Speed

[diligaf]

Hello guys, I am new to this forum and had a question. I currently have a 96 Baja 232 7.4 300 hp carburated bravo one, turning a 14.5 23P mirage plus at 4,200 rpms WOT. and would like to know if a LARGER flame arrestor would allow better breathing therefore increasing horsepower and RPM's. My problem is that I dont want to decrease pitch to gain RPM's because I wont get any more top speed. I want to run my current prop at about 4,500 to get the extra 3 or 4 mph.. How about suggestions for horsepower or speed increases... Thanks in advance... Chris

[Magic Sandbar]

It is very important that the engine runs at, or near max RPM @ WOT. Check your manuel or with Mercruiser for what the max RPM is for your engine. If an engine is running 500 RPM to slow @ WOT you could cause some serious problems with heat and carbon build up. You may want to try a 22 pitch 4 blade Bravo I prop. As far as a flame arrestor, the K&N will be the best for efficancy and HP gains. Don't get to excited, dyno tests of motors with a stock flame arrestor verses no arrestor have only shown a 1-2 hp increase. With a 1-2 hp increase you probably won't see any noticeable speed increase.

[spectras only]

diligaf,sounds like your engine turning too slow for your BBC,try a different prop.I would start with a smaller dia ,since you have the low output engine.Your air filter is fine if it's the barbron type,since it's see trough there's no restriction at all.Try to remove it for a short run and observe your RPM.I'll bet there won't be a difference.I run a K@N in my car ,because it's better than the paper type wich has more restriction.Most performance boats come with the wire mesh type flame arrestors that are maintenance free.The K@N is also lifetime service,bit require cleaning and recharging.Why bother with it? If I had some shares of K@N, I would strongly recommended for you,hehe

[diligaf]

Thanks guys, The WOT For my motor is 4,200 - 4,600 rpm's. I am running just under that at 4,150. I would like to try and get them up to around 4,450 to get the extra HP and speed. I read somewhere that 1/4 inch of pitch is equal to about 100 rpms, is this correct ???. I was thinking of trying a 13.75 Diameter 23p prop. If that number is correct I should gain about 200-300 rpm's ???. What do you think ?.

[diligaf]

oops, I meant 1/4 inch of DIAMETER is = 100 rpm's.

[StingRay]

If you're running a 23P Mirage and you're at 4200 rips you are over propped period. "If" the Mirage is factory out of the box you could have it blueprinted which is exacting the blades to identical pitch and thinning of the blades themselves. The thinner blades will allow it to spin faster in the water due to less resistance. You could feasibly get 150-200 rips more than now and OBTW, more speed. OR, pitch it down to 22, blueprint it AND add extra cup.
Ideally you want max performance with the rev gauge reading 4500 and no less. This is all conventional wisdom and will take some experimentation on your part. Most prop shops will let you use loaner props with a deposit to figure out your needs before investing. Or borrow a buddy's prop and try it. Good luck.... http://free.***boat.net/ubb/cool.gif
[This message has been edited by StingRay (edited May 24, 2001).]

[ponponracing]

No doubt in my mind that a 21 Mirage Plus will greatly improve your speed. It's important that you keep your max. rpm in the manufacturer recommended rpm band.
Before trying a fancy prop., try a good stock one, never repaired ,thinned or modified.

[diligaf]

Stingray,,, Thanks for the advice, I have been boating for most of my 31 year life. Like I said mostly with small cuddy's and stuff. I am REALLLLLY enjoying my new toy. I am doing a lot of reading and research trying to get my boat up to peak performance. The Mirage has some serious BLOW OUT problems while making sharp turns, need to throttle way back and then apply. I saw a lot of posts about people reccomending the bravo prop. I was thinking that if I went with a 22p 4 blade bravo I would gain the required rpm's as well as a better hole-shot and also much better cornering performance, and I have heard that the loss of speed w/ the bravo is NONE...... what do you think

[diligaf]

Oh, by the way, I do have the old style RESTRICTED flame arrestor, What do you guys reccomend for an up-grade, and what size to I order ??? I believe its the Webber 4bbl..

[formula93]

get a K&N Filter charger, it flows a lot more air....