So what's up with the Tillotson Cam

Big Chris

Member
A couple Tillotson engines came through my shop recently. I will not talk trash on other builders or disclose who is the owner. These engines were "blueprinted/prepared" by another shop and built to AKRA specs.........

Both engines have what I believe to be the stock Tillotson cam, and I question the legality of the this cam.

Firstly the lift at the retainer on both the intake and exhaust was about .005" above the .238 intake and .242 exhaust that is allowed. I realize this is not a function of the cam, but rather valve train geometry. Also it should be noted that if a short performance intake valve was installed, the .815 go/no go gauge would not pass. So for those building at home, the stock setup on this engine is over the allowable lift. This is an easily tech'ed item that is minimally invasive.

Also, I am a fan of the BSP4 cam and the EV6 cam for the restrictor plates, and BOTH those cams easily outperform the Tillotson cam on the dyno. Also it should be noted that both Tillotson engines had their cams installed with an ILC very close to 117 degrees, which I've got alot of dyno data that indicates this is outside the "sweet spot" window. When installing EITHER the EV6 or the BSP4 cam WITHOUT moving the crank gear the ILC of both of those cams landed on the 111-113 range. My point here is the ILC ground into this cam is about 4 degrees retarded, which IMO is a bit too much. What's interesting is for those in the know, the degrees on the front side of the lobe or the lifting action of the lobe is very similar to other cams installed at the 111-113 window. It is the trailing side of the lobe or the setting the valve back down side that is off. This leads me to believe this cam has got too much duration for our rule set.

Here are my observed results from "degreeing" this cam in, I measured both at the retainer and the pushrod.

If other builders have results that either agree or disagree with my observations I'd be interested in hearing what you have to say.

This is a Tillotson TPP196R-A model engine with serial number 180101760
Tillotson Cam .jpg
 
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