Alright, so I've been searching around and can't find a straight answer to the question of how much lift can I put into my L69? I'm looking to re-work my motor a bit and I'm trying to make sure I'm not going to crash my valves into my pistons or anything silly like that. I've had my eye on the Comp Cams XE274. Is anyone running this or larger for lift or duration? I figure this is about the max I can go on duration but want to make sure I still have clearance. Right now I'm running a Int/Exh = .420/.443 with 1.6 ratio rockers, so actually, .448/.473. I'm not having any issues now. I've heard of someone running the XE284, but don't remember the detail, like if they had flat tops or dished pistons (L69 vs. LG4).

Anyway, if someone could provide me with a number on this, I'd really appreciate it.

 

Somewhere around .480" is where the probability of the bottom of the retainer hitting something, usually gets pretty high.

Factory tolerance in that area is notoriously imprecise... no need for it to be any closer than about .030" or so because none of the factory cams even comes close to interfering... it would be the "over-processing" case of "muda" for them to make it any better than they do. So there's no "one" "absolute" "hard and fast" "precise" number for that, it's a range, pretty fuzzy.

 

Piston-to-valve clearance isn't just about max lift of the valve. Wider LSAs don't just improve driveability and extend the useful RPM range. They also give more running clearance. For what you seem to want, I'd use a Magnum 280 installed straight up. It comes with 4 degrees of advance ground in, so you'll need a multi-key timing set to offset that. It's really past the point of diminishing returns for your stock heads, but you seem to want big and nasty. This is it. Swap those 1.6:1 rockers for some 1.5:1. Intake, headers, ignition, valve-springs and exhaust permitting, this will pull 6500, don't try for 7000 with a worn stock engine.

 

When you talk about the retainer I'm assuming you mean spring retainers, is that right? I would assume this wouldn't be an issue if I got a new spring kit to go with the cam.

 

I know Max Lift isn't the only factor, which is more or less why I was asking. I figured I'd have to go back to the 1.5s, got the headers sitting in my garage, MSD box and distributor in the car.

thanks for the recommendation.

 

Bad idea, in general.

The age of the retainers doesn't change the location of the valve guides below them. So, no; that "assumption" would be largely incorrect. In general.

 

The point I realize you were making is that the retainer, or the tip of the valve stem, can only move so far. So even if there were no spring it would eventually bottom out, which is obviously not desirable. However, the point I was making was that if you do have a spring in place you are limited by that springs compressed height. Therefore if you got a different, new or not, spring kit, with perhaps a thinner wire diameter, you'd be able to achieve more lift before bottoming out your spring.

By the way, people make assumptions when they are lacking all the information or unsure of the information they are given. Since I'm on here asking for advice, I obviously am suffering from both in this instance. Thanks for the advice anyway.

 

There are few springs, if any, that would serve as the limit to the valve lift, on stock heads.

The limit is usually the bottom of the retainer hitting the top of the guide.

This is why those heads can usually tolerate only as much lift as they can, without some sort of work being done.

Since the spring itself IS NOT the limit, changing the spring won't change the limit.

This has NOTHING to do with "the tip of the valve stem".

This should not be hard to understand, and does not require arguments about "making a point". Reality is reality, entirely aside from "point".

 

Alright, I think I've got you now. The bottom of the Valve Retainer, kind of like the top of a top hat, when the spring is compressed will hit the top of the Valve Guide before the spring can compress all the way since the top of the Valve Guide stick up into the middle of the spring. So the clearance between between the two will really be your Max lift without machine work. I don't know who was arguing. I'm just trying to figure out what you're explaining.

Oh and the retainer is located at the tip of the valve stem, if your valve stem was longer there would be more space between those parts. Not that that is necessarily an option.

 

I have a rebuilt 77 305 with dished pistons, ported heads with screw in rocker studs. I'm running a solid roller, .525 lift, 226 duration at .050 without machining the pockets or guides, I'm just running a stiff factory diameter spring. It does clear the guide but I know it's close, piston to valve clearance isn't an issue though, I clayed the pistons and it had plenty of clearance.

 

Yup, I believe you got it...

While there are ways to increase that clearance WITHOUT cutting the heads (longer valves, offset keepers, beehive springs which have thinner retainers, ...) for the most part you're kinda stuck with what the factory gave you.

Piston-to-valve clearance is really more of an issue with high duration than it is with high lift .... THINK... when the valves are at their farthest open (highest lift), near about the middle of the exh and the int stroke respectvely, the piston is about halfway down in the bore. OTOH, when the valves are "changing over" (exh closing, int opening), the piston is at THE OTHER instance of TDC during an engine cycle BESIDES firing; that's when the valves come the closest.