[JLMounce]

When I rebuilt my engine last year I talked with Bullet about getting a cam made. At the time their lead was over 8 weeks. I went with a comp spec'd by Jeff Kauffman that uses the newer Q series lobes (QNI in my case) and I've been really impressed with the cam. The valvetrain is MUCH quieter than the comp XFI lobe cam I had in the engine previously.

[grivera]

Originally Posted by JLMounce

The valvetrain is MUCH quieter than the comp XFI lobe cam I had in the engine previously.

Are the XFI lobes inherently noisy? I thought your valvetrain noise was attributed to the Lunati/Morel lifters, versus the new with Johnson lifters?

[JLMounce]

Originally Posted by grivera

Are the XFI lobes inherently noisy? I thought your valvetrain noise was attributed to the Lunati/Morel lifters, versus the new with Johnson lifters?

The lobe intensity on the XFI's is pretty aggressive. They likely exacerbated the noise issues that was inherent with my Morel lifters.

If you do some searching on the XFI lobes, it's a somewhat common complaint that it produces a noisy valvetrain. The QNI lobes on my current cam, although having more lobe lift are less aggressive on and off the ramp. Comp developed this lobe profile specifically with quiet valvetrain in mind.

[Jay S]

Many times Tim will suggest using a profile with less acceleration on the exhaust side for street longevity, that is another alteration that can be done. For instance that cam would probably look like 290/303 at .006” instead of 290/298, but the .050” spec is the same.

[Steve C.]

Jay's example...

Lobe HR303/3532
303
244
157
0.3532


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[Steve C.]

Using Harland Sharp 1.65 rockers ?

If so, keep in mind their actual ratio when calculating the valve lift.

We have seen it stated the Harland Sharp Pontiac 1.65 rocker arm ratio to be 1.7, 1.72, etc.

One example. Years ago Ken Crocie used Harland Sharp 1.65 ratio rockers on a build.
The cam had 0.3600" lobe lift and based on 1.65 ratio it suggested a theoretical 0.594-inch valve lift. Yet when measured on this specific build it netted an actual 0.606-inch lift at the valve.
Here the actual ratio of the Harland Sharp rocker seems to be closer to a 1.684 ratio. This was a static measurement A running measurement 'at the valve' could be different.


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