Mi16 Superchrged Cr Advice Required

[M@tt 77]

So i and a few others on the forum that i know of are planning or are in the process of supercharging our mi16's with an Eaton M45 supercharger from a Mini Cooper S, however i have a few questions you maybe able to help me out with.

 

Now i am the first to admit i am still in the dark about alot of issues regarding the science behind "performance tuning" and although i am reading up on it, there is alot of information to take in, so please be gentle.

 

So my questions are as follows

The techsheets for the supercharger suggest that a possible 40%?? (can't fiind exact figures at the mo)increase in power can be had using the M45 which with losses etc would mean i could realistically expect to see around the 200bhp mark. So assuming i didn't touch anything internally (pistons, rods bolts etc) would the standard mi16 cope with it?

 

Now with regards to the Compression Ratio i understand that forced induction engines require a lower compression ratio than normally aspirated engines however i'm not totally clued up on the science of exactly why this is but i just know that they do. However my question is, assuming i have a fully mappable ignition and fuel management system is there any need to lower this ratio if fuel and timing can be precisely controlled or will the CR have a detremental effect on the performance achieved?

 

then jumping the gun and assuming all responses are to say YOU MUST lower the CR then which would be peoples preferred method of doing it?

1) Fitting 1.9 8v pistons (with valve pockets machined in) and rods (~£40 2nd hand)

or

2) Fit thicker steel headgasket leaving pistons and rods alone (£186 from DP engineering)

 

bearing in mind that cost is a very real factor in this project.

 

Also i've read about cam choice for the 2lturbo engines however are 8v and 16v cams interchangable? if so would it just be suitable to swap the std mi16 cams for say some 2l 8v ones?

 

i relaise its alot of questions but hope you may be able to fill in some of the gaps i have

 

Cheers

 

Matt

[Rippthrough 98]

I would say you might need at least a small drop in CR for 200bhp - the stock CR is pretty high, especially given your using an eaton charger - no doubt those with a bit more experience of boosted Mi's can give you a rough figure - the more effective way would be to fit machined pistons, then so long as the height is the same they would keep the quench area close to optimum.

Edited March 22, 2007 by Rippthrough

[saveloy 8]

If you are planning to use, say 1 bar of boost, then the standard CR will cause detonation problems.

You see, atmospheric pressure is 14.5 psi. Running an extra bar in boost means you will be forcing twice the air into the engine at maximum boost.

So, you WILL need to reduce the CR, unless you fancy going to direct injection!

The best way to do that is to fit some custom pistons. Since money is an issue, your only real alternative is to machine the pistons. The exact CR depends on your level of desired boost, thermal efficiency and fuel octane.

I would rule out a spacer plate, since that may well interfere with the squish in the chamber. And it may well make things worse, in terms of detonation.

A thicker head gasket will be a good idea, but be sure you factor in the size when calculating the CR and your machining needs.

The engine internals will be fine with 200 bhp. No hassle there.

The Mi cams are quite mild, the valve sizes are large though. Which means, unless you want to find some milder items, you are better off leaving things as they are.

Money. You want some more don't you?!

[Doof 11]

I think its probably quite inaccurate to just say you get 40% power increase. Ideally you need to look at the boost and cfm that you want to run and check how efficient the charger is.

 

With the roots type superchargers being only around 50% efficient there will be alot of heat added to the charge and so dropping the CR depends on whether or not you are intercooling. I would imagine without intercooling you definitely need to lower the CR to avoid detonation. With an intercool i think the 10.4 (correct me if im wrong) would probably be too high. Perhaps mid 9's but i'm just guessing, really you need to look at exactly what the charger will be doing to the inlet temps.

 

Do remember with roots type chargers that they benefit from having fuel injected before the charger so as to seal the blades. Unfortunately if your adding an intercooler i dont think you can do this because you shouldn't have fuel going through. I presume the fuel would condense inside the intercooler.

 

edit: According to Graham A Bell supercharged engines benefit from wilder cams as opposed to turbo'd engines (ok a massive sweeping statement but i think thats the general idea).

Edited March 22, 2007 by Doof

[TKH 0]

I am not exactly up on the M16, dont really know much at all about them to be honest. But know a little bit about Eaton supercharger. The unit you are looking at is simply small. You will be spinning the unit well past what its intended to get close to the flow your after I would think. Assuming it puts up with it the heat it produced and power it takes to turn will be significant to say the least. The unit you are looking at would be more at home on a 205 1.6 GTI.

[Doof 11]

I dont know if i'm calculating this right but i get the Mi as being around 385CFM. Based on that the little eaton wouldn't have enough flow and would actually restrict it? Surely thats not right if a 16v 1.6 bmw Mini gets 160bhp just fine with it?

