Turbo VTEC questions

**aaronng** · 21-11-2006 09:09 PM

Originally Posted by silver_screen

Ahhh i see, how very interesting. So you could pretty much control the lift and duration of either intake valve with these 3 stage vtecs... Both lo lobes r the same profile thou arent they?

The Nissan head doesnt seem to have the extra stages of valve control.. By the looks of the pic, they r either on or off. Only way to know for sure is to have the head right infront of me

There was only 1 D series engine with this 3 stage VTEC. And that engine, both low lift lobes were the same. So the only difference between this and DOHC vtec is that there is an intermediate 1-low, 1-high valve setting.

Originally Posted by silver_screen

What im sayin is that once the Hi lobe has engaged, the low lobes dont have anything more to do how high the valve will open and for long... They dont do anything for turbo spool times because its the hi lobe thats actually controlling the lift and duration of the valves... and as it seems its on both, intake and exhaust..

In low lift mode, it's purpose is to promote quick cylinder filling and efficient combustion at low RPM. So you get more exhaust gas than when compared to running high-lift mode at low RPM where you have incomplete combustion due to lower filling efficiencies from using such a high lift (bigger entrance cross-section, hence lower than optimum velocity).

More exhaust gases means quicker turbo spooling.

**iamhappy46** · 21-11-2006 09:24 PM

^^ That is also why running the car with hi-lobes locked in to see where the two torque graphs intersect would not work. The hi-lobes would not spool such a big turbo as even with hi-rpm, the exhaust wheel inertia was not already moving from low rpm/low lobe so turbo lag was excessive.

In the end, it worked out alright. Just need a better gearbox to handle the torque output

**yourfather** · 22-11-2006 01:11 AM

yeah, because you won't have the airflow to get the wheel spinning...

I guess the solution to that is to run from a point where you get turbo to spool up as late as possible (crossover), and plot that, and then effectively reduce rpm of crossover point until you get a fair idea of where the valve timing is going to be more beneficial.. so rather than having two intersecting curves, you'll get a normative baseline of what the engine would do from low rpm, late crossover point, and hopefully, as you decrease the rpm of the crossover, you'll find that there will be a shift upwards in the power curve.

and once you stop seeing any benefit in reducing timing, that would be your optimal point.

**silver_screen** · 22-11-2006 06:12 AM

If u want ur turbo to spool up quickly down low, introduce some NOS

That'll get the biggest of turbos spooling up fairly quick, but only use it to spool it up, otherwise ur cylinder pressures will get too high and ull have some nasty, conrod breakin deto happening :P

**iamhappy46** · 23-11-2006 09:02 PM

My motor has forged internals and would happily run with NOS, as the engine should take around 28psi, so 16psi + NOS would be fine. However, as the engine is designed to be street legal, I would never use it. The motor is tractable and there is no real need for NOS when I still have another 2 sets of aftermarket cams to try.

The camshaft engagement points may not be perfect but the drive by wire seems to even out any holes in the torque output. I am currently considering what gearbox setup to use that will handle such an excessive torque output

**iamhappy46** · 29-05-2007 12:48 PM

Car will be in Sydney this week. SCR800 is the name of the car(not road registered yet) with 917Nm of peak flywheel torque and over 760Nm from 6000rpm to 8500rpm. 807Kg street legal weight with around 800Hp@flywheel in current emissions friendly tune. Race ready weight will be around 740Kg + driver weight

Gearbox is a 6 speed mid engine RWD style gearbox(essentially a rear mounted FWD gearbox) with a helical LSD, made by GKN. Clutch is a custom twin plate 5.5" clutch setup, with an auto flex plate ring gear to start the car. Flywheel and clutch assembly weigh 7Kgs all up

0-160km/h runs have been consistently in the hi 5's and low 6's, depending on how the 315/25R19's hook up and the T/C settings in the ECU. Hoping to get to Oran Park one weekend for a track day, to find any possible kinks in the suspension settings and see if the engine or mechanicals misbehave.

Should see the more of the kit cars rolling out shortly. One SCR250(250Hp SR20VE engine) is currently undergoing the approval process for Qld, with another being built with an SR20DET at the moment for a customer. Also looking at fitting a K20A to one in the next few weeks as the engine bay has plenty of room. Kit price is around $20,000 or around $40,000 mark for a turn key car.

Organising a website shortly to have more pics/videos/etc

**nd55** · 29-05-2007 07:52 PM

> 917Nm of peak flywheel torque

Isn't this considered herecy on a Honda forum?

Amongst all the squabbling about cams and lobes somebody forgot to say....

WOW!!!