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MG Midget and Sprite Technical - Single Carb Conversion

Looking to convert the wife's 1966 1098 midget to a single carb!
It's out of MOT next week so I thought I'd sort a couple of jobs out on it and change the carbs etc??
Been thinking about it for a while and now decided to do it, the only problem is I cannot find a suitable inlet manifold? Loads of Mini ones, but I believe they make the carb stick up to far!??
Anyone got any ideas of where I can get one from please????
Yorkshire based!
Cheers
Bob


BOB FOX

Have you looked in the Archives? It's full of the answers to exactly this question. :). There was a thread very recently I think.

Type in HIF44 conversion in the search box.

Results----

Can you explain something to me?
Changing the starter motor for the first time.
Front wiring loom question
HIF44 Conversion
HIF44 Spring
HIF44 throtle movement?
Manifold Mania
Oselli Torquemaster
SU carb HIF44 conversion
Single HIF44 conversion. Help!!!
Thread: Single HIF44 conversion. Problem Solved
Time to make myself known!!!
Lawrence Slater

An HIF38 would be better on a standard 1098 (and cheaper than a HIF44). The midget manifold, as you say, will mean the top of the dashpot will touch the bonnet. I got a machine shop to wedge the inlet where it bolts to the head. Cost me £40 but if you have a choice of machine shops you could probably do it cheaper.

Titan made one specifically for the Midget but they are rare as hens teeth and consequently, it was easier (and cheaper) for me to use a Mini one and get it wedged.

You will need to factor in a change of needle and air cleaner etc.

Lots more in the archives (as Lawrence pointed out) but the search facility is not easy to use (use the thread titles in Lawrences reply).

Rob
Rob aka MG Moneypit

Maniflow do one specifically for the Midget.
If you get one, let me know how it goes. I am interested in one myself but Maniflow can't provide any evidence of the performance/benefits of it.
Dave
Dave Brown

agree with Rob, an HIF38 would be right for a 1098.
David Smith

Bob

Why are you planning getting rid of the twin 1.25 inch SU carbs?

If you need a single 1.5 inch SU, there may be manifolds from other inline A Series engine applications (Morris Marina, Austin A40 etc). 'Morris Minor Owners' Club forum a good place to ask.

Note HIF carbs have a different fitting, so an HIF38 from a later Mini will not suit a single 1.5 inch SU manifold for an inline A Series engine application (may be some late Morris Itals had single HIF38 carbs, but good luck finding such a car!)

Cheers
Mike
M Wood

HIF is also an SU so an "SU manifold" might be for either.

HIF do have a different bolt pattern to an HS series carb. (4 vs 2)

The Titan's come with the correct throat for a HIF38 and have to be ground out for a 44

Ital was a HIF44, or at least the one I scrapped in '91 was and the carb worked very well 15 years later on a Titan for a 1275. There are several HiF38 on eBay and I wouldn't have thought them that rare. Loads of minis will have used them.
Dean Smith ('73 RWA)

Dean

I was thinking finding a Morris Ital manifold may be tricky, not the HIF carb

Mike
M Wood

Ital manifold was a cast iron lump integral with the exhaust. Even if you hack the exhaust bit of...it sits the carb far too high and the bonnet won't fit.

I tried it :-)

http://www.eatworms.org.uk/mg-midget/projects/75-midget-frontsuspension
Dean Smith ('73 RWA)

Here's one:

http://www.ebay.co.uk/itm/MG-Metro-inlet-manifold-/311287391763?pt=LH_DefaultDomain_3&hash=item487a2ca613

I'll be bidding if it stays at that price!

All you'd need would be the heat shield and cable mounting plate, the spacer, a couple of gaskets, some studs and then attack it with a file if it doesn't clear the bonnet! (Instructions can be found in the archives)

john payne

Dave Brown.
I have the maniflow manifold and, coupled with the HIF44 it's made a huge difference in the overall performance of the car (tuned 1293). It certainly seems to breath easier and pulls well from low revs in all 4 gears. rarely exceed the speed limit (in case any cops read this) but it feels like it has plenty in reserve should I ever need it. Now I'm thinking I need a 5 speed conversion to keep up with the engine's performance.

