ok say you have a plenum thats a lil to big for your optimum setup. (every other aspect of IM design to be left out of the equation) could it be possible that a larger TB could decrease your peak power & torque compared to smaller TB?

thoughts or input?

I am wondering if I made a mistake porting out my custom IM to 70mm... this is on a k-series BTW

 

my theroy is that the plenum is just a resivor for air to your runners. the runner size creates the power and velocity of the air. you dont ever want to starve a runner of the maximum air that it can suck so the larer the resivor of air that it has to pull from the better it will be.. so bigger is better in throttle body size..

 

but what if the plenum is a 'lil too big... & the smaller TB did NOT "starve" the motor. could running a larger TB possible cause a decrease in power?

anyone else

 

Throttlebody size should be based off of the outflow into the manifold. Having too small of a throttlebody will hinder velocity and increase turbulence, but having too big of a throttlebody will create too much of a 'natural' transition and cause the air to 'hug' the wall, and not separate.

Plenum volume, if you use the most elementary form of guestimating, should be 1.3-1.4 x engine displacement.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR &raquo;</TD></TR><TR><TD CLASS="quote">Throttlebody size should be based off of the outflow into the manifold. Having too small of a throttlebody will hinder velocity and increase turbulence, but having too big of a throttlebody will create too much of a 'natural' transition and cause the air to 'hug' the wall, and not separate.

Plenum volume, if you use the most elementary form of guestimating, should be 1.3-1.4 x engine displacement.</TD></TR></TABLE>

can you explain outflow into the manifold?

I am telling you the plenum is too big. COULD a smaller TB increase velocity?

can you explain why a 2.0 K-series would like a bigger plenum than a 2.4L

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 6SPD_EK &raquo;</TD></TR><TR><TD CLASS="quote">

can you explain outflow into the manifold?

I am telling you the plenum is too big. COULD a smaller TB increase velocity?

can you explain why a 2.0 K-series would like a bigger plenum than a 2.4L </TD></TR></TABLE>

The smaller the throttle body will increase velocity.

If the 2.0L K motor is revving higher than the 2.4L then that explains the bigger plenum.

Plenum, runner size and diameter really play a key role in where you want your power to be located in your power band. So you can't really compare two different motors/plenums that have two different characteristics in their powerband or power delivery.

But as far as throttle body size, you want something that will have ~ 300 ft/sec to keep your part throttle/low throttle response optimal.

 

from what i have seen on the dyno, a small plentum will like a big throttle body and vice versa

this is based on a ton of b-series dyno's with off the shelf parts, nothing custom.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDogg &raquo;</TD></TR><TR><TD CLASS="quote">from what i have seen on the dyno, a small plentum will like a big throttle body and vice versa.</TD></TR></TABLE>

Those observations are correct, and well documented. But the terms 'big' and 'small' are very subjective when served up without a scientific formula or point of reference.

92TypeR suggests the "most elementary" form of plenum volume calculation to be 1.3~1.4 times the engines displacement. Although that seems 'small' [the plenum on my 2.0L B-Series is a touch over 4.2L] it's a point of reference that lacks the scientific formulae to work from.

I would like to see a bit more [scientific formulae] from the members here with experience and/or tools used to examine fluid dynamics in this type of system. If for no other reason, it will give those of us truly interested in induction dynamics something to research for the next few days.

 

Does anyone (and wishes to share) know the volume of the common after market and OEM Honda manifolds. That would be somewhere we can start this discussion.

Manifold design is something that has been left out with our engines. Why doesn't someone step up and fill this gap in the market? There is money to be made, maybe tuning manifolds is something left to be done on an engine dyno.

 

thank you to those that have contributed already. I plan on doing some (elementary) testing in the near future with some K-series manifolds

 

right, the terms are fairly relitive...

for small i mean, a b16 manifold on a b20vtec needs the biggest tb you can fit, but an edlebrock manifold on a b16 needs a small (stockish) tb.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B20C5 Turbo &raquo;</TD></TR><TR><TD CLASS="quote">

92TypeR suggests the "most elementary" form of plenum volume calculation to be 1.3~1.4 times the engines displacement. Although that seems 'small' [the plenum on my 2.0L B-Series is a touch over 4.2L] it's a point of reference that lacks the scientific formulae to work from.
</TD></TR></TABLE>

Are you sure your manifold is 4.2L? How did you measure your volume.?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B20C5 Turbo &raquo;</TD></TR><TR><TD CLASS="quote">I would like to see a bit more [scientific formulae] from the members here with experience and/or tools used to examine fluid dynamics in this type of system. If for no other reason, it will give those of us truly interested in induction dynamics something to research for the next few days. </TD></TR></TABLE>

Unfortunately the differential equations involved in fluid dynamics make finding point velocity and airflow distribution difficult on a scale large enough for our purposes.

