Varioram for a street machine?

[Moses]

I took the car out a nice hard run today. When the V-ram kicks in you get a really nice punch and a fantastic sound. It seems like more than the 8-10 HP quoted, but the howl from the intake might account for the perception of added power. Also any added power feels more dramatic in a smaller, lighter car.

Anyway, I don't know much about V-ram, but it appears to kick in at 5,400 RPM and only under WOT! If you ease up to 5,400 RPM, I don't feel the V-ram kick in. In a street car, how often do you sail past 5,400 RPM with your foot to the floor? I can see that it's a nice little boost when driving VERY aggressively, but I can't imagine most suburban 993 owners ever actuating the Varioram.

[masraum]

I pretty regularly hit 5400 in my '88, but I can see the greater torque tractability of the 993 eliminating the "need". I don't know that it would change the way I drive though. Possibly because the weight of your car is so much lower than a 993 you don't have to wind it up as much as you would if it were actually in a 993.

[Lewis Ledyard]

What is the redline with a Euro Vario motor from a 993? I need to have my '88 tach recalibrated for the newer motor.

Thanks

[Bill Verburg]

It's kinda like the old tripower GTOs when the secondaries kicked in. Sorta freightening the first time.

What is the redline with a Euro Vario motor from a 993?

Depends on the internal mods. Stock M64/21 power peaks @6100 and 6800 or so is a nice conservative redline. The valve train is good to the low 7ks, the weakest link is the rod bolts. which are ok for occassional bursts to ~7K.

[GenX Porsche]

I am a little scared about this post...it reminds me when I was walking by a honda dealership looking at a mercedes. The sales man came over and told me if I wanted a sports car I should check out the s2000. And then the famous line. The car is pretty fast but when the vTech kicks in...man this thing takes off. My friend and I battled off busting up laughing. I know its not the same but I got flashbacks....

[Moses]

Originally posted by masraum
I pretty regularly hit 5400 in my '88, ...

Getting to 5,400 is one thing. Getting there with the pedal to the floor is a different thing entirely. In my SC, if I push the pedal to the floor I will fly past 5,400 RPM on my way to the redline in a flash.

If V-ram actuated at 5,400 RPM REGARDLESS of throttle position it would be great. The way it is now, as soon as I hear the roar of the V-ram, it's time to back off the throttle cause I'm at the redline. There is no way I could engage the Vram in 1st gear without hitting the rev limiter. Things are just happening too fast.

[Jack Olsen]

Here's BeepBeep's old post about how Varioram works. Has anyone confirmed that it only kicks in under wide-open throttle?

Whole engine equipped with Varioram is tuned for torque, untill you hit 5800 RPM's when it shortens the intake stacks. Do you really believe Porsche would put it there if it was "insignificant"? Actually, Varioram doesn't open at all until 5000 RPM and goes trough three stages between 5000 RPM and 5800RPM:

Below 5,000 rpm (left A and top right) : long pipes; resonance intake disabled.
5,000-5,800 rpm (left B and middle right) : long pipes plus short-pipe resonance intake, with one of the interconnected pipes of the resonance intake closed.

Above 5,800 rpm (left C and bottom right): long pipes plus short-pipe resonance intake, with both interconnected pipes of the resonance intake opened.

[Moses]

Originally posted by JackOlsen
Has anyone confirmed that it only kicks in under wide-open throttle?

If I sneak up on 6,000 RPM without hitting WOT, I never notice the V-ram. Maybe it's programmed that way. Sure would be nice to have it at 5,400 RPM regardless of throttle position.

Anyone know for sure if WOT is required?

[beepbeep]

Ahh...Moses finally saw the light and hooked up Varioram!

Gut!

It was worth it, no?

[Adam]

Ok, seeing as how the system is computer controlled, could you adapt a VTEC-Controller style management system to control and engage the Vram at slightly lower revs and at less throttle than WOT?

I've driven VTEC Hondas with that sort of system and it's like they've got bigger power all through their rev range. I know the Honda system controls cams and that the Porsche system works the intake, it's just a throwaway idea.

