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Small engine - Big power - Dan
Hi everyone,

Question: how on earth does a basic 4 cylinder 1.4 produce 160bhp with a turbo?
I am of course talking about one of the early re-incarnations of the Renault 5 turbo I. Is this some sort of theoretical peak value? Or does this model have a massive turbo with a spool up time akin glacial movement??

Other models with turbo have more realistic 110bhp etc... but l've seen this 160bhp business in more than a few places, so whats the explanation?
If you could squeeze this sort of power out of a small engine why don't all cars have one!

Re: Small engine - Big power - Piers
To make power you have to burn fuel. To burn fuel you need air, or the oxygen really.

The turbo forces air into the engine (rather than the engine increasing the volume by lowering a piston hence lowering the pressure and the pressure differential to atmospheric (or under bonnet) pressure causes the air to flow into the engine on a naturally aspirated model).

A 1.4 nat asp engine has a possible 1.4 litres of air and fuel to burn in a complete cycle. However the restrictions to airflow (manifolds, filters, valves etc) limit the ability of the engine to fill the cylinders - especially at high rpm. The turbo forces air into the engine, it can therefore fit 2 litres of air into a 1.4 litre engine. With the correct amount of fuel this gives the power of a '2 litre' engine. Most turbos will have a maximum pressure of air that can be forced into the engine. If you increase this cut out pressure you get more air - with more fuel you get more power. Hence the 110 to 160 bhp difference. There is a limit to the volume of air a particular turbo unit can push though itself - so a bigger turbo unit might also be used. The cut-off pressure can be electronically controlled - a 'chip' is used to alter this pressure and correct the fuelling to give power gains.

Turbos are not cheap to fit or develop but can often work out cheaper than making a bigger engine or can be fitted to models where a bigger engine wouldn't fit. It's easier to have a car with a naturally aspirated engine with a sufficient output for most people and offer a turbo for 'nutters'! Most diesels have turbos these days - makes them much more powerful for a given size of engine. And diesel engines have to be strong (heavy) because of the high compression ratios required.

There's a lot more to turbo charging (or supercharging to be correct) than meets the eye - pressurising the air makes it heat up for example. This makes it less dense so less oxygen is available in a given volume. This is why cars have massive radiators - intercoolers - to reduce the air temp and get more power. This adds to the costs and complexity.

Re: Small engine - Big power - Dave
Dan wrote:
> Hi everyone,
> Question: how on earth does a basic 4 cylinder 1.4 produce
> 160bhp with a turbo?

Just look at almost any bike engine!

1 litre engines easily make 175bhp with no turbo.
Re: Small engine - Big power - mike harvey
Piers is spot on, and so is Dave with the bikes. Look at an F1 car IRO 800 bhp, thats 266 per litre. An engine that powerful does not last long though, 200 plus miles if you are lucky, and certainly not cheap. Car drivers want a reliable 150,000 miles plus, so a less stressed engine is the order of the day. Not many bikes do 150,000 miles. GP 500cc's 170 bhp!!
Re: Small engine - Big power - Dan
Thanks for your response but, l understand the principles of a turbo. What l meant was: The 110 bhp figure was for other models of the renault 5 ALSO with a turbo. I'd like to see a stock 1.4 (non-motorbike!!) produce 110 bhp from natural aspiration alone.
Other engines of similar size or even larger with turbos don't come close to this 160bhp, so l wonder.... What is so special about this 1.4 lump? Does it just rev at ludicrously high speeds to obtain this power? (Is that how the 1 litre motorbike engine produces 175bhp?)
Does anyone know?

Yours, sweating in anticipation.
Re: Small engine - Big power - Dave
Dan wrote:
I'd like to see a
> stock 1.4 (non-motorbike!!) produce 110 bhp from natural
> aspiration alone.

My ten year old single point injection 1.4 k series makes 95bhp. I'd have thought a modern 1.4 would be near to 110bhp.

