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MG Midget and Sprite Technical - HIF44 spacer thickness.

Does the thickness of the spacer/insulator for an HIF44 carb have any effect on the fuel mixture atomisation at the valves? I've heard that it does.
I currently have a slim (1/2inch) spacer. Would a thicker one be more efficient?

Bernie.
b higginson

Anyone? Is the distance from the jet to the valve head critcal? If so, which is the optimum thickness of spacer, as this would alter that distance?

Bernie.
b higginson

Bernie,

Have you seen David Visard's book on the a-series.There is a whole chapter on inlet manifods,quite a bit using a single SU.

Pete
P J Vass

The general consensus is that a longer inlet is more benificial.
And preferably on the manifold side, though long trumpets certainly wont do any harm ( if they are the proper full radius type)

So the thicker the spacer the better!
Onno K

The spacer also acts as a thermal barrier to keep the carb temp down. But the spacer on mine is quite slim. I think the limitation on thickness is to do with clearance between the air filter and the inner wing.


Guy

There would be room for a thicker one on my car and still clear the inner wing. Not got Vizard's book, but I'm going to the mg spares day at Stoneleigh on Sunday, so maybe I will be able to get a copy there. They are available on eBay at around £17 to £20 and also I'd like to get Daniel's book on the subject. If I see a thicker spacer I'll get that too, then I can do back to back comparisons.

Bernie.
b higginson

Re Vizard book:

or new from Amazon for £16.50 with free post

http://www.amazon.co.uk/Tuning-Engine-Definitive-Performance-Economy/dp/1859606202/ref=ntt_at_ep_dpt_1
Doug Plumb

Though it will be more efficient I doubt you will feel the difference
Onno K

Vizard says.

On the standard BL Metro manifold (Single HIF44) ---

On a tuned engine, increasing the thickness of the spacer, will make a difference. If the engine is 70-80hp or more, using two or 3 spacers to lengthen the induction tract will help.

He also says, that a gain in efficiency/hp, by a little shaping of the spacer/manifold throat into a radius, would be improved by using thicker spacers.

He doesn't mention much more about the spacers other than that. So not sure it's worth you buying the book for a small diagram, and a hundred or so words.

Not sure if I should scan and post the exact wording here, but I could send it to you in an email if you like.
Lawrence Slater

Lawrence
Have you read the rest of the book????
Off course it is worth buying!!
Onno K

Onno. Yes I have !!!!!!!!!!!!!!!!!!!!

And I stand by what I said. So not sure it's worth you buying the book for a small diagram, and a hundred or so words.

Clearly for people like Onno, I should have added, "unless you are also interested in the rest of the book, in which case it's worth the money"

Happy Onno????

Lawrence Slater

The book is worth buying for every one with only the slightest intrest in internal combustion engines.
So no Lawrence your last comment would not do ;P
Onno K

Hi Onno

I think Lawrence is just being very case specific for Bernie on this one subject and not knocking the whole book.

The single Metro inlet manifold works well as long as it is left rough. The Factory tends to go for a broad spectrum of performance ability from idle upwards. re-inventing the wheel can have disasterous consequences.

As Guy says the vital job is a thermal barrier.

Bernie....get a few dozen different spacers ( dont forget to get increasing studs too) come down to the rollers, have a free day and we will see if it builds up a picture to post on the threads.

Peter
Peter Burgess Tuning

Wow Bernie! Now THATS an offer you cannot refuse !
Guy

I used 2 spacers with my HS6 to increase the volume of the plenum and move the back of the plenum further away from the open butterfly. I bought 4 allen bolts with the correct fine thread on one end, and cut the allen drive of the end and cut the appropriate coase thread.

Maybe around 1 to 2 hours work; with the expense (very small!) and the effort (also small!).

I'm a big believer in increasing torque by improving the small things...

A
Anthony Cutler

Thankyou Peter, for understanding what Onno doesn't :).
Lawrence Slater

Lawrence
Always funny when the joker does not realise when he is part of the joke.....
Onno K

Don't give up the day job Onno, you'd starve, coz you certainly aint funny. :)
Lawrence Slater

Bernie that has to be the best Valentines day offer you'll get today.



OK

second best

:).
Bill1

Guy,
(sorry to butt in Bernie)
You photo looks like you're using your K&N twin SU cast oval filter casing with your hif. If so did you make up a new blackplate? Any chance of a look with the cover off. I don't suppose you made a template?
I'm still to get round to do my hif conversion, having accumulated all the bits other than an air filter and if I can adapt my K&N cast filter then so much the better (i.e. cheaper!)

