XR286HR COMP CAMS

360duster said

my experience with this cam (ran it in my 408 for some years now): performance significantly improved with 1.6 rockers, dropped 2 tenth on the quartermile. I did not notice any impact on the rpm range - run mine to 6500 rpm.

What vacuum is necessary for the efi? I had trouble with the brake booster, changed to manual. If i remember correctly the best vacuum was around 10 in/hg with my combination.

I think the best bet is to talk to experienced builder. Maybe a custom grind with bigger LSA is better suited for your engine.

Michael

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EFI uses the vacuum signal to determine fuel delivery, and in my case timing as well (tip in on advance etc). A weak vacuum signal with a lot of overlap on duration makes the signal fluctuate or pulse quite a bit at lower RpM. Kinda like having your fuel level set too low in the bowl on the carb I guess, and one of the reasons there are air bleeds on carbs on motors with crazy overlap. This particular system I have meant to handle 250 degrees of duration at .050 and less. 110 degrees of lobe separation is fine, which is what this cam is. I've decided on 1.5 rockers (purchased last light late) because I'd rather have the lift at the cam, and not compound it at the rocker, and the extra multiplication seemed unnecessary and would cause more stress on the valve train in my opinion. I'm giving up a little lift. I was curious to see if the rockers, even if they didn't affect the duration, would have an effect on the vacuum.