69 replies to this topic

[mini1071s]

Deleted

[DaveCoxon]

Before i waste any time answering a post that might get deleted, I'm going to ask final clarification; Some 'mod' decided that because he didn't fully agree with something, it got deleted?
Huh? Have I strolled onto Minifinity? (looks at address bar) Nope, It seems to be TMF still...

If this post is still here Saturday Evening, I'll add something.
If it isn't, then I suggest Peter - that you take it to a forum (i can think of three) where engineers who've done a bit, rather than simply 'read a book' reside...

[Bluemini]

Wow steady on guys, the post was moved to the Doc section and not deleted. This subject comes up from time to time and it was decided that it needs addressing and a clear answer finding once and for all. There is no one to blame for this, we just need to find the answer without all the stupid posts that end up in these topics of people putting thier advice in who don't actualy know what the hell they are on about.

[Bungle]

i would like to see some good answers to this question

i do use 1.5 rockers and many of the kits for the late coopers have 1.5 rockes

so lets see the pro's and con's from the people that know

[Jammy]

It was me that moved the thread into the Doc section at the request of a doc. I wanted to just copy it into the section however this isn't possible, as in it isn't possible to copy a thread, only move, close or delete one.

The reasons for this have been stated above.

[mini1071s]

Post removed

[Sprocket]

Well there you go. Valve bounce is not induced by inadequate poundage springs but rather valve train mass. The clatter caused by 'valve bounce' is actualy the follower leaving the cam and then hitting it as it recovers much like a jack hammer.

It is clear now that high ratio rockers are not all bad when used in the right aplication and preferably not on wild cams, which more and more people are fitting to road cars, which is something I will never understand.

[Dan]

I agree that oil cannot be compressed of course however the cam to follower interface is not like a hydraulic cylinder. The only side walls to keep the oil in place are those caused by its own surface tension and viscocity. The oil can and will be displaced by an increased load on it, especially since the surface of a cam follower is not flat but domed. Can you explain this point a little further?
Also If I understand what's written above then the cam only feels the actual spring load as opposed to the effective spring load. How is this possible when the lever of the rocker is present in the valve train?

And I have just one more question. I think the summary of what you are saying is that increasing the rocker ratio allows greater power to be developed within the engine for zero penalty of increased internal losses. This sounds to me like perpetual motion. Other than increased fuel useage, what exactly is the payoff for increasing the ratio?

Edited by Dan, 11 February 2006 - 05:34 PM.

[Jammy]

This morning I sent an email out to Kent Cams, Piper cams, Swiftune and Simon at Morspeed. So far I've had Simons reply:

the answer is yes and no, i have used 1.5 roller rockers for the whole 15 years of building mini engines (over 600 engines to my name) and ive seen just about everything.
in my opinion they should not be sold as a 'bolt on' extra. not because there bad, far from it, infact i use them on 90% of my engines, But because without the correct spring & seat pressure they will destroy a cam lobe. And you can bet everyone who buys the 1.5 rockers mail order is doing just that 'bolting them on'

The worst cases ive seen are the john cooper conversions, they use the minisport 1.5 roller rockers and 200lb valve springs, WHY? i only ever use a spring with that rating on a race engine giving .500" lift.

If 1.5 rockers are so bad how come mini miglias use them alongside an STR930 cam giving .485" valve lift? there cams and followers last for years and we no longer see valve guide wear like we used to.

There is so much C**p flying about with 1.5 roller rockers its amazing !!

Infact they are one of the best BHP for your money conversions ive seen, i have done many tests with 1.5 rockers and they do give an increase of 3-8bhp depending on the cam used.

To cut a long story short, i would say to anybody forget 1.5 rockers as a bolt on, but DO get them if you are having an engine built properly by a proffesional who knows what they are doing,
When i say proffesional i mean a company who has cars out there on the race track proving there engines. these are the people who can squeeze every last drop of BHP out of your road engine.

There are too many people who read books/internet or have built 1 or 2 engines and 'think' they know whats best, they dont.

[Guess-Works.com]

And I think that sums it up, and is what the underlying point of this thread should be about..

To the average Joe on the street, they are sold as a bolt on performance mod, without regard to the destructive influence which they will have on valve train wear..and here we are talking about the 1.5's in general..

1.3's are not far off std ratio ( being 1.25 ) so the benefits of less sideward load on the valve stem because of the roller, probably outweigh the issues associated with the extra .05 ratio on the lift.

[Bungle]

reading all this so far it looks like not matching the springs to the rockers is the problem and not 1.5 rockers

so my next question is what lb springs should be fitted with these rockers ?

[Jammy]

I think the point is that the springs, camshaft and rockers all have to be matched to get the best performance. This is the reason why people pay so much to a decent engine builder, they know what works together and what doens't.

[minimole]

so assuming swifttune know what they are talking about which is probally a safe bet that they do. if you where to buy the "sw5 hi lift kit" (think thats what it is called, includes hi lift rocker gear, springs and cam etc.) would it be a fair assumption that every thing in that "kit" would be matched correctly?

I ask because i have noticed that when dealing with uprated cylinder heads or anything that effects the valve train you see companies almost bragging about spring strength is this just another case of bigger is not always better?

hope that made sense :lol

[mini1071s]

Deleted

[Pickup76]

thanks for that in depth and concise explanation mini1071s. Im a first year motorsport technology student and have just completed my first module on thermodynamics and the basic principles of the internal combustion engine. Its nice to find that i can follow an your explanation and what im being tought is so very relevant as its hard to imagine its use as examples on a white board.