Dyno performance- actual readings

Dellortoman said:
For peak power at 7,800 RPM and torque at 7,000 on an 1130cc 120? engine running F1 cam timing, the number crunching tells me I need 38mm OD headers x 560mm long, going into a 50mm OD secondary.
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Is this scientifically calculated 38/50mm OD system 0.6mm wall tubing, 1/4" wall steam pipe or solid bar? Or does it not matter?
:)
 
It only has to look right Steve, so as long as the OD is right, the ID doesn't matter  ;)

FFS, I only quoted OD because that's how exhaust pipe is usually specified. If I'd said 35mm ID somebody would have said you can't buy pipe in that size. Just goes to show that there's always some pedantic bastard ready to pounce. Usually it's me  :D

Now, before you tell me you can't buy 38mm or 51mm exhaust pipe, yes, I know it's usually called 1?" or 2" x 16 gauge (1.65mm) wall thickness

 
The ones I ilike the look of are those cut and shut jobbys you see coming out of Japan.No idea if they acualy work but they do look cool
 
Dellortoman said:
G'day Paul

Your bloke is probably using similar formulas as I am (from A Graham Bell's "Four-Stroke Performance Tuning"). Bore, stroke, and timing of exhaust valve opening are the basic parameters, then you factor in where you want the peak power and torque in the rev range.

For peak power at 7,800 RPM and torque at 7,000 on an 1130cc 120? engine running F1 cam timing, the number crunching tells me I need 38mm OD headers x 560mm long, going into a 50mm OD secondary. After that, it either doesn't matter too much or it's beyond the scope of simple arithmetic to figure it out. The system I bought from you has slightly longer headers than that, so it might move the power down the rev range a bit at the expense of top end. I haven't got as far as the dyno stage yet.

I suspect the uneven exhaust pressure pulses of a 180? might throw a spanner in the mathematical works, so your development work on the dyno is pretty much the only way of solving the puzzle. Must be costing you a heap in dyno runs and exhaust mods though.  ;)

Cam
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A 180 is just a four with one pulse missing. All calcs for those are easy - normal 4 cylinder practise applies.
The 120's though are a little different. The short headers work because of overlapping wave action - which gives you the case where you can get pulse amplification due to two ex valves being open at the same time - or at least their opening periods overlap...What has been described earlier on in the thread is basically half of a six cylinder setup. Have a look at the old textbooks describing inline six systems.
Away from the 120's header length sets the torque peak RPM and overall system length sets peak HP rpm. Within the right overall length you can fudge header length to get the widest power band, but there are limits to this. Too long headers will cost peak HP. For the RPM range most of our older motors operate in, a total system length of around 58inches is pretty right. Sorry, I still think in imperial for pipes....My rule of thumb for post classic race pipes is at least 20inches from collector to start of muffler.
 
Dellortoman said:
G'day Paul

Your bloke is probably using similar formulas as I am (from A Graham Bell's "Four-Stroke Performance Tuning").
Click to expand...

I reckon he might be just a little bit further up the road and round the corner than that Cam....
 
Dellortoman said:
FFS, I only quoted OD because that's how exhaust pipe is usually specified. If I'd said 35mm ID somebody would have said you can't buy pipe in that size. Just goes to show that there's always some pedantic bastard ready to pounce. Usually it's me  :D

Now, before you tell me you can't buy 38mm or 51mm exhaust pipe, yes, I know it's usually called 1?" or 2" x 16 gauge (1.65mm) wall thickness
Click to expand...

With all due respect, you're a disgrace to the artform of pedantry if you don't even know the difference between pipe and tube.
:p
 
Pipe, tube ... who cares. It's all just a cylindrical hole with metal wrapped around it.

A few years ago I bought some stuff called "hollow bar". The ID was about half the OD, so bloody thick walled stuff, but it's still pipe as far as I'm concerned. It was actually used for the propeller shaft tube on a steel boat.
 
Dellortoman said:
Pipe, tube ... who cares. It's all just a cylindrical hole with metal wrapped around it.
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Of course, in other parts of the world, the tube may have a square, rectangular or any other shaped hole, around which metal is wrapped. Maybe the modern shapes have not yet made it to your shores  :D

Just feeling a little pedantic this evening.
 
could not give a fuck what it is called or made from or the size or shape, as long as it makes good power right through the rev range and clean to the redline at 8,900 rpm, it is good
that is all that matters



 
I don't think you would be allowed to ride that during Harvest Bans  :eek:
 
redax5 said:
inlet side, we are just using velocity stacks at the moment but you just reminded me that I need to make custom stacks with reverse airflow technology built in to them, like the backside of an aeroplane wing, totally forgot about that, my CNC man is dropping in tomorrow, he has the program already for the inlet stack shape, will order a set, believe they will be good for at least another 4hp by themselves
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and here they are, bit of machining to get them to fit, mainly the middle stack to clear the frame tube
suck better then Linda Lovelace these puppies, awesome

off to the dyno in the morning for a few more runs, if we crack 120hp will call it quits and go racing




 
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