throttle body plenum to manifold spacer, power increase if removed?

[Mr spinalot]

a mate told me to take off the thick rubber gasket/spacer that goes on that small 90 degree plenum that the throttle body bolts to, not sure if this is true or not please let me know
thanks guys.
PS. its a VR S2

[moff_man]

Buick and Ecotec V6 Performance Upgrades
read this thread dude, its all there. also its up the top in a sticky

[Andrew426]

Called a bellmouth. You can remove it if you want, or cut it up and put it back in. Wont make a noticable improvment though.

[Mr spinalot]

if i remove the "bellmouth" what would i put there to replace it??? eg. gasket...because i'd rather not hack up the bellmouth just in case i want it back on.

[Brett_jjj]

The early VN's had no bellmouth fitted at all.Theres just a gasket where the bellmouth goes.Just use a gasket between the two joints when you remove the bellmouth..The early VN's did seem to go a bit better than the later releases.I vaguely remember reading somewhere that some early VN's idled a bit rough, and the bellmouth supposedly made the V6 idle smoother.I dont know how true this is though.If you have a look at a bellmouth,it definitely makes the inlet plenum have a smaller diameter for the air to have to go through,which would have to inhibit or interupt the airflow a fair bit in my opinion.It was not in the original inlet manifold design,so it doesnt need to be there anyway..

[Mr spinalot]

yea ok mate thanks i give it a go.

[Andrew426]

.It was not in the original inlet manifold design,so it doesnt need to be there anyway..

Bit of a weird way of putting it.

[Brett_jjj]

Bit of a weird way of putting it.

How is that weird.The first releases of the V6 here in Aus didnt use any bellmouth.It was added later on.Hence its not part of the original design.

[ashzv6]

does this part affect fuel economy at all?

[Andrew426]

How is that weird.The first releases of the V6 here in Aus didnt use any bellmouth.It was added later on.Hence its not part of the original design.

Well neither were bearings in the bases of the rockers. That doesnt mean you are better off with out them.

[gr8shag]

the bellmouth goes in the manifold and goes past the back two inlet runners, so removeing the bellmouth gives the air a shorter path thus increasing thottle response. removeing from a stock s2 vn - vr does not do much. but if added with other mods they run a little ruff, but nothing a good tune wont fix

[Brett_jjj]

If the bellmouth is removed and you cant notice any difference,then theres most likely something else wrong, and the engine is probably not running 100% to begin with .I have helped a couple of young blokes around here remove the bellmouth,one was a VN, one was a VR,and both times there has been a small noticable improvement.There is definitely a small low down power increase.Also its probably the same reason the first releases of the V6 went better than later releases.We bought a brand new 88 calais,when they were first released.The V8 wasnt even available when we got the V6.It was one of the very first VN calais made.Actually I still have the spare key and remotes and the owners handbook for it..It went a lot better than the later models of VN ,VP ,VR, that I have owned or driven, even though the power rating for the engine had gone up each time,none of them went no where as good as the Calais we had.I always thought it was just a "freak" one,until I drove another 88 model calais,and it went the same as the one we had,again,it had a fair difference over the others I had driven.So it either had to be the bellmouth or maybe the ECU had a different chip for the ealry releases of the VN.The engines inlet manifold and its setup were pretty much exactly the same,except for the bellmouth.The power increase had to come from somewhere though.

[hsv91ss]

I Removed it from my old VR and hated it, The Improvement was so small that it wasn't worth removing, the Idle became rough and only thing I noticed performance wise was it broke traction a little easier in first. I put it back in and if I end up with another buick V6 down the line I will not remove it a C.A.I works so much better then this so called mod.

[savage1987]

Not worth removing, leave it there, it's there for a reason.

Do exhaust and tune instead if you haven't already.

Extractors $150 second hand, fit yourself
Cat back $50-100 for a second hand 2.5" system, fit yourself
Tune, $70? these days from "nicefrog" on ebay, =greenfoam

[savage1987]

We bought a brand new 88 calais,when they were first released.The V8 wasnt even available when we got the V6.It was one of the very first VN calais made.Actually I still have the spare key and remotes and the owners handbook for it..It went a lot better than the later models of VN ,VP ,VR, that I have owned or driven, even though the power rating for the engine had gone up each time,none of them went no where as good as the Calais we had.I always thought it was just a "freak" one,until I drove another 88 model calais,and it went the same as the one we had,again,it had a fair difference over the others I had driven.So it either had to be the bellmouth or maybe the ECU had a different chip for the ealry releases of the VN.The engines inlet manifold and its setup were pretty much exactly the same,except for the bellmouth.The power increase had to come from somewhere though.

