Extension Boxes
 

I have a 29 Outlaw with twin 502's. With it stock on the Gaffrig speedo it did 82, added Imco Power Flow manifolds and RPM kits hit 86. Now I just added Crane Roller Rockers 170 with Keith Eickert 2 piece valve covers and hit 88. I'm thinking of going with Extension Boxes to get a bit more out of it. does anybody here have them on a 29 to give me some feed back. If so did you go with shorter drives aswell?

WOW!
 

That is impressive speed. There is someone on this board who had a 29 Outlaw with extension boxes. Forget who. However I thought he picked a few mph with his. Before long you'll get an answer.

What kind of RPM's are you
turning on the top end ???
What size props are you running ???

Don't get your hopes on the speedo readings,
my gaffrig is off (to the bad side) 3 to 4 mph
on the top end as compared to my gps.

I too have thought about adding extension
boxes, but I really don't want to dump any
more money in a boat I'm only going to
keep for a couple more years.

If you x dimension is relatively low,
the transom may have to be replaced
and recut to get the drives high enough
to see any gains

Shorter drives is the trick I'm thinking of
trying, theres alot less involved,( different steering rams
wing plates, raising and moving the motor mounts)
if they don't work, I think their more marketable.

just my .02
jt

I ran Gameman's 29 with 502's at last years Lake Travis Poker run and top speed with 502's was 76 gps, it previously had 500 efi's and ran 80 or 81

I'm running 27 Mirage Plus's @ 4900 RPM.

I think your speedo is off. Not trying to bust your bubble. Those speeds at that RPM would be difficult, especially with the added mods you have done.

I agree that your speedo is off quite a bit.

27" Prop Spinning 4900 RPM thru 1.5:1 drives gives you a speed of 83.5 MPH with Zero Slip. Anything below 7% slip in my experience is starting to get very efficient. 7% slip would put you at 77.67 MPH.

I would struggle to get below 10% slip with my 272.

27/12=2.25 ft per Rev.
2.25/1.5 x 4900 x 60 / 5280 = 83.52 MPH x .93 = 77.67 MPH

Note: This is assuming you have 1.5:1 drives

Alrighty then....I think someone on the board has his zippy down. 82 with 502's.... I have a 02' 29 w/496's that runs 93*on the bull$hit meter (with fresh batteries, ofcourse). I waxed the bottom with turtle wax and gained 17 mph.


* Boat speeds subject to change depending on the vehicle towing it. :D :eek:

Picked up 2 mph by adding 1:70 rocker arms?

I'm not ragging on anyone, it just seems a little optimistic.

Hi, my name is Tim. I have twin 7.4s detuned to keep my 302 under 100 MPH (at least until the Turtle wax wears off).

I never said that my speedo was accurate just letting you guys now what it says with the mods I've done. My whole point of this thread was to see what kind of gains anybody's got with extension boxes cause that might be my next project. Would appreciate a response by someone who has tried them.

Don't sweat it John. Just breakin' your balls.