Marine 273 build

[TRBenj]

Howdy FABO, first time poster here... have enjoyed the terrific knowledge base for a while and figured it was finally time to register.

I, along with a few friends of mine over at CorrectCraftFan.com have some vintage Chrysler muscle in our vintage inboard ski boats. Ive seen everything from Poly 318's, various LA/LM's (273/318/340) as well as some of the RB big block (426 and 440) engines installed in older Correct Crafts- primarily mid-60's to early 70's vintage. There are a few differences in the marine stuff from the automotive- namely exhaust, ignition and carburetion limitations... but a lot of the same parts and knowledge can be leveraged- which brings me to today's question.

A few of us are looking at modifying our 273's. Marine 273's (at least the ones we're familiar with) were rated at 200hp from the factory. The ones Ive seen all came with 4bbl AFB's, and they used (larger chambered) 318 heads (like the 675 castings). They move our 1600 lb, 16' boats pretty well- to the tune of ~45mph or so... every bit as capable as the 289 and 302 4bbl Fords (~210hp) that were offered during the same time period.

Anyways, while swapping out to a 318 or 340 is always possible, we're looking at what it would take to extract a bit more out of the 273 without adding cubes... so we're looking at head, cam and intake options.

Heads We are thinking that something with smaller chambers will help get compression up from the stock ~8.5:1. Also, something with smaller valves would keep us from having to notch the cylinders. Based on what Im reading, automotive 273 heads (315 or 920) or the later 302 castings might be good options. Are any of the above more preferred than others? I assuming porting would be recommended with any of the above?

intake The one intake that has been identified to work well is the LD4B. Are there others worth considering? It sounds like the regular Performer is less than revered, and I *think* the RPM is a bit taller than the LD4B... is that true? We do have height limitations in order to close the motorbox- but I know the LD4B fits.

Cam This is the trickiest, as our vintage boats are all reverse rotation. Reverse cam blanks are in short order, but we do have access to 2 options that we know of. Both are hydraulic flat tappets.

1. Gross Valve Lift: .410/.411, Duration @50: 198/199

2. Gross Valve Lift: .429/.444, Duration @ .50: 209/220
(This is essentially the reverse rotation version of the HO 340 cam from what I understand)

The latter worked great on a built up 340 (approx 330hp). We also tried one on a 273 with the stock (low compression) heads and it performed a little better- but not drastically. Might have been too big? Which of the above options would work better for lightly modded 273?

Carb Are the original AFB's the best option? What type of CFM should work best? I need to pull the model numbers off mine to see how big it is. Would a Holley 450cfm work better?

This isnt the first time we've modified engines in these boats, so just a few things to keep in mind... We dont spin them very high (5200-5400 is about the max we'd prop them to spin at WOT). High-ish compression is ok (we've had a that ran great at 10.x:1). "Off idle" or "low end" power is largely unimportant to us, as the prop slip coming off idle gives us a lot of instant rpm (2500+) just like a high stall torque converter.

Oh, and one last question... since my buddy has the following parts already collected, what do you think he's looking at for hp once he gets it assembled?

[FONT=&quot]273 +.030 with factory replacement 10.5 domed pistons from Egge
[/FONT][FONT=&quot]Cam: 429/444” (210-220) rev rotation marine cam[/FONT]
[FONT=&quot]Ported 273 heads (2465315)[/FONT]
[FONT=&quot]Edelbrock D4B intake[/FONT]

As everyone loves pictures, this is one of the Chrysler powered Mustangs in our group. This one came with a 273 that was swapped out for a 340... one hot little ride.

Thanks in advance for any and all feedback!

 

[65Val]

Hey, thats neat!...273 in a boat! A lot of your assumptions above are bang on. The "302" heads are the ticket as they have hardened exhaust seats already, and smaller chambers (to help with compression). Does marine fuel have lead still? Since you aren't worried about low RPM torque, I would think you could go with a single plane-type intake, maybe a bit on the "high rise" side for higher RPM use, as opposed to a dual plane (L)D4B style.

...or you could go with a "D-Dart" style build. If you're not familiar with them, the "D-Dart" was equipped with a factory built hi-performance racing version of the 273 putting out 275HP. It had a BIG mechanical cam (not sure if a rev.rot version is available), and 750(?) Holley carb. These were built for high RPM and good power, similar to what you would want in a boat?

Here's Dave Mape's 273 page with a bunch of info...

http://users.erols.com/dmapes/THIRD.HTM

 

[TRBenj]

Hey, thats neat!...273 in a boat! A lot of your assumptions above are bang on. The "302" heads are the ticket as they have hardened exhaust seats already, and smaller chambers (to help with compression). Does marine fuel have lead still? Since you aren't worried about low RPM torque, I would think you could go with a single plane-type intake, maybe a bit on the "high rise" side for higher RPM use, as opposed to a dual plane (L)D4B style.

...or you could go with a "D-Dart" style build. If you're not familiar with them, the "D-Dart" was equipped with a factory built hi-performance racing version of the 273 putting out 275HP. It had a BIG mechanical cam (not sure if a rev.rot version is available), and 750(?) Holley carb. These were built for high RPM and good power, similar to what you would want in a boat?

Here's Dave Mape's 273 page with a bunch of info...

http://users.erols.com/dmapes/THIRD.HTM

That d-dart package sounds pretty cool! I vaguely recall reading something about it- one of the few >1hp/ci engines from that period, right? Were the only differences between the commando and d-dart the cam and carb?

Unfortunately, the aforementioned cams are literally the only ones available besides the stock grind (which I'm not sure but assuming is at or below .400).

Glad to hear we're thinking along the right track with the 302's.

A single plane (if not too tall) might be a consideration. Low end power isn't he name of the game but we don't rev them to the moon either. The ld4b worked awesome in that ~330hp 340.

 

[toolmanmike]

I have read articles about 273's in I/O's. Very interesting info you have. Keep us informed. Some of us might be looking for 273 powered boats. LOL I rebuilt my 273 and you can see the progress on my build link just below. toolmanmike

 

[67Dart273]

That is VERY interesting. I do have a question.................why do you see single engine boats in reverse rotation? (I always figured it was "left over" stock from twins that didn't get built)

 

[jimjimjimmy]

out of all the marine I have seen they were all reverse rotation maybe regular rotation was the odd one on the duel engine app.

 

[69 Cuda 440]

Hey TRBenj,

My father "Machine Shop" in Peekskill, NY built a lot of small block Mopars
for 'In-board Engine Boats', for Viking Boatyard (Hudson River), and Mahopac Marine
{Lake Mahopac} and few other boatyards in Northern Westchester County,
New York as well as a few guys from Candlewood Lake, Connecticut.

For Camshafts, 'Camcraft' out of Arden, North Carolina is a good source for Marine
Camshafts.

The 'engine', will it have a 3500 to 4500 RPM 'primary' operating RPM.

 

[j061093409]

my friend has marine sb marine 4v intake for sale
located in hartford, ct

 

[69 Cuda 440]

On the Intake,

Most Mopar Small Block Marine Engines will utilize the 'angle-deck'
Carb mounting surface. {see Manifold photo below}.

That Carter AFB Carburetor on the current 273 is most likely a 500 CFM Rating
with a 1 7/16" Primary and 1 9/16" Secondary {Mechanical Secondaries}

I would 'not' use an Aluminum High-Rise {ie; Edelbrock Performer or Performer RPM type unit}
as clearance will be an issue, and a low-plane Intake works better on that combination.

I'll see if I can find a photo of the recommended Intake.

Below is the 'stock' Marine Intake.

The throttle bore openings at 1 11/16" which was called a 'Free-Flowing Intake'.

 

[65Val]

Good stuff, Cuda440...You can also buy just the "wedge" spacer and use it on a regular automotive intake to get the req'd carb angle. I have one in my garage somewhere...looks like this...

 

[daliant]

That is VERY interesting. I do have a question.................why do you see single engine boats in reverse rotation? (I always figured it was "left over" stock from twins that didn't get built)

And in some applications the engine turned standard rotation but power was taken off the front of the crank to get the propeller to turn counter clockwise, these were mostly old flathead inline 6 and 8 cyl engines. Chris Craft also used this type of drive set up in the 60's and 70's using a standard rotation small block chevy engine, the transmission was bolted to a special timing cover and was driven off the front of the engine.
The whole marine engine reverse rotation thing must have something to do with the propeller but I still haven't found out why.

