Timing for high compression hci builds
Timing for high compression hci builds Not looking for exact figures to build my timing table, just looking for experiences as far as timing adjustments you guys had to make after going with a rather high compression cam and heads setup from stock or bolt-ons.
For example, I used to run anywhere from 23-27* of timing on a stock compression LS2 with bolt-ons. Since doing the heads (with a redesigned combustion chamber) and cam, I find that I cannot run much more than 17-23* of timing even with a rather rich mixture. This has been the experience over many many tanks of gas from different brands so it's not the case of just bad gas.
For example, I used to run anywhere from 23-27* of timing on a stock compression LS2 with bolt-ons. Since doing the heads (with a redesigned combustion chamber) and cam, I find that I cannot run much more than 17-23* of timing even with a rather rich mixture. This has been the experience over many many tanks of gas from different brands so it's not the case of just bad gas.
I've run 18 to 28 on high compression. Depends on the setup.
Seems you have more efficient heads and if you dont have a donkey dick cam then i would run lower timing than 20-22.
I hope to take it to a dyno in the near future to really see how the different timing/mixtures react in terms of power...but I was just curious as I didn't expect to be so timing limited even with the higher DCR.
Can you touch up on that a little more...what different factors allow for more (or less) timing when dealing with a setup vastly different than stock? For example, xx size heads/cam you can run more timing while xy size heads/cam you can't? Or is it not as simple as that?
To elaborate more on the setup, the heads are ported AI 243 castings (with their re-contoured chamber) and a mid 220s cam with tight LSA and +2 advance. SCR is 11.5 but with the early IVC of the cam the DCR is upwards of 8.9.
I hope to take it to a dyno in the near future to really see how the different timing/mixtures react in terms of power...but I was just curious as I didn't expect to be so timing limited even with the higher DCR.
To elaborate more on the setup, the heads are ported AI 243 castings (with their re-contoured chamber) and a mid 220s cam with tight LSA and +2 advance. SCR is 11.5 but with the early IVC of the cam the DCR is upwards of 8.9.
I hope to take it to a dyno in the near future to really see how the different timing/mixtures react in terms of power...but I was just curious as I didn't expect to be so timing limited even with the higher DCR.
29 degrees on an ls2 on pump gas? I find that hard to believe unless it has a big cam and bleeds off most of the compression in a sense.
That's what it liked on a load bearing Dyno? I have only tuned 1 ls1 that actually wanted that kind of timing. It was a 13:5 427 race motor though. 99% of the vehicles i retune I end make more power with a lot less timing.
