What to do when those 8.1s near the end of their lives

sbw1

Well-Known Member
Oct 10, 2006
8,183
West Michigan
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These engines are wonderful, expensive and out of production. I have been wondering for some time what good options exist at replacement time? Internet searches for rebuilding them end up in dead ends when it comes to locating a current source of repowering options. We are approaching the time horizon when owners will be looking at the need to fix what has been a nice, high HP, high torque engine. I have heard that 8.1s can not be rebored, and it will be interesting to know if this is in fact true. Owners of Crusader engines will likely be unhappy at the prospect of switching to Mercs if this turns out to be the only option at rebuild time. Are there any knowledgeable folks out there who have first hand experience and expertise with aging 8.1s? It will be interesting to learn from your experiences.
 
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View attachment 77041 View attachment 77040 These engines are wonderful, expensive and out of production. I have been wondering for some time what good options exist at replacement time? Internet searches for rebuilding them end up in dead ends when it comes to locating a current source of repowering options. We are approaching the time horizon when owners will be looking at the need to fix what has been a nice, high HP, high torque engine. I have heard that 8.1s can not be rebored, and it will be interesting to know if this is in fact true. Owners of Crusader engines will likely be unhappy at the prospect of switching to Mercs if this turns out to be the only option at rebuild time. Are there any knowledgeable folks out there who have first hand experience and expertise with aging 8.1s? It will be interesting to learn from your experiences.
Bump.
 
Not sure you have any Crusader options other than a rebuilt long block since the casting is no longer made. Your ER and engines appear to be in pristine condition.....how many hours do you have on them?
 
If I had to buy a new gasoline marine engine off the shelf, it'd be an Ilmor...no questions asked.
 
its a big block chevy - tons of aftermarket support - even new blocks - either build a new 496 with a merlin block and heads and scat crank and rods, or just buy a 502 - it will bolt in too - as far as boring one, limit it to +.030 - if worried have it sonic checked
 
The 8.1 was GM's bastard child. It's a metric motor and does not share any parts with the 454/502's.
Does not appear to be any new blocks available from anyone. Don't confuse this motor with the stroked 454's that share the 8.1 displacement.

Summit racing offers it in remanufactured only, which means it can be bored.
 
Bell is the same , not sure about the mounts. To swap in a 502 you would have to have everything, soup to nuts and that would be very expensive. Summit wants less than 4k for a reman long block if you supply a core, which gives an idea of how scarce these are becoming.
 
If ilmor is using Gm blocks what do they do about the advertised 7.4 in their lineup. How do they supply that.?
 
View attachment 77041 View attachment 77040 These engines are wonderful, expensive and out of production. I have been wondering for some time what good options exist at replacement time? Internet searches for rebuilding them end up in dead ends when it comes to locating a current source of repowering options. We are approaching the time horizon when owners will be looking at the need to fix what has been a nice, high HP, high torque engine. I have heard that 8.1s can not be rebored, and it will be interesting to know if this is in fact true. Owners of Crusader engines will likely be unhappy at the prospect of switching to Mercs if this turns out to be the only option at rebuild time. Are there any knowledgeable folks out there who have first hand experience and expertise with aging 8.1s? It will be interesting to learn from your experiences.

I thought you said goodbye to boats for now. Did the allure of the sea call you back?
 
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Not sure you have any Crusader options other than a rebuilt long block since the casting is no longer made. Your ER and engines appear to be in pristine condition.....how many hours do you have on them?
They are still pristine with about 900 hours so no danger of failing for many years. New owner is enjoying a problem free boat. But, with so many boats out there with 8.1s, I'm curious what people will do when these engines begin to fail. There appears to be no easy solution. I suppose old Tiaras will likely be converted to diesels? Just wondering about a problem that will likely be showing up in the near future.
 
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The 8.1 was GM's bastard child. It's a metric motor and does not share any parts with the 454/502's.
Does not appear to be any new blocks available from anyone. Don't confuse this motor with the stroked 454's that share the 8.1 displacement.

Summit racing offers it in remanufactured only, which means it can be bored.
What I have heard about boring is the cooling channels end up being closer to the bored out cylinder walls and overheating shortens the life of the motor. Do you know anything about that issue. It seems like racing guys don't worry too much about blowing up motors, but with boats this gets to be very costly. A boat designed to be run on big, high torque v8s would see its value in the used boat market take a real beating with no repowering options. Hopefully, there is a good alternative to the 8.1 for boats that are stout enough to be repowered after years of use.
 
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In my neck of the woods boaters are just using the current Mercruiser 8.2. Speaking to a Mercruiser tech he did prefer the 8.1 though.
That is probably a good option. But they are very expensive, just as the original 8.1s are. Would probably cause an owner to look at the diesel repower option since you would be redoing the whole ER.
 
Volvo Penta has a new 6.2 380hp V8 with variable valve timing that apparently outperforms Merc's 8.2 in all aspects. It looks like a real performer but not sure if it would even be available for a replacement inboard engine. Also, the cost might be quite steep even if available.

If mine ever go and they couldn't be rebuilt, I'd probably look at fresh 454's or even look at the possibility of getting a pair of stroked 454's to get the same punch as my 8.1's. Hopefully mine have lots of life left in them. I know they are quite detuned from what power they are capable of producing...
 
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There is a big difference in the 8.1s vs. 454s when it comes to torque. Would be even bigger with 6.2s. All three are great engines but the 8.1s will really be missed. The Merc 8.2 or diesels may be the best two options for replacements.
 
View attachment 77098 There is a big difference in the 8.1s vs. 454s when it comes to torque. Would be even bigger with 6.2s. All three are great engines but the 8.1s will really be missed. The Merc 8.2 or diesels may be the best two options for replacements.
What do the 8.1 make for torque?
 

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