vacuum after poncams

[gezed]

I've recently started my engine with Tomei Poncam Type A's installed and noticed the vacuum is only at ~ -6.5psi

I am checking everywhere for vacuum leaks but can anyone tell me if the vacuum numbers looks like for a rb26 with poncams? I may be just overthinking but i think the standard value is like -10 psi

thanks!

[Dragon Humper]

It's inches of mercury not psi......don't know the metric equivalent off hand.

6 inches does sound quite low, my car has similar cams and I pull about 16 inches at idle. Even though my cams are the HKS version of the "pon cam" Infini racing still adjusted the cam timing via just slotting the bolt holes on the stock cam gears and adding offset hole plugs in drilled dowel holes ( easy and cheap to do if you have a milling machine). My CAS is also WAY out of whack to get the base timing at 20 deg.

You should make sure you base timing is set with a light and not just "CAS set back to where it was". If you have the time, it takes a good couple of hours, you should check the cam timing on int. and ex. to make sure they arn't off by 5 or 10 deg.



Jon.

[gezed]

its not 6 inches, i converted the units already, its 350mmhg or -13inhg or -6.7psi

also, checked on my pfc, timing is jumping between 21-25 deg with the iac unplugged

[Skym]

I think is around - 8.5psi to - 9.5psi with stock RB20DET cams, depending on idle rpm (I think - 9.5 psi is with idle around 1000rpm, maybe slightly under).

Tomei mention raising idle rpm with cams (I gather because you run engine richer with aftermarket cams) and mention by how much with idle rpm (vs cam specs) and by how much with A/F ratio (vs cam specs) in link below -

http://www.tomei-p.co.jp/_2003web-catalogue/e140-157_reytec_page/e154-157_te-info.html

It's under "initial setting".

As far as I know, ECU adds ignition timing to what CAS is set at and CAS is used to know when to inject fuel, so it's critical to get CAS set right.

Basically with CAS settings, etc -

20 degrees BTDC (CAS setting) + 25 degrees (an example, not what actually is shown on ignition map) = 5 degrees ATDC when ECU fires sparkplug. Not all cells on ignition map use the same timing figures, so if CAS is set incorrectly, can get flat spots or vice versa (depending on how CAS is set, i.e retarded or advanced) across ignition map.

BTDC (Before Top Dead Centre or before piston reaches top of cylinder on cylinder 1)
ATDC (After Top Dead Centre or basically when piston has gone past TDC and is on the down stroke)
TDC (Top Dead Centre or when piston is at top of cylinder and stops moving)