AWOL

Both a 59-3364 K&N and removing the majority of the mesh of the gaffrig flame arrestor yielded the similar results. ~200rpm loss for the K&N, and ~300rpm for the mesh removal. Im just trying to understand the logic of whats happening when improving the flow to the carb/engine and why it is having negative affects. With more restriction, it's happier, so that must mean its lean to begin with?

SB

iTrader: (1)

Very well could be. Test and test. This is what makes some boats/cars fastet than others.

One if examples: Mild 350 boat I did this with:
Almost 2mph gain taking off 10x3 K&N
3 mph gain removing slip in mufflers.( this required 2+ jets larger when muff’s removed)
5-7mph gain installing shorter Alpha Ss outdrive.

Small boat. All changes usually result in minus or plus mph change .

drumerjb

​​​​​​ I'd be jetting based on new air flow if that's the air flow you want. I'd be bringing outside air in at all times never inside warm air.

articfriends

iTrader: (1)

When I dynoed my 462 cu inch pontiac in my transam, we saw 580 ish hp, with k/n 3 x 9 we saw a 40 plus hp loss and map reading at manifold went from 97.5 to sub 95 , closer to 94

BUP

iTrader: (9)

Also intake manifolds play a big role in fuel distribution per each cylinder. Depending on the intake manifold AFR s per each cylinder can be all over the place.

The intake runners with a carb application, each runner does not have the exact same nor equal fuel distribution running thru them.

If you were to put O2 s in EACH exhaust tube and monitor the AFR s, one would see the big differences for those numbers per each cylinder especially on a poorly designed Intake.

Some carb spacers can help for trying to equalize that, not completely but help.

articfriends

iTrader: (1)

I see this on my dyno with 10 o2 sensors all the time, victor junior, super victor and dart intakes are no exception either. When I dyno tune a MEFI engine I also see over 2 points afr spread from cylinder to cylinder, I often switch to "double firing" the injectors on the black motors as this helps to even up the tune, I WOULDN'T, however , advise doing it if you were only bench tuning or on water tuning a mefi controlled engine as the injector dead band/latency has to be accounted for when its fired every cycle vs every other cycle, Smitty

SB

iTrader: (1)

Yup, The K&N 3364 is what cost almost 2mph (vs nothing on carb )on the mild sbc boat I mentioned. It is prob the most popular K+N used on boats.

But again, this boat responds either - or + to everything. Some boats don’t.

ThisIsLivin

When I selected my K&N I called the factory and asked what the filters were rated at as far as flow. I'm running a modified Pro Systems (Holley) 950 on a 524cu. in. at up to 6000rpm. Based on that the smallest filter I could go with to keep the pressure drop to near zero is the 14"x4". The typical K&N would pull over 2" of vacuum. Most of the stuff out there is designed for the old 330 454's or smaller.

Rookie

iTrader: (4)

Please refer to post #6. Snake oil...

AWOL

So, just for follow up. Adding more jet with the majority of the flame arrestors screen off (same amount removed as before) reduced rpm and speed further. I think I need to go the other way with the jetting and reduce the jets, and that the increased flow is actually making it rich by increasing the signal and drawing more fuel.

I talked with a local performance shop guy and proposed this same hypothetical and without me saying anything, he indicated it would be richer. I even stumbled upon an old thread here from a dyno session where the flame arrestor leaned the motor out a full point vs no flame arrestor.

To put this to rest, I purchased an AFR meter and will be having the risers sealed and o2 bungs welded in to find out whats going on for sure. It's such a drastic change that I want to figure this out.