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Old 02-01-2012, 03:54 AM   #1 (permalink)
womprat
Lead-footed Econewbie
 
Join Date: Apr 2009
Location: Wellington, New Zealand
Posts: 52

Ceffy - '97 Nissan Cefiro 25 excimo
90 day: 25.21 mpg (US)

Demio - '07 Mazda Demio Sport
90 day: 30.99 mpg (US)
Thanks: 4
Thanked 5 Times in 2 Posts
Fiddling with a variable manifold - locking it in high rpm mode

My car has a variable intake manifold, that switches between a long runner'd intake with a low volume plenum, over to short runners and a reasonably large resonance chamber positioned about half way along the intake runners. This kicks in about 5500rpm and fills in a torque hole from there to the redline. Actually has quite a strong effect, takes the 2.5L engine from about 165hp @5600 to 190 @ 6500. But below 5000 rpm it hurts torque.

Now I wonder if locking this open in it's high-rpm mode would provide some low-rpm efficiency gains. Mainly by allowing the throttle to be wider open. It noticeably dulls response at low speed, need put foot down further to get the car going. Am I on to something here or would the two effects cancel each other out? Being an automatic I'm probably inviting more kick-down but I can mitigate that by putting transmission in snow mode - really resists kick-down then.

(Car is a 97 Nissan Cefiro imported to NZ from Japanese domestic market, has the variable plenum not fitted to the almost identical 4th gen US Maxima, the Japan and Middle East version had a variable intake for a kick of top end power - jokingly known as MEVI for Middle Eastern Variable Intake).

Only other mod I have on the engine at the moment is a WAI and grill blocks. It'll be a while before I can test any effects it properly, but thought I put the idea out there for now.

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