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| To valve or not . . . ? https://slantsix.org/forum/viewtopic.php?t=27843 |
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| Author: | Michael [ Fri Mar 14, 2008 6:49 pm ] |
| Post subject: | To valve or not . . . ? |
I have a very late (87) nos head and would like to know if installing the 1.77, 1.44 valves is preferable to stock ones? This head is for an aluminum engine that will be street driven with the goal of some pep and mpg. (63 Val vert w/ offy 4 bbl and 3.23 rear.) I plan to have it milled .60 or .80 tops with some mild port work. One competent machinist complained that the induction hardening of the later heads was very inconsistent and that the hardened seat could break through to the softer metal beneath. Is this more likely with the larger valves? As I like saving money and work, what would be the best route? I recently saw that Doc recomended them for a head rebuild but since this is a new one, I just have to ask. I have 4 other good heads (68 -72) and both sets of valves. Thanks - Mike |
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| Author: | dakight [ Fri Mar 14, 2008 8:28 pm ] |
| Post subject: | |
As I understand it, and I'm sure others will chime in, the induction hardening was rather shallow and would be taken out by a couple of valve jobs anyway. If you install larger valves you will want the machinist to put in hardened valve seat inserts. I don't believe the induction hardening should even be a factor in your decision. The larger vlaves will help breathing if you also do some other things to open up the flow capacity of the head. Bowl work, gasket matching, and valve relief are all equally important to satisfactory results. Unless you also plan to do those things then oversize valves will be of limited value. |
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| Author: | wvenable [ Sat Mar 15, 2008 5:43 am ] |
| Post subject: | |
Michael, Thanks for bringing this up again! Yours being a new head, you should be avoiding the problem Doc was describing with the repeated valve jobs. I understand that the porting and gasket matching is very benificial and could be something you could do yourself to save money. I just am sceptical if a 5% increase in valve size is going to be a major player on the street. If your a bracket racer trying to bring down that ET it makes sense. I will follow Doc's advice if I need to start replacing valves etc.-supersize me! But if the head looks good I wil try the stock valves first! I think Aggressive Ed might have some good Imput on this one! |
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| Author: | 66aCUDA [ Sat Mar 15, 2008 7:19 am ] |
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Micheal Go with the bigger Valves. You have list the 4bbl and 323 rear as things you will be using. To take advantage of the 4 bbl carb you will want the most flow out of your head. The head is one of the single most important pieces of the puzzle. If it flows good then the 4bbl and Dutra Duals can really make it shine. My 02. And have fun. Frank |
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| Author: | tophat [ Sat Mar 15, 2008 9:28 am ] |
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One thing that nobody else has mentioned. You might need to be careful how much you mill the head if it is going on an ALUMINUM block. From what I understand from reading here the aluminum block and special head gasket can't take much compression. The aluminum block has no deck surface to help the gasket seal. I am sure somebody with experience building aluminum slants can help you more on what compression is safe. TopHat |
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| Author: | Doctor Dodge [ Sat Mar 15, 2008 9:52 am ] |
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Quote: ...somebody with experience building aluminum slants can help you more on what compression is safe.
9 to 1 max. or 160 to 165 psi cranking compression. (the cam choice and position will influence cranking compression)Matching the head to the empty block and resurfacing both items are 'must do's" DD |
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| Author: | Michael [ Sat Mar 15, 2008 10:56 am ] |
| Post subject: | |
I'm shooting for a modest 8.5 to 1 comp and will carefully cc the head. The cam is a MP 244. I've had really good results with the Holley 390 just from a driveability standpoint and that's the main reason I'm keeping it. I now feel that I will install the stock valves - the larger ones can go into a head that needs a more thorough refurbishing. The porting and matching should still help a bit. Thanks for all the input!!! |
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| Author: | wvenable [ Sun Mar 16, 2008 8:38 am ] |
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Michael, please let us know how this project turns out! Not all of us drag race. I love to hear about diff streetable combinations. |
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