Hi Guys, this is my first post to this forum.
I,m at the stage where I am trying to decide what to start building, so I,ve come to the font of all knowledge for a little help.
Am I correct in thinking that, regardless of the maximum BHP output @ stupid rpm, the torque output is the component that actually provides the car with ACCELERATION?
So - for example, having read on here that the venerable RV8 is supposedly low power output for it's size, I believe it's torque output is quite high. This would lead me to believe that because this engine is also quite light for it's size, then it would make my car accererate b****y quickly.
If any one can understand what I'm dribbling on about I would welcome any BHP/torque comparisons on different engines you may have and also any comments.
Phil the possibly ex-biker.

PS. When I suss out how to use some of these buttons etc, I'll try to make my post look a bit more interestin'

Hi Desmo,

Welcome, especially to those with names that make em sound like fellow Ducati Riders! (Paso?)

RV8 is nice engine to work with a lot of parts availabiity and at reasonable prices. Torque levels are good but weight may cause probs.

Others will advise you to build to book spec (beause its straightforward) and fiddle things afterwards once your sure you need the extra power.

For accelaration I reckon you need to keep a locost as light as poss. therefore the low torque - Hi revs - low weight of a bike engine may be something to consider.

Check out hte bike engined car section.

ATB

Dave

Thanks for the reply Dave.
It was a 900SS, followed by an Aprilia Mille. The wife had a Monster 900. Sold 'em both - now devoid of toys, hence the current interest in this subject.

my amateur appreciation is that bhp - eg power - is what makes an object acellerate - and i think thats in mr newtons laws. A certain amount of power will make a certain weight accelerate at a certain speed.

Where torque comes in is the ability of the engine to acellerate and maintain those levels of revs needed to attain the power. For example, a bike engine, beign high power and low torque, needs to be revved high to get the power band and have close gears to keep it up there, as the low torque makes the engine less willing to rev up to the power band under high loads.

low torque will cause the revs, and therefore power, to fall, if for instance, going up a hill.

Thats a pretty crappy excplanation and im sure someone else will be a lot my scientific about it!

[Edited on 13/9/03 by stephen_gusterson]

A lot of people critisize the Rover v8 for being too heavy when in fact it is lighter than a pinto engine.
If you can squeeze one into your chassis, do it. You will be spinning the tyres at any revs. Try doing the same with a similar power pinto engine.

Steve explained the differences pretty well.
However, it depends what do you want from your car!
Do you want something that is buzzy with a lot of gearchanges to keep it in the power, or do you want instant get up and go regardless of the gear you are in?

It all depends on your driving style I suppose.

Terry

Getting confusing ain't it?
I reckon that power (bhp) is always the amount of torque per unit of time.
I remember that 1hp = 550 ftlbs/min. That's why I'm convinced that torque is more relevant to acceleration of a given object (car in this case) than outright power.
Anyway, my experience with bikes over many years has shown me that a good spread of torque over a wide rpm range makes for a vehicle that is easy to drive on real-world roads.
Easy to drive = easy to drive fast.
That's one reason why Ducatis do so well in Superbike races.
So - the RV8 shouldn't pay a significant weight penalty compared to a Pinto?
But what about a Zetec?
Or a Vauxhall 2.0 Tcam?

Also - does the physical size of the RV8 mean that it sits further forward in the engine bay? If so, what does that do to the handling?

the rv8 may not be as long as you think......

my V6 cologne is shorter than the pinto.....is cos the banks of cylinders are overlapped by approx half a bore. So, a V8 may only be the equivalent of 4 1/2 or 5 cylinders long of a comparable 4 cylinder inline (comparable meaning a 1.8 litre four).

width may be a different issue...... but then a V is biger at the top, as is the case with a locost engine bay...

atb

steve


[Edited on 13/9/03 by stephen_gusterson]

Hehehe

" The Engine Dilema " strikes again.

TBH I went for a tuned X/F because:

A) Simplicity
B) Reasonable weight and overall size
C) Keep to the book
D) Cost
E) Drove MK 1 and 2 Escorts as a yoof and like the Fraud Kent for sentimental reasons.

