Cam Theory

[jlopes]

Here is a great article by David Vizard on camshaft design. http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/index.html

After reading the article I decided to see what would be the best for our 200 cid engines.

Using http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/photo_11.html of the article the recommended cam would have a LCA of 112 degrees. Using this the following charts http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/photo_07.html and the following statement:

To arrive at the duration when the overlap and LCA are known, we take the overlap (in our example 66), divide by 2, add it to the LCA (108 + 33), then double it (141 x 2 = 282).

Then the best cam for the 200cid with 50 degrees of overlap and 112 LCA is (112+50/2)*2 = 274 duration.

Now if we want a torque monster with 108 LCA which would probably mean more overlap then the calculation comes out as the following
(108+60/2)*2 = 276 degrees

Does this seem correct to those out there with way more engine experience than I.

 

[JackFish]

While I have very little relative experience I can verify that my cam has a 112°LC and 274° exhaust/264 intake. It seems to work rather well, but does require tuning to get the most out it.

So Clay Smith must agree with David Vizard.

 

[jamyers]

Bump, this is a really interesting article - got me thinking about recamming my Ranchero!

 

[MPGmustang]

Interesting...

I'm running the 264/274 110* .450 clay smith cam

known facts
the log head won't breath much after .400 lift so I have .385 as my avgerage lift/flow of the head, I could bump it up but no point IMO vs the price point/hp increase.
according to this we want the intake to be 274 duration, which means that the exhaust is working at peak but the intake is not.

another link to read... Calculating Overlap

A stock cam has 28* of overlap
264/264 112 450 has 40* of overlap
264/274 110 450 has 49* of overlap
274/274 112 450 has 50* of overlap
274/274 110 450 has 54* of overlap

I don't know if the shorter duration for intake is 'beneficial' both are at the top of the daily driver.

It is obvious that the stock cam is 'underpowered' and leaves much to be desired. from driving a cam with 49* of overlap I wonder if I'm in the upper range, I would like to try something in the 35-40 overlap range and compare notes and data that I have on my current cam. I think they would provide more torque and not much different HP.

still searching but very intresting

 

[jamyers]

...
Does anyone know the duration of how long both valves are open?
264/274 110 450
274/274 112 450
I would appreciate the info, CSC don't have that info and I've never seen it on a card on CI's website.

At CI's site, from the hydraulic camshaft page, clicking on the "details" link and you'll see:

264/274 112:

274/274 112:

I'm assuming the answer you're looking for is 224* on the 274 lobes, and 214 on the 264 lobe. Otherwise, we'll have to use the raw opening / closing numbers?


EDIT: Nevermind, just read your edit above.

What's interesting (to me) is that the Vizard article leads me to believe that we can use cams with WAY more overlap and duration than I previously thought practical.

 

[170-3tree]

okay, I did this with my engine, being a 173ci (overbore). I got some VERY interesting numbers.
I did it doing the low end of the street/strip overlap or high end of Performance street with 70* of overlap.

173/6=28.85
28.85/1.84=15.7
Lca=114*
Overlap=70*
114+35=149
149*2=298

Using 60* overlap to be more... conservative gave me about 288*

I am sure that vizard is right but not sure i am? or that this would be a good idea to even try?

 

[MPGmustang]

1170-3tree,
you are very right, but the catch on such a high duration is that you need higher CR as your planning the AL head your engine will be able to use the cam, but I fear that you will need 12:1 CR, and 110 octain, your choice of 70* of overlap is VERY radical, stock is 28* of overlap, but because u want the AL head you could support that. this would be more of a drag engine, WOT all the time.

IIWIYS, I would set the head up with 50cc compression chambers, I know you would like to eventually go 200/250 route, so I wouldn't take any mroe off if possible. then get some flat top pistons, this will give you close to 9:1 CR, with that I would run the 274/274 112 cam, it has 50* overlap, IMO is a good cam, and will take ur alum head into very nice RPM ranges due to the short stroke of ur 170ci, overboreing your engine can get you 9.1:1 with .040 overbore. when you finally do go for the bigger ci engine, you can use that same cam, it will smooth out some due to longer stroke, but should give more torque. and you won't have to purchase another cam.

I honestly think you would have alot of fun with the 170 AL and a 274 cam, it gives the impression that it could run into high RPM's easily, probably 7k safely. granted if you built the bottom end to be bullet proof.

