Head Notching

[Summiteer]

Something for all you Techie type smart guys to figure out.
I've talked to a couple of guys that say that putting a notch in the exhaust side of the head(inside) on your sled seems to make a difference in performance. Something about creating turbulence near the exhaust reducing temperature and preventing detonation or something like that.
Now I'm not a mechanic (or even a really good electrician for that matter), but I thought that the whole reason behind porting was to smooth things out and make the holes bigger to reduce turbulence and increase airflow. I also read somewhere that sharp edges inside the cylinder create hot spots which can cause pre detonation.
I'm just trying to get my head around the theory of this notching business. The guys I know that have done this are pretty smart dudes and they swear it makes a difference.

 

[lucm]

Something for all you Techie type smart guys to figure out.
I've talked to a couple of guys that say that putting a notch in the exhaust side of the head(inside) on your sled seems to make a difference in performance. Something about creating turbulence near the exhaust reducing temperature and preventing detonation or something like that.
Now I'm not a mechanic (or even a really good electrician for that matter), but I thought that the whole reason behind porting was to smooth things out and make the holes bigger to reduce turbulence and increase airflow. I also read somewhere that sharp edges inside the cylinder create hot spots which can cause pre detonation.
I'm just trying to get my head around the theory of this notching business. The guys I know that have done this are pretty smart dudes and they swear it makes a difference.

ck this site out and it explains what you are talking about ........

 

[BIGFOOT]

...Some more info.

fire slots in piston domes - Speed Talk

 

[Summiteer]

It kind of looks like no-one is really sure that it works......or that it doesn't....in a four stroke.

 

[sumx54]

It kind of looks like no-one is really sure that it works......or that it doesn't....in a four stroke.

Well we could always have a "head notchin" party, break out the ol angle grinder and giver a try on that thar unit of yours Summiteer :d I think at one time K-Lynn Kenny told me a story about him or his brothers doing this on their machines for considerable hp gains. I think they called it diamond cutting or something. I really didn't pay too much attention to the story as I thought he was blowing hot air up my arzz I guess there's a bit of truth behind every story.

 

[northstar23]

That got me thinking ...and I'm thinking not

 

[Modman]

That got me thinking ...and I'm thinking not

I'm thinking its a good way to screw up a perfectly good cylinder head. Can't see how that would help except increase combustion chamber volume and decrease compression. Yes, sharp edges are possible hot spots and can promote pre-ignition. Not sure that a notch in the cylinder head will prevent detonation, (caused by the fuels ability to resist deto).

I always hear these statements - "they swear it makes a difference."

I heard a guy say he put a coffee can muffler on his Honda Civic and he "swears it made a difference" too....LOL...I'll bet he swears it "feels" like he has more power with his 23 extra decibles.....

Seriously though, not knocking your buddies, but the only thing that convinces me are dyno sheets, combustion chamber burn patterns, and piston wash and plug readings. Factual info is needed before I begin cutting notches in my motors.

 

[lucm]

Well we could always have a "head notchin" party, break out the ol angle grinder and giver a try on that thar unit of yours Summiteer :d I think at one time K-Lynn Kenny told me a story about him or his brothers doing this on their machines for considerable hp gains. I think they called it diamond cutting or something. I really didn't pay too much attention to the story as I thought he was blowing hot air up my arzz I guess there's a bit of truth behind every story.

Ken at K-Lynn here in Whitecourt has done numerous 2 and 4 stroke engines, including his Chevy 1/2 ton and he also has dyno sheets on many on the engines he did. The dyno sheets show an increase in the power band range as well as in hp??????????
He helped me do the head in my '05 800 summit 2 years ago and I haven't had a problem yet........I dropped 2 needle sizes and get excellent mileage with the sled(15% better than before) but I'm not exactly sure what kind of power increase I got out of it but I did notice a difference after it was done.......I don't know if that was in my head or in reality