318/360 heads,with thumper cam

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7duce swinger

7duce swinger

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So for the past two weeks ive been reading,and reading and reading,but the more i do so,im left with more questions.What im gonna ask is how can i make the 318 i have now a better performer?As of two weeks ago its down to block,cam, and pistons,I removed the heads,and they appear to be 61,or 62 cc's(if i can remember correctly) the intake is a stock 77' 360 4 barrel,i have a 600 cfm edel,and also a holley 650 vac-secondaries,headers are fenderwell type that i will finish welding up as i get the heads back on,the reason i took the heads off is to get them milled,as i hear they are not too good on a stock pistons 318 motor,but i don't know how much they should be milled,i think i was lied to by the seller i bought the car from,he had said it was"fully rebuilt",if so how do i tell if the engine is bored over???the pistons are flattops with no valve reliefs.i want close to 300- 330 horsepower with using some of what i already have.
 
The cam thats in the block now is a comp cams thumper cam,the smallest of the three,.486/.473 lift,279/296 duration, dur @.050 227 on intake,241 on exhaust,107 lsa,and 1500- 5800 op range,oh and it is a hydraulic flat tappet.My questions is,is this a good cam to make the power that i want,or would a different cam be used for that power range.It is brand new only month old,i do not want to have to change it out if its ok to use.The heads are 360 596' heads, it will be a street car,no strip time, has an 8 3/4 rear end with 3.23 gears,i am currently running a 904,which supposedly had a shiftkit in it.what is a good estimate on power with what i have listed,and what can get me to where i want to be.I want to get the motor back up and running asap,so any help would be great,any intake recomendations,or different cams??thanks for any help.
 
I would look for .030 stamped into the tops of the pistons and measure how far down the bore they are at tdc. What is the casting number on the heads you are using.
 
The heads are the key. Get some good heads and have a reputable shop work them porting them and installing bigger valves and whatnot.
 
I you don't have a dial caliper you can get a digital one from harbour freight on sale for $10. Measure the bore and if it is 3.91" you bottom end is stock.
 
They are 4027596 heads,i think 1.88/160 valves,i have a peacock dial caliper,just not too familiar with using it.Is the thumper cam ok to use since i already have it,or would one of the extreme cams be better?anyone running the base thumper cam?
 
Shaving the heads is a pain. You have to mill the intake to match the heads. If it is done improperly it will leak coolant. The cam you have is fine if you have 9.5 to 1 compression or more but won't perform very well at 8 to 1. I would determine if you have stock pistons or not before you decide to do anything. Just measure how far they are down the bore at tdc.
 
I once put 10.5 pistons in a 318 and had trouble with it overheating due to the high compression. I then swapped a set of 77 360 heads with the 10.5 pistons and was down to 9.2 and no more overheating. It ran great.

So basically, if you run 10.5 318 pistons and put 360 headw on them, you can get to a reasonable 9.2 compression without having to mill the block or heads.
 
Well if i read this thing right,it looks like it is 3.93",the pistons do not have any .030 stamped,only letters like c,d,u,g, on all of them,also they have a notch,on every single piston towards the front of the block,are these stock pistons for this year?the block is dated 10-18-71.thanks for the responses guys..
 
7duce swinger said:
Well if i read this thing right,it looks like it is 3.93",the pistons do not have any .030 stamped,only letters like c,d,u,g, on all of them,also they have a notch,on every single piston towards the front of the block,are these stock pistons for this year?the block is dated 10-18-71.thanks for the responses guys..
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Notches are correct for a stock rebuild, looks like a .020 over regulation rebuild to me?
 
As for how far down the hole it looks like somewhere around, .050?so the notches in the pistons seem like overbore or no?imma get a digital one from harbor freight like mischeifdart said just to be sure.thanks for the help guys,do the heads need bigger valves,or are the stock ones good for street use.
 
7duce swinger said:
As for how far down the hole it looks like somewhere around, .050?so the notches in the pistons seem like overbore or no?imma get a digital one from harbor freight like mischeifdart said just to be sure.thanks for the help guys,do the heads need bigger valves,or are the stock ones good for street use.
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Notches in the pistons are for orientation, facing front of the engine. I believe they are replacements and by your preliminary measurements may be .020 over......050 in the hole also looks like it could be a rebuilder type piston to me.
 
So based on what i have said,where would my compression be at,lets just say had the heads milled down to 58cc's?would it be around 9to1,higher/lower? OldManRick you say notches are correct for rebuilds?
 
7duce swinger said:
So based on what i have said,where would my compression be at,lets just say had the heads milled down to 58cc's?would it be around 9to1,higher/lower? OldManRick you say notches are correct for rebuilds?
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What i mean is stock replacement pistons usually have notches like factory pistons, but the replacement pistons are also available in multiple oversizes. If your bore is more than 3.91 then i believe it has been rebuilt at some point with a factory style piston that had a overbore that was enough to clean up the cylinders at that time.

