Rocker Ratios...variances
 

Interesting information here. Shows how different brand of rockers, can have quite a bit of different ratios from their advertised ratio. Obviously ratio effects full lift, but it also can affect valve acceleration. Here you can see how each rocker differs.

The 1.8 Ratio's are really interesting. According to this chart, the differences are substantial.

Harland Sharp .127/.649

Crane .131/.649

Comp .126/.638

Scorpion .138/.680

While they are all 1.8 Rockers, the scorpion has .680 peak lift, and the comp, .638. Thats a .042 difference in peak lift at the valve.. plus, a faster accelerating valve opening.

how old is that data?

Feb 2015 publish. Considering they are testing the Comp Cams 1828 Ultra Pro Magnum XD, I wouldn't think its that old. That rocker hasnt been out that long. Looks like it debuted at 2010 Sema show. https://www.youtube.com/watch?v=NSLIIrujyzo

I can attest, that there is a significant difference, in the geometry of a Crane Gold, Scorpion, and older style Comp Steel rocker when studied back to back on icdedppls engines, doing valvetrain geometry checks. The sweep patterns, and roller tip placement varied quite a bit between the 3, when setting the rockers up using the mid-lift method.

Good reads! I've been interested to find out why some cams/builds use a 1.7 and 1.8 rocker combo. I understand what they do but the benefit would be interesting to see.

Wow !

I believe because generally speaking, the BBC likes intake valve lift, more than it does exhaust valve lift. I also believe, it was very common for cam companies, to use an intake lobe, for an exhaust lobe. Like when you see cams with .630/.630 lift. The modern trend in cam lobes for bbc stuff, seems to be going with more intake lobe lift. From what I have seen, most bbc's respond better with 1.8 intake rocker, and 1.7 exhaust rocker, on those older cam grinds. You not only gain more peak lift, but more throughout, and a quicker opening valve.

The author of this particular book, mentions how normally a 1.8 intake rocker, is a way to go when using a dual pattern camshaft, with 6-8* more exhaust duration.

Given that these are new production items I'll assume that they used modern manufacturing methods to build them, Cee-N-Cee, basically ruling out tolerance issues.

Does the article make any mention of the arm's installation method or the spring's installed height? I'd also like to know how they measured the valve lift. Small geometry changes from setup to setup will definitely show up in the results. Fr'instance, maybe they used a dial indicator to measure travel and didn't get it back in the exact same spot every time.

He does not get into the specific details of the test.

I am always purchasing new literature regarding engine building, cylinder head porting/design, blueprinting and machining, to attempt to educate myself further on these topics. Mainly, because I am not interested in "opinions", or "theories" any longer. I like graphs, charts, data, and results. I have several of David Vizards books. Each one, I have found vastly informative, on all aspects of things. As far as big block chevy stuff goes, not only does he have vast experience in all types of build combinations, he has tested thousands. He is familar with, used and ported, Darts, AFR's, Brodix, RHS, Trick flows, and tons of stock offerings. From cranks, to rods, to blocks, to valvesprings, he's been around them all. Not a guy who's only dealt with one brand , and thinks its the best. He rarely has a negative thing to say about any brand, he simply gets to the point, and shows his results with data. The man started porting cylinder heads in 1950's, and has intensely studied the effects of the actual combustion process, heat transfer, airflow turbulence, and so on. He has over 500,000 dyno tests under his belt in his day. Spent a lifetime testing theories.

With that being said, I have no reason to doubt his procedure of this particular rocker arm test, or his knowledge of valvetrains. I am pretty certain, the man has learned valvetrain geometry basics, and how to use a dial indicator by now, considering he speaks at events like PRI, writes tech articles for engine builder magazine, etc.

Basically, I just thought it was interesting information, some may like. His contact information is on the web, as he has a website. I'm sure one can email him directly, and ask him about his test procedure/accuracy.

He does do a lot of testing and a lot of his info is valid.

Some, well,,,,,I'd have a hard time believing (we all have opnions) and some times he turns into a marketing guy.

Well worth to read his stuff, I dunno if I'd believe it all.

Anyway,
Here's some data:

500,000 / 365 days = 1 Dyno test every single day (no day off) for 1370 years.
= 2 Dyno tests every single day for 685 years
= 4 Dyno tests every single day for 343 years
= 8 dyno tests every single day for 171 years
= 12 dyno tests every single day for 114 years
= 16 dyno tests every single day for 86 years

Again, every day a week including Sundays.

The first thing anyone should learn in any statistics class is... "You can make the numbers look any way you want"
If you consider 1 pull on the dyno a test (which it should be) and you do 30-40 pulls/day it would get lower. Also, if that is your daily job/passion it is more reasonable. :)

I'm just having fun, nothing more.

30 Dyno tests every single day straight for 45.6 years = the claimed number.

I have over 500 desktop dyno runs under my belt, and delivered 2,986 loads of gravel, does that count?

I posted this before as I have taken David Vizard 3 day school classes that he teaches in the USA. The guy by far is so super knowledgeable about this stuff. I run into him once a year and he told me at one time that he has tested / dynoed 18,000 cams in his lifetime. he also has stated that his daughter can pick a better cam than the cam manu's for your app. Just saying.

he loves mini coopers and is good friends with engine builder Terry Walters in Virginia who also does a lot of his engine machining.

That's 1 cam everyday in a row for 49.3 years

or

2 cams everday in a row for 24.7 years.

