How-to: VTEC Window and how to use it.

[AKEP]

You'll see it on the dyno, once you do the low cam and high cam over lap. Kinda tired right now but I'm not familiar with flipped pin performance on the dyno. Low end tq sounds better than you probably describe it since the offset valves cause the swirling fuel inside the cylinder. In my head it sounds like your non vtec tables will make good power for much of the rpms before your full vtec tables cross on the dyno, thus raising your lower boundary. Typically the more aggressive your primary lobe, the higher that lower boundary goes. Like tsx cams. If you compare z3 cams (let's assume the vtec lobes are the same) with their lower profile primaries, they should have a lower lower-boundary than a tune on the tsx cams, given its running the same engines.

[USAF EP3]

You'll see it on the dyno, once you do the low cam and high cam over lap. Kinda tired right now but I'm not familiar with flipped pin performance on the dyno. Low end tq sounds better than you probably describe it since the offset valves cause the swirling fuel inside the cylinder. In my head it sounds like your non vtec tables will make good power for much of the rpms before your full vtec tables cross on the dyno, thus raising your lower boundary. Typically the more aggressive your primary lobe, the higher that lower boundary goes. Like tsx cams. If you compare z3 cams (let's assume the vtec lobes are the same) with their lower profile primaries, they should have a lower lower-boundary than a tune on the tsx cams, given its running the same engines.

After reading this and the rest of the thread I understand why my friend's engine VTEC crossover is so low and why some engines have the crossover higher or lower.

Case in point:

He has a built K24 block using Wiseco's 12.5 CR pistons in a K24 but using a STOCK K20A2 with stock profile K20A2 cams. When he got his car tuned the VTEC crossover point had to be set at 3800 RPM because the car was choking when they were setting it around 5k area.

Compared to my car I have a stock K20Z3 bottom with Honda overbore pistons (86.25mm) and my built K20A2 with oversize 0.5mm intake valves and Crower (not Brian Crower) Stage 2 cam profiles (much mroe aggresive than stock) and my car was having bogging issues with the crossover set at 5200. The tuner finally settle the crossover at 5800 RPM and my powerband saw gains midrange BEFORE the crossover and my engagement was almost nonexistent (you couldn't see any type of bump where VTEC was engaging in the powerband graph).

[Ba82Ep3]

You'll see it on the dyno, once you do the low cam and high cam over lap. Kinda tired right now but I'm not familiar with flipped pin performance on the dyno. Low end tq sounds better than you probably describe it since the offset valves cause the swirling fuel inside the cylinder.

It does make noticeably better power part throttle (2500-4500, columns 5-7 and 8 when its cold out) than WOT on the lo cam. My xover is 4800 and i strive to shift at 4500 around town since 95% of my driving is on the lo cam. Its definitely a different beast. It even liked 40 degrees of advance on the small ass exhaust im using, which surprised me.

I need to go back and gradate the cam advance from idle to 2krpm. Its 0-5-10-20 to ease initial tuning and if im smooth on the throttle i can feel it change, since its climbing up that big lobe. I can imagine it would make life easier on the roller rockers if i did.

Ill mess with a window again once the 87x86 12.5cr block is done... ive gone too far down this road to start over. lol

[Her-Name's-Ally]

good shiii tony k