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57_BN4
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I had my BN4 cam reground to what was supposed to be a BJ8 profile but it looks like the grinder has possibly done something else to it. The idle vac is only 8-9in.hg and it should be in the 16-20 range. The idle is lumpy and it stalls when the clutch is pressed fully down to the carpet if I don't pull the choke a little to raise the idle first. There is also a definite boost in power around 4000-5000rpm on the road but it is a bog standard engine downstairs and supposedly redlines at 4800 so not ideal.
BJ8 cam data I sent to the cam shop:
Intake open - 16 deg BTDC
Intake close - 56 deg ABDC
Duration - 252 deg
Lobe centre - 110 deg ATDC
Exhaust open - 51 deg BBDC
Exhaust close - 21 deg ATDC
Duration - 252 deg
Lobe centre - 75 deg ABDC
valve lift 0.368
Data supplied back with the cam- each value has changed by about 1 degree from the BJ8 profile
Intake open - 17.65 deg BTDC
Intake close - 55.43 deg ABDC
Duration - 253.08 deg
Exhaust open - 52.26 deg BBDC
Exhaust close - 21.85 deg ATDC
Duration - 254.11 deg
valve lift 0.35252
Questions: what vacuum should a BJ8 cam produce in a fairly standard engine?
Is a change of approx 1 degree on the opening and closing values enough to make it sound like this?
I'm going to set the tappets at about 20 thou to see if it de-cams it enough to get the idle vac up, then I'll have to try and degree it to see if what is in there matches the spec sheet. Kind of thinking at the moment that the profile of the cam in the engine isn't what is on the spec sheet.
Andy.
BJ8 cam data I sent to the cam shop:
Intake open - 16 deg BTDC
Intake close - 56 deg ABDC
Duration - 252 deg
Lobe centre - 110 deg ATDC
Exhaust open - 51 deg BBDC
Exhaust close - 21 deg ATDC
Duration - 252 deg
Lobe centre - 75 deg ABDC
valve lift 0.368
Data supplied back with the cam- each value has changed by about 1 degree from the BJ8 profile
Intake open - 17.65 deg BTDC
Intake close - 55.43 deg ABDC
Duration - 253.08 deg
Exhaust open - 52.26 deg BBDC
Exhaust close - 21.85 deg ATDC
Duration - 254.11 deg
valve lift 0.35252
Questions: what vacuum should a BJ8 cam produce in a fairly standard engine?
Is a change of approx 1 degree on the opening and closing values enough to make it sound like this?
I'm going to set the tappets at about 20 thou to see if it de-cams it enough to get the idle vac up, then I'll have to try and degree it to see if what is in there matches the spec sheet. Kind of thinking at the moment that the profile of the cam in the engine isn't what is on the spec sheet.
Andy.