318 la head vs magnum head swap help

-
7

72 slant 6 swinger

Well-Known Member
Joined
Dec 22, 2010
Messages
93
Reaction score
7
Location
W.Va
ok guys i'm in a spot and need some advice on a few things.
so i'm just gonna start with some background on the motor first.

a couple years back i took a 79 318 block with 40,*** miles, cleaned,
and honed it, new clevite berings, stock sealed power rings, stock crank, stock rods,
stock pistons, it has a milodon windage tray and melling hv oil pump,
comp magnum timing chain and a comp xe268 cam. i already have: 1.5 shaft aluminum roller rockers, intake, (holley street dominator), carb, headers, msd dizzy and full 6al setup for this motor too.

the shortblock is done and has been sitting on the stand,
i decided to go as cheap as i could on the bottom end
since it was in such good shape, and spend the extra money
on the heads, milling, porting, 360 valves, etc. the heads have
been milled .060 thou. and they are about half ported, (other
projects in the way). the reason i'm getting back on this one
is last week a buddy priced me a decent mileage 318 magnum
for 200 bucks out of a wrecked jeep hes got. i'm buying the motor to layback.

now here is my problem, i'm thinking about goin with the mag. heads off the jeep motor. cuz theres still a lot of work and money to spend on my la heads. eithier way i'm going to be out about the same money with the magnum head swap. if i use my la heads, i'm going to spend for: larger valves, valve job,finish portjob, custom push rods, valvesprings.

if i go magnum swap: pushrods, headbolts, intake, valvesprings,valvejob.
now i figure compression will be about the same with the mags. and i would clean up the ports a little with some sand paper rolls. regardless of which heads i use, i'm going to have to buy, headgaskets, pushrods, valve job, valve covers, valve springs. so basically the only real difference is the cost of a new intake and head bolts. ( my new comp lifters are the same as the amc motors, so i have that covered already).

now here are my ?'s

1. can i use the stock magnum rockers, with new springs, and new mag. pushrods?

2. i really think the stock 1.6 rockers will make my xe 268 cam too big for the setup, what do you guys think? any cam suggestions? i have a couple new smaller cams on the shelf too.

3. does this sound like a logical setup? i mean should i go with the magnum swap? or continue with the la's?

4. have i missed any parts needed for magnum head swap? headbolts, pushrods, intake, ... (already have amc style lifters)

5. also, can i use la style valvesprings on mag. head? like comp 901-16?
 
TONS of info on this if you search. Just recently discussed too.
 
And no, the 268 will be great. It only affects the lift. Doesn't really make the cam "bigger", but it does give more lift. Dats a good thang.
 
0.060" thou off is from what I understand is 12cc so depending what the chamber size was that's probably 60cc now so the Magnums might give a little CR bump but ported 360 are gonna flow more than the Magnums so I don't see any advantage in this swap save the 5.2l for another build.
 
StrokerScamp said:
And no, the 268 will be great. It only affects the lift. Doesn't really make the cam "bigger", but it does give more lift. Dats a good thang.
Click to expand...

ok then, i figured up the lift and it was 508/512, so yeah those numbers scared me off a little lol. thanks stroker
 
If you really want to be safe, you COULD have the guides shortened a little. I really think you'll be ok though. It's worth checking on assembly though.
 
273 said:
0.060" thou off is from what I understand is 12cc so depending what the chamber size was that's probably 60cc now so the Magnums might give a little CR bump but ported 360 are gonna flow more than the Magnums so I don't see any advantage in this swap save the 5.2l for another build.
Click to expand...

i haven't cc'd the la heads, i was thinking about the same thing low 60's probably, stock pistons/deck so i'm hoping high 8's c/r is possible with eithier head, and a thin gasket..

just lookin for some input since i had a couple different options, i'm goin to do some price checking on headwork to see how much i'm gonna have in the la heads when i'm done. if the difference isn't much if any, i'll probably run the magnums, since i can run them on a better motor down the road.
 
273 said:
0.060" thou off is from what I understand is 12cc so depending what the chamber size was that's probably 60cc now so the Magnums might give a little CR bump but ported 360 are gonna flow more than the Magnums so I don't see any advantage in this swap save the 5.2l for another build.
Click to expand...

12ccs would be like 2 compression points...so I don't think that formula is right. USUALLY .060 is close to 1 compression point, but not quite.
 
StrokerScamp said:
12ccs would be like 2 compression points...so I don't think that formula is right. USUALLY .060 is close to 1 compression point, but not quite.
Click to expand...