 

[170-3tree]

Mpg,

I know had been thinking about the idea of using that cam all day today and knew last night that it wouldn't happen. My bottom end was rebuilt sturdily, but no where near what one would want to rev much over 6k often. The current 170 is back together and about to drop in so I don't want to do the cam after getting it all buttoned up. I might, later on down the road do the 274 or 280 but special order 115* LCA's. Just to see how right this is.
The 170 is a Four main block so I didn't want to invest much into it as I plan on doing a very VERY extremely thorough build with a 200ci and seven mains. I just wanted to be sure that my mental math machine was working properly. and as much as I intend to do to the new block, transfering cams is not likely an option.
according to the chart 70* would be pretty streetable, but probably vastly higher than what my end goal with this car is. ATM I am just afraid that I extemely undercammed my engine with 264/264-110* so with all the free dyno time i get at school I will likely attempt to go to something a bit closer to what Vizard points me to.

Thanks,
Gerald

 

[xctasy]

Where Vizards idealised cam over lap and LCA sellection falls down is when intake and exhast flow are restricted by log head design. As has been noted elseware, it won't compensate for a 1-bbl engine serving a larger six cylinder engine verses, say, a 2-bbl or 4-bbl carb feeding a small 4 cylinder.

Compare your 1-bbl 1963 four bearing 2800 cc inline six to the 2-bbl 1983 vee six four bearing Cologne 2800 used in the Bronco II. Practically the same bore and stroke, rod ratios and valve sizes, but the resulting power curves are very different. Internal frcition losses were the same, as bearing sizes were the same The Vee-six has a German derived cam profile to suit what was a 135 flywheel net hp engine in its native Germany. By the time it got to the USA, it lost one point of compression ( 8.2:1 rather than 9.2:1), and got smog gear and a mechanical secondary carb from a 2300 Pinto engine, ...it lost 26 flywheel net hp on the journey over the pond. If i recall, about 104 to 109 flywheel net hp for that year. Same with the Chevy 2800 173 CID engine in that year...114 hp stock, or 135 hp 660 Hi Performance. Each of the Cologne and Chevy V6's had a cam profile closer to Vizards idealised numbers

I've worked extensively with another 2800 cc in line engine with the same carbuartion as the 1979 to 1985 Chevy and Ford 2800 V6's, and I can tell you that the cam profiles for the I6 were 185 at 50 thou, and about 256 total with less than 400 thou lift. Lob centre was 110. Power was 102 hp at 4400rpm, and torque142 lb-ft. Gearing was 5-speed Borg Warner with 3.36:1 gears. The carburettor was a Rochester Varajet, ignition HEI, and the car in question had EGR and ran on 97 octane unleaded. It wouldn't rev past 4500 rpm, and wouldn't do a 18.8 second quarter mile. The cam profile was the similar to the GM 1900 cc engine used in J cars and that used to rev to 6000 rpm, and yet in the six cylinder application, it would be had pressed to do 5000 rpm. The engines werew 1982 production four and six cylinder engines in the Australian Holden Commodore VH. The four was called a Phase 3 variant of the Starefire Four, and as a 4 cylinder it was 67% (2/3rds) the size of the XT5 six, with the same cam, carb, compression and head, pistons rods, stroke bore, but made 77% of the power at 78 hp at 4800 rpm verses 102 hp at 4400rpm. Torque was 102 lift vs 142 lb-ft, and 72% of the torque. So as the engine gets bigger, the cam needs change. In the same car, it did a 20.7 second quarter mile with the 5-speed same gearbox in a 2548 pound car, 110 pounds lighter . Based on the hp to weight ratio, the 4 cylinder had 77% of the six cylinder power.

There are issues of comparing two engines with just a capacity difference with the same carb, but what I think this means is if the same cam profile is used, the larger engine will loose power if the lobe centre and overlap is not optimized. I'd have expected 117 hp and 153 l-ft, so the six cylinder lost 9hp and 11 lb-ft on what should have been there based on a 67% bigger engine.

Details of the Phase 3 and XT5 engines were both 3.5 by 3 bore:stroke, 5.25" rod ratio, 1.9" crank pins, 2.5" main bearings (seven in the six, five on the four, 1892 cc in the four, 2838 cc in the six). Each had non divided port head, 12 ports in the six, eight in the four). Carb was the same as the V6 Chev Varajet 2-bbl, basically half a quadrajet with metering rods and machanicall secondaries

 

[170-3tree]

Except I almost longer have a log on my 170. I switched to aluminum.

 

[xctasy]

See
http://www.fordaustraliaforums.com/foru ... y&p=369716

How does a 250 Fox Mustang sized Cortina with 256@50 584 lift exhast and 265@50 607lift intake with 107 LCA split grab you?

