Question about a Nascar Valve train setup.

VW Racer · Post by **VW Racer** » Mon Jun 06, 2005 4:00 pm

Hi I was wondering if someone in the know can clear something up for me. I was reading some info ( on the net )and was wondering if there is any truth to this because it doesn't sound right to me.

First, Do nascar engines run Beehive springs?
Second, are the cams and spring rates set up as such that the lifter actually "lofts" or launches itself off the cam lobe to achive a higher at valve lift?

Thanks.

Leon Sterett · Post by **Leon Sterett** » Mon Jun 06, 2005 10:05 pm

No to all the above.

Leon

OldSStroker · Post by **OldSStroker** » Tue Jun 07, 2005 8:32 am

Leon Sterett wrote:No to all the above.

Leon

No (intentional) loft?

The last thing I heard, there was some of this being used. Cam velocity (lift/degree) is physically limited by the lifter diameter of course, so controlled loft can be useful.

No offense, but where did you get your info, Leon?

let r eat · Post by **let r eat** » Tue Jun 07, 2005 8:44 am

They've been doing this in Briggs and Stratton engines for years.

Post by **SchmidtMotorWorks** » Tue Jun 07, 2005 3:54 pm

I haven't see it but heard from a reliable source that some NASCAR engines do not have adjusters on the rocker arms. I guess they adjust the level of the arms or change pushrods.

joe · Post by **joe** » Tue Jun 07, 2005 5:19 pm

at one time they got a ballistic effect from pushrods that weren't sufficiently stiff too properly translate all the cam motion to the rocker . The pushrods would bend as the lifter raised then when the lifter reached its plateau the pushrods would straighten themselves and loft the valve a small amount.
From what I've heard they found this out after the fact . They put stiffer pushrods in and dropped some hp so they made the cam more aggresive to compensate.

jacksoni · Post by **jacksoni** » Wed Jun 08, 2005 4:59 pm

joe wrote:at one time they got a ballistic effect from pushrods that weren't sufficiently stiff too properly translate all the cam motion to the rocker . The pushrods would bend as the lifter raised then when the lifter reached its plateau the pushrods would straighten themselves and loft the valve a small amount.
From what I've heard they found this out after the fact . They put stiffer pushrods in and dropped some hp so they made the cam more aggresive to compensate.

Is my understanding that bending pushrods break sooner rather than later, that lofting valves is bad for longevity of all the valve train and I think Brad Morgan (Darins brother) says on their CD that they picked up power when they put stiffer pushrods in and got better valve control. Might work for a Briggs but not so sure of a 9-10k rpm nascar or prostock motor.

Robert Kane · Post by **Robert Kane** » Wed Jun 08, 2005 7:10 pm

I would think that lofting the valves is an unavoidable occurance in any high end pushrod engine, with the aggressive cam lobes and high rocker ratios. I would assume that engine builders / cam makers work some amount of "controlled" lofting into their combinations, and it would seem valve bounce is a much bigger problem from a power standpoint. I do think a Cup engine would need to control lofting much closer to be able to stay together for 500+ miles than a Prostocker does.

OldSStroker · Post by **OldSStroker** » Wed Jun 08, 2005 10:15 pm

Robert Kane wrote: Lofting the valves is an unavoidable occurance in any high end pushrod engine, with the aggressive cam lobes and high rocker ratios. Engine builders / cam makers work some amount of "controlled" lofting into their combinations. Valve bounce is a much bigger problem from a power standpoint. A Cup engine would need to control lofting much closer to be able to stay together for 500+ miles than a Prostocker does.

Sorry for the edit of your quote, Robert, but the way it reads here ^^sounds like you know whereof you speak. Are you just being modest? I have heard almost those exact words from folks very close to the situation. Methinks you might be one of 'em.

Shaun · Post by **Shaun** » Wed Jun 08, 2005 10:24 pm

I've heard .750 lift, .040 - 0.60 loft. 175 seat, 500 open . After lofting, the valve supposedly lands with about 1200 lbs of pressure.

Ron C. · Post by **Ron C.** » Wed Jun 08, 2005 10:31 pm

From what I hear it alines with Kane's comments. Pro Stock cams can get away with a little bit of controlled drop where a 500 mile motor would never make it to the finish line.

Racer7088 · Post by **Racer7088** » Thu Jun 09, 2005 5:29 am

They all have some loft going on and yes at some tracks they use beehives as well. The Beehives have been on the lower rpm plate engines when they have shown up and they have loft too. Cup shops have spintrons and they use them a lot.

CNC BLOCKS · Post by **CNC BLOCKS** » Thu Jun 09, 2005 7:54 am

My partner that had worked with me for 12 years now works for one of the top Cup teams in there engine shop and is also the engine tuner and the last Cup race I went too while he was adjusting the valves he checked the seat pressure and they were 160 at the seat and low 400 over the nose the springs are 2000 dollars a set and there not the behive type and the rockers are adjustable and the plate engines run less pressures then that and there valve train componets are super lite the size of the valve stem are tiny compared to what most of us deal with. All ther cams are ground in house and haveing a spintron to test everthing on helps as well.

Robert Kane · Post by **Robert Kane** » Thu Jun 09, 2005 9:52 pm

OldSStroker wrote:
Robert Kane wrote: Lofting the valves is an unavoidable occurance in any high end pushrod engine, with the aggressive cam lobes and high rocker ratios. Engine builders / cam makers work some amount of "controlled" lofting into their combinations. Valve bounce is a much bigger problem from a power standpoint. A Cup engine would need to control lofting much closer to be able to stay together for 500+ miles than a Prostocker does.
Sorry for the edit of your quote, Robert, but the way it reads here ^^sounds like you know whereof you speak. Are you just being modest? I have heard almost those exact words from folks very close to the situation. Methinks you might be one of 'em.

Wish I was one of them! No, I am just a young man in my journeymanship who worked with a very talented but aged machinist, now looking to start my own engine business with my father. I try and learn as much as I can. This IS my passion- engine development, and I like to think if I had the funds in time I could be with those you speak of. This is a great place to exchange ideas and problems, so many talented minds. Also very encouraging to find my thoughts and quieries very close to those who have reached such levels of success. I just wish I could find more places to ask questions and pick some of the great minds.
Thank you for your kind words.
Robert.