One thing with the Maniflow - you have to tell them whether or not you want a vacuum advance take-off adding.

Graeme
graeme jackson

Thanks guys, it's the wife's car really and I just play around with it!
I also want to put a slightly bigger stainless exhaust (complete with manifold) on it.
I thought I may as well convert it to a single carb while I was there, so to speak??
Also planning on changing the suspension, front and rear at some time in the future, if not this year certainly next, so I will be back on here for advice on that also.
Seen some good stuff, although quite expensive on the Frontline website.

Thanks again for the help and advice!
Your not a bad lot are you! LOL

Bob
BOB FOX

Does the HIF44 really add power? I thought it gave more torque but less top end.

Anyway, having gone back to a twin HS2 setup, with K&Ns, stub stacks and a 3 branch, as I've said before, I think the engine is punchier with the twins than with a single HI44 with the same accessories.

Out of curiosity. How much do the collective think a well running clean and in very good condition HIF44 complete with manifold would be worth? Maybe I'll sell it.
Lawrence Slater

possibly worn twin SU's can be swapped for a cleaned/refurbed/reconned single carb so there should be improvements
Nigel Atkins

Worn twins, only really cause a problem in balance at tickover. Once the throttles are open, it evens out. And a wide open HIF44 is 1.75", compared to twin HS2's with a combined 2.5". So aren't the twins better performers?

Has anyone compared twins versus a Single HIF44? I looked in Vizard, but he doesn't seem to have done.

No comment on my potential sale offering? What's it worth?
Lawrence Slater

got to be 75 to a ton I'd have thought. Do you have a shiny air filter for it? That would definitely help.
David Smith

Cheers David. Yup, I could muster up a filter. I might bung it in as an extra(100 on the price) as a sweetner for when I sell my Midget.
Lawrence Slater

Lawrence...
"And a wide open HIF44 is 1.75", compared to twin HS2's with a combined 2.5". "

The single 1.75 is going into all 4 cylinders. Due to the way the twin inlet manifold is set up, each pair of cylinders only sees one carb i.e. 1.25.
graeme jackson

...and you're only talking about the diameter, not the area of the venturi.

Cross-sectional area of 2x 1.25" is 2.45", as opposed to 2.40" of 1x 1.75", but as Graeme says, you don't get the full 2.45" with the twins.
Dave O'Neill 2

Edit: the area is in square inches, obviously ;o)
Dave O'Neill 2

Because only one cylinder is inducting at any one time, the twin carb set up has the advantage of feeding one cylinder at a time with a bigger time lag between each; thus the charge has double the amount of time between each induction to change direction. So the area (and thus volume pumped) of the inlet tract is only of interest when the volume is less than that able to be inducted at full revs.

The twin set up with an average manifold is thus much better than a single set up with an average manifold. But if you have a really excellent manifold on a single then you might see benefits.

My 1500's twin 1 1/2 inch SU set up is bog standard, other than needles, seats and my custom filter arrangement, because the standard manifold is pretty good and I'm not after massive high revs on my torquey road engine.

By comparison, a standard A-series manifold for a single carb is not very good (the 'log' type being really bad)so to take advantage of the simplicity of the single set up you'd have to spend money on a really good manifold and various ancillaries to fit the cable, springs, filters and so-on.

If I had an A-series Midget, I'd keep the twin SUs and spend money on a good manifold.
Nick Nakorn

in the worn twins I was thinking in all parts, most of which are doubled up, and including the linkages which are obviously absent from a single

with worn I should have also included damaged and set up incorrectly

it was a very quick post to introduce another line of (as often incomplete from me) thought of old against new(er)
Nigel Atkins

interesting Nick, I assume you are referring to an inlet manifold for the twins on an A engine, if I'm right what manifold would you consider good and worth spending your money on, cheers
Nigel Atkins

If the firing order is 1-3-4-2 then so is the induction stroke. Two revolutions will have induction strokes 1-3-4-2-1-3-4-2 so in a twin carb arrangement front and rear carbs have 2 consecutive induction strokes with a rest of 2 strokes.
With a single carb there are 4 induction strokes with no rest.

