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Discussion Starter #1
I've been sitting on the sidelines for awhile watching the discussions on cam selections. I've got a few thoughts for you guys to ponder....

- the cam sets the character of the motor. The valves follow the cam lobes unerringly. The intake and exhaust timing events along with the lobe shape and then total lift set the tone.

- you need to know what the heads are doing with intake and exhaust flow at the different lifts. from TDC overlap and every 50 and 100 thousandths up to the peak lift of the cam

- all the parts from the inlet, to the exhaust tip need to be working together. There are things on the carb/throttle body and the intake manifold that can be done to optimize the flow velocity and cylinder fill.

- there are certain combinations that are known to work by the folks that cnc or hand port cylinder heads.

The cylinder heads are like a two way street and the ports/valves can be tailored to work with various cam grind and lift schemes. Getting the best cylinder fill and purge for all the key operational areas makes the motor work at it's best.

If you mismatch the cam to what the heads are actually able to deliver or get the velocity wrong at certain drivability regimes, you get a quirky motor and no amount of tuning will straighten it out.

Bottom line is, pay attention to those that have done their homework and have known combinations and then adhere to "the combination", INCLUDING which exhaust pipe workswith it. Can't tell you how many people get it almost right and pay a lot of money to do a build and then screw it up with a set of pipes "that look good". You know what I'm talking about. ;)
 

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Go fast or dont go.
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absolutely....do your homework.
 

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MaxHeadflow
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Ya know Tote,

I would say from some of the good builds here that there are a number of people building things right. Kind of wonder what might be the must not do's. It's kind of obvious to me that you need to set your corrected compression to some good number that puts the CCP at 185 to say 205 and has a good quench. What about port sizes? Obviously the port needs sizing to the motor so that the peak velocity is not too high or way too low but how does the cam come into play on this? The cam can provide more duration and fill at higher RPM or less duration for more TQ. Anyway other than what seems obvious to me above, is there a formula or numbers you can look at to say that the cam is not right for a particular head. Or is it just empirical??

Bruce
 

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Tote, been thinking a lot about cam selection thing too, cam timing vs compression mostly, When you have two very similar cams with slightly different intake closing numbers is there really a lot to be gained from milling heads, thin gaskets etc to boost compression only to use a later intake closing number just to keep cylinder pressure in check. There seems to be a fine line with regards to cylinder pressure, hard starting, pinging etc, like Doc stated in another post a short time back "there is no free lunch" and everything has a trade off of some sort.
 

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Discussion Starter #7
when you start going beyond mild bolt in cams, you need to start paying enough attention to port flow and velocity to get it correct for the build at hand. As we know, bigger isn't always better for valve sizes and intake ports if it allows the velocity to drop too low. The low end and response suffers. Too small and then the motor can't breathe above a certain point and it is slow to spool up.

How about looking at what is going on in the intake at one stroke length from the valve seat? Might be a good spot to create the peak velocity. Some think an ideal intake "funnel" has a 7* slope. Then there is a optimum amount of how much volume is in the intake tract behind the one stroke length out point, this volume if right, helps charge the cylinder fill when the intake opens.

All I'm getting at is, you need to understand what the cam does. Basically it's an air flow traffic cop. The lobe ramp profiles position the valves at certain points in time relative to piston location in it's travel for the cycle it's on. Timing of flow and how much at what point in time. If the ports, valve sizes or intake configuration or exhaust pipe personality or any combination thereof aren't working right for the combination, a cam change usually isn't going to fix the problem, if the problem is elsewhere.

BVBOB, absolutely right, as Doc said, there is no free lunch and there are trade-offs for certain choices..... but then there is characterization of parts and optimization of certain combinations and there is a lot to be said about that.

I'll be quiet and let those with more experience and knowledge do the talking.
 

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I like that- "the cam is just a traffic cop" What does the road look like? It's directing traffic. When you port and add more traffic to the road, unless you know what that traffic is in the road system, you can't just put a cop out there waving his arms the same way every time. You have to control the road differently to what you put in. So you can not arbitrarily pick a cam not knowing what the heads are doing. It will do something, but how do you know that it's right. Are you in the hot part of the woods? I'm going to send you a cam with 4 degrees more opening to blow off more heat. Other wise it's heat and pressure that creats detination so I've got to get rid of heat because I know that the pressure is going to be there.You don't design the cam first and then the head around the cam.
 

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ovanay elinquentday
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KingofCubes said:
......You don't design the cam first and then the head around the cam.
Not sure I understand that one. Seems like if one picks a starting point and knows the limitations of the cam, the head, etal, can be intelligently selected and ported. I thought the whole point was to pick a performance/parameter base and design as a package?
 

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GPO03FatBoy said:
Not sure I understand that one. Seems like if one picks a starting point and knows the limitations of the cam, the head, etal, can be intelligently selected and ported. I thought the whole point was to pick a performance/parameter base and design as a package?

im with you dude, the cam selection always dictates the rest of the build. thats why the customer interview is always the most important piece of the puzzle.

too many people jumping on a bandwagon and being dissapointed in expensive build. more so lately!!!!!!!!
 

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On some sportsters, the racing guys used to mismatch the cams differt grind for the front and rear cylinders. some cam manufacturers (most) have symetrical lobes and all intake and exhaust are the same. Others experiment with asymetrical lobes - opening is different than the closing(noisey).

