There is a lot of discussion around the best intake systems. Some people go for total flow capacity for peak power. Others chase torque and some try for a compromise.

If we look at race engines, they typically have large diameter, short length intake runners as they are chasing peak power. If we look at road cars very long and narrow diameter runners are used for high flow speed, good mixing and excellent torque at the expense of high RPM flow. Look at many new cars and their plastic intake runners would be 400mm long. Many modern manifolds have dual lengths to mix & match.

Visard's book details how long inlets can add torque to a mini and I have tried this and it really does work. The Doc has researched intake manifolds for minis and found that long, straight, high flow, large volume manifolds are the best but has said that some have excessively large diameters.

People have criticised some heads or port-jobs are being too large in the ports so I guess the same is true for intake systems. Too large diameter is bad. Too small diameter is bad. The same is discussed for Weber carbs with the 45 said to be too big and often choked at just 38mm.

For a mini getting a really long intake 'runner' length is hard because it either has to go through the firewall (or grille for cross-flow heads) or it has to have bends but bends are bad if too tight.

My earlier design of EFI intake manifold for a 5-port mini head had runners of about 300mm total length and a diameter that started at 41mm ID and reduced to 38mm ID. This was a complex design that was hard to make (ie beyond my skill level ). There were only 2 runners of course and for a period there is some valve overlap.

I am currently trying to work out an intake system for a cross-flow 7-port Pierce head. There aren't many options for long intake runners unless they are curved. If they are curved, the smaller ID tubes have tighter bends. If I go for small diameter runners I can get good length. If I go for large runners I'll get very short length, perhaps as low as 50mm. Now I don't fancy making more than one intake manifold! So I'm hoping for learned advice from others. Note it is a single throttle set-up, not a quad, so there'll be a plenum to fit too.

The ports on the Pierce head are 40mm diameter at the manifold face and quickly reduce down as they approach the valve.

What would people consider to be the ideal combination of intake runner length and inside diameter for a 1275 engine reving to about 6300 (ie not a $$$$ race motor) and primarily for street driving???

I haven't decided whether to put the head on the mini or the moke. The moke will have stacks of room but the roundy is a design challenge!

M

Since this will be an EFI manifold and you don't have to worry about fuel separation due to bends (assuming you will be pointing your injectors down the port), then you can have a reasonably tight bend without too much loss. There will be some pressure drop and flow reduction due to the bends, but you have to have some compromise to fit it in the "package" to quote Matt Read.

Have a look at similar sized modern engines with similar mass flow characteristics.

Or going off my weber manifold, somewhere between 5 and 6 inches long and 36mm diameter would do your hypothetical engine nicely. 36mm seemed to be a key number as my weber chokes, manifold, port all seem to be this diameter. Could GR have been on to something there?

cheers
michael

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the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

Thank Michael, 36mm is smaller that I expected but thinking about it probably right. With stock tube sizes being what they are, 38mm may be the go. I'll go ask the local ricer fabricator what he can do me mandrel bends in alloy for. Or maybe I'll just give him a drawing and get him to make the manifold. My last attempt was less than perfect.

It probably could be argued that there is not much point in going too much larger than the intake valve.

aye

_________________
the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

I dunno, if the aim is to reduce pressure drop then there would be a good argument for going larger. Pressure drop across restrictions are all additive, not set by the biggest one.

Anyway, it's all looking academic. I have spent some time this weekend working out what will fit and the answer is bugger all!! The distance between the Pierce manifold flange and the inside of a roundy bonnet is just longer than then length of a 45DCOE or about 130mm. The options look like:

Weber carby --> Zero room for a filter or stub stack so cut bonnet and ugliness.

Weber replacement throttle body. Some are shorter than the Weber http://www.compsystems.com.au/images/st ... TS_bbw.gif
These could be used with ram stacks and filter socks. Not cheap though. The fuel rail may still clash with the bonnet.

Single throttle intake with plenum --> very short straight runners about 40mm long into plenum directly in front of head. Simple plenum to build

Single throttle intake with plenum --> short 90 degree bent down runners about 120mm long into plenum sitting low, just above the dissy. This would give better runner length but the plenum needs to be a Z shape to get the throttle body back up over the gearbox. It would be very fiddly to build.