Does this make sense or am I talking through my exhaust?

Rob

Rob aka MG Moneypit

Nigel, the Vizard book has a whole section on inlet manifolds but, on the whole, a straight route is good while sharp corners are not. There also needs to be space for the gasses to change direction and thus blunt or curved 'dividers' - hence the use of plenum chambers on some performance cars. What you need for a good manifold is a straight-ish route and soft dividers.

Rob, I think you are right. If 1&2 and 3&4 have a carb per pair then the turn-around is effectively 213421342134 so turns between 2-1 are more problematic than between 1-2; clearly the twin set up doesn't eliminate fast turns all together.
Nick Nakorn

The table below shows the stroke order for the A series.
I = Induction, C = Compression, P = Power, E = Exhaust.

1 2 3 4
I C E P
C P I E
P E C I
E I P C
I C E P
C P I E
P E C I
E I P C
I C E P
C P I E
P E C I
E I P C

In a twin carb setup there are 2 consecutive strokes for both carbs with two consecutive strokes with no induction.

A Single carb setup has 4 equally spaced induction strokes.

In the twin carb setup the two stokes without induction allow the air to slow down (it won't stop immediately due to inertia), then it's got to accelerate again when 2 starts it's induction stroke. So 2 will get slightly less charge than 1 and 3 will get slightly less charge than 4.

In a single carb setup each cylinder will get exactly the same charge.

I conclude, therefore, that a single carb setup will be more efficient.

Feel free to discuss.

Rob
Rob aka MG Moneypit

Rob, you're right about the firing order and your useful above chart. But in a single carb set up the change of direction is problematic for all the induction strokes because the inertia is in the wrong direction at the start of each induction stroke, whereas in the twin set up it is only problematic for some of the time. So the twin is better in my view.
Nick Nakorn

sorry Nick I thought you had one in mind, cheers for info anyway
Nigel Atkins

Nick, yes you are correct. 2 strokes left then 2 strokes right looking into the carb. But the airflow through the venturi is smoother with a single carb but the change in direction throws a spanner in the works.

Why did BMC use 1-3-4-2. It might have been better to do 1-3-2-4 so induction strokes are evened out. It must have been something to do with crank balancing or something.

This is definately a more interesting thread than Urine testing!!!

Rob
Rob aka MG Moneypit

Rob,

The firing order is usually chosen to minimise torsional vibration issues in the crank. I don't really know a lot about it but have heard that this certainly was really specialist work at least before the days of computer modelling and the more cylinders you add into the mix the more complicated it gets.
David Billington

I'm not sure about the physics involved here but I find it interesting that when BL introduced the MG Metro it went for a single HIF44 rather than twin carbs for their performance model. Not conclusive of a better performance but indicative I feel.
Chris Hasluck

Twins don't feed only the pairs in the way suggested. The log connects both pairs of cylinders. It may not be very efficient, but it does have an effect.

Has anyone got a documented test of twin HS2's versus a single HIF44, on a sprite, using any inlet manifold?

What was the mini cooper(s) carb setup? I thought they were twins, not a single.

Nobody taking the piss here Rob. lol.
Lawrence Slater

The Mini Cooper and S used similar 1.25" twin carbs to the Spridget, only mounted at a steeper angle.

When the 1275GT was introduced, BL fitted a single HS4 1.5" carb.
Dave O'Neill 2

Going back to Vizard, he searched high and low for a single carb manifold that performed as was possible and (this is going back many decades) he couldn't find one so designed his own incorporating a semi-plenum; effectively a void joining the pipes near the ports with a specially shaped surface to aid the direction changes we have been discussing. I've never seen one. The log does have the plenum function but all the angles are so acute that the inlet charge flows very badly due to turbulence.
Nick Nakorn

The single is way better in my opinion apart from under bonnet aesthetics!
I think it's particularly telling that BL went down the single route with all the A+ engined cars, I think the benefits are in fuel consumption, performance and longevity, I've never seen a worn out HIF but seen lots of worn out twins.

