getting better mpg from Daimler straight 6

Acc0rd

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Hopefully someone might be able to offer advice, or point me to another forum, I want to improve mpg, here goes ...

I have a 1952 Daimler Consort. It has a 2.5 litre straight 6 petrol engine. The head is not a cross-flow i.e. the inlet and exhaust ports are on the same side, with push-rods up the other side, so I cannot fit a cross-flow head (even if a straight swap existed).

It has a single SU carb. It is 70 bhp at max rpm of just over 4000, but even at only 50mph it only returns around 20mpg !!!!

I don't want to increase power, but I want to improve mpg. Obviously I could swap the engine and gearbox for a RWD diesel, but that would be drastic. However, I don't mind changing the exhaust, and/or the inlet manifold.

Someone suggested to me that fitting individual carbs would help (eg motorbike carbs), if that means having 6 inlets and setting up 6 carbs, I am prepared to go that far. Does anyone know if this has been done on cars of the 50's and 60's to improve mpg, and where to start looking ?

I know that I can also go down the LPG route, but I was also told by the same person that it is best to set up individual carbs first, any advice on this too ?
 

obi_waynne

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Has the carb been thoroughly cleaned and serviced? I would probably just go with a twin carb setup, 6 would be a nightmare to balance. More power can actually mean better economy if the engine is running more efficiently and providing you don't drive it in such a way as to use the extra performance.

It would also be worth leaning up the mixture a little and advancing the timing very slightly, a good old school tuner can sort this for you.

I think the big problem with these cars is the weight they are carrying around, can you reduce the weight at all? Take out the spare wheel for starters and carry a can of tyre repair gunk instead.
 

Loz

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I can't see six carbs being more efficient if anything it might be worse imo. What about converting her to fuel injection?
May be you could borrow the injections gubbins from a BMW straight 6? The only downside I suppose is that you'll need an programmable ECU & loom, which could prove expensive.
 

SLEEPER

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I think that 20mpg is not bad at all and pretty much what you should expect from a seriously heavy car with an outdated engine . (please note thats not to say its a bad car just an old one)
Cars of that age and size just didnt do 30mpg I had a Mk10 jag that did no more than 10mpg !

Normally Id say fit a later engine but I dont think the later 6 cylinder jags were much better
 

Yugguy

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It probably weighs a hell of a lot too, they used proper metal back then. You could look at ways to lighten it without having to change too much. For instance a gel battery will weigh half that of a normal one.
 

Acc0rd

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It weighs one and a half tons. It has cross ply tyres too.

Obviously a diesel with gearbox from a RWD car would be more efficient, the problem is that these old engines are justincredicbly inefficient.

I did strip the engine down and rebuild it 25 years ago, and I think it is time to do it again.

Just wondering what I could do to improve the efficiency. You're probably right about 6 carbs, sounds a nightmare. I hadn't thought about EFI, but yes it would be interesting to fit injection and get a programmable ECU. It could be fun programming it, hell an engine like that is not going to sufferbadly while I experiment with it.

Obviously the ECU will need an rpm sensor, but would it need a lambda sensor, and what else ? Which programmable ECU (cheapest and simplest) ?
 

Acc0rd

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Thanks for the links, and yes maybe I will start to put pics here. I am a member of the DLOC (Daimler and Lanchester Owners Club) but I thought (and have found) that there would be more useful info about my topic on this forum ...after I had discovered this "pre 1980" section.

I have had the car since 1974, the body is nowhere near mint, but the chassis etc is, because in the 1970's I stripped it all down (apart from taking the body off) and used rust inhibitor etc on the chassis and suspension.

I think that the reason the engine is so inefficient is not only because it is not a cross-flow head (with only one inlet and one exhaust vale per cyl), but it has a low compression ratio of 7:1. When I got it in 1974, I used to put 2 star petrol in it, which was cheaper than 4 star, and was OK for such a low compression ratio. Bore x stroke = 2.74 in x 4.35 in.

If I had the head skimmed a bit to increase the compression ratio, would that help improve effficiency ?

I will not be doing that to start with, my plans at the moment are:
(a) get the valve guides done
(b) get new liners made and new piston rings
(c) fit an electric fan (fan presently driven by engine)
(d) as proposed here, look into fitting EFI and also control the spark timing from the ECU.

If I keep the compression ratio low at 7:1 for the time being, I am unlikely to cause any damage when tinkering with ECU maps ....I guess ??

My goal, if achievable, is 30mpg. Then maybe do an LPG conversion, and maybe change the compression ratio (I also have a spare head and spare block).
 

SLEEPER

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with a standard body and engine I cant see that 30mpg is acheivable , 25 would be something special.

Best bet I would say isnt to skim the head but instead polishing and matching all the ports should help. Maybe the manifold as well as on an engine that old the gas flow will be rubbish .
Also getting a modern or more accurately a more modern carb could help as well.

