Here a 3800sc or what ever engine can be had for for $490 out the door with everything, engine trans, all hang ons, ECM, everything.
Hell we had a 3800sc/trans at the shop for $1000 complete for like 9 years and no one wanted it, for the first few years it was even cheaper.
But to get back to the thread as Fierobessed said the crank is just weak, we droped one to watch it break, now you being in the boat business, go for the 3.0L mercrusier crank, get the later year one, I forget years, as the later year can be machined DOWN to fit, where the early years can't be machined UP, IE you have to fill the holes with bolts cut them off flat, have it lathed down and use a repair sleave to get a nice new surface. HUGE differance in cranks compared to the stock duke, that is the weak point, the next point hurting higher rpms is the coil, get good low ohm wires and it will rev higher with more power in the upper rpms.
We have test fitted a 3.0l mercruiser crank in a Fiero duke block, fits and spins great, you get 2 counter weights per cyl, instead of 1 per 2 cyls.
To build a "big bad duke" you need/want the murcruiser crank.
and saying that you couldn't get over 100 hp on the stock heads, the 87-88 dukes had 98HP so 2hp is not that hard to get.
If you want a ton of power I would say go different engine swap, but I love to see a duke pushed as everyone says, "do something different" so it makes it all the more fun. and the only reason I see to do it, I always wanted to do a duke all the way, and boost the hell out of one, just to do it and cheap parts.
You have the perfect place to start dealing with boats, but look at the 3.0L not the 2.5L.
I wish you luck and I hope you blow everyones minds on what a duke can do.
"DRIVE IT LIKE A FIERO"
engine to be determined '87 Duke (Sold)
'87 Quad 4 H.O.
'87Blue GT 3.4L Swap Completed!!!!!!!! Boosted!!!!!!!
^^^^ Now in the Construction Zone^^^^
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