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post #1 of 16 (permalink) Old 4 Weeks Ago Thread Starter
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Cag port timing

Hello, I am looking to improve my mini moto engines port timing and squish. What is a good base setting ? The supporting parts are a dellorto 14/14 copy and jet pro exhaust and carbon reeds. I have managed to get 35mph out of it in my gps. 7/62 gearing I think will have to check this evening.

Last edited by edek91; 4 Weeks Ago at 03:20 AM.
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post #2 of 16 (permalink) Old 4 Weeks Ago
Re: Cag port timing

CAM2 probably has some port degrees for the degree wheel.

Empty Pockets Racing: The difficult we do, the impossible takes longer.....
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post #3 of 16 (permalink) Old 4 Weeks Ago Thread Starter
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Re: Cag port timing

Cheers, so I have put the degree wheel on and got

Exhaust opens at 100 from tdc

Boost opens at 120

Tranfers open at 125
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post #4 of 16 (permalink) Old 4 Weeks Ago
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Cylinder is one piece or two/three piece.
Were is the piston on bdc when you look into the exhaust port. Port timing is better when measured in duration. Your exhaust port should be open for 160 and the mainport 110??

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post #5 of 16 (permalink) Old 4 Weeks Ago Thread Starter
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Re: Cag port timing

The cylinder is 3 peice, Barrel,cooling fins, combustion chamber. The piston is at the bottom of the exhaust port. Okay I'll work it he duration out.
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post #6 of 16 (permalink) Old 4 Weeks Ago
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Squish can be set to 0,5mm max.
Duration 175 exhaust and 125 main, you can try to get a smaller headgasket( normaly a 0,5mm copper ring) and then push the timing by set up more cylinderfoot gaskets.

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post #7 of 16 (permalink) Old 4 Weeks Ago Thread Starter
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Re: Cag port timing

So if my working out is correct

Exhaust duration is 160

Transfer duration is 110

Boost port duration is 120


I have got .65 squish so I'll matching .15 off top of the cylinder to get the .5 squish
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post #8 of 16 (permalink) Old 4 Weeks Ago
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Re: Cag port timing

Quote:
Originally Posted by edek91 View Post
So if my working out is correct

Exhaust duration is 160

Transfer duration is 110

Boost port duration is 120


I have got .65 squish so I'll matching .15 off top of the cylinder to get the .5 squish
0.5mm is roughly 20 thousandths of an inch..That would be a compression ratio of about 17:1.Better get a welding glove to pullstart it if you go that route

At .050" squish youll get about 140-150psi......I run my squish mainly at .030"...Ive run them as tight as .024" and got piston to dome interference and had to modify the pistontop on a mini lathe to true the top up..




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Last edited by CAM2; 4 Weeks Ago at 03:53 PM.
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post #9 of 16 (permalink) Old 4 Weeks Ago Thread Starter
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Re: Cag port timing

If I set my ports at

Ex duration 175

Tranfer duration 125

Ex from tdc 92.5

Tranfer from tdc 117.5

So I'll have to machine the ports higher in the cylinder.

I already use my snap on gloves to stop me getting blisters ha. I was just worried too much squish will cause me to lose revs.
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post #10 of 16 (permalink) Old 4 Weeks Ago
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Re: Cag port timing

Quote:
Originally Posted by edek91 View Post
If I set my ports at

Ex duration 175

Tranfer duration 125

Ex from tdc 92.5

Tranfer from tdc 117.5

So I'll have to machine the ports higher in the cylinder.

I already use my snap on gloves to stop me getting blisters ha. I was just worried too much squish will cause me to lose revs.
Yep the good old hand rub......As far as machining the ports...Yes you will need to...Keep the same roof angle at the top and youll be good..

To do the exhaust port its easier to cut it in angled or better known as "Canted"..The Canted exhaust port will flow aces and not thin down the aluminum dangerously at the exhaust flange inner snout........


As far as the squish...Good old mildly modded performance engines start out at .060"-.065" of squish on a stock head without a basegasket...

2pc/3pc cylinders start delivering descent power at .045" of squish..I prefer a nice even .040" for a descent overall and easy to tune playtoy...


I finetune the squish of the 1pc cylinders using a piece of granite tile with a 2 1/8" hole cut in it and use 100 grit sandpaper glued to the granite with center cut out aswell to put the cylinder on and spin back n forth til I get the desired squish then I adjust the ports and even grind-in an extra boost port

Another thing I wanted to touch base on is the difference in pistons.....On my builds where I want the tightest squish without having to grind the base or mill the top lip you can simply take a piston ported 43cc/49cc piston and use that aslong as your crank has a 10mm pin..

