v4 turning 6800 rpm

[chynewalkr]

well i finally got a working tach in my boat and found to my suprise its turning 6800 rpm at wot at 61mph. this is a stock 115 non bubble back crossflow. 6" setback 3" below the pad on a hydrostream vandal

my questions:

is this ok?

should i be going faster speed wise?

should i look for a 25 srx ? ( im using a 23 srx and 22 raker they both do about the same speed and rpm)

[chris_lacey]

No such thing as a 25P V4 SRX (actually they were SST-RX). You can get a 24P Raker for the V4 or have a 24 or 26 merc inline chopper rehubbed for OMC.

[JWTjr.]

you should be:

1) higher on transom (propshaft even with pad or within 1/4"--possibly will have to close off top water intakes and modify lower ones, monitor water pressure and temperature to ensure adequate water)

2) turning larger propeller (26" small-ear Mercury Chopper will work well rehubbed for V4, or have a 27" SRX cut down to 14" diameter and rehubbed for a V4; if your hull is lighter, a solid hub 27" OMC cleaver will work also but these are low-rake and therefore will not lift bow well without lots of setback and all extra weight removed from in front of boat's CG)

3) turning that larger prop 6000-6200 rpm @ approx. 66-68 mph. Change to a 140 powerhead and turn it 6600-6800 for speeds of 74-76 mph.

JWTjr.

[stokernick]

is your project back from the South and what`s the result??

[Paul Vaillancourt]

Seems like your getting too much prop slip. You should be able to do 61mph with that prop at around 6000 rpm, at .9 or 90% prop slippage efficiency.

With that prop you will probably not be able to go any faster than high 50's to low 60's, are you sure that the tach is accurate? I have never been able to rev any of my stock motors that high.

The prop that works best for me, that i have, is a 26 pitch mazco Re3, It got me 65 @ 5500rpm using a 1993 115 evinrude on a viper, and 61 @ 5500 with a 1973 135 evinrude on same boat. The 1973 has a less efficient gear case than the 1993, the 1993 has a nose cone on it and that is why i think that the boat went faster with the 1993.

[squarles]

I've got a 24 raker on my 115 and it works great. Turns 5800 at 60mph. I've got 3 1/2" of static set back and the motor is mounted through the top holes in the bracket. I've got a jack plate but haven't installed it yet. My boat is probably heavier than your Vandal. My 20 raker I use for skiing and it turns 6300 and slips more speed is only 53. I drilled the vent holes to 1/2" on the 24 and the hole shot is much better.

Stephen

[Laker]

What year is the motor?
Older models have different gears and bullet design.

[chynewalkr]

paul, the tach is a brand new livorsi 8000 rpm unit. so im sure its working (or it at least looks accurate while cruising and idle)

JWTjr., as for raising the motor up, im going to try that this weekend now that i have a h2o gage, i plugged the 2 top holes already.

laker, the motor is a 1984 , so i assume it has the 2:1 gears and definitly has the pointyer bullet.

the boat is extremely light and has tons of bow lift, so much lift an extra passenger only slows the boat by 2-3mph on top

didnt omc make a 25 srx 14" in dia.? that should fit, i borrowed a 14 x 24 raker that was rehubbed to 13 spline and it fit under the vent plate.

[Rickracer]

6" Bob's hyd jack, light fuel load. Turned a 24 Raker 8300 rpms, no GPS, but calculated out to 80+ .

[JWTjr.]

Yes OMC did make a 14" x 25" SRX. Hard to find these days. 25" or 27" you'll need to have it worked in order for it to work well. The best at these is John Janaky (DAH Pro-Pellers, Burlington, WI). He learned from the best. The 25" is not nearly as good a prop as the 27" though, and you surely can turn a 27". That's a 1983 cowl on the outboard in your photo, no matter as the 83/84 115s are the same.

If you really want that hull to go, you should swap to 140 parts, blueprint the bottom, and remove those windshields (save them they're rare). I ran one of these in JP then later as a lake racer with a hopped up 140. As a stock JP it ran high 70s down the straights with a circle boat setup, and with a mod motor 84+ set up for top speed.

JWTjr.

[chynewalkr]

jwtjr

i have the parts to make it a 140 (heads 1-3/8 carbs and the bubble, no stuffers though) ill do the conversion once the weather turns.

Yes i guess the motor is an 83, i get confused between the boat and motor since the years are close. i put 85 stickers on the cowl

ive dealt with john before and have nothing but great things to say about him. maybe ill give him a call, he's usually got some obscure stuff over there

unfortunatly one of the windshields was cracked when i got the boat so i had too cut them down, on the other hand they look better smaller and flex less at speed.

i raised the motor so the propshaft is 1-1/2" below the pad, and ill try it out tommorow

[Ted Stryker]

Don't forget about the OMC Streaker.. Had a 23" on a 16' Allison(slightly mod 140) and it ran really well... Never had a chance to get hard #'s from it, but my other props were running me 70 in the 1/8 mile- the Streaker was definitely stronger..

[chynewalkr]

with the propshaft 1-1/2 below the pad, i ended up loosing 1 mph?? and my hole shot sucks with another person in the boat.

my water pressure was still very good though. on the bright side the boat chine walks much less, almost not at all.

[Joe Raimondo]

Thats a lot of RPM out of a stock motor.What are you guys doing to keep the rev.limiters from kicking in.I have a V-4 115 Yamaha what kind of RPM do you think it could turn without harm ?

[chynewalkr]

my engine doesnt have a rev. limiter, and it suprises me that it turns that many rpms.

i think the yamaha motors have 1 wire you can disconnect to remove the limiter.