3 cylinder 600cc engine, question?

Posted: Mon Nov 07, 2011 10:58 pm

Hi, I'm currently in my second year of studying automotive engineering, with no previous experience on engines ( the design of them at least) I was given a task and I don't know how to get my head around it so i thought that maybe some of youse with experience will give me a helping hand.

The task is to change 4 cyl Honda CBR 600RR engine into 3 cyl ( the task is to design the crankshaft and cylinders) now the cc of the engine can't be over 610cc (formula student regulations) and also the engine must be high performance.

so.. I've been working out different stroke bore ratios etc. and i came up with
bore : 72.6mm, stroke: 48.7, b/s ratio: 1.49:1, cc=605cc

those values give me quite a nice b/s ratio and also the stroke is kept short for the best torque (well i think its best to keep it short? correect me if im wrong)

Obviously the phase i'm gonna use is 120 deg, but now im not sure how many bearings and what type bearings, space between cylinders, what materials to use, how many valves per cyl, what shape pistons etc.

could anybody point me a way on how to begin that project? or anybody knows an example of similar engine to the one i need to design.

all help accepted, i'm stuck and i dont know where to go with that project.

Posted: Tue Nov 08, 2011 1:52 am

Hi Dolcevita, hoping these may be of help, http://www.totalmotorcycle.com/school-SectionSix.htm & http://www.compactengines.com/MZ301manual.pdf ok the 2nd is 2stroke but at the bottom are some schematic drawings, not best quality, over the years various motorcycle and even car manufacturers have produced 3 cylinder engines, kawasaki did it on the h series, triumph stil running triples on the speed triples, vauxhall and ford producing small 3 cylinder car engines and thats just to name a few, good luck with it.

Posted: Tue Nov 08, 2011 2:01 am

and another 2 ive found for you http://www.autozine.org/technical_school/engine/smooth1.htm & http://www.e31.net/engines_e.html

Posted: Tue Nov 08, 2011 2:10 am

Reading through what youve written at 120degrees the amount of vibration will break the crank, also if you want a torquey engine its not a shorter stroke but a longer stroke, shorter stroke = very revvy

Posted: Tue Nov 08, 2011 2:17 am

and this may help with bearing and crank design http://knol.google.com/k/swarna-murthy/design-of-crankshaft-pgdie40-group-no-8/1ugmrldj5ott3/6#

Posted: Tue Nov 08, 2011 9:26 am

thanks a lot, ill have a look at it later on during the day, i know that short stroke = more revs but it also means it accelerates quicker? im not really bothered about top speed because the straight line is only about 200m long therefore there is no chance of the engine getting on its top in that short distance?

Posted: Tue Nov 08, 2011 4:03 pm

thanks again, its very helpfull, i've already started drawing drafts of the crankshaft itself, ive got something in mind, however do you know what con rod length i should go for ?

Posted: Tue Nov 08, 2011 5:53 pm

Your conrod length should be aprox double the stroke of the crank, i run bikes running 58mil cranks using 115mm length rods with packing plates under my barrels, but i also know of mates running 58mil with 108mm rods and standard length barrels, the best way to determine it would be to have the measurement from centre of wrist pin/little end pin to skirt of piston, then your barrel height and min big end distance from the skirt of the barrel, ie as if the piston were at tdc, of course thats on 2stroke engines, but this site may help you http://www.lunatipower.com/Tech/Pistons/CompressionHeight.aspx

Posted: Tue Nov 08, 2011 7:03 pm

http://www.turbomagazine.com/tech/0703_turp_engine_block_math/index.html http://www.stahlheaders.com/Lit_Rod%20Length.htm and by my maths a 90mm rod should work with your 48.7 stroke giving a 1.85:1 rod ratio

Posted: Tue Nov 08, 2011 8:01 pm

I've had a discussion with my colleagues at Uni and most of them go for as long stroke as possible ( like you said for more torque ) but one or two wanted to do more revy engine like me, I'm only doing it because i want my project to differ from theirs. I'm sure our lecturer will "rape" all off our projects as he is simly too clever ( he writes books etc. a great man ) he only does this assignement to check our creativity. Now i need to calculate the forces on the piston when at
certain revs etc. tonight I'm gonna draw all my prototypes of crankshaft, piston and rod and see what he thinks tomorrow:) ill let you know with the progress. thanks for getting involved

Posted: Tue Nov 08, 2011 11:32 pm

No probs Dolcevita, all my knowledge is self taught or gleaned from the internet, having had a read thru some of the 3 cylinder stuff online it seems a hell of a lot of companies are going that way, less fuel usage but pushing out as much power to an equivalant sized 4 cylinder engine and cheaper to produce with less vibration thrown in to boot

Posted: Wed Nov 09, 2011 12:11 pm

yeah, it's one of the ways to make the car more efficient however they do many tricks such as putting low resistance tyres; better fuel consumtion however no grip at all in wet(so people be carefull when you buy new cars, make sure they put decent tyres on them) my lecturer said that possibly ceramic engines are on the cards as these could be much more efficent, nowadays engines either petrol (25% efficient) or diesel (35% efficient) lose lots of energy in form of heat. Ceramic engines could prevent it to some point, making the engine much more efficient. we will se what the future brings

i've heard of plastic engines ( used in racing ) but i dont think this type of engine did its job Very Happy

Posted: Wed Nov 09, 2011 2:07 pm

Funny you should say about ceramics, in the 2 stroke tuning world people have been dabbling in ceramic coated pistons for a while, using aluminium barrels with a nicasil liner, only problem is recoating costs if anything went wrong

Posted: Tue Nov 15, 2011 10:14 pm

I can imagine that being very expensive !! Rite i got on a bit with my project, been doing cad drawings etc. ( didnt specify the dimentions yet )

I worked out my con rod to be approx: 73.1 mm (3:1 ratio)

also I'm trying to work out the mass of the piston and rod end. I did some callculations assuming Mass of the piston is 250g and rod end 375g.

the acceleration of the piston came out to be 64547 ms-2

and force = 24205N ( is this possible :O ) im gonna need some strong material to withstand those forces ! this was at 13500 rpm which i believe will be around its highest acceleration point.

i'm worried about bearings and lubrications, havn't a clue what type of materials to use etc. any ideas/clues?

Posted: Wed Nov 16, 2011 12:56 am

I reckon your workings are right but you may have forgotten to put in the decimal point 64.557ms-2 and 24.205n otherwise your piston is travelling faster than the speed of light and pushing so much force itd take off to the moon. Have you a local bearing suppliers near you? Maybe talk with them on what bearings you would need. Reference lubrication i reckon you'd want a good quality fully synth oil maybe 5w30.

The cost on re-nicasil lining is around £120 a pot for a bore 70mm and length 105mm, ceramics ive not looked at myself but know its bloody expensive, however i have dabbled with cryogenicsing of my gearbox parts to take the increased bhp and torque thats being pushed out, ive got 1 engine i built, that started life as a 200cc with a paltry 7bhp and 6 torques and a top speed of 60mph on the road that i fettled and re-bored to 225cc thats been dynoed at 33bhp and 28 torques and has been clocked by gps at 98mph and i was still pulling away

Posted: Wed Nov 16, 2011 9:37 pm

nope 6500g sounds about right for a piston acceleration and also 24000N is a true value ( 2,4 tones sounds about right ) however the plans have changed a lot ! with previous values my r/l ratio was 1.49 which is crap ! for a racing car enginge I'm looking at ratios between 1:1 and 1.1:1 ( means more torque ) so i'm currently trying to faf on with that ( already got some values ) managed to negotiate some time for the class giving us deadline after christmass. RESULT !!