[mkpontiac]

Cliff or Others
In a recent thread on XE cams you noted that power in many engines using XE cams drops off significantly at around 5000 rpm due to valvetrain instablity.

Is this problem more prevelant in Pontiacs because of heavier valvetrain components?
What can be done to reduce the valvetrain instability?

You mentioned reducing weight by using stamped rockers, using thick wall push rods and playing close attention to valvetrain geometry.

Are there specific valvetrain components that are lighter? Recommendations
How much stronger springs would be necessary?

Mark

[stu72]

Is this problem more prevelant in Pontiacs because of heavier valvetrain components?
What can be done to reduce the valvetrain instability?


If you Google about these XE cams you will find that pontiacs are not the only ones with these sames problems. But everyone has there own experiences.

[ponjohn]

read here: http://forums.maxperformanceinc.com/...d.php?t=609652

All the XE HFT info you'd want to know.

[Steve C.]

Some of this will be considered overkill on the street by some but I'll throw it out for conversation, not necessarly a firm recommendation.......

Don't skimp on $$$ for the valve springs, use a good quality.

As we know, the spring must be sufficient to control the valve action at the highest expected engine speed without being excessive. Trick is determining how much, I suspect most use the cam manufactures recommendations.
Many people mistakenly think that using higher seat pressures causes a reduction in horsepower. According to some articles this is a common misconception. And don't forget that once run in a valve spring typicaly looses spring pressure, a 10-15 pound reduction in seat pressure might be typical with many springs.

If the need for a differant length pushrod and it's 5/16 you might consider getting them with a thicker 0.116"-0.118" wall thickness rather than the typical .080"-.083".
Manton or Smith Brothers would be my choice. I also understand Comp now has them in a 0.125" wall.

"The effective increase in weight between the two pushrods may be small but provides a huge increase in valve train stability. Remember the valve side of this valve train is the critical side where any weight savings will make marked improvements. No matter what we change, valve train stability is the goal."
http://www.mantonracingproducts.com/Pushrod-Info.html

Consider a stud girdle, to me a must with a aggressive solid cam. But in this situation a luxery with a small flat tappet. It was Dick from Indian Adventures that commented about watching under strobe lights the rocker studs move around like "hula dancer girls" without a stud girdle. An overkill for most street combos, but some consider a shaft-mounted rockers to improve both durability and stability.

Consider hollow stem valves to reduce weight. Obviously, lightweight valves require lower open pressures and tend to reduce pushrod flexing and valvetrain separation.

Rocker Arm Geometry And Valvetrain Alignment
A Detailed Explanation Of Valvetrain Alignment Goals
http://www.circletrack.com/techartic...try/index.html

Now a question to the engine builders or in general here about the use of stamped rocker arms... what's the situation ? Is it a reduction of weight or are they stiffer than a good quality rollerized rocker arm ? Something seems fishey here, unless its required for a certian class of racing.

[Steve C.]

Not Pontiac specific, nor a tilt toward 'street' operation or in the rpm realm of most, but some will find this of interest. And it relates.


"Rocker Arm Comparison Test - Design Matters"
We Break Out The Dyno Mule To Test Whether Different Rocker Arm Designs Affect Power

http://www.circletrack.com/techartic...son/index.html

[ponjohn]

Steve-

I need to ask: if the cam, lifter and pushrod are compressing the spring. The resistance the spring offers greatly exceeds the valve weight, how does the valve weight play into this?

[Steve C.]

Also consider Beehive springs.
Higher RPM with less spring, means nore power and reliability.

http://www.compcams.com/Community/Ar...ID=-1483018418



John, I'm parroting material from a magazine article. I'll go back and look for details if they were presented. Or hopefully someone here might chim in on the subject.

In the meantime....

The Science Of Better Valvetrain Control
Finding Power Gains By Considering The Valvetrain As A Whole - The Science Of Better Valvetrain Control
By Jeff Huneycutt
Photography by Courtesy Comp Cams
http://www.circletrack.com/techartic...rol/index.html

[66 Glide]

[Steve C.]

Watch a valve bounce of the seat towards the end of this video...

http://www.youtube.com/watch?gl=DE&hl=de&v=_REQ1PUM0rY


And this....

PUTTING THE VALVETRAIN ON A DIET
http://www.enginebuildermag.com/Arti...echnology.aspx

A lighter valve means the engine can rev higher, pump more air and produce more horsepower. A lighter valve also means less stress on the valve springs, retainers, rocker arms, pushrods, lifters and cam lobes. According to one supplier of hollow stem performance valves, the valves are good for 300 to 350 more rpm with no other modifications (same springs, rockers, pushrods, etc.).

http://www.enginebuildermag.com/Arti...ce_valves.aspx

[Steve C.]

Similar question or situation on a Buick board.....

http://www.v8buick.com/showthread.php?p=1494071

Ideas or opinions are stated but often no details for cause and effect are presented.

[ponjohn]

The more I read about this XE "crap" the more I think about making a cam change even if I don't replace the heads.

In the other threads I mentioned an UD lobe that is very similiar 240/246 to the XE grind. Might be a very good comparison. See if it pulls harder.

