Roller lifters
 

Has anyone run a high lift (.591 or bigger) with the stock GM OEM roller lifters that come in the Gen VI motor??
I just had a rebuild on my GenVI 502 and went back to the OEM lifters hoping for quiter operation. The cam I have is a Comp Cams roller 226/234 with .591/.601 lift installed at 110 ILCL.
I made only two significant changes when the replaced the piston that I burnt, decked the block to have a .041 quench, and changed to the Dart single plane rectangular port intake.
I had been running this cam before the piston melted and it was setup with the propper springs set at the right height and pressure.
The only other thing was to change from the replacement CompCams roller lifters back to the stock OEM roller lifters. The motor made good power on the dyno 520 hp at 5100 rpm but after going in the boat I am 200rpm down from before it broke (5200)??? I am very confident in the work that was done. The motor runs great, strong acceleration, good temp & op, but just hits a wall at 5000rpm, where as before it ran to 5200 rpm. Prior to the piston going (ran to lean jetting) I had the Comp roller lifters in the motor but where a little noisey.
Could the stock roller lifter be bleeding off so I am not getting full lift??

Can only share my experience, had ggod luck with stock gen vi lifters with 587/610 lift cam. Crane said they would work fine when I was picking out the cam.......I don't think your problem is lifters.

Tom- On a Gen6 lifter body length is critical because of the lifter retainer plates. On a smaller base circle lobe [usually means higher lift] the top of the lifter can go below this retainer. The retainer is not a precision part as a lifter bore would be and so you only want this part to keep the lifter from turning in its bore, it really can't work as a proper guide. IMO your lifters are going below the retainer plates. This could very well be the reason you thought your COMP lifters were noisey....they shouldnt make any more noise than the OEM lifters. Crane and others make these long body lifters just for this reason. Hope this helps & good luck.

Running the engine lean before the rebuild could have given you those extra 200 rpms and hp. A lean engine will make more power than one running conservative----at least for a little while. :eek:

Brad,
Thanks for the reply, I'm going to swap back to the other intake and see if that brings me back to the original rpm. I may not be reving high enough for that intake. The motor runs so good otherwise i hate to take those lifters out!

Thanks to the rest of you guys.
The motor runs great, very responsive mid range and pulls strong right to 5000. then flat!! No missing, temp is good, oil pressure good, motor idles smoothe and quite.
I do know that the engine builder jetted on the rich side on purpose. The plugs have a good light chocolate color, wonder if a 4 hole spacer instead of the open and jet down just a little?? I am very confident that the block work & cam setup where done right. I only suggested the OEM lifters as the problem because I thought they might be starting to bleed down with that rpm?? The engine builder suggest trying the stock Magnum intake with an open spacer which is how it was befor the meltdown and see what we get.
I did upgrade the fuel lines and filter/seperator so I do have better flow now as far as the fuel system goes, which may have been why I ran lean in the first place after a long run!

You might try seeing what is going on with your timing when it goes flat. I had a buddy that thought he was floating springs because it just went flat and made a different noise. Turns out his timing was jumping up to 50+ degrees right at that point!!

On the single plane, maybe others can shed more experienced light, but in fooling around with desktop dyno, the single plane was good for 30 odd more hp that the dual and only lost maybe 10 lbs torque down low around 2000rpm. After seeing that, I don't know that I would ever use a dual on a big block again.

You might try reducing the plenum volume in the new intake most automotive designs have to much volume for marine use.

Good Morning OSO World,
I appreciate the input. I took the intake off this Am and I did notice that the lifters do sit lower than the top of the retainers as liquid lounge had suggested that might happen with a higher lift cam, but not below the bottom so they are still keeping the lifters in the right position.
I did have another conversation with the engine builder this AM and we are both thinking lifters, only because we are both confident that the low end is put together correct and the only thing that was changed on the top besides the intake was the lifters back to OEM from the Comp lifters that the Comp tech people said I needed to run.
The theory is that the stock lifter because it is lower in the bore could possibly be letting a little too much oil bleed out reducing pressure and when the most force is being applied that combined with the lifter plunger not being strong enough ( which is what the Comp Guy suggested because the Comp roller cams have very aggressive ramps) so the cam is effect not getting all the lift to the valve.
I am going to swap lifters to the Comps and see what happens. and see wha

I ordered a comp kit last year for my gen 6 motor. The tie bars bottomed out on the block. I ended up using Crane roller lifters with the comp cam. My cam is about the same size as yours.

KC,
I thought they were close, but didn't actually make contact.

TomR
Remember that when you change the lifters and cam for that matter you should also adjust your pushrod length to keep proper valve train geometry.

onesloyrd,
Good point, already on it, I will switch the pushrods back to the ones comp sent with the cam and lifters, they are a little longer.

Mine did and when I called comp they where of no help. I did use the comp push rods that came in the kit.

I was going to put them in tonight, I'll double check each one to make sure.