Know I'm going to catch a terd on this one , but I'd like to at least try the cc Q-jet and cc dist. Can someone explain the factors involved so I'll know what might possibly happen.... Another thing, I know a visual is nothing to go by, but there didn't seem to be much difference in that cam(268) and my lg4..so I got out the calipers and I saw about a .050 differ in the lift. Will the .050 make that much of a difference? I'm sure the dur. and other specs are out there too.

 

I don't know squat about CC Q-Jets, or the CC dissy for that matter, but I can tell you that .050" of lift is a lot if you're talking at the lobe.

Multiply that by the rocker ratio and it's .075" more lift at the valve. Equivilent of changing a .425" lift cam with .500"

 

yeah, it's at the lobe..if I done the math correctly.. one thing I didn't understand was that on the stock cam the backsides of the lobes were wider than on the 268 comp. This makes me believe that when I go to install the 268 my lifters will be further down in the bores...So do I get longer pushrods ..In the learning process here now

 

Yes, you may have to get longer pushrods.

The reason the back of the lobes look more narrow on the newer cam is actually a simple explanation.

In order to increase the lift of a cam, they have to make the low spot lower. They actually have to do it this way. They can only increase the "height" of the lobe a certain amount otherwise it wouldn't clear the holes (aka bores) in the block where the cam slides in and rests on the bearings.

Since they can't make the lobe taller, they make the base shorter.

I hope that makes sense. 90% of the time what I mean and what I say are two different things.

I guess it's like the high jump in the Olympics. They usually raise the bar right? Well instead of raising the bar 2", they could just dig a trench in front of the bar 2" deep, and you'd still have to jump 2" more to clear the bar. Make sense?

 

I make picture

#1 would be stock. They can't make #2 or else it wouldn't go into the engine so they make #3.

BTW, you can get an adjustable pushrod from www.jegs.com or www.summitracing.com that will help you find the correct length you need.

 

Just so you know, on another engine, I went from a stock LG4 cam to an XE268 and didn't need to change pushrod length - it ran fine in this case.

 

I run a 268XE in a 355 with stock smogger 76cc heads and about 8.6:1 CR, I have a Jet Streetmaster stage II Q-jet (non CC) and I idle at about 650 with 13" vaccum, with my old non modified q-jet I had the idle screws backed all the way out and the throttle stop screw in about 6 turns and it idled at 850-900, big midrange flat spot. Jet redoes the idle passages and reworks the primary circuit.

Comp insisted I should have 15-17" of idle vaccum with this cam but I have yet to meet anyone who pulls this much with it.

It likes a 2200 stall converter much better than the stocker as well.

Eric

 

Thanks AJ, me understand lots more:lala: Maybe when I tighten the rockers down the nuts won't bottom out before the arm seats snugly..

 

Thanks for the info everyone....Having second thoughts about the cc Q-jet and ccdist.... Can my carb be reworked to accomodate the 268HE or can I get a custom chip ...or both? Will my timing also have to be modified...?

 

I have the same issue. Sometimes I think comp is on crack. I have the XE262 and it pulls 10-12" vacuum at idle. Comp claims 18".

 

I have a XR264HR in my 305, it pulls about 15-16" of idle vacuum....

It's all in the tuning.