On the 'general discussion' site a recent 'test' suggested that the car was superb but could do with more torque at lower revs. Does this worry anybody?

My present car which is turbo charged does have the push in the back feeling when the foot is floored. The RX8 apparently will not have this sensation but will still reach 60 mph faster. This I do not fully understand, can somebody please treat me to a childs explaination.

rael.

 

it's because the power delivery is so linear.another reviewer recently likened it to a toy car (like a matchbox car)rolling down a steep track, it just keeps building speed allowing it to make those great times. if you are used to that turbo push it might take somegetting used to. remember tho if one want a little extra kick in the back you have 9000rpms and 6 gears to chosse from, just drop down a gear. the television reviewer said it didn't push him in the back at 3000 rpm in 6th gear if he punched the throttle. i find it strange that he would do that in the fuel saving gear, he should have just down shifted.

 

Rael,

This is also the biggest worry for me coming from a turbo. I really want to like this car.

I guess we will have to wait until we drive it and see.

Mark

 

Here goes:

Power is torque multiplied by rpm.

Imagine two cars, one with a high torque engine and one with a low torque unit (each car having identical weight, wind resistance etc). If the engines are producing the same power, the cars will accelerate at the same rate. However the high torque engine will be spinning more slowly than the low torque unit (i.e. they will be in a different gear).

Acceleration is thus determined by power - not torque.

The shape of the power curve (i.e. power vs rpm) is also very important as this determines the rate of acceleration at any given rpm as you sweep up through the rev range. For true propellorheads, it is the area under this curve (between the min and max revs typically used) that is most important. Highly tuned race engines will have a sharp power 'peak' over a very small rev range (typically at high revs) whereas a road car will have a broader, flatter curve.

A gearbox is a torque/rpm converter. A low torque engine can provide plenty of torque at the wheels by going through a low gear, but the engine will be spinning quickly. Think about the teeny electric motors that power an electrically adjustable seat - they are very low torque but spin quickly as they are geared down a lot.

So the bottom line is that people who believe that cars with high torque engines will accelerate faster are wrong. Low torque is fine, as long as you are happy with high rpm.

I've already seen a couple of reviews that made comments along the lines of 'the RX8 doesn't feel as quick as the Impreza [or whatever] due to its lack of torque'. As stated, this is nonsense. The RX8 just produces its power at higher rpm.

So why do we care about torque? Because we like to know the answer to questions such as 'how fast will my car accelerate from 2000rpm?'. This provides an indication of how flexible the engine is around town, how often you need to change gear etc. You probably don't want to tow a caravan for 500 miles at 9,000rpm. But it's not so much of an issue on track (and less still if the engine is smooth, quiet, reliable and reasonably economical at high rpm).

Hope that helps.

 

WOW!

Simon you petrol head you.

Thanks for that.

OILMAN

 

Impressive stuff Simon, many thanks.

Presumably that therefore mean to get best out of our engines (re acceleration) we need to rev high and play a lot with the gears. ie to get a speed spurt to overtake need to change down as opposed to the existing gear offering required acceleration

rael.

 

Yep. Generally we have to get comfortable with driving at higher rpm than we might do in other cars. Although the engine is reported to have a broad, flat torque curve, you may need to change gear more frequently when driving it hard in order to keep the rpm up towards the top of the range where the power is highest.

There is another trap that a couple of the reviewers have fallen into - namely that the engine must be amazingly efficient to get 237bhp out of 1.3 litres. To make a sensible comparison with a conventional engine you have to take some other factors into account.

The Renesis is described as being 1.3 litres, which refers to the number of rotors multiplied by the 'swept volume' per rotor. The swept volume is (by my understanding) the volume into which the fuel/air mixture is drawn multiplied by three (since in one revolution, there are three inductions/compressions/detonations/exhausts).

In a conventional four-stroke engine, however, each cylinder produces only one power stroke for every two rotations of the engine. For example, in a six-cylinder engine, only three cylinders will fire in each rotation. Hence the rotary engine is 'using' its full capacity in every rotation but the conventional engine is 'using' only half. To get a meaningful comparison, you have to double the capacity of the rotary (or halve that of the four-stroke).

Anyway. I must be sounding like a right anorak. Let me know if anyone disagrees with the interpretation of rotary engine capacity.

 

I wish I could disagree, way over my head but sound impressive. Does that mean I will really have a 2.4 engine if compared properly?

Importantly, clearly the car will be no idle tourer and will need gear work to keep the revs up for any real power. This may take some time getting used to and overtaking initially will need some preparation and consideration.

rael.

 

No , you'll have a 2.6. This is a 13B engine.
The old 12A engines gave eqiiv of 2.3.

Its easy when you think about it.
To fire all pistons on a 'normal' 4 stroke engine the crank will turn twice. That is to say on my 1.8 4cyl, when all 4 pistons have fired the crank will have turned twice and 1.8 litres of fuel/air will have been burned.

On a rotary you have an 'eccentric shaft' , but to all intents it is actually a crankshaft. (there is another discussion to be had here with why this means lower torque...).
To get the eccentric shaft to turn twice (a la crankshaft) each rotor fires twice. Therefore your rotor goes 'bang' twice as much as your current pistons , hence they double the capacity for comparsion.

Clear ?

Real interest will be do we get lower tax . Government could go 2 ways - they used to class as 2.6 , but all reviews are now saying 1.3. We wait and see.

Morgan.

 

To be honest I understood that after Simons input.

My continiung concern relates to how hard I will have to work the revs and gears to get any real performance out of it compared to (say) a 1.8 turbo or 3 litre engine. On the plus side I understand that the engine loves to rev and will redline very easily so the problem may be controlling the output via correct gearing.

rael.

 

And I do hope that the gearing will be correct meaning that top speed will be achieved in 6th and all gears are useable for spirited driving. From what I have read until now, it looks like I might get disappointed. Roll on the test drive!

 

Isn't five gears of accelleration enough?

I only have five at the moment, and can accellerate quite will in fith, but I really miss that sixth gear.

I for one prefer that the top gear is set for fuel economy, my pockets arn't bottomless and as such on long journeys the cost saving provided by the sixth gear will be very welcome.

 

6th gear is just for motorway economic cruising. You will probabaly find that you will use 5 gear mostly (especially if it needs revs) and top speed will be in 5th.

rael.

 

Too bad (if it turns out that way). In a car with relatively low torque, close ratio gears are good for spirited driving. For my taste, a sports car should not sacrifice even a bit of performance for things like an overdrive gear.
Look at BMW gearboxes. Top speed is usually achieved in final gear (no overdrive). Furthermore, fuel economy at high speeds (e.g. 200 km/h) is usually slightly better when compared to e.g. Audis and dramtically better when compared e.g. to a Subaru WRX (our current large car).
BTW, my only concern about fuel economy is that it is a limiting factor in operating range. Having to stop for fuel after less than an hour of real <edit> fast driving (WRX) is ridiculous ....
FWIW, YMMV, and I hope that a thorough test drive will show me that 5 usable gears are ample for the engine of the RX-8.

 

The way I see it is that you will have to use the gear more on the RX-8 than say a forced induction unit.

I can't wait to see how quickly it can get up to 9000rpm and hear the buzzer going off at 8500rpm :D

Nice explanation Simon.

 

Contigo,

Nice private plate, are you hedging your bets with this one in case you decide to get a P1 instead of an RX8?

 

Recent RX8 reviews posted continue to point to the cars low torque as the main (and seemingly only) problem.

I did read somewhere that the gear box is supposed to be one of the best on the market and therefore regular gear changing to keep the revs up should be easy. Also, as the engine revs very easily this should not be a problem.

If this is not a issue just wondering how all these experts are unable to drive a rotary properly! Considering this feedback it would be no surprise if a turbo package was added to the first model revamp.

I think that many of us will need a little time to fully understand what this will mean. For example, it took 6 months to enjoy my Audi TT after my XJS. The reason being that the Jag 3.6 engine was auto and no work was involved. Initially in the TT I used to change gear at about 3500 revs so missed out on all the rev fun. I then went on a TT 1-2-1 driving day and was taught how to drive using higher revs. I think the same will apply to the RX8.

