ESE's works engine tuner

[Buckets4Me]

Are we talking in the next decade or what?

about the same time you manage to make it up is my guess

[TZ350]

There is any amount of information on Port-Time-Area for Inlet, Transfer and Exhaust, but precious little information on Blowdown-Time-Area that I can find.

As the need for more Blowdown-Time-Area increases with increased HP and/or RPM.

It’s not enough to work out the Port-Time-Area for the Transfers and Exhaust, the Blowdown-Time-Area also has to be considered but I have not found much information on it.

I find its very easy to get transfers that fit the bill and an exhaust big enough to do the business but there is not enough blowdown to do the job. HP and RPM are just as closely tied to blowdown as it is to the other ports.

So if someone has sized the transfers and exhaust properly using the charts in Jennings book and are not getting the power expected the problem could be in the Blowdown-Time-Area. The Blowdown-Time-Area requirement is not specifically talked about by Jennings or displayed on his graph.

The ways to increase blowdown are:-

(1) To raise the exhaust port (increased time) and/or widen (increased Area) out to 70-75% of the bore width.

(2) Reduce the height of the transfers for more blowdown time. Keeping the transfers low (reduced transfer time) and wide (increased transfer area) to get back to the required Transfer, Exhaust, Blowdown, Time-Area relationships.

But how to make sure that there is enough Blowdown-Time-Area for the HP and RPM. In the past I have transposed between the lines on Jennings graph for the exhaust and transfer ports and guestimated it, but now use this Porting Calculator.



Planning the Port-Time-Area for the Transfers and Exhaust,



Checking the Blowdown-Time-Area.

This handy (and cheep) Porting Calculator from:- http://www.porting-programs.com/ is based on Blairs and Jennings work. And not only does it work out the Transfer and Exhaust time area requirements, it also gives the Mean Area of Blowdown required for the planned Power and RPM.

By using the Porting Calculator I was able to see that my 27 rwhp engine.



with its big as exhaust that’s opening 80 ATDC (200 duration) and widened out to 75% of the bore width, and with the transfers set lowish opening at 114 ATDC (132 duration) and wide as possible. Has pretty much run out of options for increasing the Blowdown-Time-Area for more HP at 12K rpm.

So for more power the next step will be digging side exhaust ports for whatever extra mean blowdown area I can get from there.

[speedpro]

Small mistake with the specified carb size, or did you get the rules changed?

[TZ350]

Small mistake with the specified carb size, or did you get the rules changed?

Eeeek.....what....where..........

Oh......Ok.... if your looking on the screen shot, then that is the porting calculators suggestion for the carb size required......

[kel]

But how to make sure that there is enough Blowdown-Time-Area for the HP and RPM.

Blow down area, so what is the answer?
My current port timing allows for the following calculated time areas
Exhaust .015543, transfer .008304, blow-down .0007708. (All measurements in sec-mm^2/cm^3) As you stated TZ Jennings suggests port time areas while he doesn’t state blow-down time area requirement.
Blair subscribe to calculated areas based on BMEP, his example 125GP racer calls for an exhaust time area of .0162 and a blow down requirement of .00113 at 11500 rpm.
So while my exhaust and transfer time areas would seem pretty close to optimum I don’t seem to have anywhere near enough blow-down. As you state TZ options to increase blow-down include – 1. Raise or widen the exhaust, but neither would seem reasonable considering my current porting (Im at 72%) 2. Drop the transfer timing, which will surely make the thing to peaky 3. Exhaust boost ports, the cylinder studs won’t allow for this one either. So Im at a bit of a loss.
From the screen shot the software you’re using seems to state the required blow-down vs where you’re currently at? Do you have the necessary numbers to append blow-down area requirements on to a copy of Jennings angle time-area graph?

[speedpro]

It's a bitch. Something else that meeds to be considered is the port entry angles which affect area values by the cosine of the angle, plus the port duct taper and radius.
It does seem that you cannot get the desired exhaust time/area without some extra exhaust ports. You also can't get the seperation between the exhaust and transfer ports timing wise, whilst maintaining acceptable transfer time/area, without very wide transfers which may cause short-circuiting as they approach the exhaust port/s. The blowdown time is critical and generally has been overlooked in the past. It makes sense though, if the motor is revving higher there is less time for cylinder pressure to drop once the exhaust opens before the transfers open so the motor will need a bigger exhaust port or lower transfers to create more time or area for blowdown to happen.
Then you can design a pipe taking into account what port timing and time/areas you ended up with.

[wobbly]

What you guys need to understand is that we ( you) are trying to emulate GP cylinder power numbers with shit porting derived from road bikes.
Having a single Ex port will limit power capability - end of story.
And trying to get the big bmep numbers means that the only way is to make the ports higher and wider.
Having 205/138 numbers is la la land, sure it will go - but it will never work properly with even the cleverest pipe design on the planet.
Blowdown is the single most important number in the spec sheet.
The other thing that seems to be overlooked by many is that Hp=T*rpm.
An engine with a 50mm stroke "should" be peaking at 13000,and be running on to 14000.
But when you have to use very high exhaust timing this tends to shut down the power over the top.Also anything but a square bore/stroke ratio makes it doubly hard to get the port areas needed.
To show what can be done, here are the STA figures for the 38 crank 125 with tripple Exhausts and as much transfer width as can be crammed in.
As its a big bore at 56mm the Ex area is low but this is of lesser importance than the blowdown.
Notice the relatively low bmep needed to achieve the power at 13000, with very normal timings of 194/132.

[TZ350]

Blowdown is the single most important number in the spec sheet.

Confirmation of what we were starting to figure out for ourselves........... thanks.

Having 205/138 numbers is la la land, sure it will go - but it will never work properly with even the cleverest pipe design on the planet.

Glad I heard this before I started hacking into my next barrel........

The other thing that seems to be overlooked by many is that Hp=T*rpm.

An engine with a 50mm stroke "should" be peaking at 13000,and be running on to 14000.

A GP125 Turning 13-14,000RPM should be interesting........ frigtening, but in a good sort of way ....

[kel]

What you guys need to understand is that we ( you) are trying to emulate GP cylinder power numbers with shit porting derived from road bikes.
Having a single Ex port will limit power capability - end of story.

Yes GP motor BMEP figures based on Blairs work with single exhaust port 54mm square motors.
I currently have exhaust port set at 194 degrees, problem is in the sizing of the crap transfers and the lack of room for the aux exhaust ports. Your calculation sheet illustrates perfectly the need for auxillary exhaust ports to achieve required blow-down. Damn thats going to be expensive to add to the KE.
I'm not looking to produce anything like 38hp but I may have to re-think things if thats where its going. Hopefully your calcs for 13000 rpm are based on the DT rod and bearings as thats exactly what ended up in my motor! (not allowed to use YZ rods and bearings people)
Cheers for your input Wobbly.

[wobbly]

The DT125 setup using a TZ125 piston i havnt transferred to a 100cc sleeved down watercooled yet, as I wont have the parts here for a day or so, but with the smaller piston, reving to 13000+ wont be a problem at all.
NoMates RG150 sleeved down uses a very light kart piston and could go much higher in rpm and power, but 4 years ago his 28RWHp was more than enough for a couple of easy champ wins limited to just 12500.
Now we have the MB100 finally approaching the potential numbers I did back then as well,then 35 crank or around 30RWHp @13000+ will soon be the required benchmark.
But even these numbers can easily be beaten with good workmanship and good basic layout of the ports/pipe/head/ignition - sorry, but a single Exhaust just aint no good at this level of performance.
Tripple or a properly designed T port are the only way.

[F5 Dave]

There have been people who have made T ports but I'm not sure they ever ran them for long. Unsupported bridged sleeve would surely seize. I sub ex ported my MB 13 years back, but it got killed a bit by a welder. One side looked good, the other not so much as it broke through the vertical barrel stud hole, Damn asymetrical layout! Was nicely curved, but had to put a dowel in the way which encroaches the tunnel a bit.

By coincidence I only just o-ringed it today trying to resurrect it (& yes the groove will be a sight better than the CPI barrels).

[bucketracer]

TeeZees motor as it is now, thats 27 RWHP and 3.5K power spread.

In the interest of real world science here I would say that 27 RWHp from a 125 is nothing to jump up and down about.

With all this talk about big HP numbers we are forgetting what TeeZee has achieved with his old GP125 ...........

Hands up anyone else with an F4 Aircooled 125 2-Stroke thats making 27 RWHP or 26 or even 25, any takers at 24???

It's just all talk untill its done.

[TZ350]

.

The smile says it all...............



Look at the power spread



I make it at least 5K wide, no wonder these things are hard to beat.........

[TZ350]

.

Ok....... this is where I am at now.



This barrel was one I have used before and it had been ported to Ex opening 81 ATDC 72%, Trans 112 ATDC

I am now trying to see if I can cut side ports into it, just to see if it can be done to a GP barrel............

[F5 Dave]

I tried to take a pic but the crumby one at work isn't much chop so I adjusted the brightness a bit. Can't see the o-ring (or the porosity).

The rubbish in the barrel is swarf. The pic makes the ports look rounded but they are quite a bit more square. The real damage when welding into the barrel is evident in the ex port where you can see the ally coming away. I'm pretty sure this will seize as there isn't any ally left over the bridges, but on the other hand it is considerably wider than a T port, so maybe it won't. I have another barrel to start again, this one was headed for the bin 13 yrs ago.