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I'm getting close to switching to a roller cam in the big block!

HawkRod said:
2) The reality is for a street engine, having installed height differences of even .030 isn't going to kill you.
Click to expand...
What I'm wondering is how can a couple ten thousandths of an inch matter when the cam companies call out for the same valve spring for several different cams, with different durations, and different valve lifts. I also want to know if anyone uses the valve springs that come with new heads, or do people just chuck those? Like Trick Flow, for instance, sells several different part numbers of the same head, but one will have "Hydraulic roller" valve springs, and another will have "Hydraulic flat tappet" springs. WTF does that mean?
 
V_TastyTacos_V said:
What I'm wondering is how can a couple ten thousandths of an inch matter when the cam companies call out for the same valve spring for several different cams, with different durations, and different valve lifts. I also want to know if anyone uses the valve springs that come with new heads, or do people just chuck those?
Click to expand...
This could get detailed, but I'll keep this very high level: The ONLY JOB of a valve spring is to keep the valve following the cam profile. In very general terms, if it does that, then you are fine. As a cam profile and/ or RPM increase, then the spring must be stronger to keep the lifter from doing a "ski slope jump" off the peak of the cam. That's bad. There are all kinds of details to worry about at high RPM. For example, springs get some sideways harmonics, and designing the height so they are NEAR but not at, coil bind will reduce that. There are many more details that could be discussed too.
The bottom line is spring pressure is not like horsepower - more is not always better. But as long as the spring works to keep the valve following the cam profile, you are fine. Most of our street engines don't get stressed in RPM to a point where we need to be that crazy about the specs. For that reason, many springs will work for an average street engine. 100# "ish" closed and 300# "ish" open woks for a broad flat tappet range. If you have a roller cam, then spring pressures need to be upped a little bit. (If you are building a high RPM race engine, then ignore this post and sweat the details.)

V_TastyTacos_V said:
Like Trick Flow, for instance, sells several different part numbers of the same head, but one will have "Hydraulic roller" valve springs, and another will have "Hydraulic flat tappet" springs. WTF does that mean?
Click to expand...
A flat tappet cam has a lifter with a (nearly) flat bottom that rides directly on the cam. It spins and does stuff to avoid wear, but you have metal on metal and wear can be an issue. A roller cam has a lifter with a little wheel on it and it (somewhat) rolls on the cam, leading to much reduced wear.
Generally, all our old cars had flat tappet cams, and all new cars have roller cams. But they make retrofit kits that allow builders to put roller cams into old engines. In general, roller cam engines have stronger springs.
1759500000989.png


There is LOTS missing in the above details, but hopefully that covers some very high level basics. :thumbsup:
 
Something that has had me curious for years is this:
Looking at the profiles of the lobes of a roller cam versus a flat tappet....

1759502385981.png


If both cams have identical peak lift, the rollers always seem to have much more duration at both sides of peak lift.
I have a hard time understanding why I don't see this reflected in the published specs of the cam.
For example, first....here is a picture of the cam in my engine now, a Lunati solid lifter flat tappet:


50 R.JPG


Below left is the '528 solid flat tappet cam that went bad in June 2022. Note the shape of the lobes compared to the roller cam on the right. The published specs for the roller cam are similar for duration but higher for lift. The old Mopar Performance cams didn't come with a @ .050 number, later they caved in and told customers to multiply the gross duration numbers by .85 to get an @ .050 number. The '528 was listed as a 284-528 so 284 x .85 is 241. The roller cam has similar numbers at 238/244 degrees. I understand that duration numbers are taken at .050 of tappet lift but the amount of duration from there...to peak lift and back to .050 on the other side is a whole lot more yet I don't recall it being explained.

RC 2.jpeg


RC 5.jpeg
 
Kern Dog said:
If both cams have identical peak lift, the rollers always seem to have much more duration at both sides of peak lift.
Click to expand...
Not true - you are thinking about duration wrong.

Duration is measured from when the lobe begins to raise the lifter until it goes back to the base circle (typically at .050"). Both a flat tappet and roller cam might have the exact same duration (and exact same lift), but the roller cam has a STEEPER SLOPE. This means that there is more area under the curve, or in simple terms, it will open the valve faster and hold it "more" open for a longer time, allowing for more airflow than a flat tappet cam of the exact same lift and duration.
 