I was going to go with 1.8 intake rockers and was told by several builders that it is not a good Idea for engines running extended RPM. I shook my head thinking how bad could it be going from 1.7 to 1.8. They all said the same thing, that it would be to aggressive and bad on parts. I am hard enough on parts as it is, so I didn't even entertain the thought after that. I would love to go that route. So, Joe get them in some motors... Or anyone else that has used them with success in marine engines that are run hard for extended periods, please chime in.

Okay Lions lost. Ha ! Time to get some zzz's.

Again, having fun,

Most people (even me) like what Vizard says/does.....but remember, just because you like + trust (and what have you) a guy, doesn't mean you have to believe everything he says.

I've been running 1.8's since 2008 and I know others that run them as well. I know someone that has run 1.85's for the last 12yrs.

I'm certainly no expert on the hard numbers with that. Generally, I think your guys are correct. Generally.

I think it goes deeper though. For one, whats defined as aggressive? As we know, you can have two cams that might have same .050 numbers, and one accelerate the lifter faster than the other. So, whats to say, a certain cam with 1.7 rockers, won't be harder on the valvetrain, than a milder lobed cam, with a 1.8 rocker?

I've had guys tell me the same. Don't use a 1.8 rocker. But when you ask them about the difference in lobe profile measurements other than .050, they aren't sure. Heck, some cam specialists don't even provide anything other than .050 numbers on thier custom cam cards. How is one supposed to be able to determine anything about the camshaft, with simply providing .050 duration and xxx lobe lift? I guess most don't care to know, and simply trust their cam guy to know whats best. Or the effect of big lift lobes, coupled with short duration, etc. What kind of detrimental effects are we talking? What kind of HP gains are we looking at? Is it worth the expense? I really don't know.

I know Mike Jones from Jones Camshafts discusses some of this stuff on other forums. From what I gathered talking to him myself, is that for marine offshore hydraulic stuff, he simply isn't a fan of short durations with lobe lifts over .370ish for valvetrain longevity/stability, talking standard cam core bbc stuff. Seems like his thinking, coincides with what Crane, Comp, and some others offer for marine endurance hydraulic bbc profiles.

It wasn't too long ago, BBC's with HFT and HR ran into valvetrain instability in the upper 5k rpm region. If it was spring related, people added more spring psi, but then the lifters ran into stability issues. Leaving you kind of stranded at the same rpm point.

Enter the 1.8 rocker 'less durable' remarks. The 1.8's seemed to make this rpm 'fuss' point happen 200-400 rpm earlier.

Anyway, today's day and age gives us lifters with better internal clearances and valving where the lifters can sustain a higher rpm. Better spring quality with lower weight, has also let us get past this point.

So.....if you have the right valvetrain pieces in place, you can up the rocker ratio ..

SB you`ve made 416 post a year, can you really be trusted??

Yes, you can trust me for snide , condecending, and off the wall remarks...plus, you can really trust me once in a while a great female bikini photo.

http://getabikini.com/photos/wp-cont...ini-girls2.jpg

Thats 1.13 posts per day.

I like just having fun calling people Jackass's

And sir , you are a JACKASS....

Yep, I "discovered" the same when trying to get a decent valve tip pattern using the mid-lift with standard Scorpions. Exhaust pattern was landing too close to the edge for my comfort. Tested with a set of Scorpion Marine Endurance and found that the distance between the tip and trunion was shorter, which brought my pattern into an acceptable range.

Yep, as Samuel Clemmons once said, there are three kinds of lies - lies, damned lies, and statistics. :)

Performance 540cid Marine I/O

How would this work:
Custom Spec'd / Ground by LSM

Intake Duration at .050" = 226°
Exhaust Duration at .050" = 228°
Lobe Lift Intake = .300". With 1.7 Rockers = .510"
Lobe Lift Exhaust = .300" . With 1.7 rockers = .510"
Events at .050"
Intke Opens : -1° BTDC
Intake Closes 47° ABDC
Exhaust Opens 48° BBDC
Exhaust Closes 0° ATDC
ICL = 114° ECL = 114°
LCA 114°
Overlap -1°

What ratio works best with a 3/4 race cam? 1.275's or 1.35's? :drink:

3/4 Race 1.7's would be 1.275's.
3/4 Race 1.8's would be 1.35's.

They do make 1.6's for the big block, so maybe this is a better bet for a 3/4 race cam......since 1.7's can be considered full race.

I couldn't go back and edit this.

The edit is that LSM ground the cam. They did not pick the cam. That was done from the engine designer.

just looking at those specs and I know who designed it.

.300 lobe ? This engine have peanut port heads with smaller valves installed ?

No, quite typical 540cid performance build. Rectangular heads and the like.

This was the cam that was put in it.

So I know that I'm oldschool and out of touch with this new stuff so way back when we had to design our own engines. just sayin! many of us were engine designers ahead of our time! Pioneers

Don't want to hijack the thread I just had a brain fart reading that info Sorry

Joe,
I'm certainly not trying to discredit the man's work, just trying to make sure the variances lie in the rocker arm itself versus other engine specific variables. Sorry if it came off that way.

Someone should model a big block assembly in SolidWorks (I'm sure it someone has, but I bet it won't be seen by us) as well as various components. Add in your cam lobe, valve spring installed height, rocker arm specifics and see how it cycles. I'm nearly positive one could generate all sorts of neat reports from the data. Alas, that level of precision would be time consuming as all hell to create.

Ok, back to bein a nerd.

I was shocked initially by the data, wondering how pushrod geometry played into the testing, going to assume it was set perfect, if so the numbers are a GOOD reason to avoid certain rocker arms!!

I just noticed they used Scorpion 1.7' and 1.8's.
Apparently I have been running 1.932's and 1.79's for years. :cartman:

That gives me 0.734" IN lift and 0.680" EX lift.