Matthew
Matt1275Bucks

Spot on Matt!
Previously I had twin SUs which I rather liked, if only for the look of them. Eventually I decided that for the sake of an extra 10mpg I should change to the single HIF 44. I used the twin-hole backplate as a template and cut a replacement from some 1/8" ally plate that I happened to have (old bus-stop sign). Then I used the carb to mark out the holes and drilled/cut/filed to fit. (don't forget to drill the air balance holes as well!) Inside there is room for a bell-mouth trumpet. I will see if I can get a decent photo with the front off, but it is pretty simple really.

I thought someone was going to pick me up on the plumbing/ lack of it to my Titan manifold. Answer: work in progress. At that stage it was still working with the chrome pipe seen in the background. The HIF44 was £5 from the local scrappie. The Titan bought from someone via the BBS but I cannot remember who. I know the price was a lot more reasonable than is often asked for them these days!
Guy

Sorry for not coming back sooner, I was away on a Valentine's night do in a hotel catching up with old freinds. I tried to post on my not so smart Blackberry, but it would go so far then implode, so I had to wait till I got home today.

Peter, thank you for your incredibly kind offer, I'll certainly take you up on it. I'll email you off thread to arrange it.

Lawrence. I think you may fall foul of copyright law if you reproduce anything without permission, but thanks for the offer. I've been meaning to get the book anyway, knowledge for knowledge's sake and all that, so it won't be a waste.

Bill. At my age, it IS the best offer I'm likely to get. LOL.

Anthony. What results did you get?

Thanks again chaps.

Bernie.

b higginson

Bernie, even if you don't read the book all the way through, and I would just for the read, as it's a good one, you can use it as a mouse mat. I do. :)

Matt,
I also used a K&N filter, from my twin HS2 setup. It's not as elegant as guys solution, but seems to work very well. Actually mine is one of the pair of single round KN air filters. There doesn't seem to be much difference between the size of the filter for the HS6/HIF44 and the HS2. So I just made up a round back plate to fit the HIF44, and bolted it together. I've tried it without the front cover to see if the HS2 KN filter is restricting flow, and it doesn't seem to be. When I find a cheap 2nd hand HS6/HIF44 on sale, I'll do the proper job, and sell my pair of HS2 K&Ns. But for now I'm happy.
Lawrence Slater

Guy
I would not plumb it in.
I have seen several who rotted through...
And it will cost power and only give a slight economy gain.
Onno K

I've just fitted a Titan manifold with an HIF44 to my car and I don't intend to plumb it to the water circuit for the reasons Onno mentions. Kim at Magic midget sold me a fancy red ITG filter for the carb. It's quite large and actually touches the underside of the bonnet when the lid is closed, but as its all plastic I don't think that will matter.

Oh, and I have a thickish spacer between the manifold and the carb.
Mike Howlett

I read a solution, -- somewhere but can't think where ---, to the corrosion issue of plumbing the manifold in. It involves a liner of some kind. Apparently the resultant reduced bore doesn't restrict the flow of coolant enough to matter.
Lawrence Slater

My Titan is plumbed in

not rotten yet


:-)

I shouldn't think plumbing it through a smaller diameter pipe would affect the heater much though and running the right mix of anti-freeze should stop it from rotting

I'd be amazed if de-plumbing it would give me any better MPG than I already get
Bill1

Bill

You are right plumbed it does give marginal better MPG but unplumbed it gives (slightly) better power.

The pipe heats the manifold it does not cool it.
And according to the laws of physic a cooler intake charge holds more mix and creates a bigger bang.

The rotten ones where run with a good mix of anti-freeze...
Onno K

That photo of my HIF44 and Titan is around 5 years ago. It only stayed like that for a week or two and has been plumbed in since then. I'm quite happy with it - although it isn't quite as clean and sparkely as it was then!
Guy

Onno, you are quite right there is a better MPG against power return but I am happy enough with a Midget that has been measured to do 113mph, uphill.

And gives me about 50 to an Imperial gallon ish.
Bill1

That sounds good Bill. Wanna build me an engine like yours? :)
Lawrence Slater

Guy,
Many thanks for the info. I take it you just folded the sides of your ally plate in a vice or similar to give you the retaining lips for the filter?

