Is 50 mph about right?

It's official: the jetski I coerced into pacing me said my '69 Barracuda was doing 50 mph. That's a freshly-rebuilt Chrysler 318 with a few special enhancements and an ACME 540 3-blade prop. For some strange reason, the tach suddenly started working and claimed 4200 rpm. It wouldn't wind any higher.

So how does that mph stack up against the rest of you? My redline is at 5000 rpm and I'm wondering if I can get a little bit more if I can get the linkage to ask the motor for a few more rpm. I doubt the linkage is right, because I'm having trouble getting it to drop back down to idle after it's been wide open.

Thomas

Thomas,
When I got our boat, a SN with the 318 ReidP told me that those engines were designed to run wot at about 4200 rpm. I pushed mine up to 4500 a couple of times and speedo puts me at around 42mph. I can go more with it, but I like skiing and don't want to think of rebuilding, so never have pushed all the way to wide open. Keep in mind that I'm using my airguide speedo and I'm not sure how accurate my rpm gauge is. I also checked out a Chrysler Marine Engine Site they recommend the Chrysler LM318B 4000rpm at wot.
Chuck

5000 rpm redline was an estimate from memory. The redline on the tach is actually marked at 5300 rpm. I know that isn't the final word on what the motor is actually capable of doing, but I suppose it has some relationship to prudent operation.

No doubt I have cable and maybe carb issues. The carb was rebuilt last summer, but I'm not sure I have the cable hooked up just right.

When I shut down and re-start, the engine will idle properly, even though it was racing right before shut-down. It just doesn't return to idle after running. I need to putter around with the motor cover off and fiddle with the linkage to see what's actually going on, but I've been having too much fun just running to worry with the details.

Thomas

Find someone who has gps, then you'll know how fast you are going. My Mustang is built to hold a constant 6,000 rpms, roller rockers etc, but it will never see it.

The speedos say 50 and we are happy! Gps...tells the truth! Even when you calibrate the speedos...uasually to 36 mhp based on tournament settings...the speedos will be slighty off at lower and higher speeds.
Anyone getting 45-50 (gps)on any of these older boats is running strong...anything that nears 50mph for a stock engine is exceptional!

Thats hallin booty! I am hoping to get near 50 with the GT40's and allum. intake...I guess I still will be seeing just your stern...but a little closer

Gary,

I get 49 out of the 81 , 351 with the 540 Acme topping out at 4800 rpms. That was with a hand held GPS. Dead stock except for a IE conversion kit and a rebuilt carb. I've toyed around with the idea of adding some bolt ons for performance but I hate to touch it until it breaks.

Yeah its sad that when all is said and done no matter what I do to my mustang or 2001 my fastest boat is still gonna be my 60 mph trimmed up 115hp outboard... but man does it sound way more bad a$$ in the correct crafts to do 47...

My engine is far from stock. It's a 318, but it now has 9.2 compression, a roller cam slightly warmed over stock, and fully ported and polished heads.

79 nautique: if all other factors were stock, are you suggesting that changing from the factory prop to the ACME 540 would add no mph to the top end?

Thomas

tleed wrote: 79 nautique: if all other factors were stock, are you suggesting that changing from the factory prop to the ACME 540 would add no mph to the top end?

don't know where you came up with that crap but 1-2 at most and that's with a gps and not some other boat running beside you or from the speedo's in your boat which are only good for between 30-40 if calibrated right otherwise there not acurate.

I'm already at 52 mph on a GPS and use a prop that is for the 1.23:1 trannied motors (13x15.5 .110 of cup)

So with the new heads that have 57cc combustion cambers and 1.94/1.60 valves with .600 lift springs, stud mount scorpion roller rockers, aluminum edelbrock exhaust manifolds and a re-curved distributor advance, I don't see it as much of an issue getting a three or four MPH out of it with those mods.

guess you didn't know the motor was all ready .020 over, balanced and has a decent cam, aluminum intake and a re-jetted Holley, and a completely rebuilt drive line. now did ya? didn't think so. You can ask Gary and Brian they saw enough of the back end of my boat at GL and it wasn't even tuned up then.

79nautique,with the rest of the mods waiting for the install,i know the engineer gears are turning ,whats next??????????   331 or 347 stroker w/twin turbo's or the counter rotating Paxton? idle minds promote evil thoughts..............boat dr

TRBenj wrote: Riley wrote: Better add a helicopter turbine to your list of mods if you want mid 50s in a 79 Nautique. Thats a pretty ignorant comment. I dont doubt the speeds '79 is running considering what hes done to his motor and the hull he's running on. Why would you think adding 10 MPH to the top end is so difficult? I want to see Bill's (SS-201) Nautique that'll do 70. Now that's something to shoot for.

I don't doubt what 79 says. If he's getting 52 GPS now, that is screaming and I'm impressed. It get's really tough to add speed once you get near 50 with these boats. They weren't designed with high speed in mind, but maybe that older hull gets up out of the water and it'll happen.

My source for the reverse rotation roller cam swore me to secrecy. Seriously. Said he didn't want a run of special orders for them. They did not come from the factory and nobody has them laying around. They do not exist in the wild. In fact, I'm almost willing to bet I have the only one.

Suffice it to say that it's the most expensive part in my engine. But if you're really interested in getting one, maybe I can point you in the right direction.

I used a 1990 truck 318 because my block was cracked. And I wanted a roller cam. And higher compression heads.

My poorly calibrated seat-of-the-pants tells me I'm well above 40 mph. How much is up for discussion. Guess I'll have to track down one of those gps thingies.

Thomas

My boat is a '69 Barracuda and the original motor was a 318 Chrysler. I'm a Mopar guy; my source is not. I don't know if he can do reverse rotation Ford cam, because I didn't talk to him about that, but if anybody can, he can.

The real problem is not so much grinding one, but finding or making a core. If you can find the core, you're pretty much home free. My source had one core available last spring and I got it.

Thomas