I am working on drawing up one or two concepts and will post pics when there is something to see.

M

Ok I have some progress pics. I have had the set-up on the bench to measure. I don't actually have a car with the engine in the bay to measure off so it has been a bit hit & miss.



That got me sketching. Here is a comparison between Moke and Roundy engine bays. The head's mounting face is the left edge of the carboard. To the right is the grille. The black on the left is the plenum mounting flange.

Moke is about 20mm longer and much higher. Some sketches of plenum location options blue for Moke and red for roundy. I think Clubby engine bays are 80mm longer than roundy and as high as a Mokes so they are easy peasy.



Then I knocked up the simplest one in Inventor. It has been years since I drove Inventor so it has been clumsy progress. Of course this design doesn't yet have the radiussed inlets to the runners but it is just to show what may fit. It isn't pretty with very short runners and small diameter plenum. Fine for a forced induction set-up though

To get the fuel rail to clear the bonnet (maybe) I have pushed the injectors as close to the head as possible. That means the red part has to mate to the head using the bottom Weber mount studs and two new studs between the inlets. Throttle body flange is just a mock-up. It doesn't represent the actual throttle.

This first image shows the approximate bonnet and bonnet slam panel positions. Very ugly around the fuel rail area.






I'll try to have a go at a Moke high rider plenum tomorrow and maybe a roundy long-runner-low-plenum some time soon.


M

I've had some time to do more sketching today. Here is a layout of a much longer set of inlet runners. The plenum box is a bit rough around where it lines up to the throttle body but I couldn't be bothered making it pretty. It is all about whether the runners fit in and if the spark plugs and mounting nuts can be accessed. It looks ok but the top of the plenum may clash with the bonnet catch mechanism. Also, it may hit the headlight bucket of a Moke. More work to do.

These runners would be about the same length as the total of a Weber and trumpets/socks inside a clubby.









Next is to do a similar arrangement but with all pipes pointing down and across. It will need a plenum with a goose-neck to get the throttle body back up.

M

What about something like this? (its an elder 8 port, but perhaps the basic idea could work?)



More images and info here about it:http://www.starchak.ca/8port/efi.htm

I'm trying to work out what to use on my 7 port too. Tossing up between a set of gsxr quad throttles off ebay or something like the above.

Andrew

Thanks for that. There are a few things I'll have that are different. I would like to keep the stock alternator position/size which would push #1 runner to the gearbox end more. I'd like to keep the distributor as my plan is to make a hybrid dizzy to use the Mazda CAS from an MX5. (this is part of my cheapo EFI plan that has me using an MX5 programmable ECU and all the engine bits from an MX5) That really stuffs up the height. That head has the inlet ports at the same height as the ports on a 5-port. The Pierce head has the inlets raised up and out towards the grille to provide the DCOE flange pattern. That make the fuel rail higher towards the bonnet.

I will have a crack at something like that though.

M

Can you put the injectors under the inlet tube to keep the fuel rail much lower?
You'd have to angle then slightly away from the spak plugs though.

I looked at that. The issues I had were that the injectors had to be at strange angles to avoid the plugs and leads and the spray pattern would all be on the roof of the port. Top mounting the injectors let's them point down the ports and allows a straight fuel rail. I found from my last attempt that the rail was as hard to make as the manifold. I am actually hoping to use MX5 fuel rail as it has 4 by 90mm injector spacing and the pierce head has 90, 93, 90. Another part I can get from the wrecker and not have to make.

hey Mark,,, you`re doing an absolutely fabulous job i reckon,,, well done man

but,,, can you come around here , bring that program with you & teach me how to use it???



please?



i`ll shout the drinkies & feed you

it`s not the program that the boys use with the CNC machine but it may give me some time to play with it at home & get items designed close enough to allow less time at the machine shop,,, if i can help it

_________________
No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

or--->

_________________
No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

just need to adjust the tappets....

ahhh.....

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Planet Earth is blue and there's nothing I can do...



“A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster.” - Jeremy Clarkson