177 blower on 350 for jet boat?

[F-BIRD'88]

If you must swap to a 177 blower you still want the build to have a compression ratio of LESS than 8.5:1 for this job.
Your cr is TOOO high for pump gas. Ditch the pistons and get -22,-26 or -30cc dished pistons and big chamber heads.

Lower cr is better. (for this job)

[F-BIRD'88]

With exhaust headers and real good heads you can reach your power goal (500hp @5000rpm) easily with a naturally asparated 383.

Build a simple 9.8:1cr 383 with AFR 195 cc heads and use a hyd roller (224+/- ish duration .530-.550" lift) and use a Edelbrock street tunnel ram
and two 750cfm carbs (Ya you read that right) This tunnel rammed 383 with mild Hyd roller cam will have great power and BIG torque right where you need it. Will run forever at 500hp output @5000 rpm, on pump gas, on the water.

You don't need the blower. Sell the 671 to finance the 383 crank kit and AFR heads and TR.

Being able to run exhaust headers as opposed to marine manifolds and the Edelbrock tunnel ram allows this easily.

[wyrmrider]

Jumping in late here but I have built lots of blown boat motors and blown up more than my share
BBC- take a hard look
Keep the 6 71 believe what they said about belt tension
note the intercooler in another thread today
" Probe slugs milled to flat top" and may end up too thin
way too much compression and no quench
you want tight quench and a big D Dish
deep bolt is a good idea
lots of good ideas in the Engine master motors for a broad torque curve motor,, which you need for a jet boat
make a decision on exhaust before even thinking about a cam
think high ratio rockers on the intake and if wet exhaust on the exhaust too with the low overlap cam recommended
you are also going to end up with the lobe centers spread out over a na build but work out the opening and closing point requirements and the LCA will take care of itself- it's a result not a cause

[KnightEngines]

Ok, a bit to think about here.

The blower he has is just a blower - no manifold, has the wrong snout on it etc. There is $$ to be spent to use it, it's set up for a holden (rare) - so it's worth a good few bucks to sell which will cover a good chunk of the 177 kit.

I know how hard boats work motors , (I build some ski race & circuit boat stuff - all NA so far) so I'm very wary of running the 6/71 without a steel crank & crank support, sticking to a budget is all good unless it breaks - I won't put together something that has a decent chance of failure, I'd rather put together something that may not quite hit the target but stays together.

Some of you guys seem to have missed that I'm in Australia - a BBC is not a quick trip to the boneyard away, guys want gold for the damn things over here, I'd pay $1000 for a bare block, probably $2-3k for a core motor with oval port heads & all the parts required cost 1.5x what you guys pay.
I will make a call to a guy I know that has a bunch of BBC stuff tho, maybe I can gather the bits to screw something together at a decent price.

My calcs show a 383 running at 105% VE will only make 400hp or so, a 177 blown 350 will top that easy.

Comp ratio would be 9.2:1 with 76cc heads & zero deck, would have thought that'd be ok with 8-10psi boost, but I'll bow to the greater knowledge on blown engines on here - perhaps the egg beater 177 would heat the air a bit much for 9.2:1.

So, what to do - budget wise keeping as much of the existing motor as possible is the best option due to the cost of bits over here & the lack of value in the existing motor.

Do you lot think going to a steel crank with a BB snout & the bolt hole drilled deeper & running it with no crank support would survive the constant on/off throttle & high load seen in a boat?
Would using the 6/71 reduce intake temps enough to keep comp at 9.2:1?
Piston crowns are pretty thick, I could machine a small dish to get comp down to 9:1.

[cjperformance]

What temp will you be running the engine at, what cooling system?
I would run the 6/71 and drive it 'just' hard enough to hit target hp, but not without a crank support for this app.

[KnightEngines]

Cooling is your regular setup, no heat exchanger or anything fancy, just a pump, river water & thermostat.

I guess I'm gonna have to hunt down a crank support, fisher want $1450 for one, may give Darren a buzz, maybe he can source something at a decent price, he can probably set the blower up as well.
I guess at low boost with a crank support we could just run the stock crank, $ spent on a steel crank with BB snout could probably buy a crank support.

We need new lifters as well, so that block you mentioned with the ford lifter bores may be an option.

Dunno, customer is dropping past today, I'll see if he can stretch to a few more $, I know he's keen to use the 6/71 if he can without busting shit.

[PackardV8]

We ship the occasional engine and/or pieces to OZ. Usually, the buyer has a contact with a freight forwarder who does a container a week or whatever out of LAX.

If you figure out the freight and customs on your end, we can send you all the BBC cores you want. Would even include heads and any of the build kits.

[KnightEngines]

Thanks, but I'd have nowhere to put em!

Found a crank support for $550, 6/71 it is.

[KnightEngines]

Customer just dropped past, budget has gone up

She's getting a fresh block, fresh iron heads, fresh slugs & crank support.
Blower will be here shortly & will go out to be set up for SBC.

Happy now, I can build it right & hit the targets.

[KnightEngines]

Craig - cheers for the hook up, gonna grab that block, she's already line honed with studs, lifter bores trued with ford size, .030" over but will go .040" no probs, price is right, winner!

[wyrmrider]

Iron heads and a jet boat type shorter than v drive cam
what did you say for exhaust?- I forget if you did
I'd question 9:1 depending on gas even with low boost
and do keep it at just enough
ask the forum again now that you have selected on GMC blower
do you have budget for premium exhaust valves
use viton seals
I like dual springs

[KnightEngines]

Headers are dry.

Getting new slugs, I'll drop comp to 8.5 or so.

I pulled the old heads down, intake valves are 2.055" & good, exhausts are cheap shit, so I'll be sticking some decent exhaust valves in it.

Heads are going to have to be Dart iron eagle, not much choice in iron heads it would seem, I'll go for the 200cc runner, 72cc chamber angle plug heads.

Haven't throught about cam yet, any suggestions?

Lifters look to be a problem, another thread coming soon, or now.

[wyrmrider]

Have you thought about later design heads with a better chamber?
Enginequest or?
X2 on the exhaust valves I like hard chrome stems and I OD hone them
I knurl the guides not all the way through for oiling- unleaded gas
X2 on the compression unless others have had success over 9:1 in a high loaded application
http://jonescams.com/marine/
got guy on rocker ratio, head choice, boost, etc

[F-BIRD'88]

Your calc is wrong. Garbage in ='s garbage out.The n/a 383 combo I outlined will make a lot more than 400 hp.

[KnightEngines]

Pipemax doesn't usually lie.

382.668 Cubic Inches @ 5000 RPM with 105.0 % Volumetric Efficiency PerCent

Required Intake Flow between 188.2 CFM and 198.3 CFM at 28 Inches
Required Exhaust Flow between 130.7 CFM and 146.9 CFM at 28 Inches

600 RPM/Sec Dyno Test Lowest Low Average Best
Peak HorsePower 378.4 394.0 401.8 409.6
Peak Torque Lbs-Ft 440.7 458.8 467.9 477.0

HorsePower per CID 0.989 1.030 1.050 1.070
Torque per Cubic Inch 1.152 1.199 1.223 1.246



There is a good reason why you see blown engines in jet boats, an NA small block just won't cut it.