Bored TB w/stock H23 plenum– worth it?

[H.M.]

I’ve searched on this subject and haven’t found enough info to know if this mod is worthwhile or a waste of money for me.

My setup: A6 w/SRI. My only other engine mods would be a bisi heat reducing intake gasket and either a gutted IAB or a Blacktrax spacer. Waaay down the line I might opt for a camshaft upgrade. After that, nothing.

If I do a H23 plenum and throttle body install, does having maxbore.com bore out the TB offer any benefit if the plenum remains stock? Would a bored TB benefit me?

Some people say no, others say the difference in sizes increases velocity of airflow and thus is worthwhile.

My little lizard brain says the smallest diameter in the intake will be a chokepoint and restriction of airflow but I don’t understand anything about fluid dynamics that I haven’t learned from playing with a garden hose when I was 6.

[HondaFan81]

Keep the H23 intake manifold & throttle body stock for your mods. The H23 IM itself will help. Get a short ram intake, header and 2.25 or 60mm exhaust to help out.

If you want more performance and can afford, look into a Bisimoto camshaft. Look into nitrous or cylinder head porting after that, or both. All comes down to your budget. Keep in mind that the camshaft, nitrous and head porting will require tuning equipment & dyno tuning which adds to expenses.

[mndude07]

Keep the H23 intake manifold & throttle body stock for your mods. The H23 IM itself will help. Get a short ram intake, header and 2.25 or 60mm exhaust to help out.

If you want more performance and can afford, look into a Bisimoto camshaft. Look into nitrous or cylinder head porting after that, or both. All comes down to your budget. Keep in mind that the camshaft, nitrous and head porting will require tuning equipment & dyno tuning which adds to expenses.

I have to disagree. I have similar mods with the h23 plenum and throttle body bored by maxbore, and it significantly improved my throttle response. Friends that are used to m3's and such always comment on how good the response is.

The reason is mass flow. The throttle has to open less to create the same mass flow through it, but the intake velocity through the ports is determined more directly by the plenum and runner geometry, which is staying constant. Heel-toe downshifting is easier than ever. The amount of pedal feathering you can do is awesome.

[H.M.]

Thanks for the comments but, as stated, I am NEVER going to have nitrous, cylinder head porting or a larger exhaust. I ALREADY have a SRI.

I'm only interested in examining ONE variable - the bored TB on a stock H23 plenum.

Is this worthwhile?

[mndude07]

Thanks for the comments but, as stated, I am NEVER going to have nitrous, cylinder head porting or a larger exhaust. I ALREADY have a SRI.

I'm only interested in examining ONE variable - the bored TB on a stock H23 plenum.

Is this worthwhile?

In that case, yes do it. Send the plenum to maxbore also. It costs a little more, but they can match the plenum to the new throttle body diameter, which is totally necessary. Otherwise you have pretty significant flow losses in that sudden step-down of inlet diameter.

[H.M.]

Thanks.

The ONE variable I'm seeking opinions on is: bored TB on STOCK plenum.

An improvement?

[mndude07]

Thanks.

The ONE variable I'm seeking opinions on is: bored TB on STOCK plenum.

An improvement?

If you aren't going to send the plenum to be matched, don't bother.

[wed3k]

id just wait and get a h22 upper plenum and tb and have that sent in.

[Gtseviper]

well the point the guys are trying to make....try blowing through a straw..kinda free flowing isn't it..Well try blowing throw the straw and then pinch part of the straw..it now became restrictive..that is why port matching is important

[wed3k]

yea except, pinching a straw is like blocking 90% of flow. of course it's not going to flow. a little lip on the intake manifold is maybe 1% size difference?

the benefit is the taper in the throttle body because that increases air velocity which in turn increases throttle response. the lip just creates turbulence.

[BLUBB2]

id just wait and get a h22 upper plenum and tb and have that sent in.

Is there a difference betweem the H22 TB plenum and H23 TB and plenum at all?

[splitsecondcb]

Is there a difference betweem the H22 TB plenum and H23 TB and plenum at all?

there is no difference for a H22 Tb plenum and H23 TB plenum in size beside the bolt pattern to da head. even the throttle body is the same size. i have both of the parts laying in my garage.

[Gtseviper]

yea except, pinching a straw is like blocking 90% of flow. of course it's not going to flow. a little lip on the intake manifold is maybe 1% size difference?

the benefit is the taper in the throttle body because that increases air velocity which in turn increases throttle response. the lip just creates turbulence.

well you got the idea...well I wasn't trying to make a exact example (hopefully you can see that, which you didn't), anyways, it was just for reference

[HondaFan81]

Sorry for general response.

Direct answer to your question. It would cause turbulence between bored TB and stock plenum bore transition. The simple H23 IM swap in itself will help.

BTW, keep your IAB functional, do not gut plate. You will lose low RPM performance. If anything, add an IAB spacer for more torque across the RPM.

[H.M.]

Thanks, this is what I'm looking for. The Increased Velocity vs. Greater Flow argument.

Any more opinions on this?

I should add that I'm keeping a functional IAB and adding to that a gutted IAB or Blacktrax spacer. I'm currently researching port matching (between the runners/IAB/spacer/plenum and also the runners and head) to see if I can make improvements there. I already have the Bisi gasket, the runner's EGR ports are threaded and everything will be squeaky clean before install.

Having the plenum bored to match the tb sounds like a good idea but I'm not sure the additional $90 would register on the butt dyno.

And on this thread I'm trying to see if I would notice an improvement in boring the tb for $110, and if it's a $110 improvement. I'm getting to the point where I'm spending too much money on this car so I'm trying to weigh return on cost.