It still looks like even with identical duration numbers, the roller opens the valve wider than the flat tappet between .050 and peak lift.
 
Kern Dog said:
It still looks like even with identical duration numbers, the roller opens the valve wider than the flat tappet between .050 and peak lift.
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Yes, that's what I'm trying to say in post #205. That's why roller cams can make better power than an identical flat tappet cam.
 
I guess my point is that it seems from what I have seen, there is no standard spec to measure that "area under the curve" like duration, lift, LSA and installed centerline.
 
Kern Dog said:
I guess my point is that it seems from what I have seen, there is no standard spec to measure that "area under the curve" like duration, lift, LSA and installed centerline.
Click to expand...
You are 100% correct.
 
Kern Dog said:
I guess my point is that it seems from what I have seen, there is no standard spec to measure that "area under the curve" like duration, lift, LSA and installed centerline.
Click to expand...
I think they call that lobe intensity. Regardless of the lifter type, a cam lobe can have a faster or slower rate of lift, and I think one can get an idea of how fast or slow that is by comparing the advertised and @.050" duration values, with less difference indicating a faster, or higher intensity, which is what you're observing when you see more duration @.050" on roller vs. flat tappet cams. I'm sure one can have a faster, higher intensity flat tappet cam vs. roller, but the longevity won't be very long, but a high intensity roller won't, either, which is why OEM roller motors can go hundreds of thousands of miles, but a high performance roller cam V8 need constant maintenance and inspection.
 
V_TastyTacos_V said:
... a high performance roller cam V8 need constant maintenance and inspection.
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There are about 9-10,000 miles on my 400 based 500 cubic inch roller cam engine with about 675 lb ft of torque. It has never needed anything other than a replacement intermediate shaft (bronze). Valve train? Never had any issues. Sure, I've checked it, but it never needed any adjustment.
 
Yeah, I saw that and disagreed as well.
I've ran solid lifter cams since 2013 and even then, I haven't had to relash the valves.
 
I agree.
Forgive my lack of experience on this, I'm sure it shows in how I express myself in this matter.
The flat tappet there does have less overall lift @ just .528 compared to around .544 but that is so small, I doubt anyone can notice.
The roller lobes look sort of like an oval while the flat tappet ones look like eggs. I'm used to hearing of duration measured with the lobes .006 off the base circle, .050 and recently, .200.

RemCharger said:
.050 numbers vs .200 numbers tell the story.
Click to expand...

This is interesting and does seem to answer my question about comparing that "area under the curve". I'm tempted to actually run the car on a dyno with the existing cam and then with the roller cam to compare the power curves. Dwayne estimated that it will peak below 6000 rpms, likely around 5500-5600 I recall.
 
A roller cam has a different method of moving the lifter than a FT cam. Trying to compare the two is like trying to compare a petrol engine to as diesel engine. Rate of lift of the FT lobe is limited by the lifter diam. That is why mushroom lifters were invented: to increase the rate of lift AND give more total lift [ area under the curve ]. With the roller lifter, a larger roller also increases the rate of lift.
 
Kern Dog said:
Dwayne estimated that it will peak below 6000 rpms, likely around 5500-5600 I recall.
Click to expand...
As installed in my car, my horsepower peaks at 5146 RPM. You can darn near put a straight edge on my torque, pretty much at max torque all the way from where the dyno run starts at 2500 RPM until about 4000 RPM where it slowly starts dropping. It is this torque that makes my car so much fun to drive on the streets. It is not intended to be a race car. As installed, my engine suffers from a restrictive intake - I have to fit the air grabber and that must be in an exact position. My exhaust and Edelbrock RPM heads likely also limit things a bit, as do my heavy wheels. But I wouldn't change a thing. The car looks the part and drives excellent.
 
Cheapsunglasses said:
In my crude exaggerated drawing you can see how a roller has “more” duration

View attachment 1927177
Click to expand...
You could think of those two lobe profiles as doors. On the left, the door opens and shuts quickly. On the right, opens quickly and stays open for awhile, then finally closes down shut.
 
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