Pinoy,
As you can probably guess, I don't agree with Neffster or Crawford on this point but that's OK. We can politely disagree.

You can use the 1/2" spacer and have good results with stock headers, Crawford headers or any kind of aftermarket headers.

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

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

As you can see, the reduction of pressure drop is asymptotic and inversely proportional to plenum spacer height. 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. If you raise 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 HP!

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.

As you can see it isn’t changing much beyond a 1/4”. So within the first 1/4" of lift, the pressure drop above the runner inlets is so dramatically reduced that the added HP gains are rapidly diminishing. So weather you use a Crawford, AAM, Kinetix or Motordyne the end results will be essentially the same.

Although plenum height is the foremost mechanism for increased performance, there are other details that will affect fluid flow and pressure drop but I won’t go into these now.

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 dyno
Same day
Same tank of gas
Same ambient temps
Same engine temps
Same ECU starting conditions
Same fan position
Same fan setting
Same everything
The 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 1/4" of lift. There is only a 1.664 HP difference between the 1/4" and 1/2".

This suggests that nearly any kind of plenum mod is a huge improvement from baseline.

Tony Colette
Motordyne Engineering

 

I am curious here SixFive, you say "nobody shows 11 HP who doesn't have other mods"
Even Crawford is only claiming 9 hp at peak and Neff says he told him 20hp if he did cats too.. that would be inline with the dynos on the spacer. Obviously improving the breathing on intake and exhaust is the way to go.

Also you stated in a prior post that "You felt no need for a dyno"
I understand that, I didn't ethier, when my spacer went it it was like a new car
it offered obvious power all the way across the power band. (this was verified at the dyno day last week end) so here is my confusion...

- You didn't get a dyno... hey fine
- say the crawford does better ?? based on what ?
- The claims of 8hp by Hdrazine, are due his nature of insuring the customer gets at a minimum what is expected (he underates) rather than overstae as so many mods do.
I think all dynos have shown a lot better than 8, it is the heavily modded cars where the increase is not as large I think. Due to already improved breathing.

There is no doubt that some of the folks have gotten a bit heated, and are being defensive or even offensive at this point. But keep in mind, that was started by a number of people posting and claiming the "spacer was snake oil"... and it was they who did so with out data, and even continued in the face of hard data.

I may very well purchase a Crawford V5 for the next dyno day and swap that vs a spacer and stock plenum so that a apples for apples compare on the same car can be done. This would not be to prove anything, as I expect the results would be with in the couple of HP noise/error of the dyno.... I would do this because I become curious, my curiousty has driven my engineering career for 25 years, so to me it is just interesting.

The thing I find so interesting in all of this is that some crawford plenum users claim it works Better, but have not substaniated that, or been able to offer any reason it does/would work better.

I am blown away that so many people are arguing with the "this one is better than that"... if we did that on every mod (wheel, tires, brakes, intakes, oil, you name it)

Why can't we post data, impressions, ideas, etc without all this crap....

In other words (and this is to everyone) SHUT UP, if you are asking questions, posting data, offering help... hey great, but if you are pissing and moaning about "mine is better" or "I know it isn't as good - but can't say why"
Man this has gotten old....

 

Tony Great post. You do deserve the MOD" of the year award. I not using your spacer but for what its worth I will be first in line for your next VQ upgrade. Its always nice to see someone get there company off to a good start with a good product. So what's next?
---------Dennis

 

Here is the Crawford advertisement:

"The stock plenum, due to the slope towards the front, which Nissan designed to clear the stock strut bar on the 350Z, restricts the airflow to the front cylinders. Our design raises the front of the plenum as shown in the picture below, allowing more surface area and greater, equalized airflow to all cylinders. Greater airflow equals more power. On average, our plenum produces an increase of 9 hp at the original peak, and a solid 17-20 hp at redline."

20hp at redline eh?

Should we just take Crawford's word for it that their V5 plenum makes 20hp on average? That would mean their plenum must be superior to Hydrazine's "5-7hp gain" spacer. I guess we will find out when the dyno comes in. I am anxious to see a 20hp gain from the Crawford.

