i've been reading up on tbs for a bit and i was reading thru wiki's section on them when i came across this interesting piece of info:

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Wikipedia.org &raquo;</TD></TR><TR><TD CLASS="quote">Some engine tuners may install multiple throttle bodies to increase air-flow however, a single larger throttle body can yield greater air-flow (but possibly not as great air velocity *citation needed*).

Example: A single throttle body with a typical 60mm diameter opening has 2827mm˛ of surface area, adding an additional 60mm throttle body will double the intake area to 5654mm˛, but upgrading to a 90mm diameter (50% larger) throttle body will give 6361mm˛ of surface area.</TD></TR></TABLE>

the numbers make complete sense to me. it would seem a single large tb would have the advantage over itb but what if that part about the large tb not being able to yield as great air velocity is true? i'm just curious on any info you guys know about this. sorry i don't know all the technicalities on tbs so go easy on me


Modified by _BB6 at 1:11 AM 1/1/2007

 

isn't there a limit to how much you can widen the opening on a intake manifold to match a bigger TB? you can't just say you'll slap on a 50% bigger TB.

also this example is comparing a single TB to two TB's, not ITB's.

 

true i understand that what im more curious about is the effect of air velocity in tbs. okay to correct myself let's just double it? itbs vs dual large tbs? what kind of role does air velocity play in tbs.

 

air velocity is like poor mans F.I.

If you want to learn more about intake design I think you should do some reading on 2-stroke tuning. Everything counts big time on a 2-stroke, but many of the tuners are more like mad scientists. Actually there may not be alot of info and since carburation is still the biggest problem with a stroker you may not really find anything.

this used to be the best site around, but I haven't been a member since he made it a pay forum. http://www.macdizzy.com/

so basically this post was crap

 

lol

say you have one 70mm throttle body, that is 15393 mm^2 of area

then look at a set of 50mm ITBs, thats 7853mm^2 apeice, or 31415 total....

thats about double the area....more area is going to give more air, period.

An intake arm, throttle body, plenum setup has a velocity advantage, but getting as much air in there as ITBs can supply is the shortcoming.....plenums also have pulsation advantages....

 

One thing to keep in mind is that the engine doesn't breathe through all 4 ITB throttle openings at the same time, so you can't just add up the cross sectional surface areas of each throttle body opening for an ITB setup and compare that to a similar calculation for a single TB plenum setup.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bb4ever &raquo;</TD></TR><TR><TD CLASS="quote">say you have one 70mm throttle body, that is 15393 mm^2 of area</TD></TR></TABLE>

Something doesn't make sense to me here. Cross sectional area of a cylinder is Pi * r^2, correct? So if the diameter of the throttle plate opening is 70mm, then wouldn't the cross sectional area be 3.14159 * (70/2)^2 = 3848 mm^2 = 38.48 cm^2.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bb4ever &raquo;</TD></TR><TR><TD CLASS="quote">then look at a set of 50mm ITBs, thats 7853mm^2 apeice, or 31415 total....</TD></TR></TABLE>

I get 1963 mm^2 = 19.63 cm^2 each, or 7852 mm^2 = 78.52 cm^2 total, for what it's worth.

 

very true, good observation....

 

a bigger tb may flow more air but it will do so at a lower velocity. the trick is to find a perfect balance.

equal length
less charge robbing
pulse wave tuneable
=ITB's FTW

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 117 &raquo;</TD></TR><TR><TD CLASS="quote">

Something doesn't make sense to me here. Cross sectional area of a cylinder is Pi * r^2, correct? So if the diameter of the throttle plate opening is 70mm, then wouldn't the cross sectional area be 3.14159 * (70/2)^2 = 3848 mm^2 = 38.48 cm^2.

I get 1963 mm^2 = 19.63 cm^2 each, or 7852 mm^2 = 78.52 cm^2 total, for what it's worth.
</TD></TR></TABLE>

good call.....my stupid *** was using diameter....lol

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AzCivic1.6 &raquo;</TD></TR><TR><TD CLASS="quote">isn't there a limit to how much you can widen the opening on a intake manifold to match a bigger TB? you can't just say you'll slap on a 50% bigger TB.
</TD></TR></TABLE>

Yes, if the manifold is overbored you will break through to the duct that runs to the iacv motor. If thats not a problem you can "gut" the manifold out and cut that wall out completely and use a block off plate over the iacv ports on the front.

On my 70mm through tb I had to use an adapter becasue on a bigger bore the stock honda bolt pattern gets too close to the bore. Keep in mind though that most 70mm tb's arent 70mm through so that may not be the case with all of them.

 

thanks guys. that cleared up a lot for me. phew i was expecting to get my *** flamed to perfection. btw happy new years.