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SB Chevy rocker arms on a Magnum head?

Posted By: 69L78Nova

SB Chevy rocker arms on a Magnum head? - 01/29/11 04:55 AM

I have pretty much gathered up all the parts needed to swap Magnum heads onto my 78 360. I have been reading about the use of small block Chevy 1.6 roller rockers on Magnum heads. If rollers would work, wouldnt 1.6 ratio stamped steel rockers work as well? Summit sells 3/8" stud kits for as little as $12, and a set of 1.6 ratio stamped steel rockers for $61. I have always liked the idea of adjustable rockers with a hydraulic cam, especially when a custom length pushrod is to be used. Also, am I correct in assuming a 1.5 ratio arm wont work? This is all going on a 78 360 shortblock with a Comp XE256 cam. Could I use the stamped steel units, or do they have to be rollers?
Posted By: Wedgeman

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 05:00 AM

Drpending on what you will do, stamped steel will work
Posted By: 69L78Nova

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 05:03 AM

Its just a cruiser. I picked up a set of brand new Magnum heads for free, and a dual plane Magnum M1 for next to nothing. Im just messing around with it and maybe looking to get a little more out of it. Its in a 4000lb 78 Fury so its not a strip terror or anything like that. Should I go ahead and still plan on using the aftermarket 7.65" pushrods as well too?
Posted By: Wedgeman

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 05:11 AM

Remember, you need rods that oil trough, and lifters that do the same job
Dan
Posted By: 69L78Nova

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 05:20 AM

Yeah the Comp lifters have the oil hole, and I do have the correct oil-through pushrods already. Am I stuck using 1.6 rockers, or can I use 1.5 ratio? The only reason I ask is because the 1.6s will increase my lift to .477/.485", and with 1.5s it is .447/.455". The advertised duration is 256/262, and at .050" it is 212/218. The car weighs 4000lbs, and Im running a 2400 converter, 3.21s, headers and 2 1/2" duals. I dont want to have any kind of a rough idle or lose what little bottom end I do have when I need to get this boat moving.
Posted By: goldmember

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 05:51 AM

You can run the chevy rockers and the 1.5 ratio will work. I'd just slap the stock magnum rockers on it and call it a day.
Posted By: ahy

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 05:56 AM

The 1.6 ratio rockers shouldn't affect idle quality much. That's petty much determined by cam timing which is not radical at all. The 1.6 rockers should not hurt low end torque much either... and should increase mid-upper range torque. As long as the valvetrain is set up for 1.6 with correct pushrod length and clearanance, it should be a plus vs 1.5.
Posted By: Kern Dog

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 07:45 AM

You guys DO realize that the MAGNUM 5.2 and 5.9 engines came with 1.6 ratio rocker arms, right? Factory stock and cheap.
Posted By: runinonmt

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 02:32 PM

I use Magnum heads with the stock rockers (1.6)on a 360 with a Comp XE268 cam in my Duster. Idle is quite smooth and low end torque is plentiful. With a 256 I can't imagine a problem. Set up your Distributor so initial is at least 16 Degrees (mine is 19). Up to the point of spark knock the most advance will give you more low end grunt. I even use the stock converter. With the 2400 converter it may appear to be weak on the low end but I doubt it. That's pretty close to a factory performance converter. My Stepson has a 2800 in his roadrunner with the 268 cam and complained about this until I had him brake it to raise RPMs before launch. Kind of like slipping a clutch. After he had some seat time with it, he was happy.
Drive ind enjoy it
Ron
Posted By: 69L78Nova

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 03:42 PM

Quote:

You guys DO realize that the MAGNUM 5.2 and 5.9 engines came with 1.6 ratio rocker arms, right? Factory stock and cheap.



Yes, I'm quite aware of that. Let me try this again. The whole point of the post was to see if I could use SBC rockers on my Magnum heads. I want to use an adjustable rocker arm. I was concerned about the idle quality when using THE STOCK 1.6 rockers and the cam I'm running. That's why I asked about the use of 1.5s. You can read all of this in the previous posts above
Posted By: Wedgeman

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 04:40 PM

Just use the 1.6.......

I would really use a higher stall though
Posted By: 69L78Nova

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 05:17 PM

Thats the thing though. I dont want to run a higher stall or run some ridiculous low gears. This is a daily driver that Im just looking to get a little more power and torque, and take advantage of some of the benefits Magnum heads have to offer. I repeat, this is not a race car, and Im not loking to turn it into one. Its a stock 78 360 shortblock with an XE256 cam, headers and duals. But if the 1.6s would be better, then then Ill just go ahead and run them.
Posted By: 62maxwgn

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 05:53 PM

This is just like going to an all Mopar show and seeing a beautiful 34 Plymouth coupe with a small block Chevy.
Posted By: slantzilla

Re: SB Chevy rocker arms on a Magnum head? - 01/29/11 05:54 PM

I don't think you'll see enough difference to even worry about.
Posted By: racincuda

Re: SB Chevy rocker arms on a Magnum head? - 01/30/11 12:11 AM

Th 1.6 rockers will increase th grunt factor across entire rpm range and I bet hav no noticeabe effect on idle quality, go for it
Posted By: HotRodDave

Re: SB Chevy rocker arms on a Magnum head? - 01/30/11 10:44 PM

1.6 will only help not hurt in any way. Just slap the stock rockers on it and sleep well at night. I too have an XE268 with magnum heads on a 360 in my 68 cuda, 2.76 gears and stock 318 2bbl tq converter and it does not lack any TQ off idle even with an M1 single plane intake. Your cam is several sizes smaller and you have a dual plane intake so low speed TQ will not be an issue with the factory 1.6 rockers. If you want to run the chevy rockers you will also need guide plates that are magnum specific or some kind of adjustable ones, the stock ones don't use any of that junk.
Posted By: 69L78Nova

Re: SB Chevy rocker arms on a Magnum head? - 01/30/11 10:49 PM

You're using the GM 3.1/3.4 springs and retainers too, correct?
Posted By: HotRodDave

Re: SB Chevy rocker arms on a Magnum head? - 02/01/11 04:46 AM

Quote:

You're using the GM 3.1/3.4 springs and retainers too, correct?



YUP!
Posted By: patrick

Re: SB Chevy rocker arms on a Magnum head? - 02/01/11 04:33 PM

point of reference, in my 3950lb 5th ave, I had an LA 360 with a comp XE262 (~8:1) compression, 3.55's, and a MP166k converter that brake stalled to ~23-2400, flashed to 2800. moved the car along just fine. would light them up at will.

switched to a magnum headed 318 with a 259/259 roller, .506" gross lift, using hughes #1110 springs and stock magnum rockers. has the same power as the 360, would prefer the MP166k converter, but lives with the stock, low stall (~1400rpm stall) converter because of a crack I found in the snout of the 166k.

you'll be fine with the stock magnum rockers, GM3.1/3.4L springs or the hughes springs w/2.2L retainers with the gear, stall, & weight. with headers, it'll be a low-mid 14 second car, maybe even nipping into the 13's.
Posted By: 69L78Nova

Re: SB Chevy rocker arms on a Magnum head? - 02/01/11 09:00 PM

Quote:

with the gear, stall, & weight. with headers, it'll be a low-mid 14 second car, maybe even nipping into the 13's.



Well, I already have the headers, 2.5" duals, 2200-2400 converter, and a 3.21 sure grip. Do you really think it would run that good with the stock pistons? I obviously can't use a spreadbore carb on the M1, so do you think a 600 Edelbrock will be ok? What do you think of the Hughes 7.64" pushrods?
Posted By: patrick

Re: SB Chevy rocker arms on a Magnum head? - 02/01/11 09:11 PM

both engines I ran/am running an eddie 1406 on an RPM air gap.

my 360 was an LA headed, stock long block rering that I did a little bit of home porting to the heads with the XE262, it hung with a 300C (5.7L hemi) from 20mph roll. measured compression with the fel-pro gaskets in the kit was 7.9:1

magnum heads will boost that to about 8.5-8.7 depending on head gasket. if you can find some of the MP .028" thick gaskets, get them.

the 318 is running a reground roller cam that is 208@.050, 127@.2" and .316 lobe lift (while .050 duration is 10 degrees smaller, at .2" lift duration is only 3 degrees smaller than a comp XE262, with .008" more gross lobe lift, almost .050" more lift at the valve). with stock pistons and the thin MP gaskets, I'm running a measured 9:1 compression.

dunno about the pushrods, I lucked out an was able to reuse the stock magnum pushrods. I'd get a length checking one and measure your needs to be sure.
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