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Turbo certainly makes a difference.

I have read of a few people that changed the comp snorkel to a ram head as the noise was too much. And it is BAD for airflow too. BAD!
i do recall measuring the top of the windshield area (like where a rear facing snorkel would draw from) as being a low pressure area and even a vac area close to the surface of the car as the flow must be not attached at certain speeds due to the angle of the windshield.

moving to a roof rack/light bar and to utes with a headboard/canopy and a little roof rack and this area became a high pressure as the air must be bunching up on all the resistance of things.

so perhaps its ok like this....
I would still prefer forward facing myself for a multitude of reasons, however my gut is telling me to do drive pressure testing back to back to verify that gains can be had there as well. (to validate)

So when considering everything in the big picture of our patrols, the ONLY reason i can see to run a rear facing is if you are in a damn hurry to be some where in dense bush...

I have plenty of other stuff that could be ripped off my car by low hanging tree branches so i will just slow down a bit and clear the tracks where necessary.
If i was to go rear i would probably want 5 inch, as while we should not under estimate the power of atmo pressure, we should also consider the aero of the vehicle and i at a guess i would think that 5 inch over 4 would likely make the noise issue worse.
 

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GQ Dual Cab. TD42Ti with fruit.
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Low pressure spots etc I do not know about, except to say that owners have reported noise when in this position.

Straight cut pipe is not good for airflow - air does not like to flow around corners. Do a bit of googling on OEM intake designs going back decades and you will find bellmouth designs dominate. This is to promote airflow. Oldmav did his own testing many years ago, and found that almost anything was better than straight cut pipe. Ram heads work well, he even cut slots in pipe with a grinder and bent the pieces out like a flower petal and even that was better!

Straight cut pipe is good on comp trucks.
 

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1985 SD33Ti MK LWB Wagon
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If it is significantly louder when you wind down the passenger window then it's likely your snorkel. Full metal piping carries a lot of induction noise, and your roof sound deadening has likely made it better than it would be otherwise.

Try it out, wind down the window, even just a little, and see if it's much louder.
 

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Turbo certainly makes a difference.

I have read of a few people that changed the comp snorkel to a ram head as the noise was too much. And it is BAD for airflow too. BAD!
Yeah I changed to ram head alot quieter ish the borg just sings either way but easy 20% quieter
you'll get used to the noise or turn the radio up and
If you Post up a video everyone can get a better idea
 

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Comp style, straight cut reverse facing snorkels are not suitable for highway use in my opinion.
I have read of a few people that changed the comp snorkel to a ram head as the noise was too much. And it is BAD for airflow too. BA
Absolutely. Add a Safari etc forward facing head. Can make a shlt load of difference to noise with no power loss.
 
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