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| Sorry more head questions. https://slantsix.org/forum/viewtopic.php?t=33430 |
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| Author: | Mike_64_Valiant [ Wed Jan 21, 2009 7:53 pm ] |
| Post subject: | Sorry more head questions. |
I have read many posts and have more questions. My head is at the machine shop now and it is getting ported and oversized valves. I have planned to mill the head .100 because thats what others have said works well. The machine shop says thats a ton to take off and doubts that is what I was wanting. He wanted to know what the piston deck hight was and if it was at zero deck? The only way for me to know the piston deck hight is to measure it with the head off but right now I cant do that. I know its not zero deck just not sure how deep in the hole. The machine shop seams to think if I took .100 off that the compression ratio would be extremely high. I would like to see 9.0-9.5. Will .100 off the head get me in that area and if I do cut it .100 will I need custom push rods? Thanks. |
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| Author: | THOR [ Wed Jan 21, 2009 8:13 pm ] |
| Post subject: | |
The pistons can be anywhere from .120" to .170" in the hole factory. The numbers may be higher/lower depending, those are just the two extremes I've seen. Depending on how far yours are down, you will "probably" get either a little higher or a little lower than 9.0:1 CR. With a CNC machine it takes maybe a couple hours at most to mill .1" off the head... I've done it. Let your machinist know that the pistons are plenty far enough down in the hole, and actually, taking that .1" off will get you pretty close to about where you want to be. You "shouldn't" need custom pushrods..but it does happen occasionally that you will. If you get a chance, have him CC the combustion chambers to see how much volume they can hold. Factory stuff is usually in the mid to high 50s, and as high as low 60s, from what I've seen. The number you get will better prepare you for determining actual CR. Otherwise, low 50s or high 40s are "typically" what the combustion chambers end up being after a .1" cut. "Your mileage may vary." ~THOR~ |
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| Author: | Joshie225 [ Wed Jan 21, 2009 8:16 pm ] |
| Post subject: | |
The pistons should be at least .145" down the hole if the block deck hasn't been cut. Yes, .100" is a lot, but these heads can take it no problem. I said to the last machinist that questioned cutting the head 100 thousandths "It's not a Chevy." You must measure the piston deck height and combustion chamber volume to calculate the compression ratio. Period. You will probably be able to use your original pushrods, but then again you may not. |
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| Author: | flowerman [ Wed Jan 21, 2009 8:19 pm ] |
| Post subject: | boy does this sound familar, amigo |
Your going through the same thing I am going to do at the end of feb. I am milling,porting, valving, and putting a cam in my 85 d100 I was told 100 off will put the comp in the area of 10 to 1. I have been told by many others that there is plenty of room to shave on the 225 head. clearance was not the issue. the issue is high comp. how hi do you want to go. You must measure to be sure. if you have him take it off and for some reason it is too much it will be a bad day for all. I live in benson and drive to north tucson where I have a store. yesterday on the way home I had a hard time pulling 55 with the head wind. I am anious to rework this motor. |
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| Author: | SlantSixDan [ Wed Jan 21, 2009 10:05 pm ] |
| Post subject: | |
Whoah, there. Don't just pull a number off somebody else's build and shave that much off the head! That's a total shot in the dark and is as likely to work out poorly as well. Given the amount of effort, time, and money involved in building an engine, it's totally worth it to CC all six of your combustion chambers and find out where you're starting. Stock heads are all over the place, and there can even be significant variance between the combustion chambers at the front and those at the rear (which can be cleaned up with special angle-milling). You're really very likely to wind up less than satisfied if you do this by guess and by gosh. Measure, check, test, calculate. |
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| Author: | sandy in BC [ Thu Jan 22, 2009 7:18 am ] |
| Post subject: | |
In my opinion you should consider decking the block and just cleaning up the head. Shaving 100 off the head will not get you 10:1....that much is for sure. |
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| Author: | Aggressive Ted [ Thu Jan 22, 2009 8:20 am ] |
| Post subject: | |
Mike, I decked the block and shaved the head for 9.5 compression. You got to measure first though to see if anything has been cut before. In my case it had been surfaced once before. We went ahead and reground the cam for a taller lift and for more torque and so I could use my stock push rods. By regrinding the cam it offset the head and block decking. The old stock push rods fit perfectly. Hope this helps! 
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| Author: | stonethk [ Thu Jan 22, 2009 8:21 am ] |
| Post subject: | |
Measure twice, cut once.... |
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| Author: | Reed [ Thu Jan 22, 2009 8:33 am ] |
| Post subject: | |
Somewhat off topic- how do you CC a head? I assume you get a piece of plexi and a gradated syringe (in CCs of course) and see how much water it takes to fill each combustion chamber? If you find discrepancies, how do you correct them? 
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| Author: | wvenable [ Thu Jan 22, 2009 10:09 am ] |
| Post subject: | |
There are some excellent posts on ccing cylinder heads right here on the forum. Any weirdness might indicate a warped head. Hit the search button!
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| Author: | Reed [ Thu Jan 22, 2009 10:13 am ] |
| Post subject: | |
Duh. Thanks! |
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| Author: | mopar_nocar [ Thu Jan 22, 2009 10:40 am ] |
| Post subject: | |
I have to back sandy on this one. You can do a lot more with milling the block. In my experience, it is more costly to have the block milled than the head. That's the only downside I have found. Use are wire cup brush or some such to clean the block deck. Put the #1 cylinder at TDC and measure how far down the hole it is. Mine was .140". Repeat for all cylinders. sb |
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| Author: | Aggressive Ted [ Thu Jan 22, 2009 10:50 am ] |
| Post subject: | |
Reed, If you have discrepancies it could, be from the way the valves may have receded into the seats or the head shape could be a little off from extra deposits or previous grinding of the head or deposits on the valves. |
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| Author: | Reed [ Thu Jan 22, 2009 10:53 am ] |
| Post subject: | |
Thansk Ted. I haven't done any measuring yet, but I want to work over my big-valve head to achieve the most efficient combustion chambers possible. This is a future project, but I need to learn how to do it. |
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| Author: | Joshie225 [ Thu Jan 22, 2009 10:54 am ] |
| Post subject: | |
When I was turning a warmed up street engine into something better I milled both the block and the head to raise the compression. That engine had stock rods with ARP bolts and TRW forged pistons. Had the K1 rods and pistons been around back then I would have spent very little more to get the compression up and had stronger rods and lighter pistons to boot. |
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