Engine Porting - Gases out, Fuel Air in

mastermechanic5 said:

well looks like i screwed up, i got everything back together and took it for a spin and it lost a lot of low end and doesnt top out as fast:???: maybe if i replace the intake manifold i will get some of that back? i did a lot of porting on the intake manifold. so i gess i need i new head now right?

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ok...check for any air leaks. warm engine, turn idle screw up a little, and spray brake wash or carb cleaner all around. where the jug meets the bottom, head, carb/intake connection, intake/jug connection. if your rpms change (up or down) thats where you're sucking air. IF thats what it is. just a thought.

well i sealed everything up with black high temp RTV sealent so there probaly arnt any air leaks i even sealed the bowl on the carb but i didnt use a gasket on the intake just sealent but i think that should be good enough

careful with the sealant. What you squeeze out you squeeze in, not good on the inside. You can use just sealant but I let it set up first, and just enough to wet the surface. I have never had an engine loose power from porting, that is how they keep the power at 2 HP, take the restrictions away and you get the power back. I would not try for speed just power and clean running. Have fun, Dave

mastermechanic5 said:

well i sealed everything up with black high temp RTV sealent so there probaly arnt any air leaks i even sealed the bowl on the carb but i didnt use a gasket on the intake just sealent but i think that should be good enough

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PS: A pic of the skirt cut for more intake timing, this is the easy way.

Exhaust pipe mod

I have just found a great mod you can do to your HT motor. if you pull of your exhaust pipe you will notice that the port is rectangular shaped and the pipe flange is a circle. What I have done is file the gasket and the pipe opening to match the size and shape of the port. This resulted in a decent performance gain. I cannot quantify the actual speed and power increases but the bike takes on hills like they didn't even exist and I seem to have about a 5mph increase in top speed. this is with a stock 44t sprocket. the exhaust is also stock.


when the exhaust port opens the exiting gasses form a shock wave which travels outward when it strikes the gasket wall part of it reflects back into the cylinder when you have a tuned pipe you want this but the geometry of the pipe is such that this will spoil the scavenging effect.

Take a look at the intake, they are just as bad....

I've merged your thread bikeuser with this one as its all about the same thing. The mismatched exhaust manifold and port is restricting it by about 25%! I'm definetely going to open this up over the weekend. The newer Starfire Gen 2 Happy time engines have got round ports now that match perfectly, so Grubee must have realised they were going wrong.

Fastboy

I've been looking into all this porting and fine tuning business. Theres a guy on Youtube who is learning from gordon jennings books and some others, he is explaining all his mods and porting jobs. Well worth a look if you want some ideas or advice.

Porting Intro
Cylinder Porting
Intake Porting
Intake Port Matching
Porting Basics

mastermechanic5 said:

well looks like i screwed up, i got everything back together and took it for a spin and it lost a lot of low end and doesnt top out as fast:???: maybe if i replace the intake manifold i will get some of that back? i did a lot of porting on the intake manifold. so i gess i need i new head now right?

Click to expand...

I was wrong the bike is actually faster and has more torque the reason why it was so slow that day was because it had rained earlier and the air was very humid

Interesting Videos, and a good book. It is interesting that he is trying to figure out what he needs. I am puzzled as to why he does not have the reed cage in the intake runner he is fiddling with. He is looking at the size and thinks he needs to increase the size of the runner, except the flow is not restricted there it is in the reed box, so the runner is OK. That is a crankcase inducted engine, so they have ports we cannot have. All the port matching on a Happy time engine is not necessary as this engine will not flow enough air to use it. Port timing on the other hand is well worth the effort, no need to go crazy just get them in tolerance, 1.1" from the top for the exhaust and .25" lower for the intake. Keep the stock shape unless you know what you are doing. the bottom end would never hold up to big ports, or a big hand full of throttle. Have fun, Dave

I did some grinding on my intake and exhaust ports but no real difference (maybe slightly). I didn't remove that much but was trying to much the ports with the exhaust /inlets manifolds etc.

Also there are the two additional ports on the side of the cylinder. Do these need to be make bigger?? I'm no sure if I should take some more of the exhaust and inlet ports as well? I have the zbox 48cc and still doesn't really have that much torque going up a hill, hence the reason for finding more power etc.

And feedback welcomed!!!!

PS: Forgot to mention that when I took my head off it had not head gasket. Is that standard from factory or did they forget to put one in??