Okay before we even get into this question can we please keep this very simple and stick to the facts. And THANK YOU ALL in advance for any, and all, replies/input regarding this question.

So my question is this:
What is the MAX diameter that one can bore a F23A1's upper plenum in order to port match it with a larger TB? In other words, how far can I go before I run out of metal and begin cutting into IAC and vacuum ports? And for anyone who doesn't know the stock bore is 60mm.

Again thank you all for your help, in advance, it's greatly appreciated.

 

Why? The lower plenum of the F23A* manifold can be gutted(like the H23's lower) for more benefit. A larger throttle body may not be of any benefit on the stock camshaft. General rule of thumb for a street car: Large plenum, small throttle; Small plenum, Large throttle. It's all about velocity vs volume. Until a someone can dyno prove that a larger throttle body makes any more power, it's really kind of a waste. It'd certainly help throttle response, but I really don't see it as too much of a restriction. Gutting the plenum MAY increase power(it's certainly plausable), but mostly by shifting the powerband higher. Done right, there will be no loss of torque, and a potentially large increase in the upper end of the powerband where these engines really need it, ie past 5800RPM to about 6500rpm. Lots of factors. Boost changes the whole thing up considerably.

TLDR; probably not worth it on a near-stock engine.

 

First off let me say, thank you... I appreciate the reply. Unfortunately, I still need to know to what extent I can bore out the TB inlet on the upper plenum? I hate to seem like a ***** but that was almost exactly what I was alluding to when I asked for everyone to, "plz stick to the facts". All too often you'll see this happen in these forums; someone poses a simple, straightforward question, in need of a simple answer and they're met with page after page of assumptions, speculation, and opinions. Not to say that YOUR reply was all of those things, because you did bring up some legitimate points, but still I'm just pointing out that my question remains unanswered. Regardless, as I said before, Ix DO appreciate the reply.

 

LEE MAJORS!!!

Santa- You've been a real good boy this year!
Mrs Claus - You sure have!

Probably net better results for such a question in the All Motor/Naturally Aspirated form. We here in the Accord Forum tend to stick to the odd turbo installation or H22/H23 swaps. More maintenance than modification here.

 

LMAO!!! @LEE MAJORS!!! That's classic man hahahha! And you have officially exposed your age good sir! Very few remember good ol' Colt Seavers. lol!

As for the reply, thank you Mike, I didn't even think to post it in there..? But now that you've brought it to my attention, it should've been a no brainer So should I just start a NEW thread there or request that a mod move it for me? I don't want to upset anybody by double-threading? And thanks again man.

 

I'll track down my digital caliper and take some measurements today for the stock sizeon my spare upper and where the other ports are. If I had to guess, I'd say probably 65-68mm is where you'll run into issues.

 

Stock bore for the 98-02 TB and opening per my digital caliper was about 56mm. Its a lstraight shot through, hardly any tapering.

I'll snap a couple of pictures tomorrow.

 

Thank you Chrisnick, I really appreciate that. If you're getting a 56mm measurement it sounds like it'd be a big STRETCH to get a 68mm TB on there. Something tells me there simply won't be enough meat on the bone? Hmmm....Lmk what you come up with man?

 

Is it 68mm at the opening, throttle plate or exit?

 

I'm sending you a pm now. Plz forgive my ignorance Chris... I didn't realize just how well versed you are on this particular subject. But after doing some investigating I see that you REALLY know your ****. So I hope u can forgive me? At any rate, plz chk your inbox when u have time.

 

Was there ever a definitive answer on this?! I went to a machine shop this morning and dropped off my F23 mani and a TB with a 62mm bore (exit is a little bit bigger). I stood there looking at it and it doesn't look like there's quite enough meat on the mani. Anyone know?! Thanks!

 

So I paid a shop $100 to hog this out for me. They didn't actually do much so I spent 20 minutes with a carbide bit and removed as much material as I dared. My TB has a 68mm exit so I tapered the flange of the plenum to match. Portions of the casting on the plenum are rather thin.

As for the IACV hitting the TPS, I have a TB spacer so that eliminates some of the problem. I cut off about half of the length of the water nipples from the IACV and this works without having to sweat on some other fittings.

 

What are the chances that I'd be revisiting this thread right around the same time you were having this work done?! It's crazy! At any rate I LOVE what you've done there with yours! And just to answer your question; NO, there was never a definitive answer to this. But from the looks of it you figured some things out on your own which is great! Now I have a few questions for you because I'm literally DAYS away from starting/completing a major boost build and I just received my OmniPower 68mm TB and when I put this thing up against my upper plenum it simply goes right into the IACV port!? So my question to you is: How did you avoid this!? I can see your IACV port has been modified/filled with something and I'm curious what you used AND more importantly how it's holding up for you? I also noticed you have the block off plate so does this mean you're using the F23 IM on a different motor? F22A/B or something? Please lmk man and hopefully we can help one and other out on this!? Thanks in advance bro and great work btw!

 

70mm sk2 alpha on an f22b1 i.m

 

70mm at the throttle body opening or is that 70mm at the throttle plate?

 

Not sure tbh..it's skunk2 if that helps.

 

I was able to get about 64mm out of it total when I did mine last year. I ended up busting through the aluminum near one of the bolt hole areas when doing it. Had to seal it with some JBweld. To get smooth flow and actual benefits I ended up taking the 1" spacer I was using and tapering it to match the 70mm throttle body and 64mm opening on the intake. Throttle response was improved and it picked up a bit of power across the whole range. Results may vary as that was on a turbocharged application.

Edit: It was a bit less than 64mm. You can see the hole where I busted through the aluminum in this pic.

 

I should've upped these awhile ago but never did sorry fellas.
I never measured it myself but this was straight from Omni Power
"Throttle Body opening is tapered bore for strength. Inlet measures 68.9mm Outlet measures 67.9mm"



OmniPower gasket on F23 Upper plenum...




Scribed and JB Welded...




bored and drilled....




all done!