custom inlet manafold
Turbo Mini Forums

happy new year every one, i start'd making the flanges for all my manafolds today but i still feel i need more information on the inlet manafold and plenum. My plan for the inlet manifold is a piece of tube running inline with the head (act as a mixing chamber) and two more conecting to the ports. Can anyone see anything wrong with this and are there any senser's or hoses i need to allow for? The other thing im still planing is the plenum chamber. I remember reading a topic that stated a percentage of the engine capacity is the rite volume for the plenum, i've also heard the larger the better? Also what is the function of the restriction ring, im guessing so there is a preassure difference between the plenum and the fuel bowl, does this ring restrict the throat of the carbie? sorry one more question, are the three smaller holes above the throat open to the plenum? Even a picture of the face of the plenum would be extreemly helpful!

Any help is greatly appreciated, i've never actually seen a turbo mini apart from on this site.....fukin australia, lol

998 turbo

your plan for the inlet manifold sounds about right, im no expert on these factors, but youve basically described the original metty turbo one. Take offs depend on what else you are running, ie servo, dump valve etc......

PLenum wise, have a good read of td's thread about fabricating a plenum chamber, and bear in mind that there are people on this site who have forgotten more about these cars than most will ever know.... theyve also tried eveything and found out what doesnt work by experience, rather than just being told it doesnt work........ i personally have no idea about plenums, but i would pretty much take a lot of that thread as gospel!!!

There are a few photos of plenums on that thread, but if you dont find what you need, then drop me a pm with what you need and your email addy and i will be more than happpy to pop down the garage with the digi cam..... will only take me a couple of secs. (today only..... im happy to take them any time, but im away for a week after today-work-great!)

Pete

And on the 7th day........... God created turbochargers!

great, thanks a stack, i might pm you in a week or so, making these manafolds should ceep me ocupied untill then

998 turbo

If you used a well flowing inlet (not that there is that much space). What would REALLY happen? I have heard the rumours, but I'm not convinced.

Bugger off, I'm getting there.

Concerning the stock inlet. On mine, the ring that faces the head is "higher" so to speak than the manifold floor. This is B A D !
Has anyone modified this in any way? I was thinking of having the floor on the intake runner welded up, and then ported so that everything is neat and flat.

Do you guys use those rings?? As far as I see, there is no downside using these.

Edited by Vegard on 3rd Jan, 2005.

i'm "guessing" the result would be more power. I live in australia and i havnt ever actualy seen a metro turbo engine in person but i think the origional inlet manafolds are cast, this means there are ruff casting marks on the inside, this ristricts the air/feul mixture from getting into the engine. A well desind inlet manafold would have a smooth surface on the inside, no sharp bends or curves and the igzac same distance from the carbie to the inlet on both sides. This lets more fuel into the engine quicker and results in more power.(if thats what you mean by the question) but then again i could be talking complete shit, lol, if anyone else has an explination it'd be good

998 turbo

vegard: so like the two holes dont match up?

998 turbo

The fuel/air coiming at the floor of the inlet runner hit the steel ring as this is higher than the lowest part of the inlet. As most of the fuel/air charge travels at the bottom of the port this is NOT good.

Edited by Vegard on 3rd Jan, 2005.

All the fast turbo minis use the standard item.

I personally use the ring to located the manifold to the head.

The few rough casting mark can be smoothed out with a drill or something.

My manifold has been flow by myself, taking out the alloy where "i think" it will help, no flow bench as i live in the real world.

Remember there is little space with a standard exhaust manifold and the Boggo inlet fit perfect.

Clubby do you need an inlet??

I have relations over fron Aus.

Edited by giallofly on 3rd Jan, 2005.

I removed the rings and "dowelled" the inlet to the head. My cylinder head is heavily ported so manifold was ported to almost match, leaving a slight "step" to help stop flow reversion, and to give slight turbulance to aid mixture.

Phil.

WWW.TURBO-MINI.COM

giallofly: The only problem with grinding a inlet manifold is that you cant get into the bend where there is the most resistance anyway, by making it out of say....aluminium pipe you have a smooth, even surface through the intire manifold, i'v also heard that the standard manifold didnt always meet up with the ports corectly and this also creates resistance...........however i could finish my inlet and find out it's all gone to shit so i might pm you in a few months about a standard inlet depending on how mine works(thanks for the offer)


vegard: when i make my manifold im goin to get the igzac same size pipe as the inlet port and bend/(cut, weld and grind) it so i should hopefully get what you described as the "preferred inlet shape" im also planing on making the over all design of the inlet ruffly the same as the origional so that clearences arn't to much of a problem incase i decide to swap to an origional one later (hopefully i wont have to)

when i work out how to post pictures i'll show you's where im up to!

Once again, this is my first time working on a mini so i apologise if im talking shit


Thanks for the input and ceep it up. chris

998 turbo

clubby: forget it mate, you are wasting your time the blower is not botherd about port matchings presision etc manifolds itl just blow by them, use your skills and time to go to other avenues to make a GOOD motor

Well mr clubby do it your way!

When you do a sub 13.62 second quarter mile let me know!!

Remember the manifold was design to create turbulance so the fuel/air mix doesnt seperate.

The MG metro (n/a 74 bhp) model had a well designed and there is vertually no difference in flow as proved when we flow bench tested one.

Both turbodave and i run heads with just tad,maybe a polish over standard on the port.Proving you don't need tunnel ports to get results

Jon.

Edited by giallofly on 3rd Jan, 2005.

Clubby,

My manifold is box stock - aside from drillings for sensors and the like. As a few have said, it's a cracking piece of kit, and it would be easier to purchase one of these.

