Montalto

Here's the deal, hopefully someone can help. I recently purchased an '87 22 Pachanga with a stock 350/alpha gen II combo. motor was shot. I had a 383 custom built (420hp) and the drive rebuilt as well. I am not savvy enough to understand some of this but here is the question. The stock 350 (285hp) pushed the boat (at WOT) to 52mph (GPS verified) all day for 28 years... now with an additional 135 hp and a much more torque based motor, WOT pushes to 50????? ran the same 3 blade prop to start and also tried a 4. no change top end. Drive is doing great surprisingly (I am aware of its limitations) but the stock ignition module will not allow past 4800 rpm. Mechanic said motor will only go to 5200 anyway better to keep it there.. I am new to the forum but my knowledge of this boat and the cult like following behind it has shown this boat again with a stock 350 pushing 50mph and a stock 454 (325hp) pushing 60... can anybody help??

phragle

iTrader: (3)

First, where did the 383 come from? How it makes power is as important as how much it makes. Next, who set it up? If the rev limiter is eating 500 rpm it's not set up right, which brings to question, if the ignition isn't set up correct, what else isn't ?

There are 2 ways to make your boat faster

1. Enough power in the correct spread to spin a bigger prop

2. Or spin the same prop faster

So post the motor specs compression cam heads etc and dyno sheets if you have them

ezstriper

something is wrong...from this point could be 50 things, something stupid like 2 plug wires crossed to the cam not working in this app, even they missed the cam timing marks by a tooth. Going to be tuff from here, ck all basics, buy without running on a dyno to see if it really makes 420hp

corey331

Well, if you are running the same prop as the old 350, with the same ignition and rev limiter, you are going to see the same top speed as the 350. You'll probably just get to that same top speed a little faster.

Montalto

How do i post a pic of the build sheet? it won't show up for some reason.. sorry for the delay

Montalto

how do i post a pic of the build sheet? wont let me upload

SB

iTrader: (1)

87 was Tbolt IV, therefore no rev limiter. A TBIV with MSD coil will go 6200rpm+ without missing a beat.

This is where rigging and tuning comes in:

1) Verify throttle cable bring carb to wide open (throttle blades straight up and down)
2) Fuel line sizing from tank to pump (3/8") is fine. Get rid of anti siphon valve. It is the straight barb coming out of 90* at fuel tank.
3)Fuel pump keeping up ?
4)Carb tuned or just slapped on ?
5) Total timing should be 32-34*. When you check total, keep reving it until advance stops and go a few hundred rpm. This can be as much as 4200rpm depending on module.

As Cory said, if you do for some reason have a rev limiter, then you won't go any faster at that limit than any other motor or build...all using the same prop.

Montalto

here's the basics:

383 Alpha Gen 2

Block
Deck ht - 9.025
Piston ht - 1.433
Rod length - 5.7
Stroke - 3.75

Crank
Rods - 2.5 Mains 2.0
55 w/ moly - 75 w/oil

Pistons K/B 9912HC-030
Size - 4.028
Bore - 4.030
Clear - .002
honed finish 818

Camshaft - 08-417-8
(XM270HR-12)(1200-5200rpm)

Engine assembly:
Clevite bearings
Liberty rings
fel pro gasket
rods - 5.7
ring end gap - 028/022
comp cams
lobe centers 112
intake center 110
bushing 0
lift int 495 ext 503
rock ratio int 1.5 ext 1.5
pv int +100
pv exh +100
PH 050
c.r. 9.5 to 1

Heads:
cc before - 72
spring ht 1.785 tension int 130 open 1.290@325
spring ht 1.785 tension ext 130 open 1.282@330
type spas 1521x16 valves int 1.940 ext 1.5

Balancing:
piston & pin - 537/107
pin locks - 4
rings - 59
total rod - 627
rotating rod - 448
insert 47
insert 47
oil 5
over bal. 0

bob weight 1881

Gm delphi lifters - HC-2140
Gm bowtie intake
Pro Topline 215cc Heads - 1.94/1.500

Quadrajet 750 (may be swapping for quick fuel 750)
PROP is SS 4 blade 15x17

distantthunder

What gears were used to rebuild the drive? Is it the same ratio as previous?

Faster7

Nothing stands out as an issue in the build. Depending on what the heads are, at a limit of 5200rpm I'm not sure where I would estimate the boat/flywheel horsepower to be-- if it was the same heads that were on the 285hp 5.7 but freshened, I'd be betting for it to make something like 340-370hp but would make great torque compared to the original motor and would certainly see SOME top end increase. Sure ***IF*** you spun it 6000rpm through healthy exhaust in a car it could be a 420 flywheel HP engine...

Do you know what rpm you spun the previous engine to for ~52mph?