If only v twin BEC was viable - for me that would seem perfect balance weight/power/torque/sound!

ATB

Dave
1989 Ducati 900 supersport

quote:

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Originally posted by Desmo904
But what about a Zetec?
Or a Vauxhall 2.0 Tcam?

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Though i haven't really got my head around the real difference between power and torque, the units sum it up quite well:

Torque is a turning force, units lbft or Nm, in other words a spanner with a weight on it, but not necessarily moving.

Power is the amount of energy coming out of a device, bhp muddles things as the unit is really watts. one watt is one joule per second, and a joule lifts a newton (0.1kg on earth) through a metre.

Engines are measured in both cos they go hand in hand. With no torque the engine couldn't rev up (though its not possible to have no torque cos the unused power must be represented, it makes the engine rev up) and so the car could only accelerate by slipping the clutch. Having said that if there was no torque there would be no power either so the car would disappear in a puff of logic...

Torque and power are really very different things if you think about it...

as a last point, when the engine is bouncing off the rev limiter, it is producing no torque i think because it can't speed up anymore, but is still producing lots of power. The only torque would be from resistance to motion if the car was moving, so it would be a twisting force on the prop shaft.

Anyone clever know if thats right, that a stationary engine being redlined isn't producing any torque? Sort of lost myself there...

If I remember correctly, BHP = torque x engine rpm. AS with all things in life, it is better to have a few things in moderation than one thing in excess, or in other words a big bhp number may sound good but if the engine in question makes 150 bhp@6800rpm, redlines at 7200rpm, but only makes 75 bhp@5800rpm it'll be sod-all use. The engine that makes 135 bhp@6500rpm, redlines at 6900 rpm but makes 100 bhp at 2500 rpm will be much more driveable.
As to which engine to use, I am being complicated and using an engine no-one else has as yet (to the best of my knowledge) just to be different and cos they're cheap and 'cos they're pretty powerful (Citroen 16v, 1905cc, 167bhp) but I've stuck to four cylinders for simplicity & cost reasons. V8's sound cracking and produce big wodges of torque but have 8 of everything and are slightly more awkward to package due to their width. I'd imagine also that they could be a beggar to work on due to limited engine bay clearance.
Both of the engines you mentioned, the Zetec and the Vauxhall are going to be good bets. The Vaux is a bit old now but still good if you can find one and has the benefit of age on its side so it has been tuned to produce some incredible power outputs. The Zetec is very much the engine of the moment and there are several variants to choose from. They are a compact and quite lightweight unit and benefit from being a modern design/manufacture engine so tolerances are tight and expected life should be long.
Finally, remember that your average seven replica weighs nearly half as much as a contemporary saloon/hatchback and torque is less of an issue. Still, torque does allow you to loaf along in fourth all day if you can't be armholed to change gear a lot. It's a chuffin' minefield this engine selection game!

In a nutshell:

Torque is the twisting force at the crankshaft.
BHP is the relationship between torque and rpm.

Neil.

This is great- I'm getting loads of info here. So while I'm doing so well, does anyone have any figures for power & torque figures for standard engines?

quote:

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Originally posted by Sideways 2 Victory
Hehehe

" The Engine Dilema " strikes again.

TBH I went for a tuned X/F because:

A) Simplicity
B) Reasonable weight and overall size
C) Keep to the book
D) Cost
E) Drove MK 1 and 2 Escorts as a yoof and like the Fraud Kent for sentimental reasons.

If only v twin BEC was viable - for me that would seem perfect balance weight/power/torque/sound!

ATB

Dave
1989 Ducati 900 supersport

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quote:

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Originally posted by Sideways 2 Victory
Hehehe

" The Engine Dilema " strikes again.

TBH I went for a tuned X/F because:

A) Simplicity
B) Reasonable weight and overall size
C) Keep to the book
D) Cost
E) Drove MK 1 and 2 Escorts as a yoof and like the Fraud Kent for sentimental reasons.