.060 milled off i came up with about 9 or 10 cc's, i can't remember the formula exactly. i think its for every .06 milled =1 cc off the chamber. so .060 would be 10 cc's or so, all i know is it should help the comp. a bunch lol.,

also stroker i read your frankenteen buildup, nice project btw.. if your running the lunati 60403 with 1.6's and no problems, then i shouldn't have any clearance issues with my xe268 setup, i will check it to be sure, but i highly doubt it.
 
In 3 of my books say its 0.0048" for 1cc on 340/360 heads so 0.060" would be 12.5cc but I've never measured any of this for myself so you could be right.
 
72 slant 6 swinger said:
.060 milled off i came up with about 9 or 10 cc's, i can't remember the formula exactly. i think its for every .06 milled =1 cc off the chamber. so .060 would be 10 cc's or so, all i know is it should help the comp. a bunch lol.,

also stroker i read your frankenteen buildup, nice project btw.. if your running the lunati 60403 with 1.6's and no problems, then i shouldn't have any clearance issues with my xe268 setup, i will check it to be sure, but i highly doubt it.
Click to expand...

My guides have been milled down, too, FWIW.
 
273 said:
In 3 of my books say its 0.0048" for 1cc on 340/360 heads so 0.060" would be 12.5cc but I've never measured any of this for myself so you could be right.
Click to expand...

Well.....everything I've read or seen discussed says like .0067 for 1cc. BUT, the absolute best thing to do is CC first, then mill X amount and CC again. See, the thing is this. Different shaped chambers have different amounts to make the same changes. If that makes sense. I've done this very procedure in the past and HAD the formula.....but that was a long time ago. Crap doesn't stick with me like it used to. LOL
 
StrokerScamp said:
My guides have been milled down, too, FWIW.
Click to expand...

my bad, i didn't think you had any guidework done.
also i might be running a small shot of nitrous on this motor later on. a max of 100 shot, just depends on what it runs on motor. do you think it will last with a small shot every now an then? i have a few other cams too, i'm probably not gonna beat the xe 268 i already have, but i just wanna make sure i cover all the bases on that subject. whats your oppinion? one is a "power adder" cam from crower, designed for small blower or nitrous. its a straight pattern, 227/227 @.050, .467/467 114 lsa, 2000-6000 rpm. it will probably run like **** on motor, then pick up a lot of e.t on juice. then i have a old school crane 272 energizer 218/218 @.050, .454/.454, 2000-5000 rpm. i know its old school and kinda small, but i would rather be a little undercammed and have a smoother idle and torque, than overcammed and sound great at idle, but run like dog **** thru 1st gear lol.
 
Im swapping an la 318 with 1.88 J heads that haven't been milled so it is around 7.7 to one compression to a Magnum 5.2, the la has that crane cam in it and its garbage performance wise. I had my magnum cam reground almost exactly to the first specs you listed (112 lsa vs 114, 224 vs 227 duration at .050, and 496 lift with stock magnum 1.6 rockers). Hoping for a noticeable difference from my last cam in my low comp 318.
 
I also plan to do a 100 shot of the bottle on my Magnum motor btw.
 
Rockerdude said:
Im swapping an la 318 with 1.88 J heads that haven't been milled so it is around 7.7 to one compression to a Magnum 5.2, the la has that crane cam in it and its garbage performance wise. I had my magnum cam reground almost exactly to the first specs you listed (112 lsa vs 114, 224 vs 227 duration at .050, and 496 lift with stock magnum 1.6 rockers). Hoping for a noticeable difference from my last cam in my low comp 318.
Click to expand...


well, your comp. probably wasn't helping the cam much, but thanks that was all i needed to hear, the crane cam thought is gone now LOL. the specs on the crower make it seem like it would be a pretty good cam for the setup, it would be around .498 lift with the 1.6's.. i read somewhere once that magnum heads tend to like straight pattern cams because of their exhaust port design and flow.
 
Rockerdude said:
I also plan to do a 100 shot of the bottle on my Magnum motor btw.
Click to expand...

i hope to do the same, i'm sure it would take it fine. i watched my buddy spray a 150 shot to a bonestock 8:1 350 chevy for a couple seasons, with nothing more than timing retarded, and colder plugs,. my father ended up with the motor, its still runing today and still holds 50lbs oil press. goin down the road. that thing was a dog off the bottle LOL i don't remember what it ran on motor but it only ran 8.20's 1/8th mi. on the 150 shot Lmao so if a chevy can handle it, i know a mopar motor can easily.
 
72 slant 6 swinger said:
my bad, i didn't think you had any guidework done.
also i might be running a small shot of nitrous on this motor later on. a max of 100 shot, just depends on what it runs on motor. do you think it will last with a small shot every now an then? i have a few other cams too, i'm probably not gonna beat the xe 268 i already have, but i just wanna make sure i cover all the bases on that subject. whats your oppinion? one is a "power adder" cam from crower, designed for small blower or nitrous. its a straight pattern, 227/227 @.050, .467/467 114 lsa, 2000-6000 rpm. it will probably run like **** on motor, then pick up a lot of e.t on juice. then i have a old school crane 272 energizer 218/218 @.050, .454/.454, 2000-5000 rpm. i know its old school and kinda small, but i would rather be a little undercammed and have a smoother idle and torque, than overcammed and sound great at idle, but run like dog **** thru 1st gear lol.
Click to expand...

It'll be fine with a little gas. Two things. Run a wet system and don't run it lean. Find one like .520 ish and 230-240 ish @.050 on like a 112. That'll split the difference and run good nitrous or not.
 
StrokerScamp said:
It'll be fine with a little gas. Two things. Run a wet system and don't run it lean. Find one like .520 ish and 230-240 ish @.050 on like a 112. That'll split the difference and run good nitrous or not.
Click to expand...

i'll probably just run a powershot kit with a 75 or 100 shot. i've had a little bit of experience with nitrous after helpin my dad the last few years. i figured it would be ok, but i thought i would get a 2nd oppinon on it. i guess i'll spend most of my lunch break today on the internet lookin for a cam similar to the specs you gave lol.
 
This is a little big on duration, but it'll work.

http://www.summitracing.com/parts/CRO-31321/

Are you racing it more than street? If so, you can use that one. The KB167s will be an added plus. They would bring compression right on up. Do your stock pistons have valve reliefs? If so, you can play around with the deck height and thinner head gaskets and milling some off the heads. You need compression up around 9.5 with that camshaft so it will run well on motor. I wouldn't go over that though and I'd run a GOOD head gasket. Remember to, with magnum heads, comes the 1.6 rockers. That will be .563 lift on the exhaust side of that cam. BUT, the pushrod angle of the small block will knock some of that off. I think generally, it's about .020". Go to the Hughes engines site and click on the magnum section and look for your springs retainers and locks there. That's where I got my stuff. That's a pretty big cam for a teen, but if you're doing mostly racin, it's a dang goodun. It'll make great power with nitrous and run very well on motor if you give it enough static compression, converter and gear.

Oh and don't forget about shortening the guides if you go with that cam too.
 
StrokerScamp said:
This is a little big on duration, but it'll work.

http://www.summitracing.com/parts/CRO-31321/

Are you racing it more than street? If so, you can use that one. The KB167s will be an added plus. They would bring compression right on up. Do your stock pistons have valve reliefs? If so, you can play around with the deck height and thinner head gaskets and milling some off the heads. You need compression up around 9.5 with that camshaft so it will run well on motor. I wouldn't go over that though and I'd run a GOOD head gasket. Remember to, with magnum heads, comes the 1.6 rockers. That will be .563 lift on the exhaust side of that cam. BUT, the pushrod angle of the small block will knock some of that off. I think generally, it's about .020". Go to the Hughes engines site and click on the magnum section and look for your springs retainers and locks there. That's where I got my stuff. That's a pretty big cam for a teen, but if you're doing mostly racin, it's a dang goodun. It'll make great power with nitrous and run very well on motor if you give it enough static compression, converter and gear.

Oh and don't forget about shortening the guides if you go with that cam too.
Click to expand...

its going in a all original 72 dart with built 727, tci 10in. verter, and at least a 3:55 gear, most likely it will be 3:91's. that cam looks like a good bracket 318 cam, but i'm not looking for a pure racer, and would like to stay with a hydraulic flat tappet.

i just want good street strip action, it will probably see the strip 3 or 4 times a summer. i haven't looked at it in a while, its bagged up on the stand, but i'm pretty sure its got flattops in it. mainly what i'm hoping for is around mid to high 13's on motor, and still have decent driveability. i'm just so afraid of overcamming, i've had a few motors before that were overcammed by the previous owners, sounded great at idle but sucked on power. i'm starting think it would probably be best if it was a hair under .500 lift, and a few degrees less duration, maybe a max of 224 @.050. yeah, i'm going to run a good gasket, and new arp head bolts.
 
You must log in or register to reply here.
-

Back
Top