Early VNs had a slightly(SLIGHTLY!) higher lift cam, and a couple of other oddities and probably were different in the tune, I don't know, I could ask greenfoam about this if you're really interested, or 88greenVN may know a thing or two.

[gr8shag]

apparently there's also a slight difference between s1 and s2 vn intake manifolds

[savage1987]

Yes there is, couldn't tell you how much difference there is in the actual air path though.

I left my bell mouth in, cut it angled on the end so it poses no restriction but still delivers air to pretty much the centre of the manifold. Seems to me if you're chasing power, you don't want 2cyl running rich, and 2cyl running lean do you???

[Brett_jjj]

Its only air getting sucked down into the cylinders, how rich or lean it runs depends on how much fuel is injected into the cylinder and mixed with that air.And each cylinder only has the same amount of volume for that air to fill.(unless you pump it in via supercharger or turbo).I doubt the plenum inlet being closer to the last two cylinders would make much difference to how the engine breathes.As far as I can see Its only the diameter of the bellmouth that puts a bit of a restriction on the air flow.Not where the air is released into the plenum.

[savage1987]

Its only air getting sucked down into the cylinders, how rich or lean it runs depends on how much fuel is injected into the cylinder and mixed with that air.And each cylinder only has the same amount of volume for that air to fill.(unless you pump it in via supercharger or turbo).I doubt the plenum inlet being closer to the last two cylinders would make much difference to how the engine breathes.As far as I can see Its only the diameter of the bellmouth that puts a bit of a restriction on the air flow.Not where the air is released into the plenum.

The reason they introduced in the first place was that the rear two ran slightly lean and the front two ran slightly rich I can't remember where I read that but it was designed primarily to help with evening up air distribution in the interests of tuning / longevity.

[Brett_jjj]

Ive heard a cople of stories about it.Ive read somewhere on here that holden had some complaints about excessive wheelspin in the wet with the first releases of the V6 and they fitted the bellmouth to tone down the low end power and pickup of the engine,and thats the reason why the later ecotecs were built to have have the same characteristics of having less low down grunt and more mid range and top end.And as I mentioned previously,Ive also read somewhere that the bellmouth was fitted to fix a rough idle.The only thing I do know 100% is that the 2 young blokes commodores that I helped remove the bellmouth from, definitely ran better down low with it removed.Better low down pickup.So it has to do something.I think that if someone removes their bellmouth and doesnt notice any difference,then their engine is most likely not running 100% to begin with.I own a VS so I dont have to even worry about it.But these young blokes wanted them removed,I helped them do it,and it did make a noticeable difference both times.I drove both cars before and after.

[savage1987]

Yeah I know the feeling you're talking about, it does make a difference down low, enough to notice. My VN was an early V6 to begin with = no bellmouth. I ended up putting one in, and didn't lose much if anything down low (mind you at this stage it had intake exhaust and tune done).. it just smoothed up the idle nicely. Later on I built and fitted a higher comp 3800 from a s2 VR, and initially left the bellmouth out, running same intake exhaust tune setup in the same car, just the motor changed. After a while I modified the bellmouth I had laying around and dropped it in, no power loss anywhere noticeable and ran smoother...

End of the day if you want your VN to be faster / punchier off the line you can do better than removing the bellmouth.. greenfoam tune = instant burnouts and awesome fuel economy

[Brett_jjj]

Yeah,definitely. A tuned chip is the way to get the most out of a mostly standard engine without having to spend heaps.I told that to these young guys that removed their bellmouths .

[immortality]

the s1 cam was different (short duration, high lift) and a different tune with more ignition timing. they changed it in the s2 to reduce the tendency to wheel spin. the bell mouth was added to even out the air distribution in the manifold.

the best solution with the bell mouth seems to be as Savage1987 said, cut the top part off and put it back in