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#1
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Will milling 906 head .06 give me enough valve clearance?
Hi,
Thanks for all the good answers to my endless questions. As you all know, planning one change seems to always require thinking about every possible factor that may be influenced by my monkeying around. SO here is the latest question: I have a low compression 72 440 in my 70 road runner. It aint fast that is for sure, but it came in the car when I got it and the car is pretty damn nice. I got a set of 906 heads on the way and I am planning on milling them .06 to bump the CR to around 9.0-1 or so. I have been told, but am not sure, that my engine has dished pistons to lower the CR to 8.2-1 but that due to factory tolerances etc, my actual CR is probably about 7.8-1. I am planning on installing a cam and intake that are compatable. I havent decided on the cam yet but know I am going to go for around .500 of lift. So my question is this: Am I going to run into interference problems doing this? Will a .500 lift combined with the reduced Chamber depth cause the ole valve/piston sandwich? I am thinking that the dished pistons will help provide me some clearance here so I dont need to worry. Still the last thing I want to do is see all my time and money go down the drain because I didnt check out this issue before hand What is the factory clearance on that engine? how do I calculate the new clearance at max lift? Burn Rubber, Charles |
#2
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Milling will most likely NOT give you a problem, however you should always measure the clearance...P to V... I had a similar 440 with the old TRW replacement 9:1 pistons (2266's) and I took .100 thousandths off of my 906's (Plus port & polish).. and installed a Hughes HE3038BL cam (.521/.536 lift and 230/236 duration @.050 if I remember correctly)... I also installed double roller chain and Harland Sharp Adjustable rockers.... My pistons were soooooo farrrrr down in the hole (Over .150 thousandths)... The motor was new so I worked with what I had.. and it really woke the thing up... It took a full second off my 1/4 mile times.... Now I have a 12 second street car that will run on low octane...
and it's by far the funnest car I have ever driven.. and I have had other people drive it that I drag race with.... and they love it even though they are Chevy Guys! Go Figure... |
#3
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As long as you stay at that lift cam and 1.5 rockers you could go 60 off the heads with out the loud expensive noise, your pistons are more than likley about 0.125 down in the hole, but ALWAYS MEASURE (TWICE) start several times
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#4
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Thanks all for the advice.
Now how the heck do you make that measurement? I am planning on doing this job over several months and I dont want to take the car off line for that long. Do I just remove the head, get a piston to top of its travel and then measure the distance between the high part of the piston and the top of the bore and add this to the chamber depth? What tool do I use to take this measurment? Thanks, I am new at all this -Charles |
#5
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With .050 thou shaved off the head and pistons sitting .050 thou down the bore I had to have flycuts in my pistons. Cam lift was 550 @110 lobe Always check clearances. An easy way to do this is the clay method, but requires a solid lifter. You can also setup a dial indicator on the tops of your valves. If the pistons actually do sit down .150 in the bore, going to a 500 lift cam sounds safe, but check clearances. Have fun with the build up,
FB |
#6
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I use the MP 484 cam in my 383 on a 104 centerline with stock pistons .040 down in the cyl. I milled my 452 heads .060 to get
9.6 and I have right around .120 piston to valve clearence. You should be fine but I always measure it to be sure. Ron |
#7
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.509 cam install
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