Cam profile design 10

[EngJW]

Hello,

Just discovered this forum. I have been searching for a forum on camshaft design. That is, actual design like ramps, profiles, materials, machining, and so on, as opposed to "what cam should I use?" I found a gear forum but no cam forum. Anyone know of one, or is this forum the appropriate place?

Thanks,
John Woodward

 

[ShaunT]

I wish to stress something that I have said before, but a bit off the subject from the last few postings to this thread/subject. As Intake Port volume increases in addition to utilizing longer connecting rods, but not running a longer stroke crank( I.E. higher rod to stroke ratio) one needs to be aware that some(Super Stock style) cams with an extreemly high/fast initial acceleration rate before TDC will drastically hurt power and torque because the piston won't create the velocity in the Intake port. When a longer rod is used in place of a shorter one that was origionally used when the origional engine/hed/cam combination was designed,I usually back off on seat duration and tighten the LSA a couple of degrees and suggest a tight lash cam because it has a bit slower initial(before TDC) opening.
ANother trick for any combo (I will use a small block Chevy in this scenario) is for the guy who wishes to run 1.6 or bigger Rocker Arms. May I suggest keeping the 1.5 on the Exhaust. The bigger ratio on the exhaust really sacrifices the low speed torque for very small gains up stairs. The 1.6 on the intake offers the most bang on the big end but spares the low speed to the guy who needs it. When I became a W.D. for Air Flow Research Heads, I shared this with many dirt racers along with info that the Dyno proved. It has really helped make some wannabe's become very consistent winners. Happy Tuning.

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

 

[ShaunT]

Cam profile design. What about rocker arm geometry and fulcrum points? You can and should always check rocker/push rod geometry anytime a cam is changed or the heads/block is worked. It will take some drag off the motor, and it will save the guides and valve job. As for fulcrum points, it is gratifying to take a motor with all of the springs and components in running condition, and turn the motor with a torque wrench. I have seen 50-70lbs required to turn motors even with the plugs removed. I have also seen the same motors require 20lbs or less when a shaft mounted rocker arm assembly is installed that changes the fulcrum point as compared to the standard stud style seen in your typical small block Chev or Ford. I love to see the leverage work the magic. This is some fairly nice increase in power too. Some of the shaft style rocker systems are becoming pretty affordable too.
I love this stuff!!

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

 

[enginesrus]

About all this flat tappet cam break in stuff.
And minimum rpm to do such.
I know some of the thoughts on why.

But there are many engines that have flat tappets that never go over 1300 rpms. So kinda blows holes in that one.

 

[ivymike]

hmmm... maybe it's a "minimum average rubbing velocity" question, then? A 1300rpm engine most likely has a larger-diameter cam than a 5000rpm engine... whaddya think?

 

[ivymike]

nah, come to think of it, there are sbc-sized cams in slow engines too, with flat (crowned) followers

 

[patprimmer]

It's about throwing enough oil off the crank onto the cam. The 2500 to 3000 rpm I use to break in cams was all on SBC, so I have no experience with other applications.

When I hotrodded air cooled VW's, the boxer configuration with the cam below the crank, ensured plenty of oil, even at idle, so I guess it's horses for courses, depending on variable factors like surface contact area, oil supply, metalurgy, spring pressures, valve train inertia etc etc etc

eng-tips, by professional engineers for professional engineers

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ShaunT]

On the subject of cam profile design as it relates to making cylinder pressure and how this affects performance.
The single most critical element of the cam in this scenario, is the actual point the Intake Valve closes(degrees after BDC) When an intake valve closes, compression begins. Even though the piston may be moving up on the compression stroke, it wont start building the pressure untill the valve closes. It will be Hicupped back into the intake. The sooner it closes, the sooner it starts, and therfore the higherit will go. The sooner you close it, the more detrimental it will be to your goal of making this pressure build when the valve re-opens unintentionally from the valve bounce because cylinder pressures increase RAPIDLY with every degree of crank/piston movement. This also makes for a great hicup/burp into the intake. As I have said many times hence, it will also be the best recipe for murdering Torque and delaying the engines power making RPM range. It can be pretty detrimental to the overall health of the valve train, too.
Some realize this problem from the Dyno's information.(I personally can hear it) Their only way to stop it is to up the valve spring pressure. This is a Band-Aid approach! To a point it is par for the course because the valve train weight must obviously be dealt with, and that is the way. After you have managed that, there comes a point when adding spring pressure to control valve bounce becomes rediculous. The cam may have a very high negative decelleration over the nose, or a high rate of seating velocity, or both. Therefore, I repeat another statement I have said many times:Throw that @$^*&@^ valve train wrecking camshaft in the trash!

Have Fun!

