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

thats a nice box but they stick you with there steering that should be a option, when I put my 2''shortie on I picked 8mph with a carb change too went from bg 850 to nickerson 1050 I was happy. my x went from 7 1/2 to 5 1/2 I think or it was 7 to 5 ha hah. works good can't wait for the new power 1050hp

That box is 8000.00 without the steering as I already have Latham Steering on my boat, so this isn't a option..I'm going to check all my measurements first and see where I'm at. If its too high I'll put 1/2" spacers on it and see where I'm at there...I just don't want to loose speed in the process as this is another one of my problems the boat isn't running the speeds it should with HO's...Still have somemore prop testing to do in the spring as well.

Thanks for the replies.

Irish, I did all this over the summer on my 342. I went with Stellings which some love and some hate... But I wanted the adjustability. Either way, you have to buy new tops for your latham steering to keep your present rams. Then, becasue of the way they are connected, you need a new tie bar too $1600 when it is all said & done. You can always do IMCO and use shorties but I think shorties slow the boat down under 85 mph because they dont give enough bow lift like stock merc lowers. Also, the cost of 2 shorties takes the project up another $6000. FLEG is right though - 4.25 is the area you need to be for x dimention. FYI - If you go with the Stellings, PM me there are a half dozen things you need to be prepared for.

I had a 302 and extention boxes would do wonders for it... Heck, my 342 feels like a different boat.

Keith,
Did you get it dialed in yet ?

Did you change the X when you pot the HO's in? What is your current centerline? if it is around 7 to 8in - that is stock... If you werent blowing out with the Mags what has changed.

Yeah, finally - I might even go higher and/or try 5 blades...

It wasnt the boxes or the depth. The u-joints from the Stellings boxes were setting off the knock sensor and retarding my timing 20 degrees. I had the ECU's reprogrammed from Whipple to stage 2 and it slightly desensitized the knock sensors. Now it is at 76MPH and still some prop stuff to try. Took me 6 damn months to find that problem with 4 guys and the Merc computer.

I didn't change anything. It has always blown out I'm just trying to correct it for once.

There is a fine line between blow out and another 1/2 to 1 inch and you are decreasing top end. Try 5 blades from BBlades? Or let me know, I have a set of 1/2 inch spacers you can borrow for your current set up. The IMCO lowers slowed me down. Get some help from Smitty, Fleg and Jay Tee. They all had great ideas and knew their stuff when I was fooling with Baja ext boxes. Start now, it takes a couple months of fooling around to dial it in...

I've got the setup for you! -3" Drives on neutral IMCO boxes, 380 tabs & 4 blade wheels.

Running stock 496HO power???

Problem I got is the water is solid up here will be until April. So anything I do now is mainly just guessing, but I have to start somewhere.

Put more hot chicks in it and go slow. No one will care if you can't get on plan then. :cool-smiley-027:

Sure. It wouldn't scare me at all, knowing what I know now. Besides, you can always go down with spacers, it is the shortening up part that is a b!tch.

First your trailers missing, now you want to
get rid or all the stuff hangin off the back
....something smells fishy here:D

I don't want to get rid of anything on the back except for a bunch of weight. I think I have that figured out.

So you want to sell your hardware?

U re-rigging it with these:D

http://www.mercurymarine.com/engines...ives/vazer.php

Only 573 #'s

Huh, yea. That is it.

I may be selling my engines, but I can't say 100% for sure yet.

If your selling your driveline give me a call if you still have my #

I will be keeping everything on the back of the boat, just thinking about changing engines out to keep me occupied with the boat.

Gotcha I thought you were talking about selling it a couple posts back, but you must've meant new. Liitle out of my budget to do all that new.

Well back to this subject again. Jeff was up and we measured the drives and came up with 7.25" so they are too deep. I'm back to thinking extension boxes. with shorties or running the stellings.

I've found a few other things that need corrected as well. But these only have to do with speed and performance not the blowout issue. Anyone know why the 302 likes to shoot the moon in the rough stuff? I'm thinking the boxes would help with this as well as a set of 380 plates to replace my 280's.

7.25"?!!!! That is in the basement! You need -3" drives.

I assume your referring to Imco Extremes and boxes.

Are you running Stellings,Latham or Imco boxes?

Yea, I run IMCO boxes. I like them better because they are easier on the drives because they keep the Mercruiser rubber coupler.
Stellings uses a 2 piece driveshaft that bolts to the flywheel. I think with anything under 550 hp a person is fine with the Stellings box, but I think the driveshaft & added u-joints & lack of a coupler are harder on the drive. Also the lack of the coupler sends bad joo-joo down to the drive by way of harmonics, in my opinion.

your shooting to the moon cause of drive height, if you can get the 3'' raised boxes from imco, other wise just do the 2'' shorties. but don't go with straight boxes you will be even deeper, once you bring up the drive height the boat will fly more level, been there

If you do +3 boxes from IMCO you have to raise the engines 3" which means raising the exhaust 3" which means custom tails if you have headers.
A neutral IMCO box with -2" shorties will get you where you want to go.
Stellings with -2" IMCO lowers will give you the most flexibility & that would be the route I would take in your shoes.

I know every boat is different. When I bought my boat it had 2" imco shorty's and no boxes. I shot straight in the air and blew the drives out. After adding imco neutral boxes the boat gets on plane very easy.

I used my existing steering and kept the same tie bar. No major changes. I have latham and if you talk to them they will tell you you have to do everything that was said above. You don't! Works perfect. After it was done seems too easy.