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| How much to cut... https://www.slantsix.org/forum/viewtopic.php?t=51496 |
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| Author: | jhdeval [ Sat Mar 23, 2013 1:22 pm ] |
| Post subject: | How much to cut... |
Okay We are going to cut the head and or block this week. How much should I take? What would be recommended? |
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| Author: | DusterIdiot [ Sat Mar 23, 2013 1:32 pm ] |
| Post subject: | What color is the sky? |
That question is kind of ambiguous at best... The answer is based on a few things: 1) What camshaft have you decided upon? 2) When you disassembled the engine how far down were the pistons from the deck at TDC for the piston? How many CC's were your chambers after they cleaned up the head and did the vavle/seat work? With #1 we can ball park the SCR how best to approach it (i suspect from previous e-mails you are building a slightly better than stocker). This givers us the "answer". #2 will help determine the other end of the equation and eliminates some variables so we can solve for the deck and head cuts. -D.Idiot |
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| Author: | sandy in BC [ Sat Mar 23, 2013 1:45 pm ] |
| Post subject: | |
#3 ....are you cutting the block or head? If you are installing larger valves you may want to do some work in the combustion chamber which increases volume and unshrouds the valves. If you cut the head it means you may have to notch the bores to keep the valves from being shrouded or hitting the deck . Either way lots of math or guessing is involved. I prefer guessing,,,,but math gets better results. Delay cutting till you know exactly what you are doing. |
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| Author: | jhdeval [ Sat Mar 23, 2013 1:50 pm ] |
| Post subject: | Re: What color is the sky? |
Quote: That question is kind of ambiguous at best...
1) Oregon Cam Grinders 791The answer is based on a few things: 1) What camshaft have you decided upon? 2) When you disassembled the engine how far down were the pistons from the deck at TDC for the piston? How many CC's were your chambers after they cleaned up the head and did the vavle/seat work? With #1 we can ball park the SCR how best to approach it (i suspect from previous e-mails you are building a slightly better than stocker). This givers us the "answer". #2 will help determine the other end of the equation and eliminates some variables so we can solve for the deck and head cuts. -D.Idiot 2) I am replacing the Pistons with Silv-O-Lite a) Did not measure the distance. b) We have not CCed the chambers yet. So basically I need to finish the head before we do any cutting. Also as for the valves I went with enginebldrs from eBay. As for cutting head or block it doesn't matter to me as long as I hit the 10-10.5 compression I am looking for. |
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| Author: | DusterIdiot [ Sat Mar 23, 2013 6:46 pm ] |
| Post subject: | Ugggh.. |
Quote: 2) I am replacing the Pistons with Silv-O-Lite
Well, you are blind at this point...you will have to install the crank and a couple of pistons to get the deck height to determine the cut, then uninstall everything... It's typically better to cut on the block than the head, so if the head has an issue or you need to have it cut a little more you can take the head back in.a) Did not measure the distance. b) We have not CCed the chambers yet. I initially measure the engine's original deck height so I know where it sits before I start carving it up. If you are using standard piston replacements by Silvo-Lite they will be similar to the Fed-Mog pistons (I think only one manufacturer makes these now, since I have a boxed set of each brand and they are machined the same). I just handed off an engine to another board member today who will be shooting for 10:1 as well...it has a deck height of .088, so he will be shooting for a 48cc chamber...per my build sheet, the block had an original deck height of .175 so I had the machinist cut .090, but the new pistons had a little more height than the stockers...I then had the head massaged for the proper chamber size (in this case it started at 53 cc stock, and has it cut 5x.0066 = .033 clean up scrape...) Make sure your machinist doesn't "crap" on taking a large cut like that off the deck...I had to line out a machinist on my 11.7:1 motor and took .100 out of the deck and head to make it right, they couldn't believe that it needed to be that way...(not like someone has a set of Jahn's domed pistons from the mid-60's laying around any more). -D.Idiot |
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| Author: | sandy in BC [ Sat Mar 23, 2013 7:58 pm ] |
| Post subject: | |
I had to explain to the machine shop that I wanted ,120 off the deck......"almost an eighth!". They were shure I wanted .012.......... " Yes I know how much .120 is......" They did .80......I had to go back. |
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| Author: | jhdeval [ Sat Mar 23, 2013 8:07 pm ] |
| Post subject: | |
I have been going from the beginning letting him know that many have taken .1 off so he is prepared for the possibility. I am going to finish my port and polish tomorrow hopefully. Rainy and nasty here in Georgia. I will then CC the chambers and see what I have. Should I be shooting for 48cc? If not can you recommend a cc to shoot for? |
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| Author: | DusterIdiot [ Sat Mar 23, 2013 8:23 pm ] |
| Post subject: | Deck Height... |
Quote: Should I be shooting for 48cc? If not can you recommend a cc to shoot for?