Cannot wait now.

rael

 

Agree, its going to take a while to get used to. I've not driven a V-tec Honda, which has a similar sort of high reving side to it.

I think it'll take a while to get used to it and it'll be like having 2 cars. One for town, which could be difficult to drive and one for the motorway, where you can rev the **** off it.

Again, we'll see when it comes, but bearing in mind Mazda have spent millions, it should be decent!!

 

I have a Honda V-Tec at the moment. You really do have to wind it up, but once there it is great. :D

Mines only a baby 125 bhp model though.

 

I have the type-R VTEC (1.8 NA - 187BHP).

It is perfectly drivable around town. Feels the same as any other 'normal' car. No real low-range torque , but nothing to notice.

In fact it does nothing until 6,000rpm when the VTEC cuts in. All of a sudden the engine note changes , the acceleration doubles and before you know it 9,000rmp is showing and it is time to change.

People have said that the RX8 engine has a little kick at 6500rpm so I am just expecting it to be quite similar.
Now my integra is really like a switch - no real grunt until 6K then mad power until 9K.

Anyone who has driven an S2000 will have a better idea what to expect. Power just gradually builds all the way to 9K.
Renesis will be a smoother version of that.

You will get used to it - and learn to love it !

Morgan.

 

If it has to be kept high revving to make it go then surely the fuel consumption will be astonishing compared to a higher torque lower revving piston engine?

 

Not really.

The cars with lots of low-end grunt are either large displacement (Z350), or with turbos (TT). These engine types can push a lot more fuel through the engine at low revs, which is where their power comes from.

The RX8 pushes less fuel per revolution than these so needs more revs to push the same amount of fuel through, to get the power out.

Petrol driven internal combustion engines are all still basically at the same level of efficiency (I know that's a bit of a stretch, but within a reasonable tolerance is true ).
So the power out is roughly proportional to the volume of fuel going through.

Cars with great mpg figures have lower power outputs (and tend to be smaller/lighter/simpler drive trains).

So if you want to drive any car frugally, be gentle with your right foot.

My Honda CRX is happiest at between 5000 and 7000 rpm, but still gives 38mpg) beacuse the engine is quite small, and there is no forced inductance. I can drop that to 29mpg any time I want though :D :D

 

(I'm in Devil's Advocate mode of course):

If the Renesis is inherently faster spinning then won't it wear out sooner (or at least it's main bearings)?

 

A bearings life is indeed dependant on how many revs it makes, and how quickly. But that's what they've been designing it to do.

Friends tell me my honda won't last long if I run it at 7000rpm. Not so. It was designed to work at 7000rpm consistently. That's why the power band is all up there. The engine has never failed me, never needed anything more than routine servicing and is coming up to 100,000 miles.

An interseting point about the Renesis engine, is that the crank is turning 3 times faster than the rotors. That actually means that the torque at the rotor is 450 lbft.

Top that if you can :D

But of course that means that the top speed of the rotor is 3000rpm.

So you can call this car a 9000rpm engine generating 150lbft of torque,
or a 3000rpm engine with 450lbft of torge.

It's called gearing ladies and gentlement.

What counts at the end of the day is power to the wheels through the gearbox, and how linear that delivery is.

This car rocks !!!





:D

 

Another fine reply for which I'm grateful, especially as I've been plagued with doubt regarding the torque available to the RX-8. It's obvious from the various reviews available that the car is underpowered compared to the top expectations and in comparison to speciality acts like the 350Z (my previous choice - apparently the UK spec doesn't allow sat-nav: doh!) but I'm sure you're right that it will be an interesting experience. Certainly compared to my current Rover 214 Sei! I wonder though why we are going to feed it so much fuel when it is gently cruising if the engine only starts to require substantial petrol when it is revving at the upper range? It (apparently) drinks like a 350Z (at least) but doesn't offer the same rewards of mad power. Any ideas please?