I don't know what Woods' cams are like, but i would like to see some cams that are ground for a single type build, one with the same porting and C/Rs. I bet that the best for a certain range would all be different assymetrical grinds. this would be a speciality cam and expensive.
 

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route66paul said:
On some sportsters, the racing guys used to mismatch the cams differt grind for the front and rear cylinders. some cam manufacturers (most) have symetrical lobes and all intake and exhaust are the same. Others experiment with asymetrical lobes - opening is different than the closing(noisey).

I don't know what Woods' cams are like, but i would like to see some cams that are ground for a single type build, one with the same porting and C/Rs. I bet that the best for a certain range would all be different assymetrical grinds. this would be a speciality cam and expensive.
you mean like Q, PB, PB+? i remember those days.
 

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GPO03FatBoy said:
Not sure I understand that one. Seems like if one picks a starting point and knows the limitations of the cam, the head, etal, can be intelligently selected and ported. I thought the whole point was to pick a performance/parameter base and design as a package?
The problem with this is if you put a good cam; a 37 or a tw6 in your engine without changing anything else, it won't run well. if you put a hot cam in; hi-lift, you will have problems immeaditly because the stock springs are wrong and the valves won't work properly.

You might be able to change out heads with a street port and springs that would work with a higher rise cam, but then you are going to have to remove the heads when you do put in the big cyls and pistons, and you would have to remove it again if you don't want to buy adjustables. It is a lot less work and money to do the big 3 all at once.

It is a real good idea to figure out where you want to be at first, that way you won't be replacing the parts that you just bought. It would be cheaper to save up 1/2 the money for the full build and then finance the rest, and then pay it off as fast as possible.
 

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Let er rip!
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claydbal said:
im with you dude, the cam selection always dictates the rest of the build. thats why the customer interview is always the most important piece of the puzzle.

too many people jumping on a bandwagon and being dissapointed in expensive build. more so lately!!!!!!!!
Does cam selection determine port shape?

Does cam selection determine valve size? Valve size may be overkill for certain builds, but that's more of a stage thing than it is selecting heads based on the cams. Then again, will the larger valves in higher stage heads allow a little more compression without pinging problems.

I thought it was mostly the cam/piston/compression combo to avoid ping, the quench, and obviously the spring set up to accomodate lift.

I get questions on the heads I'm trying to sell, and guys are assuming that my heads can only be used with the 615/585 cams that I had. Not true at all..........
 

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ovanay elinquentday
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route66paul said:
The problem with this is if you put a good cam; a 37 or a tw6 in your engine without changing anything else, it won't run well. if you put a hot cam in; hi-lift, you will have problems immeaditly because the stock springs are wrong and the valves won't work properly.

You might be able to change out heads with a street port and springs that would work with a higher rise cam, but then you are going to have to remove the heads when you do put in the big cyls and pistons, and you would have to remove it again if you don't want to buy adjustables. It is a lot less work and money to do the big 3 all at once.

It is a real good idea to figure out where you want to be at first, that way you won't be replacing the parts that you just bought. It would be cheaper to save up 1/2 the money for the full build and then finance the rest, and then pay it off as fast as possible.
Like I said, I thought the whole point was to pick a performance/parameter base and design as a package...
 

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I always port the heads based on the cam they are going to use. It doesn't make sense to have a head that flows good at .600+ lift with a .500 lift cam. But if I was in the head mfg. business & I came up with a head that had good flow in a certain range I could then design a cam to match it. same idea, different point of view.
 

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The cardinal rule I have always heard is "You build a performance engine from the heads down".
 

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Good Stuff



For me, it would be great to understand the math behind cylinder fill/drain versus cam timing,lift, and duration versus intake and exhaust port system dynamics.

I'll bet there is some piece of software out there these days that the big engine builders have that can provide a 3D image as cam dynamics are altered. You know, how each change would affect oveall flow. I'll be willing to bet these NASCAR engine development engineer have these kinds of tools.

On the other hand, its much easier to just purchase an engine package where all of the parts are supposed to work with each other. After all, isn't that part of what we pay for when we buy a certain build?

If you think about it, before the computer age, many of the top engine builders must have known their Math :yikes: :xhere: not to mention being able to convert their math into reality and make it all work.
 

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KingofCubes

KingofCubes said:
This is why I use Reggie Sr because he understands all of these events and how they work together, he is my software program. He is a beta tester for Andrews Products.

:hmmm: I hear ya! It sounds like your friend has been in and around for quite some time too! Whereas some riders like me could only wish that we had that kind of time to spend working with different cam profiles, compression rates, and cylinder head porting ideas to actually find what works best. Not to mention the materials and resources to make one off parts as we need them.

The people who work in the performance engine arena are able to pretty much able to dial in their cam of choice to make it work with a displacement setup that is pretty much imposed upon them, kind of like NASCAR would/does. I do realize that different race tracks will switch bores and strokes (keeping the overall displacement in tact) on a track by track basis because they know what works best on each track too, weather it be Bristol, Talladaga, Texas, or Dover. So for them to design a new profile cam and other guts to go with it, is a collection of CNC software they have aquired for each profile. Thats just my take.
 
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