As some of you know, I have purchased a lower plenum section for a 287 HP motor intending to some porting and modification similar to the much discussed Mrev+. Here are a few things that I have learned about this plenum that surprised me.

First, the individual runners are NOT equal length. Each side has three different lengths, 5.20", 4.33", and 4.795". The order of the lengths is reversed on each side. Very interesting! See the photo to understand the arrangement.

Second, the port designs are not uniform. The front and the middle ports are smooth, but the rearmost port on both sides has a deep groove cast into the floor or the port.

I wonder if there might be an advantage in terms of broadening, and flattening the torque curve to having unequal runner lengths? Do you suppose that there is any potential for more power from equal lengths?

More to come.

 

hey this is great stuff, good luck on the project its definitelly nice to see ppl go out and try some new DIY projects

 

Subscribing, please keep us posted.

 

Outstanding! Please keep up posted on your findings.

 

i applaud your efforts. maybe the different sizes have something to do with the shape of the upper plenum?

 

A few additional photos. These show the underside of the lower plenum, and I have placed a brass wire into the small drilled hole that goes through each intake port. This hole is where the crankcase pressure is vented. Next, The milling process begins. Photos tomorrow.

 

The chips fly!

I began milling the top of the two front runners. I am removing about 1/4 inch (5mm). As with all other aspects of the plenum, each side is a different height! I will have both sides exactly the same when I finish.

More to come!

 

wow, what ru using to do that?

 

a mill

 

Real men would do that with just 200 grit sandpaper and elbow grease.


lol j/k, nice work you've got going there!

(subscribed)

 

subscribing

 

woa.............great job......keep it up

 

O.K. some more photos. The milling machine work is completed. About 5mm was removed. Next step is to grind and blend the flattened area to achieve a smooth radius. I will attempt to recreate the dome shape that Nissan originally designed into the runner tops. Additionally, I will clean up any flash and casting flaws for the smoothest possible flow.

 

Nice job and great observations, bilinghm.

I did mine the hard way. With a file, sandpaper and a Dremel.

The next one will be better!

DaveO

 

You do nice work! Very impressive. Did you lower the front ports or just polish?

 

subscribing

 

Front ports are lowered, blended and polished. The remaining sections of the lower collector are blended, relieved where necessary, all casting marks are removed and all internal surfaces are polished smooth. My dyno-butt likes the results.

Here's a picture of the #2 port lowered and about 80% blended.


DaveO

 

Looks like good work! is this something the ave. person like me could do with sandpaper and a power drill with "grinding" bits? very intersesting in doing this. is it just as course as the outside of the plenum?

 

Answering the second part of you question is easy. All the lower collectors I've seen (maybe 35 or 40) are rougher on the inside than the upper collector's outer surface.

It's real hard to answer the first part of your question... at least for me.
Are you real good with controlling power tools. How about doing tedious, detailed work? You know one serious slip with a cutter or grinding wheel and the collector's mating surface is history. Your description of tools--a power drill and grinding bits--leads me to believe you may not have a background in this type of work. If you don't this might not be the best project to start with.

bilinghm, please add your thoughts. Your descriptions, observations, measuring marks and milling results indicates to me you're real familiar with these types of modifications.


DaveO

 

looks good!

why not shave the top of all of the runners? Is the thought that the front cylinders are lacking air flow and this is to equalize it...what about shaving them all down, but doing the front a little more?

thanks,
Peter