Powerboat Forums at SpeedWake banner
Cancel
Create thread New Forums

Air Filters Restrictive

Jump to Latest
1 - 20 of 38 Posts
G

gilla

· Premium Member
Joined
·
4,913 Posts
Discussion starter · #1 ·
Most high HP engines in the racing and automotive world have bigger air intake/air filters than on boat motors. Are boaters restricting hp due to the small air intake filters? CFM-What you think?

Got more room-why not use it?
 

Attachments

#3 ·
I would be surprised if you would see any difference with just a different flame arrestor. I think in combination with something else perhaps but, Merc seems to do a pretty good job of getting the free ponies it can with thier systems...D
 
#4 ·
Measure restriction by vacuum. If there is more vacuum behind a piece than in front of it there is a restriction. So, you'd have to tap a hole and install a vacuum/psi guage behind on the flame arrestor and in front of the throttle body to see if there is more or less restriction

Flow bench data is usually given on the piece - not the whole system put together.

Meaning - well, example.

Say you here : "200cfm more than stock"

Well, if the arrestor, throttle body, intake manifold, cylinder head are mounted on a flow bench with the valve lifted at the CAMSHAFT'S highest lift, and both flame arrestors are tried, and the end result shows no difference, then your motor probably will not see any difference.

The only companies that flow test this way are those like us that only care about what actually goes into and out of the combustion chamber with everything bolted together vs one piece vs the other.
 
#6 ·
gilla said:
Most high HP engines in the racing and automotive world have bigger air intake/air filters than on boat motors. Are boaters restricting hp due to the small air intake filters? CFM-What you think?

Got more room-why not use it?
Click to expand...
Back to the basic question, yes, many boats are losing hp due to flame arrestor flow and other airflow characteristics.

Which?

Usually carbureted ones.

Why?

1) Restriction to flow and airflow qualities.

A carburetor has to meter flow thru the use of incoming air. If the air is turbulent going into the carburetor then the air bleeds and boosters may not be metering air or fuel correctly. A prime example is the use of velocity stacks or Hood Scoops, especiallyu hood scoops that are sealed off to the top of the carb. Turbulent flow can really screw up the metering of the carb and cause some majorly bad drivability/power/etc issues.

With carbs, the bigger the better with a well designed base will usually solve both issues. Enough flow to meet engine demands and smooth entry of airflow so that the carb can do it's job correctly.

FI does not have boosters or airbleeds that need special attention like carbs do, so in fact, it is easier to have a airfilter or flame arrestor do its job.

For carburetors, there are devices that work real well for applications that have the correctly sized carburetor - K&N stubstack, K&N Air Flow Control, smoothly + correctly designed drop bases, etc, etc.

For carburetors, there are devices that work real well for applications that have too small of a sized carburetor : K&N Flow Control, Air Hat, etc, etc.

Possibly more to come as I have more time for this subject. :bigsmile:
 
#7 ·
gilla said:
Can't you work it backwards-cu in x rpm ? to find what you need through the filter
Click to expand...
For a baseline mathematics guess, yes.

Again, what a part, by itself, measured on a Flow Bench does not always tell you the whole story.

Everything must work together.

Great analogy? Here's a try.

If you married the best woman on earth and your personality doesn't fit well at all with her's - is she really going to be the best wife for you?
 
#8 ·
The easiest way is to make a baseline run, record tach readings and meaured mile or GPS speed. Do the same exact run asap with the arrestor off and look for diffs. Then do the same with the hatch off or slightly open (secured with ropes or something). Most carbed boats Ive tried this on saw an increase of 100-200 rpm from one or the other, especially stockers. The plate type flame arrestors on the older 7.4's are really bad.
 
Discussion starter · #9 ·
Nope.

I disagree:
you will be happier with her than any other women

and, you know that part of the equation is as good as it can be, whether you work on the other parts or not.

It should be easy to get the best AF possible, where the perfect combination throughout the whole engine is much more difficult and probably never 100 percent attainable.

So, how much CFM does a 502 CI engine need at 5300 rpm to run at optimum efficiency?
 
#10 ·
One of the magazines did a test on several different flame arrestors a few months back. (all carbs) Cant remember what they said or which mag it was. So I guess I'm not much help. It was either Family & Performance or maybe Hotboat.
 
Discussion starter · #12 ·
Making some assumptions here:
If an engine is an air pump-then the first limitation is how much air it can intake and process, with performance based on the amout of air it can cycle each stroke. I know all the other things have to be right. CI is the volume each cyl can hold each stroke x 8 x rpm should get the minimum cfm needed. Then cr is probably a factor.
I know all has to be matched-as many sbc ran better with 750 to 780 carbs than they did with 850's.

