Why is there no sportscar engine which revs to 13k rpm?

[pattyg]

Novice question here I'm afraid.

Honda used to make a big deal about VTEC going to about 8.5k but how come we don't get a 2 litre engine which revs to 13k for modern sportscars? Surely the performance would be unbelievable and if a bike engine can be reliable at these revs why not a road car engine?

I know there will be an easy answer but always wondered anyway.

Thanks

[Yazza54]

Bikes are light. Bike engined cars are light and low geared. Production cars are not light. At 13k rpm all the power is right where it isn't useable if you have heavy car.

Also to rev to this amount you need to have an over square engine in terms of bore and stroke. You'd end up with a very short stroke an large bore engine to get to 2.0 I would think. Which again is good for revs if the car is light enough, but not great for torque. A heavy passenger car requires balance, it could be done but in the real world it wouldn't be as good as what we already have, which is why it hasn't been done.

[anonymous-user]

Can we please stop saying "large bore engines don't make torque because of the short stoke"

the simple fact of the matter is that large bore engine tend to be optimised for power, which means torque at high rpm. At high rpm engine friction is high, so for a given IMEP minus the FMEP, then the BMEP will be lower (hence torque is lower)

From a pure geometery point of view, take engine A (square 86mm x 86mm) and engine B (oversquare) and see that the extra piston area of the oversquare engine is exactly cancelled out by it;s shorter "lever arm" (the shorter stroke)

square oversquare
bore(mm) 86.00 95.00
stroke(mm) 86.00 70.48
capacity(cc) 499.6 499.6

crank radius (mm) 43 35.24
piston crown area (cm2) 58.1 70.9

piston area x crank radius 2498 2498


(note, to simplify i have just assumed the torque is produced at 90DegATDC, which it isnt, but the comparison is valid)


As for why no road cars that rev to 13krpm, centripetal acceleration (and hence out of balance forces) go up with the square of the rotational velocity. In a production car, it is not really worth the hassle / compramises to get to a peak power at those kind of engine speeds. It's MUCH simpler just to boost volumetric efficiency with a turbo and get a decent shaped torque curve & real world performance!

Edited by anonymous-user on Monday 4th October 23:29

[Mr2Mike]

pattyg said:

Novice question here I'm afraid.

Honda used to make a big deal about VTEC going to about 8.5k but how come we don't get a 2 litre engine which revs to 13k for modern sportscars? Surely the performance would be unbelievable and if a bike engine can be reliable at these revs why not a road car engine?

How many bike engines the rev to 13k last well over 100k miles and only need oil changes every ~10k miles? To make an engine rev that high reliably means all the internal components have to be as light as possible, which also means expensive and/or more fragile.

Just because you could make an engine rev to 13k without destructing it does not mean that performance would be "unbeleivable".

[thong]

pattyg said:

Novice question here I'm afraid.

Honda used to make a big deal about VTEC going to about 8.5k but how come we don't get a 2 litre engine which revs to 13k for modern sportscars? Surely the performance would be unbelievable and if a bike engine can be reliable at these revs why not a road car engine?

I know there will be an easy answer but always wondered anyway.

Thanks

Remove the flywheel,bike engines don't have them,they dont need them,sorry your car has to have one go figure

Edited by thong on Tuesday 5th October 00:28

[Yazza54]

thong said:

pattyg said:

Novice question here I'm afraid.

Honda used to make a big deal about VTEC going to about 8.5k but how come we don't get a 2 litre engine which revs to 13k for modern sportscars? Surely the performance would be unbelievable and if a bike engine can be reliable at these revs why not a road car engine?

I know there will be an easy answer but always wondered anyway.

Thanks

Remove the flywheel,bike engines don't have them,they dont need them,sorry your car has to have one go figure

Edited by thong on Tuesday 5th October 00:28

No flywheel or light flywheel will rev up quicker but it doesn't mean you can take the limit higher.

[stevieturbo]

pattyg said:

Novice question here I'm afraid.

Honda used to make a big deal about VTEC going to about 8.5k but how come we don't get a 2 litre engine which revs to 13k for modern sportscars? Surely the performance would be unbelievable and if a bike engine can be reliable at these revs why not a road car engine?

I know there will be an easy answer but always wondered anyway.

Thanks

V-tecs can be horrible enough. Why on earth would you want a road car engine to rev so high ?

[IanMorewood]

Same question could be asked why does no one make a 2 litre v12 road car engine?

Answer would simply be more efficient/cost effective engines exist which suit the mass car market.

[ringram]

Valvetrain control is a biggie.
Rotaries can spin pretty hard though.

[Mr2Mike]

ringram said:

Valvetrain control is a biggie.
Rotaries can spin pretty hard though.

Rotaries want to rev hard, but they quickly destroy themselves if allowed to. There are no rotaries that can match the highest revving piston engines AFAIK.

[andygtt]

I've always thought it is all about cost?

to make an engine rev the rotating mass need to be light... the higher the power and revs the stronger the internals and thus higher weight, which hurts the revs, to get them back to being light you have to start making the internals from exotic stuff and thus costing a fortune.

far cheaper to stick with a heavy but strong rotating mass and get power a different way and gear the heavier car to take advantage of it.

