Rotrex M42 Build - 285bhp little update

[GeoffBob]

Well done Matt. Will be very interested to hear how she performs once you get her on the Dyno.

Recall my post of May 19, 2009 (almost exactly a year ago) from your Rotrex thread:

Appletree, See below my prediction of your power, torque and boost as a function of engine speed for a Rotrex C30-84 with 140mm engine pulley and 80mm Rotrex pulley. This prediction was made by pulling data points off the calculated loadline, exactly as I described to you in my earlier post.

If I have not overestimated your engines volumetric efficiency, then you'll be making torque all the way up to your 6800RPM red line. If I have over-estimated it, then the torque curve may peak a little earlier at a lower value. We'll have to talk more later to make sure you have the correct size injectors and exhaust so that you don't see a self-imposed premature peak in any of these curves. Note that boost is in kilo-pascals (not pascals like I've written on the side of the graph) so that I could plot it on the same scale as power and torque.

Whether your engine is strong enough to handle this, well that's up to you.



The most important thing about this is that it happens without crossing the surge line!

I’m afraid I can’t remember whether this was a calculation of total or flywheel hp ?? I suspect that it may be total, in which case you have to subtract the power to the compressor, water-pump and frictional losses, although I can’t see why I would have plotted your net engine power output (in place of flywheel power) as that’s not much use to you. I wish I had been more explicit when I typed up that post. These days I can’t remember what I was doing last week, yet alone last year. Maybe I should revisit those numbers for you if I get a chance. I’m curious to see how close I can get to predicting your dyno results before you post them up.

Matt, for my information: what are your pulley sizes, and what is your new compression ratio?

[GeoffBob]

Oh, and one other thing. Your engines torque (and thus power) are a direct function (as one might expect) of the mass (and hence density) of the air inducted into the combustion chambers. And since the density of the inducted air is a direct function of the temperature of the air coming out of your intercooler, it is logically concluded that you torque and power curves will be a function of the how well your intercooler performs.

I know we have discussed this before (and I recall that you undertook extensive experimentation on your intercooler, taking quite a few measurements) but it doesn't hurt to remind you to make sure that you have adequate airflow over your intercooler while your car is on the dyno. Ideally you would like your intercooler outlet temp to be as close to that which you experience while the car is on the track, as that will produce a dyno-graph that is most true to reality, although this is of course quite difficult to achieve on a dynamometer.

[appletree]

Now up to 250miles set off ealy this morning and went to cleethorpes an then back and around the local area, nipped in to halfords and picked up some more mineral oil and filter to swop. ive also recieved some race oil from guy at opie oils after abit of research we went for the silkoline pro S fully synthetic race oil 10w/50 which will be more suited to my engine in its new guise.


Engine pullys 140mm and the rotrex one is 80mm, Geoff its going to be mapped fiday so i will be putting a post up late on fiday night all being well with a result graph to prove it, hope your right with your prediction, i also thought you did the graph as a figure of flywheel horse power not at the wheels or with out subtracting the chargers power.

As for the airflow and air temp, daves dyno cell is airconditioned iirc and i take the font bumper off the car which as the front valance is cut out behind the bumper means theres air flow to the whole of the intercooler.

If dave doesnt mind and its not to difficult i might try and plug the thermo couples i had last time in and see whats happening, although i wont have a way of logging it unless dave has a way, which he might do with all the fancey stuff hes got at the dyno

[rix313]

Jealous tbh... can't wait to see the results you deserve it!

[appletree]

Few pics to add.
The car after the first run just checking for any leaks.


Engine bay shot


The little problem with the throttle pot position sensor wire, its all fixed now, there was no way the crimp terminal was going to come out of the plug socket so i had to cut a spare plug off a loom i had and used three in line connectors.


Pic of the car on the road on one of the "running in" runs.

[rix313]

What bearings did you use and where did they come from? Need to start looking at getting mine soon and getting this bottom end built up.

[appletree]

Metric merchanic uprated conrod shells either teflon or try metal cant remeber but think it was the ty metal ones.

As for the mains i used metric merchanics 360 degree thrust bearings with the mode to the mains cap to except the larger tang.

have you got any of your hose kits in black? how much for just a top hose in black to?

[rix313]

Got any parts numbers and prices for me?

The kits are made to order by SFS so need to be all 3 if you wanted it

[appletree]

How much is a set in black then rich, inc postage?

i'll have a look at the prices probably Pm or call you about them

[appletree]

Going to write a bit better detailed post later but just got back from Daves thought i'd share what happened


Car on the rollers being mapped


Dyno result- 284.5bhp and 219.4ft/lb at 7083rpm very pleased with it.


Unfortunatly i caught my tyre and rim on a kurb on the way home pulling up out side a freinds house, the drop kub didnt match the normal kurb and the was a bout an inch sticking out were they wernt flush which is what did this fooker! realy pissed off with my self, first wheel ive ever caught.