Re ECU I doubt it will help because the engine is just too inefficient to benefit and fitting one would be a pain - how is it going to get the info a modern ecu needs.

The above isnt meant to be neagative more realistic so best of luck
 

Acc0rd

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Hey don't worry about the post, I read it as realistic.

From a link that Loz put, the sensors can be bought and I can fit them. But yeah if I'm not going to get 30mpg then it's a no brainer .... stick a RWD diesel and gearbox in .... will be cheaper and simpler.

Though I must admit, I never thought of fitting EFI to it, and even if it didn't get me anywhere it would be fun to do on a solid old engine like that !!

So overview of rebuild will now be:
(a) get the valve guides done
(b) get new liners made and new piston rings
(c) fit an electric fan (fan presently driven by engine)
(d) fit a better inlet manifild and carb(s)
 
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thexav

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A 3 or 5 angle valve job will really help boost your mpg as well. Look into high compression pistons as well, if the ECU comes with a knock sensor it should be perfectly safe to run at higher compression.

A thermostat change to run the car a bit hotter than normal also keeps things working efficiently.

Some reading material in here about MPG tuning....
http://www.torquecars.com/tuning/tuning-mpg.php
 

Yugguy

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Wish i could help more, but the oldest daimler I have experience with is my Dad's 1987 Daimler 3.6, XJ40.

It has an issue with the charcoal canister being blocked which affected the running but I doubt very much yours would have such a thing.
 

Acc0rd

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Thanks for the further info. I've now read the thread posted by Xavier. Not sure what a 3 or 5 angle valve is (I could hazard a guess).

Apart from doing the major work required (a,b,c in my list), the inlet manifold has to be the main "joke".

I already took the head off in the summer, and here are the head, and inlet manifold in all its ingloriousness.
DSCF0509.jpg


By today's standards, this inlet manifold has to be "well we need to get some petrol vapour hovering near the inlet port when it opens, and the end cylinders are just for show really".
DSCF0513.jpg
 
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SLEEPER

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As you can see there is so much "meat" on the metal you could enlarge/match the holes by loads without it being near to cracking.

If you line them up and you will probably find that the flow isnt at all smooth .
Ive lnown manifolds on old cars out by as much as 20% from the head
 

Acc0rd

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Also, it just seems to be an enlarged version of what you'd see as a manifold for the water circulation in old central heating i.e. no desgin principles of gas flow, just a "manifold" for supporting an SU carb and hoping that the fuel mixture finds its way along the manifold ...bearing in mind as wel that in those days petrol and oil were as cheap as tap water is today.

As well as porting, it just seems to need piping of equal lengths to each port.

Would it be worth just abandoning this inlet manifold (which is why someone once suggested 6 motorcycle carbs to me) ?
Seems there are a few arrangements for me, to port and get flow of equal lengths:
1. Adapt some other more modern equal lenght 6 cylinder manifold if I can find one with a similar staggered layout (very doubful).
2. They did do a Barker Special Sports with twin carbs but I've never seen under the bonnet of one and I doubt if it is more than the same with just 2 carbs shoved on somehow. I cannot see how twin carbs worked efficiently on a 6 cylinder.
3. Make 3 manifolds (triple carbs), one for the central pair, one for the outer pair, and one for the "middle" pair ?
4. Finally the 6 separate carbs principle with 6 equal length pipes ... but go the EFI journey instead (more fun setting up ECU maps) ?
 

SLEEPER

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Quite a few of the sports versions of older cars 6 cylinder had twin carbs . It seemed that one big carb didnt work that well .
I think that making a new manifold is a serious amount of work whether its for 2 , 3 or 6 carbs
Maybe another model (or make ) had the same engine with a better set up inc a different head and/or block or even engine.
The daimler conquest which replaced the cosort had a very similsr engine with an alloy head for example - its quite possible the engine would drop straight in

Its far easier and usually cheaper to do a swop than make something new

With projects like this it is so easy to forget what option you have.
.
 
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Acc0rd

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Yeah I know what you mean.

On the basis of swaps, I might as well transplant another RWD engine/gearbox which would not be difficult as there is a massive amount of space in the engine bay (and I mean massive). That would only mean jigging about with engine mounts and prop shaft. This would make the car more useable, but it would no longer be "original".

The point is that the chassis and engine of this Daimler is known as the "DB18", which dates back to 1938. If I do not do an engine swap, then it is my intention to strip the existing engine down completely and spend a lot of time rebuliding it properly, probably going to the expense of new cyclinder liners (rather than rebore and then expense of new pistons).

If I go down that route, then I would then want to have the seats recovered and other interior restorations. Once I have done all that work, changing the inlet manifold would be a small compromise to "modernise" the engine performance while keeping everything else original.

My goal is to keep the car as original as possible, but somehow improve mpg on what is basically a very conservative 1938 engine design. If that is an impossible goal, then I should forget originality and swap the engine/gearbox.
 

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