3K RPM L48 Build

[enkeivette]

I found out that my SS350 Camaro motor in the boat doesn't have the Camaro heads, it has the 882 heads (which I believe are the same as my L48 heads).

Anyways, I've decided to pull that motor and try to sell the shortblock to some Camaro purist since it prob has some value and my L48 apparently does not. And with the 882 heads, those motors are prob making the same hp anyways.

So in goes the L48!


The old motor was torque limited to 3K rpm, which was surprising to me. So assuming the L48 won't do much better, how should I build it to make the most torque at 2500-3500 rpm?


First of all, if I remember correctly I can mill the 882 heads to bring the compression up to a max of about 9.2, does that sound right? Will it be worth the $100 to do so? Secondly, what sort of cam will work best at a low rpm like that? Does more duration equal power at a higher rpm? I'm thinking because this is such a low rpm motor, an aftermarket cam might not do any better than a stock cam, or it might even do worse. Other than maybe another half inch of lift which could help? Help me out gurus. I will swap over the edelbrock dual plane and 650cfm AFB.

Also, how necessary is it that I buy new lifters if I get a new cam?

 

[TimAT]

Big RPM numbers in a prop driven boat make no sense. The prop will literally spin a hole in the water and cavitate. You need to figure your prop pitch, gear ratio, and engine torque peak to get max efficiency out of everything. If you put a speed prop on a displacement hull, you'll never get into the "zone". Same with a cruise prop on a planing hull.

 

[enkeivette]

It's a jet.

 

[JeffP1167]

why not just look for some cheap 5.0 h.o. 416 heads. They can be ported to flow decent and have 58cc chambers. That would surely take you to 9.5:1 without a problem. I might have access to a set you can have for free, just have to pay shipping.

 

[JeffP1167]

new lifters on a new cam is mandatory since they spin and get concaved. this will quikly wipe out a new cam if they are re-used

 

[mrvette]

new lifters on a new cam is mandatory since they spin and get concaved. this will quikly wipe out a new cam if they are re-used

this is totally true and very accepted practice....

but decades ago before I knew nothing more than a torque spec on a head bolt....I swapped '67 GTO 400 cam and lifters into my '72 350 Lemans engine...heads too....and never kept lifters in order...never knew to DO that, back when....

that damn stupid engine didn't know no better and ran another 200k miles, serious as heart attack, knew the next owner who drove it as a delivery vehicle....

the oil pump finally run up the red flag and said NO MORE...but yet that stupid engine didn't miss a beat for some couple hundred miles but they were easy miles as it was determined to scrap the car over several month's time....it was Wash DC, land of millionaire .gov rip off artists, but us hotrodders were a cheeeeeeep group....

:goodnight:h:

 

[Ozzy]

3K with a small block jet,I would think that is going to be a real slug.
I also don't understand what you mean by rpm limited?

I'd start out finding out what impeller you have and either build an engine that will work with its power curve, or get an impeller that will work with your engine.

The pump is little more than a water dyno, if you don't have the ponies, it isnt going to spin up.

 

[enkeivette]

It does about 45-50mph, I think the problem is the compression. Those 76cc heads aren't helping the situation. Maybe if Jeff hooks it up and I can get it up to 9.5:1 and order a cam to match it'll sing.

Jeff, PM sent.

 

[JeffP1167]

It does about 45-50mph, I think the problem is the compression. Those 76cc heads aren't helping the situation. Maybe if Jeff hooks it up and I can get it up to 9.5:1 and order a cam to match it'll sing.

Jeff, PM sent.

a jet that only does 45-50? my old bayliner capri with a 4.3 V-6 and mercruiser could almost do that.

 

[TimAT]

The impeller in the jet is pretty much the same as a prop. Different pitch and design.
The hull of a boat is still pretty much the determining factor in how fast it'll be. You can plug 1000hp into a boat that is designed for slow cruising and all you get is more fuel consumption, noise, and maybe a couple of knots in speed. I know of one guy that put $85k into his boat's engines - and picked up 17 knots. And those engines were making enough power he had to install clutches- the outdrives were breaking just putting them in gear. And I'm not talking about the "everybody has one" standard drives- these were both heavy duty offshore racing stuff

Find out what the maker of your jet pump recommends for RPM and build for that. Make the torque curve, RPM, and HP come out as close together as you can.

 

[enkeivette]

It does about 45-50mph, I think the problem is the compression. Those 76cc heads aren't helping the situation. Maybe if Jeff hooks it up and I can get it up to 9.5:1 and order a cam to match it'll sing.

Jeff, PM sent.

It does about 45-50mph, I think the problem is the compression. Those 76cc heads aren't helping the situation. Maybe if Jeff hooks it up and I can get it up to 9.5:1 and order a cam to match it'll sing.

Jeff, PM sent.

a jet that only does 45-50? my old bayliner capri with a 4.3 V-6 and mercruiser could almost do that.

It should do closer to 60, and should if I can get the motor over 300hp. But Jets aren't known for speed, they're known for quick acceleration and tight turns. It's like a Vette that's stuck in 1st gear.

I've made some gut wrenching turns in that boat that would put a Vette to shame.

 

[mrvette]

enk, You maybe want to consider putting DPFI on the boat.....

I had a '85 20' Bayliner with Volvo 2100 cc engine and Volvo i/o with 3 bladed prop when I bought it used in '93.....

having finished the Pontiac FI project on the tow car, and getting frustrated with the typical carb operation, I was more interested in starting and fuel economy on the water, I burned a tank in like 2 hours running the kids all over the river.....

so on went a Volvo 240 turbo injected manifold, and I ran it with a GM computer...Grand Am 2300 4 cyl.....obviously not in closed loop due to water jacketed exhaust mani....no O2 sensor.....wired it up with some LED's on front of the crank pulley to tell computer when to fire injectors.....

trick is, I picked up THREE prop sizes, went to a cupped stainless Mercruiser prop, hubbed for a Volvo/Penta outdrive.....

I need not have bothered with the 14" to 15" step up....being cupped stainless was really quite enough....

the dig outta the hole was increased a LOT, as in start and GO, no crapping around with no choke carb Solex shit....

I really dunno what bearing this all has on your jet drive, but the overall efficiency of my FI install was I could really wear out the kids with 4 hours on the river, instead of just two....just about doubled my fuel economy...seriously....

the operational charactoristics of that boat changed for the better by a really great amount.....came outta the hole and on plane in about 1/3 the time, could carry 3 adults and 3 kids at one shot, used to have a slug of a time getting up there, with the FI mod...best be settin down when I crack that throttle....

:yahoo::friends: