but an engine question.

The 1991 350 truck engines came with just plain flat tappet cam setups. If I wanted to go roller, do I use a retro kit, or a roller kit for 87+? Reason I ask is because most of the 87+ kits always say that their for engines with previous roller cams. But would GM cast 2 different blocks for rollers and non-rollers after 87?

 

You can identify whether or not the engine is OE roller cam compatible by the lifter bore in the engine block. The roller cam motor has a raised boss around the lifter bore to keep the lifters aligned, and 3 or 4 screw holes (I can't remember how many) in a row down the center of the oil valley where the spider plate is bolted. If not, then you will need an aftermarket roller lifter kit.

Also, a factory roller cam engine has a retainer plate that keeps the camshaft from sliding forward into the timing chain cover. If there is no provision on the engine block for the retainer plate to bolt on, then you cannot use an OE style roller camshaft. You will have to use an aftermarket roller camshaft that comes with a spacer that literally rests against the timing chain cover and keeps the camshaft in proper location. Not only do you have to consider what type of roller lifters to use, but you also need to know what type of roller cam to use.

Good luck with your project.

 

GM didn't cast different blocks, but they did machine them differently.

Many of the truck engines that did not get roller lifters had all of the provisions cast in but none of them machined. The question you have to answer with one of them is whether getting the machining done would cost more than retrofit parts.

Some of the truck engines were machined, however. Only way to know is to pull it apart and look. If you're lucky, all you need to do is swap over the factory roller parts. The 330 HP 350 HO is one such engine - not roller, but provisions cast in and fully machined.