4 inch snorkel airbox to feed V8

[GUEEY]

Hi

Just picked up my 350 GQ from having a 4 inch snorkel and airbox fitted.
Snorkel and job done very nice!
But!!!! it wont feed my straight petrol 350 with a 600 CFM carb.
as soon as wide throttle is opened it starves for air/fuel.
i pulled over and removed the filter and it made no improvement.
The carby has a nice alloy hat on the top, 4 inch high and 10 inch diameter with a 4 inch round outlet on it.
then piped to a donoldson type airbox and filter, which also has a 4 inch inlet and outlet going onto the 4 inch snorkel.
as soon as i drop my 14 inch standard aircleaner back on my truck flies!!
i will talk to the guy tommorrow about other options.
what setups do others have.

Cheers

Grant.

[Struth]

How many bends are in the snorkle from the inlet to the carby?

bends slow up air flow heaps. I have a similar problem with my 5.0, dyno tuners reckon I'll see another 10 rwkw if I free up the airflow and it's pretty straight already.

Cheers

[GUEEY]

How many bends are in the snorkle from the inlet to the carby?

bends slow up air flow heaps. I have a similar problem with my 5.0, dyno tuners reckon I'll see another 10 rwkw if I free up the airflow and it's pretty straight already.

Cheers

only 2 bends.
i am worried that 4 inch may not be enough to feed a 600 cfm carby,
as soon as the secondries open , it dies!!

Grant

[-Nemesis-]

I'm not sure on the science of it, but it has a lot to do with the length of the pipe. The longer it is the less efficient air draw becomes.

If you're carb breathes through a 4in inlet, I'd be betting you need more like twin 3 or 4in snorkels to feed it.


A good example is with my blower, which has a 3.75" input.
If I run a long 3" intake it will peak at 5psi.
A 4" intake it will hit 7psi, even though it's bigger than the charger mouth, it's about a meter long.
A filter straight on the 3.75" opening and it's closer to 9psi!

[skootin]

I dont think the 4" pipe is the problem not wit a 600 holley anyway.
I made and fitted a 4" snorkle to a worked 350 with alloy heads and roller cam with EFI 1000cfm throttle body and no problems.
Mate had a 355 with group A twin throttle body feed by a 4" pipe from a modified 80ser airbox and it spun to 7500 all the time.
Just check the vac pot on the side of the carb dont have a hole in it and its not working. Y ou can also get lighter springs to open the secondaries early and a rear metering block conversion to change the jetting if the 350 has a bit of work done to it.
NOTE if its a manual a double pumper would give better performance and drivability. Vac secondaries are better suited to auto's.

[its aford not a nissan]

could always have the carby retuned to suit the snorkle

[HG]

Hmmm something strange happening there, have you checked that it's not blocked with something?
I would check the vacuum part of your carby as well check the state of tune as the new air box & snorkel would have thrown the settings out as way more air is being let in now.
I feed my 355 Turbo with an air Pod in a custom air box fed by a 4" snorkel and it will supply enough air to produce over 500hp no worries as well it will happily rev to 6800rpm

[its aford not a nissan]

you cant really compare an injected motor to a carby motor as the injected motor will self adjust the fuel , a carby motor wont

[GUEEY]

Dropped into my Dyno guy today.
The problem is not the 4 inch snorkel.
It is the alloy hat sitting on top of the carby.
We took it for a spin with the snorkel disconnected and the air cleaner removed.
It still fell over on med-full throttle.
The dyno dude said the air is pulling through the 4 inch inlet on the hat and causing a swirl affect and upsetting the air delivery into the carby.
Alloy hat is 4 inch thick and 10 inch diameter and snail shell shape.
We are modifying the alloy hat to put the aircleaner element back ontop of the carby.
That will fix it according to the dyno guru.

[GUEEY]

Hmmm something strange happening there, have you checked that it's not blocked with something?
I would check the vacuum part of your carby as well check the state of tune as the new air box & snorkel would have thrown the settings out as way more air is being let in now.
I feed my 355 Turbo with an air Pod in a custom air box fed by a 4" snorkel and it will supply enough air to produce over 500hp no worries as well it will happily rev to 6800rpm

According to my Dyno guy Turbos and snorkel/Airbox setups work well due to the turbo pulling the air through and delivering it evenly through the throttle body.
A carby is more sensitive to air flow and requires it instantly without any disturbance.
I traditional airclear on top allows the air to be pulled even into the carby as required. So the theroy goes!

[skootin]

Yeah the carby is a very sensitive thing.
Im sure some good R&D will get you sorted again.
As soon as you get rid of that snail.

[want33s]

NOTE if its a manual a double pumper would give better performance and drivability. Vac secondaries are better suited to auto's.

Other way round mate..
DP for auto... VS for manual..
Manuals bog down with a gutful of fuel that a DP delivers via 2 accelerator pumps, whereas you stab the throttle in an auto (with DP) and the extra fuel is used because the kickdown makes engine rev harder.

[HG]

My motor is running straight LPG through 425 mixers.
Prior to fitting the turbo I ran an oval shaped air cleaner on top of the mixer with great results and it had a 4"snorkel attached to it.