Flame Arrestor Killed My Dyno Power
 

We ran my BBC on the Dyno yesterday after we made a few changes in the heads, and cam. This is a mild engine, but was making power up to about 5200 before it started dropping off. We were just not making enough power. After fooling around with a few things, I took the flame arrestor off and added a velocity stack. We got 30 HP on the next pull, and exhaust temps, which were not bad, dropped further. I'm running a standard 4 inch high by about 8 inch diameter arrestor. Anyone got any ideas what to use and still be compliant with the law?

9X5 K&N Marine.

Several others here have reported the same thing as you. Some have gone to the K&Ns on the dyno and did not see the decrease...

O K,
Who handles K&N Flame arrestors besides Rex Marine?

CheckmateF1 just went through this with his HP500, now a 509. He tried several different Flame Arrestors, and the K&N was byfar the best, and it looks the best too. Do a search for his results.

I got my K&N's from CP Performance

Me too.

30 hp !!??!! Holy crap... wheres that cp #

Was that on a efi or carb??

flat base?
 

Is the base of your flame arrestor flat, or does it have a smooth upward slope as it goes from the outside in towards the carb? I was told that a flat base creates turbulence at the carb - isn't the one on the HP500 a flat base? That's what I thought CheckmateF1 was dealing with.

I JUST (about an hour ago) ordered 2 flame arresors tonight. Online at 4filters.com. Prices were the same as everybody else, user freindly web site and 5 dollar shipping per order, not per item. Make sure you remember to order the breather tube kit with your arrestors if you need them. Good luck!

4filters.com......Am I reading their web site wrong?? Only $85 for a K&N filter?? Does that include the element?? Or is it just the stainless parts. And where do I find the breather adapters??? If I can get into this arrestor for under $100 I'd consider ordering one.

Do we have a group purchase discount forming? Sign me up!

I'm pretty sure thats everything. (I hope!) Go on the official K & N web site for the part number for the breather adapters. I just got the email back confirming the order $202 and change for everything...

Most of the marine filter kits come with a 2 3/4 X 9 element. You need the 5 inch element. You will then need to order the 6" breather tube adapters. Your total cost will be around 150-170 depending on who you order it through. I had the stainless top and bottom and had to order the taller element and the breather adapters. I ordered these through O'Reilly auto parts for less than 90 bucks no shipping. I think Advance auto parts is cheaper.(I found this out later!)

stevejohns
Yes the 30HP is real. We backed that figure up with another pull, so it was not a fluke. The carb is a 750 Q-jet and I had a new Graffig 8 inch dia 3inch high element. The base plate opening is actually 5 inchs at the carb throat, with a quick transition to accomadate the 8 inch element. Kook you may be correct about the turbulence. Remember this 30 HP is in a dyno cell with a lot of air movement. What would be the acutual lose in a confined engine compartment? Now I need to make sure I can get a new base to fit the Q-jet throat with as large a K&N element as I can use. And yes, I will require crankcase breather tube mounts that I see CP performance carries. I will check out this other supplier also.
Thanks Guys

Has anyone seen this type of drop on a smaller displacement motor? I've got a 355 in mine and it seems to run out of steam on the top end sooner than it was built for - but I'm also running the small stock (about 5" dia, 1" high) flame arrestor....

If anyone wants to sell one of their "larger" flame arrestors from a big block I'd like to try that and see if I pick up some HP!

What kind of hp and torque numbers were you getting Larry?

Hi Fred,
Good to hear from you. We got 440 HP and 498 ft lbs. We did not get a chance to run the engine at Katech, where the kid works. We have had it together for about 2 months and was waiting for dyno time. Katech is very busy with GM work so I went to an independent guy in the area. I wanted to get the tuning close, but I wanted to make sure everything was tight, before it went in the boat, and didn't end up with a bilge full of oil or something. Also I wanted to break the new cam in out of the boat. My son went through those heads, and there was no problem. We did however, install a lighter set of springs as we though the ones on the heads were on the heavy side. The engine ran well. I just think there is a little more there with some fooling around. The guy on the dyno ran it up to 5750 on one pull, and I was not pleased. What was this guy thinking? But no damage was done. How is your new boat?

Those numbers look great Larry....that 498ft lbs of torque will get it up and going are you done on the dyno or tweaking more?...My Excalibur 40 Hawk is running good....still cleaning up things on it, have spent 10 nights on it so far.....good thing it's got air on it.....it's a tank in the rough stuff and the best speed so far was with Waterfoul at the wheel half a tank of gas (100 some gallons) and 4 people on board it went 58mph on gps....lighten up the load and fuel with the right water should get 60 out of it...have another exhaust to put on it, its a ceter riser, the set on it now is the old riser in the rear set up with 3" tailpipes, the center-riser set with 4" tailpipes that I have should help it breath better, also I just don't want to tear it apart now to change it over....Fred

One other thing Larry, was that arrestor you were using the metal layer type unit?....Fred

Fred,
The engine is going in the boat now, and soon as I get it dressed. I'll play with a few things later. I would still like to try a 830 CFM Holley to see if what some people say is true.
Hey that Excalibur sounds like a real ship! If you bring it over to this side of the state, get in touch, we may get together.

Hey Larry, If you need a hand let me know, Also I have an alignment tool if you need it.

K&N makes a CG approved velocity stack flame arrestor I ran one on my 24' and it fit under the hatch with a Dart single plane intake.

Lee,
Thanks for the offer. The engine should be in the boat by the middle of next week.
I was going to order a 9x5 K&N over the internet. I think it will fit just fine under my hatch, but I'm not sure. My manifold is about an inch higher than stock, plus I am running a 1 inch spacer under the carb. It seems like I had plenty of room with that. But I won't know for sure untill the engine gets back in the boat, but I would like to not wait until then. Do you think I should gamble?

WK.. is te K+N setup you refer to the velocity stack with the K+N filter attached on top. I was looking at the KN website and assume thats the right one. Let me know if you could. sj

steve,
I went on the website that was suggested, 4filters.com and went into the Marine general application area. The one I am getting is the 59-3370.

Fred, the Gaffrig I was using is the standard wire mesh style.

Get the K&N with a velocity stack. When we were dynoing one of my 540's we went from an "open" carb to a K&N and picked up 3-4 hp! The K&N's were about $85 each with everything.
Also, It's good that you're being cautious, but unless you're running cast pistons; I don't think 5750rpms on the dyno is too much to be concerned with.

I WAS MEASURING UNDER MY SUN PAD...... THE SHORTEST STACK I CAN FIND IS 4.5 INCHES TALL. THAT LEAVES 1.5 INCHES TO THE UNDERSIDE OF THE DECK. THAT DOESNT SEEM LIKE ENUFF????

Due to the recent upgrades, my K&N's are going to be less than 1 inch from the underside of the hatch. I don't think this should matter performance wise, I just hope the deck doesn't flex and come down on the flame arrestor.

Performance wise, should I be concerned?

I was thinking about simply gutting my stock arresters and installing the approciate diameter K&N , that way I could add a little hieght and all my stock breather suff would still work. Doug