trying to get a general idea of how much i can mill 317's
03-20-2012, 07:04 PM
#1
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trying to get a general idea of how much i can mill 317's before i get flamed i know that you need to measure ptv to be certain. i got an lq4 pretty cheap and the internals look pretty good gonna re-ring it and get it hot tanked. I ordered the eps 230/234 on 112 lsa a couple of weeks ago and talked to Geoff today said should be here next week. Im just trying to get an idea of how much would be possible to mill without fly cutting. also what gaskets would be best? I'm guessing the 7.425 push rods i ordered before the ls1 blew wont work either.
03-20-2012, 07:50 PM
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this is going to sound mean of me
but with what your wanting to know I think it
would be a good idea to do a search on this site or even google for
your answers if you have to.
What your asking is impossible to try to give an answer
were not building the engine it sounds like you are
although this site does have good sound advice from most
ptv clearance? how much is the block decked?
how thick is the head gasket?
what size of valves?
i am only suggest to do alot more research
03-20-2012, 08:52 PM
#4
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A 230/234 - 112 is going to have you really close to the minmimum recommended PTV without any milling at all. Anything you mill at all will be eating into the safety margin. I would think you would be playing with fire with anymore than 0.020", even if you cam is right on the specs. If you were even a couple degrees off the advertized numbers, you could kiss piston. If you don't mill there is a good chance your pushrods will be ok, but you may be running towards the high end of the lifter preload. You can check it by putting together and checking the number of turns it takes from zero lash to the full torque spec on the rocker. There are a couple formulas out there to predict lifter preload based upon turns you can search for, but about 1.5 turns is about normal.
03-20-2012, 09:04 PM
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Would it be best to just try to find a set of 243s then? I've seen a few for around $350 or just stick with stock 317s and low compression anorrery for at least 360 rwhp with my mods
03-20-2012, 10:00 PM
#6
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Well I have read that 1 point of compression is worth about 25 RWHP on an LS1 F body. I think that is a very rough estimate, but have read it as a rule of thumb. The 243 should give you about a half a unit more compression than the 317s. I'm not sure I would swap heads for that, about 10-15 hp? And the 317's would be more tolerant of lesser quality fuel as well. There are worse ways to spend $350 bucks?
03-21-2012, 12:26 AM
#7
i ran a 230/238 on a 112+2 and it kissed but he is running a lq4 with dished pistons.. i was running a ls2 with the stock (flat top ) pistons... im 99% sure you would be fine milling the 317's .040 and running a stock thickness gasket... but if i had to choose between a 317 and a 243/799 id go with the 243/799 heads. BUT you should be fine milling the 317's
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03-23-2012, 12:43 PM
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i can get some 241s with a 3 angle valve job new seals and freshly decked for for $125 would that be better than having to mill the 317s and worry about clearance issues?
03-23-2012, 11:43 PM
#10
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I would think that the 317s as is would be very close to the 241 in power production. A little less compression, not much about 0.2 point, but better flowing than the 241's because of the better runner design like the 243. So it is give and take.
If it were me, here is what I'd do. I'd probably justt run the 317's with about a 0.10 milling just to make sure they are square. That should give you about 0.060-0.70 clearance with the stock pistons. You should check it to be sure before running the engine. If you haven't bought your gasket yet, you could chop them like 0.030, and then check PTV and buy the appropriate gasket thickness, to ensure you have enough PTV. This may mean running Cometic gaskets or such, and you will pay a little more for them if the standard 0.051 MLS GM gasket is too tight. It would still be cheaper than buying another set of heads, and I like the 317 head, I believe it is under-ratated, and is pretty much equivalent to the 243 for power production if prepared properly.
If it were me, here is what I'd do. I'd probably justt run the 317's with about a 0.10 milling just to make sure they are square. That should give you about 0.060-0.70 clearance with the stock pistons. You should check it to be sure before running the engine. If you haven't bought your gasket yet, you could chop them like 0.030, and then check PTV and buy the appropriate gasket thickness, to ensure you have enough PTV. This may mean running Cometic gaskets or such, and you will pay a little more for them if the standard 0.051 MLS GM gasket is too tight. It would still be cheaper than buying another set of heads, and I like the 317 head, I believe it is under-ratated, and is pretty much equivalent to the 243 for power production if prepared properly.
03-30-2012, 04:24 AM
#11
Sorry about the thread jack OP but does anyone know exactly how much a 317 head can be milled until its no longer use-able? Trying to build a 13.5:1 LS1 and I have some nice 317s I wanna use. The compression calculator says I would need 50cc chambers to achieve this compression.
03-30-2012, 07:22 AM
#12
That would take a bit more than .100"! I have heard of .070" working successfully, but beyond that you are on your own. The intake will need work beyond a .050" - .060" cut( carb intakes- no experience with plastic stuff). The oem deck thickness is aprox. .470" thick.
03-30-2012, 08:46 AM
#13
What about having the chambers welded up and remachined to get the cc you want and keep your stock ptv? If you find a good machine shop they can do this pretty easily.