[BigBen]

stevieturbo said:

pattyg said:

Novice question here I'm afraid.

Honda used to make a big deal about VTEC going to about 8.5k but how come we don't get a 2 litre engine which revs to 13k for modern sportscars? Surely the performance would be unbelievable and if a bike engine can be reliable at these revs why not a road car engine?

I know there will be an easy answer but always wondered anyway.

Thanks

V-tecs can be horrible enough. Why on earth would you want a road car engine to rev so high ?

They are quite heavy engines, perhaps supporting the claim that stronger and heavier bits are needed for higher revs.

[JontyR]

Mr2Mike said:

Rotaries want to rev hard, but they quickly destroy themselves if allowed to. There are no rotaries that can match the highest revving piston engines AFAIK.

May I ask where you have come up with this decision? Our engine will rev happily to over 11,000 rpm, and has a redline of 13,000....do you want to show me the Piston engine you are matching this up against?

[chuntington101]

JontyR said:

Mr2Mike said:

Rotaries want to rev hard, but they quickly destroy themselves if allowed to. There are no rotaries that can match the highest revving piston engines AFAIK.

May I ask where you have come up with this decision? Our engine will rev happily to over 11,000 rpm, and has a redline of 13,000....do you want to show me the Piston engine you are matching this up against?

NO.... but i would like to hear more about this 13000rpm rotory. sounds very intresting!

Backto the OP, cost is the main thing. You need a much larger engine in a car than you do in a bike. To build an engine that can rev, half reliably, to 13,000rpm you are going to need to build something like a 4.0 ltr V16 using say R1 engione as a starting point (bore/storke etc). This will still give you naff all torque.

This is still not going to be to most people teasts as you going to have to spin the motor to 6krpm ++ just to pull away form a set of traffic lights.

Its muich better to build a bigger engine with lower rpm limits. or take an existing prodcution engine and modd it to rev higher.

Chris.

[Slinky]

Surely it's about tractability? An engine that revs to the heavens is unlikely to generate a sufficient level of torque in the lower RPM band to be usable on the road, unless the gearing is setup in a peculiar way (splitter gearbox on a road car anyone??) ..

Whilst "sports cars" can be delivered with some compromises, they still need to be usable day to day..

[Mr2Mike]

JontyR said:

Mr2Mike said:

Rotaries want to rev hard, but they quickly destroy themselves if allowed to. There are no rotaries that can match the highest revving piston engines AFAIK.

May I ask where you have come up with this decision? Our engine will rev happily to over 11,000 rpm, and has a redline of 13,000....do you want to show me the Piston engine you are matching this up against?

There are numerous piston engines fitted to bikes that will rev far higher than that e.g. ZXR6 limits at 15600 and that is a completely standard engine, is yours?. Obvioulsy in terms of competition engines F1's rev higher again up to 20,000RPM - show me a competition rotary that revs this high?

[JontyR]

Mr2Mike said:

JontyR said:

Mr2Mike said:

Rotaries want to rev hard, but they quickly destroy themselves if allowed to. There are no rotaries that can match the highest revving piston engines AFAIK.

May I ask where you have come up with this decision? Our engine will rev happily to over 11,000 rpm, and has a redline of 13,000....do you want to show me the Piston engine you are matching this up against?

There are numerous piston engines fitted to bikes that will rev far higher than that e.g. ZXR6 limits at 15600 and that is a completely standard engine, is yours?. Obvioulsy in terms of competition engines F1's rev higher again up to 20,000RPM - show me a competition rotary that revs this high?

I see your F1 engine and bike engines...that really arent designed to go into cars! and raise you £6k. Try getting an engine to meet the spec you have just mentioned and fit into the budget Ive just put down on the table

Anything is possible with the right money!! Hell Im sure we could fit a turbine engine from a helicopter.....that would be far higher than 20,000rpm

[andygtt]

well the zx6 engine costs less than £6k for a start... the entire bike is only £9k.

pretty sure you cant buy a rotary engine brand new and mod it to do the same revs for under £6k.... must admit i love the idea of the wankle engine, with more wide adoption i think it could exceed the std piston type design.... anyhow we digress.

[tristancliffe]

But the bike engines produce as much torque as a snail (which is fine on a bike that weighs the same as a feather), whilst a car engine (be it rotary or reciprocating (or any other type) needs to produce quite a lot more to get 'reasonable' performance.

My road car produces more torque than an F1 engine. My brothers road car produces more torque than about 6 F1 engines. Neither of our cars rev very high (6.5k rpm ish), whilst F1 cars were getting on for 21k rpm.

Besides, on the road a torquey, lazy, vibration free, quiet and economical and long lasting engine is far more important than a meaningless maximum rev limit.

[Pumaracing]

tristancliffe said:

But the bike engines produce as much torque as a snail (which is fine on a bike that weighs the same as a feather), whilst a car engine (be it rotary or reciprocating (or any other type) needs to produce quite a lot more to get 'reasonable' performance.

Absolute rubbish. You have no comprehension of how engines, gearing and actual vehicle performance really work.