advertised and .050" duration for a solid lifter cam

[MikeB]

My 327 has a CompCams XS262S cam with advertised duration specified at .015" tappet rise. With .016" lash and 1.5 rockers, the valve starts moving at .011" tappet rise. So, the 262 degree intake spec is equal to a zero lash 262 cam being spec'd at .004" tappet rise right? Of course, Comp specifies their hydraulic cams at .006". Go figure.

Now the .050" duration spec gets strange because it's really more like a .039" spec. But I won't even go there, because thinking about it makes my head hurt! Needless to say, my 224 @ .050" solid cam probably acts more like a 220 or even 218 hydraulic cam, although I realize the lobe shape may be more aggressive. Is there a way to determine what a comparable hydraulic duration would be?

I just got a Lunati hydraulic cam with 268 advertised duration (at unknown tappet rise) and 218 @ .050”. Just trying to get a feel for how it compares to my current cam. I think it may still be on the big side of what I’m looking for to work with the 3.08 axle I’m building.

 

[grumpyvette]

each cam manufacturer in effect plays by his own rules to some extent, your correct that the lunati cam may be a bit bigger but its not a huge jump, lunati cams tend to have a bit more aggressive ramps but when your dealing with cams that small the difference will not be huge, but it should be noticeably.
Isky claims that the Comp XE cams violate the 47.5% rule. The 47.5% rule applies to flat tappet cams for SBCs with 1.5 rockers but the concept is still the same for other configurations where the designs are "on the edge" or "over the edge" for lobe intensity. For 1.5 ratio SBCs, the duration at .50 must exceed 47.5% of the total valve lift or your asking valve train problems. For example, take a Comp Cams Magnum 280H, with 230 duration and, 480 lift...230/.480 = 47.9% which exceeds 47.5% therefore would not pose a threat to components. We do not regularly hear about the older, safer HE and Magnum designs rounding off lobes anywhere near as often as the XE cam designs. Unfortunately, some of the Comp Cams XE dual pattern lobes break this 47.5% rule on the intake side so they are likely to be problematic. The design has "steeper" ramps that are too quick for durability and reliability according to other cam manufacturers. They will wipe lobes in a heart beat especially if you have not followed the proper break-in procedure. Other designs are more forgiving during break-in and less likely to fail.

 

[Indycars]

Since the Lunati is a "High Efficiency Cam", would it be correct that it has -2 degrees overlap or did I enter some
specs wrong. Here are the cam cards, are they correct ones Mike ???


I ran some numbers thru DynoSim5, below is what it shows. Mike I did see in another post where you are using the
Brodix IK180 heads.....right??? Just so happens I had the flow specs for them since I'm using the IK200 on my engine.

First is the specs for the engine. Assumed a static CR of 9.0. Let me know if I need to change something to be closer
to your situation Mike.

 

[MikeB]

Rick, thanks for the simulation. Yes those are the correct cams.
You're right about the Lunati cam's overlap @ .050 tappet lift. -5 + 3 = -2

I have a new PC and can't find my old DD2000 CD anywhere , so, would you run it again using 9.5:1, 650 carb, and 4.030 bore?

And how about doing this Erson flat tappet hydraulic cam compared to the XS262s?

PART NUMBER E110022
INTAKE "LASH" DUR. 280
EXHAUST "LASH" DUR. 280
INTAKE DUR @ .050" 214
EXHAUST DUR @ .050" 214
LOBE SEPARATION 110
ADV. OR RET. DEG. +5
GROSS VALVE LIFT INT. 0.443
GROSS VALVE LIFT EXH. 0.443
INTAKE OPEN 35
INTAKE CLOSE 65
EXHAUST OPEN 75
EXHAUST CLOSE 25
OVERLAP @ LASH 60


INTAKE OPEN @ .050 2
INTAKE CLOSE @ .050 32
EXHAUST OPEN @ .050 42
EXHAUST CLOSE @ .050 -8
OVERLAP @ .050 -6



And also do a CompCams 260H, if you have the time.

I appreciate it!

 

[Indycars]

Ok, made these changes to the basic engine parameters, CR=9.5, Carb=650CFM and Bore=4.030".

DynoSim5 can estimate the lifter acceleration if it knows the valve timing numbers at both Seat-to-Seat and
at 0.050" Lift. The Erson cam is the only one that had this much info. When DynoSim5 estimated lifter acceleration
for the Erson cam, it came up with a number of 2.24 on a scale of 1 to 7. The default value used in ALL prior
simulations to this point was 3.0, since all the numbers were NOT available.

Below is the Cam Manager for DynoSim5. In the TOP RED BOX all the numbers for estimating Lifter Acceleration are provided
for the Erson cam. In the LOWER RED BOX box is the actual estimation of 2.24, significantly lower than the default of 3.0.



For the HP/Torque graphs below, I manually set lifter acceleration at 2.20 for ALL camshafts. I felt this would provide the
fairest comparison, when trying to compare all four cams. The graph gets pretty crowded with four different simulations, so
I made the graphic much larger than I usually do.



So which camshaft would you use at this time ???
.
.
.

 

[MikeB]

Rick,

Based on the charts, the smaller Comp 260H cam makes the most torque at the RPMs where my engine spends the most time. Horsepower fades fast after 5000, but realistically, the engine will spend very little time up there. But, man, my current XS262S really shines. I would have expected it to make less torque up to 3500 RPM than the other cams.

I’m also surprised it’s “out-horsepowerd” by the Lunati, which looks pretty darn good overall. I would have guessed the Erson cam would have made more torque, not less than all but the Comp 260H.

I’m not buying those actual numbers though. 450 lb/ft and >400 HP from a mild 327? No way. I’d guess more like 320-340 lb/ft and 375 HP max. You used a 3.25” stroke, right?

However, I do need to check out that program.

Thanks for your time.

Mike

 

[Indycars]

No doubt you are right, the numbers are too high.

Also I remembered advancing the Erson 5 degrees, I read the numbers wrong from your post.

PART NUMBER E110022
INTAKE "LASH" DUR. 280
EXHAUST "LASH" DUR. 280
INTAKE DUR @ .050" 214
EXHAUST DUR @ .050" 214
LOBE SEPARATION 110
ADV. OR RET. DEG. +5
GROSS VALVE LIFT INT. 0.443
GROSS VALVE LIFT EXH. 0.443
INTAKE OPEN 35
INTAKE CLOSE 65
EXHAUST OPEN 75
EXHAUST CLOSE 25
OVERLAP @ LASH 60

I went back changed that parameter for the Erson and compared it to the +5 Advance, see below.



Then I run the comparison on all four camshafts again, see below.



Attached you will find a 19 page report on the engine with the Erson 110022 installed Dot-to-Dot. Maybe you will see something I didn't.