IGN-1A

Who here has used an Inverse Radius Camshaft ?

G Atsma

Would you describe what that is? New term to me...

IGN-1A

The IR Cam Lobe has greater width at the crown than in the middle.

G Atsma

So the ramps are actually "concave" rather than "convex" or even flat?
I would think that to be a bumpy ride for the valvetrain, but I'm far from being any sort of expert on such matters...

93Z2871805

iTrader: (5)

The lobes are almost peanut shaped when looking at it from the nose. The idea is it creates more valve lift area under the curve. The best way I can think to describe it is, it is designed to almost "hover" the valve off the seat to get more airflow before and after peak lift.

G Atsma

How hard is that on the valvetrain? Much heavier springs required?

93Z2871805

iTrader: (5)

I have no tangible data to back this up, but I don't necessarily think so. If there are 2 cams, one being a traditional flank style and the other being an inverse radius, both with the same peak lift, I wouldn't imagine exercising the spring more often under the peak would stress it any more. However, that would assume that harmonics are being properly addressed as I assume that freeing the valve off of the seat for a wider window would increase the probability otherwise. That's all just my theoretical assessment though.

G Atsma

It is the possible harmonics that concern me.
Want to chime in on this, Lance?

IGN-1A

Yes, I agree.
One method is to specify higher valve seat pressure

G Atsma

What are positive aspects that are exclusive to this arrangement? Possible reduction of idle lope due to excess overlap?

IGN-1A

The Piston/Valve distance is much higher with this lobe design at TDC.

G Atsma

Ahh..... at those critical times of max overlap but mid-lift when things CAN get dicey with the above clearances. Restating your facts by me thinking aloud to clarify...
So many times we read among these forums about those worried about TOTAL LIFT, when it is DURATION and LSA that are cause for concern.
And now a cam design to help alleviate the P/V clearance issue. Is this picking up steam, or still living in partial obscurity?

Che70velle

iTrader: (6)

I’ve never ran an IR camshaft, but have followed the tech for years. It’s been around for a long time. I do know that there are Diesel engines out there running IR cam technology, and it works pretty well due to the low rpm of the diesel. The pro side of IR camshafts is increased torque and the con side is drastically reduced valvetrain life expectancy with high rpm. The valve itself lasts longer because the IR profile sets the valve down easy, but it also beats the snot out of the spring. I remember reading that Crower was heavily invested in the tech wayyy back when Menard was running the V6 in Indy.

NSFW

Concave! I would not have believed it, but there are some good pics in this thread...

https://www.yellowbullet.com/threads...files.1751738/

It the concavity is subtle, but it's there.

n2xlr8n66

iTrader: (3)

Straight to the point from two of best cam guys in the industry (one of which has left us):

- Not new tech (the two aforementioned designers / grinders were doing it in 1979, and still do)
- It's not harder on valvetrain; conversely, it is easier on valvetrain unless you start tinkering with the lash in the wrong way.
- The idea is to get more area under the curve, without increasing the opening and closing velocities.

They work- almost every flat tappet in Nascar is designed this way, though it would be tough to measure without the correct equipment.

AwesomeAuto

They have their place. Its important to note that they behave very differently between hydraulic and solid setups.
They also have different manners between street and the track than normal lobe designs.
Just another one of those things where you need to weight the pros/cons for your particular setup/usage.

C409

iTrader: (1)

I have been running a Mike Jones asymetrical lobe (IR) cam in my gen one 421 sbc for 4 years & thousands of eighth mile passes ... no detrimental wear or tear to the valvetrain that can be detected on a running engine ... the IR lobes keep the valves on the seat a little longer without losing the effects of the overlap , especially in the mid-lift range ... this cam taught me to be careful with lash settings particularly when using higher ratio rockers ... how many of you calculate the proper lash by comparing the rocker ratio on the card vs that stamped on your rockers ? you need to divide the lash by the cam card ratio then multiply by the actual to arrive at the optimum lash setting for your combo ... this keeps the IR and geometry in a happy place ... degreeing an asymetrical cam is different too ... you degree by valve events (I.O./E.O.) and not by ICL ... 261/266@.050" ... .699/.713 lift ... nice torque curve , engine dyno pulls start at 5000rpm @561 ft/lb and stay over 500 to 6600rpm ... 635hp @ 6900rpm ... 421ci , 11.2cr , Brodix CNC 227 , Vic Jr EFI 4150 4bbl TB , 1 7/8" headers , E85 .

Dian

the only disadvantage of the concave profile is the cost to make it. you need small grinding wheels that deteriorate fast.