I know its long but please read!

Ok.. so all this valvetrain discussion (FM Cam Cores and stuff) has me thinking a little bit more about correct preload. With using one of the calcs I recently found here... and going off specs right off my cam card... I would like to get a couple Qs answered and any opinions you guys might have. Im getting on the dyno this week, probably monday or tues... with my new setup, procharged, custom cam, 6.0L heads, etc. So if Im out of whack on this I need to know ASAP so I can fix it before I make some runs.

From what Ive read it seems like there is no real set standard on stock preload... seems to be all over the place and from what Ive read this could be attributed to things like stock p-rods being longer then normal, instead of 7.38 they could be closer to 7.400 (7.395 is what Ive read).

It seems some people are dead set on getting the exact numbers where some say it doesnt have to be extremely accurate, just close enough.

I want to get this right.. so lets take a look at what I have going on.

I have a custom cam.., .22X/.22X 114, BC is 1.465 (intake) and 1.480 (exhaust). Ive recently put on a set of 6.0L heads (not milled) with OEM GM replacement MLS gaskets, Ive read this is to be .054 compressed. Running Yella Terra 1.7 RRs... not shimmed. Im currently running 7.400 p-rods and stock lifters with 46K on them. FWIW the car doesnt seem to run weird or anything.. my idle is a little rough but Im assuming its because I have a totally diff cam now and havent tuned with that cam, just finished SC install. I used to have a TR224/114, my tune is for the old TR224.. got the TR 7.400 p-rods with the kit. BTW I cant find what the TR224 BC is? Anyone know?

Now.. based on doing the regular TDC a piston and count the turns I came out at about 1 1/4 turns/preload, maybe a little less. I was told that as long as it was no more then a 1 1/2 turns total Id be ok. So Ive been running the 7.400s for a couple hundred miles now.. maybe a half a dozen of WOT runs with the new cam.

Using this calc: P-rod Calc I come up to needing a 7.426 p-rod (intake) and a 7.418 p-rod (exhaust).

Pushrod Length Calculator Diameter (in) Base Circle (in)
Intake Lobe Base Circle...............1.465...... 0.7325
Exhaust Lobe Base Circle.............1.48....... 0.74

Milling (in)
Cylinder Head Milling................ 0
Headgasket Thickness.............. 0.054
Total distance closer to cam..... -0.002

Stock Pushrod Length (Intake)........... 7.38
New Pushrod length (Intake).............. 7.426
Stock Pushrod Length (Exhaust)......... 7.38
New Pushrod length (Exhaust)............ 7.4185


My question is this.. using that calc.. does it tell me what p-rod to use if I want to remain at STOCK spec preload? This may tell me what to use to get to stock preload, but dont I want more preload for aftermarket stuff? Should I be running a 7.425 to achieve "stock" preload, or 7.450 to get a little more preload?

I want to get this right on paper.. then compare actual measurements. Right now Im trying to get it all out on paper.

THANKS.

 

Up.. I know its a lot to read but help a brotha out!

 

The calc doesn't take into consideration the shape of your rockers, your valve size etc....
My advice is get a p-rod checker and measure it with everything installed.
Then run the p-rod with the closest measurement to the highest one you determine.

 

It also doesn't take into account the size of your lifter. For example, Morels are longer than stock.

 

I was told by Chris Straub that Morels are the same length as stock, from roller tip to pushrod cup, but the overall lifter is longer. I have mine here, but don't have a stock lifter to compare with.

As stated above, valve stem height, etc. also come into this. I did have the fortune of measuring some stock parts yesterday, with an adjustable pushrod checker. I found the stock pushrods were indeed 7.395 in Overall Length, which includes the length reduction due to the oil hole. Additionally, the measured stock preload was 0.100". Not sure this answers your question, but it does give a target value.

 

Ahh, I was going off this post:

https://ls1tech.com/forums/generation-iii-internal-engine/467267-these-lifters-look-decent.html

 

Im currently running .011 more preload than stock. Car runs great. No lifter pump up shows on the dyno graph to 6700. I dont think id want much more preload than what ive got. I wouldnt be opposed to running less either, but not by much less. I was .030 undersized with my last setup, and it wsnt all that noisy either. Id say just shoot for whatever pushrod comes closest, over or under. Looks like 7.425 would be a perfect a match as you could hope for.

 

You know.. on paper without physically measuring it 7.425 seems like it would be right. However I discovered a good friend of mine, that also has a LS1, had a Comp p-rod checker. So today I borrowed it.

These are what I came up with... FYI my cams BC is intake 1.465 and exh. 1.480.

Basically.. so I dont have to type all my numbers out.. I physically measured the checker with a digital caliper/micrometer. I installed the p-rod checker twice on the intake and twice on the exhaust. Each time I physically measured the checker twice as well. So I took a total of 4 measurements on intake and 4 on exhaust.. then averaged them out.

I also checked length per the checker standards too.. IE each turn = .050. My results were actually significantly different by measurement vs the 1 turn = .050 method.

By physically measuring the checker I ended up with 7.331 on exhaust.. tip to tip. On the intake I ended up 7.356... tip to tip. The difference between the two are approx .025. Which the cam card states a .015 difference between intake/exh. Whats more odd is the checker "turn method" was a diff of .0375 difference. IMO thats way off. So I decided to go off of my actual averaged measurements.

With a 7.400 p-rod I have a .069 preload on my exhaust lobe and a .044 preload on my intake lobe. I guess I could put a 7.425 p-rod in on the intake lobes but Im not sure if it would be necessary? I didnt realize until right now that that would bring preload exactly the same on both lobes. Should I?

 

Keep in mind that the 7.400 aftermarket pushrods are closer to 7.415 or 7.420 when actually measured. .069 and .044 shoudl be okay, but still a bit lighter than stock. Id shoot closer to .100, but not necessary. I think im running closer to between .110 and .120 on mine right now.

 

Do aftermarket lifters like that much pre-load? Or is this just stock lifters?

 

Im running melling lifters. Morel only likes arouns .030. Comp 875 probably want less than stock as well. Unsure about the 850's.

 

Please clarify, are these Comp pushrods? Comp uses "Gauge Length", most other manufacturers use "OverAll Length (OAL)" so the result and measurement depends on manufacturer. Sure wish there was some consistency

 

Comp and trickflow. Not sure about the others.

 

Yep, that makes sense since they sell their length by gauge length. Manley and Crane use OAL.

 

So now taking all that into consideration... OAL vs Gauge Length.. are those differences going to throw my numbers off?

I guess it doesnt matter much since I physically measured in OAL... both the Comp p-rod checker and the TR 7.400 p-rods.

 

If you physically measured both, you are OK. But some companies sell their length in guage length and if you measure the end to end distance on the adjustable pushrod, its not the same.