duke what do you think of this??

[Terry F.]

Re: duke what do you think of this??

I see why people try to make full roller rockers out of aluminum. But, I heard aluminum can't handle it for the long haul. Based on what you have said, I can't see how a full roller rocker like comp cams wouldn't limit the valve train. You can't hide that tip and the rest of the lifter body can't be significantly lighter. At least I can't immagine it to be. I will try to ask those guys and see what they say. I am sure the mid-section of the rocker is compareable or less, but that has very little effect on what is going on out at the tip when things are flying. So full rollers have there application on gorilla springs when they can compensate for the added weight of the rocker tip. What a drag, burst my bubble I would like to measure the torgue/force differences required to rotate a conventional rocker arm vs. a full roller rocker arm set-up. Does the reduced friction compensate for the added weight of the rocker tip in allowing the valve spring to force the valve shut?? It would be helpful to actually see the hp/torque curves on two identical engines (designed to develope peak hp/torque at around 5500 RPM) but with the different valve trains to compare what is really occuring at 5000-6000 RPM. Thanks for all the advice and insight, Terry

[Clem Z.]

here you are duke

http://209.85.165.104/search?q=cache:CsL8Cskbi2MJ:www.sae.org/automag/technewsletter/070402Powertrain/04.htm+viper+variable+camshaft&hl=en&ct=clnk&cd=1&gl=us

[Duke W.]

Re: duke what do you think of this??

What parts list? Who published it? Part numbers? specs?

Is this thread becoming some kind of riddle? We have to deal with specifics - part numbers and specs from known reliable sources.

The '67 AMA specs show the identical valve spring specs for all 427s: 94-106 lbs. @ 1.88", 303-327 lbs. @ 1.38". The circa 1979 service part number for all '65 to '72 396, 427, 454 except L-88 is 3970627. This is probably the late sixties replacement for the early springs that had high failure rates, and I expect it, too, has been superseded by a later part number.

Clem or Joe L. can probably give the whole littany of BB valvespring evolution from the mid-sixties to the early seventies. The first design springs lacked durability and failed frequently. They were redesigned for more durability, which may have involved just a material and/or process change. IF the load specs did change the new specs would be in later CSMs.

Duke

[Duke W.]

Re: duke what do you think of this??

Roller trunnions will show less friction and require less oil cooing capacity, but this is only an issue on racing engines that spend most of their time at 5000 revs or above and have dynamic forces that are pushing the limits of durability, even for a two hour race.

What fraction of time is a road engine going to spend at this rev level or above?

Aluminum is one-third the density of steel, but is also only one-third as stiff. That's why aluminum rockers have to have such large section thickness. So the extra material digs into the weight saving over steel or cast iron, and only cleaver design will show aluminum to be superior. Rocker arms that deflect excessively due to lack of stiffness are probably worse than overweight rocker arms.

Distilling specific numbers out of all this will take an engine, a good certified engineering test lab with appropriate dyno facilities and whatever parts you want to test. Figure about $50,000-$100,000 for a week or two of testing assuming you do most of the wrenching. Add a few hundred more for their lab to make precision mass measurements and measure the rotating inertia of rocker arms. Then maybe you could get them to do a complete ANSYS or NASTRAN dynamic analysis of the valvetrain. If they've already used one of these generic structural analysis programs to analyze valvetrain dynamics it probably won't take them long to get results once they have all the input data, but it won't be cheap!

Wanna fund it?

Duke

[Duke W.]

Thanks...

Very clever design, but a WHOLE lot more complicated to manfacture than grinding a cam from a blank on a 50 year old cam grinding machine. But for the price of a Viper, I guess it's affordable.

Duke

[Terry F.]

Re: duke what do you think of this??

"Do I want to fund it?" I don't think so. There are some who have deep pockets. Last time I checked either someone had sewn by pockets shut or they where those kind that just look like pockets and are not.

I appreciate the discussion. I ran a cross a set of original design Comp-cam stamped steel rocker arms for BBC. Have you ever heard of them being made to more exacting rocker arm ratio?

I guess, I could just build my engine with both standard and full roller and report back on how it acts (subjective).

Well, I think I pounded this one into the ground for now. Thanks for the in put, Terry

[Duke W.]

Re: duke what do you think of this??

No rocker arm has constant ratio. The only way to determine their behavior is to measure the ratio across the lift range, which is easy to do with a couple or dial indicators.

The OE rockers work just fine, and using the funds that you might otherwise put into aftermarket rockers is better spent on head massaging and a bulletproof bottom end.

Duke

[Terry F.]

Re: duke what do you think of this??

Got it! Thanks, Terry

[Terry F.]

Re: duke what do you think of this??

Check this web site out. They show a different part number for the 1x4 and the 2x3 regarding the 68 corvette 427....http://www.rockauto.com/catalog/raframecatalog.php

As far as sping pressures are concerned, I went to 4 different sources and found 4 different answers (sort of)

68 over haul manual: 94-106# closed @ 1.88

303-327# open @ 1.38

Rock Auto. Com: 3x2 96# closed @ 1.88

230# open @ 1.46

1x4 76# closed @ 1.88

220.5# open @ 1.25
Note* Rock Auto also shows a different part number for springs on 2x3 and 1x4.

Crane Cams factory grind card (Cam #969391 grind 3883986)

90# closed @ 1.875

251# open @ 1.415

1967 chevrolet lit: 94-106# @ 1.88

303-327# @ 1.38

You really cant compare the open values because of spring height but the closed values can be compared. Sort of interesting. Terry

[Clem Z.]

Re: duke what do you think of this??

F/M spring VS-1581 is recommended for all BBC both solid and hyd lifters. i would use GM 3970627 if they are still available. never saw one of these spring break. a kit with (16) 3970627 springs is part# 12371061. the VS-1581 spring is rated at 370#/inch and the 3970627 is rated at 450#/inch and both are 105# @ 1.880 installed height. you can calculate the #/inch over the nose by using the lift spec of the cam you are using.

[Clem Z.]

correction,should have posted spring pressure

in #s at over the nose for your cam at max lift not #/ inch.

[Clem Z.]

some interesting reading about spring pressure

http://209.85.165.104/search?q=cache:tVt0ggR2lfAJ:www.cranecams.com/%3Fshow%3DnewsLetters%26no%3D239+carburized+camshaft&hl=en&ct=clnk&cd=11&gl=us

[Terry F.]

Re: duke what do you think of this??

I printed your recommendations. Into my rebuild file they went!!! Thanks, Terry

[Terry F.]

Interesting.....

Thanks for the info. Terry

[Terry F.]

Re: some interesting reading about spring pressure

Clem, any chance you would have the weight in grams of a standard bbc rocker arm? Thanks, Terry