Extension boxes on a 302
 

Any of you guys from Baja know if they ever tested boxes on a 302? I get alot of blowout taking off running 30p 4 blades labbed with HO's. I'm pondering trying neutral boxes hoping to help on getting on plane as well as upper speeds. I have no idea where the X is setup on this boat, but I feel theres more to gain just don't know where to start.

I remember seeing a 302 tested in Powerboat
mag back in 96' that had stellings boxes on it, it also
had HP500's in it, boat ran 83 as I recall.

They also did a bunch of prop testing on it,
the X was probably lower than what you would
see now days, 4 blades weren't really "in style" yet they didn't have bravo 4 blades to test ( they didn't make them yet), they tested it with a few different aftermarket 4 blades and mirage + 3 blades.

Top speed wise, it was a tie between the mirage
and one of the sets of 4 blades, but the 4 blades outperformed them everywhere else.

If you're going to do neutral boxes, better
figure on short lowers to get the prop shaft height
where it needs to be.....something along the line
on what Jason did on his 29 O/L.

I have a 33 w/ boxes and a high X and I can still blow them
out any time I want to.

A couple of things that I've found that will
reduce the blowout is:

1. turning the props in...they tend to dig in rather than paddle.
2. Run 5 blades.

Or, you can always add spacers to lower the drives down.

What I've figured out, on my application, is that you
accelerate to no more than 3200 rpm, don't let it exceed
that til it rolls over, and the boat will come on plane every time
empty or full, 1 or 7 people, 4 or 5 blades, never
blows out, takes a little bit longer but it always works.

Tabs down?

Doesnt matter.

If you don't break the 3200 RPM rule
that's all that matters.

I have 380 K Planes, and I leave them at "3"
( which is basically parellel to the bottom of the boat)
at all times.

The boat runs fastest at this setting too.

Thats where I run my tabs as well, but I just got the feeling that my drives weren't in clean water and I was blowing out...I'll play with it a little more in the spring.. I can get it on plane no problem using tabs, but I feel I shouldn't have to...Its almost like it just sits there and digs a hole then goes up on plane...

And to think a few months ago you were going to sell it and now you are trying to think what upgrades you are going to do to it.

Oh it's always been forsale, but with current economy I'm not taking a bath on it. I quit trying to sell it back in March of 08. After putting the HO's and windscreen on it I've sorta decided to make it more mine until the economy picks up where the prices come back up to get the money out of it...

just remember if you go neutral boxes it puts the drives deeper in the water so like JT said you will need to put lowers on it to bring the X up just a bit.. I have my prop shafts right at about 4.25 and it works really well with the boxes.. Although I think if I wanted to I could put lowers on mine and still be good to go.. JT's right about the 3200 r's though when coming up on plane!!!!:ernaehrung004::ernaehrung004:

If you go with the boxes bring it down and I'll help you put them on..

And I'll watch!!:ernaehrung004::ernaehrung004:

Jeff,
What I'm wondering is if they aren't deep enough...Latham makes a 7" extension box and pondering if that might be the answer????I know nothing about this, but I don't want to have to start buying lowers as well...At that point I'm better off to look for more HP..

http://www.lathammarine.com/extension-boxes7.htm