If only v twin BEC was viable - for me that would seem perfect balance weight/power/torque/sound!

ATB

Dave
1989 Ducati 900 supersport

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Spydy

I think the major problem with a v twin bike engine is the exhausts.

Because the cylinder heads sit at opposite ends of the engine it is difficult to engineer a route for the front pipe when the engine is fitted into a car chassis.

Possible to route it ok but this messes with the back pressure and spoils the engines power characteristics.

Or at least this is what I've read on the net - fwtw. If i'm wrong let me know cos I'd love to build a duke powered BEC next

ATB

Dave

2ltr 16v vauxhall 155bhp, 150lb.ft (that's as standard - 180bhp, 160lb.ft with webers)
iron block, alloy head, maybe slightly lighter than a pinto, not as wide as a rv8.

all IMHO

Ned.

ps see my website, under shows- stoneleigh for pic of that v8 bike derived engine, remember it cost £14k though! 302bhp @ 10500rpm!

[Edited on 15/9/03 by ned]

Desmo,

See pics in my archive for an idea of how tight the Rover engine is in a +4" wide chassis!

As for power, got this off a Cummins Diesel website:

Formulas and Conversion Tables

Brake Horsepower bhp = (bhp) rpm x Torque/5252
Torque
Torque = bhp x 5252
rpm

Rover V8 weighs 130kgs/box another 60kgs, about 155/165bhp and 200 ftlb torque

My 'busa engine AND box weighs about 60kgs 175bhp and 101 ftlb torque.

I have absolutely no idea which engine will make my car quicker. I do know that I'm going to enjoy the R V8 in the car, and the 'busa engine in my bike!!

ATB

Simon

Had a bit of fun discussing this at Donnington. Bike engines cars are cool. I was lucky enough to passenger in Jaspers car and it was pretty awesome, punching through the gears, engine screaming away at 10,000rpm and above and a very firm setup... it felt like a big go kart. Brilliant. However, he built his for track use mainly and for that it's fantastic. For road use I think I'd prefer (and it's all down to personal preference after all) something more laid back and beefier. Hence we are going V8. We also want to sound, bike engines don't sound too great at low rpms, but V8s do. It'll still be quick and more than a bit fun... oversteer anyone?
The main disadvantage with the V8 is size. Advantages, well they are cheap, simple and comparatively light and sort of a bit special. The thought of a high output 16v four makes sense on paper but those units don't quite have soul from my point of view.

It's your project, go with what you feel as much as what you think (or can afford ). You just have to be prepared to put the effort in if you deviate.

Bike engine @ redline IS producing enough torque to overcome friction forces in crankshaft etc. that is why you need rev limiters as the engine will (hopefully?)always produce more driving torque than frictional torque- and rev itself into oblivion.
If the engine is in gear at a constant speed, then the torque of the engine is equal to the force needed at the contact part of the tyre*the distance from axle centre. If engine torque is bigger (open throttle) the engine torque wins and you accelerate. Modern units for torque as said elsewhere are Nm (Newton.meters) its a measure of the turning effect of a force. Power tells you how much energy you are using per second.

I have 1600 toyota, 135bhp don't know torque figures, but it does rev to 8000rpm withour changing anything inside :-). Its not a bike engine but can sound a bit more like one than most normal car engines. The world is you oyster make one that stands out in a crowd.
Now does anyone have a scrapped evoVII ?

I have a Nissan CD20DE (I think) 2 litre as fitted to Primera's and in turbo form to the RWD 200sx. Mine revs past 8600 in standard form. It's quite remarkable really. Rated at 150bhp in n/a trim.

Neil.

Primera 2L engine is an SR20DE. My daily, humdrum, hardtop, non-knicker-elastic-snapping car is a primera 2.0 slx, quoted 125bhp. The eGT has the same block but quoted 150bhp. not sure where the extra 25 come from.

'tis indeed a 2l eGT. Lacking in torque a little from LPG conversion but cheap

A guy from Rouche(?)/ Ford USA compared the engine to a motorbike as we were pointing at the rev counter nr. Wolverhampton recently.

