Intake & Exhaust Questions and info regarding various aftermatket exhaust systems for the G35 (Headers,Y-Pipes, and Cat-Back Systems)

Plenum spacer

  #1  
Old 03-12-2005, 08:49 AM
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Plenum spacer

Hey guys don't kill me. I did a search and found extensive installation procedure on this spacer. What I was really looking for is somthing explaining what exactly is this spacer and what it does. Someone please educate me .
 
  #2  
Old 03-12-2005, 10:23 AM
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The plenum spacer is designed to add volume to the intake plenum. There is a proven restriction to the front cylinders in the OEM configuration, probably due to component sharing with the 350Z. Increasing the volume balances the flow and adds HP. This is the theory behind the Crawford, Kinetix, and soon-to-be-released APS plenums.

Dyno tests of the Motordyne spacer show it equalling or outperforming the aftermarket plenums!!

This is a win-win mod IMHO. The website for additional info is: www.motordyneengineering.com

Good luck and happy modding.
 
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Old 03-12-2005, 12:01 PM
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good summary of the available information
 
  #4  
Old 03-12-2005, 02:39 PM
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Originally Posted by ChicagoX
The plenum spacer is designed to add volume to the intake plenum. There is a proven restriction to the front cylinders in the OEM configuration, probably due to component sharing with the 350Z. Increasing the volume balances the flow and adds HP. This is the theory behind the Crawford, Kinetix, and soon-to-be-released APS plenums.

Dyno tests of the Motordyne spacer show it equalling or outperforming the aftermarket plenums!!

This is a win-win mod IMHO. The website for additional info is: www.motordyneengineering.com

Good luck and happy modding.
Only difference in our opinions is this statement...
Originally Posted by ChicagoX
Increasing the volume balances the flow and adds HP. This is the theory behind the Crawford, Kinetix, and soon-to-be-released APS plenums.
Since the plenum spacer has not been flow bench tested there is no "proof" that the just by increasing the volume "balances the flow". In fact, Doug Stewart at Crawfordzcar found that the flow was NOT balanced by adding spacer height. You would need to have the front and rear runners receiving equal amounts of airflow with NO OBSTRUCTIONS. This was the reason that the Crawford Plenum top is parallel to the mounting flanges on the lower manifold. Also, Doug tried a version of the plenum w/o any posts inside of the plenum to not obstruct air flow (stock has 6 posts). Unforutnately this plenum cracked on Doug's own car (similar to what's happening with Kinetix) due to thermal cycling, etc.

I'm not saying the spacer doesn't work, I'm just saying it does not "balance air flow". Some people may not care as long as they get increased power, some will... especially those who are going for equal length headers and want the two mods to work well together.
 
  #5  
Old 03-12-2005, 03:45 PM
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Neffster......I have not read this bit of information before.....but I'm a little confused....you said the plenum spacer has not been bench tested (I have not found anything on this subject either) but Crawfordzcar found adding spacer height did not balance the flow.........could there be a difference between how Crawfordzcar added spacer height and this plenum spacer? Also, did Crawfordzcar get a balanced flow with their design, even with the posts? Do you know how much taller the Crawfordzcar plenum is at the front compared to stock?
 
  #6  
Old 03-12-2005, 06:25 PM
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First: I believe some flow testing was done by the designer of the spacer... I will let him jump in though.

Second: Balanced or not, is almost a secondary issue. The front cylinders are being starved for air, adding a spacer improves that situation. An aftermarket plenum also improves the situatuation....

Is one better than the other ? who knows, there is however no doubt that stock a slight problem exists, and also no doubt that the spacer or an aftermarket like crawford improves the situatuation.
 
  #7  
Old 03-12-2005, 06:40 PM
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What else is Crawfordzcar going to say! The spacer mod is much less $$ then theres.
 
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Old 03-12-2005, 06:41 PM
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sickone,

just got the email that my 3/8" spacer was shipped today. I remember you said it made quite a difference after you reset the ecu....did you do the quick gas pedal method or the 12 hour battery disconnect...or does it make a difference which method is used

thanks
 

Last edited by maxpower; 03-12-2005 at 06:59 PM. Reason: misssing word
  #9  
Old 03-12-2005, 06:51 PM
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Originally Posted by maxpower
sickone,

just got the email that my 3/8" spacer was shipped today. I remember you said it made quite a difference after you reset the ecu....did you do the quick gas pedal method or the 12 battery disconnect...or does it make a difference which method is used

thanks

You know - I've tried to do the quick gas pedal ecu reset - to no avail. loser!
But I still notice the difference in the way the G pulls - but I'm really wondering if a reset would make a bigger difference.
 
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Old 03-12-2005, 07:01 PM
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when did you get your pdf instructions from Tony? I got the shipping # but no pdf file

ps. do you think you are going to make it to borders tonite?
 

