Would you recommend this cam profile for a 3500lb car running primarily on the street.
AOD transmission, 3.73:1 rear. I like the idea of staying as close to a Ford design as possible. Iron closed chamber heads, Blue Thunder intake, Holley 780...
Great information that just is not availible elsewhere!
Yes
i have a cam spec comp cam gvl int. .520 exh. 531 duration .006 tappet lift 282 288 .050 int. open 5 btdc close 45 abdc exh. open 56 bbdc close 0 atdc specs for cam installed @110 intake centerline duraton@,050 intake 230 exh. 236 lobe lift intake .3010 exh. .3070 lobe seperation 114 multiport fuel injected. thoughts? i love the dicussion on cams it confuses me but very interesting. one of those never ending topics. on the side george do you have pictures of your new rims 18" and 17" i know different thread.
Carl, since there is 6° difference between intake duration and exhaust duration the cam you describe reminds me of a cam designed using one of the laptop dyno programs.
The first thing I noticed is the cam has fast ramp lobes (52° lobe intensity) yet only 0.520"/0.531" lift. Seems as though whoever put this cam together placed emphasis on duration at 0.050". The 351C 4V heads are going to make peak BHP at 6000 rpm even if the duration at 0.050" is only 205°! That's the intake duration of the Cobra Jet cam. The 351C 4V power band is not as dependent on duration as it is with other engines, but to make power the valves need to be opened as high as possible (within the limitations of engine longevity) to take advantage of the cylinder head air flow potential. Lobes are available today allowing valve lift in the 0.550" range (or more) with reliability.
The valve event timing is just fine, the overlap is low (57°), it is more or less centered within the window it should be centered within, that window is the piston's "dwell" time at TDC. However due to the 52° lobe intensity, overlap at 0.050" is 5°. I'd like that better if it were closer to zero. The exhaust valves are opening and the intake valves are closing where they should be based on advertised duration. But I'd prefer it if the intake closing at 0.050 was 40° or 41° ATDC instead of 45° ATDC. Those are the various boundaries I try to stay within to insure good low rpm performance.
The cam should work fine, but if lobe intensity were 57° instead of 52° (225°/231° duration at 0.050) that would correct both the issues I cited. The lobes are symmetric, if they were asymmetric that too would correct the issue I have with the intake valve 0.050" closing event. Power would improve if the valves were lifted higher.
I haven't purchased wheels yet, I'm working behind the scenes with someone on a project related to that subject. I won't make a wheel purchasing decision until I know if the project is go or no-go.
The first thing I noticed is the cam has fast ramp lobes (52° lobe intensity) yet only 0.520"/0.531" lift. Seems as though whoever put this cam together placed emphasis on duration at 0.050". The 351C 4V heads are going to make peak BHP at 6000 rpm even if the duration at 0.050" is only 205°! That's the intake duration of the Cobra Jet cam. The 351C 4V power band is not as dependent on duration as it is with other engines, but to make power the valves need to be opened as high as possible (within the limitations of engine longevity) to take advantage of the cylinder head air flow potential. Lobes are available today allowing valve lift in the 0.550" range (or more) with reliability.
The valve event timing is just fine, the overlap is low (57°), it is more or less centered within the window it should be centered within, that window is the piston's "dwell" time at TDC. However due to the 52° lobe intensity, overlap at 0.050" is 5°. I'd like that better if it were closer to zero. The exhaust valves are opening and the intake valves are closing where they should be based on advertised duration. But I'd prefer it if the intake closing at 0.050 was 40° or 41° ATDC instead of 45° ATDC. Those are the various boundaries I try to stay within to insure good low rpm performance.
The cam should work fine, but if lobe intensity were 57° instead of 52° (225°/231° duration at 0.050) that would correct both the issues I cited. The lobes are symmetric, if they were asymmetric that too would correct the issue I have with the intake valve 0.050" closing event. Power would improve if the valves were lifted higher.
I haven't purchased wheels yet, I'm working behind the scenes with someone on a project related to that subject. I won't make a wheel purchasing decision until I know if the project is go or no-go.
Can this custom Cobra Jet cam be ground for use with solid roller lifters?
Danford1
Danford1
quote:Originally posted by Danford1:
Can this custom Cobra Jet cam be ground for use with solid roller lifters?
Danford1
I was going to make the same inquiry.
Also with the proper valve springs & titanium valves, would this cam have the characteristics to allow the motor to rev to 7,000rpms!
