Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Variable Geometry Intakes

This month Sport Compact Car mags has a great article detailing the different types of VGIs. They talk about how some have variable length, some have a butterfly to close off half of the runner and how some,like our 2.5L, have both. It is a well written article and explains the bennefits and how they work. In other words keep your IMRC and if you can optimize the lower to get the most out of your top end.

I believe DemonSVT has removed his intake butterflies and his car runs particularily strong (14.7s@96mph). I don't know how he didn't loose some lowend torque when removing the butterflies.

Variable intake manifolds are very simple in design and are extremely effective. It's a shame more companies don't use these setups.

My 96 Maxima only uses long intake runners which make for good torque, but kill my topend rpms. My car runs out of breath at 5400rpms on the dyno. HOWEVER, a 6 months ago a group of Max owners found out that the 96-01 Japanese/European Cefiro (Maxima) runs a variable intake manifold. There are approximately 7 guys at maxima.org running these JDM manifolds right now. On the dyno power to carried straight to the 6500rpm fuel cut and people are noting a .3-.4 second drop in ET and a gain of 3mph. My JDM manifold will be here next week 100+mph traps here I come. I will probably get a JWT ecu to extend the rev limter to 7000 and add some more midrange power.

Dave

well i untill i see a dyno comparison with/with out the VIM downlow i cannot see the same performance

My SE 3 liter without secondaries had a very smooth/flat looking dyno at SZ02. Just needed a bit more fuel control via the Greddy Emanage that's sitting at home to compensate for the added airflow that my MAF calibrator just couldn't quite handle. I out torqued Mark's SC'ed 2.5 with functioning secondaries up to around 5,300 RPM. Is that good enough?

yea that sounds nice but 2 completly diff. cars. I would like to see what your car dynoed witht he secondaries. From what I have understood having these buttlerflies closed downlow makes the car act like a torqier 2v motor and then when the RPMs get up there it lets the car act like a typical high reving 4v. but cutting down one of the runners in creates a better intake charge with greater fuel velocity and air velocity.

I do have some low rpm power loss.
Below 2000rpm it's a dog (who freakin' cares, it's not a tractor :rolleyes: :p )
Below 2500rpm there is a small, but noticeable loss.
2500-3000 is about the same.
3000 and up is stronger.

Since I barely even get below 3k in normal cruising I don't see any drawbacks personally & the benefits are numerous...

I have the PCM giving me timing & fuel advance ~2500rpm instead of the stock 3400-4000rpm where the long runners have long run out of steam. (~3200-3250 on a stock SVT the short runners surpass the long runners - lower rpms on modified engines)
I also can tune the A/F with the S-AFC.

jiako,

Send $100 and I will spend $200 on two seperate dynos tuning sessions.

One with butterflies, tuned for proper a/f ratio.
One without butterflies, tuned for proper a/f ratio. Then we will have an answer.

The problem with most "pinned" secondary dyno results is that it doesn't adjust for the new found air increase. True mod comparison is done with 12.5/1 a/f ratios. Otherwise the PCM can't adjust for the added air.

IMHO, slapping on any kind of air or fuel modification like an intake, exhaust, et al, without proper a/f tuning is not a good way to compare. TB and MAF sizing dyno grafts are another false comparison. They change the TB without increasing the fuel.

Anyone with 14s or less 1/4 mile times have a/f tuning, or did you not notice. ie DemonSVT, Bnoon, Warmonger, et al.

My .02

I agree with a/f tuning that is why i am running with an SAFC but i also do a lot of city driving so i need the extra oomph downlow.

Like I posted. If you need the extra oomph of torque below 2000rpm. Buy a freakin' tractor and ditch the DOHC beauty of an engine you have.

Hello people!!! Get this ancient pushrod V8 mated to a slushbox thinking out of your heads...
Even if you make that extra 10 TQ at 2k and below. Who cares. It's not truely usable for anything "performance" wise anyway. If you are driving this car the way it was intended you will never see such low rpm's to begin with. Even cruising I never hit 2k or below. It's just stupid to lug the engine when you have the option (MTX - downshift) not to.

{insert old man mumble here} :p

Yeah!!! I love the sound of a hord of bumble bee's when I'm traveling at 45 MPH! I also love the extra wear I put on the engine turning all those extra RPM's to do the same thing my 4 cyl. turbo car does so easily at 2000-3000 RPM. Yep makes perfect sense to me! :rolleyes: