What is the intake CFM on a 3B-T???

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Awl_TEQ

Awl_TEQ

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Searched for a couple of hours and ended up off on a tangent so I'll start a new thread...

I am thinking ahead a few weeks and if I don't go with the stock (but modified) air filter system I want to size a Donaldson system for my turbo'd 3B. Hence the title of this thread - I need at least a ballpark CFM figure to properly size and choose a filter housing.

Backstory: I am swaping a 3B/H55f/split case into a 78 FJ45. Currently I am mocking up the engine bay and so am building my own custom exhaust header for my T3/T4 turbo. The turbo, alternator, right battery+bracket and air filter housing are all in close proximity to eachother and I'm not sure I can fit them all in there. I will also be building my own snorkel (safari knock-off in aluminum) with a pre-cleaner so I need to leave room for the inlet through the apron. And if that's not enough I have intercooler piping to route.

Back to the question: CFM... how to calculate? RockDoc had a recent thread where he said to take the displacment of the engine converted to CFM and multiply by the 1/2 the max RPM (assuming 100% volumetric eff.)

3.4L = 0.12xxxCF x 4100?rpm/2 = 246CFM:meh:

Does the turbo change that equation? In what way? How much?Is that equation correct?:meh:

When I search the Donaldson site for a nice 246cfm unit it has very large inlet and outlets - 4.00" - is that too big? The top of a Safari snorkel is 3" or 3.5" and the inlet on my turbo is like 2.5"???

All replies and comments welcome - my build is in the sig
 
With 10psi at 3500rpm, 290 Cuft/min at 100% VE.

But at 3500rpm, you're probably going to have ~80% VE which would be around the 250 cuft/min you've already calculated.

Donaldson filters are convservatively rated and rated for flow at a given pressure drop. A smaller one will work fine.
 
Thanks Dougal - :cheers:
 
Too funny!! - I forgot about this thread and did a search....... "3B CFM" only to find this thread :doh:

New related question - I have built myself a snorkel and I am looking at the Donaldson "Top Spin" pre-cleaner. Top Spin data link

Model #H002437 - rated for 90-200 CFM
Model #H002425 - rated for 200-450 CFM

The problem :- 200 CFM is a terrible spot for the cutoff between the two models. At 2220 RPM I should be pulling 200 CFM given the following equation.

(CID x RPM / 3456) x VE = CFM

CID = cubic inch displacment
VE = Volumetric Efficency factor - some say a turbo is 1.5

(207.5 x RPM /3456) x 1.5 = 200
RPM = 2220

That means (according to this gear ratio calculator) I will be at the limit of the smaller unit when traveling at 100 km/hr (63 mph) - or - put another way..... I will have restriction from the pre-cleaner when in low gears and higher rpm off road. At 200CFM they show a restriction of 4.5 inches of H2O (1.15 kPa).

It also means that the larger unit is too big for every other situation.


The question(s)

1- is my equation correct? Dougal??
2- is the smaller unit (90-200 CFM) big enough? Does it have more in it than advertised?
3- is the larger unit doing anything at less than 200 CFM? Will it serve it's purpose?

Kevin
 
Agreed and yes this is all theoretical calculation. It's just that with a snorkel/ filter/ turbo/ intercooler there is a long path to the intake and the last thing I want to do is restrict the flow at the inlet from atmospheric. I have oversized all my tubing so far, perhaps I should do the same for the pre-cleaner :meh:. Trouble is, I would prefer the small unit - less chance of hitting it and it would look better IMO. Daily driving I should think I won't get over 2500 rpm and the whole point of the diesel and toybox is to wheel slow and steady.

I would greatly appreciate any other opinions and info from those in the know...

Kevin
 
I know what you mean, when I hammer it to 15psi I can really hear the air being sucked into the snorkel - like a giant hoover vacuum cleaner, I wonder if the piping is too much - but I need it for water fun.
 
lshobie said:
I know what you mean, when I hammer it to 15psi I can really hear the air being sucked into the snorkel - like a giant hoover vacuum cleaner, I wonder if the piping is too much - but I need it for water fun.
Click to expand...

Ask louis, My turbo almost sucked in my OEM plastic pipe before the air filter.
 
Awl_TEQ said:
Too funny!! - I forgot about this thread and did a search....... "3B CFM" only to find this thread :doh:

New related question - I have built myself a snorkel and I am looking at the Donaldson "Top Spin" pre-cleaner. Top Spin data link

Model #H002437 - rated for 90-200 CFM
Model #H002425 - rated for 200-450 CFM

The problem :- 200 CFM is a terrible spot for the cutoff between the two models. At 2220 RPM I should be pulling 200 CFM given the following equation.

(CID x RPM / 3456) x VE = CFM

CID = cubic inch displacment
VE = Volumetric Efficency factor - some say a turbo is 1.5

(207.5 x RPM /3456) x 1.5 = 200
RPM = 2220

That means (according to this gear ratio calculator) I will be at the limit of the smaller unit when traveling at 100 km/hr (63 mph) - or - put another way..... I will have restriction from the pre-cleaner when in low gears and higher rpm off road. At 200CFM they show a restriction of 4.5 inches of H2O (1.15 kPa).

It also means that the larger unit is too big for every other situation.


The question(s)

1- is my equation correct? Dougal??
2- is the smaller unit (90-200 CFM) big enough? Does it have more in it than advertised?
3- is the larger unit doing anything at less than 200 CFM? Will it serve it's purpose?

Kevin
Click to expand...

The factor for your turbo is a little high.
10psi gives you ~35% more air than no turbo, so at 100% VE the factor would be 1.35
But if you start by considering 80% for the non turbo motor and increase that by 1.35 you get 1.08.

So using 1.08 at 2200rpm you get:
207.5x2200/3456 x 1.08 = 143 cfm

Which is what I get doing it the long way around.
 
Thanks Dougal, I figured that factor was a little high. I searched the net for a good equation and found that there was a fair bit of conflicting "free" info out there. Actually finding diesel info rather than gasser was tough. The site I got the 1.5 factor from actually suggested anywhere from 1.5 to 3.0 :eek: - must be some guys running 30+ psi out there - daft buggers :hillbilly:

When I look at the stock toyota pre-cleaner one sees in photos it is physically around the size of the 90-200 cfm unit I am looking at - though that means nothing without comparing the internal structure. I believe I will get the smaller unit - worst case, if I find it doesn't flow enough I can put the bigger one on.

Thanks for the help guys!
 
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