Which Plenum Spacer ?

[mycoupe8urs]

Ive done a search and cant find the answer im looking for. i have a 2004 coupe and am trying to figure out which spacer i should get. is there any difference between 5/16, 3/8, 1/2, 5/8 plenums. which one would give the best performance gain ? Any insight would be great

[Sentientbydesign]

You're kidding right?

Check my sig.

*EDIT*

When searching for threads, be sure to use the option that searches in the thread body as well. Also, use the "Archived Threads" option. And finally the G and Altima forums are kind of on their own. So you'll have to intiate the search within them for best results.

[G_whizz]

Just go with the 5/16.

There are 1254896332254478822654411285 threads on this question if you do a search...it's the HUGE red blinking feature up above that says SEARCH

Go to our modification database area and educate yourself a little bit.

If you also want...go to http://www.everythingg35.com and read up on the spacers.

[mycoupe8urs]

LOL i feel stupid as hell... didnt even notice the blinking red search up top. i always used the google one. thanx

[TeflonG35]

Lol ive been here some time and ive never noticed that big flashing search either.

[Sentientbydesign]

Lol ive been here some time and ive never noticed that big flashing search either.

I think it was bigger at one point...like an advertising banner lol.

[G_whizz]

LOL i feel stupid as hell... didnt even notice the blinking red search up top. i always used the google one. thanx

No worries my friend! After you read up and have educated yourself (we can't do ALL the legwork for ya) hit us up with anything!

[joe603]

Read the differences from the Motordyne website:

http://www.motordyneengineering.com/techinfo.htm

How the Motordyne Plenum Spacers Make Horse Power on the 287 HP Engine

The Motordyne plenum spacers alleviate an airflow restriction that exists above the first two intake runner inlets. The inside top of the stock plenum is very close to the top of the lower plenum runner inlets. There is only about 1/8" clearance between the first two inlets and the plenum cover. This creates a significant air flow restriction that reduces engine breathing and power output.

If the height of the flow area above the runner inlets were increased it by 1/8" it would reduce the flow restriction (pressure drop) by a factor of 4. If the height were increased once again by another 1/8" or to a total of 1/4" it would reduce the pressure drop by a factor of 9. If the plenum were lifted by a total of 3/8" it would reduce the pressure drop by a factor of 16. If it lifted by 1/2" it will reduce pressure drop by a factor of 25.

Reduction of pressure drop is asymptotic and inversely proportional to flow area. In other words this means the greatest benefit will be realized within the first 1/8" of added height. Fluid dynamic theory, dyno data and flow bench test data support this.

As an example, assume the pressure drop above the intake is equal to 3 PSID at high RPM. By raising the plenum even 1/8" the pressure drop will decrease to 0.75 PSID. That's a significant inlet pressure recovery that will translate into more horse power!

A 1/4" spacer will reduce that same pressure drop to 0.333 psid.A 3/8" spacer will reduce that same pressure drop to 0.1875 psid.A 1/2" spacer will reduce that same pressure drop to 0.120 psid.

Although pressure drop is continually decreasing, the rate of change rapidly diminishes beyond the first 1/4".The same applies to gained HP. The pressure drop above the runner inlets is so dramatically reduced the added HP gains are also rapidly diminishing.

The attached plots are for three sets of tests 1/2", 1/4" and baseline in that order with three pulls each. The results of the 3 pulls per set were then averaged together. These test conditions were very tightly controlled to provide accurate, repeatable results.

Same dynoSame daySame tank of gasSame ambient temperaturesSame engine temperaturesSame ECU starting conditionsSame fan positionSame fan settingSame everythingThe car wasn't even taken off the dyno.

So even if the absolute values aren't correct, the deltas are. These plots show the largest change in gain comes within the first ¼ ". There is only a 1.664 HP difference between the ¼" spacer and the ½" spacer. And weather the car is NA or FI, the reductions in pressure drop will always be proportional to the air mass flow rate. Thus for a given spacer size, FI applications will see even greater gains due to the higher air mass flow rates.

So for NA or FI, nearly any kind of plenum mod is a significant improvement from the stock configuration.

Motordyne Engineering

[mrsmithGrider]

So Joe......out of all the verbiage I just read, which size is best?

[Sentientbydesign]

I'll answer for him

5/16" Gains above that are minimal and produce some issues with FSTB fitment and Engine cover fitment.

[mrsmithGrider]

Sentientbydesign: If 5/16'' is the best, why do you have 5/8''?

[Sentientbydesign]

Because there's no way in hell I'm going to spend over $200 on a plenum spacer. I got the blox spacer for $110 out the door.

Motordyne offers the IsoThermal spacers for $260-$300, the Blox spacer is made of some kind of plastic which does the same thing as the IsoThermal spacer does, plus it doesn't require a gasket.

If blox made a 3/8" spacer, I would have gone with that, but the 5/8 was the only option.

[Beancooker]

5/16 or 3/8. That way you can easily fit a FSTB.

[Andy_V35Sky_350GT]

I'm guessing the thicker the spacer the greater the growl?

Which one sounds best?

[joe603]

Motordyne's testing basically says that the larger spacers, after 5/16's, the flow increase was exponentially less. Look at the website's dyno results. You lose power with thicker spacers compared to the 5/16's size...unless you have FI.

However as SBD mentioned, the Blox spacer is only available in one size, 5/8. If I bought a spacer today (Blox wasn't around when I bought my motordyne), I would have considered the Blox...

[Andy_V35Sky_350GT]

How heavy are the Blox spacers? I am assuming they are lighter than the Motordyne ones due to being made of polymer/plastic resin as opposed to steel?

Only reason I ask as the two different Ebay quotes for shipping to AUS are pretty ridiculous, one is $90 (and the spacer sells for $90) and the other is $56...

I only live across the ocean..... If they are heavy then I'll pay it but they certainly don't look it...