A nearly new proxy needs to be replaced now, another £70 down the crapper although it is still leagal and looks to be ok in a safty point of view it looks a mess and i'm not happy with it.

[rix313]

Coool how does it feel?

[appletree]

Like warm apple pie lol


rapid rich you'll love yours

[Ant]

Superb results there Matt

made up huh !

[appletree]

Ya realy pleased Ant I was aiming for 300hp but 285 bhp is close enough for me, for a 1800 4 banger to be making that on 12psi and still be driveable I can't realy complain.

I must say though that standing next to it while it was doing 7000rpm lift offs was one of the most nerve racking things I've ever done!

[GeoffBob]

Well done Matt, a truly great result and an epic thread.

I completely forgot about my last post and so never got around to re-looking at the numbers during the week, it appears however that it really wasn't necessary. 15hp off what I originally plotted really is very good. One thing that is nice to see in your dynograph is that your boost, and hence torque, are climbing more-or-less linearly, indicating that your Rotrex is performing as it should (no surge now I bet ). One difference that I noticed, however, is that your boost pressure does begin to tail over above 6000 rpm, which tells me that (if not as a result of the Rotrex and/or your air induction pipes/air-filter) your intercooler is beginning to present itself as an obstruction to the airflow. If you got this sorted (so that your boost continues on up) I have no doubt that you will hit your desired 300bhp figure. TBH though, I doubt it would be worth the effort and money for the extra 15bhp, and you've done a stunning job on your car already, so well done and enjoy

[Gunni]

First thing I see is that your torque isn´t dropping of hard enough to stop revving , with a few more hundreds of revs you will see more power.

Secondly the AFR I find rather leanish compared to what I normally see, but it´s not to say that it´s not right.

Overall excellent results and a very nice linear power curve which makes for very fun driving

[Ant]

looks to be around 13.2 AFR right through no ?

I was thinking 12.8 would give more margin for error/safety but if Dave Walker is happy, then it should be ok.

not 100% but I think that graph has been smoothed out a little by the plotting software, no fiddle factor implied in anyway, just looks like a turbine power delivery

[GeoffBob]

Matt, am I mistaken in thinking you may have something of a record here for an M42?

[appletree]

May well have Geoff, there's a few out there boosted but not many in the UK that I know of, think Ant did a turbo one but Ive not seen a thread on the car if the guys posted one.

The most powerful one I've seen is over on the M42 club its a 2.1 turbo running 350bhp iirc but that's in a proper race car.

I've been out in mine most of the afternoon and it realy does shift once its up there.

[DanThe]

Well done Matt, great result

[Gunni]

Let´s leave the turboed ones out of it, there have been some 600hp+ ones in Sweden ;)

[appletree]

Well maybe in the UK then? Any links Gunni? Would be interested to have a read. I saw a turbo one in Greece running 500bhp in an E36 but it was a bit of a shabby install.

The thong is there isn't much done with these engines as obviously there are easier ways to get the same power with an engine sell.

Heres the link to the turbo one in the US, pritty nice build.
http://www.m42club.com/forums/showthread.php?t=9663

[smith4130]

fairy play again matt.... great result.

impressed and inspired....

cheers.

[oakey]

As said... great result! I bet that's great fun to drive, chasing the redline

[Jhonno]

Nice...

Could you not let it rev a little more..? Seems to want to keep producing the goods..

[Ant]

New engine though, I'd want a few K on there before giving it more of more

[JWaller360]

Jeeeesus, thats a fair old increase! 145bhp over standard!

I think I know what to do when I tire of the standard M42

[appletree]

At 7200 I think with the pully ratio I have i'll be at the max rpm of the charger anyway, the only way to go bigger then is to go for a bigger charger like the C30-94 which from Geoffs calculations wouldn't realy work well at lower/middle range rpm just at the top which wouldn't be any good for driveablity.

Suppose that's the pay off for using a supercharger over a turbo atleadt with a turbo you get a bit to play with on the waste gate.... and within reason spec any flow characteristics you want if you have the money.

[GeoffBob]

At 7200 I think with the pully ratio I have i'll be at the max rpm of the charger anyway, the only way to go bigger then is to go for a bigger charger like the C30-94 which from Geoffs calculations wouldn't realy work well at lower/middle range rpm just at the top which wouldn't be any good for driveablity.

Suppose that's the pay off for using a supercharger over a turbo atleadt with a turbo you get a bit to play with on the waste gate.... and within reason spec any flow characteristics you want if you have the money.

As you say Matt, the C30-94 is not ideal for an 1800cc M42. This is for the simple reason that the C30-94 is designed to flow a lot more air than an 1800cc engine can induct unless a) it is boosted to high pressure or b) has the nuts revved of it. This may work well on a high revving 1800cc Jap engine (aka Honda) destined to be a track only car, but not on your M42 IMO. Best to leave the C30-94 to the M20B25's.