As you can see the piston ported piston top is like almost 1 1/2 millimeters higher than the reed inducted piston..Both pistons in the picture below are linked together on a single 10mm pin for accuracy...


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Last edited by CAM2; 4 Weeks Ago at 01:15 PM.
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post #11 of 16 (permalink) Old 4 Weeks Ago Thread Starter
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Re: Cag port timing

I currently have .5mm gasket with .65mm squish

Cam2 are you talking 40 thou e.g. 1mm squish or .40 of a mm ?

Doesn't removing the base gasket effet your blow down time ?

Have you ever tried building up the bottom of the exhaust port ?
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post #12 of 16 (permalink) Old 4 Weeks Ago Thread Starter
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Re: Cag port timing

I currently have .5mm gasket with .65mm squish

Cam2 are you talking 40 thou e.g. 1mm squish or .40 of a mm ?

Doesn't removing the base gasket effet your blow down time ?

Have you ever tried building up the bottom of the exhaust port ?

How much higher do you set your boost port to your Tranfer ports
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post #13 of 16 (permalink) Old 4 Weeks Ago
Re: Cag port timing

1mm is .040"

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post #14 of 16 (permalink) Old 4 Weeks Ago
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Re: Cag port timing

Quote:
Originally Posted by edek91 View Post
I currently have .5mm gasket with .65mm squish

Cam2 are you talking 40 thou e.g. 1mm squish or .40 of a mm ?

Doesn't removing the base gasket effet your blow down time ?

Have you ever tried building up the bottom of the exhaust port ?
I quote my squishbands in inches or thousandths of an inch...


I realized now you used mm's but didnt add the mm's...I thought you forgot the zero because the 2 and 3pc headkits Ive built they started in the .054-.058" of squish without basegasket and standard copper ring with varying thicknesses so I assumed you meant inches.....


It seems your on the right track and yes Ive built up the bottom bases on engines....


Youre getting a lil critical of a tool based engine and blowdown timing...If we were talking Polini, Blata and BZM or IAME it would be a different perspective...

These engines are built in a retarded state to maintain a descent amount of torque to get the job done and also get the longest life longevity possible out of it...In tool engines its about how hmuch fuel and air you can pack into the whole engine and do it with as much velocity possible...Euro engines start their life out in the 16.5/17:1 range as a comparison and have a short lifespan,,

Racing engines are built in reverse of these Chinese tool engines....Theyre ported aggressively with tight and exacting squishes to compression ratios and also deliver the power packed goods for a much shorter period of time..


Once you start exerting that type of cylinder pressure through a cylinder where the transfers are open and exposed controlling blowdown timing is virtually just a number with zero meaning and operates on a principal of size to design......

Once you upset that happy medium it comes with consequences like erratic powerband,,overheating and being really hard to start ,tune and keep running..

In a euro engine choking out as much empty space delivers power because the intake is designed to be smack dab in front of the transfer ports also to mention fed by a big honking azz carburetor....

In a tool engine having a crankcase that can handle excessive fuel is needed to flow the fuel into the transfers so the more fuel compacted into the crankcase the better the upward push of power adding mix gets into the cylinder...

Seeings the mix has to pass through the crankcase the crankcase must become a storage vessel.. Eliminating the internal area eliminates the fuel that feeds it per stroke...the more it can inhale per stroke the more power it puts out...

3/4 of the stuff they claim is HP stuff for these tool based engines are actually just bolt-on bling bling with very minimal to no increases in overall performance without causing other types of problems .

When you look at the 2 stroke building websites these two stroke masters n such you can really get a lot of valuable info but also the wrong info as the engines theyre using as examples are Japanese made MX dirtbike or snowmobile engines....

If you want the right info on how to hop up tool engines go back to the race kart days when they converted chainsaw engines into performance engines....

That's where youll get all your pertinent info from......There were no full circle cranks for them either but they belted out the goods regardless......LOL

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Last edited by CAM2; 4 Weeks Ago at 02:23 PM.
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post #15 of 16 (permalink) Old 4 Weeks Ago Thread Starter
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Re: Cag port timing

Yeah i should have said i removed the copper gasket at the top of the cylinder head and lapped the faces for a good seal.

I know I'm getting a little critical of a tool engine haha. I just wanted to see what is possible to get out of them with a little work.

I have actually got too high squish already then. I'll modify my cylinder and report back my results.

Thanks for the great advice
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post #16 of 16 (permalink) Old 4 Weeks Ago Thread Starter
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Re: Cag port timing

Once I have got bored of this tool engine I'll move onto something made to go quickly.

I have been looking at kart engine design as the principle is the same with only one gear.

I really appreciate the advice as I know most engine tuners have their secrets but won't share them but you do
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