408 C5 Corvette 6450 rev limit

[edcmat-l1]

An intake manifold or other restriction won't do that though. Not even an elbow collapsing or something will make MAP higher. Pressure would continue to fall off with a restriction as engine speed climbs. Nothing in the air intake system can make the pressure go back up unless there's a big hole that opens up and vents to atmosphere. Though why it wouldn't leak more at low speed/high vacuum doesn't make sense. Know what does make sense of all these various oddities? Valve float.

Yes I agree. Not sure why you're trying to argue with me. After looking at it closer yesterday, I agree it doesn't look like an intake/throttle body issue.

My comments about it not pulling to 7500 rpm are complete aside to that.

[Alvin]

Do you have roller rockers on this? What type of rocker?

I agree that this mostly looks like valve springs.

I'll bet you have 20 rwhp in a good intake and a decent throttle body but that isn't going to cause it to nose over like this. I doubt you would see 10 rwhp from the throttle body alone.

Sure the cam is not off a tooth? I've been seeing that a lot lately.

[JamesTheriot]

I'm positive that the cam gear is not off a tooth.

I think the easiest thing would be for me to pull the covers, loosen the rocker adjusters and adjust them to 1/2 turn after zero lash like most people do and go run the car one time and see if it makes a difference. Maybe I have them a tad too tight and the valves are hanging open at high rpm, I'm not even sure that that is possible unless you have the lifter bottomed out. It'd be easy enough to check though.

My main issue with thinking that one of those parts is wrong (springs, rockers, pushrod length, ect) is that this engine was in another car and shifting over 7000 rpm. I did not change the valvetrain at all except for changing the BTR nitrous cam for a BTR NA cam. I also reset all the valve lash/preload when I assembled the engine so its possible I just have them tighter than they need.

[Alvin]

I've never seen roller rockers make power on a LSX.

I've consistently seen them cause setups to nose over far sooner than they should. Weight over the valve tip is always higher and causes valve train stability issues.

[edcmat-l1]

I'm positive that the cam gear is not off a tooth.

I think the easiest thing would be for me to pull the covers, loosen the rocker adjusters and adjust them to 1/2 turn after zero lash like most people do and go run the car one time and see if it makes a difference. Maybe I have them a tad too tight and the valves are hanging open at high rpm, I'm not even sure that that is possible unless you have the lifter bottomed out. It'd be easy enough to check though.

My main issue with thinking that one of those parts is wrong (springs, rockers, pushrod length, ect) is that this engine was in another car and shifting over 7000 rpm. I did not change the valvetrain at all except for changing the BTR nitrous cam for a BTR NA cam. I also reset all the valve lash/preload when I assembled the engine so its possible I just have them tighter than they need.

That may be your problem. I've seen aftermarket roller rockers cause weird stuff up top. Just like yours is doing. You really can't do much better than stock rockers with trunnion kits for 99% of the applications out there on the road.

I've never seen roller rockers make power on a LSX.

I've consistently seen them cause setups to nose over far sooner than they should. Weight over the valve tip is always higher and causes valve train stability issues.

Exactly this.

Not to mention no one spends the time to get the pushrod length and fulcrum point in the right position to get the roller centered on the tip which causes further valve train instability.

[SiriusC1024]

Offset the weight of the roller tips with titanium retainers. Check wipe pattern with a permanent marker.

[JamesTheriot]

I did check the roller pattern with a marker when I assembled it. It was very close to centered, not perfect, but nothing I would consider a problem. Definitely not close to either edge at all. I will post up a log tonight after I loosen the adjustment up.

I also have Titanium retainers on it now.

[ns158sl]

Im pretty sure ls7 lifters should be .070 to .100 preload. I think I'd double check with a dial indicator when you reset preload.

[edcmat-l1]

I did check the roller pattern with a marker when I assembled it. It was very close to centered, not perfect, but nothing I would consider a problem. Definitely not close to either edge at all. I will post up a log tonight after I loosen the adjustment up.

I also have Titanium retainers on it now.

Did you drop in solid roller lifters to check? Install checker springs? If you didn't at least use checker springs it's not correct.

You can't just use the hydraulic lifters and the installed springs. There's too much spring pressure to check by cranking the engine over by hand. You'll always have the lifter bleeding back when you roll the motor over and it opens the valve.

Edit: I've never seen a set of roller tip rockers that didn't need some amount of shim to get them right.

[edcmat-l1]

Im pretty sure ls7 lifters should be .070 to .100 preload. I think I'd double check with a dial indicator when you reset preload.

Any of the stock style lifters, if not limited travel should be fine at 1 turn worth of preload which is almost exactly .050. I think it's .048 actually.

[SiriusC1024]

Check spring install height as well. Shim as needed.

[JamesTheriot]

Did you drop in solid roller lifters to check? Install checker springs? If you didn't at least use checker springs it's not correct.

You can't just use the hydraulic lifters and the installed springs. There's too much spring pressure to check by cranking the engine over by hand. You'll always have the lifter bleeding back when you roll the motor over and it opens the valve.

Edit: I've never seen a set of roller tip rockers that didn't need some amount of shim to get them right.

I thought a little about this when I was checking the pattern. I ran the adjustment all the way down to take the slack out of the lifter before I began checking.

The rockers are shimmed, came that was when I bought the engine. Every shim is the same size.

When you say "should be fine at one turn of preload" are you talking one turn on a pedestal adjustment, or pushrod adjustment?

