Tuning Cam gears based on vacuum and HC's?

[Doug99RS]

I've done quite a bit of parts swapping on my cars and tons of repairs on customer vehicles. What I'm lacking in though is true tuning experience.

I was saving the work for a dyno day but don't see it happening any month soon. Based on experience and emissions standards I've found my current cam gear settings (zero on both) not only has really high hydrocarbon emissions but a poor vacuum reading. Vacuum started at about 12-13 inches of vacuum (stock engines usually read about 18-20 inches) and my hydrocarbons were at 450-500 ppm. Neither of these were acceptable to me.

First thing I did was put it on the emissions analyzer at work and hooked up a vacuum gauge. I was able to adjust the exhaust gear with relative ease since I can reach it. I bent my alan wrench trying to get the rear one broken loose. Fixed that, explain later. Adjusted the exhaust to 3 degrees advanced. Vacuum came up about an inch, hc's down to 350. Performance felt slightly better (@$$dyno) and gas mileage seemed to improve (from 200 up to 250 miles per tank maybe).

Next I finally got the rear set screws loose and replaced all six screws to prevent problems in the future. After trying advancing and retarding the intake I finally settled on 3 or 4 degrees retarded on the intake and 3 advanced on the exhaust. Vacuum is up to 15" and HC's down to 50ppm.

My questions are: Hs anyone else tuned in this mannor and if so to what affect?, I'm increasing engine vacuum, reducing fuel waste so that should be a good thing right?, Any other methods short of a dyno that can be used?

Things I do understand is that with cam grind variances come different valve duration, overlap, and lift. As such engine vacuum may change from factory specs with aftermarket cams.

Thoughts?
Doug

 

[RipperXX]

Should have got the HKS cams... I have not ever heard of anyone haveing to adjust them.

 

[Doug99RS]

I was kinda hoping to get response a lil more... I don't know... Technically educational. I'll try to keep that in mind next time I post in the Advanced tech section.

 

[zac83]

You're going to have to tune that on a HP dyno. Your HC will depend COMPLETLY on valve overlap. all cars will respond differently to how the fuel is tuned and what the timing is set at so any modifications make it impossible to 'guess' with vaccume and HC readings. anyway: a car with monster cams and a monster turbo shouldnt make very much vaccume...

 

[Doug99RS]

I understand that the dyno is going to be the best way to tune based on max performance gains. Thanks for bringing a few more tid bits of info for me to think about.

Just for the record in case the screen name and sig picture were overlooked, it's a 2gnt that's still n/a. A big turbo isn't going to be one of the factors here. Thanks again,
Doug

 

[92redman]

Why do you want higher vacuum? Unless you are not talking about at WOT, because you want 0 vacuum at WOT. Or am I just totally not thinking of the same thing you are

 

[Doug99RS]

All of my vacuum readings are taken at idle. Naturally once you start opening the throttle plate manifold pressure will start to get closer to atmospheric pressure and I wouldn't be able to "tune" to much of anything. WOT I would like to think it would be best to achieve as close to atmospheric pressure as possible. Atmospheric pressure in the manifold, at WOT, for the longest amount of time should mean it's operating at 100% efficiency.

My problem is that I know good from bad as far as manifold pressure readings in a stock engine. 19 inches is good and 16 or less generally indicates a problem.

I've got less than 14 inches of vacuum now and wonder what "normal" is now that I've got over-sized valves, cams, and the rest of the headwork. I'm not so much asking anyone for answers specifically about my engine and it's set-up or even a different yet specific engine's characteristics.

Basically my question should probably directed like this:
To anyone who has taken engine vacuum readings, at idle, on multiple cars with multiple cam combinations. What has the tendency in vacuum trends been so that I can determine if my engine vacuum is normal or not?
Doug

 

[zac83]

You can see anywhere from 25 to 50% vaccume loss at idle with a mild-moderate cam. crazy cams will kill most vaccume so if you've got 14in. - Your in the right area.