I need a solid roller cam that has decent idle & streetable driving qualities, yet will rev to 7,000rpms!!! I have 180 headers & WANT THAT Can Am SOUND!!!!!!!!!!!!....
Much like my 1991 Ferrari Testarossa!!!!...Mark
https://www.youtube.com/watch?v=gmUpLypFts0
another clip..car leaves dealership at 2:10 of video & drive-by at 2:26....notice the front-end lift under the torque of the flat-12.
https://www.youtube.com/watch?v=_UQkr_x-Y9k
quote:
Originally posted by Danford1:
Can this custom Cobra Jet cam be ground for use with solid roller lifters?
Hi Dan, the answer is yes. Comp Cams makes a series of camshaft lobes called "High Energy Street Rollers". There are a pair of those lobes in their catalog that should do the job fine. Would require using different rocker arm ratios between intake & exhaust. Net valve lift (0.020" lash) either 0.575", 0.585" or 0.610" depending upon the intake rocker ratio (1.7:1, 1.73:1 or 1.8:1).
quote:
Originally posted by 1Rocketship:
... Also with the proper valve springs & titanium valves, would this cam have the characteristics to allow the motor to rev to 7,000rpms!
I need a solid roller cam that has decent idle & streetable driving qualities, yet will rev to 7,000rpms!!!
Mark, with the "right" valve train any type of camshaft you choose can rev to 7000 rpm; hydraulic flat tappet, solid flat tappet, hydraulic roller tappet or solid roller tappet.
Here's the sound of a V8 equipped with 360 degree - 8 into 1 exhaust
http://www.youtube.com/watch?v=w1xvZ0c59Ic
http://www.youtube.com/watch?v=OxQAz_tJuWw
George, Do you grind the solid roller version? If not, who would we contact?
Thanks
Dan
Thanks
Dan
I've always thought that in a 351-C, what cam duration etc worked well was also dependent on whether the engine used stock iron heads with their curled-up exhausts, or modern high-port heads with more flowing exhaust ports. Seem intuitive that modern heads would NOT need the extra cam timing traditionally used on 351-C exhausts to make power. Yes?
bosswrench that sounds logical. george i forgot to tell you that i'm using my old 4v quench chambered cast iron heads. would that make a difference?
quote:
Originally posted by Danford1:
George, Do you grind the solid roller version? If not, who would we contact?
I don't sell parts. I give you the information you need so you can contact the cam grinder yourself and have the cam manufactured. I don't like sending people to Comp Cams, but in this situation they offer the lobes you need.
For the intake lobe use catalog number 1498, ground on 112° ATDC mathematic centerline.
For the exhaust lobe use catalog number 1476, ground on 116° BTDC mathematic centerline.
I'd use a 1.80:1 ratio rocker arm for the intake valves and 1.73:1 or 1.70:1 ratio rocker arm for the exhaust valves.
If you need more info than that let me know.
Thanks George.
Do you know anyone that had one ground already? If so then Comp might have the info on file.
Since the cam would have a 112 ICL would it need to be installed straight up?
Thanks for the help thus far. If I need more info, yes, I will be asking :-)
I went to Comp's lobe profile catalog and used those lobe numbers.
1496 268HER-2 224 @.050" .610
1476 288HER-2 244 @.050" .613
That is a 20 degree spread intake to exhaust.
Is that correct?
Danford1
Do you know anyone that had one ground already? If so then Comp might have the info on file.
Since the cam would have a 112 ICL would it need to be installed straight up?
Thanks for the help thus far. If I need more info, yes, I will be asking :-)
I went to Comp's lobe profile catalog and used those lobe numbers.
1496 268HER-2 224 @.050" .610
1476 288HER-2 244 @.050" .613
That is a 20 degree spread intake to exhaust.
Is that correct?
Danford1
quote:
Originally posted by Bosswrench:
I've always thought that in a 351-C, what cam duration etc worked well was also dependent on whether the engine used stock iron heads with their curled-up exhausts, or modern high-port heads with more flowing exhaust ports. Seem intuitive that modern heads would NOT need the extra cam timing traditionally used on 351-C exhausts to make power. Yes?
Not really ...
Forgive me Jack if I explain things too basically, I don't mean to insult your intelligence, but there are many readers of varying levels of understanding, and I want to make this explanation as understandable as possible to the greatest number of readers.
