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| Raise Compression https://slantsix.org/forum/viewtopic.php?t=32233 |
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| Author: | DadTruck [ Wed Nov 12, 2008 3:22 pm ] |
| Post subject: | Raise Compression |
I have seen the posts where a .100 fire deck head mill is generally accepted as not resulting in structural issues to the engine. I am assuming that with a .100 stock removal premium gas would be needed. Are there simular convictions on how much can be milled off, to improve engine performance and still allow the use of regular (what is posted as 87 octane)gas. I am working with a 1987 225 head. Is calculating the effective compression ratio as simple as measuring the volume of the combustion chamber with head gasket, and adding that to the full cylinder volume then doing the math? thanks |
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| Author: | Joshie225 [ Wed Nov 12, 2008 3:32 pm ] |
| Post subject: | |
My '67 225 was right at 8:1 stock. The head I put on the engine was milled .080" which took it from 62cc to 50cc. My new compression ratio with the thicker than original replacement head gasket is right about 8.5:1. When the weather isn't too hot it runs fine on regular 87 octane gas. The fire deck as you put it is quite thick on a slant 6 head so milling .100" off is fine in most cases. There are plenty of compression ratio calculators on line. I like the one on the KB pistons web site at kb-silvolite.com http://kb-silvolite.com/calc.php?action=comp |
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| Author: | Doc [ Wed Nov 12, 2008 5:10 pm ] |
| Post subject: | |
This is a hard question to answer because production tolerances result in different, "engine to engine" compression ratios. The way your engine runs is really a result of its dynamic compression ratio, which takes cam timing and volumetric efficiency into account. So, do you plan to make any other changes besides adjusting the compression ratio? DD |
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| Author: | DadTruck [ Wed Nov 12, 2008 6:37 pm ] |
| Post subject: | |
This 83 D-150 is certainly not fast, but does have decent pep and can consistently touch 19 mpg in daily driving. Goal is to add power and increase mileage by obtaining improvements in engine efficiency, ( as well as just have some cool parts in / on the motor) planned improvements (parts accumulated so far) 1) HEI ignition module and NOS vacuum advance distributor 2) Aussiespeed 2BBL intake 3) Dutra Duals 4) Spare Cyl head, will do OS valves, clean up porting, gasket match, and considering milling looking for advice on 5) cam options 6) carb choices and the milling / reg gas question as a note, plan to do a rebuild on the crankcase, stay with stock pistons, valve train, unless someone has compelling reasons for a change here. This old Dodge has ran well for the past 25 years, plan is to go through it once and run it even better for another 25 years. thanks |
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| Author: | wvenable [ Thu Nov 13, 2008 5:03 am ] |
| Post subject: | |
Dadtruck if you plan on a short block rebuild, wait on milling the head. This way I could help you determine your actual compression ratio so you can choose where exactly you would like to be when you go back together. I will pm you later. |
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| Author: | wvenable [ Thu Nov 13, 2008 12:00 pm ] |
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DadTruck, do a search for Matrix for engine build combinations. Take a look at Aggressive Ted's setup for torque and mileage. See if this helps. |
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| Author: | DadTruck [ Thu Nov 13, 2008 6:06 pm ] |
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thanks I had typed "cam" in to the search engine and saw 258 responses, so perhaps that is a meaningful question,, but unfortunately I don't have the time to digest it all. Did see aggressive Ted's comment about 254 duration, .435 lift, so perhaps that is a start (vanishing) point, But I also saw Marine Cams, RV Cams ......, I comprehend that engines are air pumps,,,. Breathing is what it is all about. Looking for a jumping in point for a street power slant six,.. |
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| Author: | wvenable [ Fri Nov 14, 2008 7:42 am ] |
| Post subject: | |
Anothe good thread to read is Max torque 87 octane build recipe! |
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| Author: | Aggressive Ted [ Fri Nov 14, 2008 9:46 am ] |
| Post subject: | |
DadTruck, That is what I wanted from my rebuild. It worked out very well. I have about 40,000 on the engine now. The only change I would make would be to use a double roller timing chain. There is a huge torque hit right off idle that can cause chain stretch with a heavy vehicle. |
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| Author: | Doc [ Fri Nov 14, 2008 9:56 am ] |
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You are on the right track, you really need to decide on some performance goals and develop a nice build plan around that. You answered one important question, fuel quality, (pump 87) Next is deciding on the power band / max RPM. And in general, is the focus on economy or on max power? With at info, you can develop a pretty good combination parts to meet those objectives. careful cam selection with a matching compression ratio is the key to success. DD |
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| Author: | wjajr [ Fri Nov 14, 2008 12:53 pm ] |
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Is it me, or is the search engine function here a bit difficult to use? I queried: Aggressive Ted's setup for torque and mileage and Max torque 87 octane build recipe, and got no usable hits. One search listed a few hundred entries, the other two entries non related. I think I have seen Ted's build list before, but be damned if I can find it again. What is the trick to using this function? Befuddled old fart... |
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| Author: | Doc [ Fri Nov 14, 2008 1:02 pm ] |
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Using "and & "or" between key words helps. I also limit the search to the Engine forum to get faster / fewer hits. When I serched for MATRIX I got some good hits... including the Engine Build Matrix thread: http://www.slantsix.org/forum/viewtopic ... ght=matrix DD |
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