C2 327 Heads

[Robert Jacobson]

Hi All

I'm rebuilding my 67 327CID/300HP Engine and I'm looking for some
input about the heads. I'm thinking about using roller tip rocker arms on
the original studs. Am I correct in thinking that I need to install the self aligning type rockers so that I do not need to install guide plates and screw
in studs? The heads have the # 3890462 are these 64cc chamber heads?

Any input on this matter will be greatly appreciated
Thanks Bob

[John H.]

Re: C2 327 Heads

Bob -

The 462 heads have 66cc chambers. If you're talking about Comp Cams Magnum roller-tip rockers, I've used the standard (non-rail) type in the past on other project cars, and the C.C. instructions for that version definitely require guide plates (which also requires machining the heads for screw-in studs). I would think that the newer "rail" type (which I haven't seen personally) don't require guide plates, as they'd be fighting each other. Check the C.C. website or their Tech Line and they can tell you for sure.

[John H.]

Re: C2 327 Heads - Addendum

Bob -

If you decide to use the regular (non-rail) type with guide plates and screw-in studs, you'll also need hardened pushrods.

[Robert Jacobson]

Thanks John for the info *NM* *NM*

[Duke W.]

Re: C2 327 Heads

If you're rebuilding the engine to 300 HP specs with the "929" cam or even "upgrading" it to a SHP spec with a L-79 cam or high performance aftermarket cam, investing in aftermarket rocker arms is a waste of money.

The OEM rocker arm system is inexpensive, very reliable, and doesn't produce excess friction unless you plan to spend a sustained amount of time over 5000 RPM, and the improvement in top end power with high ratio rockers is marginal at best.

It would help if you would state the general goal of the rebuild, but pocket porting and port matching the heads will pay signficiant dividends in terms of top end power for either a 300 HP or SHP engine, and is a much better investment.

If you want more of a SHP feel to the engine, install the L-79 cam, but NOT if you intend to pursue a Duntov award as the L-79 cam will guarantee that you fail PV due to it's signficantly different idle quality.

Pocket porting, port matching, and a carfully executed three angle valve job with .040" inlet seats and .060" exhaust seats will improve top end power by 7-10 percent without affecting longevity, idle quality, or low and midrange torque. If you want to "upgrade" the valves, I would recommend staying with the 1.94" inlet but increasing the exhaust valve to 1.6" has some benefits because of the restictive exhaust port, especially if you use a single pattern cam like the 151 fromn the L-79.

It's also useful to "relieve" the chamber overhang adjacent to the valves, and it is particularly bad adjacent to the exhaust valve.

Big cams and fancy rocker systems are just a crutch for the relatively poor flow of vintage small block heads (compared to modern heads) and they kill torque. The best way to system engineer the engine is to select a cam that give the bottom end torque you need and them work the heads, manifold, and exhaust system to get as much peak power as you can.

Duke

[Robert Jacobson]

Re: C2 327 Heads

Hi Duke

First off thank you for the info. I'm trying to rebuild the motor
close to original 300HP specs. I'm just trying to tweak a little more HP
out of it.

Thanks Again
Bob

[Clem Z.]

Re: C2 327 Heads

if you install screw in studs and hardened guide plates you MUST enlarge the original double "D" shaped push rod guide holes to prevent a binding of the parts.

[Duke W.]

Re: C2 327 Heads

Excellent! The 300 HP is a great, torquey engine with a smooth idle. If you massage the heads it will make another 20-30 HP up top, pull strongly all the way to the 5300 redline (or beyond), and still have a nice, smooth idle and pass a PV without a second look.

With the exception of pocket porting and port matching the heads and perhaps a three-angle valve job, just use OEM or equivalent replacment parts including the 929 cam. Chances are your rockers and balls are in good shape and can be reused, and if it's never pulled a rocker stud, it likely won't do it in the future, so just leave them alone.

Don't grind the crank, mill the block deck, or the heads unless absolutely necessary. Most shops like to "take a cut" just to "clean it up" and make sure everything is flat and the crank journals are round.

Well, there are tools to measure for flatness and roundness. My philosophy on restoring an engine is to not cut metal unless ABSOLUTELY, POSITIVELY necessary.
Of course, you have to cut metal to pocket port and port match, but don't cut any more metal off the factory machined surfaces.

Duke

[Patrick H.]

Re: C2 327 Heads

John,

Do you mean that these rockers (see link below) require pushrod guide plates? I thought the advantage of them was that they were drop-in, and DIDN'T require taller valve covers or guide plates.

Patrick


Comp Cams roller tip rockers

[John H.]

Re: C2 327 Heads

Patrick -

Every set of small-block Chevy CC Magnums I've installed have been VERY specific in the instruction sheet that they require guide plates in order to avoid damage to the rollers, including a cryptic note that says "Note - this may require machine work". The last set I installed was about five years ago (on the Grand Sport) which had Edelbrock RPM heads on it, and they had screw-in studs and guide plates already. Maybe they've reconsidered since then. I think they have three advantages - reduced valve guide wear, they won't break, and they'll fit under stock valve covers.

[Clem Z.]

Re: C2 327 Heads

john, i think the reason they do that is because of the distance from the holes in the head to the rocker and this allows a good chance to bend a pushrod if you have heavy valve springs. on race engines with heavy valve springs i use the step up guides to support the pushrod as close to the rocker as possible. i have never had a problem with any roller rockers without the stud mounted guide plates using stock valve springs. maybe i was just lucky.

[Patrick H.]

Re: C2 327 Heads

Clem,

To date, I've not had a problem either. There were no such instruction with my rockers 6 1/2 years ago, either. As I worked directly with Comp Cams at the time (on an article), I made sure to get pieces that wouldn't require such modifications. I think I'd check with Comp Cams, but I don't think that the restriction is in place any more. I don't see anything on this on their web site either, which is mostly a reproduction of their catalog.

Patrick

[Pete Whelan]

Re: C2 327 Heads

Bob,
I have a '66 327/300 that was slightly tweaked to give the performance improvements that you are after. I also recommend pocket porting the cylinder heads. I used stainless steel valves (1.94" and 1.50") but if yours are in good shape a three angle valve job will do the job. I also used an aftermarket camshaft (Crane HMV-260) that provides a little more lift on both the intake and exhaust valves and increses duration on the exhaust valves as compared to the 929 cam. The intake valves close a few degrees sooner to build more cylinder pressure at low engine speeds. This cam needs a slightly stiffer valve spring (105 lb. seat pressure versus 80) so use their springs or an equivalent if you take this route. This cam provides a smooth idle (20" vacuum), increases torque (and horsepower) in the 1000-4500 rpm range and will outperform the 929 and 151 cams up to 5000 rpm. The pocket porting will help improve the torque (and hp) in the 4500-5500 rpm range. The rest of my engine uses factory replacement parts. Actual (measured) compression ratio is 9.4:1. I also recurved my distributor to enable full mechanical advance by 3000 rpm. Good luck.

Pete

[Robert Jacobson]

Re: C2 327 Heads

Hi all

Thanks for all the feedback on my questions. I was looking at the CraneCams stamped steel roller tip rockers and you guys are all talking about the CompCams Magnum roller tip rockers, is there alot of difference between the two of them?

I called CraneCams Tech Line and asked about the guide plates, their answer was if the heads had a circular hole where the pushrod comes thru the head then I need guide plates, If the heads have a slot type ( double D )hole then I don't.

I purchased the "929" cam from CraneCams along with the valve springs that they recommend (for 67 and up) and a roller type timing chain & gear set which is also suppose to free up a little more HP.

Thanks again for all the info
Bob