Matthew
Matt1275Bucks

Matt,

Given that you're making the filter retaining plates from aluminium, ideally a soft grade, it's quite easy to form the whole filter shape with a flange using a pattern to beat the material over. Make the main former that the part will be beat around out of a piece of steel, ali, or a good hardwood, and make the piece to clamp the plate out of any reasonably stout crap like the odd bit of kitchen countertop. Cut the material about 8mm or so larger than the shape and clamp the material between the formers and hammer around the exposed flange. You want to use a soft face mallet, such as rawhide, or a wooden block between a hammer and the workpiece. Working repeatadly around the piece and you should quickly form the flange.
David Billington

The front and back plates on my K & N filter housing are only flanged along the top and bottom long straight edges, not around the curved ends. It was therefore a very easy job to fold over a lip with the plate held between a couple of bits of angle iron in the vice. No need to make up a template. You can see where the lip edge ends just before the start of the curved bit in the photo.
Guy

Thanks chaps,
I'll just keep my eyes open for a old bus stop sign! I'll be up in the lakes at Easter Guy so if the number 66 fails to stop where you expect it you'll know I've been busy!
I presume having such a big filter area and box for a single carb is no bad thing and I'll get me one of those shiny ally domed rams that were discussed here amonth or two ago.
Matt1275Bucks

Yeah, you need a ram pipe inside the filter. I have a very smooth looking one in my big ITG.
Mike Howlett

This seems to be a very popular conversion,fitted a Titan Manifold & Hif Carb today, have just ordered new choke & acc cable as old choke cable not long enough & old acc cable badly frayed,found an interesting article on google,giving details of how to plumb in,reccomends MG Metro acc cable & Minor 1000 Choke cable, Does this seem ok to all those who have done this conversion? Paul


p kiely

I've reactivated this thread to post the results of my day with Peter Burgess.
To cut a long story short, on my engine (1133cc) it made no difference at all how thick the spacer was. There was no net gain in BHP or Torque. Peter played with ignition timing, different needles, different plugs, all to no avail.
I think that the claims that Mr Vizard makes for a longer inlet tract applies to much larger capacity and more highly tuned engines than mine and more so with Weber carburettors.
So I'm now back to the 1/2" spacer I started with.
BTW. On the way back from Peter's I blew my head gasket. Ho Hum.

Bernie.
b higginson

Sorry to hear about HGF

that's one of the 'joys' of ownership one step forward and three back :(
Nigel Atkins

rotten news Bernie

:(

but very good research
Bill1

Bernie's carbie sports a most wonderful K&N radiused plate, messing about in later runs we tried the power with the plate off, just an open mouth to the carb. No difference in power at all. At first this seems to fly in the face of flow theory, however, I have seen 105 at the wheels with a single HIF44 so is it surprising the radius plate is unecessary with around 50 at the wheels with less air required for the bhp?

Peter
Peter Burgess Tuning

Bernie

On a RR, you're mostly tuning for best torque/power at WOT - with the butterfly horizontal; in this state, the air past the 'fly meets a nice round divider at the far end (not very far in fact, just a few mm!) which allows the air/fuel to flow down either runner according to suction with (hopefully) minimum turbulence. The trailing edge of the 'fly projects significantly beyond the carb face into the manifold's (very small) plenum.

Let's say you're now on 1/2 throttle (maybe 3/4 plus power potential?) - the butterfly is at ~45 degrees, and the fuel/air mix is now deflected by the 'fly to the bottom (IIRC - need to check which way the cable pulls..) of the plenum which is likely closer to the edge of the 'fly and which also presents a more restrictive x-sectional area. This will cause turbulence and potential loss of torque.

An extra spacer will help this condition.

So my suggestion is that an extra spacer have bigger effect when throttle is 1/4 to 3/4 open - the sort of thing that makes an engine feel 'lively'.

The effect with WOT will depend on how carefully you've sculptured the small plenum for best flow. (I opened mine up considerably and made a nice blunted-round air-flow 'divider'.)

A
Anthony Cutler

What an absolutely refreshing and honest thread well done Bernie, and great stuff from Peter.

For many many years I have mostly ignored these claims of vizarding carbs and stub stacks per se and all these as I call then "gimmicks" that lead to huge power increases.

I welcome the comment from Peter
""No difference in power at all. At first this seems to fly in the face of flow theory, however, I have seen 105 at the wheels with a single HIF44 so is it surprising the radius plate is unecessary with around 50 at the wheels with less air required for the bhp?""

Of course that is exactly right as is the same with the extremely slight benefit that may be gained from vizarding the carb.

Actually what all that means is that you need to find out what the "restriction" to power is before you know what can cure it. If the restriction is not the diameter of the carb throat and it is actually the size of the port and inlet valve then making the carb throat more efficient will gain almost nothing.

