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Question on Milling heads and a cam for my 72 Dart
OK... i know i asked before for some advice on Milling my heads...but im so absolutely confused. I've asked several people and they're got me running in about 5 directions. Someone told me in order to achieve 9.5-1 compression in my 318 w/ 360 heads is to get new pistons....i know that it is ONE of the ways..but i was more into looking at milling the heads slightly... Im not sure how far or how much to mill so that i'll have proper valve clearance... the heads i bought at chryslers @ carlisle... they've already got a 3way done...new double springs..ect. A friend of mine said he would mill the heads for me... $30 a side.. all i have to do is tell him how much to mill (and that is where my dilemma comes in).
My waterpump went out last week, so i've put the car off the road. I have a new edelbrock 3 keyway timing chain sitting on the kitchen table waiting to be installed...and i figured this would probably be the best time to go ahead and install the cam as well. Im not sure what the best one to go w/ is considering there are so many out there... what kind of lift and duration would you recommmend for my 318...ill be taking it to the strip every now and then, but its not going to be full out race. I dont want too lumpy of a cam... well... hope i haven't confused too many of you. I appreciate all and any help. Thanks Jessica |
#2
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let me get this straight, your going to the strip now and then, but your not going to full out race?please elaborate?
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#3
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Kinda like me... want something that can go out to the track kick arse and drive to work.
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Which engine are you starting with?
If it is one of the low compression 8.5:1 CR 318, you would have to mill an excessive amount off the heads to get 9.5:1 compression because the pistons sit too far down in the engine bore to start with. |
#5
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mopargirlie63
Lets start with a little info from you.
What year is the engine we have here. This can help us find out the compression. If you have the shortblock near you, tell us exactly how far down the piston is in the bore when the piston is at top dead center. ALSO, to help figure the comp. out, what gasket are you useing? The gasket bore and compresed thickness is a need to know before you start milling. HEADS Head milling reduce's the head chamber volume. On a 360 head remove .0048 from the head surface per 1cc of chamber volume. For each .010 removed from the head, remove .0095 from the intake face of the cylinder head. This way the intake can bolt up nicely. You'll need to remove about 10-12 cc's from the camber of the head. Or mill .048-.0576. If the 360 heads are 72cc chambers, you need to mill to 60cc's. This will give about a 9.0-1 ratio. To get to 9.5-1, you will need a 55cc chamber. Milling to .072 may be to much. P.S., keep the 1.88 valve and pocket port if needed. CAM This depends on the type of driving and of course, rear axle ratio and torque converter to be used along with the "How fast do ya wanna run in the 1/4" question. An excelent cam for everyday driving would be the P4452761...268-272 w/.450/.455 lift. This is the replacement 340 cam. The problem with cams is that it like an opion, EVERYBODY has one. And they love to tell you that theres is the best and/or there maker is the best. Don't get to wraped up in a cam. Best 2 ways to chose is ethier by the RPm power range that you drive in or just call up a cam company and ask. They are very very helpful. |
#6
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a low comp 318 has about 8 to 8.5:1 comp,add 360 heads and its a 7.5:1 motor(yuk),mill the heads .060 and its a 8.5:1 motor so stick to a real small cam something like 430/260,keep in mind youll have to shim the rockers......PRO.....
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#7
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How about another idea?
If the engine is in good condition, it may be a good canadate for a supercharger or turbo, then the low compression will be fine. |
#8
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Welcome aboard Jessica!
Go with the old steel shim head gasket. Also put some copper coat on it before installing this will aid in sealing. One thing to look for on milling is the deck surface on the heads. Dont mill them too much or they could be ruined. Your machinest will help you deside on how much to mill. Also dont choose a cam that will bleed off compression afterall this is going the oppsite way you want to go. Your best bet would be a small solid cam from Mopar or Comp Cams. This will give you great mid range power to upper power your lookin for. But can be trouble some because of lash adjustments,but hey if you like workin on cars no biggy. Also to help out on take off go with as much gear as you can stand maybe 3.91 for hot street and somewhat streetabilty. A low compression engine should be made to rev fairly easy. A loose converter will aslo help give Dynamic a call on that. Go with a Performer RPM intake and a 600-650 Double pumper carb. This intake despite what they may say is the best street intake avaliable and the new Air Gap design is great. Dont forget the tranny cooler which maybe needed to help cool your auto trans. If thats what it is? |
#9
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Lot's of good ideas...
