Tartilla

'86 Cobalt 300 Condurre (Carrera SS9M) restoration.

Original owner bought in '87, ran in Lake Washington. Occasional trip to San Juans and Gulf Islands.

Came with Merc 400 BBC TRS drives, ealry '90s had a change to ASD-6 Arnesons. Used 454 Mag style marine long blocks, with 420 MegaBlowers.

Ended up on the back burner in '94. Sat ever since.
​​snagg
I snagged it June of 2023.

Finally got my shop extended to fit the trailer tongue and drives.

This spring/summer will be just getting the engines and drives gtg to get her in the water. Need to get data on performance and handling. The hull didn't like going past 4600 rpm with 5 blade 25 pitch +cup Rollas with 1.32 reduction. One issue is the engines are shoe horned into the front of the engine bay. The Doug Nash trans and Arneson input shaft make a long package.

Arneson and engines have about 25 hrs. Hull has 144 hrs.

Tartilla

Made an I beam lift diagonal on my 14.5ft ceiling joists.

This way I can move the trailer back and forth a little to align the loft trolley left and right easily. Also lets me get the engines over the side without moving the boat or removing the engine hatch.
​​​​
Didn't have much extra clearance on the hoist to make it over the gunwale...that sits about 7ft from the ground. Engine and trans package was too long to get out of the engine bay length, so blower pulley and about a 35° angle lift to get the clearance. Wasn't keen on separating the trans in the engine bay.



The engine bay firewall slopes back, so the crank pulleys are even tucked in a bit from the top access. Not ideal, but no other way to mount them without a standoff box.



Forgive the hanging plug wires...could reach them to get them off before the lift.

Tartilla

Nice to actually get close to the goings on in the engine bay. Current rigging has the seasteainers under the front of the engine. Not accessible at all unless the engines are pulled. There is of course a stainless ball valve at the raw water inlet.

I'm thinking about locations at the transom to re-locate the strainers.




I've put some time into cleaning up the bay after the photo. I'm keen to do a lot of sanding and smoothing to get a nicer finish, but I'm thinking that's best to do for phase 2, where I may set the engines back 10" with standoff boxes.

The battery box is nicely tucked away at the transom, and up high, but the riser tail would have to be removed to pull it out. Not the worst thing considering the tight real estate. The tab pump and Arneson pump are both located tight to the exhaust manifold. Makes changing plugs pretty hard...to downright impossible. I may move them forward.

Power steering pump only on the starboard engine. So I'll need to plumb and rig a pump for the port engine, and a check valve system with a single reservoir feeding both pumps.

Fresh water cooling is a must. Remote coolers and an expansion tank seem to be the best coa.

I'm leaving the port engine in so I can use it as a reference and size-up for the new rigging.
​​​​
I'm thinking of fabricating a DT15 EGR cooler into a heat exchanger. For a full system. The Stainless Marine manifolds have never seen salt water. I like that the exh man will be warmer and create less condensation to drip into the heads.

PNW water is never warmer than 70°F. The heat exchanger has an advantage. The converted DT15 EGR cooler has about a 1200hp cooling capacity. Uses 316 stainless tubes and a 304 stainless outer shell.

316L doesn't mind cold salt water...but I doesn't like hot salt water. 304 doesn't like salt water much. Zinc anode bungs are a must.
​​
I think the heat exchangers would fit in front of the engines in the bilge. The offshore mounts make it difficult to locate them anywhere else.

Twin O/B Sonic

Way cool project!

First time Ive seen the Carrera connection.

Always liked the Cobalt version but being so different from their normal offerings, figured had different heritage.

Love the lines!

Good luck on it..

Quite the science project!

Quinlan

Nice Project.

Cary 29

Tartilla keep up the good work. It's a nice project that's different which we all love to see. You will be enjoying and feeling a sense of satisfaction in the end...

Tartilla

There's never been a lot of offshore boats up here in BC. I always had my eyes on the '80s Formulas. 311 being the hull of choice.

Now that I'm deep in the Cobalt, I'm really enjoying the look and the classic lines. Adding in the racing pedigree, of Damn Carrera, I'm looking forward how the hull will perform in Straight of Georgia with the 26° vee.

I've been watching the few Damn Carrera racing vids on YT, to see how the hull works the water. Noticed that Damn Carrera had staggered engines. I think they were small blocks, around 425hp.

So weight forward isn't unusual for the hull. Maybe just the extra cabin weight that was the issue for the reported bad manners.

The Blowers add a lot of weight. If the hull can only reasonably use 550 hp per engine or a bit more, I may just build new NA engines with aluminum heads. Less moving parts the better + less weight.

Tartilla

Thanks Cary. She's really growing on me. Despite not being layed up by Carrera, I think Cobalt made some good additions, and the combined styling made a big improvement in many ways.
​​​​
My goal is to get her stable to 90mph. Probably fast enough. Cruise in the 40-45mph area, while keeping out of boost (0psi man pressure) and not into the carb secondaries.

Tartilla

I've got the stbd engine torn down.

The Marine long block from Pleasure Craft Marine is essentially a 365 Mag Mercruiser. These were rated for 390hp @ 5200 rpm.

Forged crank and 7/16 rods. Forged pistons. 088 heads.

It has inconel exh valexh...so bonus there. The 2 piece style, stem is magnetic about 1/3 the way up. Guides are reasonable from just an initial wiggle test. Seats when cleaned up are pretty good. I think they'll just need a lapping in. Cam is the 6209. 224° single pattern with 0.510 lift. 115.5 LSA.

088 heads are horribly prepped from the factory. The ports are just straight machined. Square lines everywhere. Exh ports are the worst. Very poor flowing. Chad Speier has some info on porting 088 heads for the tractor motor sports that spec factory heads. He does a really good job of them, but still xan't do much with the exh port. 90% of my running will be cruising, so maybe the smaller exh port will help with lower flow vs the WOT dyno style testing where most engines are measured.

I'll do some mild head porting, just to clean them up.



The cyl bores are pretty good. There is some evidence of scuffing. Maybe from over fueling of over heating. These were of course raw water cooled in fresh water. Rings still look good...though of course replacing them.

The rough part of the tear down, is getting the good news on the cracked valley from the freezing. Both sides. They go into the decks...but not the bolt holes. This engine is the worst of the 2. Port one isn't as bad. I managed to find a good low mileage Gen 5 block, and a 600hr Gen 6 marine long block. (For the block). The issue being, I need to use the 4.250" factory sized pistons, that require a good bore.

RSCHAP1

I will repeat it too!
Very cool.
Awesome to see it getting taken care of