2088cc Mi Bottom End

[PumaRacing 2]

Yeah...it will be over-square then.

So given the same cylinder head fitted to both, an engine of Xcc that is oversquare will rev "better" or "higher" than an engine of exactly the same cc that is undersquare?

 

How odd. I never knew that. That must be why those very undersquare Honda Civic and Integra engines only like to grunt away at low rpm then and the Ford Cortina Pinto with a 91mm bore and 77mm stroke flies past 8000 at the drop of a hat. Glad we've got that cleared up.

[Jay 1]

I think that comes from the basic BHP equation of:

 

BHP= (rpm x lb/ft)/5252

 

In thoery, the more rpm your engine is capable of, the more power you'll make BUT only as long as you have torque at that rpm to create it. However, get more torque at lower rpm and you'll also make more power.

 

In GTi-R tuning circles a lot of the early development was spent making the engine rev to 8500-9000 rpm. However, couple that with a monster turbo with the corresponding huge amounts of lag, and you had a very peaky and narrow power band, ok on the strip but useless on the road. Now the general concensus is to use 2.2 stroker kits, which develop possibly only 20 or 30 bhp over a similarly spec'd high-power 2 litre engine, but produce far more torque which builds much earlier in the rev range and makes for a much quicker car (I have been in a 2.2 stroker with a HKS3037 tubby and that thing is terrifying even before it comes on boost!).

[DrSeuss 0]

The formula one engines are all extremely over-square to reduce the forces involved on the pistons. Since they rev high the acceleration forces are lessened at tdc and bdc though of course this brings the problem of heavier pistons and a need for a really well flowed head.

 

As for you mr puma racing, your just quoting specific examples to ignore the question being asked. If you can fill a chamber fully at higher revs or less fully but do even more revs you'll get more power out. Thats why you don't have torquey relatively long stroke F1 engines, those things rev up to 22k for a reason and you know it.

[PumaRacing 2]

The formula one engines are all extremely over-square to reduce the forces involved on the pistons.

 

Forces on pistons has nothing to do with why the engines are designed oversquare.

 

Since they rev high the acceleration forces are lessened at tdc and bdc though of course this brings the problem of heavier pistons and a need for a really well flowed head.

 

As for you mr puma racing, your just quoting specific examples to ignore the question being asked.

 

I wasn't aware I was answering any question. All I saw was two comments which I made some observations about in the form of my own questions. I haven't seen those answered yet though.

 

If you can fill a chamber fully at higher revs or less fully but do even more revs you'll get more power out. Thats why you don't have torquey relatively long stroke F1 engines, those things rev up to 22k for a reason and you know it.

 

19k actually but that's not the issue. I'll ask a question again then. The Mi16 is 83mm bore 88mm stroke. If one was to redesign that engine at 88m bore and 78.3mm stroke to keep it at 1905cc and put the same standard cylinder head on it how much extra power would it produce (and why) and how much higher would it rev (and why)? The stroke has gone down by 11% is that's any help. Feel free to use the facts that piston forces scale directly with stroke length, directly with piston mass and with the square of rpm in your calculations.

[GtiMad 1]

I wasn't aware I was answering any question. All I saw was two comments which I made some observations about in the form of my own questions. I haven't seen those answered yet though.

 

You really are a miserable bastard. I am sure you have some usefull imput on this intersting subject but I am also sure I am not alone when I ask you not to talk down your nose at people it's like you are doing us some massive favour with your posts.

 

Nobody else feels the need to be rude on this forum and I am unsure as to why you feel that you should.

 

 

edit: can't type

Edited September 22, 2004 by GtiMad

[PumaRacing 2]

You really are a miserable bastard. I am sure you have some usefull imput on this intersting subject but I am also sure I am not alone when I ask you not to talk down your nose at people it's like you are doing us some massive favour with your posts.

 

Nobody else feels the need to be rude on this forum and I am unsure as to why you feel that you should.

 

 

edit: can't type

Don't read my posts then if you don't want to. I'm not on here to be some sort of automatic question answering machine. The aim is to try and get people to think things out a bit more for themselves. If thinking isn't your forte and you just want things handed out on a plate then go elsewhere - or STFU.

[PumaRacing 2]

The formula one engines are all extremely over-square to reduce the forces involved on the pistons. Since they rev high the acceleration forces are lessened at tdc and bdc though of course this brings the problem of heavier pistons and a need for a really well flowed head.