 

I have been dying for this comparo. There was one in socal that where they compared the two prodcuts but apparently the shop wasn't too worried about being as consistent from run to run and didn't even monitor the coolant temps, which will significantly affect output if even 10 degrees different from run to run.

It would rock if you also put the plenum with the spacer for a run. The only runs taht I've seen show negligible increases but I am very interested if those results can be repeated. Extrapolating off of what Hydrazine said: it seem like adding another 1/4" to an already 1" rise from the crawford (at the front only) would be futile. Anyone wonder if it could be that combining the concepts of Crawford and Motordyne would provide the best reuslts?

 

Which dyno comparison are you talking about? I haven't seen another Crawford vs spacer comparison other than the one Hydrazine and I did. And like I said before with that day, the conditions were kept constant.

(gas, coolant temp, radiator fans off, dyno operator, car remained on dyno the entire time, ECU reset, etc.)

Incidentally, the ECU reset made no difference on my car.

If we do another dyno day at Church Automotive, I can go back with the combo of Crawford and spacer. But since it would be a different day, it would be harder to make absolute statements on the gains.

 

Sukairian: This is how bad info gets started....

Crawford Claims 9hp at peak and up to 20 at redline, this is based on the fact that at readline the stock engine is falling off due to an inablity to breath, i.e. the staement is claiming that a stock car putting 230HP to the wheels at HP Peak, would get 239 with the Plenum, at redline the stock would be less than the peak 230 due to breathing issues, the plenum effectively extends the useful RPM range....

The Motordyne spacer will do the same thing.

Again, you have to look at all of the variables. i.e. Are you comparing a stock engine Plenum vs Spacer, or a car with other mods ??

In anycase, the dynos I have seen - and some I was present for last weekend where some before and afters were done. the spacer yeilded 8 - 9hp up to 12 - 13hp depending on car, mods, etc.... basiclly the same as the crawford from all I can find.

 

Yes, I am working several other mods. Two of which will be highly unusual to the industry. They are inherently more complicated and thus will take more time to develop.

But I am working on them! I cant wait. It should be a lot of fun to test. It should also be equally interesting to see how the market will react to such a new type of mod. It'll be something to see. I can't wait.

Yes, this is absolutely true about engine temps affecting dyno results... I am curious, how did you hear about the SoCal comparo of the cast plenum and spacer?... I didn't see much of anything posted about it. I certaintly didn't post anything about it.

And yes it was done. On "ZBOY" (Matt's) 350Z. He won the raffle for a plenum spacer. He had the cast plenum already installed on his car so his baseline was with the cast plenum. He later redynoed with a stock plenum and the 1/2" spacer.

But like you said, the dyno operator didn't give a damn about controlling engine temps or even monitoring them for that matter. So the results are questionable. Considering the tests were not properly controlled, the pre/post differences as shown on the dyno plot are too large to be posted. It would not be fair to Crawford. Not to mention the Nuclear flame war it would start!!!

 

Oh yeah, forgot that ZBOY had a Crawford Cast plenum as his "baseline" run. I left before he did the "after" runs, so I never knew that he did a second run with stock plenum and spacer.

I'm looking at all six of his runs right now on the viewer program. I would have to agree with your last sentence.

 

Haha. So I take it the spacer put the hurt on the Crawford again ey?

 

FYI - ZBOY (Matt) sold his Crawford Plenum on MY350Z.com forum this week for $299 after the dyno day. He only had it on his car for a short time.

Hmm, I guess Tony's Spacer does work.

 

Well... Zboy came to the event with a full "Crawford Package" including the cast plenum and headers and he drove home with a stock plenum and a new 1/2" spacer installed...

He said performance wise, the butt dyno indicated there was "no significant difference".

He must of evaluated what each mod offered and what best fit his application...As Kieth said, Zboy sold his cast plenum a couple days later.
.
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I know its very important to apply the right amount of torque pressure to the bolts and I believe its 5pounds. When should I check the torque on the bolts after the first install? I have the spacer on for 3 days now. Can somebody please help.

 

You can re-torque if you want but it isn't really necessary.

 

WOW, if that isn't the ultimate testimonial then I don't know what is