Only two ways to increase BHP Dan. Increase revs or increase torque. If it's a powerful engine it must have big values for one or both of these...
Re: Small engine - Big power - Dave Marshall
The Honda Integra type-R puts out 190bhp from a 1.8 and not a turbo in sight.
Or if you want more, I think the S2000 has the highest output per litre for any road car at 120bhp/litre
Re: Small engine - Big power - Tim P
Big power from little engines is nothing new.

It costs money and takes a long time and they are not always the last word in reliability.

However... if you look in the latest Max Power there is a Renault 5 GT Turbo running 370bhp on a 1397cc 4 cylinder 8v engine.

That translates to 170mph and a sub 6 second 0-60.

As clarkson says, 'get ya spanners out'.
Re: Small engine - Big power - Dan
Examples shmamples,
How is it acheived? Dave said two ways:

Increased torque.
Increased Revs.

Revs l understand (F1 cars all sound like hornets..) as a way to increase hp.
Torque l'm a little unclear about. I was under the impression that gearing could be altered to provide more torque sacrificing power (BHP) and therefore top speed to do so.

Is it just a case of highly engineering everything: multiple valves, DOHC etc and losing a bit of reliability in the process.

What l'm trying to ask (if not particularly clearly) is: what is particularly well designed about the R5 turbo (or have they just fiddled to provide overboost and upgraded the likely-to-fail components) and if it such a powerful stock engine for a 1.4 4cyl 8v why isn't it more widely used??

Re: Small engine - Big power - Piers
There's nothing that special about the Renault engine. If it can make 160 bhp it's just from the amount of 'boost' pressure being able to push more air in. The rapid burn of the fuel using the available oxygen pushes the piston down. Exactly like a bullet from a gun. Put more powder in and the bullet goes faster - ie has more power as the mass of the bullet doesn't change. The piston is connected to a crank shaft and produces a turning action - torque. If it fires once then the amount of power realised - one bullet = dueling pistol - isn't much. However if it fires 3000 times in a minute it produces a lot of power - Uzi. Hence a car engine produces more power at 6000 rpm. The torque will drop off due to the air not being able to flow into the engine as well (air has mass and so inertia to overcome to get it into the engine) and hence less efficient cylinder filling leading to a smaller push on the piston. But because the cylinder is being pushed down more often in a given period (a minute for example) at higher revs the power produced in that minute is greater.

A bike engine revs very highly compared to car engines but produce less torque (they are tuned to get air in at high rpm but have sufficient power at lower rpm). Due to the bangs per minute you get lots of horsepower. The capacity of the engine only matters with regard to the ability to fill that capacity. Higher lift cams with lots of overlap are the common ways of tuning a nat asp for more power - it allows more air in at high rpm and mucks up low speed running. The turbo charged engine will have more torque (because there is more air and fuel to burn) and so can produce higher power outputs at lower rpms. The strength of older engines is sometimes much stronger than required as they weren't designed by computers and the extra cost of all the calculations and testing would be uneconomical compared to just having thicker blocks and beefier rods. The 1.4 renult engine is possibly one of these - agricultural and strong and can take bigger forces than the designers were happy to allow whilst they were providing the warranty!

Basically -

more air and fuel = more torque

More revs = more power

If you have more torque and more revs then you are sorted. Of course the more revs you have the harder it is to get good torque. Hence torque curves and power curves! The value of your torque and power can go down as well as up.........
Re: Small engine - Big power - Dave Marshall
The "standard" R5 turbo was 125bhp - it was only the heavily tuned mid-engined rally special one which was 160bhp (can't remember the model name).
R5 turbos are known to collapse at 40,000 miles with bottom end problems.
It's a push-rod engine that dates back to 1957.....
Re: Small engine - Big power - Dan
Cheers for that Dave,

Does this mean that push rod engines deliver more power but have a lower lifespan.
For example is it true that sustained periods of high revs simply disintegrate push rod engines?

Re: Small engine - Big power - Dan J
Sustained periods of high revs will end up wearing out any engine much faster, pushrod or otherwise and this is especially true on tuned up engines. Engine output is reliant on an exceptional number of variables of which I would imagine whether or not it is a pushrod would make an exceptional amount of difference.

