has anyone else had that problem?

3) I also have a 'spare' Stag gearbox with overdrive attached. Humber Sceptre used same Laycock o/d unit so I'm wondering, with the 4-speed comer box, is it possible to remove the extension piece and bold an overdrive on instead? or is it a different gearbox altogether ?

thanks in advance..
 
Hi Doug...

The MG's were single carb I think plus I think SU are just better. I have the SU switch too and went from 20mpg and poor power to 30+ and more power.

Not heard that they are prone to blown head gaskets - mines alloy and never has had one go

On the stag thing - no wouldn't work. You can't even add the standard Commer overdrive unit to a 4 speed box as it needs a longer output shaft I think.
 
Thanks jimberlake, that's really handy info -

We're hoping to enter the Commer scene fairly shortly :-D

Wow 20mpg to 30 just on a carb change? That's brilliant ! I'll have to tap you up for more info when the time comes.

That kind of makes me wonder what mpg my Stag would have done with the v8, had I swapped from the Strombergs to SUs. Best it got was 26mpg. alas the engine did what they do and is now 'no longer with us'.

I've seen on Triumph forums recently that SU seem to be generally better than Stromberg. there's some resistance to that, but it's a belief which has only just come to light for me.
I'm a triumph Stag (2500s engine) and morris minor man so some bits are common-ish (carbs, overdrive etc) and most principles the same.

Except the vinyl roof on my Sceptre ..
 
SU's all the way, the difference is night and day:)
The alloy heads rotted away because a lot of people put plain water in the cooling system which is bad:( Even on an iron engine alloy will corrode in water ( water pumps, thermostat housing etc), and it doesn't do cast iron much good either. so it's essential that a proper coolant is used
 
I guess my Sceptre must have been a duff one- It was only 12 years old when I got it and the previous owner was quite good with it I think, bless him. It blew 5 times in the end. I learnt a lot while sorting it out, and got so good at replacing the gasket I did it in an (extended) lunch break once.
I was a student at the time and thought I couldn't afford to have the head skimmed. I later found out it's not that expensive. We live and learn !
 
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