Question for two stroke experts regarding port height and jetting

**powerabout** · 03-25-2016, 07:45 PM

Originally Posted by Euroski

I lost about 5 psi raising the ports

But once the engine is in the power band I would think cylinder pressures are higher? I'm only guessing...

sure..
your exhaust design can add to that at certain RPM in fact enough to make the engine detonate
cylinder pressure sensor needed for that, which is not too expensive to buy.
as they say it all has to fit together and the guys that have a dyno next to the work bench have all worked this out

**Mark75H** · 03-25-2016, 08:17 PM

Originally Posted by powerabout

rotary valve not related to anything re an outboard

Don't tell Konig drivers that ... the 4-60's and Anzani's used crank rotors

**powerabout** · 03-25-2016, 09:10 PM

Originally Posted by Mark75H

Don't tell Konig drivers that ... the 4-60's and Anzani's used crank rotors

Hopefully they are not reading this thread as they make so much hp/ci they are miles in front.
they also dont have an intake going through a hollow crank which is why i was saying the data is irrelevant to production outboards.

**pointer** · 03-25-2016, 09:15 PM

Wow - a lot of information in this thread.

Could those of you who have posted contributing with information state how your information was gathered and on what engine application?

There are members who are well educated in the school of real world outboard performance who are getting lost in this thread.

For the record my experience is limited to set up and props, very little internal work on outboards. Internals on snowmobile engines, as well as exhaust, clutching and gearing. Some auto experience, and a bunch of R/C, primarily with piston port 23 and 26 cc Zenoah. Everything from stock, prop, setup, fuel (methanol), oil ratio, compression, port work, case matching, and tuned pipe mods.
Most of my findings boil down to a few simple observations: Few really know what the heck they are doing; set up and prop are the best bang for the buck mods; what works for a snomo engine doesn't work for the R/C stuff and vice versa; HP, torque, fuel charge are best defined by the application; moving more fuel and air doesn't always translate into more power; and last but not least, the best nut to keep an eye on is the one at the controls - some guys and gals can really get things motor-vating!

pointer

**Chaz** · 03-26-2016, 08:40 AM

I'm just waitin for Mr. D to pull the reeds out , put glow plugs in and run it on 60 % pop ... (CH3NO2)

**ChrisCarsonMarine** · 03-26-2016, 09:16 AM

Originally Posted by Chaz

I'm just waitin for Mr. D to pull the reeds out , put glow plugs in and run it on 60 % pop ... (CH3NO2)

LOL,remember "H",anhydrous hydrazine...mixed with a nitro...off you went like a homesick angel,some of the time...

**dwilfong** · 03-26-2016, 09:51 AM

I have a can of propylene oxide in the shop............VP sells it by the gallon at the speed shop. only problem is it disappears very quick. That can be a good thing........

Don't mention the H word.........that is bad mojo.........

**dwilfong** · 03-26-2016, 10:03 AM

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Her you go $350 worh of pop goes the weasel..................LOL
This won't even get a top fuel car down the track.........................................
Thake this mixed with castor and spray it in you eng........NOT A HAIR ON THEM......................

**FMP** · 03-26-2016, 12:45 PM

We hope to have that happen. If the higher rpm pulse is stronger and if it's hitting the port at the right time the plugging effect will increase.

**dwilfong** · 03-26-2016, 01:10 PM

The problem is nitro takes up volume in the air stream.
Need a large case and runners to flow the extra volume.
Spraying it right at the port will account for this and atomize it.
The closer to the cylinder you do it the better.
Drilling a hole in the block at the boost port and spraying it there may work.

**Mr. Demeanor** · 03-26-2016, 04:43 PM

Nitro now...really LOl

**FMP** · 03-26-2016, 04:46 PM

That should cure the drips .

**dwilfong** · 03-26-2016, 05:51 PM

You want that little 4 banger to haul ass now don't you????????????

Don't bee skeerd it only hurts for a split second................LOL

**patchesII** · 03-26-2016, 05:55 PM

Propylene is nasty stuff. I've been tempted to try it, just don't really need to grow a third arm right now

**dwilfong** · 03-26-2016, 07:02 PM

It's not the third arm that's the problem but brain cancer...............................
Prope will run threw you so fast that you can taste it instantly.
Spill it on the ground on a hot day and it will evaporate in front of you.
By the time thy take a fuel sample it is gone with the wind..........................................
If you do mess with it do it at your own risk and don't get any on ya...................