Porting a 70 barrel

i wouldnt run avgas its a dead fuel designed to be used in planes with a massive surface area and so not to flash off

get some race gas or add some toulene to your normal fuel
it will give more power

 

I've got a massive 5 gallon drum of avgas 'obtained' off the raf camp, run the lawn mowers on it and have done for the last year or so.

Never thought to use it in a ped.

 

Hmm, a 17:1 methanol scoot. Is the stock head the same bolt pattern as a mhr rep? Methanol with bean oil smells like pure sex!

Minor, I have had a bit of experience with "racing" fuels. I like VP and elf because of their consistency. The trick is to use a fuel that has a high turnover in your area. Oxygenated fuels do go off. You never know, that 60 litre drum of boutique race gas may be 2005 vintage and all the aromatics have turned to dogshit.

Also, If you are buying 205 or 60 litre drums, decant it into smaller containers for storage. The airspace in a half full drum absorbs the lighter elements and knocks a few MON points out of it. We were getting the VP ms103 in 205's and decanting it into steel 20 ltr drums as soon as it arrived. I would probably use steel 5 ltr cans for a scooter.

You've got me thinking. May have to buy some deto lights and start tipping the can again.

 

Wax is right with the toluene. (also known as methyl benzene, or MB)

This is a fuel that I've run in ski's to great success.

In a 20ltr fuel churn:

3 litre MB
600ml formula xp-s, castrol TTS or redline oil
16.4 ltr shell RF100 (basically avgas without the drying agents)


You can run it up to 20% in premium pump fuel and get around 105 MON. I call that blend "ghetto elf".

This blend would probably be a good thing on air cooled scoots especially. MB has a high latent heat index so it would improve the cooling effect of the vapourisation/atomisation process. Maybe someone could try a 10% blend in an aircooled scoot and post the results. Especially the hot run results? I can guarantee it won't fuck your engine as it has a similar calorific value and specific gravity as petrol.

You don't want to get it on your skin too often as it goes straight to your liver and fucks it. There are more enjoyable ways to fuck your liver.

Make sure your float needle has a metal or viton tip.

MB also has a nice side effect. It is a very effective blending agent. It helps keep exotic polyoester oils and cheater additives like nitromethane and propylene oxide in suspension.


disclaimer: Hey kiddies, before you run down to your local paint shop and buy a gallon of tolly, it won't make your scoot go any faster. It will probably make it go a bit slower. (unless you have an aircooled scoot, then go and do it and post the results!)

Adding race fuels to an engine that's built to run on pump fuel don't work. You have to up the compression, timing or squeeze the stinger, or a combination of these to get the engine into a zone that it actually needs the higher deto resistance to make it happy.

 

so if I made my c/ ratio to say... .6mm I would have to run on 99/ 102 octane fuel, like scoobys and evos? lol sounds interesting

lads in college say that it stops it from pinking or something (pre-ignition)?

 

The lads at college are right. Pinking or pinging is the sound a trained ear hears when an engine is pre igniting. Believe it or not, even at 20,000rpm, the fuel/air mixture isn't exploding, its in a controlled burn. You want the sparkplug to initiate the combustion event and nothing else. pre ignition is when some other factor lights the fire before the sparky. It may be a glowing object in the combustion chamber, carbon deposit or earth electrode on the plug. In other words, something in there is too fuken hot. Unless your scoot has been running on crap oil and has carbon deposits, this is caused by an error in tuning, or too lower octane.

Detonation is literally an explosion. It can be caused by all the above reasons and also self ignition (dieseling) caused by too lower octane.

A rough guide is pre ignition is the engines way of saying somethings wrong, detonation fucks things.

All high performance engines have some deto. To eliminate all deto you would tune the engine to be gay. The combustion event in a 2 stroke is surprisingly a hit and miss affair. 10% deto @ max torque point under load is the rule of thumb.

You can buy a device called "deto lights" This is a washer that goes under the plug thats actually a glorified microphone. It's tuned to the frequency of detonation. It's hooked up to a display that shows the percentage of deto through a series of led's. They are fuken expensive but very handy.



Squish and comp. ratio are two entirely different beasts. Squish is the clearence between the piston and squish band on the cylinder head.

Comp ratio is how hard the piston squeezes the air/fuel mixture at top dead centre. TDC.

I use a graduated burette to measure head volume and resin core solder to measure squish.

If you are cutting heads, measure the installed cc's then the uninstalled cc's. That way you can compensate for the piston crown profile and squish. Then you don't have to assemble the engine to measure CR between cuts on the lathe.

 

thanks for pointing that out realised what I said then, got myself mixed up :wtf: , c/ratio is also the ratio of squish into the swept volume of the piston right?

 

Sorry mate, I edited my post before you posted.


Squish and CR are two different, but closely related things. You can have a very high CR with 3mm squish if that rocks your world.

Squish is simply the clearance between the head and piston.

CR is how hard the gas gets squeezed. If you have a 100cc swept volume cylinder and a 10cc head, you have a CR of 10/1.

OK, bear with me. If you have a 13.5:1 engine with 1.5mm squish and you want to pull the squish down to 1mm and keep the CR at 13.5:1, you take 0.5mm off the head or cylinder deck. This will give you your desired squish of 1.0mm but has raised the compression ratio because the head volume is smaller now.

Now you have to remove some material from the head dome area to get back to 13.5:1.

 

yes its total clearance volume

Think about this , since the fuel in the squish area doesnt burn well enough to make any decent power then to large a squish clearance will waste fuel
the less squish the higher percentage of fuel in the combustion chamber

 

Also, too much squish can burn pistons. You don't want any fire that close to the ring in the early stages of combustion. The high velocity A/F mix combined with the boundary layer effect tends to pull a fair bit of heat outa the piston crown. Too much squish allows hot gasses to migrate to the edge of the piston prematurely and the piston temps skyrocket.

A theoretical perfect engine wouldn't have a squish band for the reason waxhead mentioned. Unfortunately, we live in the real world so we need the turbulence that a squish band creates.

 

Wouldnt that be nice eel

 

wax, fuck no!

I like the fucked, inaccurate, wierd and mysterious world just the way it is.

Anyway, What's the story in Balamory?

:hitit:

 

this thread is like fuking awesome, learnt more helpful stuff reading this then anything i was taught at fukin school. nice 1 people... great help..

 

Thats why scooter shack is the "Real Deal" tuning forum

 

aiiiiii!!! its jolly good! :w00t:

 

(denny) thats Eel and i come from a background of tuning jetkis

www.waxracing.com is my website

Denny is very good at porting stuff

Actually here is a pic of my cases i have been doing for my scoot

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The pics dont look that great because of the flash but its going to go around the sleeves now not under it

 

thats some sweet ass porting...! :drool:

 

Thanks man
if you couild see the cases in the flesh you would see how it goes in on the side along way to let the charge up the side

This engine is getting an hpi ignition
corsa cylinder
21mm oko carb
v-force reed etc

It should go well
im hoping for power stands