Valve or cam timing

[Forumadmin]

Since the Javelin section seems to have been taking over by sporty talk on distributors and the Bradford section with similar sporty talk, I thought I would bring some sporty talk to the sedate Jupiter owners.

Cam timing. I recently adjusted the timing chain wheels on my Javelin engine which mysteriously seemed to be different from the book set up (12 thou lift at 12 degrees). Maybe the engine has a modified cam in it and I will find out when I road test!

But how about a discussion on cam timing like the one on spark advance timing? After all where the spark should occur depends on the quality of the mixture in the cylinder and that depends on the carb, the inlet tract and the exhaust tract. Exhaust tuning discussion anyone?

We sort of started it on valve lift and cooling exhaust valves elsewhere on the forum. It is all about getting as much charge of mixture into the cylinder and dispelling all those unproductive burnt gases. Have you gas flowed those heads as per the tuning notes? (see Jowett.org tech section). Have you profiled the valve ports to the correct angles and ground the valves for the best contact width? Set the tappet gap? Profiled the cam to give that extra lift? Profiled the cam for some extra opening?

[Keith Andrews]

The old school thought..40s 60s boy racers, thought high lift was the be total answer....yes it helps but the piont at which the galleries/heads flow is a limiting factor.
Cam profiles are still a art.
The 1st secret is to design the engine for the use it is going to have
eg
A stump puller low rpm economic highlt responsive off the mark good towing street car and lot of bottom end torque.
Personally Im a great fan of this approach althu it is not a popular one...I mean who can brag about a low lift, small carb, narrow runners...but it performs
Or
A racer high rpm, not much down low, high diff ratios that make it feel as if u need another gear at cruise...track car.

Drive around for a few months, find what rpm range u like the sound of, then build to that without compromise
Ex factory designs are a compromise to suit a wide customer base.

There are things like high lift, then there is the rate of lift (forgetting things like spring rates) a fast lift is good for the track but sucks on the street and visa versa
Duration, over lap, lobe centers are all critical.

One can take a high rpm cam designed for an engine with a blower, advance it 2 or 3 degs and it turns into a bottom end economic stump puller of sorts

There are good and bad brand cams..cams are something that price often signifies quility...ie the acrruccy of the machining of each lobe...unless one speeds a lot of money on a cam the chances are just throwing into the car doesnt work...out with the degree wheel

Cam design is a huge subject with so many variables, unlike jetting a carb etc...it IS the HEART BEAT of the engine.
The 1st cam I designed for the Camaro took me over 6 months of calcultions, and even then I only sort of got it right.
The 2nd cam I spent 3 months on, and again improved but no where near targets for economy or 1/4 mile
The 3rd cam.. this year, I have nailed it a little above expections.
Althu the principles are the same a retink of ramps/ lobe centers, a dramitic increase in lift, pulled back on duration

A good place to start is some of Smokey Yuniks books on basic cam principles. concepts have changed dramitically since the writing, but he does explain in easy terms.

[Forumadmin]

A number of people over the years have designed and made or reprofiled cams for Jowetts. If you have used one please relate your experiences.
It is unlikely Jowetts got it perfectly correct, and anyway motoring has changed in 50 years. Cruising at 70mph or the stop/start of traffic jams is now the norm.

[Keith Andrews]

An important part of cam design is historical knowledge, saves a lot of time/ money
Pat can u post specs/profiles of these cams and the stock spec
Lift, rate of lift, lobe centers, durations, point of lift and over lap
We can then have a look at them.

Over heating problems can usually be traced back to not re jetting, dizzy curve and other parameters at have not been changed correctly to suit the new design.
The balance of all these components of an engine is critcal...cahange one and it causes a chain reactionright thru the engine design.
Ie to run bigger jets would need a suitable cam lift, to optimis this the runners valves may need matching the cam flow, the timing curve changed and posible exhaust flow.
or just adding headers or change of exhaust can cause lean conditions even with bigger jets...scavenging and will show rich at the pipe but lean at the plugs.

Pat or anone please post the cam spces and comments to these that have been used over the yrs....WE NEED THESE.

[Keith Andrews]

Pat....

Quite frankly i would not bother as you are messing about with somthing the jav jup engine was not designed for in the first place.

Some of use are interested in bothering...

I see no harm of u and others letting others know the specs of cams u have played with...There are others, now and in the future who may wish to look into these aspects..be it out of interset or as has been mentioned by others here, there is a very good chance in the not to near future when older cars may HAVE to be brought into line with modern legislation.

Do Do Do tell us the practical procedure of setting and tuning a Jup Jav engine if you know of course

You are very well awhere of my background and experiance, as I have explained in personal corrospondence and elsewhewre in these forums.
It is very apparent you have a hidden aganda, the repeated question is no more than to manipulate my creditablity and cover your own inadqueces.

