Bucket Shim vs Valve Sprung

[Joshstix]

For a race engine the benefits outweigh the costs that's for sure.

Cost benefit equations for this kind of thing are entirely up to the desires of the end user. If you're building a nice tough turbo street engine then no I'd not say there is good value for money in machining for larger buckets. If you're building an NA race motor for a class where a few horse power can be the difference between first and mid pack then is there really a price that negates the benefits?

[jfallen]

I've put the CAA22 project on hold while I organise my move interstate, but would love to see if you can better that price.

hook me your email adress and I'll forward the PDF.

Cheers
Jordan

[ed]

[email protected]

[Nim]

There are advantages to running rockers in a DOHC engine for road use. Running a variable lift and duration system.

Yes, I'm defending VTEC (And VVTL-i) again.

[rossgw]

the ducati bikes have a good setup... its called DESMO..... been a while since i looked into it,

Desmodromic valves have been around since the 50's, used in the 1954 W196 Mercedes race cars and 1955 300 SLR

[slow laser]

[QUOTE=Ben Wilson]You'd think so, but then why do F1 engines use finger followers?QUOTE]

umm last i heard F1 cars use a pneumatic valve system thats feed under pressure, ie no springs... still have cams though (because of ruling)
and as for someone saying they use followers, well they dont have the weight of the valvetrain hanging off them... its only used to trigger the sensor to open the valve.

as for the shim over or shim under, its no major differance unless you intend on really reving the motor. only bad point of view with shim under is there a !@#$ to pull out and re-shim but i guess thats a good pay off, if your head eats a shim its going to be more of a pain


edit :- also on that note about ramp rates and lift... heavier valve springs can stop the lobe from losing contact with the bucket/shim and crashing into it. but than u lose power through the cams having a higher load.. so its never ending really. use more power, to make power

[Billzilla]

[QUOTE=slow laser]

You'd think so, but then why do F1 engines use finger followers?QUOTE]

umm last i heard F1 cars use a pneumatic valve system thats feed under pressure, ie no springs... still have cams though (because of ruling)
and as for someone saying they use followers, well they dont have the weight of the valvetrain hanging off them... its only used to trigger the sensor to open the valve.D

The pneumatic valve spring has nothing to do with how the valve is actuated, and in that case Ben is right, they pretty much all use finger-followers these days and that's to both let them control the valve timing & lift, and also get more lift than you can with a cam-on bucket system.

[slow laser]

[Billzilla]

Yeah I know about that diagram - I've had it on my site for over five years.
It's an old one, they don't look like that anymore.

[slow laser]

yeah i figured that much, but as you would know they are a lil tight lipped (or should i say arsed) to let any info out about how they work. (was only meant to help them understand how there isnt a "valve spring" so to speak.)

[Billzilla]

yeah i figured that much, but as you would know they are a lil tight lipped (or should i say arsed) to let any info out about how they work. (was only meant to help them understand how there isnt a "valve spring" so to speak.)

Have a poke around Scarbs F1 site (dunno the link) there should be some good info there.
Yes they still have a valve spring, it's just pneumatic not metal.

[oldcorollas]

one major benefit of the pneumatic system... apart from reduced inertia... is a fairly constant "spring" force.
with conventional spring, the force increases with distance (by F=kX), but pneumatic can have relatively fixed force which changes the profiles you can run (esp closing rates)

[Ben Wilson]

A more modern motor.



Notice the variable inlet length (now banned)..

[oldcorollas]

ahh, so they are just using the followers to increase the ramp rates....

[Ben Wilson]

More to allow greater ramp rates. If you look at the inlet cam in that picture*, and try to imagine it running on a bucket, you can see that it would hit the edge of the bucket. With the follower in place, it can stll get a nice, linear lift going on.

* probably a little excessive, call it artistic license....

The BMW M5 V10, uses buckets with a curved top to allow the same effect.



Notice the pin to stop the bucket rotating.