How fresh is this motor? How much does this car weigh? 3450? What rear end is in it 7.25?? 72 Dart....904 tranny? Heads sound good...Portland Engine Rebuilders Halloween Special $895.00 zero deck 360 short block w/flat tops, less $25.00 if you supply cam...just bolt your heads on, add a performer manifold and a 650 Speed Demon w/elect. choke kit and you'll be set. Almost everything will transfer over from your 318. I'm sure there's good rebuilders in your area that have similar pricing. Think about it and study line #1 in my signature..... ...and.... Why!!!! is there a cam gear set on the kitchen table? That's for over hauling carbs...the cam gears go on the window sill...just chuck those flowers in the trash can and make room. |
#10
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LOL, you selfless promoter you.
I prefer to hang my chain & gears in the window. Does anyone know the safe limit to milling heads? .060 is allready alot. |
#11
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Till they bleed, then plug the hole with JB weld
....I miss my 17:1, all aluminum, 410 CID, alky injected, 880 HP, 1375# car..... ...well maybe not....I was gettin' dizzy going around in circles all the time.... |
#12
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In my 318 the pistons were in the hole for about .080" I believe most 318's are about the same since there is not too many different rebuild pistons available. When calculated, with 70cc 318 heads and a Fel Pro head gasket this engine was right at 7.49:1. In a low CR engine milling the heads does not have near the effect of raising thre CR than in a 10:1 or 11:1 engine. So, I milled my 318 heads .090" which is quite a lot, and ended up with a whopping 8.66:1 CR! This amount of milling causes problems with the intake fit, lifter preload etc etc. So I highly suggest that if you do have even a small budget, which I didn't, Get new pistons with a bigger compression height than the stockers.
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#13
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After an .080 shave, a reduction of about 17cc's you should have went up 1.77 in compresion to 10,27.
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#14
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My advice is CC the "Already built" heads to know how big the chamber is. Do both heads and one chamber from each end. Make sure all valves are the same design and both heads are similar castings. This will eliminate any confusion as to guessing the final CR. The block is next, with the head off CC the bore with the piston a TDC. Add the head gasket CC and now you can make a plan to get to the goal. As for a cam, carb, exhaust, valve size, CR, car weight and use all factor in. This info will get more specific results.
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#15
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I looked up some numbers, and if the stock 318 piston has the 1.658" compression height, the piston should be 0.164" down in the cylinder at TDC. This is from the specs for a stock low compression replacement piston SL-1278. If yout 360 heads are uncut and have 68cc chambers (this is what my 360 heads measured at.) and you used a 0.020" thick gasket your compression ratio would be about 7.22:1!
To get about 9:1 compression the head volumo would have to be about 45cc, so you would have to mill off close to 0.110", but it may take more because the open chamber part of the 360 head is likely only about 0.080" deep, once you mill it into a closed chamber head, more milling will take off less head volume (smaller open area being reduced.) This much milling (if possable) will also make it hard to fit the intake manifold as the ends of the manifold or block may need to be milled for the intake to sit that low, and the intake port side of the head and/or intake will need to be milled so much there mating surfaces will be pretty thin. If you have the higher compression replacement piston (SL-1266) with a 1.741 compression height , things are a bit better. The piston should only be about 0.0810" down in the cylinder at TDC. Un-milled your compression ratio would be about 8.2:1. For 9.0:1 compression the chamber volume would have to be 59cc (still using a 0.020" head gasket.) To get 59cc you would have to mill the heads about 0.040" to 0.045". (add another 0.020") if you plan to use the felpro head gasket. You would need 54cc to get 9.5:1 compression (again with the thin 0.020" gasket), so mill for 0.065". If you replace the pistons with the Keith Black #167 with a 1.810" compression height the unmilled compression would be 9.16:1. 65cc head volume is 9.47:1 (with a 0.020" head gasket.) 65cc would only require about a 0.015" mill cut (assuming the heads are 68cc to start with.) Again add about 0.020" if you plan to use the fel-pro 0.040" head gasket. |
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