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| Subject: which valves to buy? | |
Author: BuRn__ | [ Next Thread |
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] Date Posted: 10:27:21 01/19/03 Sun well, ive started buying parts to rebuild my head, but im stuck at which valves to get. www.FWDPerformance.com lists two different kinds of exhaust valves; "36.8 exhaust valve" and "36.8 exhaust valve (+1mm)" what does the +1mm mean if they're both listed at the same size? [ Next Thread | Previous Thread | Next Message | Previous Message ] |
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Author: mpbiv [ Edit | View ] |
Date Posted: 12:22:05 01/19/03 Sun E-mail Cindy (she runs FWDPerformance), but it probably just means they are literally 1mm larger than the standard 36.8 valves. Oversize valves would also required machining of the head I believe. Also make sure you are getting the right valves for the head you have, make sure to tell her in the e-mail what the casting number on the head is. This is important because the valves for the G and fastburn head have different stem lengths. [ Post a Reply to This Message ] |
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Author: tonyz2897 [ Edit | View ] |
Date Posted: 14:30:14 01/19/03 Sun I may be wrong, but I don't imagine you'd see much gain from going with the oversized valves unless you also did some port work to the head to make it flow better. Plus you'd have the cost of machine work necessary to install them. If you're going to port your head while it's off, it might be something to consider though. Just my .02 Tony [ Post a Reply to This Message ] |
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Author: BuRn__ [ Edit | View ] |
Date Posted: 19:19:41 01/19/03 Sun im not gonna port the head, but was told when i take it to have it machined to "mill your head to minimal tolerances". would that have any effect on the valves? also, i plan on replacing the valves and all that stuff myself, just taking it to a shop to have it machined. is there n e thing i should watch out for? [ Post a Reply to This Message ] |
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Author: tonyz2897 [ Edit | View ] |
Date Posted: 11:19:40 01/20/03 Mon I wouldn't go any farther than what's necessary to get the head back into spec as far as the flatness of the gasket surface. Planing excessive material off of the head will increase your compression ratio which would increase your octane requirement at high boost. In other words, increase the compression too much and you may get detonation with pump gas at a boost pressure that you would otherwise be able to run. I've also heard that compression made with boost makes more power than the equivalent static compression. I have never seen documentation to back this up though. Tony [ Post a Reply to This Message ] |
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Author: BadAndy [ Edit | View ] |
Date Posted: 07:53:03 01/25/03 Sat That's not the worst of it.....you forgot the fact that milling changes your camshaft timing as the area between pullies has been shortened. [ Post a Reply to This Message ] |
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Author: BuRn__ [ Edit | View ] |
Date Posted: 12:00:32 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. [ Post a Reply to This Message ] |
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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 ] |
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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 ] |
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Author: BuRn__ [ Edit | View ] |
Date Posted: 20:27:19 01/20/03 Mon i called around to a few shops around here. the 1 im taking it to on wednesday said that they charge $90 for a valve job, $30 for surfacing, and $whatever for parts. not too bad. and he said at the worst case scenario, (cracked head), itd cost me $395. all in all, less than i was expecting to pay. [ Post a Reply to This Message ] |
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Author: dodgeshelby87 [ Edit | View ] |
Date Posted: 02:29:38 01/22/03 Wed The +1mm valves are for the 86-up 782(swirl) casting head. [ Post a Reply to This Message ] |
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Author: squirrel [ Edit | View ] |
Date Posted: 10:43:10 01/27/03 Mon Do not have the head milled if at all possible!!! Yes you will have to open her up for +1mm oversized valves. If you are not porting it don't bother. [ Post a Reply to This Message ] |
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Author: BuRn__ [ Edit | View ] |
Date Posted: 17:42:42 01/27/03 Mon im not having the head milled, im just buying a new reconditioned head. cuz my head is basically shot. :-/ [ Post a Reply to This Message ] |
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Author: squirrel [ Edit | View ] |
Date Posted: 19:36:15 01/27/03 Mon Recon heads are not without there problems be forwarned. They are heads that have been through many rounds of abuse. They are used just like any other head new parts added aren't always up to par. [ Post a Reply to This Message ] |
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Author: tonyz2897 [ Edit | View ] |
Date Posted: 11:16:34 01/28/03 Tue Squirrel makes a good point here. I just wonder what the chances would be that a remanufactured head might have the wrong exhaust valves. It'd be worth asking about. Tony [ Post a Reply to This Message ] |
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Author: tonyz2897 [ Edit | View ] |
Date Posted: 11:17:00 01/28/03 Tue Squirrel makes a good point here. I just wonder what the chances would be that a remanufactured head might have the wrong exhaust valves. It'd be worth asking about. Tony [ Post a Reply to This Message ] |
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Author: BuRn__ [ Edit | View ] |
Date Posted: 19:39:36 01/28/03 Tue well, either way, im still getting a fairly good deal. i just need to get my car back up and running. its my daily driver and ive been without a car for 2 weeks now. even if it has the wrong valves, those are pretty cheap to replace n e ways. [ Post a Reply to This Message ] |
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Author: squirrel [ Edit | View ] |
Date Posted: 05:04:39 01/29/03 Wed I just wanted to let you know before the head was installed. They are not so cheap when they actually fail or break... [ Post a Reply to This Message ] |
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Author: BuRn__ [ Edit | View ] |
Date Posted: 07:09:56 01/29/03 Wed yea, i found out the hard way that they arent cheap to fix when they break while still on the car. lol. how do i tell the difference between turbo exhaust valves and NA exhaust valves? also, even if the head is used, as long as it has new parts and is surfaced correctly, etc. it should be like new, right? [ Post a Reply to This Message ] |
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Author: squirrel [ Edit | View ] |
Date Posted: 08:30:18 01/29/03 Wed The head could have unknown thin but not leaking yet cracks hidden in one of those unbeknownst high mileage heads that look new. [ Post a Reply to This Message ] |
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Author: squirrel [ Edit | View ] |
Date Posted: 11:01:32 01/29/03 Wed I'm thinking there is a T stamped or embossed in the head of the valve or something like that??? [ Post a Reply to This Message ] |
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Author: BadAndy [ Edit | View ] |
Date Posted: 21:54:19 01/31/03 Fri I "think" the turbo valves have a "T" on them .....it's been awhile and I'm not for sure. Daily driver or not I would make sure that you have turbo valves before assembly....it's much cheaper to do it now vs. if it snaps a valve head off and beats the crap out off your cylinder walls. If I remember correctly you can use the 1mm over valves with stock seats although I read somewhere that it actually hurts flow. [ Post a Reply to This Message ] |
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Author: BuRn__ [ Edit | View ] |
Date Posted: 09:51:55 02/01/03 Sat i called and ordered the head on thursday. i made sure the valves that were getting put in were turbo-spec, and the guy i talked to said that he would make sure they were turbo-spec valves. [ Post a Reply to This Message ] |