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| Subject: Re: which valves to buy? | |
Author: BuRn__ | [ Next Thread |
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] Date Posted: 12:00:32 01/20/03 Mon In reply to: BuRn__ 's message, "which valves to buy?" on 10:27:21 01/19/03 Sun so, higher than stock compression would require me to run higher octane regardless of PSI? hm...maybe i wont be doing that then. [ Next Thread | Previous Thread | Next Message | Previous Message ] |
| [> [> Subject: Re: which valves to buy? | |
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Author: tonyz2897 [ Edit | View ] |
Date Posted: 14:56:48 01/20/03 Mon "so, higher than stock compression would require me to run higher octane regardless of PSI? hm...maybe i wont be doing that then." ------------------------------------------------------------ Sort of, but I doubt you'd get it that far with just a head shave. More acurately, higher compression would limit the PSI you could run on the same gas. For the sake of discussion, lets say you are running an intercooled car on high test pump gas at 30 psi with no detonation. Now that's going to be getting pretty close to the limit. Ok, now shave a few thousandths off the head. You're likely to find that you have to drop the boost a little or retard the timing to keep from detonating. Personally, I'd rather keep the static compression low, and add more boost. I'm actually considering trying to lower the compression on my engine when I rebuild it. Also, shaving the head to the limit now will force you to buy another head in the future if it should become necessary to resurface it again. It kind of compares to boring a block to it's limit. Sure, you get a few extra cubic inches, but is it worth having to throw the block away later instead of being able to bore it again? On the other side of the argument, you'll probably see a slight increase in power from idle to the point where your turbo starts to build good boost with the higher compression. I guess it all just depends on what you want from the car, and the maximum boost you plan to run in the future. HTH, Tony [ Post a Reply to This Message ] |
| [> [> [> Subject: Re: which valves to buy? | |
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Author: HP=(mph/234)^3*weight [ Edit | View ] |
Date Posted: 16:35:24 01/20/03 Mon To "rebuild" a head as cheap as possible: Disassemble the head and take it to a machine shop. Have them check the flatness of the mating surface and only do what's absolutely necessary. Excessive milling will raise your compression and screw up your cam timing. Buy new, stock size valves. I'd recommend buying back cut valves or having them back cut. Lap them into the head yourself. This is a simple procedure that requires a good valve lapping compound and either a lapping tool (cheap) or I've also used a cordless drill on the valve stem. Larger valves WILL flow more without porting the head, but will require the valve seats to be cut by a machine shop to accept the larger valves. This would be a great step in the right direction if you can afford it. Port work gets expensive as its very time consuming. Spend what you can in this area and you won't be disappointed. [ Post a Reply to This Message ] |