Flow Benches and head porting

[phoenix]

Originally Posted by Denis Bassom

For info my Formula Atlantic spec 1600 16 valve makes a figure of 13.37.

Is that at peak torque, or peak bhp?

[Notso Swift]

Oops! Actually it looks like I transposed the 8 and the 9, I think it is 895 not 985 (based on 745.7 Watts to a HP) 1200 *0.746= 895. Phoenix, 883 would be PS, which is 735.5 Watts. (results are rounded)

AU N EGL, to do it with torque you use the torque to HP Conversion previously talked about. So, keeping it all imperial for you:
HP = (ft.lb x rpm) / 5252
and
BMEP = (HP * 895) / (Cap.Litre x RPM)
so
BMEP = (ft.lb x RPM x 895) / (Cap.litre x RPM x 5252)
The RPM cancel each other, but sine 895 and 5252 don't go into each other easily we will leave them as whole numbers, so
BMEP = (ft.lb x 895) / (Cap.litre x 5252)

[greenamex2]

Peak bhp.

[phoenix]

Originally Posted by Denis Bassom

Peak bhp.

Very good!

What is your peak torque and at what rpm?

[AU N EGL]

Originally Posted by Notso Swift

AU N EGL, to do it with torque you use the torque to HP Conversion previously talked about. So, keeping it all imperial for you:
HP = (ft.lb x rpm) / 5252
and
BMEP = (HP * 895) / (Cap.Litre x RPM)
so
BMEP = (ft.lb x RPM x 895) / (Cap.litre x RPM x 5252)
The RPM cancel each other, but sine 895 and 5252 don't go into each other easily we will leave them as whole numbers, so
BMEP = (ft.lb x 895) / (Cap.litre x 5252)

Thank you Sir.

[bdwoody]

what does b m e p stand for ?

[Notso Swift]

Brake Mean Effective Pressure.
It is the average cylinder pressure over the working stoke. The higher the pressure the more energy being put into the piston-rod-crank. The higher it is, the more the design has been "optimised". The key thing about BMEP is that it takes into account engine rpm, engine volume and engine power output. It’s the only equation to use when comparing engines from the perspective of saying which is more highly developed, BHP/Litre doesn't represent the work being don/rpm. So two 2 litre motors bother with 150 bhp, one does it at 5000 rpm the other at 7500 rpm, the one that can do it at lower revs is obviously more effecient (and this would be reflected in the BMEP... pulls out spread sheet and 13.44 vs 8.96)
To help link it all in together: max torque, BMEP, and VE are usually at the same point

[AU N EGL]

Originally Posted by Notso Swift

To help link it all in together: max torque, BMEP, and VE are usually at the same point

Ok Max torque is not at max rpms, which we know already and max torque can not be above 5252 rpms as HP = TQ at 5252 rpms.

then there are some cars that have flat torque curves from oh say 2400 right up to 4800 rpms or almost flat.

Nothing like torque to get out of corners and up to speed

[Notso Swift]

Not true max torque most deffinatly can be above 5252, it is true that they cross at 5252

[graham bahr]

Originally Posted by bdwoody

what does b m e p stand for ?

as others have said, brake mean effective pressure, in other words its an engine efficency calclation, its got nothing to do with power or torque as such but to do with the amount of pressure applied to the pistons on the power strokes, its a handy way of compirin two totally different engine capacity engines you could find a 1500 cc 4 pot would have the same bemp as a 3000 v6 even though power and torque figs would wildly differ.

[bdwoody]

so if the two cars had the same bemp and the same power to weight ratio they should be comparable on performance on the track yes?

[greenamex2]

Ok, using todays version of the formulae -

BHP BMEP = 13.55
Torque BMEP = 13.52

Near enough given I am reading the figures off a graph.

Peak torque is 127 ft lb at 7500. Just a bit higher than 5252!

Out of interest it drops to about 120 ft lb at 9000 and only makes about 105 ft lb at 6750.

[greenamex2]

No, they would just be considered equally 'efficient', all other things being equal the large capacity engine would still be 'faster'.

Probably the figure is best though of as a benchmark on how well tuned your engine is.

[phoenix]

Originally Posted by Denis Bassom

No, they would just be considered equally 'efficient', all other things being equal the large capacity engine would still be 'faster'.

Probably the figure is best though of as a benchmark on how well tuned your engine is.

I would put my money on the lighter car being 'faster'! To quote (or maybe paraphrase) Colin Chapman: 'More power will make a car quicker on the straights. A lighter car will be faster everywhere'

[greenamex2]

Unfortunately in a competitive series all it then takes is someone to put the effort into making the car lighter AND having the more powerful engine and you are stuffed.