2600 pound car, high 11 sec quarters, nothing special to the bottom end, but a good alloy head, a 650 cfm 4-bbl and that wild Ivan Tighe camshaft which uses NASCAR valve gear and after market 460 roller cam gear.

There's plenty of flat tappet or hydraulic cam profiles milder than that which will suit what you are doing with the CI head. Save up, plot and enjoy the outcome, becasue all the gear you need is at your finger tips, and its US made.

 

[Buddy Rawls]

You have to really watch thew stuff that follows David Vizards articles, write-ups and books. there are some liberties taken that do not necessarily apply globally in all instances.

First and formost, Lobe Separation Angle is not determined by cid and usage. there is a HUGE peice of the puzzle that needs to be addressed. that piece of the puzzle is the availability of inlet capability and exhaust capability in comparison to the displaced cylinder over the rpm range in question. Essentially, this is the flow and port velosity aspect of the big picture. To leave this out of the picture can really put you in the outfield if you are not within the "parameters" the model was set-up for. If you have very large cross-sections (versus the cylinder volume) or very small cross-sections versus the cid, then you are going fall outside of the model parameters.

Most of Vizard's equations appear to be set-up for a hard coded inlet capability. For example everything is based off of a default crosssectional area of inlet capability. As the cid increases for a given rpm, the exhaust placement delays, in other words the LSA narrows. this is all good, but only for the parameters of the initial criteria. If crosssectional area of the inlet and outlet are different than the model, than assumptions are no longer valid. Or what if you use proportional inlet and outlet parameters to the displaced volume. Vizards stuff was originally constructed based on small block Chevy builds. unless your motor has a similar proportion of flow capability versus cid and rpm, the equations are not going to be valid.

Also, Overlap is a relative term. It is measured in terms of angles EC to IO, but it is actually associated with an amount of charge per unit of time. A very large cross-sectional inlet and outlet will require very low overlap angles. the same amount of charge is getting by, but the door is so large it does not need to be open long. If it is open too long, the velocity at TDC overlap dies, then the inlet charge is contaminated and the overall idle and low speed operation can really take a hit. On the flip side, very restrictive motors have very high velocity, but mlow flow capability. the amount of time required for the charge exchange needs to be lengthened. This is apparent when the CID is increased for a given inlet parameter and rpm. the velocity increases and the exhaust needs can be retarded (LSa is narrowed). to hardcode an overlap value without considering port capabilities versus cid can get you out in left field easily.

In general, valve events are the real deal. the relationships of the valve events (intake to exhaust) are what defines the lobe seaparation angle. Not the other way around. So many write-ups seem to group LSA into a usage category, as a sort of first step. the first step is determining what the inlet events need to be to acheive the desired rpm. This is based on inlet capability and cid relationships. Then the exhaust can be worked, based on the exhaust capability versus the displaced volumes. The LSA is not even part of the process. The LSA comes into the picture when you go to select the cam or have it ground.

A very restrictive motor does not need to be exhaust biased (unless it is INCREDIBLY more restrictive than even the intake is), and it certainly does not need early exhaust activity (wide LSA). Very restrictive motors respond to lots of ramp rate (not lots of seat timing) and delayed and shortened exhaust. If a header and open exhaust is added to a restricted motor, then the need is for less exhaust is even more drastic. the reason 2 barrel restricted race engines need very narrow LSA and intake biased cams is not because the car has numbers on the side. Its because that what the flow parameters are. Building a tow truck or grocery getter is no different. the same exact equations are valid. On the flip side very high flow capability will require decreased valve timing and ealier exhaust activity. Case in point 290 cid comp eliminator motor with huge heads, versus a 283 superstock motor with the small heads. Both are race for sure, so obviously they will need the same LSA. the only problem is if you really look at the needs the SS motor will be using a 104-108 LSA and the Comp motor will be needing a 112-118 LSA. the difference is in the all the other stuff that relates to the displaced volume, not the displaced volume by itself, as write ups like this would have you believe.

A motor's cam needs are defined by inlet and outlet flow parameters (flows, areas, velocities, etc), displaced cylinder volume, rpm. the variables that have to be adjusted are typically going to be compression. If the compression is not high enough, then the rpm has to be lowered, or the flow parameters increased. what this does is utilize less cam for a given rpm. more flow requires less valve timing (for a given rpm). less flow requires more valve timing (for a given rpm).

 

[THE FRENCHTOWN FLYER]

Good advice Buddy.

