Changing the degree of cams to increase vacuum.

[can04cobra]

Òk guys i have 2.9 whipple built engine running comp cams 106460. Car is a monster makes great power 730 on only 17.5lbs of boost but has the bucking issue that most due under 2500rpm.i have talked with Malcolmv8 and he suggested that a 8 to 10 degrees negative overlap would cure the low vac situation and driveabilty would be back. Now I am considering re degree the cams, but want to know what you guys would suggest and your theory behind it. Would you run the negative over lap? And if you would, would you change just the degree of the exhaust advance it or would you split the difference and retard the intake as well ? I believe my car to have about 12 degree positive overlap. So that would mean a -20 to -22 adjustment in the cams. So let's hear it. What would you do and why. thanks in advance for your input.

 

[SecondhandSnake]

It's a possibility, but that's a pretty big adjustment. Question is; what are your ICL/ECL and LSA now? How you adjust them and where they end up will determine the characteristics and how they will impact your performance.

 

[gt347mustang]

I know Malcolm is a great tuner but sometimes a second set of eyes on the tune will help a lot with drivability.

Are you experiencing surging or bucking?

 

[can04cobra]

It's a possibility, but that's a pretty big adjustment. Question is; what are your ICL/ECL and LSA now? How you adjust them and where they end up will determine the characteristics and how they will impact your performance.

They are 114IC and 118 ecl with a 116 LSA it's a 7 degree over lap so I guess I'd be in the 15 to 17 degrees of adjustment and symptoms are under any bit of acceleration car bucks unless I work the clutch like I would taking off from a light anything over 2500 I can do anything with throttle and no bucking.

 

[can04cobra]

The car has the low pressure boost bypass installed the original one wouldn't open as the car is only pulling about 6hg of vac .

 

[Soap]

Malcolm knows what he's talking about. I'd follow his advice.

--Joe

 

[can04cobra]

Malcolm knows what he's talking about. I'd follow his advice.

--Joe

Agreed but he just said negative overlap when I asked him about what he would do like adjust exhaust cams only or split the difference he has yet to get back to me so i thought I'd post up and ask the community their thoughts on the situation