A+B=CHow far down your pistons are in the bores are going to determine how many CC your head needs to be be to reach the target. Static Compression Ratio is determined by the volume of the chamber, the volume of the compressed head gasket, and the swept volume of the bore (volume of the bore with piston at BDC, and volume of piston at TDC). If using a felpro gasket, overbore the block at .040 over, and the cut left the deck height at .088 on the block (pistons down in the bore at TDC), then yeah a 48 cc chamber would put you in the 10.3:1 ball park.... The problem with our algebra and geometry problem here is without the known deck height the rest of the calcs can be off badly (enough that if you cut too much you may need more octane and $$$ to keep it from pinging badly). It's a little tougher to go the other way, CC the head and then determine how far the pistons need to be down the bore at TDC...this gets into a grey area for the block also...if you take a fair amount off the deck, the head bolts may not thread all the way into the remaining holes, or they will need washers to shim them for proper head retention...(the block I turned over has ARP studs in the deck and have almost 1 full thread showing when installed properly... You should check online for a compression ratio calculator and play with the variables to see if you can 'fudge' together a plan...I would also recommend using a DCR calculator to see what the DCR is, if you over shoot too much, advance the cam too mcuh, it will give you a ball park of what Octane you will be running. -D.Idiot |
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| Author: | slantsik [ Sat Mar 23, 2013 10:23 pm ] |
| Post subject: | |
Throw your crank and at least #1 piston back in ( good to put #6 back in too) .Measure piston-deck height at tdc. measure bore etc. Use this calculator to find what you need to measure. Dont guess ,measure and calculate. http://www.kb-silvolite.com/calc.php?action=comp Here are some numbers to help get u started. Stock bore 3.4" Mine was 3.440" Stroke 4.125" My Piston to deck height was 0.200" Now 0.100" My cylinder head cc was between 59-60cc Piston head volume is 0 for flat tops + X cc for valve recess Compressed gasket thickness between .035" .045" My felpro gasket bore diameter was 3.525" Stock rod length about 6.7" Intake closing ..... you need to calculate using intake centerline,+ 1/2 of duration @ 0.050" + 15 will give closing point. Mine was 41* ABDC. (Close to a stock type cam) Eg . IN c line 107* ATDC Duration @ 050" =198* /2 = 99* 99* + 107* ATDC =206* ATDC or 26* ABDC + the 15* = 41*ABDC Intake closing I ended up with 8.8 SCR and 8.1 DCR This should be safe with any old fuel. I hope! Brendan. |
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| Author: | 65CrewCabPW [ Sat Mar 23, 2013 10:36 pm ] |
| Post subject: | |
In my case, I measured my pistons as being .128 below deck... I bought the stainless oversize valves from engnbldr, directly from them over the phone. I had to CC the head 3 times, but we ended up cutting more than .120 off the head to get the chambers down small enough to get to a calculated 10.48:1. I originally estimated I needed .160 off the head, but the chamber size dropped faster than a couple people here said it would. BTW, my head had chambers all within 2 cc's of each other after the machine shop put in the oversize valves and hardened seats. I used the middle size for my measurements. |
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| Author: | Rug_Trucker [ Sun Mar 24, 2013 9:11 am ] |
| Post subject: | |
You live in Jawjah? Depending on where you live you can have some real crap fuel. In Nashville the fuel in summer is 7.6lb. Winter and rural year round fuel is 9.0 Atlanta is 7.2 or so. |
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| Author: | patrick henry hague [ Sun Mar 24, 2013 8:31 pm ] |
| Post subject: | Head mill |
Here is an idiots guide to your head mill, the head can be milled .125 with no problem "usually" -If it has not been done before - safe bet go .090 -. Now what I've read from all the other posts here there right on target with there information. Note this years ago when built my first Slant 6 I took off .125 checked the piston to valve clearance by putting clay on top of the piston, turning the engine over without a head gasket and measuring the clay between the valve and piston found there was plenty of clearance no problem the lift on that came was .448 and the duration was .268 it worked real well, great matter of fact and it was behind a four speed, it did idle kinda lumpy, from all the information posted here and my 2 cents worth you've got a lot of information I wish you the best. |
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| Author: | jhdeval [ Sun Mar 24, 2013 9:00 pm ] |
| Post subject: | |
Well some new revelations have come into play. I am boring the cylinders .040 over Felpro gasket Stock 225 rod so should be 6.7" Intake closing is 39 degrees (As per OCG Sheet) If I CC'ed the first bore correctly looks like 58-59cc's Based on what I have been reading this CC seems to mean the head has never been milled. I realize I have not CCed ALL cylinders but how much CC drop can I expect per .010 being taken off? |
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| Author: | jhdeval [ Sun Mar 24, 2013 9:01 pm ] |
| Post subject: | |
Quote: You live in Jawjah? Depending on where you live you can have some real crap fuel. In Nashville the fuel in summer is 7.6lb. Winter and rural year round fuel is 9.0 Atlanta is 7.2 or so.
Fuel here is a crap shoot. One week station a may be good and then bad the next. The QC is terrible here
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| Author: | DusterIdiot [ Sun Mar 24, 2013 9:49 pm ] |
| Post subject: | Head conversion... |
Quote: Based on what I have been reading this CC seems to mean the head has never been milled. I realize I have not CCed ALL cylinders but how much CC drop can I expect per .010 being taken off?
Assuming it's under about 42 CC per Doc's Stroking article and the Service Manual, 1cc = .0066 cut on the head... so if after the valves seats are cut and final install of the valves occurs if you are still at 58 CC then to get 48 CC (if that's the target) then you need to cut 10x.0066 = .066.That's easy...but you will still need to install the crank and at least the #1 and #6 rods/pistons and run them each up to TDC and get a measurement of how far down in the block they are before cutting on the head... -D.Idiot |
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