Let's try another thought experiment. Buckminster Fullerene has been developed to the stage where virtually unbreakable components that weigh next to nothing can be made from it. A crankshaft weighs 1kg instead of 15kg. Pistons that weighed 500g now weigh 25g. Conrods are 30g, valves 5g and the valve springs that go with them will never reach valve bounce. You can now take a common or garden road engine and rebuild it with components that will withstand any rpm you can imagine using.

 

Crank stroke and piston forces are no longer an issue. Your Mi16 will sit at 20,000 rpm all day long. With no mods other than those which reduce component weight what happens to the power output? Does your 20k rpm Mi16 now produce 2/3 the power of a 3 litre F1 engine? If not why not?

 

You now have no reason to pick bore and stroke for a given capacity to minimise piston forces. What reasons do you now use to choose the bore and stroke? How does your choice now differ from what it did when components weighed 10 to 20 times as much?

[Doof 11]

Course your not an automatic answering machine, is anyone else on here that answers questions? no didn't think so!

 

Makes it sound like your the only one who knows anything, whilst i'm sure you know your stuff (dont cum mate) other people know things too!

 

I can totally see what Rich is saying, it really feels like you look down on anyone that knows less that you on the subject at hand. Also i dont think its really an option not to read your posts, what is otherwise a very interesting topic (this) would be very hard to follow without reading your posts.

 

Remember, you can get people to think more, but you dont have to patronise them in doing so, everyone starts somewhere and cant you respect these people for at least trying to learn! Theres a million others out there driving Novas who are completely the opposite, by all means go patronise them, but not people who at least try!

 

Anyway, where were we...

 

PS: Thats more like it, gets people thinking and doesn't patronise! (the post above this)

Edited September 22, 2004 by Doof

[Hilgie 16 2 Cars]

@Pumaracing:

 

In GENERAL square or over-square engines can cope with higher revs. I *think* that is due to smaller forces on the rods because they have less stroke. Am i right there?

 

@all others: I'm sure Dave is just trying to help. In anyway I'm not offended by the his reply on my post. Just another lesson learnt.

[PumaRacing 2]

Another thought experiment. The rules in F1 are changed. Instead of limiting engine size to 3 litres you can fit anything you like as long as it doesn't produce more than 900 bhp and all engines are dynoed before each race. Number of cylinders and engine capacity is totally free so what do the designers do? Even smaller lighter engines that rev higher, larger capacity engines that rev lower, how do you pick the number of cylinders and the bore and stroke for a given engine size when the choice is infinite?

 

Why did V8 F1 engines like the early Cosworth DFV give way to 10 and 12 cylinder engines? Would even more cylinders be better?

 

It may seem unrelated but a crucial question is why elephants can't jump but cats can. Why can an ant easily carry several times its own body mass but a human can't? How do mass, strength and surface area scale with size? Where does flow fit in? How is cooling and thermodynamic efficiency affected by scale? Why do ship's engines have bores 1m across and why do they give better fuel consumption per bhp generated than engines with smaller cylinders but less bhp per litre? What differs between the choice of bore size and number of cylinders for a ship's engine and an F1 engine?

 

If you increase the length of a component, say a conrod, what do you have to do to it's cross sectional area to preserve the beam strength and how does this affect the mass and inertia? If the component is coiled, like a valve spring, how is its force affected by its diameter and the diameter of the wire it is made from?

 

I know, far too many questions, but if you want to actually understand engines instead of just wasting money on shiny crap that does nothing these are the sorts of things you need to get to grips with.

[miamistu 1]

I thought the oversquare pistons were used to keep it cooler inside the liner at the expense of efficiency - or am I talking bollocks?

 

//off to nose about on the internet for the answer

Edited September 22, 2004 by miamistu

[Butler 0]

I thought wide bore and short stroke = high rpm, bhp and less torque.

Longer storke = more torque. etc etc

 

Bike engine are a could example. But I guess for a given CC a wider bore allows better flow and bigger valves.

 

Anyone know of the Honda NR750?

[stew205 17]

I thought wide bore and short stroke = high rpm, bhp and less torque.

 

This is how understand it.

 

 

 

Sorry if I offened you Pumaracing

[Deadliest Pug 0]

The way I understand it is this.

 

You have a long conrod on an engine to reduce the side loads on a piston.

You have a long stroke on an engine to be more efficient, doesn't this give a better cylinder fill at lower rpm's? You have a short stroke because it means at higher revs you get a better cylinder fill?

