VH45DE stock intake VS ITB with N/A

[elwesso]

So today I was doing some deep (or maybe not so deep) thinking... What I was thinking about was doing a combination ITB setup with unequal length runners, and using the stock intake runners..

We know the 4 middle runners (i think that go to 3,4,5,6) are longer than the outer ones (1,2,7,8).. My thought was to just slap ITBs on those.. The longer and shorter runners would create more power at different ranges and maybe help with a broader powerband... Thoughts?? Seems kinda shoddy and extremely objective, but its a thought?

Ive also been very skeptical how ITB's would help on a N/A motor, unless we're talking a bunch of HP. I can see why some people might do something different for boost, but for N/A i dont think it gets much better than the stock manifold.

What do you guys think??

[gs14racer]

I cant tell you on a VH yet.... But over on the honda forums people are picking up 25-40 whp with tuning of course, i think with a decent cam the itbs should pick up like a mofo on the top end.

[Carl H]

i think the real key to itb success is to have equal lenght runners...but im not sure about that.

[Q45tech]

Using 3rd order Helmholtz resonations, each inch is around 250 rpm for a 4,000 rpm torque peak.......depending on air temperature and density.

Remember the purpose of the runner tunning is to time the reflected wave/waves to exert a final puff of air/fuel into intake valve just before it closes...........this extra air/mixture adds 5-9% in VE [at torque peak].

Once you get too short the reflected wave occurs too early [valve lift high] and nothing is gained.

Remember all ITB do is reduce the 6" WC restriction that the single TB creates at max rpm............unlikely you can even get a 50% improvement so 3/27.7 x 6.8% = 0.77% not even 1% more air flow to head.

However losing the MAF and air filter and plumbing/plenum gains 14" WC so that would be ~1/2 a psi or 3.4% or about 4% in total at 6900 rpm.

Never seen any engineer gain success with different length intakes on a small displacement engine.

These should help:http://upetd.up.ac.za/thesis/a...n.pdfh ... thesis.pdf

on page 34 see graphs of different runner lengths:http://www.webs1.uidaho.edu/ni...9.pdf

[Jeff Taylor]

I don't want to shoot down your idea, but unequal runner lengths would disrupt the power balance of the engine between cylinders. On an engine pushed to its limits, this power variance could put the engine out of balance enough to cause premature rotating assembly wear.

I heard a story about GM's Northstar motors having premature bearing and cylinder wall failure due to their idea of "shutting off" certain cylinders during part-throttle in order to maximize fuel economy. The problem was that they were shutting down the same cylinders everytime, which threw off the power balance of the engine. This led to premature engine failure.

To remedy this problem they eventually alternated which cylinders got disabled during this mode, so that the stress (in the long run) was equally distributed across all cylinders. Still, I can see this causing a higher rotating assembly failure rate than a normal firing order.
Modified by Jeff Taylor at 11:14 AM 12/7/2007

[John Dixon]

One thing to bear in mind is with big cams you'll never get a good idle with a plenum, you need ITB's.Got mine on now too, still need to do the linkage but haven't been near the car for months, damn work Some pics http://www.photobox.co.uk/album/7228323

[maxnix]

Well, in my old 2L Alfa, it has ITB, but leading to them are long runners for torque.

[John Dixon]

Well, in my old 2L Alfa, it has ITB, but leading to them are long runners for torque.

I'm planning to build one big air box over both banks on mine, then can very the runner length between about 6 and 20" on the dyno and see what works best.

[Q45tech]

To properly tune you need to vary runner diameter and taper and the volume of the plenum for each increment in length.Always a problem to decide at what air temperature to tune as the speed of sound changes 7% from 30F to 100F [1% per 10F] and thus the runner will need to change 7%.....................proper taper and diameter at inlet horn can broaden [acoustic impedence] the tune to give you a 1% match over 15-20F range.

Any runner length shorter tha 13" + 3" in head will cause a dramatic dip [>20% torque loss] at 6,000 rpm.All this design work as been done over the past 20 years and is easy to find and adapt with mild mathematics.http://www.webs1.uidaho.edu/ni...9.pdfh ... akeln.html

[David Steele]

Using 3rd order Helmholtz resonations, each inch is around 250 rpm for a 4,000 rpm torque peak.......depending on air temperature and density.

Remember the purpose of the runner tunning is to time the reflected wave/waves to exert a final puff of air/fuel into intake valve just before it closes...........this extra air/mixture adds 5-9% in VE [at torque peak].

Once you get too short the reflected wave occurs too early [valve lift high] and nothing is gained.

Remember all ITB do is reduce the 6" WC restriction that the single TB creates at max rpm............unlikely you can even get a 50% improvement so 3/27.7 x 6.8% = 0.77% not even 1% more air flow to head.

