Rotary Car Club - View Single Post

gmonsen · 01-08-2011, 02:37 PM

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

01-08-2011, 02:37 PM	#10
gmonsen The Ancient One Join Date: Mar 2008 Location: Eastern Pennsylvania Posts: 144 Rep Power: 18	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 __________________ 1993 Rx7 R1 20b NA 1994 Rx7 20b supercharged project 1991 BMW 850 6 speed 1991 BMW E30 M3 Evo II