Need advice with new heads

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T56MaxTorq

T56MaxTorq

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So I plan on some RHS heads for my 360 but am wondering what compression ratio to run. With a tight .040 quench and shave .025 off the heads I could get 9.7:1 with my step dish pistons. If I leave the heads alone and run a safe .054 quench my ratio is 9:1. I could also mix it up and run anything in between or more if I shave the heads extra. Motor is in a heavy truck and runs above 5000 feet and has a Comp XE274 cam.
 
If it was me I'd put a roller setup (cam, lifters, rocker arms) in it because the roller setup will put you in the power curve sooner and keep you there longer, which is great for a truck that needs torque. If you go this route make sure your cam has a cast iron gear on it or you'll be sorry later down the line.
 
I have the roller cam, I pulled the block out of a 92 van. I do plan on adding roller rockers to the RHS heads as well as an air gap, cheap hooker headers, and a demon carb. As far as the gear goes, I don't know if the cam gear was cast or not. Either way, I added a brass gear to the oil pump drive if that's what you're talking about.
 
Bad idea! Pull that bronze gear out now before you get the motor going! The bronze gear breaks down quick and leave filings in your motor which will tear up your bearings. If your motor is a magnum block it should have a cast iron gear on it but I'd pull the cam to make sure. If it does just use a hardened intermediate shaft and you'll be just fine (got mine from summit for ~39 bucks). If the doesn't have a cast iron gear get a different one. That bronze gear you got is designed for racing because those guys are always in that motor changing and cleaning the inside (think nhra top fuel dragsters). Has far had the roller rockers go I use comp pro mag series but yours is a mag block and should have mag heads. If they are mag heads you could get that out of a junkyard from a newer motor. If you go this route I'd take the arms to a machine shop and have them checked out first before I used them
 
Dang! I have ran the motor, for about 2000 miles. Though it is an LA block, not magnum. If that makes any differance to the cam situation. My machinist supplied the cam and the brass gear. I think the cam is for retrofitting older LA blocks and is billet, which needs a brass gear? I konw it has the provisions for a fuel pump eccentric which I use. But I will check up on this before I run it again (It will be parked for a while) I have the stock rebuilt heads on it now but it just doesn't have the balls. I calculated my compression in the high 8's with open chambers and stock valvetrain.
 
Yeah meaning that if the machinist used a bronze gear it's got a billet gear on the cam. I'd change the cam and shaft if I were you. I'd also pull the thing back apart an expect everything. You might get lucky on the wear of the gear and only have to change the cam and shaft. To answer your question about the billet gear (on the cam) you need to run the bronze gear with it. I got my cam from crane but others out there have the cast iron gear on it too. Something to thing about in your truck is what rearend gears you got , what is the torque converter your using and the size on the wheels you are using. Getting a better cam will help as well. The RHS heads with a 2.02 in and 1.60 out (use stainless steel valves, I have Ferrea valves in my x-heads) with a high flow exhaust will pump up the power as well. The only other thing you can really do to it to push more power (heck if you got 8 to 1 ratio that screams supercharger right there!) is change the pistons to a dome setup to raise compression
 
Good question there moper! I just assumed that it had a dish piston because of the compression ratio
 
With a .040" quench run the higher compression. Running less quench with less compression is a loose loose proposition.
 
1970Duster - I will make sure I have to correct gear for the cam. I want to say it was a cast gear when I stabbed it in there but I honestly don't remember. This was my first build and I really left a lot of trust into my machinist who kinda stiffed me in the end. I was going to go with 1.92" intake valves, probably assembled by hughes since their springs have the same open/seat loads my cam needs. As for the gears I will be swapping in 4.10's with 33" tires. The torque converter is stock.

Moper - It has keith black 362, a step dish piston with 19.4 cc head volume.

340Fastback - I was wanting to run the closest quench possible but am wondering what a safe quench would be, taking piston rock into consideration. Is .040 safe?

There are just so many jokin possibilities floatin around I really just don't know what to do with the dang truck anymore.
 
My only real concern is the deck height of the pistons. If it's .018" above like the catalog says, you need a thick enough gasket to keep the head away from the piston. With a 4" bore you can go to a piston to head distance of .030 with no issues from rocking. Between .030 and .050 it's affective. Once you get wider than .050 there isn't much positive effect. Past .060 there isnt much of anything.
 
Those pistons have the same 1.675 compression height as the KB107 which is about 0.012 below deck at a nominal 9.600" deck height. I wonder why they say they sit 0.018" above in the notes?
 
The pistons are sitting at zero deck despite what kb's website says. Not sure why they say they will protrude on magnum blocks. Do mag blocks have a different deck height than LA?

Moper - With .030 being a safe distance, I will probably go with a .039 MP head gasket and shave the heads down to 60 cc's from 62 cc's. This will calculate my c/r to 9.5:1 - This should be safe for pump gas at my altitude eh?
 
If you stay at 5K ft I think you could go even higher depending. I think for a working truck 9.5 is safe.
 
5000 feet would be the minimum it would go. Anywhere from 6000-11000 feet is usually what it would see. I think I'll try 9.5:1 and if I'm burning 85 octane no problem I'll bump it up some more one day.
 
T56MaxTorq said:
340Fastback - I was wanting to run the closest quench possible but am wondering what a safe quench would be, taking piston rock into consideration. Is .040 safe?
Click to expand...

.040" is plenty safe. If you are running a milder cam the 9.5:1 compression should work well on low grade pump gas.
 
if you have it zero deck now, go with a cometic .030 head gasket or if thats too tight for your liking...a .036
http://www.4secondsflat.com/cometic.html
With your combo I would shoot for 9.7, at 5000ft...you can get away with a decent amount on pump gas-less air density.

with a closed chamber head @5k ft, no problem...u could even go a lil more.
 
I have read some threads on here about cometics not fitting RHS heads, specifically the enlarged water ports. Although cometic was notified, I'm still unsure if production gaskets have actually changed. My luck I'd get an old style gasket that has been sitting on a shelf for the past couple years. Unless they phased in a new part number for the new gaskets???

I'm going to go with a .039 quench with MP or Fel-pro gaskets (a lot cheaper too). Then deck the heads .010 to obtain 9.5:1 overall compression ratio. Thanks guys for helping me put it all into perspective. Now onto custom ball/cup pushrods for roller rockers
 
I didn't know they made cup ball roller rocker arms. Mine are ball ball
 
I was going to run hughes roller rockers and they have a cup type adjuster.
 
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