Not sure either where the horses come from, probably more rpm.

Neil.

Maybe. my tacho redline is 6500 and the rev limiter kicks in somewhere soon after 7000. Not sure exactly where, I was just being enthusiastic in second gear one day and noticed I lost power. Thought "crap" and changed up before I noted the revs.. I don't want to blow up my engine. it's already noisier than when I bought it (15000 miles ago)

Well what a cracking thread.
I have opted for V8 power after having had a go in Dax's 4 litre Rush demonstrator. I have never been in anything with such constant, massive , quiet , smooth, head pinningly fantastic acceleration.
Saying that a chap turned up whilst i was there with a Turbo Busa powered Rush. I can’t think of any superlatives to explain how fast that thing was. Needless to say it would have given Captain Kirk a run for his money and left the V8 in the dust
I guess the thing to keep in mind, as already stated is the bhp/weight figure.
Also as already said the rover engine weighs less than a the trusty ford pinto.
You can easily get a rover V8 to give 200+bhp just by changing the cam and most of that power is available throughout its whole rev range, hence its smoothness.
I have just sold my Robin hood and that had a 2litre pinto injection engine. If anyone wanted a strong, fairly powerful, easy to work on and cheap engine then this isn’t a bad lump to start with, plus a lot of kits are now Sierra based and you can use a single donor vehicle all the way throughout.

Cheers
Julian Brewer
Cumbria

I've not had the pleasure of a ride in a V8 7 but I will! Give us about 18 months Maybe..
I've read reviews of the Wesfield SEight and they usually contain "insane, stupendous, spits fuel at you" etc. Mind you that's with 270bhp. We are going with a standard 3.5 out of an SD1, can't really afford to do much more than change the cam for a "fast road" really but that should still give us 160-170bhp and over 200lbft of torque at a guess. Maybe in future we can upgrade it with such things as a Weber 4-barrel and higher compression pistons etc. That's if we feel the need for more power, no doubt we will
[Edit]
I'd be fascinated to drive an S2000 powered 7 of some description though. I had a Civic Type-R for a month and was smitten by that engine and 'box. S2000 is better still!
I'd not imagine that being low cost though.

[Edited on 24/9/03 by mackie]

Julian,

Quick point to bear in mind:

Rover V8 and box etc £350 upwards

Hayabusa engine £3500, plus Turbo £4000

If you've the money, the choice is yours and you won't hear a bad word from anyone on here

I'm going for a V8. I don't expect it to be spectacularly quick, but certainly enough to amuse me.

Plus there's the bonus of two exhaust pipes within 4' of me ear 'oles.

Fantastic.

ATB

Simon

quote:

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Now does anyone have a scrapped evoVII ?

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As Simon has quite aptly pointed out there is another factor higher than torque or bhp to be taken into account.
It’s the pound to smile ratio.
Buying a £50 fiesta and extending the brakes, pedals and steering, and welding a swivel chair to the roof and driving it from there would achieve a very high pound/smile ratio. Do the same with a STI Impreza and the factor goes down.
I’m not a Robin Hood apologist but it’s this factor alone that sells their cars.
1300 escort engine tied upto a paper cup..... yes please!

Cheers all

I'm a torque man myself.

When I'm wasting the boy racers at the lights I like it to sound like I'm not really trying.

- Greg H

Having been riding Bikes for about 20 years, I know a lot more about M/cycle dynamics than I do about the same issues concerning cars.
There is a school of thought that says bikes with big V-twin engines (high torque - lower revs) enjoy better traction and "driveability", especially exiting corners.
Because of this, the bike is easier to ride quickly. High revving, high power 4 cylinder engines tend to produce power which is less manageable, danger of high-side crashes etc. (This is where the rear tyre breaks traction)
I wonder if the same is true for cars?......

