Pushrod length with ProMagnums?
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
I've read that stock L98 pushrod length is 7.8" so that's what I ordered to go with the ProMagnums. Now that I have the stock pushrods in my hand I see they measure only 7.2" in length (btw, my motor does NOT have roller tips on the stock rocker arms, as I had thought).
I realize the ProMagnum shape differs from my stock rockers so that the 0.6" may be compensated for, but am not sure. If I have the wrong pushrods I would like to bring in the correct size before I need them for the job.
Does anyone have experience along these lines?
I realize the ProMagnum shape differs from my stock rockers so that the 0.6" may be compensated for, but am not sure. If I have the wrong pushrods I would like to bring in the correct size before I need them for the job.
Does anyone have experience along these lines?
Safety Car
Joined: Apr 1999
Posts: 4,623
Likes: 2
From: Ohio
Wrong pushrods. Just went through this. The late '86+ up L98 stock roller lifter motors used the 7.178". If you have not done any special machining on the engine/heads, you should be able to use the stock length PR's.
Having said all that, if you use a standard pushrod checker, you will find that the geometry looks off, and that the stock PR's are too long. (by .150") The tip of the roller (rocker arm) is very close to the outside edge of the valvestem at TDC, and the angle of the PR is pretty severe relative to the valvestem. Now, there's supposed to be a formula used to calculate the correct PR length used with hydraulic roller lifters, but I can't find anyone who knows it. Check around, and if you find someone who *knows*, please advise. Thanks.
Having said all that, if you use a standard pushrod checker, you will find that the geometry looks off, and that the stock PR's are too long. (by .150") The tip of the roller (rocker arm) is very close to the outside edge of the valvestem at TDC, and the angle of the PR is pretty severe relative to the valvestem. Now, there's supposed to be a formula used to calculate the correct PR length used with hydraulic roller lifters, but I can't find anyone who knows it. Check around, and if you find someone who *knows*, please advise. Thanks.
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Looks like I should have gone to the Summit tech line before ordering.
Comp Cams tech support just recommended their 7.200" long Magnum pushord #7608-16 for this application. Since they use UPS Red, won't be in till Mon; I'll post how they fit.
Comp Cams tech support just recommended their 7.200" long Magnum pushord #7608-16 for this application. Since they use UPS Red, won't be in till Mon; I'll post how they fit.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Correct me if I'm wrong, but I thought the length needed to be tweaked by 0.050" for the 1.6 rockers to maintain proper position on the valve stem (valve geometry). This is per Crower.
Burning Brakes
Joined: Apr 2000
Posts: 900
Likes: 0
From: New Jersey
Maybe I'm wrong but, I bought Comp Cams Pro Magnum roller rockers that were used from my friend. I remember that the roller rocker push rods were not the same length as the stock rocker arms. I can't remember which were longer. If I had to guess, the roller rocker arm push rods were slightly longer. I have a 1988 L98 and the ratio for the rollers were 1.5's.
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
If I have it built up enough by Mon when they come in, I'll post how the 7.2s fit (roller contact zone from closed to open).
Gees, it sure would be nice to have this info collected somewhere so the next guy who tries this with #113 heads doesn't have quite so much fun.
Gees, it sure would be nice to have this info collected somewhere so the next guy who tries this with #113 heads doesn't have quite so much fun.