 

[67Dart273]

We had one 'ell of a time with an old marine setup that used the front of the crank for power, back when I sold parts.

I've forgotten what engine, but it was something you don't see much, therefore no one was familiar. The customer kept INSISTING he needed a "rear seal" and whatever we ordered was the wrong one!!!

Of course he was talking about a front seal, regardless of the way it was installed in the boat!!!

 

[TRBenj]

Lots of great feedback- thanks!

Toolmanmike, yes I ready your entire build last week- and I believe we are shooting for something similar with our prospective 273 builds. I recall you thinking that you were shooting for ~300hp? Id be tickled with 250-275hp, all in by say 5200rpm. Could you give me some more info on what you did for heads?

Reverse rotation in single engine inboards… good question. As others have mentioned, early marine engines utilized car engines were mounted “flywheel forward”, driving the transmission via the crank. Propellors rotated right (as viewed from the rear), and drivers were placed on the right (starboard) so that their weight counteracted the torque of the propeller. As the starboard helm became the industry standard, reverse rotation engines were required to turn RH props when they spun the engine back forwards and drove the transmission via the flywheel. It is important to get the boat riding as level as possible with just the driver aboard, as it evens out the ski wake. Correct Craft still utilizes RH props on their direct drive inboards- though as of ’89, they’ve been able to use LH (standard rotation) engines to achieve this (the transmission reverses the direction of rotation). Engines were almost exclusively reverse rotation through ’88 though.
’69 Cuda, you are correct- the 340 HO (reverse rotation) cam that I mentioned above was believed to have been built by Camcraft and sold under various other brands (Clevite, etc). Theyre NLA but we have access to a few of them. Funny you mention lake Mahopac- my sister’s ’69 Correct Craft came from that lake (though it is Ford powered).

Youre correct that the marine intake has a built in wedge. When going to an aftermarket intake, its common to install a separate wedge spacer, though the AFB/Eddy is more susceptible to the angle change than a Holley. We have successfully installed the LD4B intake and fit it under the hood- so that is the way we plan to go for these new builds unless the RPM is known to be similar in height. No need to go low rise. We do need to make modifications to the cooling passages to an aftermarket/automotive style intake, but that is something we are prepared for.

So back to one of my original questions- how do these parts look as far as hp goes?

273 +.030 with factory replacement 10.5 domed pistons from Egge
Cam: 429/444” (210-220) rev rotation marine cam
Ported 273 heads (2465315)
Edelbrock D4B intake

I suppose it really matters how good the port job is on the heads? Can someone give me a range? 235hp with minimal port work? More? Less? Just curious how much time (or money) needs to be spent here.

As we all all like pictures, here is the very nice 273 that was installed in the blue boat pictured above (prior to being replaced by a 340). It was dressed up like marine version of the Commando. Oh, and a quick video of our splash test last year… a scorching 46mph, ha.

[ame]http://youtu.be/U3E4hQB_tpY[/ame]

 

[65Val]

Now thats PPUUURRRTTTYYYY......

]

 

[69 Cuda 440]

That is one nice 'wave rider'.

The 273/235 HP Commando is really closer to 215 HP {true NHRA racing numbers}.

The 340 Camshaft will probably add {+15 HP}.

And the Intake and Holley {600 CFM} Carburetor will probably add another
solid {+15 HP}, especially above 3000 RPM's.

The Cylinder Heads, more of 'any little porting helps over no porting'.

Generally, even a 'general smoothing job', and matching the ports {gasket port match}
is worth an easy {+10 HP}.

 

[67Dart273]

Thanks for the interesting thread!!

 

[SSVDP]

Can't add anything to the 273 discussion but did have two Correct Craft Ski Nautiques. They are top shelf rides, very well made by a small family owned company. I'm an average skier at best and me skiing behind one of these boats would be like taking a Saturn V rocket for a Disney vacation.

 

[TRBenj]

That is one nice 'wave rider'.

The 273/235 HP Commando is really closer to 215 HP {true NHRA racing numbers}.

The 340 Camshaft will probably add {+15 HP}.

And the Intake and Holley {600 CFM} Carburetor will probably add another
solid {+15 HP}, especially above 3000 RPM's.

