Does anyone have any experience with issues surrounding valvetrain velocity and higher engine rpms?

I am planning a sbc that will for a street engine turn some pretty high rpms. My question has to do with selection of roller vs flat tappet.

Question: does the weight of the roller valve train begin to have a counter productive effect above certain rpms, say 6500rpms for example, due to it's excessive weight?

Some theory has it the flat tappet is lighter therefore can perform better during higher rpm duty. Also, I've read a few cases of 4 inch bore roller blocks cracking in the valley under high rpm loading supposedly because of the stress of the heavy valvetrain.

I am familiar with the functional trade offs between roller and flat tappet cams and lifters eg, wear, driveability, emissions, etc and don't really want to get into that debate.

Cost ($$$) is an issue. I am aware you can buy roller setups that will spin to 9k without issue but I don't want a $12k motor. I also do not want to build a grenade first time I hit the gas it lets go.

If I go with roller then I need a roller block if not any 4 inch sbc block will do. At this point valvetrain selection is a fork in the road. Do I go roller or not? The engine will be capable of 7500rpms.

 

You can get 7500rpm reliabily with either a flat tappet mechanical cam or a roller mechanical cam.

But the valvetrain (springs etc must be matched to the specific cam.)
A roller set up can/will lift the valve much faster (and weights more) so it will need a spring with more pressure. May also want to use a "rev kit".
A roller setup can tolerate these higher spring pressures without the wear penalty.
But again, 7500-8000rpm is do-able with a flat tappet setup. You need to consult with the cam manufacturers tech dept to get the right valvetrain setup for the
cam.

Wether roller or flat tappet, a cam designed for smooth
extended high(er) rpm operation will have a different lobe shape than a cam designed for torque but with a lower rpm limit. (rate of lift).

Got to ask, Are you just infactuated with haveing a super high reving motor or does the motor's design require such a high rpm range? Radical, high rpm race motors do not make good street motors.

 

i don't think there's any point where a flat lifter out preforms a roller. you can put a roller into any block it doesn't have to be the factory set up. actually you'd be ahead for a preformance application to use a non roller block and use the original roller design and not GMs.

 

Except the $$ bang for the buck$$$ point.

Generally speaking a roller setup will out perform a flat tappet setup but you can make tons of power with a
flat tappet setup.

The roller set up is going to cost you more money no doubt.

What kind of horsepower numbers are you after?

 

a soild roller setup could easily net you the ability to spin the valvetrain that fast...


going hyd roller will cost a lil more since you'll need a rev kit.....


i donno about a hyd flat tappet spinning that fast... someone has probly done it, but i have never seen it done and the "common" off the shelf parts i know of wont do it..


for any performance app, id stay with a roller.... if you needed to spin it that fast, id stick with a solid roller.



poke around enough online, and you can find good used aftermarket solid roller lifters for around $100...

and no, you do NOT need a "roller block"....

 

yeah f bird you're right cost is like nite and day between rollers and flat cam set ups. cost always seems to enter into everything we do doesn't it. i keep thinking i'm going to make a post some time "whats the best way to spend the most money for the least preformance gains" should be fun to see the responses.

 

a HUGE list has already popped in my head...



athough rollersetup isnt really anywhere in there... atleast for a street car.

 

The flat tappet setup is less costly initially, but will be more expensive in replacement parts and labor in the long haul - especially under higher stress applications.

As for the least Bang/$$$ -

• TB airfoil?
• Underdrive sheaves?
• MAT relocation kit?
• 52mm TB?
• Chrome covers?
• "Designer" plug wires?
• Bosch +4?
• Blue headlights?
• 10-blade wipers?
• TPS amplifier kit?
• HyperTech PROMs?
• 1.6:1 Rockers?
• Grocery cart spoilers?

 

Does anyone have any experience with issues surrounding valvetrain mass and velocity at higher engine rpms?

 

i think pretty much everyone replying in this thread does...


so whats your question?



if its "should i go roller?" that depends on how much you want to spend AND how long you have to get the parts..

if you're not in a rush, you can do what i did and score a set of solid roller lifters (that work in ANY small block chevy ) for $100 ish
new is closer to 500... and its not too hard to find slightly used for 150...


other then that, $10 more or so for the roller cam timing chain and a $7 cam button theres not much else too it....

of course that assumes you dont already have, the correct length pushrods and are going to get what you need... and you havent bought valvesprings yet... just get the right ones for the cam you buy and you're set...


for the cam, look around online... used roller cams are everywhere...

 

btw, if you're asking us if you need Ti valvespring retainers or anything exotic like that........... no, not really.... use the correct valvesprings for the cam......

btw, no matter how much power you're after, you probly wont have to spin it past 7k.... *shrug*

 

you left out:

• K&N filters
• performance chip (well you said hypertech, but i thought id mention it again )
• premium gas in mostly stock engines
• MSD or any other ignition on a mostly stock motor
• big one... catbacks before headers.... waste.
• electric waterpumps
• 160* thermostats - cheap but worthless.
• GAUGES.... gee lets spend $200 to have a cool lookin way to see what the engine is doing.
• obviously anything cosmetic.. from shaved handles to wings to new grill...

 

Peak velocities of valve train components are probably not as much a factor as the valve acceleration rates (which will determine the velocity at ant given RPM). That will indicate the spring rate you'll need, and whether or not you need to lighten up the valve train or add a rev kit. At some RPM, shaft rockers are almost essential to distribute the load. Exactly where that RPM point might be depends on many variables, and you'd have to calculate the masses and kinetic of the valve train components to decide if you need the extra styrength of shaft rockers (or stud girdles).

Also remember that valve train component acceleration rates can be kept lower if higher ratio roackers are used, liek 1.6 or 1.7:1.

 

In addition to what was has already been mentioned, I would also like to add that any weight (or mass) added to the pushrod side of the valvetrain will have little effect on overall performance/reliabilty. This is especially true with higher ratio rocker arms, where the spring force is multiplied on to the pushrod side of the valvetrain. The valve side of the rocker arm is where a change in weight will make a significant difference. If you have a particular cam from a certain manufacturer that you're interested in, also install the related valvetrain components that they recommend, and you should be good to go.

 

Only if the cam is designed for this. ( lower lifter volocity)

Increasing the rocker ratio withe same cam tends to lower the rev limit with the same valvetrain.

An important consideration is the natural harmonic resonance that occurs in the springs themselves and
and the whole valvetrain as it moves and flexes.
The higher the mass the lower the natural frequency of resonance. Sometimes a larger spring actually lowers the rev limit even thou it has more pressure.
Something to consider.

Crane Cam's "Hi low No Pop" high rpm cams address this. (valvetrain harmonics)
CompCams has simular special high speed lobes.