Last edited by maxpower; 03-12-2005 at 07:03 PM. Reason: added ps
  #11  
Old 03-12-2005, 08:37 PM
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Originally Posted by G352NV
What else is Crawfordzcar going to say! The spacer mod is much less $$ then theres.
In all fairness you are correct. The spacer is cheaper. In fact Doug designed a cheaper spacer himself and it is 15% of the price of the spacer everyone here is referring to. He will tell you about the spacer testing he did and why he choose 2.5 years ago not to make a spacer and went down the plenum route. (And no, it wasn't because he didn't think about making a spacer.)

Check out this link... 1/4 inch plenum spacer.

There are issues that are way too deep to get into (partially because I don't fully understand them). Call Doug and have a conversation with him and see if what he has to say makes sense. Words like Scavenging, pressure drop, (something about "dead spots" in the manifolds where air doesn't flow properly which change with each approach taken to increase volumetric efficiency), etc...

When you're all done, do a bunch of research on my350z.com performance section and see what you end up with. I've done this and have been really careful not to "bad mouth" the plenum spacer.

IMO, I'd stick with Crawford Products but that's just me. $200 or $400 isn't really the issue for a car I'm going to keep for 5+ years. Then again, my goal is to try to "ring out" as much 'safe' NA horsepower out of my vehicle as possible. Your goals may not be the same as mine.

As always... Your mileage may vary.
 
  #12  
Old 03-12-2005, 09:21 PM
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MaxPower: Yes I did the gas pedal reset, I am far to lazy to disconnect the battery and wait 12 hours Even if you don't reset, the ECU will catch up after some driving (some number of hours or miles)

Robbdogg: it takes a few tries, I have gotten better and can always do it in 1 or 2 tries now... use a watch, timing matters

neffster:
As a complete solution, a redesigned plenum is likely better. I doubt anyone argues that. On the other hand there is absolutely nothing to indicate the spacer isn't a great solution, at half the cost, which also allows keeping your engine cover.

Flow, turbulance, dead spots, scavenging, presure drop, all valid things... then comes the real question. After 25 years in engineering/design the question I must ask often.
What is total difference... in other words, lets assume the crawford is better in all areas... OK, by how much ? If I buy a $500 stereo amp, vs a $5000 one, do you realize the actual sound quality and distortion is only better by less 1/2 of 1%... not enough for most people to hear.

The same is likely true here.

Also to say "my goal is to try to "ring out" as much 'safe' NA horsepower out of my vehicle as possible. Your goals may not be the same as mine." indicating that spacer is not safe, or you feel it might not be,,,, is crap.

If you expect Crawford to tell you anything other than "Ours is best, we tested, we did it all" true or not that is of course what they will say.

Since you openly admitted you don't understand most of the issues involved, you might want to leave your judgements out of your posts, weren't you the one that trashed this in another thread, claiming the only dyno data on the spacer came from friends of the designer.... yet you keep popping off like a friend of Crawford products.

If you have some real data that disputes what everyone is saying, by all means post it.
 
  #13  
Old 03-12-2005, 11:15 PM
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Sickone - Well stated.

Neffster - NOT everyone that has purchased the Motordyne Plenum Spacer is from Calif. There are buyers of the spacer from all over the country, and even from the Southeast. Sickone started a thread with his review on various mods done on his G35. You jumped the thread by discrediting the Motordyne Plenum Spacer and Kinetix products while giving praise to Crawford products. There must be something to the spacer if Crawford is now producing one at a lower price than Motordyne's.

Crawford makes good quality products (high priced), but all of Doug and your opinions are not unbiased.
 

Last edited by Keith N; 03-13-2005 at 02:48 PM.
  #14  
Old 03-13-2005, 04:26 AM
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Keith: we'll have to meet up sometime, I'd love to meet other G owners... OK I am an old fart, but I find myself acting like a kid with and about this car
I missed out on the meet in Chino a couple weeks ago, was swamped with design due date.


neffster: it is not my intent to hammer on you, but it seems you have been going out of your way to hammer on the spacer. Which by the way is not the only spacer being offered, AAM for example also has one. So to assume the only design that has any history or testing is Crawford is a bit rediculous.

More interesting to me given your passion for trashing a 'Non-crawford' solution
is that when I went to your website/club site... low and behold Crawford is one of your big sponsors..... and you had the nerve to question the validity of the results on the motordyne part claiming it was biased, and done by friends of the designer.....

I love the irony.... But I would hope people would would try and put personal attachments aside and post facts to the best of their knowledge. In many cases readers of the board must depend on the info here to make a choice.
 
  #15  
Old 03-13-2005, 02:35 PM
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"Our design...allowing...greater, equalized airflow to all cylinders" This is from the Crawford website.

Balanced/equalized: are we splitting hairs here?

If you want to talk theory, maintaining the sloped design should increase the flow to the front cylinders even better through higher velocity.
 

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