The 354 and 392 Chrysler hemi engines do NOT use the same cam because the lifter bore angles are different.
By Doc Frohmader
You know how life sometimes allows you to bumble along like a big dumb puppy and then suddenly drops something on you to surprise you and stir things up? Well, a little while back Bill Hancock called me up with a piece of tech info that made me reassess what I thought I knew.
That info: The 354 and 392 Chrysler hemi engines do NOT use the same cam because the lifter bore angles are different. After a little checking around, I discovered that this is not widely known – about the Chryslers or any other engines. If you don’t know that there are quite a few engines where this is the case, you may end up with the wrong cam and never know why your engine-building masterpiece won’t perform to expectations.
Taking it from the start, it shakes out like this: In a great many cases, OEMs would update and enlarge an engine by increasing the stroke. In a fair number of cases, this was done by raising the deck height, using the same rods and pistons, and installing a stroked crank. Others did the same but also changed the rods and pistons.
In almost every case, though, the same head or at least very similar tooling was used for the head and all the geometry between the valves and rockers was maintained. In some cases the cam was raised in the block for crank clearance at the same time the deck was raised. In a few, the deck remained the same, but the cam was raised. So you see, there were a number of ways the same net effect could be attained.
Unfortunately, when this happened the valve train geometry was often altered. It meant that a different lifter bore angle was required and a different cam was required to be compatible with the new angle.
Why? Few engines are designed with the push rod and lifter on the same centerline. Most require the push rod to be angled both side-to-side and front-to-rear to allow clearance for ports and other components. Over all, the closer-to-parallel you can make the pushrod end of the rockers and lifter centers, the more efficient the valve train is.
Changing the angle of the pushrod to the rocker and cam creates unnecessary additional stresses. What changes the push rod angle and its relationship to the lifter and rocker is when the cam is raised for additional crank clearance or the deck is raised for additional cylinder area, or the rocker arms are splayed or offset to duck around the ports.
If the cam is raised, both the angle between the pushrod and rocker and pushrod and lifter gets more acute. To correct this, some manufacturers changed the angle of the lifter bore, in effect aiming it at the rocker a little better and reducing the angles. The lifter bank angle might change from 45 degrees to 39 degrees. If the deck was raised, the two angles would tend to become more obtuse (larger) and again the relationships between components and what the OEM wanted for valve train geometry would be altered. You might see the OEM correct this by changing the lifter angle from 45 to 48 degrees like the Chrysler. If both the cam and deck were moved, the lifter bank angle change and correction could be anything.
So if the lifter bank angle changed, that means the centerline of the lifter moved relative to the cam lobe. If you move this centerline, you change the timing between the cam lobe and lifter. The lifter will be on the nose of the cam either sooner or later than it is designed to be.
Picture a front view of the engine with a lifter and cam in place. The centerline of the lifter intersects the centerline of the cam. If we start with a lifter that aims at the cam at 45 degrees, the nose of the cam will be aimed at zero degrees to the lifter at peak lift. If you changed the lifter bank angle to 48 degrees, without moving the cam, the nose of the cam will still be at zero degrees and the lifter (in relation to the lobe) will now be advanced at three degrees. In that case, the lobe will be out of position by three degrees and engineered cam timing will be off by the same amount. So, as a result, if the lifter angle is changed the cam lobe profile must be changed to accommodate it.
Long time engine builder/designer/racer Bill Hancock tells me, "When the incorrect cam is used in these cases, what actually happens is one bank runs with advanced cam timing and the other with retarded cam timing by anywhere from 6-8 degrees (in the Chrysler) or possibly more in other engines."
In the case where a diligent engine builder degrees the cam on #1 and #6, it will run either advanced or retarded depending on which way the lifter bores were moved. While this may not be readily apparent in lower output engines, in a high performance engine where valve to piston clearance or tuning is very close to limits, the condition may cause an unscheduled sacrifice to the "aluminum gods."
