|
Originally Posted by 88Spyder
(Post 3581363)
I can see where they would need to play around with the carb and advance as this combo must have leaned out the @@@@ on the motor, funny because the motor actually has a burned valve in it!!!!!!!!!
I know I'm fairly new to the whole boat engine thing but a drag motor would never survive with that combo,let alone have any kind of performance. BTW, from the rods in mine (Weber carb) they did fatten it in the midrange a small amount, then leaned it up slightly at the top end. Not a lot of change there, though - Merc generally runs things fat. Compared to the std 7.4L, timing ramped faster in the midrange (2000-3000 rpm), then ramped slower to max timing at 4800. I forgot to mention that in contrast to the stock 7.4, these also got forged pistons and crank. Actually works quite well. While we often think the Merc engineers were on acid from some of the things they did, they worked from a different perspective - that of producing _reliable_ power to meet specific demands (like for cruisers) while maintaining cost. When we re-build these, we give up one part of that equation - either reliability or cost go out the window. Sometimes both! |
This last post makes me feel better about this thing(having the forged internals), the motor is actually getting a set of oval port aluminum heads,r.p.m. performer intake, 800 holley carb,MSD ignition,have aftermarket exhaust with silent choice, was thinking about the 420 hp mag camshaft?
|
don't count on the forged stuff...seen many low HP mercs all cast small stuff..sorry
|
Yep, double check the forged - even if it was a PT engine, the short block could have been changed out for one with cast internals. Ask me how I know.
Looking at your valve covers, it looks like a GenV, which the PT engine should be. Double check everything, though. No telling what the PO did. Lots better cams out there since the 420. Many folks have had good luck with the ISKY MEGA 270/280. Also consider calling Bob Madera (rmbuilder on here) for cam - it will be about the same cost, and you'll get great advice. |
Thats a given making sure first, does the combo I was talking about seem like a good mix of parts
|
The combo all depends on what you are doing with it. If you are looking for good midrange with some expanded top end, your combo is going to be pretty good for that. I'd consider the air gap intake unless you need the heat (boat often in low temps?).
It's essentially what I'm doing based on advice from some very knowledgable folks on another site: Zero deck block, flat top pistons Large oval iron heads, 2.19/1.88 valves RPM air gap intake ISKY MEGA 270/280 cam Crane gold roller rockers 750 Weber carb (upgrade later) Stock ignition Stock exhaust (needed for noise) Max rpm should be around 5000. This will be perfect for me as I need mid range for pulling the kids, ect and am not looking for max top end. If, however, you are going for max top end (or you will want to eventually), you need to re-think. This is where talking to someone like Bob Madera will help - he will first ask what you want. |
Looking for something thats a little better than the original 330hp that came with the boat,I still don't know how long I will keep the boat,have allways wanted something with twin bigblocks to play around with.
As long as it will end up somewhere in the mid 50 mph range and get me through this season and maybe next season. The combination will be going in a 1988 26' Nova Spyder, has a Bravo One drive. do have to figure out a prop as it doesn't have one at right now. |
What speed are you running now? My 26' PQ does 56 all day long with the 300 hp 7.4. Although it does have the BII, so a low slip number (7% or so). I'd think with the right prop, you should be low 50's now.
If you are thinking about trading it in, I'm not sure I'd sink the $ for alum heads. You can get a good set of take off iron heads with larger valves for $4-500 a pair. Don't know if these are still around: http://forums.boatfreaks.org/showthr...highlight=head |
BTW, my rationale for going through mine is that I have a replacement long block of unknown pedigree. Maybe a truck replacement block for all I know.
But, while I'm in there... |
Allready have the aluminum heads from a project a customer never picked up(surprise,surprise) I was thinking about starting with what the boat came with in stainless as far as the prop goes.
If anyone else has any ideas I am definatly open to them. I've had this thing for 2 years now and never got it into the water last season,don't plan on making the same mistake this summer |
| All times are GMT -5. The time now is 05:45 PM. |
Copyright © 2026 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.