Mi16 Conversion Finished..

[nick 3]

After spinning a shell a Donington over three years ago, I have finally got my Mi engine back in and running. One of the reasons for the lengthy rebuild was that myself and Martin (crf450) have been having a look at the oil surge problem from a completely different angle and have built an engine which, so far, seems to have cured the Mi surge problems. I say "so far" as the car has yet to be put on track or tried with "sticky" tyres (888's etc....) but this was an engine that would surge on the road and, as already mentioned was killed by surge at Donington on road tyres.

The main theory behind what we think causes surge is not that oil gets trapped in the head, but the fact that the Mi engine loses it's oil pressure far too quickly due to the piston located con rods. The 8v and the gti-6 engine both have crank located rods, meaning that pressure is held in the oil galleries far better than the Mi which basically has a massive oil leak from either side of the big ends, so when surge is encountered, the pressure just falls away instantly, as opposed to the 8v and 6 engine which hold onto their pressure for a few more vital seconds.

The spec of the bottom end is as follows,

Mi block and liners,

8v crank and rods,

Mi pistons (these needed machining to give the clearance on the 8v rods)

Modified main bolts with windage tray,

Diesel oil pump (with the big gears)

Oil pump cover,

Baffled xu10 sump (plus the small oil pump baffle)

The head is completely standard except for a PeterT inlet cam (plus chip)

 

On cold start up the oil pressure goes straight to the top of the gauge, but more importantly on hot idle the needle never drops below half way (this is even with oil temp on the third bar of the gauge)

So far, on the road I haven't seen any oil surge at all, but I would like to try a proper pressure gauge on the engine rather than the notoriously unreliable Pug' gauge on a trackday just to be 100% certain that this has cured it.

 

With the PeterT inlet in the car feels really strong through the midrange with a mad rush at 5k to the limiter (Note to Peter... the limiter still cuts in at the std revs) it sounds awesome as well, with a steady, but lumpy tickover..

 

All the pictures are in here Mi conversion pictures

 

I would like to thank Martin for all the work that he has put into this engine (just look at the welding on the downpipe... work of art) and for the use of his garage and tools, plus putting up with all the mess I create when doing even the smallest job...! Thanks also to Clare for all the coffee and food that I have consumed.....

 

Cheers,

 

Nick

Edited July 5, 2008 by nick

[Ethos 0]

Nice one Nick, thanks for sharing.

 

Has the downpipe been welded in two parts yes? I only ask because this is my final problem to overcome on my conversion

 

Pictures are looking good, it's surprising how helpful they are when doing these sort of things.

[Doof 11]

You git!!! When i last saw you up at Martins I was on about having a bet to see who'd get finished first...well here you are and theres mine still in a million pieces.

 

Hoping to have it running in 6 weeks now as things are making progress. Might drop round some time and take a look, be nice to get a bit of an enthusiasm boost for mine!

[Gentrix 2 1 Cars]

can someone roughly explain what piston- or cranklocated means, and how it affects the oilpressure?

 

 

thanks

 

andi

[Doof 11]

Imagine if the journal on the crank was really wide compared to the conrod...also imagine that the gudgeon pin of the piston and the cut out in the bottom of the piston was equally wide...what would happen to the con rod? It would effectively be able to move side to side which isn't good. So a crank located design means the crank journals are fairly tight to the big end of the con rod holding it in place laterally. Equally, piston located means that the rod is held laterally in place by the piston.

[Gentrix 2 1 Cars]

O.K. that´s what you mean.

 

I always thought, it would be the other way around, and that being the reason for the oilspraybars on the MI. As in "crank located - not enough wasted oil to lubricate the liners".

[nick 3]

Ethos, the downpipe was cut nearly all the way through and then bent down to flatten the curve out slightly and to get the length back after shortening it (hope that all makes sense!) if you keep shortening the down pipe, it pulls the whole exhaust forward, but flattening the curve out puts the exhaust back to where it should be. when that cut was welded Martin cut the whole downpipe in half two inches away and cleaned up the weld inside then welded it back together with little penetration (Martin showed me pictures of what was in the pipe before he cleaned it up and it was a right mess!!)

 

Doof, come on over one night and have a drive, it will definitely get your enthusiasm back!! Good explanation of the location thing too!

 

Nick

[Doof 11]

That'd be great! I've totally forgotten what a quick car is like and really have no idea what to expect from an Mi'd 205 now after years of 8v'ing.

 

I'll drop over one night during the week.

[Ethos 0]

Thanks for your reply mate, makes it clearer!

 

Who's this Martin guy and does he do home visits?

Edited July 5, 2008 by Ethos

[pee vee 1]

nice one mate!

ETHOS. if you have the 3 piece 205 exhaust, you can just put the down pipe in a vice, heat it up really hot on the bend,

and straighten it out very slightly. the extra length can be taken up by sliding the middle section onto the front pipe more.

 

its how i did mine, and have not had trouble with it blowing or scraping kerbs since. lol

Edited July 5, 2008 by pee vee

[Ethos 0]

Mines two piece as far as I can tell, the downpipe goes all the way down to the mid box halfway down the car

[nick 3]

It's easy to do Ethos, just cut the flange off and bolt it to the manifold, then just start trimming the end with an angle grinder and keep offering it up. I put the bend in it first, just where the brace for the cross member goes, if you get the car right up in the air on four axle stands it's easy to offer it up.

 

Nick

Edited July 6, 2008 by nick

[James_m 0]

Is it still as smooth as a standard Mi with the 8v crank?