And in a series with weight limits you CAN't make it lighter.

[AU N EGL]

Originally Posted by Denis Bassom

Ok, using todays version of the formulae -

BHP BMEP = 13.55
Torque BMEP = 13.52

Near enough given I am reading the figures off a graph.

Peak torque is 127 ft lb at 7500. Just a bit higher than 5252!

Out of interest it drops to about 120 ft lb at 9000 and only makes about 105 ft lb at 6750.

Something a bit off with the formula or the calculation or they are approximate figures.

HP is caculated from TQ and Peak TQ can not be above 5252 rpms. As 5252 rpms is were HP = TQ. Normally Peak TQ is in the 4800-5000 rpm range

http://vettenet.org/torquehp.html

HP = ((TQ x rpms) / 5252 )

TQ in foot pounds

[greenamex2]

Originally Posted by AU N EGL

HP is caculated from TQ and Peak TQ can not be above 5252 rpms. As 5252 rpms is were HP = TQ. Normally Peak TQ is in the 4800-5000 rpm range

Just because HP = TQ at 5252 torque can still increase after this point.

For instance at 5252 my engine is only making about 85 ft lb.

A Formula Atlantic engine (or anything else on 325 degree cams!) isn't a 'normal' engine!

[AU N EGL]

Originally Posted by Denis Bassom

Just because HP = TQ at 5252 torque can still increase after this point.

For instance at 5252 my engine is only making about 85 ft lb.

A Formula Atlantic engine (or anything else on 325 degree cams!) isn't a 'normal' engine!

How is a 325 degree cam differnt ?

So at 5252 rpms the car is producing 85 hp too.

In the States here most engine and chassie dynos are useing the SAE ( Society of Automotive Engineers) standards for determaining TQ and caculation of HP. This is now being considared the GOLD standard for all TQ and HP caculaitons. Using these standared, or to my understanding, TQ can not be greater the HP above 5252 rpms.

Now the SAE does have different correction factors do to type of engine, altitude, and barrometric pressure.

[phoenix]

Originally Posted by AU N EGL

How is a 325 degree cam differnt ?

So at 5252 rpms the car is producing 85 hp too.

In the States here most engine and chassie dynos are useing the SAE ( Society of Automotive Engineers) standards for determaining TQ and caculation of HP. This is now being considared the GOLD standard for all TQ and HP caculaitons. Using these standared, or to my understanding, TQ can not be greater the HP above 5252 rpms.

Now the SAE does have different correction factors do to type of engine, altitude, and barrometric pressure.

I think you need a refresher course in mathematics!

As a number of people have stated above, peak torque can occur above 5252 rpm and does, often, in race engines. The formula does not preclude this from happening - look again at it or get a maths teacher to explain it to you. The only thing that happens at 5252 rpm is that both torque in ft/lbs and power in bhp are the same. The torque can still be rising, and if it is so will the bhp and not just because of the rising engine speed. Simple as that.

[AU N EGL]

Originally Posted by phoenix

The torque can still be rising, and if it is so will the bhp and not just because of the rising engine speed. Simple as that.

Any one have a Dyno Graph they would like to post so we can look at these difference?

Originally Posted by Denis Bassom

Just because HP = TQ at 5252 torque can still increase after this point.

Please show me how that would work with this SAE equation HP = ((TQ x rpms) / 5252 ) TQ measurd in Ft lbs.

I think there is a difference in how we define terms and SAE corected cacluations that may be causing the confussion.

I can post of my dyno graphs latter.

[greenamex2]

Originally Posted by AU N EGL

How is a 325 degree cam differnt ?

So at 5252 rpms the car is producing 85 hp too.

In the States here most engine and chassie dynos are useing the SAE ( Society of Automotive Engineers) standards for determaining TQ and caculation of HP. This is now being considared the GOLD standard for all TQ and HP caculaitons. Using these standared, or to my understanding, TQ can not be greater the HP above 5252 rpms.

Now the SAE does have different correction factors do to type of engine, altitude, and barrometric pressure.

What has HP being greater than or less than TQ above 5252RPM got to do with the maximum possibly value for peak torque being at 5252RPM or less?

These are entirely separate subjects.

[greenamex2]

Originally Posted by AU N EGL

Any one have a Dyno Graph they would like to post so we can look at these difference?


Please show me how that would work with this SAE equation HP = ((TQ x rpms) / 5252 ) TQ measurd in Ft lbs.

I think there is a difference in how we define terms and SAE corected cacluations that may be causing the confussion.