I have no experiance on Jowett engines, I have a large and very sucessful experiance on other engines on the track and street...enough for a Rookie Dirt Track Streetstock class car take out the top 3 places of the NZ champs, Nth Island Champs, Sth Island Champs and Auckland Champs...Also other sucesses for street cars documented in these forums and other international forums.
My intersest is now appling this knowlege and experiance to Jowett for my own and other INTERESTED owners benifits.
As can be seen in other posts (bradford section) I have already started in great detail...even with a stock very well worn Bradford engine, on my 1st attempt, it is on Offical Club Records, I can achieve best encomy against other bradfords on an offical club run, and increased load power over newly built and well setup engines of those who I have the highest respect for and decades of experiance., and are prepared to share ALL info tricks with EVERYONE else.

Either help out or butt out...Stop wasting everyones time.

Either your attitude is self centered, or you have absolutely no knowledge of what used , how a cam is designed, and what combinations of paramaters of a proflle has on what....

You have added nothing to the information or knowledge experiance that is the purpose of such theads as a future refernce for those interested... and persist in doing so..

Sry about being blunt but your post do no more that run around on ever decreasing circles.......
No Im not sry, I just ran out of paticience.

If u have something constructive to add, info pertinate to the subject, do so, if not, let those who do, get on with the discussion job at hand.

My appologies to other Members and the Administration for being persistantly pushed into having to make such a post.

Steps.

[Mike Allfrey]

G'dday,

Much has been written on this topic already, and I just want to register a warning.

Some years ago, at the Bendigo National Swap Meet, I found a Mitutoyo dial indicator box and for some unknown reason, I opened the box to find a little-used Mercer dial indicator residing in there. I quickly shut the box and paid the $A9.00 asking price. I then forgot about my 'find' until it was time to set the valve timing on the Jupiter's engine.

In my haste, I didn't notice just what I had bought. I did find out at my cost, later, that the Mercer was indicating 0.0001" per division on the dial! Thus setting the cam lift at what I thought was 0.014", meant that the timing was retarded.

This caused all sorts of problems, insufficient vacuum for the carburettors to work and so on!

Correctly setting the valve timing is so vital on a Jupiter/Javelin engine. It has to be absolutely right!

Regards,

Mike Allfrey.

[Keith Andrews]

We have found the same sort of thing on the Bradfords, I suspected and confirmed as general consensis after the last Club Economy run...
I had set everything to factory, after extensive profiling of the cam lobes, came to the theritical conclusion the practice of opening the tappets up futher than factory specs as practiced by some, is a mistake.
The factory specs on a very worn engine over an reletively newish engine with the larger tappet settings made a huge difference to over all accerlation and up hill power and a lesser differance to economy.
I did close the tappets up a little under the factory specs to allow for wear on cam and followers that was apparent from comparing the actual profile to the factory specs to return to orginal lift and duration
The more I look at the Jowett the more I respect the factory engineers and their specs for the basic ex factory engine tuning specs.
I do not believe there is much or anything worthwhile to be gained out of these engines without changing interal things like cam profiles, combustion chambers, runners and the like.
Jetting and dizzy curves can be improved on simply because of modern fuel, thu I doubt these gains are significant outside the race track.

[Mike Allfrey]

G'dday,

I agree, the Javelin and Jupiter engines were lively performers, and a lot of that is probably down to cam profile.

I remember taking a camshaft to Wade's Camshafts and George Wade responded to my request for a bit more zip, by saying that the cam profile and timing were already quite zippy in standard form and timing. Since then I have left well alone!

I am a great believer in the fact that Jowett Cars Limited did get everything right with respect to the engineering of the cars. They were restricted by lack of funds and decent materials at the time of the Javelin's development.

I read an interesting point about British motor industry yesterday - When developing the Rover 75, BMW did not impose budget restraints, and the engineers at Cowley were so unused to such ways, they didn't know what to do! Thankfully for me, the 75 turned out to be a superb motor car.

Spare a thought for us down here, Victoria is burning fiercely in the east and very hot winds are forecast for Saturday.

Regards,

Mike Allfrey.

[Keith Andrews]

I believe there is still a lot to be pulled out of these engines on modern fuel, not just 'hotting up' but general performmance..modernisation.
Go from Zippy to very zippy...
I ask, if the jowett engineers where still around today, and considering the obvious pride they took in getting it right, would they be satisified to just leave it as is(old fuel tuning on modern fuel) or would they get it right for modern fuels?
I can see them going beyond just cams, dizzys, carbs...but into strokes reengineering heads, intakes, strokes. But going that far takes away the 'orginal' concept of the classic engine basic design, that as classic enthusists sort of defeats the purpose...may as well just repower with a moden jappa engine..
keeping the basic engine configuration, small tuning changes to bolt on parts..cam , dizzy, jets is simply an upgrade to adapt to modern fuels, roads without changing the classic design/concepts of the engineers.

It would be could if these guys where still around today to ask them what they think.