Between the "piston dwell period" at BDC and the "piston dwell period" at TDC there is about 120 degrees of crankshaft rotation for the piston to "push" exhaust gases out of the cylinder, no amount of additional exhaust duration can change that. BUT that is a moot point anyway because if a cylinder hasn't purged itself of exhaust gases by the time the piston begins moving upward during the exhaust stroke, it will fall on its face. This is due to the fact that the engine will have to work harder "pushing" the exhaust gases out as the piston rises on the exhaust stroke. The problem worsens as engine speed increases, the torque curve will fall-off like a brick at higher rpm. There is at least 100° of crankshaft rotation between the time the exhaust valve opens and the time when the piston begins moving upward during the exhaust stroke, this is the period in which most of the exhaust gases must be purged from the cylinder ... without the aid of piston motion.
Keep in mind that the exhaust valve is not fully open until about 115° BTDC, which is more than 65° too late! This reality is reflected in the trend these days to use low-ratio rocker arms (~1.6:1) on the exhaust valves of race engines, yet the intake valves are equipped with high ratio rocker arms (~1.8:1 to 2.0:1). The performance of the exhaust port when the valve first comes off the seat is most important, not air flow at peak valve lift. The 351C 4V exhaust port's performance is aided by that big 1.7" exhaust valve which exposes more valve curtain area for a given amount of lift than cylinder heads equipped with smaller valves. Cam timing must take into consideration not only the low-lift performance of the exhaust port itself, but also the scavenging performance of the exhaust system. You cannot consider them separately, they combine to make a system.
With a race engine the "early scavenging" of the exhaust gases is accomplished with a low back pressure, free flowing, and properly tuned exhaust system that presents a negative pressure wave at the exhaust port just as the exhaust valve opens. Engine designers try to grind the cam so the exhaust valve opens in harmony with the arrival of the negative pressure wave. However, the same is not true of a street engine equipped with mufflers, small tail pipes, long tail pipes, etc. The exhaust system is not going to provide a strong scavenging pulse when the exhaust valve opens. More than likely there will be some amount of pressure in the exhaust system (i.e. back pressure), and that pressure shall rise as engine speed rises. It is important to understand that as a piston descends within a cylinder during the power stroke the pressure within the cylinder decreases. In order for exhaust gases to begin flowing from the cylinder and into the exhaust system the exhaust valve must open early enough that the cylinder pressure is greater than the pressure in the exhaust system. Since exhaust system pressure increases with engine speed, the higher you want a street engine to rev, the earlier the exhaust valve must open. Opening the exhaust valve earlier is accomplished either by changing the exhaust lobe's centerline or by employing an exhaust lobe with longer duration.
I have good luck with most applications getting 351C 4V street engines to rev freely to 7000 rpm by opening the exhaust valve around 80° BBDC, these are engines equipped with headers and decent mufflers. But in most applications if the exhaust valve is opened just 5° later, around 75° BBDC, the engine will tend to loose steam after 6000 rpm.
That's the high rpm reason for a longer duration exhaust lobe. There's a low rpm reason too.
Overlap softens low rpm torque. The big intake valve and canted valve geometry of the 351C 4V increases the interaction between the exhaust port, the combustion chamber, piston motion, and the intake port during the overlap period. To put this another way, the big intake valve AMPLIFIES the effects of overlap.
Piston motion provides the energy during the overlap period that causes gases to flow in directions we don't want them to flow. There is a window however at top dead center in which piston motion virtually stops, its called the "dwell period". I've learned empirically that in regards to the 351C this window is about 60° wide, extending 30° on either side of TDC. If I can keep the overlap period within that window, overlap shall have less effect upon low rpm torque. If a cam has 50° of overlap, we have 10° of "wiggle room", but if a cam has 60° of overlap we have no wiggle room. With performance cams ... as overlap increases, it becomes more important to center the overlap period at TDC, if we wish to keep low rpm performance and drivability at its best. To put this into understandable numbers, a cam with 286° of "average duration" ground on 112° lobe centers has 62° of overlap.
If I time a 286°/286°, 112° LSA, single pattern camshaft to open the exhaust valve at 80° BBDC (for reasons I explained above) and to close the intake valve at 70° ABDC (for reasons I haven't explained), the overlap period shall be centered not at TDC, but at 5° BTDC.
By subtracting 5° duration from the intake lobe, and adding 5° duration to the exhaust lobe, the intake duration shall be 10° less than the exhaust duration but the resulting dual pattern camshaft (281°/291°) shall have the same average duration as the single pattern camshaft. The lobe centerlines of the dual pattern camshaft are "adjusted" to again establish opening the exhaust valve at 80° BBDC and closing the intake valve at 70° ABDC. With the lobe centerlines thus adjusted the overlap period shall also be centered on TDC, thus minimizing the effects of overlap and holding on to as much low rpm torque as possible.
Centering the overlap period on TDC is the other reason for a longer duration exhaust lobe ... and keeping the overlap period thus centered works very well. In terms of the "Cobra Jet" cam spec (the subject of this thread) combined with the 351C 4V cylinder heads the result is an engine that operates from 700 rpm to 7000 rpm; exhibiting good low rpm power, factory-type drivability, strong mid-range acceleration and a willingness to rev.
________________________________________________________________
For those of you who like to experiment, or do things on your own, here's some math:
The camshaft for the M code version of the 351C 4V had 274° average duration (268°/280°), it was ground on 118.5° lobe centers and thus had 37° overlap. The exhaust valve opened (EVO) at 81° BBDC and the intake valve closed (IVC) at 70° ABDC. Thus the overall valve event duration encompassed 511° of crankshaft rotation. With roughly 10° difference between intake duration and exhaust duration (12° to be precise) the overlap period was very well centered on TDC.
In order to open the exhaust valve at 80° BBDC and close the intake valve at 70° ABDC a camshaft's overall valve event duration must encompass at least 510° of crankshaft rotation. To arrive at that figure is as simple as adding 80° + 360° + 70°.
A camshaft having 280° average duration, ground on 115° lobe centers, is the smallest cam we can have ground today that meets this 510° valve event criteria. Cam grinders cannot or will not grind a cam with lobe centers wider than 115°. However in some cases it is difficult, if not impossible, to get a cam grinder to grind a cam with 115° lobe centers. Therefore I've adopted a self-imposed limitation of 114° lobe centers. Based upon that limitation a cam with 282° average duration and 114° lobe centers is the smallest cam that achieves 510° overall valve event duration. Centering the overlap period at TDC results in a camshaft having approximately 277° intake duration, 287° exhaust duration, 54° overlap, and 114° lobe separation. Such a "street camshaft" should employ lobes having no less than 54° lobe intensity, thus overlap as measured at 0.050" lobe lift shall be zero or less.
Here's a formula for determining a camshaft's overall valve event duration:
overall valve event duration = (advertised intake duration + advertised exhaust duration) - overlap
Computing overlap is easy:
overlap = average advertised duration - (LSA x 2)
and average advertised duration ...
average advertised duration = (advertised intake duration + advertised exhaust duration) ÷ 2
Have fun with this ...
quote:
Originally posted by 73 l:
... george i forgot to tell you that i'm using my old 4v quench chambered cast iron heads. would that make a difference?
No, not if its a street engine. I hope my explanation to Jack's question explains why.
quote:
Originally posted by Danford1:
Do you know anyone that had one ground already? If so then Comp might have the info on file.
Since the cam would have a 112 ICL would it need to be installed straight up?
You and Mark are the first people who have inquired about grinding this spec with solid rollers.
I have considered using a solid roller tappet for my own engine, which is why I knew about the lobes.
Yes the cam is specified to be used "as ground". Of course, they never get the cam indexing "spot-on" you always need to check timing and correct it with a multi-index crank sprocket.
quote:
Originally posted by Danford1:
I went to Comp's lobe profile catalog and used those lobe numbers.
1496 268HER-2 224 @.050" .610
1476 288HER-2 244 @.050" .613
That is a 20 degree spread intake to exhaust.
Is that correct?
The intake lobe is the wrong number, it should be 1498 (276° ... 12° spread). The "8" in the on-line catalog looked like a "6" to my eyes, I had to zoom-in to see it clearly. I'm glad you caught that mistake.
This ia all fascinating stuff.
Do the same EVO at 80 BBDC and IVC at 70 ABDC events pertain to other engines such as the Ford 302?
It has a 3.00" stroke so the dwell time would probably be shorter.
I have another car (66 Fairlane) with a 302 that I'm currently building for the street. I'm at the cam selection state so this thread has excellent timing.
I want it all, torque and power just off idle on up to 6000 rpm or more, works with 2000 stall converter C4, 2.80:1 highway gears, has a lope at idle and gets great highway fuel economy. I'd be using Ford hydraulic roller lifters, not solid.
The engine will have home ported Windsor Jr aluminum heads with 2.02" and 1.6" valves, 58 cc chambers about 9.5:1 compression, Weiand Stealth intake and 600 Hooley carb with 1 5/8" full length headers and 2 1/2" full exhaust.
If the timing events apply to this engine I'll start a search for a cam that has them.
I look forward to your reply.
Oh, if this is hy-jacking this thread just say so and I'll start a new thread for the 302.
Thanks.
Danford1
Do the same EVO at 80 BBDC and IVC at 70 ABDC events pertain to other engines such as the Ford 302?
It has a 3.00" stroke so the dwell time would probably be shorter.
I have another car (66 Fairlane) with a 302 that I'm currently building for the street. I'm at the cam selection state so this thread has excellent timing.
I want it all, torque and power just off idle on up to 6000 rpm or more, works with 2000 stall converter C4, 2.80:1 highway gears, has a lope at idle and gets great highway fuel economy. I'd be using Ford hydraulic roller lifters, not solid.
The engine will have home ported Windsor Jr aluminum heads with 2.02" and 1.6" valves, 58 cc chambers about 9.5:1 compression, Weiand Stealth intake and 600 Hooley carb with 1 5/8" full length headers and 2 1/2" full exhaust.
If the timing events apply to this engine I'll start a search for a cam that has them.
I look forward to your reply.
Oh, if this is hy-jacking this thread just say so and I'll start a new thread for the 302.
Thanks.
Danford1
Lets add another wrinkle. What is the difference in your recomendations if you have the Boss domed pistons?
quote:
Originally posted by Danford1:
... Do the same EVO at 80 BBDC and IVC at 70 ABDC events pertain to other engines such as the Ford 302 ...
Yes and no. How's that for a concise answer?
Theoretically the answer "should be" no. The 302 has smaller valves, in-line valve heads, different combustion chambers, different stroke, different rod length. But practically speaking, I've seen a lot of factory performance engine cams from several manufacturers with about the same timing. For instance, the Ford 351 Cobra Jet cam (1971 specs) opens the exhaust valve (EVO) at 82° BBDC and closes the intake valve (IVC) at 72° ABDC. Those same specs were used for the 390 GT, the 1968 hydraulic cammed 427 and the 428 Cobra Jet. The 429 Police Interceptor camshaft specs were very similar, EVO = 86°, IVC = 73°.
Perhaps more pertinent, Ford camshaft #C9OZ-6250-C, was a hydraulic tappet performance camshaft for the 289/302/351W, its specs were EVO = 84°, IVC = 74°. The earlier 289 performance camshaft, C4OZ-6A257-A, specs were EVO = 78°, IVC = 72°. If you advance that cam by 2° you'd have 80/70. That cam was described as having a "reasonable idle", a "strong" power curve that extended into the 6000+ rpm range.
So yes, you can use that spec for the 302, or something close to it.
quote:
Originally posted by Danford1:
I want it all, torque and power just off idle on up to 6000 rpm or more, works with 2000 stall converter C4, 2.80:1 highway gears, has a lope at idle and gets great highway fuel economy.
While you can expect a wide flat torque curve, don't expect the same wide power band as the 351C with 4V heads ... the 302 will run out of steam sooner than 7000 rpm.
Its going to be hard to "have it all" because of the gears you plan to use and the torque converter stall speed. The Cobra Jet cam normally goes along with 3.50:1, 3.70:1, 3.91:1, or 4.11:1 gears, and/or a 3000 stall converter.
The highway gears and 2000 stall converter point at using a mild cam, the mild cam will definitely help low rpm power too, but it may impact the high rpm pull. I guess we'll find out how good those Windsor Jr. heads are. Fuel economy is directly related to overlap, but so is a lopey idle. To have both there will need to be some compromises there too.
Crane offers two different series of hydraulic roller cams for the 302, depending upon if its an older engine that wasn't equipped with a roller cam, or if its a newer engine that was equipped with a roller cam (firing orders are different). Tell me which type of engine you've got, and I'll take a look at the Crane catalog and make a recommendation.
quote:
Originally posted by captaintobeys:
... What is the difference in your recomendations if you have the Boss domed pistons ...
None
Hi George, Thanks for the simple formula ! That is very interesting...
I have a newer roller block. Should have the same firing order as our beloved Clevo's :-)
Danford1
I have a newer roller block. Should have the same firing order as our beloved Clevo's :-)
Danford1