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OverdriveGear Member 
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Does anyone know what the volume of the combustion chamber is for the stock 907 motor (8.4:1)? |
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Brian Kelly Member
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Woops! Last edited on 11-16-2005 08:58 pm by Brian Kelly |
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LambandAndy Member 
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Swept Volume = Pi X Bore2 X Stroke / 4 = 3.14 X 95.22 X 69.2 / 4 = 492572 mm3 = 492.6 cc (per cylinder) Compression Ratio (nominal) = (Swept Volume + Clearance Volume) / Clearance Volume 8.4 = (492.6 + CV) / CV 8.4CV = 492.6 + CV CV = 492.6/7.4 = 66.6 cc Combustion Chamber Volume = Swept Volume + Clearance Volume = 492.6 + 66.6 = 559.2 cc This assumes that that the 8.4 ratio is nominal not actual. Hope this helps, Andy #15223 |
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Ron Earp Member 
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The chamber volume is typically defined as the area in the head. Typically, one finds this out by taking a flat piece of plexiglass with a hole in it and putting it on the head surface. Then, one takes colored water and a volumetric buret and fills the chamber up. The amount of liquid it takes is the volume and can be corrected for the head gasket thickness. SB Ford heads range from about 50cc to 75cc, with 58cc and 60cc being common. I imagine the 907 head is around 60cc or so as just a guess. One could back calculate it based on compression ratio and swept volume, since you know the swept volume of one cylinder is 492cc as provided above, and the compression ratio is 8.4:1, then 492cc / 8.4 is 58cc. Dang, my guess wasn't too bad! |
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OverdriveGear Member
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Yeah, I got 58.72 cm^3 also. I suppose I could have just done the calculation without a post on the message board, but engineers tend to be the lazy type. |
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Judson Manning Member 
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We engineers aren't lazy...we're just taught to make the math easy, which is much easier than taking a pipet and physically measuring the CC like we need to! guess that means we ARE lazy???? Several things.... The stock piston is NOT zero deck height (neither is the 10.x:1 2.2 piston), however the 9.x:1 flat-top IS zero deck height, and Delta does have some zero deck height 2.2 pistons that Garry Kemp is very fond of. The 'math' solution gives you dish, valve reliefs and the height below deck volumes along with cc volume. Also, the original head gasket is about 1/2 the thickness of the new Goetz(sp?) gasket. So that thickness is also in the 'math' solution and is worth about 1/2pt in compression. I actually remember someone posting a measured CC volume somewhere in the 40-44cc range, which is in-line with the 50-something results once you account for the gasket and deck height. I wouldn't obsess over the math and theoretical solutions, there are plenty of us who have assembled various combinations of pistons, deck heights, cams, decked heads, etc. that can tell you what does and does not work. Judson Last edited on 11-17-2005 01:33 am by Judson Manning |
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Jay Member 
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Just a thought... With the head off, another method to measure the volume of the combustion chamber would be to use something like modeling clay. Carefully press the clay into the cavity of the head, making certain that there are no voids in the clay. Completely fill and level off with a straight edge. Remove the clay and place in a small graduated beaker of water (like you may have used in chemistry class, the smaller the better for accuracy). Measure the amount of water displaced when the clay is submerged. That should get you close. Make sure to install an old spark plug to close the hole. I think this might be a little easier than using a liquid to fill the cavity. Additional corrections can be made to account for gasket thickness and piston configuration as required. Last edited on 11-17-2005 06:55 pm by Jay |
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Judson Manning Member
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Since I had nothing better to do today, I decided to compare my calculations to emperical data. This is what I found: Combustion Chamber Volume (Head): 37cc (decked 0.020") Stock Piston Dish: 17cc Piston Deck Height (.025"): 5cc The margin of error is significant in the above numbers due to the surface tension & miniscus(sp?) of the working fluid. I used both water and WD40 and the above numbers represent an average. We can massage the numbers to fit within the expected calculations to help minimize this error. Expected CCV (based on 8.4:1 c/r) = 66.7cc Calculated Piston Deck Height (0.025") = 4.5cc Calculated OEM gasket thickness (0.030") = 5.4cc 66.7 - 4.5 - 5.4 = 56.8cc Expected vs. 37cc + 17cc = 54 measured With reasonable certainty, we can expect a stock head: CCV = 40cc, and the Piston Dish = 18cc I envite everyone to examine my reasoning and to offer their measurements, observations and calculations for analysis. |
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Judson Manning Member
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Just an update.... My machinist cc'd a set of Delta's Flat-top pistons at 8.5cc I re-measured a 0.020" decked head with mineral spirits w/ a little ATF and got closer to 35cc. |
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