I am using a gsr head on my b20vtec conversion and was wondering if I should stick with the 4400 rpm crossover point because of the gsr cams or should I raise it to around 5500? Not enough money to dyno is yet.


[Modified by Vanilla4215, 3:41 AM 7/12/2002]

 

Stock 4400.

 

 

Stock at 4400 is the mid lobe, then 5800 for the high, correct? I've had an issue with all kinds of experienced Honda guys and VTEC, and I still dont' know for myself-- when is the mid lobe used, and when is the high lobe used (on DOHC VTEC)? I've heard it's a transition lobe which only acts instataniously when switching to high, and I've also heard that it's like I said the first time.

If you get aftermarket cams for turbo/all-motor/Nitrous application cams, you should really tune your VTEC x-over point on the dyno. Look to see when your Torque/HP is falling off, and determine when you should switch it over, based on the downfalls. On a previous set-up, I had mine going at about 5300rpm, my torque was falling off around 4800, but the HP hadn't fallen until about 5500rpm, so I put it at 5300, so I didn't have to deal w/ the tappering off of HP. You really shouldn't change your VTEC point, or even have a VTEC controller unless you have Cams, cam gears, valvesprings, retainers, and higher compression (for all motor applications), because it's not going to make your car any quicker.

 

To find the best point for vtec engagement you have to do some slight dyno tuning.

Set your vtec crossover point very high (6500+), that way the run will really show the HP/TQ from the non-vtec lobes. Find the peak HP from the non-vtec lobes, and set the crossover point 200rpm before it.

 

VTEC engages at 4400rpm on a GSR motor, there is NO high lobe at 5800.

5800rpm is the point at which the secondary runners in the IM open at, not a high lift X-over point, at 5800rpm the cams are spinning the high lobes which had engaged at 4400rpm.

basically there are two lobe positions on the cams - 0000 rpm- 4400rpm and 4400rpm - 8200rpm

 

So why are there 3 lobes. I know all about VVIS, and all the jazz w/ the dual runner... Why 3 lobes, why can't we just have 2 like the D16? I know more than enough about the Honda motor, I've rebuilt a couple from the ground up, but what is that middle lobe for????

 

There are three lobes for the intake side and three lobes for the exhaust side for each cylinder. The primary, secondary, and the VTEC lobe.

At low RPM and load the primary and secondary lobes are actuating the valves. They are different sizes to enhance swirl on the intake side which leads to a better mix and more complete/efficient burn.

At high RPM and load the rocker arms lock together and both valves are actuated by the middle lobe (VTEC lobe).

What is VVIS in relation to Honda?

-kenji

 

Hmmm, wow. So you're saying that one valve opens more than the other, that's interesting, but now that I think about the skimatics and the physical lay-out, it makes total sense. Cool, be honnored becuase I've talked to tons of people about this, a lot being people who have built engines or been imersed in it for over 5 years, and nobody could give me a straight answer.

VVIS is the technical term (like VTEC) for the dual runner GS-R manifold or "Varibale Volume Induction System" They called it that in a way-old issue of Velocity--