When building a vintage engine, you’ll want to make sure the cam you are using was actually ground to match the engine. Unfortunately, there are cam grinders today who do not know all the historical variations. The best way to deal with this is to know what exactly you have for a block and know if there were variations – particularly low and tall-deck versions within the same engine family.
In other words, it’s up to you to be smarter than the parts. Then contact your cam supplier or grinder and make sure you are getting the right item. Also, make sure the cam you removed wasn’t replaced with the wrong one at some point - don’t assume anything. Again, Hancock has a quick way to tell if you have the right cam for the engine:
1) Attach the degree wheel and pointer to your engine and locate both #1 and #6 cylinders.
2) Determine TDC by rotating against the piston stop clockwise and counter-clockwise as you normally do when degreeing in the cam. Observe where the stop occurs in either direction, noting the degree location on the degree wheel at both points.
3) Add the two numbers, divide by two and reset the wheel without moving the crank or pointer to the resulting number of degrees.
4) Rotate back and forth to the stop positions, and make sure you get the same number of degrees at the pointer at both stops and you can be sure you have the wheel centered at TDC. Remove the stop.
5) With your dial indicator set on the #1 intake lifter, rotate the crank clockwise (from the front) until you get the lifter at maximum lift.
6) Set the dial indicator to zero and rotate the crank counterclockwise until you get to about .060˝ under maximum lift.
7) Rotate the crank clockwise until you get to .050˝ before maximum lift and observe the number. For example, let’s use 67 degrees.
8) Continue to rotate the crank clockwise until you see the dial indictor at .050˝ again - this time it will be .050˝ under maximum lift but on the other side of the cam nose. Our example: 152 degrees.
9) Add the two numbers (67 +152=219) and divide by two (219/2=109.5) and you now have the intake centerline on #1 cylinder.
10) Without moving the pointer, repeat this procedure on the #6 intake lifter.
11) Because the #1 and #6 cylinders are 360 degrees apart in rotation, the two intake centerlines should be the same.
12) If not, then you have either the wrong cam or a defective cam. You may have 1-3 degrees variation due to tolerance stacking, but any more would certainly indicate a potential problem.
While some of the old timers will know about this, another oddity of OEM machining has to do with the occasional screw-up and the fix for it. In one case, Buick – in the late ’70s – discovered a flaw in its machining process on the 231 V6 engines. To correct the error, the lifter bores were enlarged by .005˝. Of course that also meant a .005˝ oversized lifter was required. They were fabricated, the engines were assembled, and shipped.
The problems arose when the engines failed under warranty. Buick ended up sending the dealers individual lifters on an as-needed basis or simply replacing the blocks with lifters. No aftermarket lifter or OEM replacement was ever made for these engines in the .005˝ oversize. So, of course, when you end up with one of these blocks, you need to check EVERY lifter bore to make sure you don’t have an oversized one. With a standard lifter, it will bleed oil like crazy and oil pressure will never be up to par. If you find one, toss the block and get another, preferably newer, block because it is cheaper than any alternative.
A similar situation happened with the MOPAR 340 V8 blocks. Again, through whatever errors or flaws in the process, there were a fair number of these blocks that received oversized lifter bores and corresponding oversized lifters. In this case, MOPAR was smart about it and supplied the requisite oversized lifters. Unfortunately, I no longer see any source for them other than the possibility of some NOS stuff. To save a block with oversized bores, you’re going to have to bush the bores and resize them.
Naturally, these examples are merely that, and I’m sure there are any number of other engines where this occurred. So the moral of this story is: Before you give up on that vintage block and toss it in the scrap heap, check to see if there aren’t oversized components. If not, you can still save a valuable block by bushing and remachining.
Doc Frohmader got his first car at the age of nine and has been an engine builder enthusiast ever since. email@example.com
The same disparity in tappet bank/pushrod angles exists between the low and high deck DeSoto hemi engines: 276 & 291 vs. 330, 341 & 345, and between the low and high deck Dodge hemi and polyspheric engines: 241, 259 & 270 vs. 315 & 325.
by: panic 1/7/2011