I'm starting to wonder if my pushrods are too short in my engine. Would that cause me to look like I'm losing power on top (past 5500 and look like valve float?)

I have some 7.05's right now and have some 7.2's on the shelf. I was thinking of swapping them out on the #1 cylinder only, using a permanent marker and seeing how it compared if I let the engine run for a few revolutions. is there an easy way to test this without pulling the intake and using a solid lifter? I have a comp cams pushrod checker available.

thoughts?

 

When pushrods are too short, they exert side thrust against the valve stem and valve guides, which can result in a bunch of bad stuff.

When you built your motor, did you check for proper pushrod length using an adjustable-length pushrod? Doesn't sound like it...

 

You would have to mill the **** out of the heads and deck to need one that short. I'm with Joe, doesnt sound like the builder checked it out properly.

 

To put it into perspective, I have a zero-decked block and milled heads with 52cc chambers and my PRs are 7.10" in length, ever so slightly biasing the exhaust side.

 

Is there a way I can check without a solid lifter, with the engine assembled?

 

IMO, the only way to do it is with a solid lifter. I purchased one LS7 lifter just for this purpose. I took it apart, disassembled it, and reinstalled the plunger with a small wedge of metal to keep it completely "pumped up."

 

i hear ya on the proper way, this all took a few years to come together, so it is what it is now.

on the first question i had, could a shorter pushrod look like valve float over 5500rpm?

 

here's the valve tip with some sharpie testing real quick. this is with the 7.05...

i let it run for about 5-10 seconds so that that lifter would pump up



and here's the 7.2 pushrod...



here's the 7.05 from the side...



here's the 7.20 from the side...



notice how the 7.2 side shot looks like it hangs over the valve more toward the exhaust

 

What springs are you running and whats the installed height?

 

if i recal, the 10308 (99893?)cranes they are 1.46 OD I think, i'd have to take it off and measure installed height. why do you ask about the installed height? coil bind?

they are setup for 180lbs on the seat according to the guy that did the heads.when I talked to him, he was pointing at the lifters instead of the springs.

 

If they are setup at 180lbs on the seat there's no way you're getting valve float with that cam. There's more of a chance of you collapsing the lifters with that pressure. And I hope you're running chromeoly pushrods with that much spring pressure.

 

yup comp cam chromoly. i called the guy that did the heads, he was pointing at the lifters too. they are stock lifters with about 2500 miles on them.

 

Crane 10308 spring is :

1.75" install height
165 lb seat
426 open @ 1.10"

...so if they are 180 on the seat maybe installer shimed them to 1.7x to bump up seat preasure to 180??

GM846 cam should work well with the 10308 springs

My $02 on the PR length is 7.05 based on pics.

stock lifters @ 2500 miles should be fine

while valve springs could cause you to nose over at higher RPM's I would look into ignition.

even if the springs are installed at 1.70 you won't hit coil bind with the 846.

 

There's no reason to have anywhere near 180lbs on the seat with that cam. That's approaching solid roller seat pressures.

 

i'll take the spring off and measure to confirm. The guy that did the heads asked me to bring the springs by to test them out to see if they are still ok. I'm doing all this because of my other thread about the dyno tune and trying to address what is happening at 5500-6000 on my dyno chart. https://ls1tech.com/forums/lt1-lt4-m...-dynotune.html

 

Everything has been said above. Imho, the 7.200 is giving a nice narrow sweep while being a tad offset toward the exhaust side. If you go shorter, the sweep will increase but the pattern will center up more. Imho, narrow sweep trumps a centered pattern.

 

I hear you on the narrow sweep, it won't hurt to try, looks like a 7.1-7.15 might have been ideal.

 

Stay with what you have. The sweep looks fine. Notice on the 7.2 the roller tip is not making full contact onto the valve tip.

 

He has the gm846 not the 847. And you might want to look up what the word approaching means.

For the record i was running 7.2 pushrods with that cam and the same springs he is, but the installed height was around 1.8". My point was there is no way in hell he is getting valve float with that cam with 180# of seat pressure. Crane only calls for 125 for that cam jfyi.

 

180lbs is far from "approaching" SR seat pressures. That's like still on the tarmac of the departure runway...