No it is going to be one big swap. I would have been nice to test each piece to see the results, but I just don't have the time and summer is too short. I'm really scrambling to get the boat together by Memorial day. I'm up north this weekend to work on the boat. I'll post some pictures if I make some progress that warrants taking a picture, ha.

Do you remember anything about Mopowers 272. I know it's a smaller boat, but I believe he was only able to get low 80's out of it with standard lowers. If I remember right, I believe he was around 600 hp an engine. If that is true, I'm going to use his boat as a baseline. I'm really hoping to knock on 90 mph with this set up, hopefully I'll know soon.

You run 70 now and you're hoping boxes and shorties put you at 90?or did I miss something

Great project. What horsepower are your new engines? 90 mph will be a 20 mph gain over your previous 900 HP combination. With the set back, shorties and new engines she will be a whole different animal. I imagine it will take some time finding that ideal set of wheels, but will sure be a fun process. Good luck!

Friend of mine has a 1989 272 with 610 HP a side runs mid 80s with Bravo1s & 27P Mirage+

He is putting in new 509s also

Ha- Yes I think you missed the part about new engines, I'm certainly not gaining 20 mph with just shorties. With the new motors I added 110 cubic inches and 400 more hp than what I had before. I'll now have 650 hp a side.

Here is one of the new engines. I'm hoping that next weekend I get the motors dropped in the boat.

Is that Mopowers boat?

I had 540CID 600HP late model Bravo1 DWP drives (not the club foot B-1 from 1989) on a 1989 272SR1 ran 83 with trued, thinned and balanced 28B-1 props. Not full lab.

I did not have shorties or standoff boxes.

At 78-80 depending on the water conditions, the boat would chine walk.

I could "drive it" through the chine walk and continue to increase speed to about 83. Never did test anything over that.
May have been capable with different water conditions.
But I really didn't care if I could get another 1-2 mph out of it. That wasn't my goal.
My goal was to have fun.

No. Guy on our pond.

I was thinking about opies boat too I forgot he ran that fast as well. I do remember Mopowers boat but I think he did have -2 shorties on his and he did run 80 as well.


I do remember that 272's have a hook the last 2 or 3 feet on the transom but I do not how much or even any it changed to speed of the boat. 292's a 311's are concave a tad at the transom hence why a 292 and 311 run dayum near the same speed with identical HP.

Broham you might have a little rocket on you hands!!

I don't think Mopower had shorties. I know he talked about it, but I don't think he ever bought them. So when are you going to replace the 311. I was boatless for one summer when I was 17, that summer sucked.

BOY - Those engines dressed up nicely. Lookin good.

Thanks- I'm hoping that I can get the hydraulics plumbed this weekend and possibly get the motors dropped in. How is your project coming along?

I got all of the EFI parts and pieces. I got all of the sensors installed and the computer mounted. Now all I have to do is the wiring. I got the injectors and fuel rails installed tonight after I drilled and tapped one of the fuel rails for the fuel pressure sensor.
Need to order a bunch of fuel line fittings.
Anyone have a Summit coupon there not using???

So here is the update from the weekend. I finally got one of the engines in, I really needed to get one in, so I could see how the geometry changed with the new engines. While the blocks are the same dimensions, the dart heads have the exhaust ports raised .30 inches. Not only does that move the exhaust up, it also moves the exhaust out. Not a big deal if you're using short tails; however, I'm running dry pipes that go through the transom. So with all that said, I need to pull the swim platform next week and and modify the existing cut outs.

I also removed the old cable steering and everything associated with it at the helm. Needless to say, the hole in the dash for the old helm is ever so slightly to big for the new hydraulic helm. So I will need to plug, fill and re-drill that as well.

All in all, things are moving along, but as expected, nothing goes 100% smoothly.

I am not sure I would remove the platform and recut holes in the transom.
I had the same issue going from steel stock heads to aluminum d shape exhaust ports.
Pipes moved 0.50 up and outboard from the original holes.
I cut the tails to fit. May have been more expensive on the initial change.
But cutting, filling the transom is never easy or cheap. Plus the strength of the transom will not be compromised.
If something doesn't get done exactly right, the transom is too important structurally to risk it.
Plus the standoffs will add to the loads to the transom.

JMHO

Sounds like you started one of my projects.

Thanks for the advice, but look at it this way. A triple engine boat transom is same thickness, yet has 3 drives, and six exhaust holes, and a lot more stress. They don't have any issues with structural integrity. Boats with big power are running up to 5" exhaust pipes, no issues there. I seriously doubt that enlarging the hole a .25" to allow the pipes to fit, will reduce the structural integrity of the transom any measurable amount. Now, If my transom develops issues, you can certainly say- I told you so.

Ouch. I stand corrected.
You are 100% spot on.
0.250 isn't enough to make any difference.
I was mentally going with a 2" move.
Plus you are going away from the drive cutout.
Good call on your part.
On my trip engine swap, I had plenty of room to adjust for head differences.
I had new headers made to fit.
🤑

Any updates ??

