New 20b intake plenum and runners

[gmonsen]

One of the biggest problems with running a 20b NA is getting air into the intake ports. I found that with th stock upper intake, you run out of air at about 5500 or so. So, we designed a new intake plenum and runners.

Here are some pictures of the plenum canister, the ends of it, and the first runners being made. The guy doing it, Victor Yordy, got cute and made a "G" on the end of the plenum. I am having him remake it with a "7" on it exactly like the "7" I'm using in my new emblem.

Gordon
Here's the design we started with, although it has changed in the dimensions. The plenum is now 7 inches in diameter and the runners start at 2 inches and taper down to 1.5 inches...


Here's the 7 inch diameter plenum canister...


Here's the "G" he embossed (right?) on the end of the plenum. He's going to make it with a "7" instead (like in my new emblem)...


Here's a runner being made. The max we can go at the plenum is about 2 inches in diameter and the LIM has 1.5 inch diameter runners, so that's the most taper (increase in velocity) we could do...

[Herblenny]

Gordon,

How about something like this... As I have considered building an N/A 20B RX3 when I had it and thought about this..




And they make FG intake..





More info here: http://www.efihardware.com/products/...ttle-Body-Kits

[gmonsen]

Phil... I know the guys at EFI. Good people. I am actually working towards an ITB setup. I kind of have someone on it, but want to understand the whole intake thing a bit more. Will be using the Jenvey throttle bodies.

I'm doing a video documentary in January showing the effects of different intakes and throttle bodies on power, which I am hoping others thinking about going this way can see what the alternatives are for power versus cost and refinement.

Gordon

[Twisted7]

what is the expected completed date?

[gmonsen]

Twisted... I expect it to be on the dyno next in about 3 weeks. Its supposed to be done sooner, but could be done later, if you know what I mean.

Gordon

[hades]

wow this will be awesome.

[vex]

Just out of curiosity are you guys modeling this design off of a previously developed manifold or is this completely new?

[gmonsen]

Hard to say anything is "new". We have made and seen others make plenums and intakes and we sized things and designed them based somewhat on math, but there are constraints that you have to work within. The total volume of the plenum is more than double that of the stock unit and the runners taper from 2.25" Internal Diameter to 1.5" diameter over the length of the runner. Also, we have avoided any and all 90 deg angles and have smoothed the air flow as much as possible. So, we have a lot more volume and the runners should increase the velocity of air we can get through the motor, which is the whole trick to NA motors.

Gordon

[vex]

Ahhh, I see. I was under the impression it was going to be forced induced and I was concerned about starving the end runners.

[gmonsen]

Vex... Nope. I'm one of those eccentric 20b NA lovers.

Quick update on the intake plenum and runners. Took more time than I thought to get the holes cut in the plenum for the runners and the flanges for the throttle body and mating to the new upper runners. I used a laser cutting shop and it took them a lot longer to schedule such a small job and cost a bit more than I had expected. The pieces look great, though I may use a water cutter next time.

Flanges for throttle body and runners


Here's an end on view of the new plenum compared with the old one. The old plenum was 3 inches in diameter and nearly 14 inches long. The new plenum is 6 inches in diameter by 14 inches. So, the old plenum had 98 cubic inches of volume and the new one has 396 inches of volume. This should help.

New plenum with old plenum and runners:


Comparison from another angle:


The old runners were about 1.25" going down to 1 inch over about 8 inch or so (from memory). The new runners are only only to be about 2 inches long and go from 2 inches in diameter down to 1 inch over that length of 2 inches. Since the old runners only squeeze down a quarter inch (or not at all since its hard to measure the interior of the cast runners accurately and they could essentially be 1" all the way), the runners need to be as long as possible to get any velocity. Our "fire-hose" shorty runner squeezes down by half over just 2 inches. We have to make runners that are longer than the 2 inches, so that the ends can be gripped in the bender to curve the whole runner a bit and then we'll cut off both ends to mate correctly with the LIM and plenum flanges. My hope is that the much larger plenum, combined with the fire-hose runners will solve my fueling problem at the top end.

My guy made up this curved end piece for the plenum with my initial. The actual plenum will have a "7" on the end:


I think I'm about a week away from having this done and back on the car, so we can hook up the bigger throttle body and give it a whang on the dyno and will post up pictures as we go.

Gordon

[TitaniumTT]

I love custom out-side-the-box stuff. What are you doing for fuel injectors, Gordon?

[RX-Heven]

What throttle body will you be using?

[gmonsen]

Thanks, Brian. Its a lot of fun. Not sure on the injectors once this is on. Its a lot more (4x) air. I was running out of air beginning at around 5500 rpm, not fuel. So, we'll have to see.

Rx-heven... Love your build. Still thinking about following in your footsteps. Almost did it some years ago. As to the TB, its a modified and extrude-honed Rotary-Works 90mm 20b throttle body. (They also make a 90mm 13b version.) I am wondering if that is sufficient for my power curve goals, but won't know till its all back together. As Logan's work shows, there's a lot of experimenting and new stuff to be done in NA. We're only just getting into it and yet there are now a bunch (10-15) of street NA 20b's making 425-475 whp.

Gordon

[diabolical1]

for krikey's sake, man ... less typing, and more working! i want to see this thing assembled and bolted to your car. i need a fix.

[gmonsen]

I think the new intake plenum and runners should be tac welded up by end of week and hopefully we can get it on and be sure it fits right. Then back for final changes, grinding and a polish, and back again for install and dyno. Here are a few pictures of the progress this week. The throttle body is on, the plenum roughed out, and the runners will be done tomorrow.

We have changed the design of the runners -- again -- because it made no sense to make this and still use the lower intake manifold. Mazda did a great job on the LIM in terms of fitting the turbos and emissions stuff for the Cosmo, but this manifold cannot be modified to flow well. So, we are taking the runners all the way down to just above the base of the LIM -- sort of using it as an extended flange -- and welding the runners to that as a base, so everything bolts up well to the block. We may work on the base of the LIM a bit to smooth the flow into the intake ports. Try to match them as closely as possible by porting the LIM base out. When its all done (welded, ground, and polished), I am going to have them ceramic coated an off white.

I have a real feeling that we are going to see some major horsepower jump here, because the LIM is just such a restriction. We will have increased volume by 4 times and really speeded up velocity at high rpm. This appears to be so critical at higher rpm where the combustion dish is going by so fast.

Gordon

You can see that the primary runners are quite a bit smaller (1x1.25") than the secondaries (1.6x1.6"), so the taper is greater for the primaries. It'll be interesting to see the impact on the primaries.




Here is the revised intake plenum:


And the flange for the Rotary-Works 90mm throttle body being mated to the intake plenum: