Bobs got a new 500 motor

[23champ]

I thought the rear transfers where supposed to open first?

[100hp honda]

theres probly hundrerds of variations used by different manufacturers over the years. never have the rears opened first from what ive seen but its possible i guess. the rears on the "stock" honda are pointed somewhat toward the exhaust hole, having it open first would certainly be a bad idea. rear=nearest the intake

[100hp honda]

didnt eric gorrs book recond filling the rear with epoxy to point straight across ? so many freakin different ideas it will make your head spin

[Roostius_Maximus]

i have one like that too

[dubious01]

didnt eric gorrs book recond filling the rear with epoxy to point straight across ? so many freakin different ideas it will make your head spin

I will never proclaim to be anything more than an enthusiast,


I do recall Eric stating the epoxy to change the rear transfer port trajectory was to help bottom end power,

does that mean that it would also hinder top end power though?
I know one thing, I hated his head mod, the drop in compression really killed the bottom end torque.

[Slomo]

Show up at Hoonfest 2011 and I'll let you try out my ultra trick trail ported AF. It's gonna rock!

.....no Brit, you suck too bad to ride it... sorry

[britincali]

[100hp honda]

never tried erics epoxy deal so i cant say about the low end power but the idea to aim them straight across may carry some weight. these seem to all aim to the back corner with the rear ones going straight across. be cool to see all 6 fire at once . ill see if i can make it happen tomorow

[AlisoBob]

Is that what they mean when they say " wet flow " tested ????

[Roostius_Maximus]

do it with acid so it ports the cyl at the same time

[glen howell]

If you will notice the last port he ran the water hose in was the only port that flowed right,Up over and toward the intake. That's the use a flow bench helps to check you port angles if done rite they will flow up,over,and toward the intakes but a water hose is not the best test water is a little heavy to get a accurite test. this is what it should have looked likeGlen

[/img][/img]

[Roostius_Maximus]

cant see the others reacting to it either, good to make sure nothing is blocking the port, not much else as crude as that one is setup

[glen howell]

X-2

[AlisoBob]

You let the dog lick the exhaust port? I had a girlfriend like that once....

[100hp honda]

sorry about the britincali style flow bench . its all i got

[Roostius_Maximus]

You let the dog lick the exhaust port? I had a girlfriend like that once....

nice

[glen howell]

X-2

[glen howell]

That's why all dogs go around sniffing the other dogs ass is they all went to a party and the rules of the house was to hang there tails up while they we're there a fire broke out they all grabbed each others tail being the wrong tails they got ,that's why they smell the other dogs ass is trying to find there own tail.

[britincali]

[2strokeforever]

wheres the ride report?????????????????????

[dubious01]

You let the dog lick the exhaust port? I had a girlfriend like that once....

did it make you uncomfortable?



My friend said it made him fart!

[100hp honda]

i did it on a few, including my bridgeless cyl, was trying to save some fuel from chasing out the pipe. Didnt dyno it or do anything back to back so who knows what it accomplished, i'd like to think it was working. Havent done it on the last 3 engines, been working on other areas and leaving the port work stock size and location at the sleeve, too many different things at once makes it hard to tell whats what.

good info from back in the day in grahams book.

One ploy which is very effective in giving the engine good power over a wide range
is to use staggered transfer durations. The old MZ 125 racer had the two main transfer
ports open for 136°, while the third transfer port in the rear of the cylinder had a much
shorter duration of 128°. Many of the Italian go-kart engines also used this type of
porting in past years. When Honda introduced the MT-125RII production racer in
1977, they took this principle one step further. The main transfers opened 39.2mm
from the top of the cylinder (126° duration), the secondary transfers opened a little
earlier at 38.5mm (130° duration) and the boost port in the back of the cylinder opened
the last, 39.7mm down (123° duration).

Tuners reasoned that as the back port aimed its flow towards the exhaust port
there would be some loss of charge, unless steps were taken to prevent this occurring.
Therefore the back port was opened around 1mm after the main transfers, so that flow
from the main transfer ports, being aimed towards the rear of the cylinder, would
actually form a wall of mixture in front of the boost port and thus prevent a loss of
charge out of the exhaust. Furthermore, it was felt that delaying the opening of the rear
port would allow crankcase pressure to 'blow down' through the main transfers. Hence a high pressure stream would not erupt from the back port and head right out of the
exhaust.


Today those theories have been forgotten. The majority of engines come from the
manufacturers with all the transfer ports at the same height. However, this does not
mean that staggered porting does not work. Most tuners recognise that it does; but the
transfers are staggered in reverse to the old school of thought. At this time, when a
cylinder is modified, the back port is often opened 1.0 to 1.5mm earlier than the other
transfers. Also I have found that opening the secondary transfers 0.8mm before the
main transfers benefits the power curve as well.

There are several reasons why staggered-type porting works so well at this time.
For one thing the manufacturers have forgotten their preoccupation with high
crankcase pressure. Therefore, the transfer charge enters the cylinder in a more orderly
and controlled manner. Additionally, the transfer ports have been re-aimed. Whereas
the ports were tilted upwards so that the mixture streams from opposite sides of the
cylinder gently met at a point in the cylinder just slightly higher than mid-stroke,
today's ports are tilted very little or not at all (FIGURE 3.16). This means that the flow
streams hug the piston crown, rather than shooting up towards the head to mingle with
exhaust gases. Instead, the streams crash into each other, dissipating much of their
energy. The mixture then rises relatively slowly in the cylinder, where it is trapped as
the exhaust port closes. For these reasons, we can open the boost port and the
secondary transfer ports a little earlier, as there is less risk of mixture escaping out of
the exhaust, even at lower speeds when there is more time for this to occur. If the main
transfers were opened earlier, exhaust flow would tend to turn the transfer flow around
and direct it out of the exhaust port, but flow through ports further away from the
exhaust port are not influenced to such an extent by the direction of exhaust flow.

When staggered porting is employed, it is usual for mid-range and maximum
power to increase, due to the longer transfer periods improving cylinder filling,
particularly at high rpm. Much of the mid-range power gain, I feel, is due to the
cylinder being scavenged better. With the new type of transfer porting, a pocket of exhaust gas can be left unscavenged high up in the cylinder at lower engine speeds.
Opening the boost port early would tend to get this pocket of stagnant gas moving,
because its flow stream is still directed upwards at 45° to 60°. Some fuel charge is
possibly lost out of the exhaust but, because this pocket of exhaust gas is purged out of
the cylinder, there is less dilution of the remaining fuel/air mixture. Consequently
combustion will be faster and more complete, raising the hp output.