The Cylinder Heads, more of 'any little porting helps over no porting'.

Generally, even a 'general smoothing job', and matching the ports {gasket port match}
is worth an easy {+10 HP}.

Are those numbers relative to some known quantity (stock automotive 273 maybe?)? We'd need to know the baseline configuration to base the changes on, right? Just curious if you were using the marine 273 with the lower compression 318 heads and unknown stock cam, or something else. Im not sure what the stock numbers (cam, hp, etc) were on the automotive 273.

Yep, CC's most famous model is the Ski Nautique- we have a few of those as well. Theres currently a 340 build underway for a pretty cool orange '72, actually... should be in the 310-320hp range, we're thinking. Should be fun, considering the stock 225hp 318 pushed the boat pretty well.

Im thinking a 273 with 250-275hp at or around 5000-5200 would make for a pretty good running 16' (1600lb) boat. Sounds like some mildly ported 302 heads with a LD4B and 340 cam should get me close? I'd probably try the stock (500cfm?) AFB, as well as a 450cfm Holley... though a 600cfm Holley or Edelbrock might be worth trying as well.

My bone stock 273... needs a bit of freshening up- just like the rest of the boat!

 

[69 Cuda 440]

273 {Automotive Horsepower Numbers}

273/180 HP.......................8.8-1 Compression {Flat Top Pistons} ~ 2-Barrel
Camshaft {Solid}..............{.400" Intake / .411" Exhaust ~ 240* Duration ~ 20* Overlap}
Valve Springs....................{#83 lbs. Valve-Closed ~ #177 lbs. Valve-Open}
Horsepower {actual}........165 HP

273/200 HP.....................8.8-1 Compression {Flat Top Pistons} ~ 4-Barrel
Camshaft {Solid}............{.400" Intake / .411" Exhaust ~ 240* Duration ~ 20* Overlap}
Valve Springs..................{#83 lbs. Valve-Closed ~ #177 lbs. Valve-Open}
Horsepower {actual}........185 HP

273/235 HP 'Commando'... 10.5-1 Compression {Dome Piston} ~ 4-Barrel
Camshaft {Solid}.............{.425" Intake / .425" Exhaust ~ 248* Duration ~ 26* Overlap}
Valve Springs...................{#98 lbs. Valve-Closed ~ 210 lbs. Valve-Open}
Horsepower {actual}........215 HP

 

[TRBenj]

273 {Automotive Horsepower Numbers}

The 273/180 HP {2-Barrel} with 'low' 9.0-1 Compression is closer to...{165 HP}

The 273 with low compression {9.0-1} and a 4-Barrel Intake and Carter AFB {500 CFM}
is closer to..........{185 HP}

The 273/235 HP 'Commando' with 10.5-1 Compression, and 4-Barrel Intake and
Carter AFB {500 CFM} is closer to........... {215 HP}

Was the "low compression 4bbl" available from the factory? I cant find it listed anywhere- I can only find reference to the 2bbl (8.8:1, 180hp) and 4bbl (10.5:1, 235hp). If so, what was the official rating on the engine? I assume slightly higher than the "typical" 185hp? Or maybe youre talking about a low compression factory 2bbl with a 4bbl intake and carb added? The 20hp difference you state at least makes sense in terms of the difference between the factory automotive 2bbl rating (180hp) and the marine 4bbl (200hp).

Regardless, if the 200hp marine 273 was overstated by Chrysler, then it wouldnt have been any more overstated than the competition. In my experience, the little 273 keeps up with the Interceptor (Ford's marine division/sister from the 60's) 289's and 302's rated at 210hp or so. So, when I say "250-275hp" I guess you could just say Im looking to get 50-75hp more out of a stock 4bbl 273, if that makes sense.

The "low compression" 4bbl automotive motor might have been fairly closely related to the marine version... though I believe the marine engine may have had even lower compression (~8.5?) due to the 318 heads. No idea how the cams compare.

 

[69 Cuda 440]

Tr Benj,

The 273 {Closed Chamber Heads} came form the factory with 3.3 CC' smaller
combustion chambers than the 318 {Open Chamber Heads}.