 

Sounds like an interesting solution.

[nick 3]

It had the 8v crank in when I got it, unbeknown to me, it is as smooth as all the other Mi cranked cars that I have been in and no-one ever commented that it felt harsh in any way. Like I say, we only discovered that it had the 8v crank after it spun the shell.

 

Nick

[B1ack_Mi16 67]

How much lighter is the 8v crank compared to the 16v ?

[Cameron 16]

So did it still have the Mi rods then, is that why it lost oil pressure? That's an interesting solution though, how much room is there for the rod to float on the crank on the standard Mi set-up? I can't remember to be honest.

Also, did you have to do any mods to get the rod to fit the Mi piston, other than machining the pocket?

[nick 3]

I think the Mi crank is about 4kg's heavier (but not sure).

 

I reckon there must be a good 2mm total clearance on the big end with the Mi rod, which with the 8v rod that is reduced to a matter of thou'.

 

The only mod to the Mi pistons is across the journals on the little end, off the top of my head, they need about a mill and a half taking out of each side (Martin would be more precise) to match an 8v piston. You don't need to use the circlips on the gudgeon pins then either as they are a good tight fit in the rods.

 

Nick

Edited July 6, 2008 by nick

[Cameron 16]

Cool, will be interesting to see how it copes on track. Im not 100% convinced it alone will cure surge though as there are obvious flaws in the sump and head design that may still cause starvation. Still, every little helps and it may well be the little bit of extra protection you need when teamed up with an XU10 sump etc.

[pug_ham 244 3 Cars]

Good going Nick, Martin mentioned this a few times when I've been down or spoken to him on the phone & I think he is as happy as you with the results so far.

 

Martin mentioned it sounds like no other Mi he's heard either, I'd hoped to see it last week when I was in Belper around the last Ring trip to hear & see it in action.

 

Martin also mentioned the difference in the oil pressure indication being rock solid now & you can't get it to budge on your drive to work where the old Mi used to surge on a few corners.

 

Look forward to hearing a full report once its been tested with stickier tyres or even just road tyres on track.

 

Graham.

[nick 3]

Cool, will be interesting to see how it copes on track. Im not 100% convinced it alone will cure surge though as there are obvious flaws in the sump and head design that may still cause starvation. Still, every little helps and it may well be the little bit of extra protection you need when teamed up with an XU10 sump etc.

 

What are the "obvious" flaws in the head and sump?

 

Nick

[nick 3]

Quick update on how this is going. Me and Martin (crf450) took went for a "shootout" last night, me in the Mi with full road trim etc.... Martin in his stripped out 306 gti-6 (1000kg measured weight) this has a totally std engine apart from a pair of Kent cams which are supposed to give 30bhp (not measured on this engine) and a remapped ECU, we did a rolling first gear blast and then a few third gear roll on's...

Through the gears, from first, martin slowly edged away and by the end of fourth gear was probably 1 and 1/2 car lengths in front. In the third gear roll on with Martin only using 7200 revs (to match my std rev limit) it was a lot more even, with Martin still pulling away, but very slowly (probably half a car length by the end of fourth gear this time).

 

I'm am totally happy with this result as it shows that mine is making possibly 15bhp more than std (if Martins car is making 190bhp) with the slight weight advantage of mine (I also weigh 20kgs more than Martin, so there is probably only 50kgs difference in the cars with drivers) being cancelled out by the higher power output of Martins.

 

Nick

[SPGTi 2]

What are the "obvious" flaws in the head and sump?

 

Nick

 

I think this refers to how the Mi16 head has the potential to "hold" oil, which Peugeot addressed in the GTi6 by putting in an extra oil drain.

The std Mi16 is not baffled again addressed in the later XU10 16v engines.

 

Steve

[petert 586]

Good work Nick. I just love that Stage I cam. It makes all the standard bits come together nicely. It's big enough to run the std. injectors to their max. duty cycle. I've had them at 85%, and regardless of how much more injection time you give them, the AFR doesn't change. So that's an honest 180-185hp.

[crf450 0 1 Cars]

Baffling an Mi sump does next to nothing to help it's surge issues and when people refer to problems with the head design they are just repeat stuff they've read on hear. I've never seen a post that says I've put external drains on a Mi head and cured the oil surge problem.

We've approched the surge issue from a different angle and I'm pretty sure we've got to the bottom of a problem that people have been barking up the wrong tree on for years, although it's come a bit late as most Mi engines.

Cheers Martin.

[SPGTi 2]

Baffling an Mi sump does next to nothing to help it's surge issues and when people refer to problems with the head design they are just repeat stuff they've read on hear. I've never seen a post that says I've put external drains on a Mi head and cured the oil surge problem.

We've approched the surge issue from a different angle and I'm pretty sure we've got to the bottom of a problem that people have been barking up the wrong tree on for years, although it's come a bit late as most Mi engines.

Cheers Martin.

 

There are now a few engines running that are a GTi6 head (extra oil drain) with a MI16 bottom end. I think most are using the Gti6 trapdoor sump, some maybe with the extended oil pump pickup. It will be interesting to see how these compare to Nick's engine in respect to oil surge.

Anyway oil surge apart, it looks like a top build and is giving great power. Also it has thrown something new into the equation for building a powerful, lightweight and reliable Pug 16v engine.

So...I have Mi16 pistons / rods, Mi16 crank, Gti6 pistons /rods, 8v crank, 8v piston /rods, Mi16 block / liners, GTi6 head ............what do I do ??????????????

 

 

Steve