Shaving the stock cylinder head .040

[maskmanLS6]

Im running a stock head thats shaved .040 and im getting some detonation on top end. Im running ported cylinders and 5 degrees timing with 340 mains in stock carbs also. Will a 50/50 race fuel and pump gas mix be ok?

[zach45]

What are you compression numbers

[sheerider1026]

I am willing to bet your squish is too tight

[maskmanLS6]

my compression numbers are 166 to 169 on both sides. My squish area has me a little concerned but the head wasnt shaved passed the original squish ring.

[zach45]

Your a bit on the high side. I would be running a 50-50 mix at

[maskmanLS6]

Yea i figured it was gonna be close when i was buildidg it. I wasnt sure what the compression was gonna be after the head was milled but i was hoping i could get by with pump gas. 50/50 wont be that bad though as i dont get to ride too often, maybe twice per month. Im hoping that the octane solves the pinging on the top end.

[maskmanLS6]

Looking at the unshaved stock head that i have the squish area has been milled down to the max on the head im running. .040 is probably the max amount to shave before having to cut another squish ring into the domes. I hope this is the case and i dont have piston to head contact issues. The factory squish height is around .080 from what i understand so .040 should leave around .040 to work with and that is enough according to what ive read and been told. Is this correct??

[mopar1rules]

Why don't you do a squish check and eliminate the guessing game of what your squish clearance is?? Also, don't know why people just shave a head a certain amount and then play the guessing game of what octane to run. You need to measure the trapped volume of the combustion chamber, in order to accurately determine the octane needed to keep deto away. Also, +5 timing is over kill for pump gas.

[maskmanLS6]

What conversion do i use to determine cc volume of the domes? liquid im sure but i dont know the conversion formula. As far as the squish test goes i plan on doing one sunday after i get the caliper to do it. I didnt have all the tools needed to work out all the details when i put it together.

[maskmanLS6]

Is the cc size of the domes the same cc units used to measure liquid?? If so i can just use a measuring flask to test the dome area. And how much timing can pump gas handle??

[Chip M]

Is the cc size of the domes the same cc units used to measure liquid?? If so i can just use a measuring flask to test the dome area. And how much timing can pump gas handle??

 

Yes, the measurement is the same. A plastic syringe used to measure liquid medicine works better and more accurate. If you have a flat piece of metal with a hole in the middle you can keep the metal sealed to the head while you fill with liquid from the hole in the middle. Plug must be in.

[T_Shee]

In my experience the stock squish is around .060. Obviously this varies and depends on gasket thicknesses. But I'm with gary I bet you are tight on squish. I did a stock head .030 once and it was a little tight

[sheerider1026]

TIght squish + high compression + pump gas =. Detonation demons. I would not even run a tight squish on race gas. There is power to be gained with proper dome/ squish ..

[maskmanLS6]

I was afraid it would be too tight. Ill do a squish test to be sure before i pull the head. I thought the stock squish height was around .080 but im probably wrong. I hope it hasnt damaged my pistons yet. Ive only put about 1 1/2 hours on the engine so far and only wound it up twice. Thats when the detonation occured on the top end and i havent ran it since.

[sheerider1026]

Like travis just stated.. Going .030. Is pushing it imo