It is no secret that the engines that last "forever" are, for example, unmodified VW Beetle engines and the Volvo 4 cylinders as used in the 1/200 series, all of which create a very low output for their size, but consequently last much longer than a 1.4 engine tuned up to 140 hp (what were the 1.6 Beetles, about 50 perhaps?) and spend their life screaming around at 4-6000rpm
Re: Small engine - Big power - Richard Hall
As Dave rightly says, the Renault 5 motor is an all iron pushrod motor dating back to the 1950s. The block and head casting are much stronger and heavier than they need to be, which is why you can get away with running a lot of turbo boost without the engine blowing itself apart, but the main problem with engines of this era is that they usually have weedy little crankshaft bearings, which the manufacturers cannot do much about without a total block redesign (in which case they might as well start again from scratch). Hence if you use all the power on a 5 Turbo all the time, you will be replacing crank bearing shells at about the same rate that most cars need new air filters.

Nothing wrong with pushrods in themselves, but they don't cope very well with high revs simply because there is so much weight of components involved, compared with the valve gear on an overhead cam motor. If you run a pushrod engine too fast, you get to a point where the valve gear struggles to keep up, resulting in valve bounce. There are still a few pushrod engined cars on the market, but most of them are diesels, where the speed limitation isn't a problem.
Re: Small engine - Big power - Piers
Might help.....

Horsepower = (torque * rpm) / 5252

The 5252 is just a consant to make the lb ft of torque give a HP output (one HP is 33000 ft lb).

if you are ever looking at a Power and torque curves they will always cross at 5252 rpm, as long as it's HP and lb ft.

Torque vs BHP - vin
So, if Horsepower = (torque * rpm) / 5252, what we can see is that, if torque is the turning force an engine can generate, then power reflects the speed at which the engine can deliver that turning force. (To be read in a Heinz Wolff voice). SOme people would define driveability as the distance in rpm between peak torque and peak power. Discuss.

Hence, diesels pull weight well, thanks to their torque; Ferraris deliver the rugby-scrum-in-the-back out and out power required for fast acceleration and wheelspin. Just don't mistake one for the other, because your Ferrari with a towbar will:

1. Most likely stall when you try to set off with your caravan;

2. Look utterly, utterly naff.

Stick to something totally tedious like a Citroen Diesel.

Doesn't answer the question about the Renault 5, I know.

Re: Torque vs BHP - mike harvey
Torque is like a hefty kick up the backside, Bhp is how often you do it.
Useable power. - David Woollard
Vin said........Stick to something totally tedious like a Citroen Diesel.......

Steady Vin, talk about light the fuse and retire!

"Totally satisfactory" for real world road use more like. I've just been out in the good lady's BX17TZD and thought it might need a "tune up". Leaving both the village thirty limits I floored it through 3rd/4th/5th and was taken aback by the useable power at just the speeds, and in just the gears, that most overtaking is done. I only needed the red dye and I could have been mistaken for part of the Red Arrows display team as well!

This car is capable of quickly exceeding both the speed limit and sensible driving limits in very short sections of main road. The newer HDi diesels (and the Golf TDi 130 HJ wants me to try) must be very competent.

You can't separate torque and power! - John Slaughter
Hang on guys- you can't actually separate torque and power.
At any point for an engine

HP = 2πNT/33,000

where N = engine speed
T = torque in lb.ft

(Sorry I'm still in imperial for some things!)

Diesels tend to produce greater torque at lower engine speeds, compared to petrol engines, so a comparison of the power output curves shows a power benefit to the diesel at lower speeds. What drives the car along is power, not torque alone.


HP = 2ðNT/33,000 - David Lacey

Seeing the formula HP = 2ðNT/33,000 it brought back those heady days of college when girls were the main interest, formulas as the above, as taught in Engine Technology by the very competant Mr Powell were downright boring!!!


Re: HP = 2ðNT/33,000 - John Slaughter

Know what you mean, but the formula is stuck in my head - as soon as i see the term 'horsepower' it all comes back. What's that symbol between '2' and 'N' though; it should be pi.