As I understand it, yes it is. When you have a turbo or somesuch that gives you a very peaky bhp curve, you can get caught out accelerating out of corners and, in a rear wheel drive, lose the back end.

aiui this is why 200SX's have an amount of respect (and high insurance group) attached to them

i opted for the v8 but not rover

chevy v8 producing 420 Bhp and 440 lbft and able to rev to 7000 rpm.

BTW for those in the ipswich area look out for a black jeep renagade. It's the wifes car and she's currently got this engine in it as i blew her's up last week.

hehe you can lay 4 strips of rubber in 3rd when the things got 4wd engaged and you floor it so should be fun in the 7 thing.

Tim

[Edited on 26/9/03 by timf]

Your sir, timf, are a complete nutter
How much does a motor like that cost?

parts "Imported" from the states during business trips £2500 machining etc £500
dyno time and setup £250
total £3250 not including my assembly time

Not so bad I guess. There's a UK outfit, I forget their name but they supply large ford and chevy engines for around that cost. That's very silly power to have in a 7 though. More poke than even hicost himself.
Is it an iron block?

Force = mass x acceleration
Torque = a turning force
therefore torque (at the road wheels) /weight of vehicle & driver = acceleration.

Torque at roadwheels = flywheel torque * gear ratio (box and diff)

Power = torque x rpm

RPM means that you can stay in each gear for longer before you have to change up. higher gears = less acceleration.

scenario 1

two identical cars, both weigh the same.
engine 1 = 100Nm at all revs and 7161 RPM red line. this gives 100BHP

engine 2 = 100Nm at all revs and 14322 RPM red line giving 200 BHP.,

in a drag race, these cars would accelerate at the same rate off the line. at about 32MPH, car 1 would hit the rev limiter and have to change into 2nd gear. the 1/2 second wasted changing gear means that car 2 is ahead. car 1 is now in 2nd and is accelerating less than car2. by the time both cars get to 62MPH car 2 is ahead. why? car 2 still has the same torque at the road wheel because in 1st gear the gearbox multiples the engine torque more.

scenario 2

two identical cars, both weigh the same.
engine 1 = 100Nm at all revs and 7161 RPM red line. this gives 100BHP

engine 2 = 50Nm at all revs and 14322 RPM red line giving 100 BHP.,

in a drag race, car 1 would accelerate much faster than car two to about 32MPH, car 1 would hit the rev limiter and have to change into 2nd gear. the 1/2 second wasted changing gear means that car 2 is catching up. car 1 is now in 2nd and is accelerating less than car2. by about 50MPH they are neck and neck. By 60 MPH the high reving car is ahead. why? car 1 wasted 1/2 a second changing gear. car 2 had ON AVERAGE more torque AT THE ROAD WHEEL.

it is the area under the torque curve and the gear ratios that give acceleration. a car engine may have more height on a torque graph but it hass less width (1000 - 6000 RPM typically). A bike engine may only have 2/3 of the torque for the same BHP as a car BUT it will rev from 1000 - 12000 RPM - more than twice that of a car.

given optimum gear ratios in each, a bike engine has more road wheel torque than a car engine over a broad range of speed and so is faster. The fact that a bike engine is lighter also helps.

If you prefer 0 - 30 times over 0 - 60 then a car engine is for you.

If you enjoy changing clutches for fun and want to spend your time pushing your car in reverse then a bike engine is for you.

you pays your money, you takes your choice.

[Edited on 26/1/05 by smart51]

Guys,
I agree with the approach which smart51 has taken and would emphatically agree that it is AVERAGES which are important, not peak or instantaneous power or torque. The area under the curves are useful when understanding this stuff.

However, I personally find it much easier to work with BHP than torque when calculating this stuff and using it to estimate expected performance figures. For a start the BHP curve tends to be a "simpler" shape and it is easier to find the area under it than with the torque curve, especially with "peaky" engines. Bear in mind that power is simply the rate of delivery of energy and energy is related to velocity and mass by this equation:

Kinetic Energy = (mass x velocity^2)/2

By rearranging this formula you can easily show the relationship between BHP and Velocity which is very handy for 0-60MPH or 0-100MPH calculations.

