I am going to repower my 38 Commander this winter.   I am debating between two new 7.4L carbureted engines current I have 454s or go with 8.1L fuel injected.   There is a considerable difference  in price.   I am replacing the transmissions too.   Any advise or experience with either option regarding performance or other?   If I go with the 7.4L I am hoping my shafts and struts would not need modification.    If I go with 8.1L they need changing from what I was told.   8.1L is more fuel efficient, but has more HP so fuel savings might not be that much given the boat size.    

Thanks,

Mark

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Every boat that i have come in contact with that has gone from carbureted 454's to MPI 8.1's have had a significant improvement in speed and fuel efficiency. With the 8.1's you will need to enlarge your exhaust system I believe to 5" or 6" to keep your engine warranty. You can have your cutlass bearing OD turned down to fit in the stock strut.  Several people have done this.

I think both our Chief Commander and past Chief Commander have previously opined about the 8.1’s. The performance improvement would be great but they don’t seem to have the best track record. Research them carefully before you decide to switch.

Something to keep in mind if switching to a more modern set up like the 8.1s or any engines that do not use the old school inline style tranys ,  is there will be a considerable amount of modification needed on your stringers as the new motors will sit nearly level compaired to how your old motors mount. 

Below is what the stringers looked like in my 35 after I removed the original motors which was set up for 427's

The fwd. wood blocking  on top of the stringers was then removed and the dip in the stringers where the old rear engine mounts were got built up with new laminated wood

I then did a bunch of glass work on the stringers to end up with stringers that are straight  and flat on top to accept the new motors. 

Then epoxy bilge paint went on 

I dont yet have the new motors  in yet at this point as there  are a hand full of other "while Im at it" projects going on first.

While I have no regrets on my project, I will say the switch  to new 8.1s has been far more than a straight foward one winter project. With all of the other "along the way" projects and repairs that present themselves  as I go.

If your looking for the least expensive and quickest option , I'd suggest either rebuilding what you have or installing another 454/502 as it would obviously be a straight foward swap. You could also go the route of small block stroakers like 383's which would also bolt in the same holes as your existing big blocks and put out big block torque numbers at half the weight. 

If your 454s are still paired with the old paragons , and you end up with more 454s this would also be your chance to upgrade to a more modern trany.

Another  project "while your at it" when pulling motors would be to concider replaceing the original fuel tanks. 

If you are happy with the performance of the boat, 7.4l , keep the existing hp to not make changes to running gear and shaft size.  If  you change hp you will also need props and probably stuffing boxes too. Now, even more money.   Take some time and look, there has to be a 7.4 or a smaller engine, 350 perhaps, with the same hp. in a fuel injected version.  The fuel saving will pay for it self in gassers. 

I would upgrade you fuel filtering system to multiple filters.  Clean fuel is a must. Much easier to put in new filters that fix clogs at the engine level.  Even consider a double filter system where you change filter out on the water by flipping a couple valves. 

That is an impressive fiberglass job.   I have spoken to others who installed 8.1 L in the 38 Commander and are really pleased.   Since I do a lot of traveling and like the fuel economy I am going with the larger engines.   Appreciate the advice and pictures.   Good luck.

Mark

Mark, I’ve had a lot of experience running Commander hulls since the 60’s, all in the Atlantic, running from Maine to Florida. Having owned a 35, 38, 41 and 47 (all gas powered), let me share my experience.

My 38 flybridge express was repowered with Mercruiser fuel infected 454s (Curt Radford’s boat) in the late 90’s.  Those engines put out more power than the carb version of the 454, but less than the 8.1s. They were the last version of the 454, and they were nice engines. And, since they had more power and torque than the carb version of the 454, they were sort of a performance mid-point between a carb 454 and the fuel infected 8.1.

I offer a word of caution about putting too much power in a 38.

The 38 hull is a great hull designed to cruise in the 16 to 18 knot range. Above those speeds her inherent tendency to plane nose-high is enhanced, exposing her relatively flat mid and aft sections to the waves, not allowing the sharp forefoot to do its job of cutting the seas. With the fuel injected 454s, I could cruise all day at 22 knots so long as I was in relatively calm waters. Once in seas above 3 feet at that speed she started to pound, so I routinely had to slow her down to 18 knots to avoid a punishing ride. Note in calm waters at WOT my 38 would exceed 30 knots.

These Commanders are not deep V hulls, like for example a Bertram of that era. With deep v hulls you can keep adding power and you’ll go faster and faster, but because those hulls have a sharp v all the way aft the effect of having less hull in the water at higher speeds isn’t a problem because the sharp v shape continues to cut the waves. In other words, a deep v hull has no flat sections that can cause pounding. 

Don’t get me wrong. I love GM’s 8.1, and it may be the finest big block marinized gas V8 ever produced. But in my experience it’s overkill for a 38. In a gas 42 or 47, it’s probably the ideal engine because it will provide cruising speeds in the 18 knot range, which is a perfect speed for all commanders from 35’ up.

As mentioned by others, there are other cost factors favoring 454s with carbs. Repowering will be relatively straightforward, in that you can keep your original transmission and shafting (assuming you are repowering a 38 that was built with big blocks). I had Aquamet 22 stainless shafts (1.5”) swinging 24” wheels and they worked well with my 454s as their design limit, I recall, was around 375 hp. We repowered our gas 47 in 1978, changing out the Ford 427s for carb Mercruiser 454s. Installation was easy. And those engines ran well into the 2000s, including the original Paragon transmissions!