However, if you just like tinkering, and want the satisfaction of having a scratch built intake, then crack on.

However, I'm not so sure of the need for a large capacity inlet on a carb'd setup. You'd want a reasonable size, but too much volume as this will give uneven mixture made even worse by your proposal of having the carb at one end of the plenum. Remember the firing order: 1324 - or to put it another way - 3421. Hence, the first 'gulp' from either end of the manifold is taking in air that isn't going to have the same fuel/air ratio as the air taken in by the next adjacent (shared inlet tract) cylinder...
I just think you can't assume a log inlet is filled with an equal and regular air/fuel mix, even under boost - remember the airspeed/volume over the needle is far from regular, even at a constant RPM and load.
Basically, the larger the volume of your inlet, the worse it'll be. Too small a volume, and inlets that are 'biased' towards the outer cylinders (like a stock nat-asp single carb manifold) must be avoided of course....

I've no evidence to support any of the above, other than thinking 'out of the box', but I'd be very wary of what you're planning...
As regards what to suggest, I've no real idea on improving the stock item, as i'm no manifold designer. I was thinking of well tapered long runners that form into a 'Y' shaped splitter from the carb... However, this will still serve little gain over the stock item. We are talking forced induction after all.

Maybe some delving into manifold design is called for - but remember you're dealing with a forced induction engine, and a very specialised cylinder head layout.

If you want to try something different, why not blow through two HIF38's (standard 998 metro - not 998 mini). These could be mounted so as to share one inlet each. You'd need to be looking at fitting two lambda sensors - one on each outer exhaust manifold branch, and maybe exhaust manifold temperature probes, and you WOULD see gains over a single SU, along with a very unique setup. I personally wouldn't be inclined to do this - far too much work for a small gain; but if you like tinkering.....


Someone do this fella a favour and post a pic of a stock plenum face!

how much is a standard inlet worth? well Mr giallofly i'm not after a 13.61 sec pass, but i thought it could be a chance to improve on the original manifold. I would be happy with a standard inlet manafold its just faster and cheeper to make my own, just hard deciding the design with not much to go off, i could buy a standard item n hold of for four weeks to make my exhaust manifold around it, but our company is on holidays n the factory is free for the next two weeks. U blokes obviously know wat your talking about. if someone could describe a design it would b a huge help.

thanks again. Chris

998 turbo

I bought turbo inlet manifold for 8 quid at IMM2004 in Norwich. Washed and plastic wrapped. The idea of the manifold is to create turbulence, it looks like crap but it works. All I did was cut the water heating tubes off the manifold and leave it as is.

AS for twin HIF38, like Dave said they might give some additional bonus but I doubt it. A lot more hassle with balancing, finding the correct pair of needles, well working linkage etc. Not really worth it. You need to remember one thing: if the engine is properly fed with one carb, it won?t give you any more power even if you add extra carb(s). Nor does it care how it is fed, be it carb or injection.

There are drivability and emission issues that may be improved with other setups but in my opinion single SU HIF44 on std manifold is very hard to beat, easy to fit and easy to setup. And relatively cheap of course.

I have done my share of improvements over the years and have found that factory engineers really did think before they built the engine. Inlet manifold and plenum are best left alone.

hmmmmm, for $20au i guess i'd be stupid not to get one (even with $80 freight) i alread have a hif44 carb but i dont have a plenum, how much are they worth? and are these parts hard 2 come by ova there?

998 turbo

Do a search on this site - I've written a little about modifying a stock HIF44 into 'blow thru' - ie boost sensitive...

All you really need is a seal Kit - available off Iain for a very reasonable fee! Iaian might also be able to locate a plenum for you. www.Ebay.co.uk is your best bet for finding a plenum chamber.
You could also try http://www.mini-metro.co.uk
Thay had a few turbo bits in, and are export 'specialists'. Beware - they are bullsh1tters however. Tell them exactly what you want, and if they give you a silly price, put the phone down.

i was reliably informed (by mbe) that the metro turbo inlet was the one to go for as it helped to reduce charge robbing compared to a more typical N/A manifold, so i'm going for the turbo inlet, although i've had to do some mods to get it to fit with the mirage manifolds!

I didn't know MBE had any experience with turbo's really, but I've been saying that for a few years...

not sure exactly on how much he has had either but he seems to know the a-series quite well, i've seen a couple of customers turbo engines etc down there being worked on

saw some drawings for the sequential dog box too, very nice!

i have tried the mg inlet and minispares largebore manifolds , massive loss of low end drivabillity especially off boost , top end remained about the same , its very difficult to measure each cylinders mixture on an a series in an effort to see what was the cause
td :the twin hif 38 's sounds like a lot of problems of which charge robbing would be difficult to eradicate if too close to the head

yep can do the kits of seals. also if you find a plenum (or anybody does) and you want to get it posted to me then ill post the lot at once if you like. i "may" have a spare. ill have to check.

great, thanks again every one

998 turbo

I cant see anyone turning out a nice inlet manifold out of tubing, not at home anyway.

If any of you guys are interested in trying new inlet design then i'd suggest you do it in fibreglass or carbon fibre. If you know how, it's the easiest way and will give you a nice smooth finish inside to ya ports and you can go quite mad on design.

Basically get hold of a block of wax. Carve the shape you want. Then lay up your carbon (wet lay up) onto the wax. When its all cured you simply melt out the wax. Bear in mind though that it has to be srong enough to support the loads on it and it has pressure in it. Think about how you are going to form the flanges before you start as well.