As I think you are aware from experience Matt (since you previously had a C30-94 as I recall) the air-flow over the bigger turbine of the C30-94 compressor stalls at lower turbine speeds, and thus results in surge at lower engine RPM if you fit a C30-94 to an M42. Some would be prepared to live with this phenomenon, right up until the point where the compressor blades fatigue and the engine inducts pieces of compressor blade .

Matt, If you seriously wanted to chase down that 300 bhp figure, I have no doubt that you can. Looking at your dynograph, it appears to me as if your boost is flattening off prematurely. That tells me that either you are dropping boost over your intercooler or your induction system is ever so mildly deficient. Personally, I think that if you identified where the pressure drop is occurring (following the method identified by Graham Bell in his book Forced Induction Performance Tuning using a manometer) you would be able make the necessary changes to prevent that pressure drop (bigger air filter, bigger/smoother bends etc), thus enabling your engine to induct the roughly 0.25kg/sec of air that it requires to make 300bhp at 7000rpm.

Question is, is it really worth it? I suspect that it isn't, since the law of diminishing returns seems always to apply. You could easily spend another year and a whole lot more money chasing down another 15bhp.

Congrats once again. I think, personally, that too few people realise what an achievement 285bhp is from a car that you can easily drive to work in heavy traffic. Not to mention the fact that a) you have a significant weight advantage over similar powered normally aspirated cars and b) any time you want the fuel economy of an 1800cc engine you simply drive with a light foot.

[shalmaneser]

Been following this build for what feels like forever, I've got to say I'm incredibly impressed with the thought and reasoning that has gone into the whole project. Everything looks to be beautifully made and carefully thought through and getting 300 brake out of a little 1.8 engine is an amazing achievement - and that power graph looks stunning, power all the way to the redline!

And I must say that the engine bay looks beautiful!

Of course the question is, what are you going to do now?!

Kudos to all involved!

Oh and finally do you have any idea of the weight of the whole car? Would be interesting to have some power/weight figures for comparison!

[appletree]

Of course the question is, what are you going to do now?!

Thanks for the nice comments

As for what am i going to do now, realy i want to enjoy driving it over the summer, modification wise though i doubt theres much more i can do! think i'll swop to silicone hoses for the top and bottom hoses as mine are alittle tired and maybe just tidy the bay up abit.

Need to get the IS lip resprayed at some point to though

[rix313]

Just a thought not sure how valid it is but what size pipework are you using Matt? When we fit the chargers to the Ginetta's we use 51mm pipe from the outlet of the charger up to the laminova cooler, from there it's just a reducer as it's directly infront of the throttle. Maybe if you used smaller pipe work from the outlet of the charger to the cooler, then from the cooler to the throttle it keep the pressure up and prevent it 'flattening off prematurely'?

Oh and lemi know when you want the silicone coolant hoses

[GeoffBob]

Just a thought not sure how valid it is but what size pipework are you using Matt? When we fit the chargers to the Ginetta's we use 51mm pipe from the outlet of the charger up to the laminova cooler, from there it's just a reducer as it's directly infront of the throttle. Maybe if you used smaller pipe work from the outlet of the charger to the cooler, then from the cooler to the throttle it keep the pressure up and prevent it 'flattening off prematurely'?

Rich, pipe-work after the cooler is required to be larger diameter than that before the cooler due to the fact that the air coming out of the cooler has a higher density (since its cooler) than that going in. This is the same reason why exhaust valves need not be as large as inlet valves, since exhaust gasses are hotter than inlet gasses, and thus less dense.

One of the common restrictions that gets overlooked is the pipe-work from the air-filter to the compressor, and is one of the spots where the biggest pressure drop can occur at high air-flow due to the fact that centrifugal blowers (and turbochargers) can’t suck air worth a damn. General rule of thumb is to get the pipe-work from the air filter to the compressor as large as is realistically possible within the space available. You would be amazed at what a drop in performance occurs simply by placing one 90’ bend before the compressor inlet. Ideally, the air pressure at the compressor inlet should be at atmospheric pressure (and indeed, at low RPM and hence low air-flow it will be). However, any obstruction to the air-flow before the compressor (bends, narrow pipe, long pipes, blocked or crappy air filter etc.) ensures that this is not the case. An altogether different issue, but likewise related to keeping the compressed air at as high a density as possible, is to ensure that the inducted air is as cool as possible (that is to say, not hot-engine-air).

I look forward to seeing your car finished soon Rich?

Regards
Geoff

[rix313]

Was looking forward to your response Geoff What of the pipework from the charger outlet to the inlet of the cooler? Will keeping it smaller help with reducing pressure loss?

Waiting for some issues to be sorted out with my suspension. Once that's back together I'll start on fitting the charger and sorting out the pipes although it shan't be as impressive as what Matt has achieved


BTW Matt what size spacers do I need to bolt the bracket to the block?

[GeoffBob]