Race Engine Forum UK

Hi again!

2.0TC with 43,5/36 valves, fully ported.
CR approximately 10,5:1
304 cams 10,6mm lift.
Hestec engine management with 45mm throttle bodies.
4-1 tube header 670mm primaries
straight shot intake. Lenght 250mm

My engine was on dyno, and gave generally very good torque curve, but lacks of power, because torque starts dropping from 5500 rpm.
What could I try to keep the torque up to higher revs?

http://www.putfile.com/pic.php?img=5307784

Let me first say my comments below are 'all things being equal'. I don't know the cams but let us just 'assume' that they are quite good. Let us also assume the engine has been very well built with good compression, cams dialled in properly, head and valve seats nicely executed...

Sorry but you want to know my view and I'll tell you: Those results, especially considering it's fuel-injected - are very low.

Max torque at 5500rpm 188Nm = 139lbf ft
Max power at 6800rpm 112kW = 150 bhp

I am going to suggest that it probably has not been mapped very well at all, nothing new there, happens every day of the week; perhaps a combo of injectors too big and poorly mapped ignition advance.
With that spec I could get way more than that even on 45 DCOE carbs, way more, at least another 6lbf ft torque and well over 170bhp (and peak power at over 7000).
My advice is unbolt the injection, bolt on a pair of 45DCOE with 38mm chokes with an OE distributor and go back to the rolling road and do a comparative test, you will probably find out one of two things: 1) I'm right or 2) the cams are no use.

GC

Am i right or wrong Guy, but shouldn't the two lines cross nearer 5500 revs?

Andy.

They should meet at 5250rpm but it only works on a plot of power in bhp and torque in lbf ft.

It comes from the equation for power in Imperial units:

power bhp = (torque lbf ft x rpm) / 5250


GC

Guy Croft wrote:Let me first say my comments below are 'all things being equal'. I don't know the cams but let us just 'assume' that they are quite good. Let us also assume the engine has been very well built with good compression, cams dialled in properly, head and valve seats nicely executed...

Sorry but you want to know my view and I'll tell you: Those results, especially considering it's fuel-injected - are very low.

Max torque at 5500rpm 188Nm = 139lbf ft
Max power at 6800rpm 112kW = 150 bhp

I am going to suggest that it probably has not been mapped very well at all, nothing new there, happens every day of the week; perhaps a combo of injectors too big and poorly mapped ignition advance.
With that spec I could get way more than that even on 45 DCOE carbs, way more, at least another 6lbf ft torque and well over 170bhp (and peak power at over 7000).
My advice is unbolt the injection, bolt on a pair of 45DCOE with 38mm chokes with an OE distributor and go back to the rolling road and do a comparative test, you will probably find out one of two things: 1) I'm right or 2) the cams are no use.

GC

Injectors might be too big, but why it would affect on high rpm?
The man who adjusted injection and ignition maps is absolutely the best in Finland, the author of Hestec, and I absolutely rely on the job he does. He has experience and reputation of top end motorsports in Finland. So I might think that your suggestion 2. is the reason. I had a hunch of this and have already ordered some cams to try with.

...but you were right, this engine has been earlier dynoed with 45mm Solex addhe, and it gave 10hp more. However it was 80000km before. My cams might be worn out.

Send me the ignition map if you can, let me see it. I rarely say this on this site but why not get some GC cams? I am one of the few suppliers of TC cams who really knows what power they can give. Helps in two ways - gets you reliable cams and helps pay for my website.

GC

Guy Croft wrote:Send me the ignition map if you can, let me see it. I rarely say this on this site but why not get some GC cams? I am one of the few suppliers of TC cams who really knows what power they can give. Helps in two ways - gets you reliable cams and helps pay for my website.

GC

I don't know how to take the ignition map out of the box, but I'll try.
I'd really die for a pair of GC cams, but sorry to say, I just can't afford it! I have to settle for cheaper ones :(

Thanks again!

Guy Croft wrote:They should meet at 5250rpm but it only works on a plot of power in bhp and torque in lbf ft.

It comes from the equation for power in Imperial units:

power bhp = (torque lbf ft x rpm) / 5250


GC

Someone please correct me if I'm wrong, but that should work for metric units too!

Because 1kW=1.34hp and 1ftlb = 1.34Nm, they cancel each other out.

I think the problem comes from RR operators trying to convert power at the wheels to power at the flywheel. A constant is added (to simulate drive line losses) which throws the original power/torque formula out the window. Sorry to digress!

petert wrote: Someone please correct me if I'm wrong, but that should work for metric units too!

Because 1kW=1.34hp and 1ftlb = 1.34Nm, they cancel each other out.

I think the problem comes from RR operators trying to convert power at the wheels to power at the flywheel. A constant is added (to simulate drive line losses) which throws the original power/torque formula out the window. Sorry to digress!

The factors of 1.34 do not cancel out - they compound. So at 5250rpm you would expect torque in Nm to equal power in kW * 1.34 * 1.34. From NOSferatu's plot, this looks about right (at 5250 it looks like approximately 103kW and 186Nm).

The point of intersection in a kW / Nm dyno chart would therefore be at approximately 5250 * 1.34 * 1.34 = 9427rpm, if the power and torque were plotted on the same scale. Of course, in NOSferatu's case (and Guy's plot too), the scales are different (power on left hand axis and torque on right hand axis) so the intersection is quite arbitrary.

Andrew
[edited to remove incorrect formula for clarity]

Andrew, Peter is right.
1.34Nm is 1lbf ft! A Newton meter of torque is weaker than a 'foot pound'.

Peter, as for substituting SI (kW/Nm) into the equation I cited, if you factor in the conversions 1.34/0.74 it works, sure but what you've done in effect is convert to Imperial.

For metric units use: Power = 2 x Pi x n x T

Where Power is in kW x 1000, n is revs per second, T is Nm

As far as Imperial units are concerned and graphical presentation _ the curves will intersect if the power and torque curves are on the same scale, if they are not the readings of T and P will still be the same at 5250rpm.

Nosferatu, whilst not wishing to sound 'overbearing' on the issue, using mapped fuel injection but not being 'sure' about the performance of the cams goes against everything I teach here. In any case you will have quite a battle to find the 'missing' 20+bhp just by changing the cams. However good your dyno man is he can only 'so much' in the time he is allowed and inside the budget he has been given. This is not unusual.

GC

My apologies - I mis-read the equations. However, all the remainder of my post remains valid. The factors of 1.34 do not cancel out - they compound.

Andrew

If you rewrite the forumala as Guy suggested it looks like this:

P(kW) = (pi x N x T)/30000

and as corrected by Andrew:

5250 x pi x 1.34 x 1.34 = 30000 (approx.)

Therefore, the curves should still cross at 5250 regardless of the units, I believe. The two formulas are the same.

Dear members

in order not to get way off topic please start a new thread if you want to continue the discussion on power torque curves, rather than comment on Nosferatu's original post about low power on his TC engine.

Thank you,

GC

For what its worth I really cannot see how the tuning could cause such a drastic drop in torque. I suspect a problem with the manifold(s), head or cam.

It must be the cams (or cam timing). The head in flowbench was 192hp with the manifold and the actual lift.