wwwTOPDJcom

Buying a new boat is not a option, bravo BB setup is for the right price and the sale of the 5.7 setup

Starting with a Larson Senza stepped hull 25'
what can be done on a reasonable buget
I have been attaining a wot 4700 at 50mph
but have recently found out that Im using the wrong
prop for that application 21 ss vented 3 blade
I have been told a mirage, Hydromotive,or bravo I
4 blade.http://www.throttle-up.com/specials.htm
current setup is a 350mag with a 1.5 alpha gen2
driveshower thur hub boat weight 3800 dry
Im putting thur hulls corsa quick &quiet on
K&N filter/stub stack considering
a Imco powerflow setup over the stock
manifolds, as I see it a the prop switch since
I have the completly wrong type on there, slip 24%
I shoud gain 2-3 mph and 1-2 mph for the exhaust
what cost would be invold to build the motor up 70-100hp?

Whitey

As far as the props go I have found that the Mirage plus is the fastest on my ddc hull. I have twins but under normal conditions the 3 blade will be faster than a 4 blade. As far as the engine goes I am working on ideas for my boat to gain about the same hp. I think the exhaust idea is a good start, if nothing else you will certainly lighten the boat. Dwight

blue thunder

Personnaly, I would get your 21P worked to a 20P and pick up 200 rpm. That is about the best you will do without the additional HP.

BT

Dennis Moore

I wouldn't expect much of a gain at the exhaust with the small block. The stock manifolds and the through the prop exhaust isn't very restrictive. I would say that 1 or 2 MPH would be about right. You will absolutely have to change the camshaft to increase horsepower any condiserable amount. Install a cam with 212/218 intake/exhaust duration with 110 or 112 degree lobe separation angle. Call Comp Cams Hot Line.
Sincerely
Dennis Moore

wwwTOPDJcom

Dennis, I was reading your performance tuning artical
on hotboat , I will be checking the advance on it at 3k rpm
hate to cam a 400hr motor without freshing it
besides it has the weber 600cfm carb. right now Im trying
to get her breathing a little better and get the correct prop
my slip has been calculated around 24% do to the air from
the stepped hull my vented props that I have used suffer blow out when up on plane

blown1500

I agree with Whitey about the exhaust. Small blocks need headers of better exhaust too and all the thru-prop exhaust I have seen are too restrictive for any V-8 engine. Don't know about the props, though. A cam change could be a big help along with the exhaust, even with your hours on the motor. Exhaust and a Whipple would be nice..............
Good luck anyway and if I can help, pm.

Whitey

24% slip, that is terrible. I would also ck the x deminsion and be sure it is not to high. If that seems normal I would probably look at a 4 blade prop. The 3 blade will be faster but only if you can hook it up. Dwight

21_senza_383_2

To gain 70 - 100 hp per engine, or total? Per engine will be tough without alot of work...Starting with a stock 5.7L (260 hp), I stroked the motor, rollerized the lifters and the rockers, added Corsa Captain's Call selectable exhaust, replaced the heads with World Products SR Torquers, and am running a Crane .508/.528" cam w/ 1.6 ratio rockers. Dyno tuned at 380 HP with the Rochester Q-jet. If you are only trying to get 35-50 per engine, you can get there through a cam, rocker and exhaust change. Without the exhaust, you'll be taking a chance that the extra breathing will get choked down. Alpha drive runs all exhaust thru about a 1-3/4 to 2" hole in the outdrive if my memory serves me.

Normally aspirated, if you pay attention (and don't go ballistic with the $) general rule of thumb from the Dyno shop: 1 hp/ ci and you're doing pretty well...beyond that, bang for buck goes down fast.

KCHOTBOAT

whipple or procharger blower and through the hull exhaust.

ragtop409

406 long rod Rag's