Velocity stack

**ShadowFlier** · 10-22-2019, 07:44 PM

I made my own this year. So far I haven't noticed a difference but that's because I have the face plate on the cowl still. My plan was to cut a hole in the front like the drag guys to have a direct path for the air to flow but I didn't do that this year, maybe next.

I'm no expert but air travels around an object before it gets to it. Watch cars in smoke tunnels how the air never reaches the front it just goes around. My theory was to cut a big hole in the front to eliminate that effect and have the air travel straight into the stacks. When I ran with no cowl I honestly noticed a big difference in mid to hi rpm acceleration.

**Merc 2.5** · 10-22-2019, 07:50 PM

Originally Posted by ShadowFlier

I made my own this year. So far I haven't noticed a difference but that's because I have the face plate on the cowl still. My plan was to cut a hole in the front like the drag guys to have a direct path for the air to flow but I didn't do that this year, maybe next.

I'm no expert but air travels around an object before it gets to it. Watch cars in smoke tunnels how the air never reaches the front it just goes around. My theory was to cut a big hole in the front to eliminate that effect and have the air travel straight into the stacks. When I ran with no cowl I honestly noticed a big difference in mid to hi rpm acceleration.

Damn what sum stacks haha. I wasnt lookin for power this way. just tryin make look little better when cowl comes off. I'll get a 260 cowl b4 long and I'll have options , I've done all I can with this motor without doin more port work. so I'm gonna build another 1 for the speed boat and leave this one on bass boat. Would like to see a b4 and after run on video or sumthin to get a comparison since u say it helped urs

**ShadowFlier** · 10-23-2019, 04:03 AM

Originally Posted by Merc 2.5

Damn what sum stacks haha. I wasnt lookin for power this way. just tryin make look little better when cowl comes off. I'll get a 260 cowl b4 long and I'll have options , I've done all I can with this motor without doin more port work. so I'm gonna build another 1 for the speed boat and leave this one on bass boat. Would like to see a b4 and after run on video or sumthin to get a comparison since u say it helped urs

It'll have to wait until next year, boats all put away but with no cowl the acceleration was a lot faster and I picked up a couple hundred rpm's at the top end

**bullet123** · 10-23-2019, 04:29 AM

Probably running lean with cowl off. Will run better, but wont last long IMO

**powerabout** · 10-23-2019, 04:56 AM

The bell mouth is all you need, anything else will alter fueling and torque at some rpm.
You can get a gain somewhere but a loss somewhere else.

**Merc 2.5** · 10-23-2019, 04:59 PM

Instead of starting new thread I'll ask here
Since weather coolin off. I wondering bout jetting. Cooler weather means jet down a size or (can) jet down a size? Or is it up a size ? I thought it was down. just curious, I wanna try pull few more ponies (not my reason for stacks) with cranking up timin and takin out fuel and see if I can get a seat of pants difference, of course I'll b checkin wash,plugs, etc. I've been runnin on the really safe side so I know power to b had , by next spring I'll put it back to very safe. I also found a post by t-rex I'd like to repost if u can figure it out

**FORBESAUTO** · 10-23-2019, 05:27 PM

Colder, more dense air requires more fuel. From my experience messing with carbed heavier bass boats, I make more power and turn a few more rpms a little on rich side. Leaner hasn’t proved to be meaner for me except maybe right off idle, they respond a little quicker coming off a leaner idle.

**Merc 2.5** · 10-23-2019, 05:45 PM

I cant find that damn article again to save my life!! So trex goes on to say he had the xri 200 which was still efi (mine carb) he moved pump filter to boat to open up room in cowl then vented and directed air by modding cowl and gained 600 rpm on top from that alone. Now I wouldnt b posting this unless I read it. and comin from him has just got me thinkin bout my cowl. (Same xri) it's perfect for modded for more air. He didnt have to open it up alot. Just redirect it. U no my luck I'll do it and wont c a difference but I'll never know if I dont , maybe leave my really safe jetting alone and add more air from cowl. I cant run air box so its open inside only air gets thru now is thru 6 1/2in holes behind the front cover on cowl, if I was to make the luvers functional it would have to add air?

**Motv18** · 10-24-2019, 11:12 AM

Cool air can gain you 5-600 rpm, some models used to come with a cold weather stop lever to keep rpm down or you bought a winter prop.

I dont remember rejeting though we always moved the lever or swapped props, much easier to go back and forth that way.

**Merc 2.5** · 10-24-2019, 04:15 PM

I dont fish or run in the rain so few extra (holes) n cowl wont hurt me none , with the way this cowl is set up ,a few more 1/2in holes cant do nutin but help , I'm also gonna find sumthin of sorts to (filter) the air goin in carbs , still tryin figure out what to use here

**mrichartz** · 10-24-2019, 06:20 PM

You don't fish? Is that your boat in signature why the trolling motor?
For filter Frogzkin mesh on the cowl inside then a light metal mesh to help hold it in place.. it is strong enough to make a cover over the carbs too but I just stuck w the cowl.
It's what they use on snowmobiles etc

**Merc 2.5** · 10-24-2019, 06:54 PM

Yes I fish alot. Where I fish I can see rain comin long way off. I know when get outta dodge. Yes that skin is what I need. great idea!
Guess I should say I haven't done any tourney fishin where if have to b in rain

**mrichartz** · 10-24-2019, 06:59 PM

Originally Posted by Merc 2.5

Yes I fish alot. Where I fish I can see rain comin long way off. I know when get outta dodge. Yes that skin is what I need. great idea!
Guess I should say I haven't done any tourney fishin where if have to b in rain

Oh you don't fish in the rain..got it