Jim85IROC

iTrader: (6)

Anybody here with real-world experience of breaking LS3 intake valves with an aggressive cam & valve springs?

I bought LS3 heads over L92s with the assumption that the lighter valve wouldn't take as much of a pounding with a big cam (say a 230 intake, .625 lift with an aggressive lobe). I also figured that I could get away with a little less spring due to the lighter weight in order to further reduce stress on the valve.

But, I'm also hearing that some guys are breaking the LS3 intake valves with big cams. I'm trying to see if there are some real-world examples of this, or if I might be getting worried over nothing. There seem to be a lot of LS3 corvettes and f-bodies making big power on monster cams, and if this was a common problem I'd expect to see a million posts here.

Anybody have some direct experience with LS3 valves breaking?

Squirts11

iTrader: (14)

Why would the valves be breaking unless they either made contact with a piston (either lack of PTV or valve float) or had a poor valvespring installed (either improper seat pressure, improper installed height, or underrated for cam lift)?

Jim85IROC

iTrader: (6)

My understanding is that the hollow valves are weak at the base of the stem, so slamming them shut with an aggressive cam profile can cause them to literally snap off just like you pop the head off of a dandelion.

lstvr

A friend of mine has has his valve break with a 230ish cam, it broke the head off the valve and WRECKED the engine. I have no idea if it is common or not, engine was an LS3 around a year old.

ramairJP

iTrader: (3)

Not directly related, but the LS7 hollow stem, sodium filled exhaust valves have a similar problem. They also seem to put a lot of wear into the guides (excess heat transfer?) and the resulting misalignment eventually fatigues and pops the head off.

Robin L

I have said it before and I ill say it again. 90% of all valve failures is due to loss of control of the valve.

Once you lose control it will break when it hits the piston.

I installed the LS3 valves in the GM Performance Parts CNC ported L92 heads on my LSA crate engine.

I also installed comp Ti retainers and Comp Valve Springs. I use a Lunati cam 237/245 with a LSA of 115. The lift is .578.598. On the LS3 the PTV is .100 on both intake and exhaust on the engine that I checked.
I also installed Trend .110" wall custom pushrods. With a decent spring and an agressive lobe the .080 wall can store energy and cause problems at high rpm's.

I set the limiter at 7000 RPM. The engine revs clean to the limiter and has never missed a beat.

I have heard of problems with the exhaust valves on the LS7. I would replace them if you plan to change the cam or run at high RPM's. It's cheap insurance.

Robin

Hans Grüber

iTrader: (2)

From what I read on here, more people seem to have had the L92 valve fail. The L92 are also a 2-piece design if I recall correctly.

WKMCD

iTrader: (2)

I ran stock L92 valves for about 8k miles with a .660 lift cam with no problems. I also run PAC 1521's and Morel link bar lifters all setup properly. As Robin said - lack of control is the problem the great majority of the time.

SweetS10V8

iTrader: (4)

I run lightweight LS3 vales myself and havent had any problems. I too took a lot of time, thought, and looked at a lot of data to decide how to get the most incontrol/stable valve train I could get.

I run an LSL lobed cam 219/235 .607/.621, 918s(shimmed .060" from coilbind), Tool steel retainers(6g), Stock rockers with Comp trunion upgrade, Comp .105" wall pushrods, Comp 850 lifters.

ringram

I lost a lifter roller which siezed, scored the cam and trashed the bearings. So make sure your lifters handle the pressure and lift while you are at it!

miami993c297

iTrader: (6)

A video of my 418Ci on the engine dyno...

Big intake valve 2.100 head, 5.450" length, .290" tip and a .311" stem diameter, revving to 7500rpm like a champ:



Christian

racer7088

Exactly, we haven't seen any issues with them so far at all. Also I have seen tons of deals where valve heads broke off and 90 per cent were on regular valves as they were bad setups that were out of control. Haven't ever had any of our hollow stem stuff fail ever so far.

racer7088

Jim you bought the better heads and just remember NOT to take valvetrain setup advice from those guys breaking intake valves! I wouldn't knock spring pressure way back down though if you want reliability as that will possibly cause issues depending on what you are doing with any valve. The stock stuff is designed for very low spring pressure and is a well engineered sytem but the aftermarket stuff is of course more aggressive and likes more spring pressure in general.

miami993c297

iTrader: (6)

And this is the video of the same engine with the same agressive camshaft but the wrong valve-train...

The power was going down past 6250rpm...and was identified by most as Miss-Firing due to electrical or tuning or whatever...

VALVE FLOAT sirs...



Take care of the heavy valves with an aggressive camshaft profile if you want to rev your engine past 6400rpm...

Christian

Jenson

iTrader: (32)

Im looking at doing this comp LSr cam: 239/255 - .624/.624 with their 26926 springs and tool steel retainers. Sounds like Im going to need some beefier P/rods than I had planned though.

Jim85IROC

iTrader: (6)

Are the LS7 lifters sufficient or should I be looking elsewhere?

1.8t

I broke the TC on my old LS3 coupe and even with severe piston to valve contact, none of my intake valves broke at all, they just bent. There has to be a more severe issue than just springs pressure and aggressive cams to break a hollow stem LS3 intake valve.