The way my car pulls now is hard on the low end then levels off, not a whole lot upstairs.

Ideas on an equivalent cam that stays around 515 lift.

[Mr. P-Body]

Having installed more than 250 XE cams in the last 10 years, and having not found ANY "valve train instability" issues, I suspect there's other "issues" at work in those engines with problems.

Cams and valve trains are often misunderstood, and fingers get "pointed" in all the wrong directions. In many cases, it's "easier" to blame the cam company, rather than admit one didn't use ALL the recommended valve train components, or follow instructions completely. Or that one isn't really sure HOW to measure installed height and seat pressure... Or, the most common one, "The guy at Summitt said these were the right ones!"

Sorry if I stepped on any toes, but when I read about "Comp crap", I MUST say what I have to say. I would ask the next Comp "naysayer" what cam they have in THEIR engine. I know of at least a couple around here that bad-mouth Comp, but RUN Comp. Go figger...

Jim

[ponjohn]

JIm-

I guess I fall into the category " I wonder if...."

It would run better with a different cam and would it idle better. It is a plain nasty idle at a 1000 rpm in gear (xe284). Maybe the idle is what it is.

John

[Steve C.]

Unless specified by rules prohibiting the use of roller rocker arms, or if the use of a rollerized valvetrain parts is cost prohibitied, in my limited searches I couldn't come up with a tech article or dicussion suggesting the advantages of a stamped-steel rocker arm for high performance use. Most suggest they should be replaced.

Example....
"Roller rockers are infinitely stronger than stock stamped steel rocker arms and are more resistant to bending and breakage under high spring pressures at high rpm. Stock pressed steel rocker arms are prone to failure in high performance applications. A high rate of fulcrum wear, flexing, cracking, splitting and breakage are common problems that will result in power loss or possible piston failure due to detonation of the incoming air/fuel charge. The traditional metal tip on standard rockers literally drags across the valve tip as the rocker opens and closes causing high side loading on the valve. This inside force leads to irregular and rapid valve, valve guide, and valve seat wear in many engines."

Again the material I found suggests the better quality aftermarket stamped-steel rocker arms (long slot) just offer a high-quality replacement for budget or stocker-minded builds.

[slowbird]

I have to agree with Mr P-Body we ran the xe274 cam for about 4 years shifting between 6000 to 6300 rpm and never had any valvetrain issues what so ever. In those 4 years the cam saw about 25,000 street and race miles and not one issue. Maybe we were just lucky.

[Steve C.]

Unless specified by rules prohibiting the use of roller rocker arms, or if the use of a rollerized valvetrain parts is cost prohibitied, in my limited searches I couldn't come up with a tech article or dicussion suggesting the advantages of a stamped-steel rocker arm for high performance use. Most suggest they should be replaced.

Example....
"Roller rockers are infinitely stronger than stock stamped steel rocker arms and are more resistant to bending and breakage under high spring pressures at high rpm. Stock pressed steel rocker arms are prone to failure in high performance applications. A high rate of fulcrum wear, flexing, cracking, splitting and breakage are common problems that will result in power loss or possible piston failure due to detonation of the incoming air/fuel charge. The traditional metal tip on standard rockers literally drags across the valve tip as the rocker opens and closes causing high side loading on the valve. This inside force leads to irregular and rapid valve, valve guide, and valve seat wear in many engines."

Again the material I found suggests the better quality aftermarket stamped-steel rocker arms (long slot) just offer a high-quality replacement for budget or stocker-minded builds.

[Steve C.]

IMPORTANT>>>> in this discussion keep in mind this reported Comp XE stability issue revolves around the use the XE hydraulic flat tappet lobes only... and not the other XE solid tappet, XE hyd roller or XE solid roller lobes.

[ponjohn]

Slowbird

What was the combo and times ?

[71 Ventura II]

Originally Posted by ponjohn

JIm-

I guess I fall into the category " I wonder if...."

It would run better with a different cam and would it idle better. It is a plain nasty idle at a 1000 rpm in gear (xe284). Maybe the idle is what it is.

John

FWIW I feel part of the issues with the XE drop off, so to speak, is related to spring rates. I agree with Jon about the XE284 has a terrific radical idle maybe even more radical in my 406! LOL But I'm almost convinced the fast ramp technology complicated further by my 1.65 rockers wants more spring. I'm running the Crower #68404 duals which are a very high quality unit just not strong enough. IMHO My logic is based on this BIG cam in my 406 falling off the table at only 5500 rpm's. A cam of .557-.561 @.050 .240-.246 adv 284/296 should pull easily to 6000+ given the head flow is up to the task which mine should be. JD

[roadrage david]

Originally Posted by slowbird

I have to agree with Mr P-Body we ran the xe274 cam for about 4 years shifting between 6000 to 6300 rpm and never had any valvetrain issues what so ever. In those 4 years the cam saw about 25,000 street and race miles and not one issue. Maybe we were just lucky.

same here !!! then again i got 461ci MR-P body engine with the XE284 idle is great

http://www.youtube.com/watch?v=LkLQXSygmQM 900 rpm