Fortunately, there are great CFD programs such as STAR-CD that do all the calculations for you. The more inputs you provide, the more exact the results get. I've been using STAR for a while to design manifolds for our Formula car, and it makes manifold design much more realistic in terms of expected performance.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDogg &raquo;</TD></TR><TR><TD CLASS="quote">from what i have seen on the dyno, a small plentum will like a big throttle body and vice versa

this is based on a ton of b-series dyno's with off the shelf parts, nothing custom.</TD></TR></TABLE>



One of the main functions of the plenum is to slow down the air passing thru the TB. The bigger the plenum the more it will slow down the air exiting the TB.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Master of the Universe &raquo;</TD></TR><TR><TD CLASS="quote">



One of the main functions of the plenum is to slow down the air passing thru the TB. The bigger the plenum the more it will slow down the air exiting the TB.</TD></TR></TABLE>

Can you please explain why one of the "main functions" is to slow the air down? From my understanding, it is benefical to keep air velocity up while supplying sufficent cfm. Does this only occur only as the plenium is being filled?

Its obvious that the incoming air going through the TB will disperse into the plenum and slow down given that it is entering a larger cross-sectional area.

Great topic!

 

FWIW, we did a little research on the h22 plenum.

It is only 1400cc or so, which, according to the formulas out there, this size is way off, being only about 60-65% of engine size. I suppose the humongous dual runners are supposed to make up for this....though I'm no induction expert...

Link the the h22 manifold thread https://honda-tech.com/zerothread?id=1837017

We also got a rough measure on the manifold brad Z. made for the birdman's 95x89 h build, much bigger.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chillinit &raquo;</TD></TR><TR><TD CLASS="quote">Can you please explain why one of the "main functions" is to slow the air down? From my understanding, it is benefical to keep air velocity up while supplying sufficent cfm.</TD></TR></TABLE>

Some of you may have seen this drawing before.

If the air didn't slow down how is it going to change direction?

 

sir, on a conventional plenum'd manifold with 1 side entry...

like ur diagram.. wud that usually mean lean mixture for runner 1 and 4 ? or lean on 2 and 3 ? just wondering

 

all hte cylinders dont pull air at the same time, so there really shouldnt be any cylinders running lean so long as the thing isnt made completly wrong. from what i have been lead to understand a bigger plentum will ensure this does not happen..

 

ah! nice to know...

but lets say on a stock b16a manifold... isnt it an issue? or is it sumthing we should actually pay attention to..

tnx

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 93turbo16 &raquo;</TD></TR><TR><TD CLASS="quote">Are you sure your manifold is 4.2L? How did you measure your volume.?</TD></TR></TABLE>

I used water and a graduated cylinder.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chillinit &raquo;</TD></TR><TR><TD CLASS="quote">Can you please explain why one of the "main functions" is to slow the air down?</TD></TR></TABLE>

High velocity = low pressure and vice-versa. You want the highest pressure possible at the inlet side of the runners.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B20C5 Turbo &raquo;</TD></TR><TR><TD CLASS="quote">

I used water and a graduated cylinder.
</TD></TR></TABLE>

4.2 L is in my opinion a little too big for a 2.0L motor.

Did you measure just the plenum volume not plenum and runner together... what are your dimensions?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 93turbo16 &raquo;</TD></TR><TR><TD CLASS="quote">Did you measure just the plenum volume not plenum and runner together... what are your dimensions?</TD></TR></TABLE>

Yes, that's just the plenum. The runners were a little bit harder to check but appear to be around 230cc.

 

Any photos of 4.2l manifold? Any problems closing the hood? Or does it sit on the passenger seat?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B20C5 Turbo &raquo;</TD></TR><TR><TD CLASS="quote"> Although that seems 'small' [the plenum on my 2.0L B-Series is a touch over 4.2L] it's a point of reference that lacks the scientific formulae to work from.</TD></TR></TABLE>

What type of manifold is this?