I don't know if I have an LT4 standard cam or an LT4 hotcam. I bought it as a standard cam on ebay years ago, but I looked up the part number on the box and its from a hotcam. Now, this could be a box that was used by the previous owner, just for shipping purposes. Or, it could be a much bigger hot cam. My concern is that my heads won't handle this hotcam, and I need to know if I should scrounge up an replacement cam temporarily or not.

This cam does not have a fuel pump lobe on it, but does however have the extended water pump dowel. There is a stamped number on it; GMPT-BC-17-242. I was wondering if there was anybody who could tell me what cam this is. It's definitely an LTx cam thats for sure. I can take pictures if it's truly necessary. Thanks a lot you guys, check out my thread in the signature to follow my project.

 

Check the lobe lift with a mic or caliper, and do the math. Remember that the LT4 "hot" installation used 1.6:1 rockers, so the extra lift is partialy attributable to the rockers. If you use 1.5:1 rockers on a LT4 "hot" cam, net lifts would be more like .491/.491". You would also lose about 4½° duration by changing to 1.5:1 rockers, making the cam spec at about 213/223°.

 

". You would also lose about 4½° duration by changing to 1.5:1 rockers, making the cam spec at about 213/223°.

Just curious...If the intake opens 1* BTDC and closes 37* ABDC @.050 where does the math come in that changes duration with a 1.6 rocker?
I'd like to here this one because the degree wheel doesn't lie.
I know it lifts the valve faster but where does the duration change come from? (in your opinion)
(No flame intended)

 

assuming I DO have a hotcam, will it work with my vortec heads with aftermarket springs? there is no machine work done on them, but there are new springs in place. shifty capone says no

 

.050" duration measured at the valve will increase slightly, since the valve makes it to .050" a little sooner with the higher rocker ratio; but the difference is usually trivial. The more aggressive the cam's ramps are, the less difference the rockers will make to the duration.

The Vortec heads experience the retainers smashing into the top of the valve guides at somewhere around .480" of valve lift. So no, the LT4 HOT cam will not work without some machine work.

I would recommend aftermarket springs, not the GM ones that come in the kit. Since you'll be having to get machine work done anyway, I'd suggest hetting the spring pockets cut out to 1.45" diameter, and use Comp 986 springs or the equivalent from a major cam mfr (entry-level 1.45" spring); not K-Motion or GM, but rather Comp, Crane, Lunati, Isky, etc.

 

You also might wanna think about running Comp 26918's with a conversion retainer no need to machine out the heads for bigger spring pockets. the 26918s are 1.25 so they fit in the stock pocket. You will still need to have the valve guides cut down though. Just another way to go......

 

ttt