Valve reliefs??

morkable said:
So Weston, my pistons are a negative protrusion. -.042, and my valves are hitting. I have the stock thickness head gasket with fire rings. What would my compression be?
Click to expand...

I'm assuming the late CR piston bowl @ 45.3cc's ~ 15.3.

yoshi470 said:
I'm worried now that if I lower my CR to 15:1 it will sacrifice streetability as well as HP. Perhaps even haze more. Any thoughts?
Click to expand...

Haze will increase, throttle response will dampen, but it should be manageable, mind you that a stock SO engine with a 0.020+ marine gasket would be ~ 15.8.
 
yes it is a 6.7 bowl. The pistons were cut 60 thousands to clear the valve. They have been coated (if that matters)
 
I meant late 5.9L CR, do you know the bowl cc's on that piston?
 
No I dont, where would I find that information, or how would I calculate that?
 
I have been toying with the idea of fly cutting my own pistons for a while now, great info guys!

Subscribed!
 
just woundering does fly cutting the pistons effect flow in and out of the cylinder ?
 
A couple things you could do

yoshi470 said:
Ok here's the deal guys. Got the head off the truck right now due to a fire ring mishap and noticed i had impressions of the valves and almost every piston, there wasnt any contact or lip on the piston but you could definately tell the tolerances and way too tight. Set up is a colt cam with the bigstick 181/210 grind, head has been decked .005" and fire ringed, standard thickness headgasket. What should i cut my valve reliefs on my pistons? Looking for a little bit of room to grow for future so keep that in mind. Re-using 5 pistons and putting in one new one. A few of the pistons have some knicks in the so i was gonna shave .005" off the top of them to make up for the head being decked and smooth them back out. Any suggestions on valve reliefs i should cut and how it will affect the compression ratio?
Click to expand...

You could run a 2* key in the cam and also most probably this is a spring issue. Speaking for myself I am sick of these single springs. I am now going with my 3rd set of springs and they sure aren't singles. I have used two of the most popular on the Forums and in both cases with less than 20k miles the spring pressures are all over the place. They are crap! Fletcher has some dual springs that are going on my rig as we speak.

Also Haisley has two thicknesses of Fire Ringed gasket kits. That would take care of the clean up on your head and put you back to stock clearances.

The fly cutting of which you speak are a good idea but you would need a complete tear down to do it as it would throw your pistons & rods in an out-of-balance situation and that would be a huge problem.

My suggestion above should take care of the problem. Good luck.
 
Last edited:
Looks like i might just get a thicker head gasket in it and replace the number 6 six piston and skip the flycuts....i think its a little to much to do for what im wanting to do with the truck.
 
Just for thought here. I ran my motor last year with all stock bottom end except for a scheid drop in street cam. Then this year i decieded to swap in a scheid pulling cam that required big valve reliefs. I pulled the motor and tore it down, cut my own valve reliefs of 150 thous.on my neighbors bridgeport then put them back in the same hole they come out of with the same rings. I would say it runs just fine. Made 20 hooks on it and it has hardly no blowby. It does require ether however.LOL I did this cause i didnt have time to get new piston as i started this project to close to season starting. Im not saying this is the sbsolute best way to go, but it is working and cost very little.
 
Thats a good question I think regarding the fire rings. In my mind a person would need to have thicker fire rings or they wont seal properly with the thicker head gasket
 
ILLINOISRAM said:
Just for thought here. I ran my motor last year with all stock bottom end except for a scheid drop in street cam. Then this year i decieded to swap in a scheid pulling cam that required big valve reliefs. I pulled the motor and tore it down, cut my own valve reliefs of 150 thous.on my neighbors bridgeport then put them back in the same hole they come out of with the same rings. I would say it runs just fine. Made 20 hooks on it and it has hardly no blowby. It does require ether however.LOL I did this cause i didnt have time to get new piston as i started this project to close to season starting. Im not saying this is the sbsolute best way to go, but it is working and cost very little.
Click to expand...


This is the main appeal for me to do it! My brother in law has a mill, and I figure I can find a cheap piston to practice on.

What tooling did you use? and how did you know where to put the reliefs?
 
YOUNG GUNS15 said:
This is the main appeal for me to do it! My brother in law has a mill, and I figure I can find a cheap piston to practice on.

What tooling did you use? and how did you know where to put the reliefs?
Click to expand...

First i should say that the stock so pistons were cut by scheids to .50 thous cause it was going to be a twin turbo motor. All i had to do was take them another .100 thous deeper so that did help me out. BUt if they werent, i would probably use dykem blueing fluid and twist each valve by hand to scratch the top of the piston. I used whatever tooling my neighbor had. I belive it was a 1/2 endmill bit that cut from the side. I would rather had the right size one that would cut on the bottom and run it down to the desired depth. But i figured what was i out, a set of stock pistons.:lolly:
 
Looking at the 12v marine .020" over head gasket but im worried i wont get any crush on the fire rings and the thickest rings i've found are .118", only other ones i know of are the standard .105" rings.
 
just run the marine gasket and no rings. my brother does with his 3.0 charger and no problems. I think twins you could have problems but with these singles you wont have any issues.
 
I was wondering about doing that as well. Was also wondering if i could machine some pieces to fill in the existing fire ring groove. Kind of regret even getting fire rings as this point. Didnt even plan on getting fire rings....told the machine shop i wanted o-rings and picked the head up with o-rings in it.
 
Yeah i think they will be fine without filling them in. These singles especially like the 475sx from what i have seen you wont have any problems. Heck Destination on here runs one with stock hg and bolts retourqed. I believe KXhonda ran stock setup for along time too. The marine would give you the extra room for valve lift and cut compression alittle to help with the revs. It might not be a huge seat of pants differance but you wouldnt have to touch your pistons.
 
Anyone else got any ideas here. Will a .020 over gasket with the .118" rings crush enough to last?
 
You must log in or register to reply here.
Back
Top