Let me preface by saying that I've only just recently installed my 3.5IM and only just recently really cared about my NA performance. Like within the last week. Until last week I had planned on turboing this car again.

So I keep reading about the VIAS delete that lots of people are doing. I figured that the vias plate opened up at low RPM (below 1800rpm) and at high rpm (I believe 3800 is the stock high rpm switchover).

So I unbolted the VIAS from the 3.5IM in preparation to "delete" it and what do I find but that the throttle plate looking thing is actually CLOSED in it's rest state (when vacuum is NOT applied to the vacuum actuator valve). That means, if I understand the operation and RPM switchovers correctly, that this "throttle plate" inside the manifold is actually closed below 1800, opens between 1800 and 3800, and then closed again above 3800. Is that correct? So the sequence of vacuum being applied to the vacuum actuator valve would be "no vac" below 1800, "vac applied" from 1800 to 3800, and then "no vac" again above 3800 to redline. is that correct?

if that is the case, this begs two questions.

a) why the hell would nissan bother to "close" the internal "throttle plate" above 3800rpm if there are such significant gains to be had by keeping it "open" (which is essentially what we do when we do the "VIAS delete").

b) if I am understanding how it operates correctly, why would deleting the VIAS introduce a loss of power between 1800rpm and 3800rpm at all, since it is ALREADY open between those RPMs? There should essentially be no change in power between 1800rpm by deleting it, and nothing but gains to be had from 3800rpm to redline.


Lets discuss this because as my understanding of it is right now, it makes absolutely no sense to me. it's totally counterintuitive.

 

One thing you must keep in mind when considering the performance of the VIAS is that is works in conjunction with the VTC on a stock 3.5 engine. Apparently there is a certain relationship between the opening of the valve & the variable cam timing that produces optimum performance. When the valve is simply actuated in an OFF/ON/OFF mode without regard to the variable camshaft duration, it does not produce the power it would normally. I'm sure others will elaborate further.

 

That is a good point.


One thing I'd be interested in seeing would be a true before and after dyno of a VIAS delete. I don't mean different days. I want to run a couple runs with it open and a couple runs with it closed and see where the power crosses over and analyze the dynos to figure out the optimal switchover, or, if deleting it entirely is really the best option. Next time my buddies get a dyno day together I may very well try this as it only takes about 3 minutes to do the VIAS delete.

 

I'm 100% certain that the 3.5 power valve is OPEN by default.

 

it should be open closed open.... the only way for this is if the vacuum is supplied once the engine is started....so we need a 5.5 or 6 gen to verify this by watching it on start up.... that would be the easiest thing....

i posted pictures in my thread about my 3.5 swap and there is a picture of the valve actually closed while the engine is off.... so it is closed by default when the engine is off for sure....

 

From what the FSM states and personal observation the power valve is open with no vacuum applied.


Idle-1800 RPM = no vacuum applied. The valve is open.
1800-3600 RPM = vacumm applied. The valve is closed.
3600-fuel cut = no vacuum applied. The valve is open.

 

yeah that's right....i'm an idiot. i went back through my pictures and it is open by default. my bad.

 

what is written in the FSM makes sense to me logically (it's operation is noted in the FSM as being identical to that of the MEVI, which I am well versed in). What is written in the FSM is how I assumed it worked.

Since this is apparently how it is supposed to work, why the heck would removing it entirely result in more top end? If it's already open I can't imagine that removing just that tiny little bit of extra aluminum around it (the power valve "casing" if you will) would result in 10hp more worth of air going into the engine...

 

I may be completely wrong, but I was under the impression that the majority of the top end gains from the VIAS delete stemmed from gutting the shelf in the IM, as well.

 

It's a matter of semantics but the VIAS delete mod refers to the replacement of the power valve assembly with a blockoff plate.

 

That's why we need more than a single dyno run with sketchy rpm signal, everybody is basing it on that, I would be stoked if you did that.

Also, I should have an rpm switch around that is set for 1,800, 3,800 or whatever the stock is if you're interested you can borrow it.

The whole vtc post, I don't know, I've seen similiar dyno results of gutted verse working on non vtc cars nearly identical to 5.5g's

 

It takes 20 minutes to put the VIAS in and out...if that....someone if they are motivated enough can get a dyno done at a shop for 75 bucks for 3 pulls (roughly) the first pull have the plate in or out, then swap....then compare.....

 

Thank you for the explanation

I am using just the vias delete plate
It was an inexpensive mod [40 bucks], looked good
And according to what I could read here, was worth 10 hp

At the track I turned a high of 108mph previously and now turned 108mph [with the vias delete] at the same track but on different days with different, temps and humidity
[By 5 degrees]

But 10 hp is hard to measure and could relate to temperature and humidity changes

Due to the fact I like its looks
My butt dyno reports a stronger rush from 4500rpm up. lol

However, I could tell no difference at the track
{Based on 12 runs prior to vias delete, vs 6 runs post vias delete on a 1/4 mile track at Alabama International Drag way}

vias delete run example here
http://www.youtube.com/watch?v=mCLyDIpIlLQ

 

Im motivated enough i just cant make the vias function. Well maybe the EU can. Im due for a dyno real soon

i just need to fix my oil leak.

my exhaust

get a o2 sensor for my WB controller

i need to figure out why my timing is so freaking off.

 

I've got a summit switch, just didn't get to install it the other day because I was busy with getting the car drivable.

I'm gonna do it at some point. Making a block off plate will take all of about 30 minutes. I've got access to a couple dynos that will allow unlimited runs for $100/hour and I get to operate the dyno myself (last time we were there the shop employees went and got lunch and stuff while me and my buddies did as much dyno tuning as we wanted with no oversight/encumberances) and I'll hopefully be getting my Bikirom ECU soon anyways and will need to tune the car.

Things I'll test:

VIAS installed and working as intended
VIAS closed all the time
VIAS open all the time.
VIAS with just the plate removed from stock VIAS mechanism
VIAS mechanism totally removed with flat block off plate installed in place of it

any other combinations you guys think I can test? That's all I can think of (with regards to the VIAS)

 

That seems to be pretty thorough.

Maybe a year or so ago Merlyn and I went to the track, we tied his VIAS open for one run, and closed for the next. He ran identical (well, not identical, but within a small tolerance) runs both times.

Obviously track times (especially for a 6MT) aren't a good indication of minute changes like this, just thought I'd share.

 

I did this as well, did not see any difference.

 

It's possible it could end up being just like the MEVI, virtually the same times and traps but with a marked difference in the powerband shape.

 

Neal, I've got a block off plate if you want it, let me know. You can swing by and pick it up.

 

i'm also looking forward to the dyno results. i've been debating whether or not to try this 'mod' out since a ton of people on the 6th gen forums have done it...and it's relatively inexpensive. but i also assume that the power curve will be altered slightly with the VIAS deleted compared to the stock configuration.

 

yes, I would. that would make things easier. i might actually be able to test it this weekend if i can get it from you before then. the track day i am doing has a portable dyno coming (that would prove more expensive though since I'll still need to get on the dyno to tune my new ECU later as well).

i want to get to byron or us41 on the 6th or 7th if you want to come.

 

i'm debating driving back up to chicago with the max and going to the track with you

couple 12 second max's would be cool! haha

 

you should

 

got a hold of a block off plate. now just need to get my bikisoft ecu to make going to the dyno worth my time and i'll test this out, might not end up happening too soon though. got stuff going on every weekend from now til the very end of august so time to spend on the car will be limited.