B20A Intake Manifold - Honda Prelude Forum

marcucci · 10-28-2002, 08:35 PM

Took a look tonite and did some work... a few notes:

- The JDM B20A (at least in '88) had no EGR.
- The port matching from the factory (manifold to head, manifold upper to lower to butterflies, TB to manifold) is AWFUL. A monkey with a die grinder could improve on it.
- Based on calculations for ideal runner and intake sizing, the factory hardware is balls-on for the factory motor. Unless you do some serious work (heavy cams or bottom end), don't worry about oversizing anything in the manifold.

redliner · 10-28-2002, 11:01 PM

That'll be what I should do next then, huh?

Is there flashing all over the place, or is it just extremely bad matching??

And what'd you make of the 2g JDM B20A Prelude engine? Sorry about not responding this weekend...I was buried in 'stuff to do' this weekend :-\

I wish there was more information on that...and why they didn't drop it into the 3g Prelude, is beyond me.

David

hilikus · 10-28-2002, 11:04 PM

so alittle port matching is good for a few hp?

ill check my '88 B20A6 when i get home, i'm pretty sure it has an EGR

marcucci · 10-29-2002, 06:21 AM

Looks like the 160PS (or whatever) B20A engine was designed to tilt forwards instead of backwards... making it pretty much impossible to fit.

There's not as much flashing on the manifold as the ports are just badly mismatched, though there is an inordinate amount of flashing.

What's a B20A6? What are the power specs?

David, I have an extra B20A5 manifold if you want to p/p that for an exchange. Or buy the one I have.

hilikus · 10-29-2002, 09:26 AM

well i couldnt see anything under the PCV valve
that resembled the EGR valve or its lift sensor,
pretty dark atm though so i'll have to make sure tomorrow.

the B20A6 is the engine from the australian 3rd gen, they've been dyno'd at 142hp

i wonder where exactly the 2nd gen gets it's extra 15PS
from what ive read the specs are almost identical..
so what do you guys reckon? cams or fuel map maybe?

marcucci · 10-29-2002, 11:41 AM

According to what I've seen, the USDM Prelude had a 9.2:1 CR and the B20A (160PS) has 9.4:1. That would quite get it all, but...

Knowing what I know about most JDM models vs. their US counterparts, it probably has higher CR pistons (for a higher CR) as well as higher-lift cams and stiffer valve springs with a modified intake, TB, manifold, and header/exhaust, as well as a higher rev limiter. Oh, and a more aggressive a/f and timing map. Those would all be my guess.

hilikus · 10-29-2002, 10:30 PM

hmm, does the B21 have a dual stage manifold like the B20?

SiRxLaUgHs · 10-29-2002, 10:58 PM

nope.. honda dropped the dual stage thing for the b21

hilikus · 10-30-2002, 03:10 AM

but isnt it designed to improve low and mid range torque? ..is there some specific reason honda dropped it?

marcucci · 10-30-2002, 06:03 AM

Probably because the B21 already had enough low-end torque. It didn't need it.

What does the B21 manifold look like? That's interesting... might make a good upgrade for an all-out B20A race motor.

Does anyone know if the manifold bolt pattern is shared with any other B series motors? I know it's not shared at all with the H or F series.

SiRxLaUgHs · 10-30-2002, 07:26 AM

doesn't look like anything special..
i have a spare one if you want me to take pics..

marcucci · 10-30-2002, 09:32 AM

How long are the runners? How large is the chamber, compared to the B20A manifold? Pics would be nice if you could post them, measurements would be even better.

SiRxLaUgHs · 10-30-2002, 01:59 PM

marcucci · 10-30-2002, 07:47 PM

Wow- definitely designed for higher-RPM power. The common chamber looks smaller than on the B20A, which means that it will aid less in torque and more in high-RPM (high-CFM) flow. Runners are still a tad long, but that manifold would do more for high-RPM power than the B20A manifold will. Thanks for the pics!

For anyone interested, I did some work on the manifold tonite. It was flat out mismatched BADLY at the butterflies. I removed 1/8" of material in some spots to insure proper matching with reversion. My guess is that this will be worth around 5HP+ on the top end as a result of improved flow.

Surprisingly, the manifold was pretty well matched to the head and the ports in the head are pretty clean. Didn't need to do much there at all.

Mike90 · 10-30-2002, 09:35 PM

marcucci, which manifold do you think would be a better choice? i just put in b20a in my lude and used the b20a manifold. the only problem i have is i don't have a vacuum hose to connect to the flapper to open it up at higher rpm's because my car originally had a b21. i still have most of my old engine and was thinking of putting the b21 manifold on. i'm also throwing a cel for the fuel injectors, so i'm debating what to do.

marcucci · 10-31-2002, 06:48 AM

Sounds like you have other trouble to worry about first. You can just hook up the butterfly to engine vacuum, that way at least when not WOT you will have good low-end response (around town). When you go WOT or vacuum drops low enough, the butterflies will open. Not as ideal as an RPM-based system, but better than not having anything.

For a B20A, unless you are going all-out race motor, I say stick with the B20A manifold. I do recommend you port match it, based on what I saw Honda was running some pretty crap tolerances on their castings!

redliner · 10-31-2002, 11:24 AM

Lose cable access for a day or two, and everything flys by. LOL.

Hmm, that seems pretty interesting. I guess I'll have to remove the top and see how poorly mismatched this thing is. Do you have pics Todd of what you removed?

Time to throw in some cams

marcucci · 10-31-2002, 11:30 AM

I will try and take some tonite. What I took before didn't come out. I already reworked the worst of it, so...

The worst part was on the lower portion of the manifold, where the air exits the butterfly assembly and enters it. The holes were as much as 1/8" too small around the edge, the air was flowing into that lip and had to be creating massive turbulence.

hilikus · 10-31-2002, 08:33 PM

Quote:

Originally posted by redliner
Lose cable access for a day or two, and everything flys by. LOL.

haha so true, i just got mine back today.
just started leeching the Getaway In Stockholm 3 SVCD too, mmm NSX :P

oh and btw, is there a bigger copy anywhere of the prelude cornering in your sig?
..i cant stop looking at it

redliner · 11-01-2002, 12:31 AM

Hmm. For kicks, I unplugged the butterflies today...my butt-dyno indicated a better midrange, but I didn't feel much of a loss in the bottom end. I'd like to see some side-by-sides on the dyno though. I'm not sure how much those butterflys actually help. It could also be why the dropped it for the B21.

When I get some time, I'll open my manifold, and I'll start grinding away

David