As far as comp. ratio i hope a member with access to a good formula can come close for you, but if your chambers are milled to 58cc's you should have a decent comp. for a driver, but the quench in the cylinder would suffer from the piston being down .050.

The best case scenerio would be the piston at .000 deck height, level with the deck, and mill the heads to achieve your desired comp. ratio.
 
Thanks OldmanRick,so with everything said will my hopes for having around 300-350hp be right on,pretty close or what?what else would i need to get there?also will the 3.23 gears be ok with everything i have listed,or would this package be better with other gears?whats a good estimate in power,after milling,zero decking the block,headers,600cfm carb,and will the stock 360 intake be good for the power i want,whats a good intake manifold?
 
A couple of quick questions. Is the 650 carb you have access to a spread bore (secondaries larger) or a square bore(primary and secd. the same size)?

And do you want to leave the shortblock untouched as it sits if possible?

To get to your desired power level, the compression will have to be optimized. trying to figure out the best way to get there for the least amount of time and money will take some thought.
 
OldmanRick-If it gets me to where i want,then yeah i can probably leave the block alone,but wouldnt it be better off milling,and zero decking the block?the holley i have is a 650 spreadbore,the other is a brand new 600 edelbrock,the holley is rebuilt and powdercoated to look friggin awesome lol. -ryansiki as for the magnum head deal,i was thinking about it,but imma wait n save some money,and find a whole magnum motor to build up,as theyre already set up for roller cams.thanks,i think i had read that last year,i was trying to find it bu couldnt..
 
0.040" gasket with 58cc chamber heads and piston 0.050" down the hole = 9.1:1 compression. With a 0.028" gasket would be 9.4:1 compression. Also zero decked 0.28" gasket 68cc heads would be 9.4:1 compression.
 
If I was you I'd get magnum heads, thinnest heads gaskets, eddy rpm intake put smallest thumper cam and headers, don't even touch the bottom end you'll have 350 hp and at least 9:1 compression.
 
273 said:
0.040" gasket with 58cc chamber heads and piston 0.050" down the hole = 9.1:1 compression. With a 0.028" gasket would be 9.4:1 compression. Also zero decked 0.28" gasket 68cc heads would be 9.4:1 compression.
Click to expand...

Thanks, 273.

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There's alot of smaller details here that make this difficult. If you are gonna try and move to a Magnum engine at some part, your probably will not want to put too much into that shortblock. But, you need to get the compression up to increase the power and drivability with that cam. If you mill the 360 heads that much, which is pushin' it imo, your going to have to mill the intake a good amount to fit. Now do you cut and use the iron manifold and make less power or do you buy a Eddy RPM, have to cut that also, and make more power but render it useless on another set of heads because of the milling? As far as carb. i would probably use the 650 on the iron manifold and the Eddy on the square bore manifold. 273 laid out a pretty good plan there and if you went Magnum later you could reuse some of the parts required on the new build. There's lots of opinions on builds like this, maybe some others will chime in also.

P.S. Oh yea, if you use them, the 360 heads you have should easily support the power goal you have set with just a quick clean up and a good valve job.
 
7duce swinger, please read my post #22 and should help you understand what i'm saying here. Gonna try and narrow down 1 option for you,

Gonna throw out the horsepower #'s for now. Assuming the shortblock is fairly sound, i would mill the heads a resonable amount, some threads here or one of the cylinder head guys could advise you on what's a safe amount. Have a good valve job done and make sure the springs are good for you cam. Use a thin head gasket and get as much comp. as you can.
Use the iron 360 manifold and 650 spreadbore, it will definetly need tuning for your combo. Now this combo will be a liitle soft on the bottom end with 3.23's, but you'll be able to put a good amount of timing in it and it would be pump gas friendly. Put a decent converter behind it and you should have a pretty good perfomer that sounds good for not alot of cash outlay. Enjoy driving it for awhile and save up for that new Magnum powerplant:).
 
Thanks 273,youve been great help,-OldmanRick,yea i dont want to pour to much money down this motor,but ill probly have it for awhile,so i gotta do something now,if i buy an edelbrock intake,can i mill the head surface where the intake touches,or is that not good to do?also i just want a little somethin more,i already have headers,and the thumper i have would be the smallest of the three,the motor was running before i pulled it apart,to cc the heads,theres a few good machine shops in town,one well known is charging 70$ for the milling,and the other shop wants 100$,i think ill do the milling,and thin head gaskets,then maybe zero deck the block,i have headers also.if anyone could let me know whats a safe ammount to mill the heads,i greatly appreciate it thanks.
 
Yes you can mill the intake side of heads but if you mill block as well have the intake side milled enough to compensate for that also. Google search compression calculator you can play with combos until you get one you like.
 
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