Cam and lifters for 327 365 HP

**Joe L.** · April 18, 2006, 11:39 PM

Re: Cam and lifters for 327 365 HP

Dennis-----

If you wish and exact reproduction of the original GM #3849346 camshaft used in your application, see if you can obtain a GM #12364052 camshaft kit. This is a Crane-manufactured reproduction of the original camshaft and is supplied as a kit with lifters. It is a VERY good value, but you may find that it's no longer available. If that's how it turns out, you can purchase a Crane #967251 camshaft and Crane #99250-16 lifter kit. This is, basically, the same thing that you'd get in the GM kit only it will be a bit more expensive. The GM-manufactured #3849346 camshaft has been discontinued for about 30 years and the GM mechanical lifters were discontinued about 10 years ago.

You might also want to consider switching to the 70-72 LT-1 cam, GM #3972182, which was also the GM SERVICE replacement for the 3849346 for about the last 30 years before it, too, was discontinued.

A GM, Crane-manufactured kit for it is/was available under GM #12364054. It may or may not be still available. Otherwise, a Crane camshaft #969551 will get you a reproduction of this cam. The lifters are the same as above. This camshaft might provide you with a bit better STREET performance and a bit more streetable engine performance. It won't sound quite like the original cam, though.

**Duke W.** · April 18, 2006, 11:41 PM

Re: Cam and lifters for 327 365 HP

It ain't gonna idle none too good with the stock cam neither.

The following information would be helpful in diagnosing a problem, if there is one, and determining whether or not the cam is the OE "30-30" or something else.

1. What idle speed is currently set, and what's idle manifold vacuum.

2. What is the total idle timing?

3. What is the initial timing (disconnect and plug the vacuum can signal line and measure at less than 700 revs, which is tough because the engine should barely run at that speed)?

3. What is the data stamped on the vacuum advance mounting bracket, and does the vacuum advance appear to work i.e you disconnect and plug the signal line and idle revs drop with a loss of about 16 degrees from normal total idle timing with the vacuum advance signal line connected.

Duke

**Joe C.** · April 19, 2006, 06:53 AM

Re: Cam and lifters for 327 365 HP

Dennis:

Duke has good advice, as usual. If your engine still has its original "30-30" camshaft, then it should pull no more than about 10 in-hg @ 800 RPM idle...........that is, providing lifter clearances are set properly. The idle SHOULD be quite rough!

IF, after you ascertain whether or not you need a replacement cam, and you need one, Federal Mogul's Speed Pro line of parts will provide an exact replacement grind:

CS118R camshaft
AT992 lifters

look at them here:

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http://www.21cgt.com/FMWebCatalog/default.htm

Enter required info in fields at top of page (Chevrolet, 1965, 327, small block, camshaft, etc)

Joe

**G B.** · April 20, 2006, 08:33 AM

30-30 idle vacuum

I've measured the 850 rpm idle vacuum in some injected cars with the 30-30 cam. I have always gotten 12 to 13 inches when running a true .030" cold lash (set at TDC) on the valve train. This is with full time vacuum advance using a #236 or B-28 canister. I have had problems with the Comp Cams version of this grind though. It only generated about 11 inches in two engines until I opened the valve lash to .032".

I'm constantly amazed by the responses I get from '64 - '65 FI owners when I ask them why they run less than .030" lash. Most do it because they like(?) the rough idle and poor throttle response that results. Okaaaaaaay. I then advise them to go whole hog and just jerk a couple of plugs wires to get the ultimate crappy running engine.

**Joe C.** · April 20, 2006, 10:10 AM

Re: 30-30 idle vacuum

Jerry,

I have the Sealed Power camshaft in my engine, with full (manifold) vacuum to a 236 can. It's never easy to get a precise vacuum reading because there is normally some fluctuation, and the gauge is not exactly a precision instrument. The vac generally fluctuates somewhere between 9-11 inches, with 10 being an (somewhat imprecise) average reading at about 750-800 RPM. My engine idles fine at 750-800, so I leave it there. I suppose that at 850, it would increase a small amount, to maybe 10.25 average.

I assume that the Federal Mogul grind is precisely the same as the original 346, because the specs say so, but then again, there might be small variations, which would have insignificant effect on idle characteristics. I have my lash set to .025", which is, as you know, the original setting recommended by Chevrolet.........prior to the manifestation of the fuel injected off-idle problems with the low vacuum. I originally had the lash set to .030", and measured a very small difference in idle vac with the tighter setting. Yes, I also noticed MINIMAL driveability differences. My camshaft is not degreed, so it is probably synchronized at or near zero degrees. Chevrolet didn't install adjustable cam sprockets in 1965, so I assume that the engines were originally assembled with cams neither advanced nor retarded. I suppose the engine would provide a little more "grunt" at the bottom end with a few degrees retard, but I don't need that.

I happen to agree with Duke's durability analysis regarding excessive lash. The camshaft lobe data that he researched and measured, fully support his conclusions and recommendations.

My Corvette is not exactly a "grocery getter". I have a nice, ECONOMICAL 2003 Honda Accord V6 coupe(rice burner)for that. Yes, I like the lumpy idle, the cacaphony from the sidepipes, the smell of the dirty exhaust, the lack of any power assists, etc.

Chevrolet engineering knew what they were doing when they initially set the clearance recommendation at .025". The "band aid" fix was to open it up to .030", to provide more vacuum for the fuellies. Didn't GM also recommend pouring BonAmi down the venturies to "cure" a ring seating problem........possibly in 1955, for the 265 engine?

