1nzfe valve and valve springs

[Jason@SportsCar]

Originally Posted by tsu

Thanks for your reply, I have installed a Unichip in my car which has a feature to "open" the rev-limiter.



Really up to 7800 rpms??. Actually, the cylinder head has been ported-and-polished and milled. During the dyno test, my mechanic assumes that my stock spring valves are floating at high revs because the horsepower falls steeply after 6000 rpms and the peak horsepower occurs at around 5600 rpms. He added that beyond 7000 rpms, the acceleration feels rough and sluggish (the symptom is similar to incorrect air-fuel ratio; too rich mixture. But it is not because of AFR). To be honest, I'm not sure whether it is caused by valve springs or not. However, me and my mechanic have check all the other parts and variables, and they're on the right track.

Since my cylinder head has been ported-and-polished and milled, will it limit the work of stock valve springs (valve springs float sooner)?. Or maybe, is it because my stock camshaft that cannot provide a longer "breathe" beyond 7000 rpms?. It is quite hard anyway to find aftermarket parts for Yaris in Indonesia these days, especially engine internal parts .

No way they are floating at 7000. We spent a lot of time tuning our car for the 2016 Runoffs at Mid-Ohio, and ran to 7800 with OE springs, no issues. In our Daytona motor last year we used the BC springs and ran to 9000, but as has been said we gave up VVTI control over 5000rpm because the pressure could not overcome the springs - going back to stock spring in that engine as well.

Peak power with my cams is around 7200-7500rpm, one engine has a regrind, the other has the 9.5mm Jun cams.

You need proper engine management.