[radz28]

I already know I'll be doing the crap AFM-lifter delete, and planned on doing valve springs at that time, but that's either a ways down the road, or when I have a problem. But...

Is there any consensus on adding boost to the OEM LT4 valve springs? The way my is VVT set-up (and the rest of the combination), is I'll get up to about 16-psi right now (this is a stock long block). When I was messing around with VVT and VVE tuning, I do remember some weirdness when boost got as much as 18-19-psi (this was with 0* cam retard), but, if memory serves, I was running WAY RICH and (like 0.62 EQ, for example) and ignition timing was pretty low for safety, and thought some of the misfires could have been from fueling. I know boost can hold the valves open after a certain point, but I have no idea what that is on this platform. I'm casting a wide search on that, too, but I was wondering if anyone here had experience in the safety margin for the OEM valve springs? I know the correct solution is to replace them, but I don't want to do that until I do the lifters. And - I'd been thinking about dropping from a 90mm upper to an 85mm, for maybe a little more boost. I know of one other person who's done that, and I thought that was on a stock long block LT4, too, but wanted more information before I go that route.

Thanks!

[laynlo15]

Back in the day when I had my 16ss with stock SBE I never had a valve spring failure running 18 psi of boost, we even saw 20 psi on a couple of passes. even after 180 passes and 12,000 miles. As everyone knows I did have two broken piston ring lands. Now that's not saying it couldn't happen but it didn't on mine and totally abused that engine and it finally gave up the ghost, I sure couldn't complain it, most have failed way before what I put mine thru.

[radz28]

Originally Posted by laynlo15

Back in the day when I had my 16ss with stock SBE I never had a valve spring failure running 18 psi of boost, we even saw 20 psi on a couple of passes. even after 180 passes and 12,000 miles. As everyone knows I did have two broken piston ring lands. Now that's not saying it couldn't happen but it didn't on mine and totally abused that engine and it finally gave up the ghost, I sure couldn't complain it, most have failed way before what I put mine thru.

I remembered your pistons, but didn't remember your valve train. Interesting... Maybe these valve springs are a little more robust than I thought. I'm not planning on running to 7000 RPMs (I have a hard limiter for 6800, but shifting right about 6500) or anything, if that matters, too. I'm sure that would play a role, too.

[jlaudio11]

From experience on other platforms I would say the higher you get in boost the more critical it is to not over rev or tag a limiter. Things a spring with higher seat pressure might be able to handle. So having your trans shifting correctly for the load and enough tire for the surface you're on.

[laynlo15]

Originally Posted by radz28

I remembered your pistons, but didn't remember your valve train. Interesting... Maybe these valve springs are a little more robust than I thought. I'm not planning on running to 7000 RPMs (I have a hard limiter for 6800, but shifting right about 6500) or anything, if that matters, too. I'm sure that would play a role, too.

We were keeping the rpm limits on the stock motor to about 6600 if I remember correctly, so I'm sure that had something to do with it more then the boost level. If your trying to run your motor up to 6800 or above on the stock springs your probably looking at a failure at some point. When I had my C7 and running NA we were turning that stock motor at 6700 with supporting bolt on mods and that was as high as I'd want to turn it. We are shifting the new Camaro at 6400 on 1-2 shift and 6500 thru the rest of the shifts and going thru the traps about 6100 rpms, we are going to try and stretch shifts out a little so its almost ready to shift into 7th gear going at the end of the 1/4 mile, so maybe 6450 1-2 and 6525 the rest of the shifts.

[radz28]

Originally Posted by jlaudio11

From experience on other platforms I would say the higher you get in boost the more critical it is to not over rev or tag a limiter. Things a spring with higher seat pressure might be able to handle. So having your trans shifting correctly for the load and enough tire for the surface you're on.

That makes sense. It's pretty consistent now, BUT - I went back and started reconsidering my 1-2 shift, and being a little more conservative with it. While I know I'll never have a problem on the street (because it wouldn't hook), I figure, on the strip and DRs, I could have an issue with it accelerating in 1st too fast to execute that shift on time. I don't make enough power that I'd think it would be an issue for the remaining shifts, but I did not think about the tire and surface aspect.

Thank you sir

Originally Posted by laynlo15

We were keeping the rpm limits on the stock motor to about 6600 if I remember correctly, so I'm sure that had something to do with it more then the boost level. If your trying to run your motor up to 6800 or above on the stock springs your probably looking at a failure at some point. When I have my C7 and running NA we were turning that stock motor at 6700 with supporting bolt on mods and that was as high as I'd want to turn it.

Yeah - the limiter was set to 6800, but I'm not trying to rev' it beyond 6500. Maybe I'll drop that limiter to 6600 if I go through with this, for more safety. Thanks Greg!!!

I had been reflecting on LT5s, too. It was my understanding those were running the same valve springs (as in most of the rest of the long block) as LT4s, and those are rated for about 14-psi, too. Now - 14-psi is not 18-psi, but I also know there's a safety factor that's always baked-in. Hmm...

[jlaudio11]

Originally Posted by radz28

That makes sense. It's pretty consistent now, BUT - I went back and started reconsidering my 1-2 shift, and being a little more conservative with it. While I know I'll never have a problem on the street (because it wouldn't hook), I figure, on the strip and DRs, I could have an issue with it accelerating in 1st too fast to execute that shift on time. I don't make enough power that I'd think it would be an issue for the remaining shifts, but I did not think about the tire and surface aspect.

Thank you sir



Yeah - the limiter was set to 6800, but I'm not trying to rev' it beyond 6500. Maybe I'll drop that limiter to 6600 if I go through with this, for more safety. Thanks Greg!!!

I had been reflecting on LT5s, too. It was my understanding those were running the same valve springs (as in most of the rest of the long block) as LT4s, and those are rated for about 14-psi, too. Now - 14-psi is not 18-psi, but I also know there's a safety factor that's always baked-in. Hmm...

Be careful how close you set your limiter, and hysteria to your desired shift rpm. Cant remember who said it, but that it needed to be 300rpm over your desired shift rpm. This is to avoid getting into the soft limiter etc as you are about to shift etc.

[radz28]

Originally Posted by jlaudio11

Be careful how close you set your limiter, and hysteria to your desired shift rpm. Cant remember who said it, but that it needed to be 300rpm over your desired shift rpm. This is to avoid getting into the soft limiter etc as you are about to shift etc.

Ooo. Thanks for the additional information