pitts1313

Does anyone know for sure if this stock merc flame arrestor will support 830 CFM? I have searched on forums till blue in the face. Thought about taking some of the baffles out, but I like living and don't want to be made fun of for blowing a boat up. I don't have clearance for 10" diameter flame arrestor and the flame arrestor is already at the hatch bottom. So, anyone know anything about the 8" dia x 2" height Merc Flame Arrestor CFM flow shown below?

SB

iTrader: (1)

2" has me concerned also. A 9X4 (2.75" element height) K&N Arrestor was a restricition on a mild 330-350hp 5.7 .

Any vac port on the carb ? If so, hook up a vacuum guage to it and report back what the vacuum is at WOT and top rpm. This will tell us the restriction if any.

HTRDLNCN

next time you go out make two back to back WOT runs,
one with aresstors on
one with them off,
compare speeds
this will tell you if they are hurting or not.

SB

iTrader: (1)

Not necessarily as a restricted air filter/flame arrestor will typically make the A/F ratio rich. Better arrestors could lean out the A/F and cause you to lose speed. Depending if the tune is right on now or not.

So, be careful with that.

pitts1313

I'm not too knowledgeable on carbs. My carb has mechanical secondaries, no vacuum lines. Does that mean i don't have a vacuum port?

I am surprised at the K&N restrictive. I can find just as many responses that they work better than stock and i can find just as many post that there is no difference btw the K&N and a stock flame arrestor.

Can I make a run with no flame arrestors and see if it makes a difference? or will the air be too turbulent in the engine compartment for the carbs to perform correctly?

HTRDLNCN

seeing as he hasnt checked AF it could be rich,lean,who knows,
basically taking arrestors off should do one of three things
1, run same / aresstors fine
2. run better / needs btter arrestors
3. slow down / needs arrestors and tune carbs

My philosophy is to always have an af meter even on stock setups,
just gives me a an extra level of information I normally wouldnt have

SB

iTrader: (1)

I did a bunch of back to back to back to back :smile: testing same afternoon, same water. Vac guage then testing with/without arrestor. Tuning carb for the change. Saw over 1mph without vs with.

Again, not saying anything about K&N's in general. This was a 9X4 (2.75" element height) on a 330-350hp SBC/Alpha equipped small/lightweight boat. BG650 Carb had choke tower but no choke flap.

===============================================
Choke tower to flame arrestor top and float bowl vent to flame arrestor top can influence things when too close. It's not always about airflow.

HTRDLNCN

also floor of arrestor (flat,concave,etc) can change things up as well

pitts1313

yep, read this too! read flat causes turblence.

Williams Carbs tuned everything up when they installed the carbs and questioned the size of the arrestor and said a larger one might help. Hence me asking the flow cfm of this arrestor. They have offered to lake tune the carbs after I run it awhile. I have no issues with carbs, just want to make sure I am not missing out on 1 mph or even a 1/2 mph!

picklenjim

Think you could squeeze a 3" x 8" under there? Here's a couple links to some.

http://www.rexmar.com/page193.html

http://www.cpperformance.com/c-479-flame-arrestors.aspx