History repeats itself. The turbo car is broken again and will be for a while..

Maybe no Buick valvetrain will work under boost for extended use..o No:

 

Very strange stuff here... I am not sure what the answer is, and not sure how to find the root cause now that it is broke and out of the car.

 

Me neither.. If James is breaking the stock stuff and I'm breaking the not so stock stuff and we are running somewhat similar cams.. Then what????

I'm seriously thinking of scraping the project altogether.. I'm not normally a one to give up, but I'm running out of options..

I'll take the heads to the machine shop and see what they have to say..

 

Jay, before I offer more comments, who is "James" and how is his setup both similar and different to yours?

Devon

 

I don't know how many "miles" are on my engine (mostly 1/8th and 1/4 mile passes), but so far the stock valve train is holding up.

Did I just jinx it? :error:

In Bowling Green last year I was shifting at 6200, running 8 lbs of boost.

 

He goes by "turbo455" I guess the similarities are that we have a somewhat similar cam pattern..

he has a 455 in a Camaro..

He's posted plenty of carnage on here but I've never seen anything about valvtrain issues..

 

Stock set up. I did not say anything about this guy having the rocker conversion set up. I was referring to the pictures that jay3000 posted. I asked a simple question no need to get on my case about it. The pictures looked like the roller rocker conversion kit to me. I bought my roller rockers from TA over 15 years ago and the engine has went to 6200 rpm numerous times. I also ran nitrous for 3 years straight and if that don't beat on the system nothing will.

Sorry your having trouble I wouldn't wish it on anyone.

 

Jay, sadly I don't have any suggestions either. Obviously the V6 guys have it figured out, and the cam specs don't seem that different. James has not with certainty found his cause. I'm grasping at straws, but am wondering if heat is causing the exhaust valve to bind slightly.

I'm going to do some digging in the V6 arenas and see if there is anything I can find about exhaust valve issues.

 

Sorry Guy, I didn't mean to jump on you. I've seen several suggestions here, and fear that there is some root problem here that isn't being addressed. My concern is that if Jay just throws in a bigger bolt, adds bolts, changes heads and uses a different rocker setup etc, he is just going to end up breaking something else, like James.

 

I will be more specific, and we'll need James' input at this point I think.

Which rockers has James seen fail and on which cylinder & which valves?

More info will help regarding his setup too if anyone's going to be able to draw any parallel between the two builds as has already been inferred.

What bothers me is that Jay's seen two failures in the same place now. If the failures James has seen in any way mirror Jay's, it's worth looking into. The more the builds differ, the less might be learned.

Devon

 

Am I the only one who thinks that valve float could cause extra stress on the valvetrain? Jay was using stock valvesprings that are barely adequate for a stock engine let alone a boosted one. Read my previous posts for details on why boosted engines require more valve spring pressures.

 

No, of course it's a possibility, especially if the spring(s) at that one end of the head are a problem. How remote the possibility might be I can't say.

The problem is the number of variables. Valve spring testing on all 16 would give us more insight. If one or two on that end test poorly compared to the other three corners, there you go. If not, back to square one.

Jay has to decide what to measure and what to test.

Devon

 

When I ran nitrous cylinders 2 and 4 were running the leanest. Since there is a carb with the Turbo set up one of the cylinders might be running a little bit leaner. That might be putting a lot of back pressure on the Turbo system. Remember the V6 Turbo runs with fuel injection and even so both are running the same type of cam maybe the car with the carb needs to have the valve timing events changed some. I do not think that the stock valve springs are helping the set up either.

If the other person (James) is running the shaft system with the stock rockers and is breaking them it has to point back to the Turbo system with either valve timing events because of using the carb or there is some kind of back pressure pushing on the exhaust valve before it is closing. That cylinder could be running a little leaner. I also use the Comp Cams Pro magnum lifters that use the check ball in the lifter and these have worked very well with my set up.

I do not know what holds down the bar for the conversion set up but from what I read here it sounds like the bolt set up could be done differently but it really does not sound like this is the real problem since someone else is using the shaft system and breaking the rockers is that set up. The bolt down is now below the rockers now as compared to the shaft set up where the bolt is above the rockers. Can a larger torx or a allen head screw be countersunk into the bar to help hold this down better or is there just not enough room to do this. I do not know what really is holding this bar down on the heads so I may not have the correct info here. There seems that there is going to be more of a rocking pressure on the bar from the spring and pushrod since it is below the rockers instead of being above the rockers like in the shaft system.

I am not trying to knock this system at all I am just trying to throw some kind of idea out there to get your minds going. The roller rockers from TA I see are at about $700.00 now and when I got mine I think they were at $450.00. So if the conversion set up saved $400.00 it was worth doing.

 

Got the heads off and all of the fasteners out.. I guess I'll run them by the machine shop and see what they think..

 

Don't let them lose track of which springs & hardware go with which cylinder's intake & exhaust valves.

Devon

 

I'm thinking the engine itself is just not designed to be running as hard as you guys are running them. The v6 crowd had an engine that was developed and tuned through the years to make the big power that the LC2 guys are making. Remember that it started out as a carb'd motor that made the same power as the Olds 307 did.

The Chevy guys have tons of aftermarket and even corporate development behind their engines. Plus alot of them tend to run slightly higher rpms which helps with the big hp numbers.

I think you guys are basically the pioneers and are going all out right from the start. It might be a situation where someone needs to start with a low boost setup using a conservative cam and then turn up the boost until something breaks. Then people can see where the stress really lies in the system.

 

Is that so we can tell if that exhaust valvespring was weak???

 

That and any other tiny detail that looks different in your problem area. Even stupid things that outwardly shouldn't be a big deal. Excessive guide wear, minor differences in stem heights, spring installed heights, etc. I'd even be looking at the spring dampeners. You and your shop need to have your Sherlock Holmes hats on; leave no stone unturned, so they say. You're not necessarily looking for problems, make note of anything at all that even looks different or unusual.

I'd even put the degree wheel on and see if all 8 of each intake & exhaust lobes are behaving the same.

Devon

 

I was running over 16 psi of boost on a 215 and never had any sort of a valvetrain issue. Of course, that was with a mild cam, but no signs of stress on the valvetrain. A typical exhaust valve would be seeing between one and two pounds of loading for each psi of cylinder pressure when it opens. So even if residual cylinder pressure was 200 psi (which it likely is not) at the bottom of the stroke, worst case is an initial 400 lbs on the valve stem until the seal is broken, while the lifter is still on the slow part of the ramp. That is nowhere near enough to break shafts, stretch screws in two and bend stuff.

Now I do know of something that can, and have seen it first hand. A 215 was snapping the ends off the rocker shaft, usually just about the time the engine got fully warmed up and had a load put on it. Took us awhile to figure out what was doing it, but with the increase in temperature we were getting coil bind on the springs. That may not be it in your case, but I'd be willing to bet it's something similar. Guides that stick up a little higher than stock and are being struck by the retainers for instance. That's where I'd be looking.

JB

 

Jim is in the ballpark here. The only way for this to happen is for the valve side to bind up. Stock valve springs may have 80# opening pressure and 200# at max lift (numbers are imaginary but come from what I saw on my 455 with "super" stage 1 springs.) That is simply not enough pressure to do what has happened to this motor.