[TKH 0]

I think you were working air at sea level there. The flow for the 45 is given at 5 and 10 psi. But then you have to correct the air density due to air temp and take off parasitic power loss. Cant be bothered to attempt to work it out at 1am lol.

[saveloy 8]

Doof, you are probably assuming cfm at atmospheric pressure. Forced induction means you'll increase that.

[Rippthrough 98]

I reckoned about that too?

 

Normal Mi16 needs just under ~7,000 liters of air per minute at full chat, at 14,000rpm the eaton puts out 10,500 litres of air, or it would if it were perfect - actually pushes about 9,500 or so.

You'd probably need around 6 psi of boost for 200bhp, given the loss from heating, compression ratio drop and supercharger drag?

 

Which is around about 9,500 litres, or maximum recommended rpm on the supercharger.

 

Now, you can bring the output of the Eaton 45 up to just over 10,000 litres with a little work on the inlet + exhaust, and carefully setting up the rotors. But it does mean you can't have any more boost than that M@tt, and it will still drop off a bit at the top end, bearing in mind these are beer mat type calcs. then it could need a little more, and the inlet charge temp is going to increase a fair whack after the 'charger passes 11,000rpm.

 

 

But the bottom end and midrange should be fun.

Edited March 22, 2007 by Rippthrough

[M@tt 77]

Eaton's website itself states that the M25 is suitable for 2.0 - 3.0l engines so i would have thought the M45 would be suitable for the Mi16, or are we saying the Mi16 head flow so well it's comparable to a larger engine?

 

I intend to run an intercooler so injecting the fuel upstream wont be an option i don't think

 

In trying to understand those graphs above i'm slightly confused, the lines depicting 5 and 10psi curves are they showing the the charger output psi? and is that presure above atmostpheric pressure?

 

The reason i ask is that atmospheric pressure was stated above as being 14.5psi so those pressures are below that but i would expecting them to be greater, sorry i'm probably being totally thick here.

 

Cheers

[Rippthrough 98]

Eaton's website itself states that the M25 is suitable for 2.0 - 3.0l engines so i would have thought the M45 would be suitable for the Mi16, or are we saying the Mi16 head flow so well it's comparable to a larger engine?

 

I intend to run an intercooler so injecting the fuel upstream wont be an option i don't think

 

In trying to understand those graphs above i'm slightly confused, the lines depicting 5 and 10psi curves are they showing the the charger output psi? and is that presure above atmostpheric pressure?

 

The reason i ask is that atmospheric pressure was stated above as being 14.5psi so those pressures are below that but i would expecting them to be greater, sorry i'm probably being totally thick here.

 

Cheers

 

Yep, that's above atmospheric.

 

It'll do 190-200bhp, but only just, and it's going to create a fair bit of heat doing so at the top end.

 

I'm not sure if the mini blower is the stock m45 or the 'p' version, which is updated and can go a little further (16k)

 

Air temp increase is going to be about 30-60*c

 

m62 would be a better bet.

Edited March 22, 2007 by Rippthrough

[M@tt 77]

m62 would be a better bet.

 

Unfortuntaly i think the M62 would be too big to fit in the 205 engine bay as space is a bit of a premium even if it was mounted direct to the head.

 

M45 top - M62 bottom

 

 

Based on the temp increases stated above for the M45 there is no point in directly mouting it straight to the inlet runners and into the head without any sort of cooling is there? it really needs to go via an intercooler or charge cooler doesn't it.

Edited March 22, 2007 by M@tt

[Doof 11]

I've been thinking about this and was talking to Ahl about it the other night. I reckon you could probably mount the M62 straight to the bottom of the plenum. It's a bigger charger so will have more potential and because you won't need to spin it as fast it wont generate so much heat. Makes installation easier without needing to route intercooler pipework and the M62's from SLK230's have an electric clutch which means you could run two maps and run without the charger if economy was your thing.

 

Also, looking at that picture above it doesn't look that much bigger, its only really the length but you can get short nose versions from the SLK's i think.

[M@tt 77]

Doof you might be right, it'd be interetting to see one offered up inside a bay to see what space is like.

 

I've found this M62 one on ebay which looks a bit different to the one above

but still looks a bit of a beast

 

I'm sure i read Mattsav had one under his bed at one point , Matt if you've still got it any chance you could see what it would be like space wise? an other downside is the M62's obviously cost alot more aswell (double what M45's are going for)

Edited March 22, 2007 by M@tt

[PumaRacing 2]

Now with regards to the Compression Ratio i understand that forced induction engines require a lower compression ratio than normally aspirated engines however i'm not totally clued up on the science of exactly why this is but i just know that they do. However my question is, assuming i have a fully mappable ignition and fuel management system is there any need to lower this ratio if fuel and timing can be precisely controlled or will the CR have a detremental effect on the performance achieved?