If the cylinder head was big enough then the carb could potentially be a restriction and in those cases vizarding the carb would be advantageous, however simply bunging on a slightly bigger carb would sort the problem 10 fold!!

All these extremely small power tweeks are necessary in motor sport where there are restrictions on equipment used and engines are run continually at FULL throttle, but on road cars I have to question their benefit, especially considering the percentage of time spent at full throttle?
Nice one Peter.

Bob Turbo Midget England

I swapped from a twin HS2 setup with KN filters and stubstacks, to a single HIF44, with one of the HS2 KN filters, and no stubstack. I have a PBurgess fast road head, and it goes very well. My feeling is that it would be a waste of money to add a stubstack and bigger filter, which is pretty much what Rob is saying, so I've left it as is,

However reading Vizard suggests that I should add an HIFF44 filter and a stubstack. But I haven't read it closely enough to see if the effects are only at full throttle. From what Peter says, they are, and as you say, that's not a common occurence on the road.

But if I've understood this properly, Anthony is saying that Vizarding is far more noticeable at part throttle, and is is worthwile.

So which is it?

Lawrence Slater

Hi Lawrence

Unless you are in the region of bhp that will push the flow capabilities of the carb then you will not gain with K&N filters on n HIF44. Standard filter casings tend to be restricive on small carbs (1 1/4 A series, 1 1/2 MGB and gains can be achieved with K&N and stub stacks.
If you do not run a radiused plate to the carb entrance, flow will be interrupted and may have the effect of improving fuel atomisation at low throttle openings.

Anthony

Your idea of a plenum chamber may allow fuel to drop out due to the increased distance jet to valve allowing partial pressure recovery with commensurate lowering of ability of air to retain fine fuel droplets. Personally I would be surprised to see something happen either way with a slight increase in the distance from the carb to the siamesed section of the inlet manifold. The type of flow is turbulent or fully developed in engines.
Peter Burgess Tuning

Hi Peter

I'm more concerned with the effect of shrouding due to the proximity of the 'fly with the very small plenum at less than WOT.

A
Anthony Cutler

How did you measure the difference you made when you altered the spacer distance or plenum? Surely a heated manifold would be of greater interest if you are only trying to achieve better part throttle fuelling? Again, if you expand into a large space after the butterfly you will encourage fuel separation. If you expand into the standard rough manifold the close proximity to the manifold wall will give good mixing with the boundary layer conditions.

Peter
Peter Burgess Tuning

Took the head off. Gasket blown between three and four. I checked both the head and block with a straight edge and both seem OK so I put it all back together, but this time I used some stuff called Wellseal. I believe Rolls Royce use it and a couple of guys near me, one of whom builds race engines, won't fit a head without it. Any comments?
After I had retorqued the head hot, I did a compression test and got 180/180/190/175 so it looks like I've got some leaky valves. I think Peter will be getting my head next Winter to work his magic on it. I'll just keep the revs down over the Summer.

Bernie.
b higginson

Glad it wasnt terminal.

Peter
Peter Burgess Tuning

Unless it's your rings Bernie.

More than just used by RR.

"Developed by Rolls Royce Ltd and manufactured under license, this compound is the complete answer to sealing problems on machined faces. Stag Wellseal jointing compound is non-flammable, has easy partability and is non-hardening it is formulated to give the best possible sealing performance under a wide variety of conditions.

It can be used to seal threaded connections as well as flat- faced joints and can be used with or without a gasket, depending upon the design of the assembly.

Wellseal will withstand temperatures up to 195?C (383?F)

Did you apply it both sides of the hg, or only on the block?

Will it stand the compression I suppose is the big question.
Lawrence Slater

Hi Lawrence

We have used Wellseal on the metal part of head gaskets for over 20 years, it is our insurance policy for head gaskets. I also think Wellseal helps the gasket settle into place as it is torqued down.

Peter
Peter Burgess Tuning

Excellent Peter, I'll give it a try myslef next hg I do.

Cheers.
Lawrence Slater

Lawrence. I hope it's not rings. They've only been in for 6000 odd miles.
I painted the Wellseal onto the block and onto the head, fitted the gasket and torqued it up cold ran it up to temp and retorqued it hot. So I'll see how it goes this Summer.

Bernie.
b higginson

Thanks Bernie.

I'll try that on the 3/4 area when I rebuild the spare engine this spring/summer or at least this year sometime.
Lawrence Slater

This thread was discussed between 12/02/2012 and 13/03/2012

MG Midget and Sprite Technical index

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