What part in the design of a cam affects the computer? Is it the lobe separation, LDA, duration, or what? I've heard that the computer doesn't like the vacuum "pulses" but what does that come from?

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1986 IROC LG4 "Bone Stock" (for now)

 

The lobe separate angle, plus the intake duration are what affect the computers ability to control the car.

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West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

I guess that make sense that they could cause erratic vacuum signals. Thanks

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1986 IROC LG4 "Bone Stock" (for now)

[This message has been edited by wiggy'sIROC (edited January 19, 2001).]

 

Wig,

Most technically, the valve overlap is what can ruin the world for a PCM. The typical engine control has a very narrow range of tolerance for vacuum. Excessive valve timing overlap causes lower vacuum in all ranges, which can totally confuse a PCM.

Overlap is a function of both duration and lobe separation angles. A long duration and wide LSA will result in less overlap, and a short duration with a tight LSA can have less overlap. But you can't have your cake and eat it too, so a tight (low) LSA and long duration will create more degrees of overlap, and lower intake vacuum.

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Later,
Vader
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"I'm gonna talk about some freaky sheet now..."
Adobe Acrobat Reader 4.0
KaleCo Auto Parts

 

I have run or installed over 20 cams in L69's and modified, sometimes heavily modified, engines running the computer controlled quad. The only fueling function that system controls is the master control solonoid that "adjusts" the primary metering rods. With the computer carbed system you can run a good bit of duration at .050 lift as long as it's a fast rise rate series cam - like Comp Cams Extreme Energy series - they make excellent vacuum compared to other cams with the same .050 lift duration (less over lap, yet excellent "area under the curve"). However,, no matter how you increase your power level,,, you need to know and understand how to modify the carb to maximize performance for the changes. These computer carbs will respond just as well to the old "super stock tricks" as the old quads and pull just as much air as most of them after being modified. Get HP Books #014 - Rochester Carburetors,, just an EXCELLENT source for computer carb modifications.

 

Hey BADSS, what kind of intake duration can
the computer system handle ? The XE262 is 216 and the 268 I think is 224. I am contemplating a substitution for my L69 looking something like 350 ci,Dart heads,10:1, with the above mentioned cams and all under computer control. I am now running a JET stage 2 chip so does that allow
more cam duration ?

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Tom K.
84 Z-28 M5 305 L69 HO
pulleys,coil,3:73(stock)
Jet chip, fan switch,
Al dshaft,1.6 rockers,
LCAs and brackets,BFG DRs
14.20 @ 96.74 2.02 60ft

 

On your combination the 218/224 - 110 would be a nice cam and relatively easy to tune in. The 224/230 - 110 would be do-able, but much harder to tune for. I'd recommend HP Book #14,, for anyone that could see themself working on the carb. For the other folks you better find someone that knows how to tune on the carbs,, or go with the 212/218 - 110 on a similar engine combo. The 212/218 cam should work with just idle adjustment and rear metering rod changes.

The chips for the carbed engines don't really do much more than add timing and delay the lock up, it's going to take knowing how to tune in the carb if you deviate much more than stock.