An F1 engine, although smaller ci, but with rpm of 18,000 would still have the same formula apply?

Try this.

Eight buckets filled and dumped with air at msl pressure, 5200 time in one min would take how many CFM?
 
#13 ·
Carbs go by a different rule. This is where math can sometimes screw you.

A carb has to meter fuel - it is the air that goes thru the boosters that pulls the fuel out.

You can have the correct cfm carb, but if it's metering is incorrect for it's application then your power, effeciency, and drivability can be killed.

Why are their are so many Holley carb's available with CFM ratings from 600, 650, 700, 750,800,850? The type of motor it's going on and the differences in metering that

FI is different because you program when/where/how much. Throttle bodies can be sized different because of this.

Would you run a 1000cfm or 1200cfm carb on a 500hp small block? No. The carb would be a pig. Yet, with proper programming a 1000cfm or 1200cfm throttle body may make the best power - even though mathmatically it makes no sense.

Here we get into pressure drop and vacuum under the throttle body/carb. 4bbl carbs and all throttle bodies are typically Flow Benched at 1.5"HG of vacuum so one can be compared to the next.

Is the motor they are going on going to be at 1.5"HG at WOT and top rpm? Probably not. A reading under this will pull less air thru the tbody/carb, while a reading over this will pull more air thru the tbody/carb.

So, since the 2bbl's are flowed at 3.0"HG, does that 4412 500cfm compare directly to a, say, 600cfm 4bbl carb flowed at 1.5HG" . Not really.

I hope I'm helping here. There is more to this but I'll stop for a few, to see if it's making sense to you.
 
#14 ·
this really makes me think.......... :lick:
i called k and n today, the guy took my measurements of my k&n filter and told me it only flowed 430-450 cfm.
now my motor flowed around 730 cfmon the dyno....

NOW THAT sounds like a restriction to me. I thought i needed to make the change but now i know, i suppose i could make a run with and without at the same time to see the differences.

what do you smart guys think??? :confused: might there be a few rpm there????

i will be checking vacuum under the carb next time out to see what the difference is.

CFM, i know, i should of listened before.......im all ears now!!!

kevin
 
#15 ·
yeah, but i think mine was only about 2.75-3" tall.
they said 430-450 cfm, the E-3650 element would replace it and flow 868cfm. they did not recommend using it because it wasnot stamped USCG and you can only get the entire setup not just the element but im gonna try to see what the difference is!!
 
#17 ·
I saw a K&N lose 50hp on a Chassis dyno :dead: It was on a Mustang 5.0. :bigsmile: :bigsmile:

Ok, so it had 10psi boost and 347cid with AFR heads.

It had a huge cone type filter and we never imagined it was this restrictive.

Anyone notice ATI stopped using the cone filters on the MPI and some other set-ups? Hmmm....

We are all shocked for a few days.
======================================

Anyway - go as big as you can fit.

If you can use a 14" diameter element - do it!

I have a spare 59-3414.
14" D
4" Element Height
5.62" Total Height

I have the same exact one for my 502. I bought the second for a customer, but he cheaped out. Don't ask. :confused1
 
#18 ·
Stingray69 said:
Kevin,

Your flame arrestor wouldn't have been about 9" diameter, stainless top and bottom with about 4" of filter, would it?:shocked:

450cfm?
Click to expand...
That's probably the #59-3364.
Pretty funny, actually not.
K&N catalog recommends it for everything from 4.3's to Volvos' DPX 600. :shocked:

But, for Mercruiser's HP500 they recommend:
59-3370:
9" Diameter
5.0" Elelment Height
6.75" Total Height
======================================

SO, again, if you can't go up, go wide. '
In both height and diameter, go as friggin' big as you can. :bigsmile: :bigsmile: :bigsmile: :bigsmile:
 
#19 ·
K&N states their flow data is at 1.5"HG. Same as 4bbls are rated at.

Sting - did you say you wanted a teller intake? I have that HV2000 sitting here - the one I was first testing.
:bigsmile: :bigsmile: Just joking.
 
1 - 20 of 38 Posts
About this Discussion
37 Replies
10 Participants
Last post:
cfm
Powerboat Forums at SpeedWake
posts
921K
members
19K
Since
2002
A forum community dedicated to Powerboat owners and enthusiasts. Come join the discussion about performance, modifications, classifieds, troubleshooting, maintenance, and more!
Full Forum Listing
Explore Our Forums
General Boating Discussions Powerquest News Articles