Frankly, from what I’ve studied it seems an ideal modern engine for a 38 might be the Mercruiser 383. It’s hp and torque ratings are very close to a carb 454, and it’s a lighter engine than either the original 427 or a 454. And if there’s one thing a 38 needs, it’s less weight aft. The modern Merc 383, or the carb version of a 454, will yield an 18 knot cruise. That’s the sweet spot for your hull.

Sorry for the long post. Hope it helps.

Joe Attura

Joe, sounds like you have a lot of experience with these hulls.   I do appreciate the writing.   Most people I talk to advise against putting a higher out small block in such a large boat.   I do get you point about weigh and the original 427s were not big blocks, but had much lower HP.   My cruising is done on Lake Michigan and if the weather is rough I don't go out and if I am out there I am not looking to set any speed records.    In a summer I can put on 400 - 500 miles crossing the lake back and forth and going to upper Michigan on vacation.   What I like about the 8.1L is their power and torque in the range slightly higher than what my current 454 @ 350 HP put out.   The new engines will be at 375 HP and at not too much higher RPM at WOT.    Reliability and fuel performance is important for me as I don't take crossing Lake Michigan lightly.   This summer with my engines not working right (one dead cylinder) I spent $5,000 in fuel.    At some point when I am older may even consider doing the Great Loop.    I provide this background to explain why I am going to spend way more than I could to repower this boat.     My other thought is that if I am going to spend this kind of money I might as well get the latest technology MPI.   Another Commander owner posted some performance figures of the 38 Commander with 8.1L engines on the Super Disk and they looked very good to me as follows:

2600 rpm, 20 mph
3200 rpm, 25 mph
3600 rpm, 30 mph
4600 rpm, 35 mph


I plan to put new transmission ZF63a on as well following my reliability logic above.   My commander has the original three blade Dynajet 23X25.    

Thanks,

Mark

Thank you Mark . Not an exceptionally glorious part of my restoration but I have no regrets of doing it as like you plan on keeping my boat for a long time. 

I took lots of pictures of every step that I'm happy to share.

I to have listened and read about how these hulls tend to pound and can become a little squirrelly when travling above their intended hull speed. Sure you will have more power than you will need but you wont need to use it to have a slightly faster cruise while not even comming close to overworking your motors with improved efficiently .

Im sure either one of the new motor choices would give you great reliability 

But yes theres no hiding the face that converting to any motors that that use a down angle trany will require the most amount of modifications to the boat. 



Mark Regenhardt said:

That is an impressive fiberglass job.   I have spoken to others who installed 8.1 L in the 38 Commander and are really pleased.   Since I do a lot of traveling and like the fuel economy I am going with the larger engines.   Appreciate the advice and pictures.   Good luck.

Mark

As a recent purchaser of a 1969 35 Sport Cruiser, I can tell you I wouldn't even look at anything above 31 feet that didn't  have big blocks. I have watched and even modern small block repowers seem to be a hard sell.

I agree with everything Joe said Except...... ( and you knew that was coming)

The 8.1 only had a production run of about 5 years. Some parts are scarce and pricey. 

I recently sourced a new 8.1 head for a client. A blank head, no valves or anything will cost you 1500.00 FOR ONE HEAD. Why did I need it? 

That brings me to the next issue. Water ingestion from a leaking Man to riser joint which is a COMMON issue with these engines. 

After I finished a top end on my most recent 8.1 client with new Mans and risers the cost was about 4k. 

IAC's and Cool fuel issues and the list goes on. 

I'd stick with the 7.4L Injected motors. They had an extensive production run and parts are reasonable.

Just the opinion of a tech who constantly works on those pieces of crap. People call me every week because I'm the only one locally who will fix them.... $$$$$  Sorry Joe.

Lee, no apology needed. I’ll always defer to your experience and knowledge. Interesting comments about the 8.1. I wasn’t aware that the short production run has already caused parts issues. 

I had heard that my old 47 had a riser failure on her 8.1s.  And I looked carefully at a fully restored 38 with first generation 8.2s and found that one of her engines had two successive riser failures causing seawater to enter her cylinders. It’s a ridiculously common problem with gas engines run in salt. Heck, the reason we repowered our 47 was one of the 427s had a riser failure which ruined the engine.

I recall when Marine Power was marinizing 454s that they had a cast bronze riser option. I always wonder why that didn’t become a standard thing with all gas motors.

Lee, as one who is about to install a new set of 8.1s , out of curiosity on the ones with water ingestion at riser/ manafold joint how many are salt vs. Fresh water boats?

Would you recomend going with aftermarket stainless manafolds to deal with the water problems?

Also for what its worth as of this past summer mercruiser is now producing 100% brand new 8.1s that are not remanufactured . Dart heads and blocks are now being used as the gm ones have mostly been used up. They are building up a stock of new motors and parts to support them as there has been a fair amount of demand for new non catalized marine big block gas motors. They are being sold under their Quick Silver brand.



Lee H Dahlen said:

I agree with everything Joe said Except...... ( and you knew that was coming)

The 8.1 only had a production run of about 5 years. Some parts are scarce and pricey. 

I recently sourced a new 8.1 head for a client. A blank head, no valves or anything will cost you 1500.00 FOR ONE HEAD. Why did I need it? 

That brings me to the next issue. Water ingestion from a leaking Man to riser joint which is a COMMON issue with these engines. 

After I finished a top end on my most recent 8.1 client with new Mans and risers the cost was about 4k. 

IAC's and Cool fuel issues and the list goes on. 

I'd stick with the 7.4L Injected motors. They had an extensive production run and parts are reasonable.

Just the opinion of a tech who constantly works on those pieces of crap. People call me every week because I'm the only one locally who will fix them.... $$$$$  Sorry Joe.

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