BUT, don't use your PEAK power figures when calculating this, you must use the AVERAGE power figure within the band defined by the spacing of your gear ratios. If a gear change from 1st to 2nd drops revs from 6000 to 4500 then this is your working range. If you have a rolling road power plot for your engine then you can easily calculate the average power output over this range and use it to work out 0-60 times.

In practice you will find that the AVERAGE power can be estimated as a fraction of PEAK power based on the type of engine. If expressed as a percentage of PEAK power, you will tend to find that a peaky engine will have a lower percentage than a big lazy V8 or a diesel engine. Highly tuned engines tend to be optimised to work well at particular RPM and it is essential to match this "power band" as it's often called, with a suitable gearbox to ensure that the engine doesn't fall outside this band. This is why highly tuned engines need more gears and more gearchanges to get the best from them. Conversely this is why big capacity V8's tend to be easy to drive fast because the engine produces a large proportion of peak power even outside the classic "power band"

I'm building with a Rover V8 3.5 litre by the way and I just can't wait to get it running...

Cheers,
Craig.

quote:

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Originally posted by craig1410
Guys,
I agree with the approach which smart51 has taken and would emphatically agree that it is AVERAGES which are important, not peak or instantaneous power or torque. The area under the curves are useful when understanding this stuff.

However, I personally find it much easier to work with BHP than torque when calculating this stuff and using it to estimate expected performance figures. For a start the BHP curve tends to be a "simpler" shape and it is easier to find the area under it than with the torque curve, especially with "peaky" engines. Bear in mind that power is simply the rate of delivery of energy and energy is related to velocity and mass by this equation:

Kinetic Energy = (mass x velocity^2)/2

By rearranging this formula you can easily show the relationship between BHP and Velocity which is very handy for 0-60MPH or 0-100MPH calculations.

BUT, don't use your PEAK power figures when calculating this, you must use the AVERAGE power figure within the band defined by the spacing of your gear ratios. If a gear change from 1st to 2nd drops revs from 6000 to 4500 then this is your working range. If you have a rolling road power plot for your engine then you can easily calculate the average power output over this range and use it to work out 0-60 times.

In practice you will find that the AVERAGE power can be estimated as a fraction of PEAK power based on the type of engine. If expressed as a percentage of PEAK power, you will tend to find that a peaky engine will have a lower percentage than a big lazy V8 or a diesel engine. Highly tuned engines tend to be optimised to work well at particular RPM and it is essential to match this "power band" as it's often called, with a suitable gearbox to ensure that the engine doesn't fall outside this band. This is why highly tuned engines need more gears and more gearchanges to get the best from them. Conversely this is why big capacity V8's tend to be easy to drive fast because the engine produces a large proportion of peak power even outside the classic "power band"

I'm building with a Rover V8 3.5 litre by the way and I just can't wait to get it running...

Cheers,
Craig.

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Crikey, for once I'm impressed with a torque spread explanation! Nice one Smart51!!!

Yes, the torque spread and gearing relative to traction available are the most important to the usefulness of any level of power in a car.

Guys
This is by far the best explanation that I have seen for BHP/Torque explanation.
Go down to Technical Articles and see Power and Torque 1, 2 & 3

Puma

HTH Chris

Proper turbo sizing for an engine can smooth that torque curve out so it is not nearly so peaky. You can get full boost at 2500rpm or at 5000rpm. Its all in sizing and what your intensions for the car are. In a car this light I am leary of going to a bigger than stock turbo which could give a BEC performance over a smaller turbo which can give good hp and high torque almost across the board.
Dale

What a good site, in many respects!

It also gives a very good explanation for running an with a new cam at 2000 rpm, which has been worrying me a bit (I've just put one in my engine). Lots of places tell you do it, but not why.

David

quote:

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Originally posted by cidersurfer
Guys
This is by far the best explanation that I have seen for BHP/Torque explanation.
Go down to Technical Articles and see Power and Torque 1, 2 & 3

Puma

HTH Chris

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quote:

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Originally posted by Lawnmower
So your saying a diesel is similar to a Rover V8

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