However losing the MAF and air filter and plumbing/plenum gains 14" WC so that would be ~1/2 a psi or 3.4% or about 4% in total at 6900 rpm.

Never seen any engineer gain success with different length intakes on a small displacement engine.

These should help:http://upetd.up.ac.za/thesis/a...n.pdfh ... thesis.pdf

on page 34 see graphs of different runner lengths:http://www.webs1.uidaho.edu/ni...9.pdf

''WC'' ?

[SSDwellah]

Well I know they measure pressure in inches Hg (mercury) by watching mercury rise/fall in a glass cylinder (column) based on the pressure applied. So I am guessing they do the same thing with water (non-toxic and easier to find). So I would guess that is a unit of pressure amounting to concerning 14" (fourteen inches) in a water column (I am not sure about this as a standard though nor how to convert to kilopascals or psi or bars or atmospheres etc...).
Modified by SSDwellah at 12:57 AM 12/18/2007

[mtcookson]

14" WC = 1.029782775 inHg = 3.4872447162 kilopascal = 0.5057820852 psi = 0.0348724474 bar = 0.0344164254 atmosphere (standard) = 0.03556 atmosphere (technical)

http://www.onlineconversion.com - one of my favorite tools. Convert just about anything.

[Q45tech]

It seems that people have a tough time understanding that every NA engine is already supercharged by 14.7 [adj for barometer] PSI.

What NA means is pressurized by atmosphere.

The term vacuum used by mechanics just prolongs the agony of reeducation.

What ever reference one uses depends on local language/systems.

Engineers use kiloPascalsFlow bench operators use inches of water columnTV weather men use inches of mercury.Crusty old mechanics use negative inches of Mercury BELOW normal atmospheric pressure.

[SSDwellah]

It seems that people have a tough time understanding that every NA engine is already supercharged by 14.7 [adj for barometer] PSI.

I almost agree with everything you said. I would agree 100% if you said pressurized instead of "supercharged", as supercharged implies an air charge of more than atmospheric. I'm just nitpicking here but it's true . I knew what you meant though. See definition 2 here if you need evidence http://www.merriam-webster.com...arged

Crusty old mechanics use negative inches of Mercury BELOW normal atmospheric pressure.

There's an odd consequence of using negative inches here, then you have to know that there is a certain negative value that is absolute minimum since that would correspond to zero atmospheres/kilopascals etc... (for all of the absolute-pressure based units, rather than relative to atmospheric).

[qsiguy]

I agree, it's pressurized not "supercharged" or "boosted". When someone installs a supercharger or turbo the boost gauge reads PSIG which is the gauge read boost pressure which already compensates for atmospheric pressure. So if you have 10 PSIG boost at sea level you'd have manifold absolute pressure of about 24.7 PSI (adjusted for barometric pressure of course).

Oh, and what is ITB?

[T45]

I can see the argument about the engine being pressurized by the atmosphere but have a hard time understanding it because the same pressure exists on both the intake and the exhaust sides of the engine so there really isn't any pressure difference.

If the piston stayed at BDC and didn't move, with both valves operating like normal, there would be no change in cyl pressure as the valves opened and closed.

The only reason there is a big pressure difference in a running engine is the increase in psi inside the cyl due to heat generated in the compression of the air and igniton of fuel.

If there were ZERO atmospheric pressure on the exhaust side then the intake would be pressurized. However since there is equal pressure on both sides it pretty much cancels itself doesn't it?

[T45]

Oh, and what is ITB?

OMG, you installed your own rear mount turbo and.... nevermind. lol

individual throttle bodies

[Q45tech]

You need the NA pressure to calculate the length of ITB runners was my point and the pressure drop from atmosphere thru everything to midlift of intake valve......because speed of sound changes with pressure and temperature..................as does the Helmholtz effect.

The air temperature increases slightly just passing the open throttle plate due to friction.

Actually if the engine doesn't have fuel to fire the 14.0 psi gets multiplied and heated a little by compression so the the instantaneous exhaust pressure as the valve open is much higher than atmosphere at least until blowdown and equalizartion is complete.

[qsiguy]

OMG, you installed your own rear mount turbo and.... nevermind. lol

individual throttle bodies

lol That's what I thought but wasn't sure. Almost didn't ask but thought it would be worse to assume and be wrong.

[elwesso]

LOL I thought you were joking/making a cheap stab.

[qsiguy]

LOL, I would never do such a thing! hehe

Back on subject...Check out this intake prototype. Should give you some food for thought. Looks like the primary purpose for the design was economy but they did gain some performance as well.

http://www.greencarcongress.co....html