listnner

Is it true that the short run intake tubes are only activated once the engine speed reaches 5160rpm and the throttle valve is at least 50deg open ?
ie both events need to occur to open the short tubes ?
ie WOT @ say 3000 rpm, you would still be on the long tubes ?
ie <50deg throttle at say 6000 rpm ( i mean who drives like that right, but just a hypothetical scenario) and you would still be on the long tubes ?

jrmdir

The increased low-mid range torque & power from the long tubes of VR are available below 5,000, regardless of throttle opening. Over that, and with more than 50% opening, the tubes retract.

https://www.total911.com/technology-explained-varioram/

Ron

Bill Verburg

There are 3 regimes

The RS spec is
<5160 :long tubes, closed resonance flap


5160-5920 and 50° throttle: short tubes, closed resonance flap

>5920 and 50° throttle short tubes, open resonance

On the M64-21:RoW
Engine Shut, not contact........Resonance (or tuning) flap open
Engine shut, key on contact....Resonance (or tuning) flap closed
Engine idle............................Resonance (or tuning) flap open
0 rpm to 3250 rpm...............Resonance (or tuning) flap open
3250rpm to 5520 rpm ...........Resonance (or tuning) flap closed when throttle position > 60*
5520rpm to 6640 rpm............Resonance (or tuning) flap open
Varioram extensions (tubes) solenoids (vaccum) are triggered electrically by DME @ 5160rpm, throttle position should be 60*+ (RS is 50*+)
throttle position switch:
max WOT is 84* +/-3
full load 66* + > on M64-21

listnner

I don't track my car.
Whilst I still enjoy driving it in a spirited manner, I can probably count the number of times I have exceeded 5160rpm, on one hand over the past 10yrs.
So in my case, am I right that I hardly use the benefits of the short intake runners?

LimeyBoy

You can hear the runners change length (intake note changes) - but you'll need to explore higher rpm. This engine is beautiful between 5000 and 7000+, you should give it a go 👍

pp000830

What about when this aftermarket intake is installed:

listnner

Thanks for all your responses.
I was looking to see if there is a case for ITBs on a street driven motor.
Past comparisons of ITB vs varioram for this application have always favoured the varioram, since the argument was it gave more torque in the lower rpm range.
We have established that the short intake runs on the varioram only come into play after 5160rpm.
Below that its only drawing air from fixed length long tubes.

So it got me thinking.
If for example the car is a 3.8, cup cams, machined heads, solid lifters, LWF and 200 cell cats.
What if you ran long stacks on the ITB, tuned to match the the torque of the long intake runners on the varioram ?
Yes, you may loose a bit on the top end, but you gain a super crisp throttle and intake symphony that only an ITB set up can provide from the get go.


Afterall the boutique restomodders are building 964s with ITBs rather than variorams.
These cars are being used on street and track. So the ITBs must serve a dual purpose.
Surely after spending $$$, those owners are not driving gutless cars in the lower rpm ?