 

[The_DropOut]

So, what about the store bought cams, the kinds that me the Avarage Joe can afford. Are they a rip off or are they a fair buy.

I have a rebuilt (Stock) 200 ci. Single barrel, stock compression and I'm running the 3 speed with 3.50 final drive.

While rebuiding my motor I had to take a crash course on cams. This is the first cam I've researched and I made an educated guess as to what would work.

I purchased the Schneider 256-H grind cam.

INTAKE: .000 valve lash, .420 valve lift, 256 duration, .280 camlift, 204 duration at .050" camlift.
EXHAST: .000 valve lash, .420 valve lift, 256 duration, .280 camlift, 204 duration at .050" camlift.
LOBE SEP: 112, Degree intake lobe 110

(Any other stats needed, please let me know)

I like the way the motor runs, its a daily driver and a crusier. But now I'm second guessing myself. I wonder if I made a wise choice. Could have I purchased something else that might have given my motor more pep or more pull without turning it into a 'Rumpty-Rump-Rumpty-Rump' drag racer?

 

[Buddy Rawls]

...I purchased the Schneider 256-H grind cam.

INTAKE: .000 valve lash, .420 valve lift, 256 duration, .280 camlift, 204 duration at .050" camlift.
EXHAST: .000 valve lash, .420 valve lift, 256 duration, .280 camlift, 204 duration at .050" camlift.
LOBE SEP: 112, Degree intake lobe 110...

I like the way the motor runs, its a daily driver and a crusier. But now I'm second guessing myself. I wonder if I made a wise choice. Could have I purchased something else that might have given my motor more pep or more pull without turning it into a 'Rumpty-Rump-Rumpty-Rump' drag racer?

A camshaft is a piece of steel, nothing more nothing less. A camshaft becomes something when it is integrated into the engine combination, the intake and outlet flow parameters, the displaced cylinder volume, the rpm, the static compression. a camshaft sitting on a shelf may be the exact grind that was used to set a performance record of some sort, but if installed in another motor with differing flow parameters, could end up being a waste of time or even a detriment.

The Schneider cam you provided the specs for is also available for a small block Chevy, small block Ford, nearly the same in the big block chevy, and then in the 351C (where they give it a tighter lobe separation which is completely counterproductive in a motor with that slow of port velocity), and likely most every motor they fit camshafts for.

Those motors range from an inlet flow availability versus dispaced cylinder volume 75% (typical 350cid SBC with typical cast factory heads, and similarly 300 cid SBF with factory cast heads) to 103% for the 4V 351C. The 454 BBC falls in the middle of those depending on whcih head. the oval port comes in around 75% and the square port in 90% range.

In typical form of the camshaft manufacturers, the 75% (or the SBC design criteria seemingly used by everyone) is what they offer.


The Ford 200 is at an inlet availability of around 60% assuming an inlet flow capability in the 110-125 cfm region. What this basically means is that you have taken a 454cid BBC and installed a set of 'decent' small block chevy factory cast heads on it.

While the difference between a 60% combination (200 cid ford six example) and 70% (small block chevy with factory heads) are not drastic, they are different.

In general, restrictive motors need more inlet ramp rate, but the overall seat duration needs to stay relatively low. On the exhaust side of things, the exhaust valve activity needs to be delayed (narrower LSA). The more flow capable the exhaust is, the more the lobe demand decreases (less valve activity), and the later the activity needs to be (narrower LSA). In essence for a restricted motor to work with a wider LSA and biased exhaust, it needs to have a similarly restrictive exhaust flow scenario. When the intake flow is already on the order of 110-120 cfm, the exhaust will need to be on the order of 1.25 header primaries, or torque will be lost due to the too early release of the cylinder pressure if the valve events are needing less flow capability on the exh side. With1 3/8 headers and a equally suited exh system, the intake valve activity could easily end up being larger than the exhaust, and the lobe separation 'EXTREMELY' narrow, for proper air movement in the motor.

In general, the path to take for a restricted lower rpm motor is small cams with steep ramp rates, similar intake and exh lobes and narrower Lobe Sep Angles. the more restrictive the exh becomes, in proportion to the inlet capability, the earlier the exh activity needs to be become (wider LSA) and the more the exh valve activity need to increase. A typical case in point would be a properly spec'd camshaft for a supercharged motor.

My whole initial response was based on the 300 six, sorry I did not read more indeptly that this was for a 200 six. Now, it is tailored more to the 200 cid ford six assuming an intake flow around 110-125 cfm (28") per cylinder, and 'genericized' the info somewhat.