I can post of my dyno graphs latter.

My figures ARE from a dyno graph!

[phoenix]

Originally Posted by AU N EGL

Any one have a Dyno Graph they would like to post so we can look at these difference?


Please show me how that would work with this SAE equation HP = ((TQ x rpms) / 5252 ) TQ measurd in Ft lbs.

I think there is a difference in how we define terms and SAE corected cacluations that may be causing the confussion.

I can post of my dyno graphs latter.

Here is a link to the page detailing a 2 litre, V8 engine derived from a Yamaha motorcycle engine.

You will see that peak torque is acheived at 8500 rpm and peak power at 10000 rpm.

http://www.cyclonepowerltd.co.uk/products.htm

From the information provided:

You can compute, with the formula you know and love so well, that at 8500 rpm this engine will be making 270 bhp.

You can also compute that at 10000 rpm the engine is making 158.6 ft/lb of torque.

You can also compute that at 8500 rpm the engine has a b.m.e.p. of 14.065 bar

You cannot compute what torque the engine will be making at 5252 rpm, but I would guess it will be very little.

SAE correction has nothing to do with any of this. Simply, you seem not to understand the relationship between revs, torque and bhp and it would appear that we in this forum are unable to enlighten you.

[AU N EGL]

Originally Posted by phoenix

Here is a link to the page detailing a 2 litre, V8 engine derived from a Yamaha motorcycle engine.

You will see that peak torque is acheived at 8500 rpm and peak power at 10000 rpm.

http://www.cyclonepowerltd.co.uk/products.htm

Source: http://www.cyclonepowerltd.co.uk/Image12.gif

It is difficult to see where the exact hp and tq lines cross. It does seem to be slightly above 5252 at more like 5800. So we dont know the corrected values, but does seem to be a realtively flat torque curve from 5000 to 10,000 rpms

From the information provided:

You can compute, with the formula you know and love so well, that at 8500 rpm this engine will be making 270 bhp.

You can also compute that at 10000 rpm the engine is making 158.6 ft/lb of torque.

You cannot compute what torque the engine will be making at 5252 rpm, but I would guess it will be very little.

SAE correction has nothing to do with any of this. Simply, you seem not to understand the relationship between revs, torque and bhp and it would appear that we in this forum are unable to enlighten you.

SAE corrections were desigened to allow all engine builders and tuners to use a STANDARED to compare between engines or differnt engine and chassie dynos.

Any more dyno graphs, please post them not just as links so we all can be enlightened.

[AU N EGL]

"

Dyno Correction Factor and Relative Horsepower

So what's all this correction factor stuff anyway??
The horsepower and torque available from a normally aspirated internal combustion engine are dependent upon the density of the air... higher density means more oxygen molecules and more power... lower density means less oxygen and less power.
The relative horsepower, and the dyno correction factor, allow mathematical calculation of the affects of air density on the wide-open-throttle horsepower and torque. The dyno correction factor is simply the mathematical reciprocal of the relative horsepower value.

What's it good for?
One common use of the dyno correction factor is to standardize the horsepower and torque readings, so that the effects of the ambient temperature and pressure are removed from the readings. By using the dyno correction factor, power and torque readings can be directly compared to the readings taken on some other day, or even taken at some other altitude.

How's it calculated?
The Society of Automotive Engineers (SAE) has created a standard method for correcting horsepower and torque readings so that they will seem as if the readings had all been taken at the same "standard" test cell where the air pressure, humidity and air temperature are held constant.
The equation for the dyno correction factor given in SAE J1349 JUN90,



where: cf = the dyno correction factor
Pd = the pressure of the dry air, mb
Tc = ambient temperature, deg C

The pressure of the dry air Pd, is found by subtracting the vapor pressure Pv from the actual air pressure. For more information about pressures and calculation of the vapor pressure, see Air Density and Density Altitude.

Horsepower and Torque:
Power is the rate at which work is done. When the engine torque is turning the crankshaft and power is being delivered, the resulting horsepower may be expressed as:

which can be simplified as

where: hp = horsepower, hp
t = torque, ft-lbs
rpm = engine speed, revolutions per minute

This is a great formula. Basically it says that if you can keep the same amount of torque, then the more rpm you can turn, the more horsepower you get! "


Source: http://wahiduddin.net/calc/cf.htm

There may be some higher torque numbers above 5252, but they will not be by much.

One quick observation is the RPM where the HP and TQ curvers cross. The two line cross at 5252 rpms. When you see a graph and the two lines do not cross at 5252 rpms, then the correction factor was not used, the dyno or tester is subject to question.