+1

I guess I better keep the updates coming. I spent all last weekend working the the boat, here is what is done. Exhaust holes modified to work with the starboard engine. One engine installed, and started Other than needing to tune the carb, the engine runs great, at least on a hose, ha. The old hole in the dash for the cable helm has been filled, and re-cut for the new hydraulic helm.

I'm heading back up tonight. This weekends goal is to plumb the steering, and get engine #2 ready to drop in next week.

Both lowers are now built, and I'm going to finish the two uppers next week.

So with all that said- I'm hoping that the boat can finally touch the water next weekend. I'll know for sure by the end of this weekend.

Here is an quick video of the initial startup of the new engine.

https://youtu.be/NJuldcNtQko

Ok guys- Next Sunday/Monday (19/20th) is the target date to test the boat. Second engine is in, I'll be installing the starboard drive today, and building the other upper this upcoming week. It's nice that I can finally see the light at the end of the tunnel with this project.

So here is this weekends progress, swim platform back on, drive installed, and lots of little projects completed. It's nice to finally see this coming to an end and looking like a completed boat again.

After all the work & $$$$$, I hope it performs to your expectations. Good Luck.

Hope ya drilled the bottom of that silent thunder out to lets those motors breath...

Indeed- They have been drilled out since the day I bought the boat!

Never had a issue getting water in the motors when backing down a ramp?

No, never been an issue.

How did it bro?

You' are further along than I am. Trying to dial in the EFI. I think I have a cracked spark plug. I heard a snap noise when I was installing it, removed it but couldn't find anything wrong. BUT I have a miss and occasional firing of that cylinder. When it fires the AFR gauge jumps. If you can't get a stable idle you can't go any further. I have to make a couple of temporary mufflers so I can run this thing on the hose without pissing off all of my neighbors. Hauled it to a local SMALL lake near me Sunday afternoon and tied it to a dock for 30 minutes. That is when I figured I had a miss and located the issue to cylinder #5. As I was en route home a sheriff was headed toward the lake.

Well I was very close to getting it in the water but it just didn't happen. The biggest reason was I didn't use enough sealant when I installed the carriers in the new lowers and both leaked and I didn't have any of my drive tools. One badly and the other a little bit. It WILL hit the water this upcoming weekend. I just really hope the props work, because I don't have much time now to get new ones if they don't for the 4th weekend. Wish me luck!

Sunday before I tied it to the dock I modified my X drive upper to clear the Maximus 5 blade prop with the -3 shorty. I made my own hydraulic press. Floor jack and a 7000 lb pickup. I just used two pipes on top of the jack lift pad, put the IMCO stainless cavitation plate on top of that and then put another pipe at the point where I wanted it to bend, rolled it under the truck frame and jacked up the truck. Worked like a dream. I then installed it on the drive and used a sawsall to cut off the amount that was underneath. Prop clears with 1/4 inch to spare. I then cut 1 1/2 inches of the bell off the back of the new to me Maximus prop. The Daytona didn't like the bell the last time I had a Maximus prop on it. I just love chopping up a $600 propeller.

Hey those engines sound familiar.
I thought they were loud until I fired up the 598

My Gils are dry to the tip and without the silent thunder swim platform on the engines were unbearably loud. I couldn't even give my dad instructions when he was 3 feet away, because he couldn't here me. I'm glad i didn't go with a tubular platform, because I would need to be running mufflers. Even though the silent thunder no longer holds water, it still muffles things a lot. If your 598 is dry to the tips then I can imagine it quite loud.

I'm running 30 P Bravos and like your Maximus the bell is removed. That is the only real thing that worries me, I'm sure the pitch is fine, I just hope that without the bell on the prop it will still get on plane fine. My prop shaft is still around 5" below the hull even with the shorty, so I am by no means pushing the limits. No wonder Formulas are not all that fast. With the shaft 7" below the hull, the drive was creating a ton of drag.

I finally got the boat in the water. Out of the hole is very good, cruise, cornering, trim reaction are all vastly improved. In Lake Michigan yesterday, the waves were 3-4' and the boat rode better than it ever had before. I got the boat up to 74, and if felt solid and predictable (not in Lake Michigan). With all first days on the water, there were some issues. The Starboard engine's valve cover was cracked, so I had to replace that because it was spraying oil at higher RPM's. Then the Starboard engines sea pump lost an impeller ear and restricted water flow, so that caused the engine run warm. I'll get some numbers next trip out, but overall I would say this project was a success.

Yes sounds good!

So here are some speed numbers.
56 MPH at 3400 rpms- 12% slip
70 MPH at 4200 rpms- 10% slip
80 MPH at 4800 rpms- 6% slip.

So the obvious change is that my slip numbers came way down. The props are Bravo Ones- 30P labbed by BBlades and repitched to a true 28P. With the old set up top speed was 70 at 5300 rpms and 14% slip. That was with some Merc labbed 25P B1's. Based on the old slip numbers the new props would have worked. However my slip as dropped so much I'm probably going to need to go to a set of 26's.

Now with all that said I know I have around 2 mph to gain by trimming the extra long skegs down. I'm sure the carbs are not dialed in so a bit more there. I'm guessing there is another 5-6 mph to be had by getting everything right in the set up, but for the first real run the best was 81 mph.

You have come this far! Keep the Props add more HP