Re: Torque vs BHP - Bill Doodson

as many people have pointed out the internal combustion engine is just an air pump. The more air, the more fuel can be burnt so power will increase. Bike engines tend to produce more power than car engines at higher revs, my Blackbird produces about 165bhp claimed at about 10,000 rpm from slightly more than 1100ccs. Bike engines also tend to have different internal dimensional ratios ie ratio of bore to stroke. The larger the bore in comparison to swept capacity means that the mean effective pressure:-

( the MEP is the mean pressure on the piston during its power stroke in my example, after the fuel air is ignited the piston continues to rise and pressure increases. As the piston goes over TDC the pressure will be near its maximum, as the piston falls the pressure will remain high starting to drop off as the piston moves down. At BDC the pressure will be at its minimum. The mean pressure is calculated to be the average total pressure on the piston during its stroke).

-:on the piston can create more downforce. For example an engine with 1 cylinder and a bore and stroke of 10 * 10cm has a capacity of 790cc and a piston area of 78.5 cm. If the MEP is 15 Kg/Cm2 then the average force on the piston is 78.5 * 15 = 1178 Kg. For an engine of the same capacity but with a bore of 12.5cm the piston area is 123 cm2, with the same MEP that rates at a force of 1840 Kg a 50% increase, hence more power. But other factors start to come into play the shorter stroke will mean more revs but there is less time per unit time for the force to act so less torque.

The other thing that comes into play is volumetric effciency ie how much of the swept volume is actually put into the cylinder. Due to inertia in the air stream and other physical phenomenon it is possible to get a VE of over of 100% with no turbo but within a limited rev range. All the turbo does is increase the VR more air more fuel.

Honda did tests in the late 60s and early 70s I belive to see how much an IC can rev and still fill its cylinders, As far as I can recall, and its some years since I saw the reports, they got upto the 30,000s with no problems. Other than conrods snapping I assume..1

Re: Torque vs BHP - Dave
Bill Doodson wrote:
>Honda did tests in the late 60s and early 70s I belive to see
> how much an IC can rev and still fill its cylinders, As far
> as I can recall, and its some years since I saw the reports,
> they got upto the 30,000s with no problems.

I'm sure I've seen 30,000 rpm in my '91 414i. IIRC I was overtaking a tractor and trailor. ;-)
Re: Useable power. - Bill Doodson
David W

Your totaly right about usability on the road. Torque counts, no need to drop a gear just push the pedal. Makes for far more relaxed and smooth high speed driving. The Bentley Arange with over 800Nm sounds wonderful.

Just reread my last post, could have been better, but cant be bothered Ive got to get the kids in the bath.

Re: Torque vs BHP - vin

I knew I could count on you.

Re: HP = 2ðNT/33,000 - Brian
I think that the classic "oversquare" engine was the 997cc Ford Anglia 105E (the one with the reverse sloping rear window).
If my memory serves me right, that had something like an 80mm bore and a 70mm stroke (someone is sure to have the correct dimensions) and was capable of quite substantial tuning. It was certainly a vast improvement on the E93A side valve Anglia (1949 vintage) that was my father's first car.
I had the 105E from my father at about 60,000 miles as the second car that I owned (my first was a 100E which burned petrol and oil in equal quantities, or so it seemed) and had a recon engine in for about £40 at just over 100,000 miles, which was quite good going in those days.
Ah: happy days. :-)
Re: HP = 2ðNT/33,000 - Mark (Brazil)

> (my first was a 100E which burned
> petrol and oil in equal quantities, or so it seemed

If you have a 1959 G12 Matchless and you need new rings which are mostly not available any more, then you can use the rings from a 100E. However, then your Matchless will burn a huge amount of oil as well. Believe me, I know.
Re: HP = 2ðNT/33,000 - Richard Hall
The Anglia engine lives on, although much modified. Lift the bonnet on a Ford Ka and see if it takes you back to the good old days.
Re: Small engine - Big power - Dave
Dan wrote:
> Hi everyone,
> Question: how on earth does a basic 4 cylinder 1.4 produce
> 160bhp with a turbo?

Been reading Classic and Throughbred Magazine, Dan?

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