Venom X22R 250 performance mods

[JerryHawk250]

Originally Posted by Megadan

He did the same trick I did with the port floor around the short side radius on the intake. I widened that up on the right side of the port along the outer edge of the curve. That was the only real port shaping I did besides the port match at the flange.

As far as the thinner material around the guide. Where it is the thinnest doesn't really need much material removed anyway. Most of the material removal is at the bowl and especially next to the guides just leaving the bowl along the roof of the port right next to the guide.

That's pretty much what i have done.

I wanted to make sure those who are new to porting to know this so they don't go crazy and punch a hole through.

[Megadan]

I don't mean to Hijack your thread Jerry, but I figure these two pictures of my exhaust port might illustrate what I am saying better.

This is the exhaust side unported.

After porting.

[JerryHawk250]

Originally Posted by Megadan

I don't mean to Hijack your thread Jerry, but I figure these two pictures of my exhaust port might illustrate what I am saying better.

I've been hijacked! No problem Dan, That's what this forums for. Everybody has to start and learn from somewhere. The more information that gets out on here the more others will learn.

[MeatHammer]

So you take out the hump in the exhaust port wall where the valve stem hole goes into the wall of the port or am I seeing that wrong? Sorry if my terminology is incorrect or that doesn’t make sense.

[JerryHawk250]

I figured out the headlight issue. The connector to the rectifier unplugged. Something going my way for a change.

[JerryHawk250]

Originally Posted by MeatHammer

So you take out the hump in the exhaust port wall where the valve stem hole goes into the wall of the port or am I seeing that wrong? Sorry if my terminology is incorrect or that doesn’t make sense.

You remove the material around the valve guide but not were the two valleys are on each side. That's where the head is thin. You can widen the port on each side.

[MeatHammer]

Originally Posted by JerryHawk250

You remove the material around the valve guide but not were the two valleys are on each side. That's where the head is thin. You can widen the port on each side.

I see what you mean. That picture of the cross section does a good job showing where to not remove material. I am nervous about doing my own head work but I am pretty confident I can do it. I checked with Venom and a new head is only $110 plus shipping so if I do screw up it’s not that bad lol.

[JerryHawk250]

Originally Posted by MeatHammer

I see what you mean. That picture of the cross section does a good job showing where to not remove material. I am nervous about doing my own head work but I am pretty confident I can do it. I checked with Venom and a new head is only $110 plus shipping so if I do screw up it’s not that bad lol.

That's why i posted that picture to help understand what you have to deal with. Those are there areas you don't want to remove. Just clean them up a little. The exhaust side is the most restrictive and will need the most work. The intake side really only needs a little taken off around the valve guides and port matched where the intake attaches. These head are identical to the CRF230F. The intake port is real small. maybe 27-28mm. I forgot to take a measurement. I used the intake gasket to scribe the 30mm hole as it was in perfect alignment with the intake tube. It matched up perfect. I took a bunch of pictures but didn't notice i had a big smug on the lens so most of the pics came out blurred. Me and cameras just don't work well together.

[China Rider 27]

Originally Posted by JerryHawk250

for anybody looking to port there head, I ran across this thread this morning. Very informational and with pictures. https://thumpertalk.com/forums/topic...onsiderations/

In this quote he is working on an intake port and looks to me to be some aggressive porting as he is widening and cutting the port into an oval diameter? And has added an over size valve? So the CB engine requires more flow on the intake side?

[Megadan]

Originally Posted by China Rider 27

In this quote he is working on an intake port and looks to me to be some aggressive porting as he is widening and cutting the port into an oval diameter? And has added an over size valve? So the CB engine requires more flow on the intake side?

Keep in mind that he is also trying to increase total flow through the head for a 32mm carb AND a larger intake valve in that thread. He wants to remove as much material as possible from the port roof, but can't.

His biggest complaint about the CRF port, and to some degree also true of both CG and CB clones, is the inability to raise the port floor with expoxy and then open up the port roof to match due to how thin the casting is at the valve seat, which would decrease the short side radius and increase port velocity. Since he has already removed as much material from the roof as he can he then widened the port floor at the radius going into the valve seat area to compensate.

All three motors suffer from a fairly sharp short side radius angle and port angle in general. The straighter the angle of attack of the intake is to the valve and shallower the short side radius, the better port velocity and flow is.
This has a lot to do with how "heavy" an air/fuel intake charge is. By widening the port where he did in conjunction with flattening out the short side radius it helps to reduce the chance of a low pressure spot right before the valve and thus maintaining or even increasing velocity.

All of that work combined with the valve back cutting he shows there is actually better for lower and moderate lift cam profiles than it is for high lift/high duration race cams. It's actually a well thought out approach to match a large carburetor bore to a fairly mild cam profile to get the best throttle response possible and a nice wide torque curve.

Don't take this to mean the exhaust port doesn't suck though, because it does lol. His post is mostly focused on maximizing the intake side with the upgrades in question given the limitations at hand.

[China Rider 27]

Excellent explanation. Gets down to the issues of flow for sure.

[JerryHawk250]

Okay, so my bikes been parked for about a week due to all the rain we've been having. I go into my shed this morning and noticed a nice little puddle of oil under the bike. I've been cranking it up just about every other day and never noticed it. After closer inspection i see it was coming from the cylinder base gasket. I installed a new gasket. I knew i should of put some kind of gasket seal on it. Will this streak of bad luck ever end? I don't know when i'll have time to pull it apart now that i have a carport to deal with. So no problem, I'll take the Hawk t work. Dead battery. No problem. At least it will kick start. So i guess I'll have to show the Hawk some love for a while. lol

[Chrisguga]

Darn Jerry, that sucks. Well, lesson learned on using some gasket material when I take mine apart.

Do you plan on using some hi temp RTV?

[franque]

You don't want to use silicone, Honda or Yamabond is what you'd want. Silicone can clog up oil passages.

[JerryHawk250]

I usually use the spray on Hi-temp Copper seal. I didn't have any at the time and the gasket had some type of sealant bead on both sides. I may have accidentally scraped some off when putting the cylinder back on.