ESE's works engine tuner

[Bert]

Something a little off the current topic;
Not even sure if it will work; but we will see...
one of the things I've been struggling with (with my build) is resolving the head and squish etc. the standard head could be welded up and re machined but i didn't really like the location of the sparkplug (distance away from the piston; which meant everything was always going to be a compromise...) so we have done something different.

so this is what we started with, standard TZR head complete with crappy noise reducing squish (apparently), welding this was never really going to work out well:
Attachment 234615

So we made a Homemade VHM head (water galleries to be cut). Surprising amount of meat in the cast head.
Attachment 234616

so now we have a nice two piece, fully o-ringed head, sparkplug passes through the original head into the insert. all hopefully will hold together with the standard head studs :
Attachment 234618

currently the insert is in blank form, but that's the next step.
Attachment 234617

if it works I'll be stoked.

[TZ350]

so this is what we started with, standard TZR head complete with crappy noise reducing squish (apparently), welding this was never really going to work out well:
Attachment 234615

So we made a Homemade VHM head (water galleries to be cut). Surprising amount of meat in the cast head.
Attachment 234616

so now we have a nice two piece, fully o-ringed head, sparkplug passes through the original head into the insert. all hopefully will hold together with the standard head studs :
Attachment 234618

currently the insert is in blank form, but that's the next step.
Attachment 234617

if it works I'll be stoked.

Very interesting Bert, looks good, I reckon it will work a treat........

[TZ350]

All because someone asked.

BMEP or Break Mean Effective Pressure as I understand it.

BMEP is not a real thing ………. I have always wanted to say that….

BMEP is not real, 2+2=4 is real but BMEP is not, its one of those things like the stick and ball models of atoms and molecules we all saw in science class at school.

Those models are not like real atoms, real atoms are clouds of uncertainty and require complex math to understand. The models are just simple (but very good) concepts to help us get our heads around something quite complicated.

BMEP is like that too, a concept to help us get our heads around something complicated.

A motor sucks, compresses, bangs and blows gas in a complicated way. And you can easily see that there are all sorts of positive and negative pressures on the piston during a 2 or 4 stroke cycle.

It would get messy quite quickly trying to keep track of all those positive/negative pressures and there is certainly no easy way of measuring these pressures individually and then adding them all up.

But the sum result of all of them can easily be measured as hp and hence the simple concept of BMEP

BMEP or Break Mean Effective Pressure. Break for hp, Mean for average, Effective for sum total, Pressure for force and BMEP is commonly expressed in Newtons cm2, PSI or Bar. 1 bar is basically one atmosphere or 14.5psi aprox and 1 Newton cm2 is 1.45 psi aprox.

BMEP is regarded as the amount of force that you need to exert on a piston to generate the same torque at the crankshaft as generated by the measured hp.

So BMEP can be calculated from crank hp and rpm or you can calculate hp if you know the rpm and the BMEP at that rpm.

Remember, basically hp = torque times rpm

Or work done = cranking force times how fast you can spin the crank around.

Try crank starting an old car to see what I mean about “work done” or the size of your persional hp.

To get more hp, (more work done), you need more torque (to work harder) or to spin the crank faster (work quicker) or both.

Now, torque comes from the heated combustion gas pressing down on the piston. To get more torque (and therefor hp) you need to heat the combustion gas more to get more effective pressure.

There is a direct correlation between torque and the concept of BMEP, and the hotter the combustion gas the hotter the mean exhaust gas temperature will be and the higher the resulting Torque and indicated BMEP.

In a 2-stroker a BMEP of 9 Bar results in about 500 deg C mean exhaust gas temp and 11 bar its about 600 from memory.

So, say you designing a motor for 25crank hp (22 rwhp) and knowing the rpm your going to run, the BMEP required equates to a BMEP of 10bar then you know that the mean exhaust gas temp will be 550deg c.

You need to know the exhaust gas temp as the speed of sound is faster in hotter gas, and slower in cooler exhaust gas.

Now that you know what the exhaust gas temp will be, you can design a pipe with the right tuned length for the rpm your intending the motor to run at.

BMEP is a concept tool that ties Carburettor size, Air/fuel consumed, Port-Size, Hp, Torqe, Combustion-Temp and Ex-Temp together.

As a rule of thumb, for a 4-stroke the BMEP should be better than its cranking pressure and a 2-stroke is close, but a little less than its compression pressure.

BMEP is a much more appropriate tool than hp or torque for comparing the performance of different engines.

This is, as I understand it, a quick Google will bring up a lot of info on BMEP what it means, how to use it and formula for calculating it.

[wobbly]

I simply dont "get" the correlation between bmep and Ex gas mean temp at all.
It is entirely possible to set up an engine to produce X - Hp at just about any reasonable mean temp.
The gas temp affects the pipe dynamics, and is a function of the static compression, the ignition advance, and just as importantly the dynamic compression ( that is achieved by the delivery ratio X the trapping efficiency).
We can achieve the same power using unleaded fuel running very rich with lots of advance and no com, this would give a header temp of say 1050F.
On leaded Avgas, the tuning combination would be very different , but the header temp for best power on that fuel would need to be over 1200F.

You use the bmep to correlate the port STAs with the Hp target.
The pipe temp is a separate function that dictates the pipe length needed to work with the Ex duration you have derived from the STA calcs.
The 9 Bar engine can be run at 500C or 600C, it all depends upon the tuning approach, and the fuel used, as to what the mean temp in the pipe ends up being.

[TZ350]

I simply dont "get" the correlation between bmep and Ex gas mean temp at all.

You use the bmep to correlate the port STAs with the Hp target.

The pipe temp is a separate function that dictates the pipe length needed to work with the Ex duration you have derived from the STA calcs.
The 9 Bar engine can be run at 500C or 600C, it all depends upon the tuning approach, and the fuel used, as to what the mean temp in the pipe ends up being.

Thanks for adding to that, from reading Blair, I had formed the impression that mean ex temp was directly related to BMEP.

Could you please explain STA. TA I guess is "Time Area" but the "S"?

[k14]

So we made a Homemade VHM head (water galleries to be cut). Surprising amount of meat in the cast head.

Aren't those inserts made for competition engines?

Be careful when machining, I know of a couple being stuffed up by fairly experienced machinists.

[kel]

Could you please explain STA. TA I guess is "Time Area" but the "S"?

Specific Time Area.
Time area, and the ratio between port window area and cylinder volume - according to Jennings

[TZ350]

Specific time area. Time area, and the ratio between port window area and cylinder volume - according to Jennings

Specific Time Area is that another way of saying Port Time Area or is there a difference?

[wobbly]

Specific time area (STA) is an indication of the effective port window area that has to be open for a certain length of time to allow enough gas to flow through the port to achieve the target power at the target rpm for that specific engine capacity.

Time/area is just that, a hole with a certain area that is open for a certain time period.

STA has time/area derived from the port and the rpm,plus the relationship of that to the cc of the cylinder.

[wobbly]

Just one thing to be aware of re machining the crank for case clearance.
This will drop the CCR and thus the signal seen at the carb.
You will need to go richer everywhere to compensate, more so in the bottom and middle.

[TZ350]

The gas temp affects the pipe dynamics, and is a function of the static compression, the ignition advance, and just as importantly the dynamic compression ( that is achieved by the delivery ratio X the trapping efficiency).

We can achieve the same power using unleaded fuel running very rich with lots of advance and no com, this would give a header temp of say 1050F.
On leaded Avgas, the tuning combination would be very different , but the header temp for best power on that fuel would need to be over 1200F.

The pipe temp is a separate function that dictates the pipe length needed to work with the Ex duration you have derived from the STA calcs.

From reading Blair, I had formed the impression that mean ex temp was directly related to BMEP.

But a moments thought would have shown me that its not as close a correlation as I had thought.

I was reminded by your post that the ex temp can also be affected by fuelling and ignition advance (amongst other things).

And of course on our own engines we are retarding the ignition and leaning out the mixture by closing the electric power jet so as to heat the ex gas in the pipe and thereby extend the over rev.

[TZ350]

Just one thing to be aware of re machining the crank for case clearance.
This will drop the CCR and thus the signal seen at the carb.
You will need to go richer everywhere to compensate, more so in the bottom and middle.

Thanks for the heads up, I had not got the mixture right with the new setup anyway, particuarly coming back on the throttle, and especially throttling on again from the bottom end after shutting the throttle on over run.

[TZ350]

Attachment 234636

Attachment 234635

Getting it back in the case, the clearance around the flywheel doesn't look as bad as I thought it would.

Attachment 234634

The shadows make the side clearances look bigger than they actually are.

Std the case clearance is 1mm around the flwywheel, it is now 2mm every where between the flywheel and the case.

After a lot of work the balance factor is exactly 50%.

Clearance and balance factor are the only changes, so it will be interesting to see how it goes on the dyno next week.

First up I will run with the old carb, then if things are working ok I will try the new electric power jet carb and if all that goes well and we are getting good over rev at the top I will try water injection to see if we can extend the lower part of the power spread.

[wobbly]

Dont waste your time and energy re water.
Honda did it with full PWM solenoid control - it bumped up the bottom end really well, but the water mist in the pipe kept it cool for so long down the straights that the engine never really recovered in time to get the top end back.
Another expensive blind alley.

[kel]

Your photo gives away that your injecting something direct into the cases, do tell.