 

[MPGmustang]

So, what about the store bought cams, the kinds that me the Avarage Joe can afford. Are they a rip off or are they a fair buy.

I have a rebuilt (Stock) 200 ci. Single barrel, stock compression and I'm running the 3 speed with 3.50 final drive.

While rebuiding my motor I had to take a crash course on cams. This is the first cam I've researched and I made an educated guess as to what would work.

I purchased the Schneider 256-H grind cam.

INTAKE: .000 valve lash, .420 valve lift, 256 duration, .280 camlift, 204 duration at .050" camlift.
EXHAST: .000 valve lash, .420 valve lift, 256 duration, .280 camlift, 204 duration at .050" camlift.
LOBE SEP: 112, Degree intake lobe 110

(Any other stats needed, please let me know)

I like the way the motor runs, its a daily driver and a crusier. But now I'm second guessing myself. I wonder if I made a wise choice. Could have I purchased something else that might have given my motor more pep or more pull without turning it into a 'Rumpty-Rump-Rumpty-Rump' drag racer?

I think the cam is good IMO, it's not the greatest by any means, and it's not the worse. it's a good base to go. as mentioned in this thread the i6 is low flow, low powered engine.

the benefit of your cam is the velocity of the air will be higher, less air but higher velocity, meaning more torque/response off the line. also your cruising speeds can be at a lower rpm and get better gas mileage.


the great thing about a low flowing head is we are less prone to that "rumpty" idle when using a longer duration. in fact my mild engine is quite tame at idle, it can dip in vacuum a bit but relatively smooth enough for me. the trade off is that nice low torque right off idle and the low cruising speeds (aka MPG) the benefit is the higher HP at passing speeds it really does kick

I actually wish I got more cam!!! I'm running the dual grind 264/274-110 .480 hydrolic and would like to go to a 278/278-112 .495 hydrolic. The top end would have more HP, the bottom end would suffer some but the efficiency of the engine would go up and so could gas mileage at higher speeds . IMO the dual grind cam doesn't help as much as a single grind, unless restricting the exhaust a little (say 2-4*)

all in all the cam dictates how you want the engine to run. there are caveats to it all though. lower duration is lacking in higher rpm, and longer duration is lacking in lower, but one thing is consistent, more lift = more power. by giving more lift the ramp rate goes up and the velocity of air being sucked in gets a boost because the average lift is more.

In simple terms,
For HP: we want the max average lift rate, longest duration, 45-55* overlap, longer LSA
for TQ: we want the max average lift rate, shorter duration, 35-45 overlap, shorter LSA (stock 29 overlap is too short)

 

[turbo2256b]

Issue wit ha lot of off the shelf cams for Fords especialy the hyd and lower performance stuff. The lobes are designd for the Chevy lifter dia. If designed for Fords lifter dia better performance can be attained with the cam lobe design.

 

[The_DropOut]

Thanks for the detailed info. I'll have to copy it all down into my "Future Six Build Book".

It is a tough subject to follow, because so much is happening within the motor.

Sometimes the seat of your pants is the best professor. It would be great if we had 3 different cams, installed them in the same motor and ran them on the same day to actually feel, hear and see the difference. Compairing one motor to another is more like apples to ornanges due to all the variants at play.

I'm glad that my cam is suited for commuting, that's what I wanted. The primary goal was "I WANA DRIVE!" Later I'll build a more sporty motor and see what I've learned.

 

[xrwagon]

That yellow cortina was running at willowbank on sat night, it must be the most drag raced ford six cylinder out there. runs hard and consistent.

 

[rbohm]

8) i realize that this is an old topic, but, when dealing with david vizard, you have to understand that he sees things from a race engineers perspective. with that understanding, much of what he put down wasnt for the average person to use the math to select a cam, but rather for the average person to realize that selecting a cam isnt as simple as looking at lift, and duration numbers, but adding in valve overlap, and lobe separation angles, and cylinder head flow capability. if you were to have david select a cam for two similarly built 200s with one difference, one used a modified log head, the other used an out of the box aluminum head, but everything else was the same, IE compression ratio, cylinder bore, stroke, headers, valve size, rocker arms ratio, etc. he would select two entirely different cams.

the key to selecting a cam for the average person is what the manufacturers say the cam is best for. if you are looking for a cam that will give you a good idle, decent fuel economy, and decent power, you dont want a cam that the manufacturer tells you is good from 3000-7500 rpm and has a lumpy idle.