When I first fitted the single to my sprite it made a massive difference but the old carbs were pretty worn and out of tune. But there was still an improvement when I replaced the recently refurbished (and on a Maniflow manifold) twins on my wife's Midget with another HIF.

The Maniflow steel manifold for the twins did look like a decent bit of kit though.

Out and out performance wise the HIF is amazing on my Sprite. It's the same carb I fitted to the bog standard engine but now it manages to power it to what was about 100bhp at the wheels on Peter B's old rolling road. It starts easily, runs cleanly at low ish revs and still gives better mpg than the worn out twins did!

I don't really look at all the physics behind it all, it just works so I like it!!
john payne

John, I wonder how much of the improvement was due to the carb change and how much to do with the manifold? I suppose too that the 'siamesed' inlet ports on an A-series mean the most rapid direction changes have to happen in the head anyway, as opposed to in the manifold so it might be there's less difference than one might expect. If it's half a dozen of one and six of the other, then a single set up is at least simpler to maintain and keep clean!
Nick Nakorn

My twins are the age of my '66 Sprite, and apart from new jets and needles back in the '80s, have never been rebuilt. It's fair to say they are worn. But my Sprite is faster -- pokier if you like -- and revs more freely with them, than it does with an HIF44.

Yes the HIF uses less petrol. But when I put the twins back on for an experiment in oil sucking, I was quite suprised, and it made me wonder why I ever bothered with the HIF, -- apart from balance at idle. The HIF does power the car nicely, but there is a very noticeable difference with the twins. my HIF btw looked almost new when I took it from an MG metro It still looks new.

Hasn't anyone here had their car on an RR session, with both a set of twins, and immediately after fitting an HIF44?

Was the Mini 1275GT faster than the 1275 Cooper S? Was it only a carb change?
Lawrence Slater

No, the GT was slower. 7BHP and two insurance groups lower.

It also had smaller valves and lower compression.
Dave O'Neill 2

I think someone on here once did a test between the two, can't remember the results though!
Although I think the single is better for around performance and economy, I'd probably stick with the twins on a standard car. By standard I mean looking original under the bonnet. I was never happy with the look of the single HIF on my wife's car.
john payne

Had this on the shelf for a decade or so - no idea where it came from.

Anybody know what it's for?


Nick and Cherry Scoop

Inlets to head are 1¼"
Throat is 1½", grindable to 1¾"
Centre of throat is about 1½" above centre of inlets
Carb mounting angle is 10½ degrees
Nick and Cherry Scoop

Nick

What's the distance between the centres of the inlets?

i.e. is it A-series or B-series?
Dave O'Neill 2

Good point, Dave. It's as near as dammit 6".
Nick and Cherry Scoop

That'll be A-series, then.
Dave O'Neill 2

Moss here in the States has a down draft Weber conversion. Has anyone tried one of these? Might be an option to the HIF 44.

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=37352
Martin Washington

Nick

Looks like:
http://www.maniflow.co.uk/index.php?view=product&from=154&product=1097

Looks like an aftermarket take on an MG Metro water heated inlet manifold.

Cheers
Mike
M Wood

It has a "unique Blenheim chamber" apparently!
Dave O'Neill 2

'Unique Blenheim chamber' - must have had a problem with phlegm stuck in the plenum chamber! Or is that an unusual shaped niche in Churchill's ancestral home?
M Wood

Only two Blenheim Chambers on Google:-
Blenheim Chamber of Commerce, and Dusty - a chamber maid at Blenheim Palace.

I guess this manifold is for the Mini enthusiasts.
Nick and Cherry Scoop

This thread was discussed between 06/02/2015 and 18/02/2015

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.