Posted By: mechanic190
Stock360 bottom end build - 12/22/14 08:09 AM
So I have a stock 1980 360 with 15000 miles on it. Came with a 1406 efelbrock on top a cast iron manifold. Ran a compression test and have above 110 psi on each hole. Assuming it's still stick with what 8:1 compression and small cam. I'm looking at dropping her in my pick up to get some track time next year. I want to leave the bottom end alone but will be inspecting bearings and resealing it. Also gonna change the cam and mild head work. I'm thinking I want to run around a comp extreme energy 284 I believe it is, going to have a 3k stall converter and still looking into gears right now. Have on hand 3.55 and 3.23s. I know I'm gonna have to replace valve springs, gonna replace timing chain with a quality one. Want to shave heads down and run headers. Any other suggestions? Guesses on how it'll run with the lack of bottom end?
Ps I'm not planning on using this for a tow machine or daily driver just some good summer time fun
Posted By: dizuster
Re: Stock360 bottom end build - 12/22/14 03:33 PM
Nothing wrong with the stock bottom end except for the compression being down. Mill the heads a reasonable amount to get the comp up as far as you can.
Once you get the compression figured out THEN pick the cam. Too much cam on a motor with low compression will be a dog.
We had a 318 with low compression with a .484 cam. Ran great at high rpm... went 102mph with stock 360 heads @3450lbs.
The only problem was that even with the 4.10 gear, it wouldn't get out of its own way in the first 330'. Never quicker then 14.02.
Posted By: Crizila
Re: Stock360 bottom end build - 12/22/14 03:57 PM
About .030" is all you can cut those heads before you start running in to manifold fit problems ( even then you might have to shave some off the intake to get the bolts to go in ). If your truck has a 9 1/4" diff in it I have a 3.90 gear set for it if you are interested.
Posted By: mechanic190
Re: Stock360 bottom end build - 12/22/14 04:26 PM
Well I'll admit I haven't done all my research yet been too busy and haven't had a decent amount of time off. I'm planning on milling the heads and figured that went hand in hand with milling the intake down too. I have the mopar engines book and know there is a chart in there for how much to take off the intake for the amount taken from the heads. Haven't actually read it in about two years though. What's the max I can mill the heads and intake down and how do I figure compression ratio out at home? Not too worried about running pump gas not a requirement anyway. Other than milling heads and changing bottom end there is no other way to bump compression correct? How fast can I spin a stock bottom?
Posted By: dvw
Re: Stock360 bottom end build - 12/23/14 12:03 AM
Sock bottom rpm depends on the bolts. I certainly wouldn't be afraid of 6000. That's all you will need anyway cause the cam will be small with low compression. Actual measured compression on a factory 360 comes in around 7.8-1.
You can mill the heads .060" if you mill the intake face.
Doug
Posted By: mechanic190
Re: Stock360 bottom end build - 12/23/14 12:11 AM
Ok so .060 off the face where would that put me at compression wise? Just curious on how much it'll bump it. Also planning on running shim head gaskets
Posted By: qwkmopardan
Re: Stock360 bottom end build - 12/23/14 12:35 AM
I had a 7.9/1 CR 318 in my demon a few years back. Camshaft was a Racer Brown ST-21, 254* at .050 and .520 lift. Heads were LA 360, 596 castings with very light porting, about 6 hours worth. 1.88 intake and 1.60 stock valves, 995-16 comp springs and 273 rocker arms from a salvage yard. Strip dominator intake. 750 DP Carb. 4200 flash 8" converter. 4.88 gear and 31x13 slick. Stock pistons were .08 in the hole and I was pissed when the new pistons were .100 in the hole. Pistons cost $77 for the whole set of 8. Car went 11.70s at 110 mph.
Before I would shave the heads a bunch to get a little compression, I would get a set of KB107 STD pistons for about $240. They will end up aprox. .010 in the hole. At 15000 miles the cyl walls should clean up with a light hone. You will spend more than $240 shaving the heads and manifold. And then you will have to deal with valve to piston clearance problems. KB107s will clear just about any camshaft. The KB pistons are lighter than stock so the crank would have to be balanced, so another $200 would have to be spent for balancing. Still will get you a lot of bang for the buck. Or just run it at 8/1 CR with a mild port and a cam with 240* to 250* Dur. and I think you may be surprised.
Posted By: Crizila
Re: Stock360 bottom end build - 12/23/14 01:04 AM
You will be able to spin it an easy 6K. Assume they are open chamber heads, which will put them at 68 -72 cc"s. To reduce the combustion chamber volume by 1 cc. cut .0048 off the heads and for every 10cc's you mill the heads, remove .0063 off the intake gasket sides. If you don't want to CC the heads ( and you should ), go with 70 cc's.