Best regards ,
Joe

**Duke W.** · April 21, 2006, 01:15 AM

Re: 30-30 idle vacuum

If you set the lash at .030" at TDC the actual lash is .032-.033" because both lobes are still on the clearance ramps at TDC. The 30-30 cam constant velocity clearance ramps end at a height of .017" above the base circle. This is from my velocity-acceleration-jerk analysis of the lobe data from the engineering drawing.

My rocker ratio measurements yield 1.37:1 at the lash point and 1.44:1 at peak lift, so 1.37(.017) = .02329, and my cold lash recommendation is .023". At hot idle the lash is about the same because the block/head expands about as much as the pushrod, so you can lash cold as long as the lobe is on the base circle.

If you lash all the inlet valves at 90 ATC and all the exhausts at 90 BTC you will measure true lash since the lobes are on the base circle at this indexing, and you can set two valves at each of the eight crank postions.

With loose lash the valve is opened and seated at greater than clearance ramp velocity, which will beat the hell out of the valvetrain and seats.

The lash listed on the engineering drawing is .025", which is 1.5(.017), but the rocker ratio is NOT 1.5:1 at the lash point.

For 365HP carbureted 30-30 cam engines I recommend 900 RPM idle speed, minimum. FI idle was always problematic, and I recommend 1000-1200 for FI - whatever it takes to get reasonable idle quality/stability.

Either way the 30-30 cam should have total idle timing of about 30-34 degrees, which is satisfied by 10-14 initial, 16 vacuum and a few degrees centrifugal since the centrifugal advance starts at about 700 RPM on OE 30-30 cam engines.

Duke

**G B.** · April 21, 2006, 08:43 AM

Interesting theory

Duke -

I'm sure you've done some thorough drawing research and have the calculations to back up your lash recommendations.

However, my personal driving experience with this cam is more important to me. I believe any stock 327 with a 30-30 cam that must be idled above 850 rpm has got something wrong with it. A 1,000 rpm idle will cover up a ton of fuel injection problems. That's the primary reason some FI rebuilders recommend a high idle speed.

The GM engineers made some mistakes. Some of their ideas just didn't work so well in the real world. In particular, please consider the FI Cranking Signal Valve, the '63 - '67 Corvette odometer mechanism, and the plastic-toothed camshaft gear. They all probably worked great on paper.

So far I've never pulled a used 30-30 cam that has been beat to death. If I ever start buzzing my engines between 6,000 and 7,000 rpm while cruising, I'll try out those tight lashes and report back. Until then I'll stick with the 850 rpm idle speed and good off-idle response I get with .030"/.030".

Jerry

**Duke W.** · April 21, 2006, 09:31 AM

Re: Interesting theory

It's the valve seats, pushrods, and rocker arms that will take a beating. Little if any harm will occur to the lobe and lifter.

If you set the lash at .030" at TDC, as I said above, it is really in the range of .032-.033". Instead of the valve being lifted off the seat and returned to the seat at clearance ramp velocity of .000360" per cam degree, the velocity of the pushrod is .001124, so the valve is being yanked off the seat and slammed back down at nearly three times clearance ranp velocity. Added to this shock load is lobe jerk (rate of change of acceleration), which is at its peak for the entire cycle at this point. Jerk is associated with shock loading.

This will cause noise and more rapid erosion of the seat and valve, and the harder the engine is run, the more rapidly it will manifest.

Duke

**Joe C.** · April 21, 2006, 09:58 AM

Re: Interesting theory

Jerry,

Since you didn't see fit to answer me, then I'll answer you.

My carburetted (L76) engine idles just fine at 750-800 RPM, with .025" lash, set @ 90 BTDC/ATDC. Static timing is set @ 14 BTDC. Engine was restored as stock 327/365 using all "correct" parts including stock pistons. I must confess, that I made one very key variation from original. I "tricked" the 461 heads by pocket porting, cc'd chambers, gasket matching, reprofiling valves, further unshrouding within the chambers, and a couple other mods. I have buzzed my engine to beyond 7000 RPM, and it still pulls, hard. I must back off for fear of throwing a con rod. If and when I decide to replace the stock rods with Sportsman's, or the like, the engine's true potential will remain a mystery.

Therefore, the problem is not with the camshaft design, but rather, it is with the Rochester fuel injection design. It seems to me that since the 30-30 camshaft was designed to run with .025" lash (original Chevrolet recommendation, before fuel injection complaints were addressed), then any and all necessary modifications should be made to the fuel injection units, NOT the valve lash.

**G B.** · April 21, 2006, 10:45 AM

Re: Interesting theory

Joe, I meant no offense to you by addressing my response to Duke Williams.

You were very clear that you're happy with your engine, and I'm certainly not going to argue with your success. And yes, the Rochester fuel injection system was never fully developed by GM to run properly on any and every small block.

**Joe** · April 23, 2006, 09:48 PM

Re: 30-30 idle vacuum

My 365 correct heads/intake/carb/m21/411rear known values. Unknown are the pistions/ comp ratio and cam. It pulls 18" vacuum at 800 rpm. I am deducing this is NO WAY an original cam. Question: Go with original 30-30 or LT-1 or what about this advertised compcam "nostalgia plus" 12-673-4 duration in.284/ex.291/valve lift in.504/ex.498/lobe sep angle 112 deg. Comments or just go with Duke's LT-1 recommendation and go down the road . thanks . Joe