[Bill Verburg]

my previous post re vram operation

Further Amplification from the 993RS Technical Manual



A) Vibrating tube induction

If the gap (5) betweensliding section (4) and central
intake distributor (6) is closed, the intakesystem is a
single-chamber vibrating tube inductionsystem. Intake
air flows from the central intake distributor via vibrating
tubes designed for maximum torque to the cylinders.

B) Resonance induction

If the sliding sections (4) open, switchingthe system
from vibrating tube to resonanceinduction,the air flow
branches downstream from the air mass sensor (1).
One branch is connected to the central intake distributor
(6) of the single-chambersystem and one to the r~sonance
system (7) below the intake distributor.

From the central intake distributor, part of the intake air
flows through the intake pipe extensions,which act as
resonance tubes, directly to the intake funnels of the
short vibrating tubes and to the cylinders. The main intake
air stream flows via the second throttle flap and
the first large resonancetube of the resonance system
(7) to the resonancechambers.The resonance induction
system optimizes air flow to the short vibrating tubes.

C) Resonanceinduction with open tuning flap

The tuning flap (3) is installed in the second large resonance
tube. Initially,the tuning flap is closed. At a defined
enginespeed (5920 rpm), the tuning flap is opened,
increasing the flow area between the resonance chambers.
Air now flows to the resonance chambers via all
the connecting pipes.

Switchoverconditionsfor intake pipe extensions
and tuning flap

1. When the ignition is switched on, the DME control
unit activates the solenoid valves. If the engine is
started, the intake pipe extensions and the tuning flap
are operated.When the engine has run up to idle
speed, the signal to the solenoid valves is deactivated
and the intake pipe extensions and tuning flap
are set to their basic positions.
2. If the engine speed reaches 5160 rpm and the
throttle valve is at least 50&deg open, the DME control
unit transmits an electrical signal to the solenoid
valves of the intake pipe extensions and the extensions
are operated, switching the intake system over
from vibrating tube to resonance induction.
3. If the engine speed is higherthan 5920 rpm and the
throttle valve is more than 50&deg open, the DME control
unit opens the tuning flap, increasing the resonance
tube cross section.

[Bill Verburg]

Those #s are for stock M64/20 993RS. They can be and often are chaged in custom chips(mine were).

[Moses]

Originally posted by Bill Verburg
[B]my previous post re vram operation

Further Amplification from the 993RS Technical Manual

Amazing. So it's 50% throttle. I've been babying this thing too much!

Bill, you are encyclopedic! thanks.

[Moses]

Originally posted by beepbeep
Ahh...Moses finally saw the light and hooked up Varioram!

Gut!

It was worth it, no?

It's a beautiful thing.

[Bill Verburg]

I just have a good library

[911pcars]

As Jack and Bill pointed out in their posts, the Varioram mechanism, like so many other manufacturer's induction systems, provides a variable-length intact tract to optimize torque throughout the rpm range.

Varioram is not giving you any more at WOT than it would if it merely had the right length short intake pipes. However, it is optimizing the available torque at less than WOT settings.

If you feel a kick in the pants when Varioram works, it's either because:

1. The engine has simultaneously hit the sweet spot.... or

2. The intake system was "choking" the engine (I use that term loosely) until the shorter passage opened.

In all likelihood, number 2 complimented no. 1.

Sherwood
http://members.rennlist.org/911pcars

[Bill Verburg]

It's optimizing the intake tract in an adaptive manner. Though with only 3 states it's an imperfect system. On the dyno charts there is a nice little hump in the torque curve at the transitions. The change in noise is probably what is the most startling especially the one at ~5900.

[Bill Verburg]

Here's the stock torque curves w/ & w/o vram in operation

[Jack Olsen]

50 degrees or 50 percent?

That torque chart makes me jealous. It looks like the biggest gains are actually in the midrange.

[Bill Verburg]

50&deg, thats why the vram is so desireable for street use or for use w/ transmissions that have only 5 gears(6 speed would be gravy)

The race cars used the plastic manifolds w/ various throttle bodies because they were only interested in power from 6k - 8k, and they have all those lovely closely spaced gears