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| Head CC https://slantsix.org/forum/viewtopic.php?t=38351 |
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| Author: | dakight [ Tue Dec 22, 2009 12:34 pm ] |
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OK, thanks guys for the responses. I did some more measuring and looked at the cam card and here's what I come up with... If I take another .040 off of the head to get 50CC chambers and shave the block by .110 I will come up with a static CR of about 10.25. Factoring in the rod length of 6.7" and using the 37* ABDC valve timing and adding 15 ( I don't know why; that's just what the calculator said to do.) I get a DCR of about 8.72. The calculator is from kb-silvolite and can be found here: http://kb-silvolite.com/calc.php?action=comp Sanity check... do the numbers make sense? The deck is virgin, still has the factory stampings on it, can I safely remove .110? The carb I am presently planning to run is a Holley Economaster which is supposed to be a direct replacement for the BBD. Would I be better off selling it and switching to a 350 CFM Holley 2BBL? My rear gear ratio is 3.55 and the trans will be an A-904 pushbutton. I once calculated that with my 215R60-15 tires I will be running at around 3000 RPM at 65 mph. |
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| Author: | sandy in BC [ Tue Dec 22, 2009 12:46 pm ] |
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Those numbers make sense for a 150 mill. Thats about where Im at cept I radiussed/relieved my chambers for larger valves..... You can safley remove .110 ...(less than 1/8") Id get it running on your BBD if its known to be good....and step it up later.....starting with your new advance curve. One thing at a time..... a 350-400 cfm carb is about right at WOT for your build. You will prolly need to call Smith Bros once you get the head on..... |
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| Author: | dakight [ Tue Dec 22, 2009 12:55 pm ] |
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Smith Bros.... for pushrods? |
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| Author: | sandy in BC [ Tue Dec 22, 2009 1:15 pm ] |
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.....yep. Dont worry...they are super nice to deal with ....and have the nicest shipping boxes in the industry. |
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| Author: | dakight [ Tue Dec 22, 2009 3:09 pm ] |
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I assume they can help me figure what length is needed. I dropped the head off at the machine shop a few minutes ago. He's going to shave another .040. I'll pick it up tomorrow about noon. I'll CC it again and see where I need to be with the block. |
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| Author: | james longhurst [ Tue Dec 22, 2009 4:43 pm ] |
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+1 on Smith Brothers pushrods. They were very helpful when I called and their product is top notch. I got exactly what I asked for and the worked perfectly. -James |
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| Author: | dakight [ Sat Dec 26, 2009 9:34 am ] |
| Post subject: | Head CC: latest results |
I took the head back to the machinist and had another .040 shaves from it. Here are my latest measurements. I took extra care to be as precise as possible. #1 49 CC #2 49.6 #3 48.2 #4 49 #5 49 #6 49 So, at this point I think I will run through them again to verify the measurement and assuming they don't significantly change I will even them up at 50 CC. Thoughts anyone? |
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| Author: | dakight [ Sat Dec 26, 2009 4:32 pm ] |
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I ran the measurements twice more on each chamber and averaged the 3 numbers. Here's what I come up with: #1 49.0 #2 49.3 #3 48.5 #4 49.0 #5 48.9 #6 49.0 I'm inclined to open #3 up a little and call it good. I did find, as Lou said, that my measurement error could easily be +- .5 CC. There is potential error in zeroing the burette, in consistently filling the chamber to the same place on the fill/vent hole, and in the final reading. Parallax (the angle at which the level is read) can easily account for +- .2CC on both the fill and the final read. Now I'll double check the deck height then take the block to the machinist to take .110 off the deck. That will leave a final static CR of about 10.3:1 and a dynamic Compression Ratio of 8.7:1. |
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| Author: | madmax/6 [ Sat Dec 26, 2009 8:00 pm ] |
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Am I missing something?What size pistons?and how far down in the hole are they?I must bee blind cause I dont see that,will re read one more time.Guzzi Mark |
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| Author: | madmax/6 [ Sat Dec 26, 2009 8:06 pm ] |
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See the piston size but not how far down they are,curious,Mark |
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| Author: | DusterIdiot [ Sat Dec 26, 2009 8:57 pm ] |
| Post subject: | First post... |
Quote: Deck 0.086 (after planned .100 cut).
Max...it was on the first post... I expect that was a -.086 after the cut for plugging into the formula.-D.Idiot |
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| Author: | Dart270 [ Sat Dec 26, 2009 8:59 pm ] |
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The main error is not the buret, but the plate you paste over the chamber with grease or whatever. Hard to see how you get that perfectly the same every time, and fill it the same. If you are careful, I would believe +/- 0.5 or maybe a skosh better. In any case, the variation there will be a tiny CR change and other factors will be more important in detonation control. Lou |
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| Author: | madmax/6 [ Sat Dec 26, 2009 9:47 pm ] |
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I knew I was beeing stupid,couldnt figure out where,now I get it,Thanks,dummy Mark |
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| Author: | dakight [ Sun Dec 27, 2009 2:56 am ] |
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I think I've got it sorted out now. CC Vol. 49CC Deck 0.076 Comp. Gasket 0.040 Fire Ring diam 3.67 Cyl bore 3.46 Stroke 4.125 __________________ Static CR 10.398 Rod Length 6.7 Intake close 47 __________________ Dynamic CR 9.295 After running a few numbers through the calculator I've decided to leave the head as is. Changing the CC size by .5 CC changes the CR by about 0.05 which I believe is neglegible. I'll probably see as much or more variation due to slight variations in the deck height. |
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| Author: | DusterIdiot [ Sun Dec 27, 2009 8:14 am ] |
| Post subject: | Yikes! |
You want to try and stay out of the 9's...adjust deck cut to get your DCR under the 9 mark. -D.Idiot |
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