 

then jumping the gun and assuming all responses are to say YOU MUST lower the CR then which would be peoples preferred method of doing it?

1) Fitting 1.9 8v pistons (with valve pockets machined in) and rods (~£40 2nd hand)

or

2) Fit thicker steel headgasket leaving pistons and rods alone (£186 from DP engineering)

 

I've run a few calcs through my CR calculation program for you. The standard Mi16 compression ratio as actually measured properly is 10.2

 

Fitting 1.6 Gti 8V pistons with valve cutouts would reduce that to 9.75. Not a big enough drop

 

Fitting 1.9 Gti 8V pistons with valve cutouts would reduce that to 8.4. Too big a drop.

 

So there's your answer. No easy solution by just swapping pistons. 1.6 pistons with the dish further enlarged would get the job done but cost a fair bit. So, try another tack.....

 

Replace the std 1.6mm Mi16 head gasket with 2 x 1.2mm Gti gaskets - 9.5:1

 

Use 1 x 1.6mm gasket plus 1 x 1.2mm gasket - 9.1:1

 

Nice and cheap and gives you two options depending on how much boost you want to run and how safe you want to play things.

 

HTH

[M@tt 77]

that's excellent dave thanks very much indeed

 

Again sorry if this sounds dumb is it simply a case of stacking the HG's one ontop of another or is there any need to seal them together with something?

 

Cheers

Edited March 22, 2007 by M@tt

[TKH 0]

All of there units are available with different length drive shafts. For instance the 45 is a comon charger to use on Saxos and 106s. But in this application it has a long shaft going across the engine bay and the unit end up just in front of where the battery normally is.

[Rippthrough 98]

Wouldn't the 1.6 8v pistons with a 1.6mm repair gasket give a tidy return?

[Ahl 4]

I've been thinking about this and was talking to Ahl about it the other night.

Hey hey, I know nothing - nothing! Im tempted though...

[petert 607]

Why not just use XU9J4Z pistons? They're supposed to be 9.7:1, but are actually 9.5:1. I've got a few sets if you're interested. Or, a 2mm copper gasket?

[M@tt 77]

my head has had an unknown amount skimmed off it (when i had it done i didn't realise the effect this had and never asked) so the CR is going to he higher than standard to start i think

 

is there a standard amount that is likely to have been skimmed off when i head has work done? i guess it really depends on the scale of the damamge to the head though doesn't it? mine just had some surface pitting where the HG had started to go and was filled by welding and then skimmed smooth again.

 

Peter which models are the XU9J4Z out of? a mi16 4x4?

 

i'm definitely liking the HG method as its very wallet friendly

 

i've also just spoken to a local engine shop and the only HG they have listed in their parts book from their supplier is a 1.44mm HG, so does anyone have any suggestion where these different thickness ones can be obtained? are they a specialst thing?

 

As i'm going to run the standard pulley on the SC to start with which gives 6psi of boost what is going to be the best CR to run for that? would 9.1:1 be too low or would it be OK with room for upping the boost if i changed pulleys a bit further down the line.

 

i still can't get my head around the fact that less than 1mm of material can have such an effect on the combustion process

Edited March 23, 2007 by M@tt

[petert 607]

Peter which models are the XU9J4Z out of? a mi16 4x4?

 

i'm definitely liking the HG method as its very wallet friendly

 

XU9J4Z is the DFZ model, as fitted to cat. equipped cars sold in Australia, USA, Eastern Europe etc.

 

PM me for head gasket prices.

[Mattsav 1]

Pah, M45's & M62 are for girls. Mine's an M90

 

Slight overkill but it will find it way onto an Mi16 at some point. I started making brackets ages ago and have a remote oil filter already tucked away to make a bit more room.

 

The M90's are fairly easy to find. I paid £500 for a brand new one off a Jag XKR (which I have the engine for as well, but thats another project I'll never get time to do....)

 

You'll also have to sort the Front pulley as the 2 peice Mi16 item wont stand running a charger. I dont know about the M62 but the M90 needs something like 45bhp to run it.

[allanallen 528 2 Cars]

my head has had an unknown amount skimmed off it (when i had it done i didn't realise the effect this had and never asked) so the CR is going to he higher than standard to start i think

 

Surely there must be a way of checking how much has been skimmed off, ie measuring the height of the head or the distance from the face to the valves. someone must know!?

 

matt, I'm on the look out for an m62 just incase the 45 doesnt perform, seens its mounted up though it'd be rude not to try it. Gettin my inlet fanimold welded up tommorow aswell.

[allanallen 528 2 Cars]

Pah, M45's & M62 are for girls. Mine's an M90

 

the M90 needs something like 45bhp to run it.

 

 

sweet jesus