The 318 Heads did lower Compression about {-.35} of a Compression Point,
when compared to the 1965 thru 1967 {273 Heads}.
----------------------------------------------------------------------------------------------

The 273/200 HP

Was not available on the Automotive End. It was a 'special order' for Fleet Vehicles
{ie; Livery Vehicles {Taxi Cabs} and Light Transportation Vehicles}.

It was a 'basic' 273/180 HP, that had a 'stock' 4-Barrel Intake and Carter AFB
{500 CFM} from the 273 'Commando' added on the Engine.

 

[TRBenj]

Tr Benj,

The 273 {Closed Chamber Heads} came form the factory with 3.3 CC' smaller
combustion chambers than the 318 {Open Chamber Heads}.

The 318 Heads did lower Compression about {-.35} of a Compression Point,
when compared to the 1965 thru 1967 {273 Heads}.
----------------------------------------------------------------------------------------------

The 273/200 HP

Was not available on the Automotive End. It was a 'special order' for Fleet Vehicles
{ie; Livery Vehicles {Taxi Cabs} and Light Transportation Vehicles}.

It was a 'basic' 273/180 HP, that had a 'stock' 4-Barrel Intake and Carter AFB
{500 CFM} from the 273 'Commando' added on the Engine.

Great info!

Sounds like the ~8.5:1 CR that I was assuming the 273 had is pretty darn close. That is what the 210hp and 235hp 318 LM's had for CR as well.

200hp fleet 273... any idea if those had the 318 heads just like the marine version? I wouldnt be surprised if that was the case- I know Ford and Chevy sold their longblocks as marine/industrial. Same hp rating, 4bbl intake and 500cfm AFB... sure sounds like they had a lot in common!

 

[69 Cuda 440]

Tr Benj,

The 273/200 HP 'Fleet Service Only" was available from 1965 thru 1967.

* 8.8-1 Compression Ratio {Flat-Top Pistons}
* 273 {Closed-Chamber Cylinder Heads}
* Camshaft {Solid}.... {.400" Intake / .411" Exhaust ~ 240* Duration ~ 20* Overlap}
* Valve Springs.......... {#83 lbs. Valve Closed ~ 173 lbs. Valve Open}
* 4-Barrel Intake
* Carter AFB {500 CFM} {1 7/16" Primary x 1 9/16" Secondary}

Many were used for New York City {Office Administrator Cars for the Taxi Division},
and also for {Junior Administrator Transport Cars} in Albany, New York {State Office}.

They were basic Valiant's with a 273/180 HP, that were taken to the Chrysler Fleet
Service Building in 'mid-town', and converted to 4-Barrels.

 

[BillGrissom]

Those cams don't sound big. I put a 0.422/0.444 hydraulic cam in my 1965 273, and it is termed "RV/Torquer", i.e. good for low-end torque. You can tame a big cam with Rhoads leak-down lifters, but they are "all in" by 3000 rpm, so probably not needed in a boat. The 273 excels on the high end, like 7500 rpm, but should give good power at your lower limit.

Pistons are the killer price, especially if forged, which your friend likely found when buying the Egge's. You won't find a set for $90 like a Chevy SB. Your engines likely had the HiPo Commando pistons, since came with a 4 bbl. When installing them, note that most sets have a "left" and "right" bank. Some racers would swap the banks for better performance. You can read some posts here. Either way, keep the same bank set together.

 

[TRBenj]

Im reading a little more and it looks like 273 marine heads that I keep calling "318 heads" were actually offered on both the 273 and 318. My buddy's boat had 675 castings. (This would make sense since the 675's look to have been installed in later 273's. The marine industry lagged the automotive by a year or 2 back then... our boats with these 273's were generally built '67-72). Is this head chart correct?

http://www.mopar1.us/Aengine.html

If so, then it looks like there is only a 3cc difference between the earlier 273 heads (57cc) and the 675's (60cc). Im reading on here that the 302 heads are ~64cc... so that would be going in the wrong direction, no?

Anybody have a good recommendation on a set of heads that would boost compression into the mid 9's? Swapping pistons isnt on the table (for me) at this time... though my buddy with his egge 10.5:1 pistons is looking smarter and smarter. If my math is correct, I'd need to get down to ~51cc chambers to get 9.5:1. Does such a head exist?