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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
After an oil pump pickup cost me an engine, I'm not looking to cut corners on this build. I have been in the process of checking all of the original factory L98 roller lifters for any signs of excessive wear. I got to my ninth lifter, and the roller had the slightest spot that wasn't smooth when rotating the tip. Could be a bad spot on one of the needle bearings, could be some debris in there. I decided to bite the bullet, and pony up the money for some LS7 lifters, as that seems to be the go to for most SBC builds. There are some good posts out there about the differences between the lifters, but I might be debunking any myths about the magic of these "new" lifters. TL;DR there are only a few marginal differences between the LS7 and L98 lifter. EVERYTHING ELSE IS EXACTLY THE SAME.
Here is the initial breakdown. I have many pictures of mic'ing all of these parts, but they're mostly the same. I'll highlight the differences in the subsequent pictures.
Nothing different here. Close up of the plungers. No difference in OD or the drilled hole diameter to let oil in. Chamfers, IDs, bore depths, check ball opening, all the same.
Here you can see a difference which is the OAH on the pushrod cup. OD is the same. ID for oil flow is the same. I have a quality Mitutoyo micrometer, but my cheap calipers gave me heights of .238" and .300" for the LS7 and L98 pushrod cup heights, respectively.
An interesting difference is between the check ball assemblies. The L98 check ball spring is notably shorter than the LS7 lifter spring. It is worth nothing that all of my L98 lifters were holding pressure until I depressed the ball through the plunger. I didn't count coils, and it is possible the springs could be the same when the lifters are new. Check valve ***** and the stamped retainer are identical between the two.
To keep photo count down, the next difference is the main plunger spring. Same coil count, same wire diameter. One is longer than the other, presumably to maintain force due to the extra plunger travel from the shorter pushrod cup. LS7=.635" L98=.590"
I mic'ed the ODs of the lifter bodies, and found the L98 lifters were off by .0001-.0003 due to wear from years of use. The LS7 lifters DO mic a tenth or two under the nominal (not worn) OD on the L98 lifters, but they seem pretty consistent. I'm only seeing .0001-.0002 of variance on the ODs, so their grinding process seems OK for mass produced parts. The factory L98 lifters are tighter, but not by much. Not worth making a stink over a few millionths less of of diametrical variance.
The last difference is the relief put in front and behind the roller on the L98 lifter that the LS7 lifter does not have. I don't think this is an issue unless your cam is abnormally huge.
Long story short, use your L98 lifters if everything still moves freely. They are super easy to take apart, and the LS7 lifters don't offer much of a benefit for the price, other than being new.
The only difference between the old LT1 L98 lifters, and the LS7 lifters, is the bleed rate. The LS7 lifters have a slower bleed rate. When GM was developing the LS7, they found that the 1.8 ratio rockers were causing the lifters they ran in the LS1 engines to bleed down at higher RPM's. Whenever you increase the rocker ratio, you increase the force against the hydr unit in the lifter. The higher the force, the quicker the lifter bleeds down. To fix this issue, GM had the LS7 lifters made with a slower bleed rate.
The only difference between the old LT1 L98 lifters, and the LS7 lifters, is the bleed rate. The LS7 lifters have a slower bleed rate. When GM was developing the LS7, they found that the 1.8 ratio rockers were causing the lifters they ran in the LS1 engines to bleed down at higher RPM's. Whenever you increase the rocker ratio, you increase the force against the hydr unit in the lifter. The higher the force, the quicker the lifter bleeds down. To fix this issue, GM had the LS7 lifters made with a slower bleed rate.
Makes sense. I could see the difference in the check ball spring being responsible for controlling the bleed rate. There was a noticeable difference in the amount of force that had to be applied to release the check valve from the seat on the LS7 lifter.
Makes me wonder why you couldn't swap springs out if you wanted lifters that didn't bleed down as fast. I wonder if the spring rate has anything to do with controlling lifter pump-up?
At least I am comfortable with running the stock lifters to some decent RPM, since the LS7 lifters seem to do just fine.
thanks for the post, didn't know. been pondering replacing lifters in my 305. I had a 1970 Barracuda, and swapped out the cam for a hotter cam. learned the hard way that if you dont have the right springs its real easy to bend a push rod. so I'm guessing you could control bleed rate, but be careful.
LS7 lifters are pretty much a direct swap into almost all SBC's. Just need to account for pushrod length to keep the geometry right.
LS7 lifters have gone VERY high RPM. 8000+ in some builds.
So for mere mortal engines that never go past 7k, or like an lazier L98, never even approach 6000rpm, an LS7 lifter is a rock solid option that doesn't cost to much.
