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I’m only posting this cause I thought I had seen a bad review on these somewhere before. Any feedback? Would you guys recommend that if I do buy these I send em to RC to have em checked before installing. Or any other suggestions?

 

https://www.ebay.com/itm/114009965865?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=JDl-15yLQ8C&sssrc=4429486&ssuid=QTzlFXB1S-S&var=&widget_ver=artemis&media=COPY

IMG_2985.png

I wouldn't be concerned at all, other than to suggest having them flow tested when you receive them to confirm they are reasonably similar, and then put the highest to lowest flowing ones in cylinder 6,1,5,2,4,3

46 minutes ago, Duncan said:

I wouldn't be concerned at all, other than to suggest having them flow tested when you receive them to confirm they are reasonably similar, and then put the highest to lowest flowing ones in cylinder 6,1,5,2,4,3

Thank you!

On 2/16/2025 at 2:45 PM, Duncan said:

I wouldn't be concerned at all, other than to suggest having them flow tested when you receive them to confirm they are reasonably similar, and then put the highest to lowest flowing ones in cylinder 6,1,5,2,4,3

Hey Duncan, I've always set them up from 6 -> 1. Due to slightly higher EGT's, I also add a small amount of fuel to cylinder 6 & 5. I understand why you start at 6 but curious as to why you then continue somewhat based on firing order?

Thanks

It's because the air comes in over #3 & #4. The two "dead" ends of the plenum are at #6 & #1, with #6 being a little more "compromised" (Sorry about all the quote marks) than #1, due to the shape.

So you get the dead end effect at #6 & #1 where dynamic pressure converts to static pressure, likely causing the air flow to be highest for these. The others are then just working in from the ends to the centre.

6 -> 1 is only valid for FFPs.

  • Like 2
1 hour ago, GTSBoy said:

It's because the air comes in over #3 & #4. The two "dead" ends of the plenum are at #6 & #1, with #6 being a little more "compromised" (Sorry about all the quote marks) than #1, due to the shape.

So you get the dead end effect at #6 & #1 where dynamic pressure converts to static pressure, likely causing the air flow to be highest for these. The others are then just working in from the ends to the centre.

6 -> 1 is only valid for FFPs.

Thanks for the explanation, I'll sleep a little smarter tonight! Cheers. 

6 hours ago, GTSBoy said:

It's because the air comes in over #3 & #4. The two "dead" ends of the plenum are at #6 & #1, with #6 being a little more "compromised" (Sorry about all the quote marks) than #1, due to the shape.

So you get the dead end effect at #6 & #1 where dynamic pressure converts to static pressure, likely causing the air flow to be highest for these. The others are then just working in from the ends to the centre.

6 -> 1 is only valid for FFPs.

Exactly....but I will just add that is internet science....I've never seen hard data on a stock rb25 manifold so I'm just assuming....

  • Like 1

It's also important to acknowledge that the stock Nissan side entry plenums are actually pretty good, and Duncan's first principles basis for laying out the order of leanness might not actually apply. It's also possible that #3 & #4 could get some direct shot at the air because they are directly across from the inlet.

  • Like 1

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