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| Head questions https://www.slantsix.org/forum/viewtopic.php?t=37368 |
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| Author: | Reed [ Sun Oct 04, 2009 12:00 am ] |
| Post subject: | Head questions |
My brother's van (with a 225) is leaking oil where the head meets the block on the passenger side. We have replaced the valve cover and the valve cover gasket and checked the spark plug tubes. Still a slow seeping leak. It also puffs blue smoke when it revs (the short block is rebuilt under 10k ago, the engine has been bored out .030 oversize) so I think the 1974 vintage stock unrebuilt head on there now is getting worn out. The van is a daily driver/band gear hauler. It is running a 2.5 inch exhaust, Super Six (Holley 2280 carb for fuel economy), HEL ignition with a Ford e-core coil. Future plans include a cam reground to the Erson 254 cam specs and dual exhaust manifolds into one exhaust pipe. I know the head needs to be rebuilt, but I want to put off tearing into it until I have the cam, dual exhaust manifolds, etc... all together so I only have to rip the top end off once. My questions: (1) should I rebuild the 74 vintage head on there now, or should I rebuild the 67 head I have in my garage? The 67 head is the non-revised combustion chamber (it has the "dot" opposite the spark plug). Is the unrevised combustion chamber so bad that I should find a revised chamber head for a daily driver/hauling vehicle? (2) I would like to bump the compression ratio up to 9.5. I would also like to get whatever head I am going to rebuild milled at the same time it will be rebuilt. Can someone give me a ROUGH, ballpark, guess, estimate of the AVERAGE amount of material I should get milled of the head to get my compression around 9.5? I know the correct method is to measure the height of the pistons below the deck and to CC the individual chambers to get the compression ratio exact and even between the cylinders, but this is just a daily driver, not a 1/4 mile racer, plus I would like to get one head rebuilt while the other head is on the van. Any help would be greatly appreciated. Thanks in advance. |
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| Author: | DusterIdiot [ Sun Oct 04, 2009 2:01 am ] |
| Post subject: | Couple things... |
#1) Revised combustion chamber would be helpful, I have used the other head and know the "dots" can be a source of heat spot and ping. If you are going to try for 9.5:1...you need all the help you can get... #2) It will not matter whether it is a daily driver or a racer...good engine building is a matter of taking good measurements and doing the math...you can even go one better and take you measurements and your cam grind and use one of the online dynamic ratio calculators to see what kind of trouble you are getting into... a DCR of 7.5 will eat ARCO oxygenated crap all day for fuel...and 8.0 will prefer plus and might do better with super...9.0 starts into the life of super or race fuel.... With the tolerances on heads and deck height a "crap shoot" will either leave you short on SCR (yes, I was short on Beater Valiant at 8.9 SCR...but about 7.2 DCR= I can run it on crap gas....that will be changing soon)...or you may be in the hurt locker (plane .100 off and have it be ping prone on 89....).... IF...and I mean *IF* it is a mid-late 70's engine the deck height on "average" is about .145-ish... a "447" smog head is about 53CC... using Doc's article on how much to mill off the cylinder head to bring the chamber size down you should be able to make kind of a guess on how much to carve off...if you use a non-revised combustion chamber, those heads have been known to be a bit "thick"...I have carved .080 out of one, just to get it into the 50's CC range... Good luck Reed, don't take short cuts here, you'll pay for it in the long run...doing the math and taking the measurements will ensure that you get exactly what you are wanting to do...and make life easier when you do your recurve to improve performance or cut back on "ping". If you were near Salem, I do have a couple of "447" peanut plug heads available...as I saw your part wanted ad...I know one is 54CC for sure. -D.Idiot |
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| Author: | Reed [ Sun Oct 04, 2009 8:26 am ] |
| Post subject: | |
OK, thanks DI. I was hoping to be able to take some shortcuts, but I guess I will do it the hard and the right way. TIme to start brushing up on my math, reading all the articles, and doing som emeasureing. Thanks! |
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