[edcmat-l1]

I thought a little about this when I was checking the pattern. I ran the adjustment all the way down to take the slack out of the lifter before I began checking.

The rockers are shimmed, came that was when I bought the engine. Every shim is the same size.

When you say "should be fine at one turn of preload" are you talking one turn on a pedestal adjustment, or pushrod adjustment?

I definitely don't like the sound of that. That's too much pressure bottoming out the lifter. No telling how close you are to lifting the valve off its seat. Also, no telling if there's any travel left to compress when you start cranking the valve open. Definitely not a method I would recommend. Using the zero preload zero lash method at least you have a good "feel" of all the parts while you're trying to mock it up and measure everything.

Another thing to check with the big body roller rockers (forged or billet aluminum) is the clearance between the body of the rocker and the spring/retainer. I've seen a few interfere/hit/rub, whatever.

When I say "one turn of preload" I'm referring to the stock rocker bolt.

[blindsquirrel]

Titanium retainers on a street car are great as long as you never ever get an oil analysis done, and make sure to chalk up any bearing failures to cosmic ray strikes or Mysterious Acts of God's Love. For racing engines that get freshened regularly on a schedule it's not much of a problem. But they do not belong on street cars that don't get taken apart until something has already gone wrong.

Finding zero lash with the adjusters in aftermarket rockers is real easy even on a 'dry' lifter (same for stud mount rockers with poly-locks). Lobe on base circle, with two fingers turn the adjuster down until it touches, that's zero lash. It's a lot trickier with stock style crimped locknuts on studs, that's a different deal.

[abc]

My main issue with thinking that one of those parts is wrong (springs, rockers, pushrod length, ect) is that this engine was in another car and shifting over 7000 rpm. I did not change the valvetrain at all except for changing the BTR nitrous cam for a BTR NA cam. I also reset all the valve lash/preload when I assembled the engine so its possible I just have them tighter than they need.

You may want to look at this statement again and think about what you have done wrong. Put the other cam back in it and see if your problem goes away or do as I originally suggested and test it with stock rocker arms. I have no idea of the cam profile on either of those cams but the cam profile is as important of a player in valve train stability as any other piece in the valve train.
We don't know what is wrong with your combo. but it is more likely mechanical than digital based on the info. given. I think it was suggested for you to call BTR and ask him about the cam profiles and your situation, he may or may not be able to add some insite.

Simple lash/preload adjustment is not your issue, geometry may be but not preload, unless they are way too loose, which I don't believe that is an issue as you have not mentioned excessive noise at idle. Too loose is worse for valve train stability than too tight. One of the first signs of too tight is the engine will be hard to start, if left uncorrected many other problems will be exposed.

[Alvin]

Titanium retainers on a street car are great as long as you never ever get an oil analysis done, and make sure to chalk up any bearing failures to cosmic ray strikes or Mysterious Acts of God's Love. For racing engines that get freshened regularly on a schedule it's not much of a problem. But they do not belong on street cars that don't get taken apart until something has already gone wrong.

Finding zero lash with the adjusters in aftermarket rockers is real easy even on a 'dry' lifter (same for stud mount rockers with poly-locks). Lobe on base circle, with two fingers turn the adjuster down until it touches, that's zero lash. It's a lot trickier with stock style crimped locknuts on studs, that's a different deal.

I've heard people shy from them on street engines. I've never taken one apart and saw any wild wear.. People think titanium and whoo wow... Really it is almost as hard as steel but almost as light as aluminum.. That's it.. A modern design tool steel retainer can be made with less material because it is stronger and only end up a gram or two heavier than a Ti retainer.

Still that isn't going to offset the extra weight a roller tip rocker adds. Edm backed me up... anyone who has spent a career on the dyno will tell you.. they just consistently cause high RPM issues. It would be easy to pull them for a stock style rocker..

[SiriusC1024]

Well he's going to have to figure something out. Without roller tips that cam is going to wear out the valve guides pretty quickly, especially those bronze ones. Maybe longevity is taking a back seat to power on this build?

[Alvin]

Well he's going to have to figure something out. Without roller tips that cam is going to wear out the valve guides pretty quickly, especially those bronze ones. Maybe longevity is taking a back seat to power on this build?

This what they were saying with TFS heads back when they came out.... We found you can shim the pedestal and get a nice wipe pattern on the tip. A roller tip is just a easy fix for bad geometry

[JamesTheriot]

Definitely not trying to trade longevity for power, my plan with the car was to have a mid 10 second car that I could drive to cruise nights, car shows, to and from the track, ect. I want to get this right; with the clutch and fuel system and other components I am in the build for a little over 15k now. If getting the valvetrain right is going to cost me another 2k then it just is what it is.

I loosened the rockers, didn't change much. got maybe 50 more rpm out of it but that could be random, felt the same.

Tried to install my stock rockers, The hardened pushrods that came with the engine are only 7.100". I tried test fitting my stock push rods and they were still way too short. Now I would need a checker to measure the correct length and buy pushrods just to try the stock rockers.... This is slightly irritating ha-ha.

Rockers half turn.hpl

[blindsquirrel]

If you go more than 400lbs open pressure, allegedly, the stock or stock-type non roller tip rockers and valve tips start having wear issues (and it's not just a geometry thing). The only roller tip rockers that are as light on the valve side/low MOI as stockers is $2200 Crower stainless shaft rockers. Good reason to limit the build to something that doesn't need more than 400 open.