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Does anyone know an proximate relationship of CR and ignition timing increase/decrease assuming all other engine specs are same other than CR changes?

I am looking at using a very well developed ignition table from VP engine on my VR with basically the same mods as a base map to massage when I hit the dyno this weekend. Would be far easier than trying to fix that awful stock table

How much should I decrease the table by % in order to be close to optimal but still safe enough?

Table is from 8.5 CR going to a 9 CR engine with virtually same mods.

i''d say compare a stock VP and VR timing map and see what the average differences are, that number might be as much as 4-6 degrees to account for the increased compression.

its hard to compare. factory maps are all over the shop and spiky as! the APNX and BLCD I have compared before, were there is a trough in one, its a spike in the other.

I have the greenfoam one out of my VP, I took a read the other day and its excellent! smooth as and good timing everywhere.

Do the VP and VR have the same cams and timing set ? There's more than just compression that effects timing. Auto v manual, diff gears, weight of car etc etc dictate how quick u can feed the advance in. Make sure you don't forget fresh fuel as well !

yeah its the same cam and everything.

had a look at the vn map verse vr its about 5º less in the VR but the greenfoam's one is about 5-10º more in the mid and cruise areas over the VN one and up to 20º more than the VR ones in the same areas.

high load area are similar from VN to greenfoam and even almost the same as my tweaks to those areas on the VR.

I reckon I should get very good ball park with all of this.

The biggest changes are in the vn v6 series 1. In 12P that gets the APNX tune, but all others get BLCD.

vn s1 had a different cam also. more duration, more lift but less aggressive ramp rate over the vp-vr cam.

vlad01 wrote:vn s1 had a different cam also. more duration, more lift but less aggressive ramp rate over the vp-vr cam.

Isn't it the other way around? s1 VN, high lift/short duration, VN s2 onward more duration/less lift.

no, I found legit cam specs for both and VN is more lift and duration, but the VP onward has more aggressive ramp rate so the lob profile area is larger somewhat in the later cam.

Those specs were total duration iirc not the .050 duration? So Im guessing later cam might have slightly more duration when measuring from 0.050"

VN definitely has more lift than later cam, thats for sure.

well according to this I found posted on the commodore forum the VN is more in 0.050" as well?


Standard Camshaft Timings for the early VN Series 1 V6 Engine:

Advertised Valve Timing at height - 0.006 inches
Inlet Opens - 22.4 degrees BTDC
Inlet Closes - 66.9 degrees ABDC
Exhaust Opens - 70.7 degrees BBDC
Exhaust Closes - 26.2 degrees ATDC
Inlet Valve Duration - 269.3 degrees
Exhaust Valve Duration - 276.9 degrees
Inlet Valve Lift with 1.6 to 1 ratio rockers - 0.4376 inches
Exhaust Valve Lift with 1.6 to 1 ratio rockers - 0.4373 inches
Inlet Valve Lift at TDC - 0.0336 inches

0.050 Valve Timing
Inlet Opens - minus 15.3 degrees BTDC (15.3 degrees ATDC)
Inlet Closes - 29.2 degrees ABDC
Exhaust Opens - 30.4 degrees BBDC
Exhaust Closes - minus 14.2 degrees ATDC (14.2 degrees BTDC)
Inlet Valve Duration - 193.9 degrees
Exhaust Valve Duration - 196.2 degrees
Inlet Valve Lift with 1.6 to 1 ratio rockers - 0.4376 inches
Exhaust Valve Lift with 1.6 to 1 ratio rockers - 0.4373 inches
Ramp Rate - 2.13
Valve Overlap Seat to Seat - 48.6 degrees
Valve Overlap at 0.050 inches - minus 29.5 degrees
Inlet Lobe Centreline - 112.2 degrees
Exhaust Lobe Centreline - 112.3 degrees
Lobe Separation Angle - 112.3 degrees
--------------------------------------------------------------------------
Standard Cam Timings for the late VN-VP-VR-early VS Series Two V6 Engine:

Advertised Valve Timing at height - 0.008 inches
Inlet Opens - 9.8 degrees BTDC
Inlet Closes - 52.1 degrees ABDC
Exhaust Opens - 56.8 degrees BBDC
Exhaust Closes - 14.5 degrees ATDC
Inlet Valve Duration - 241.9 degrees
Exhaust Valve Duration - 251.3 degrees
Inlet Valve Lift with 1.6 to 1 ratio rockers - 0.4066 inches
Exhaust Valve Lift with 1.6 to 1 ratio rockers - 0.4083 inches
Inlet Valve Lift at TDC - 0.0256 inches

0.050 Valve Timing
Inlet Opens - minus 20.9 degrees BTDC (20.9 degrees ATDC)
Inlet Closes - 21.4 degrees ABDC
Exhaust Opens - 26.1 degrees BBDC
Exhaust Closes - minus 16.2 degrees ATDC (16.2 degrees BTDC)
Inlet Valve Duration - 180.5 degrees
Exhaust Valve Duration - 189.9 degrees
Inlet Valve Lift with 1.6 to 1 ratio rockers - 0.4066 inches
Exhaust Valve Lift with 1.6 to 1 ratio rockers - 0.4083 inches
Ramp Rate - 2.27
Valve Overlap Seat to Seat - 24.3 degrees
Valve Overlap at 0.050 inches - minus 37.1 degrees
Inlet Lobe Centreline - 111.1 degrees
Exhaust Lobe Centreline - 111.2 degrees
Lobe Separation Angle - 111.2 degrees