Desmo904
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| posted on 13/9/03 at 05:53 AM |
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BHP or Torque?
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'
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Sideways 2 Victory
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| posted on 13/9/03 at 09:55 AM |
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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
www.nurburgring.org
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Desmo904
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| posted on 13/9/03 at 06:50 PM |
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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.
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stephen_gusterson
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| posted on 13/9/03 at 07:01 PM |
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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]
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Spyderman
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| posted on 13/9/03 at 07:35 PM |
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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
Spyderman
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Desmo904
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| posted on 13/9/03 at 08:15 PM |
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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?
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stephen_gusterson
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| posted on 13/9/03 at 08:46 PM |
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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]
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Sideways 2 Victory
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| posted on 13/9/03 at 08:50 PM |
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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 
www.nurburgring.org
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Noodle
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| posted on 13/9/03 at 10:11 PM |
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quote:
Originally posted by Desmo904
But what about a Zetec?
Or a Vauxhall 2.0 Tcam?
And of course not forgetting the K-series as used by Lotus and Cateringvan. A friend built a turbo 1.4 for his sprint
car and regularly thrashed the SBD W?stfield in his class. 340bhp on a standard head-gasket. He was asked by Powertrain to find out what the problem
was with warped heads. Reckons it was a doddle to fix. 3 x 5mm holes in the thermostat and the problem goes away.
Light, tuneable, cheap, available and compact. If you can put aside your prejudices against head-warping (arse-hole main dealers apparently cause
almost all of them).
Neil.
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JoelP
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| posted on 13/9/03 at 11:22 PM |
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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...
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Browser
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| posted on 14/9/03 at 04:28 AM |
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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!
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Noodle
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| posted on 14/9/03 at 07:09 AM |
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In a nutshell:
Torque is the twisting force at the crankshaft.
BHP is the relationship between torque and rpm.
Neil.
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Desmo904
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| posted on 14/9/03 at 07:43 AM |
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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?
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stephen_gusterson
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| posted on 14/9/03 at 10:53 AM |
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quote:
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
Ned (i think it was) posted a V 8 bike engine piccy once - two 1000's strapped to a common casing
atb
steve
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Spyderman
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| posted on 14/9/03 at 12:06 PM |
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quote:
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
There are plenty of V-twin bikes around, so there must be plenty of donors.
From reasonably low power (50bhp) CX500/CX650/turbo, upto the Ducati 900/1000 twins.
Plenty of options out there to work with!
Spyderman
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Sideways 2 Victory
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| posted on 14/9/03 at 06:40 PM |
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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
www.nurburgring.org
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ned
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| posted on 15/9/03 at 08:47 AM |
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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]
beware, I've got yellow skin
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Simon
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| posted on 15/9/03 at 09:20 AM |
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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
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mackie
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| posted on 15/9/03 at 12:28 PM |
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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.
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Chazzy
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| posted on 15/9/03 at 04:06 PM |
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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 ?
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Noodle
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| posted on 15/9/03 at 05:57 PM |
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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.
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blueshift
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| posted on 15/9/03 at 07:35 PM |
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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.
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Noodle
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| posted on 15/9/03 at 09:11 PM |
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'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.
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blueshift
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| posted on 15/9/03 at 09:31 PM |
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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)
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Julian B
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| posted on 24/9/03 at 07:40 AM |
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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
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