Shaun TiedeULTRADYNE/LUNATI Austin,TX(stiede@ev1.net)

 

[enginesrus]

Question, the new cam shaft has lots of oil. In theory then, no metalic surfaces are then touching. So then what is breaking in then??????
I'm just trying to get the thinking wheels turning here. LOL

 

[EngJW]

Bearings normally operate under "hydrodynamic" lubrication where there is plenty of oil and nothing touches. The rotating journal actually pumps the oil through the bearing. Cam and lifters operate closer to "boundary" lubrication where contact can occur. Contact area is small and loads are high, so there is a high unit loading. Engine oils have EP additives to reduce wear under high contact pressure.

John Woodward

 

[enginesrus]

Agree, so then what is breaking in?
For metal to "break in" other wise wear in. It has to have contact. A cam lobe and follower represent a very high pressure contact point. What I'm driving at is if the cam and tappets lube just fine after the so called break in at low speed. Then ????

 

[ShaunT]

There will be some wear in. The surface roughness averages are different from the lobe and the lifter. They will lap into each other. There will also be a pattern worn based on where the lifter is contacting the lobe. This can be influenced by lifter bore angle, and wether or not the cam is in a thrust plated block, and therfore wether or not the cam is walking back and forth in the block. Pre 1987 small block Chevies are a good example. WHen the cam is allowed to walk, it not only influences spark timing irregularities, it also reack havoc on the chain. THis of course retards the cam due to stretch, hurting low end power, cylinder pressure, cranking compression, exh valve to piston clearance, etc.

 

[patprimmer]

Way back in the 70's, I saw one turned by hand with the head of. As I remember, 4 pistons were at TDC at the same time, but I am recalling this to memory from over 30 years ago

Regards
pat

eng-tips, by professional engineers for professional engineers

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[motorsportsdesign]

Flat crank V8s have only 2 pistons at TDC at any time so 2 cylinders do not fire at once.

There are many current and recent applications of flat cranks. I made them for drag racing in Pro Stock and Fuel classes. They also had some flat cranks at HPD in 94 when I worked there.

Jonathan T. Schmidt

http://www.motorsportsdesign.com

 

[ShaunT]

Valve spring tech has certainly come a long way in the last ten years. I used to avoid designing some cams that were mostly ideas because I knew there wern't spring available at the time to handle the job. To an extent, cams have evolved from the advances in springs, too.

 

[TTmotors]

Shaun T do you do any work on any import/domestic 4 valves? Im in a crunch for some cams to a 3.0L v6 duratec by ford.

 

[ShaunT]

I don't produce over head cams. The tooling to manufacture is quite different. Let me do some checking.
The head could benefit from a trick 4 or 5 angle C.N.C valve job using a machine such as a Newen GII. The goal is to keep intake seat angles about .038 wide and exhaust about .060. Back cutting the intake may help too.

 

[TTmotors]

Thanks for looking into it. From the way you talk it makes it sound like most cam manufacturers have NO CLUE on what they are doing. Cat cams of britain has quite a few diffrent sets of cams for this engine but they are symmetric and the way you talk symmetric is NOT the way to go to acheive maximium power. They also seem to be pretty slow opening. THey come with a very hefty price tag of about 1540 + shipping dollars and they arnt built around your application. Further the duratec heads have a serious problem of overlap flow. As seen in this SAE article

http://www.bath.ac.uk/mech-eng/auto/txnet/983038.pdf

This makes me really wonder about if they got the cams right, because all the duratecs seem to suffer from severe overscavaging. Any help or recommendations would be greatly appreciated.

 

[ShaunT]

I guess I have made myself sound really Arrogant. I just don't have too high of an opinion of other cams. I feel that a product that has to be marketed to death with a couple of $Mill/yr shows it is inadequate. To some, I come accross as biased. I feel that is easy for one to think that untill he tries one of our cams. Then, the scepticisim goes right out the door.

Have you played wth the intake and exhaust centerlines of the stock cam? This is a dual over head cam isn't it? If it is, you can move both cams around in the motor independantly. This can help with scavenging. It definately effects cylinder pressure and cranking compression.

Symmetrical cams are a compromise.

Shaun TiedeULTRADYNE/LUNATI Austin,TX(stiede@ev1.net)

 

[TTmotors]

Iv thought about this but machining adjustable cam sprocket assemblies is pretty difficult. Moving the cam a tooth is really unacceptable to be considered tuning. The cam wheels physically lock into the end of the camshaft so tuning this way is pretty hard to do.

Now on previous 4 cylinders they were held on by friction and they could be installed off center of tdc in either direction or they had a huge aftermarket like the zetec does and i had teh availibility of adjustables.

It seems like SOMEONE ANYONE could make 4 camshafts fit to my exact vehicle/specifications/mods for 1500 dollars. Its just a high price to pay for something that isnt exactly what i want.