 

I didn't think it actually affected how it revved but more on how effiecient it is at certain revs?

 

Although this could be comnplete rubbish it was always the way I understood it. Saying that, I am a diesel mechanic so no doubt my straw hat has clouded my views

 

Dave!

[stew205 17]

My line of thinking was the 16v head flows better at highier air speeds therefore filling the cylinders better at higher RPM.

 

So if you could increase the chamber size by increasing the bore (which I thought made a keener reving engine ) rather than stroke, then I though you would see better gains then going down the increased stroke route.

 

 

This is obviously wrong and would appreciate you views on whats the best method of doing this conversions and correcting me on the above.

 

Thanks

Stew

[Deadliest Pug 0]

The problem is everyone is going for the petrol engines and leaving the far superior turbodiesels alone

 

Dave!

[PumaRacing 2]

The problem is everyone is going for the petrol engines and leaving the far superior turbodiesels alone

 

Dave!

I find it hard to disagree. Several years ago I did a VW Golf 1588cc turbo diesel for someone. Big valve head, std cam, hybrid turbo with bigger vanes and the boost upped to 15 psi. It gave 140 bhp (70 std I think) and 45 mpg on a run. Enough to see off anything 8 valve given the light chassis and just as suited to long trips with lots of baggage on board. Nowadays BMW and others have std direct injection diesel cars that combine the speed of the petrol variants with the economy of the older style diesels and in years to come they'll be the main mode of transport. If I did more miles per annum and wasn't so addicted to how my Focus ESP goes round corners I'd be thinking of a diesel too.

[Doof 11]

I didn't think it actually affected how it revved but more on how effiecient it is at certain revs?

Thats how i see it, dont know if im right or wrong but engines are designed around a particular rev range and everything about them is engineered to cope with, and be efficient at, those particular revs.

 

More power is gained by revving higher because you are processing more air but the engine needs to be able to cope with the increased forces, and the head needs to be able to flow efficiently as those revs. This would massively increase costs resulting in the compromised engines found today.

 

Am i close?

[Deadliest Pug 0]

{Off Topic} I have been lucky enough to use some very very powerful diesels, the Sunshine engine, Some VERY powerful tractors (No laughing ) and a Saab 95 Diesel that was tuned till it went pop. Diesel is the way forward aslong as they build on its strengths and stop trying to make them act like petrols. {Off topic}

 

Dave!

[KRISKARRERA 2 1 Cars]

Surely if Peugeot had made a 3 litre V6 engine with exactly the same head flow and valve size as a 1.9 or 2 litre Mi16 the increase in capacity would have been worth it?

Isn't it a case of increasing cubic capacity will give an engine an increase in torque and power without needing lightened/stronger conrods etc ?

[M3Evo 0]

How about oversquare engines can make more power than the same sized undersquare engine becuase you can get bigger valves in an oversquare engine than under?

[petert 586]

No-one has mentioned rod angles in any of this.

[Butler 0]

Yeah thats right, that why I asked if anyone had heard of the NR750.

 

Honda developed this bike that was a V4 engine. It had 8 valves per cylinder. Oval pistons and twin conrods.

 

http://www.sportbikez.net/picture/324

Edited September 23, 2004 by Butler

[Dom9 2]

Honda developed this bike that was a V4 engine. It had 8 valves per cylinder. Oval pistons and twin conrods.

 

Sort of...

 

Honda actually built a tiny 750 V8, but then they changed the regs to say you couldn't have more than 4 cylinders... So they had to chop it up and make a V4, by effectively taking the walls out between two cylinders, they ended up with oval bores and effectively two heads per chamber creating the 8 valves per cylinder chamber!

 

Very cool!!

 

Yes, bigger bores, higher rpm, lower/safer piston acceleration, allows bigger valves, smaller thrust angle on the shorter rods etc... It all adds up! Like Dave Baker says on his site... It's the flow capacity of the head that determines power... But higher rpm will allow you to use a higher capacity head which necessitates larger valves and a larger bore to reduce con-rod lengths etc etc etc...

 

Theres no point in arguing a lot of this stuff in a thread where a guy wanted to know about getting a 2088 bore engine!!

[hiflow 1]

Cannot beat Cubic capasity. 2088cc conversion are a different beast all together. Good torquey bottom end & then that +4000k rev thrust. were been doing 2092cc conversion for couple of years now. Well worth it

 

 

Andy

 

Hiflowheads