Individual Throttle Bodies vs. one HUGE one

[Guest xero]

Just curious what the benefits and drawback to each set-up are. Mostly I'm trying to figure out why tuners in Japan are removing the ITBs and puting a huge 100mm TB on a custom plenum. wouldn't the ITBs be better?

[260DET]

Could be that a single TB on a plenum makes more torque while individual TB's make more horsepower?

[Guest xero]

sounds reasonable, thanks,

[S30Z Bushido]

ITB = instant throttle response.

[Guest Nic-Rebel450CA]

ITBs do have more instant response as Bushido said. However, if not setup perfect, it can tend to rob top-end breathing as it doesnt have as much atomization time.

 

However, my best guess is just economics. One big TB costs much less than one TB for each cylinder when it comes time for upgrading.

 

My preference would be ITB with velocity stacks below the TBs to increase atomization time.

[Guest xero]

I can understand the economy thing, but when Signal is making a GT R34 and they convert from ITBs over to one large throttlebody, there must be a reason,

[MikeK280z]

This came up in a fuel delivery thread this past spring. John Coffey had this to say:

 

Personally I prefer a triple carb setup (Mikuni or Solex) over any kind of fuel injection for the sound, looks, and performance. Next to that I like the individual throttle bodies sold by TWM, again for sound, looks, and performance. I was going with the TWM option until Jim Thompson at Sunbelt talked me out of it.

 

From the development work he has done on the Mazda Protege' and Nissan QR25 motors run in SCCA World Challenge Touring (over 130hp per liter NA with restrictors) he feels a single throttle body with a tuned plenum is worth seconds per lap over individual throttle bodies. Its all about the area under the torque and horsepower curves when it comes to going fast around a racetrack.

 

FYI... my 305hp 3.0L breathes through a single 65mm TWM 2805 throttle body. Its all about velocity, not ultimate flow. [end quote].

 

I don't know Johnc so I can't speak for him, and I'm by no means qualified to speak on this subject. Just had a random memory. You might want pm him for further input.

[johnc]

Just curious what the benefits and drawback to each set-up are. Mostly I'm trying to figure out why tuners in Japan are removing the ITBs and puting a huge 100mm TB on a custom plenum. wouldn't the ITBs be better?

 

A 100mm TB? They are obviously building an engine with a 500 rpm power band. Must be for drag racing.

 

Both individual throttle bodies and a single throttle body can be tuned to provide good power and torque numbers. The benefits of a single throttle body is a tunable plenum which lets you make mid-range torque and high rpm horsepower. Ultimately it will have a little less top horsepower then individual TBs but you'll have a much broader power band.

 

But, that's only true with reasonable sized components. Intake and exhaust velocity is critical to torque. A 100mm TB can only be used for high rpm horsepower so my guess it that they are building a drag motor of some kind.

[Guest xero]

it looked 100mm, I'd say 90-100mm, but it did look larger than the Q45 TB, eitherway, it's on their GT/drag R34,

[RPMS]

Hey, Xero!

 

Remember that the larger diameter the tubing is, the peakier the power band will probably be, strictly from a resonance standpoint. What you're looking for in an intake is high air velocity while remaining laminar (non-turbulent) to help atomize the fuel and help shove the charge into the cylinder. This is why intake bells (like the spun aluminum ones on the engine pictured above) are used - they smooth out the airflow and make it easier for the engine to suck in the charge. Individual throttle bodies help by making it easier to have exactly the same air charge in each cylinder. By having a single large intake orifice, you not only reduce your intake velocity dramatically, you go back to having different lengths between your intake valves and your source air. You're virtually guaranteeing an unbalanced condition.

 

The best solution to this issue has proven to be relatively small, relatively short throttle bodies going to each cylinder. Look at how Formula 1 engines, or BMW M-series engines do it.

 

If you're concerned about air volume, remember that each small throttle only has to do 1/8 the work. Mathematically, your 100mm throttle body (7850mm2) is equivalent to eight 35mm throttle bodies (961mm2 each). This gives you total flowthrough and you still have fairly high intake velocity at almost all engine speeds.

 

If anyone catches a flaw or ten in my logic, please feel free to educate me!

[Guest xero]

is that locig still correct when a turbo comes into play?

[johnc]

By having a single large intake orifice, you not only reduce your intake velocity dramatically, you go back to having different lengths between your intake valves and your source air. You're virtually guaranteeing an unbalanced condition.

 

This is really a pointless discussion.

 

An intake manifold with one throttle body draws air into a plenum which then distributes air to 6 individual ram tubes. An intake manifold with 6 individual throttle bodies normally draws air through a cold air box. That cold air box has one opening and plenum to distribute air to 6 individual ram tubes. Even if the individual throttle body setup is running open stacks its still drawing air from the engine compartment which would induce imbalance due to flow and heat isses within the confined space.

 

Ultimately, both setups are exactly the same (both intakes are necked down to the size of the intake port in the head) except one installation has 1 throttle body and the other has 6. What we should be discussing is the length of the ram tubes.

[Nismo280zEd]

that's kinda like one huge carburator or three smaller. I would think the smaller would be alot more efficient and provide more low end torque, while the larger might edge over in top end hp.

 

I'd prefer triples, just because i think it would be more accurate with air and fuel and more efficient.

[johnc]

that's kinda like one huge carburator or three smaller.

 

Nope. All we are talking about is the throttle plate in these comparisons. Fuel metering has nothing to do with it.

[RPMS]

What we should be discussing is the length of the ram tubes.

 

I thought that was what we were discussing? Unless the engineer is a complete boob (or has other factors to work around) the intake tubes in a multiple TB setup are much closer to equal length than the tubes in a single-TB system.

 

On the other hand, if you had one large volume airbox between the TB and the intake port, you could make the resonant differences small percentage-wise. I guess this is what you're saying, John? A difference that makes no difference IS no difference?

 

And I believe you're right, Xero. When you throw a turbo into the mix, these issues become pretty much pointless and you get to pick up other ones.

[johnc]

On the other hand, if you had one large volume airbox between the TB and the intake port, you could make the resonant differences small percentage-wise. I guess this is what you're saying, John? A difference that makes no difference IS no difference?

 

Exactly. You can also screw up a individual TB setup by installing a poorly designed cold air box or the turbulence within the closed engine bay could be screwing up intake flow on the same setup.

[Guest macks]

Here's my take on it-

The stock RB26 computer uses twin MAF sensors as its load signal to calculate fuelling requirements. This is all well and good, but when going to a big hp drag car the MAF sensors provide a significant airflow restriction. Hence, they probably try to go to MAP sensing, using a pressure feed from downstream of the throttle. In any other engine, this would be in the intake manifold, but in the GTR it's gotta come from the intake runners in between the throttle and the valve - a very small volume. As a result of high lift long duration cams, the pressure signal is anything but steady, and the small volume of air does nothing useful to help damp the pressure variations. These two factors combine to make the MAP sensor read all over the shop and make tuning a pain in the pipe.

 

In combination with the Jap way of doing intake manifolds - putting huge plenums on everything that uses boost - using one massive throttle instead of six individual throttles on a plenum they're going to change anyway makes perfect sense when it lets them use the zero restriction MAP sensor through having a larger volume of air downstream of the throttle, and thus a better pressure signal than the stock GTR setup provides. This approach is not a blanket approach, but rather a calculated solution to problems associated with optimising this specific engine, so it's not accurate to say that a single large throttle is better than individual throttles in every case because a big name tuner does it to one car.

 

Just MHO.

 

Cliffnotes: Single throttle, combined with larger plenum, gives a better vac/boost signal, used to get rid of the restrictive twin MAF sensors.