4.0 cam in a 4.2 block

[mike0914nascar]

Has anyone run a 4.0 cam in the 4.2 block is doable.I'm putting a 4.0 head on hoping the stock 4.0 cam would better than the stock 4.2.I read that you have to run electric fuel pump instead.How about the timing chain and gears are there any issues between the two?Any input would be appre!!

[Bodo]

The cams are the same.

[amcinstaller]

you do need to run an electric fuel pump because the 4.0 cams do NOT have the lobe for the fuel pump. also, youll need to block that spot off on the block.

[Bodo]

Wait a sec. Are you saying that the 258 cams are different than the 4.0 cams?
Every single cam grinder catalog I've seen list cams for the 258/232 and make no differentiation between the two.

Not being a smarty pants, just asking a question.

[mike0914nascar]

I read that the older 4.0 cams had a lobe and newer ones 90 or so and above dont kow what years for sure.Does the 4.0 cam make more power than the 4.2 cam when using the 4.0 head.

[amcinstaller]

the 4.0 cams ive seen, (all but RENIX) do not have the mechanical fuel pump lobe that my 4.2 cam had for my spirit. also note, i have not seen a renix cam out of the block. maybe someone can verify, itll be an extra in between the 1&2 cylinder lobes. i dont have pictures, or the cam anymore, it was broken during a demonstration in mechanics class.

[IH 392]

Are you saying that the 258 cams are different than the 4.0 cams?
Every single cam grinder catalog I've seen list cams for the 258/232 and make no differentiation between the two.

All the 199's, 232's and 258's had carburetors, therefore they had a fuel pump eccentric on the cam, all of the 4.0/242's had fuel injection, it makes sense that Chrysler would use the leftover cam cores to in the 4.0's to use them up and remove the lobe after those cores were used up.
There are several (OEM) "grinds" for the carbed engines and more than one (3??) for the injected engines, the basic cams are the same from 1964 to 1999/00 when they went to the "thrust plate" style of cam, but the new blocks will retro to the old style of cam.

All of the aftermarket cams have the fuel pump lobe so they can be used in a carb application, I would assume? but even if you're running a carb on a 4.0 block with a cam with a lobe you still require an electric pump, there is no boss for a fuel pump on a 4.0 block.

I may??? have a RENIX cam still in a block at our race shop?, I'll see about getting over there and looking to see if it has the fuel pump lobe on it??

[IH 392]

Got over to the race shop today, the '87 RENIX core I have does not have a fuel pump eccentric on the camshaft, I can't say for sure if it's an OEM cam??

[amcinstaller]

the real answer at the bottom of this would be if there was ever a carbed 4.0. i dont see why any company would use blanks left over from 20 years ago?? and with the difference in lobe width, i doubt any 4.0 cams were ground with fuel pump eccentrics. unless i am understanding something wrong (difference in lobes from 4.0 to 4.2 to aftermarket)

[lafrad]

I think it goes more along the lines of: The narrow lobes "should work fine" in a 4.0 block... so it doesn't hurt to have all cams support the widest range of engines as possible. Grinding with wide lobes and no fuel pump eccentric would limit who can buy your stuff.

[SilverXJ]

All the after market cams I have used (crane, isky, comp) have had the fuel pump lobe on them.

[EFIeagle]

I have a 92 cam in my 83 4.2 and it does not have a fuel pump eccentric. Electric fuel pumps are not very expensive, and you'd see very large gains from a 4.0 cam. Just use an SBC FP block off plate and mount the electric there. They're identical in location and thread size to the holes used for the ignition coil on the 4.0.