Many people have asked about swapping factory roller cams (LT-1, "Hot" cam, etc.) into early (86-down) blocks as well as putting cheap, commonly available flat tappet cams into late model (87-up) roller cam blocks. Lots of questions about what interchanges, how, what parts to use, etc. Much conflicting info, and even fewere answers about "why" certain stuff works or doesn't work.

Earlier tonight I ripped apart, side-by-side, an old flat tappet SBC engine and a late model roller cam SBC engine to see what the real poop was on this subject. Test subjects were a typical 1974 350 truck engine (flat tappet) and a 1987 L-98 350 f-body engine (factory roller cam). Here's the truth....

1. Cam bearings are exactly the same and you can physically shove either cam into either block type.

2. Front end of the block where the snout of the cam sticks out is machined basically the same (no offset difference at all) but the roller cam block has two bolt holes drilled way out on either side of the cam to bolt on the factory roller cam "retaining plate" that fits between the block and the top timing gear.

3. The factory roller cam is notched or "necked down" on the front 5/32" of it's length so that it slides THROUGH the factory retaining plate and has a "shoulder" for the retainign plate to push against to retain it from walking out the front of the block. The snout of the roler cam is also ever so slightly longer overall than a flat tappet in that area becuase it's gotta slide THROUGH the rather thick (1/8") retaining plate and still have just a smidge of length left to fit snugly into it's receiver on the back of the timing gear.

4. The roller cam top timing gear also has a different amount of "offset" to it to compensate for the longer cam snout and the thickness of the retining plate, but keep the chain itself in the same location as a flat tappet cam.

5. The BOLT PATTERN and DOWEL LOCATION on the snout of the roller cam/top timing gear is smaller in diameter than that of a flat tappet cam. THIS IS THE MAIN REASON WHY YOU MUST USE A ROLLER CAM TYPE TIMING CHAIN WITH A FACTORY ROLLER CAM. You can't physically bolt the gear to the front of the cam if you've got the wrong type of timing chain.

6. The lifter bores on a LATE model roller block will accept both flat tappet and factory roller lifters- the oil feed holes to the lifters are in exactly the same location. Flat tappet lifters in a roller block will look a little funny sitting way down in their bores, but they'll work perfectly.

7. The lifter bores on an EARLY block won't take the taller factory roller lifters for several reasons. First, they are not tall enough. The factory "dog bone" retainers will be way too far down on the body of the lifter and they'll get chewed up for sure. Second, there's no way to mount the factory "spider" in the lifter valley to hold them down.

8. The original 1987 L-98 cam DOES have a fuel pump eccentric ground into the cam so you could use a mechanical block-mounted fuel pump on it if you got hold of an appropriate SBC fuel pump pushrod. Later model cams or performance factory replacement cams? No idea of they have an eccentric to drive a fuel pump or not.

Interchange possibilities....

Flat tappet cam in a roller cam block? Easy. Shove the cam in, leave off the factory retaining plate, use a standard flat tappet cam timing chain, drop the flat tappet lifters in the bores, get the right length pushrods and away you go.

Roller lifter in an early block? More difficult. Shove in the cam, install the factory retaining plate (with the "ears" machined off- just use it as a spacer), install factory roller cam timing chain, install cam button (to keep cam from walking forward now that the retaining plate no longer "retains" the cam), and use aftermarket roller lifters, retainers/anit-rotators, and appropriate length pushrods.

 

Why would anybody want to put a flat tappet into a roller cam block? There is no advantages other than the fact that they are cheaper. There are plenty of disadvantages though. The worst of which, I think, is they spend less time at their peak beause there is no gradual slope, they spend most of their time either opening or closing. Roller cams spend much more time open at their peak because of the gradual slope. Also flat tappets suffer valve float at a lower RPM than does a roller setup. The list goes on and on.

 

Thanks,
And if I might add, If you have a late model(post '87) flat tappet truck block tho, it should have the bosses for the "spider" taller lifter bores and untapped mounting pad for the roller-cam-retainer. So a direct bolt in with just minor machining would be possible.(I rebuilt a '90 Box Van 350 engine, w/really decent looking heads.)
So, just drill/tap holes in the lifter valley for the lifter retainer "spider" and front cam retainer, stick in factory: roller cam, lifters, retainer(s) and "spider" + correct pushrods....

 

Mine eyes glaze over when anyone starts talking about cams (that should explain my level of interest and expertise), however I did some how manage to read through the entirety of the Car Craft articles. According to the articles you need to buy a different kit for the older engines - something about lifter and retainer components etc. See pages 36-43.
I addition to the stuff above they also mention something about the distributer gear needing to be soft. They compare the older style engines with the factory roller style.

 

Flat tappet swap works great (remember to take the flat tappet pushrods).

The roller swap will need aftermarket and expensive roller lifters. While you are at it, just ask Comp Cams (Crane, etc) to grind the cam you want on a standars roller core and use the old style timing chain with a cam button. When you grind the ears off the cam thurst plate, it is no longer a "thrust plate", just a washer. Also, you can't install a standard cam button with the late model roller cam bolt pattern, it is smaller than a standard cam and nobody makes a button that small. Since roller cams are not preloaded towards the rear of the block like a flat tappet (due to the taper in the lobes of the cam), the cam can "walk" forward and grind up the timing cover (metal shavings are not a good thing). I would not attempt to use a new style cam in an older block, it is not worth the hassles and potential problems (failure from metal particles or angular misalignment of the timing chain causing failure). Also, the roller cams do have a fuel pump eccentric on them, just remember that most roller cams are steel billet and need a bronze tipped fuel pump pushrod to avoid grinding up the eccentric on the cam.

Have fun!

 

I've said it before and I'll say it again. You can install an 87 and later roller camshaft into an 86 and earlier block without the expensive aftermarket retrofit. All you need to do is drill and tap holes for the factory spider and lightly modify the lifter bores.