Composite Flat Tappets

[ERA Chas]

SF,
Fascinating data you've posted and much appreciated.
As a small aside, what is your determining factor for "big stroke"?
4.250 or larger, for instance?
Thanks,

[RICK LAKE]

ERA chas I think that any crank with a 4.125 throw would be a large crank. I think the biggest in an FE is a 4.400 . I am sure that this needs some BBC rods. 6.7-6.8 in length. I am looking to see if anyone is doing a 4.28 bore and 4.31 stroke setup and how it came out. An rpm limit of 6300 for this setup is about the edge of the safe limit on a motor with this configuration. High piston speed. Rick Lake

[Ant]

SFfiredog,

Have you used Jesel solid roller lifters?
I like the idea of the extra 30-40 hp that might be gained with a roller camshaft!

Having said that if the ceramics lifters are used that extra hp gap might be much less gain?

[SFfiredog]

Guys,
Piston speed is strictly a matter of stroke and rpm.
For example a 4.25" stroke crank at 6000 rpm has a mean piston speed of 4250 fpm. That's moving along pretty good!
For example a '69 NASCAR 427 tunnel port had a piston speed of 4221 fpm at 6800 rpm and a '70 NASCAR Boss 429 had a piston speed of just under 4200 fpm at 7000 rpm.
The 427s use in '66 and '67 at LeMans were limited to 3500 fpm
(5600 rpm)
These numbers are of course constant speed unlike a street engine but were also not designed to run for 10s of thousands of miles like a street engine either.
For me, if I'm building an engine that will see 4250 fpm or higher, more than a few times, I will usually step up to a set of Oliver rods. They are stronger but more important, on average they are about 50 grams each LIGHTER.
Also, the bigger the stroke (the higher the piston speed), the more important combustion chamber efficency is.
With a poor combustion chamber design the piston is moving too fast for the flame front to be completely effective.
This is one of the few places where rod length is important and can affect combustion efficency.
Somebody stop me or I'll go on forever...
--Mike

[SFfiredog]

Ant,
I have used a few sets of Jesel "dog bone" lifters. One nice thing about NASCAR is the abundance of hardly used parts available on the internet. I bought a $1800.00 set of lifters with just dyno time on them for $380.00! The lifters are like jewels. So far they are working well but they are all in race engines so I can't positively report on their "street credentials" but they sure seem to be one of the best on the market.
I would speculate that the composite lifters would be comparable in horsepower to the rollers; maybe 15 to 20 hp less. The main reason being the fact that a solid or roller cam that is ground for a street car using these lifters would be pretty similar. The specs and power the cam could make is limited by the desire for reliability and drivablility in a street engine.
One thing about roller cams that can be a detriment on the street is valve springs.
Roller cam springs are getting better every day but they still need to be replaced at regular intervals especially on the street. THe springs need to stay cool in order to live. NASCAR and road race engines use misting spray bars in the valve covers to cool the springs.
This isn't a problem on these engines because they all run dry-sump oiling systems to evacuate the hot oil from the valve covers.
I have to go but I'll post some more info tomorrow.
--Mike

[Ant]

Mike,

That info is very helpful, my application is mainly fun road with a careful warming up and a reasonable run, but not daily transport at all - sunday driver.

As far as track use the car will only see 5-8 laps of a 3 mile circuit, which equates to 7 minutes of racing, using 6500rpm - 6800rpm!
I can do my own engine work, as I have a reasonable mechanical engineering ability, providing I do my homework!

So I want to keep it simple and the Schubeck flat tappet is starting to sound good, but I would be very keen to hear anymore of your experience.

[StanJ]

We've used Schubeck's full-composite and ceramic face flat tappets with great success for several years now. The weight savings is particularly advantageous when using aggressive lobe profiles that require larger .875" or .904" tappet face diameters. The only negitive aspect we've ever seen is the fact that -- while the ceramic material used in them is extremely hard and therefore almost impervious to wear, it is also quite brittle compared to a conventional chilled-iron tappet. I'd recommend against trying to incorporate a significant reduction in valvespring pressure...unless you have the time and funds to invest in Spintron testing of your complete valvetrain package. Judging from our experience, if you "vault" these things over the nose of the camshaft lobe...even once... there's a very good chance of it turning to dust when it slams back down.

[cobrashoch]

StanJ - On my buddys Hemi a set of ceramic faced lifters were bounced around a bit and lived, due to 180/190 lbs springs, two busted srings and a maniac driver. The cam was a blower grind w/moderat ramps, .72 lift on both sides and 114 lobe centers w/very long duration on the exaust side. (wouldn't tell me duration)
Again, he beat the hell out of them and they lived and I am now convinced. Some recient data I saw on these lifters compaired harmonics data compaired to roller lifters and that data alone was enough to convince me of the long term wear characteristics even after the eqilivant of 80k miles street use with some wild lifts and over 300lbs springs. I kinda like the set it and forget it mentality if you were to use them one on a mild but blown big cube motor. They will be on my motor next summer I'd bet.
cobrashock