n2ostroker
Petty Officer 2nd Class
- Joined
- Aug 9, 2008
- Messages
- 177
This is my first post on iboats. I'm fairly new to boats as far as working on them as well as GM stuff. Grown up as a Ford guy. Not new to hotrodding or engines though. Been reading and found plenty of useful info on here.
Here is what I have. Ran into a 1986 Thompson 19' cuddy cab w/ a 230/v8 and Alpha one outdrive. I'm pretty sure it's the Sea Rge model but not positive. All my title says is 86 Thomson 19' with 8' beam. Regardless it had a fresh 305 in it. Found out the first time out the previous owner hadn't actually had the boat in the water after getting it back to Ky and let the block freeze. He didn't know about and I only gave $500 for the boat so no big deal. I built a 355(2 pc main) and swapped over all the 305 parts except the flywheel due to the 355 being internally balanced and my 305 was a 1 piece main with an imbalanced flywheel. The balancer was a 0 balance on the 305 so it worked fine. I know the 305 heads are the 58cc chamber with 1.84 intake valves. So the compression is high with the flattop pistons but with 8* intial and 93 octane with Lucas octane booster it runs great with no detonation. I also run a 1 step colder plug to help out. I had some random popping through the carb but I'm pretty sure its just some water in the tank from the boat sitting. Put a new filter/separator on for this weekend so we'll see.
My problem is the 305 heads have pretty small runners. I think it is limiting my max rpm under load. Holeshot is great as it is now. I can hit about 4400rpm trimmed right which is around 51-52mph on the speedo not gps. Still it moves pretty good. I'd like to get a few hundred more rpms up top for the smooth days on the water and to cruise closer to 4000rpms without being close to full throttle. As well as run some cheaper gas next year.
What heads would you guys recommend? Is there a particular casting number I should look for? I'm assuming the intake is the same as a 350 of that yr but may be wrong. The motor runs a Rochester 4bbl which I'm not familiar with but so far it works great. Played with Holleys and Edelbrock/Carter AFBs. I was looking at the Vortec stuff and can get them fairly cheap but don't think I really need them jsut to play for another year till I get something else. Also I think they had just put a replacement truck cam as the cam and lifters were new when I switched them over. I'd like to switch to the comp cams 256h if any one thinks it would be worth it?
Also, yes I reatained all the marine spec parts off the old motor. No auto parts on here except for the flywheel and freeze plugs. The boat is freash water as well.
The hull and transom are solid as a rock and the boat over all is in great shape minus the teak being weathered, vinyl a little dirty, and the gel coat needing shined up.
This site has been a lot of help on gaining knowledge in a fairly unfamiliar territory so far. Thanks in advance for any advice offered.
Here is what I have. Ran into a 1986 Thompson 19' cuddy cab w/ a 230/v8 and Alpha one outdrive. I'm pretty sure it's the Sea Rge model but not positive. All my title says is 86 Thomson 19' with 8' beam. Regardless it had a fresh 305 in it. Found out the first time out the previous owner hadn't actually had the boat in the water after getting it back to Ky and let the block freeze. He didn't know about and I only gave $500 for the boat so no big deal. I built a 355(2 pc main) and swapped over all the 305 parts except the flywheel due to the 355 being internally balanced and my 305 was a 1 piece main with an imbalanced flywheel. The balancer was a 0 balance on the 305 so it worked fine. I know the 305 heads are the 58cc chamber with 1.84 intake valves. So the compression is high with the flattop pistons but with 8* intial and 93 octane with Lucas octane booster it runs great with no detonation. I also run a 1 step colder plug to help out. I had some random popping through the carb but I'm pretty sure its just some water in the tank from the boat sitting. Put a new filter/separator on for this weekend so we'll see.
My problem is the 305 heads have pretty small runners. I think it is limiting my max rpm under load. Holeshot is great as it is now. I can hit about 4400rpm trimmed right which is around 51-52mph on the speedo not gps. Still it moves pretty good. I'd like to get a few hundred more rpms up top for the smooth days on the water and to cruise closer to 4000rpms without being close to full throttle. As well as run some cheaper gas next year.
What heads would you guys recommend? Is there a particular casting number I should look for? I'm assuming the intake is the same as a 350 of that yr but may be wrong. The motor runs a Rochester 4bbl which I'm not familiar with but so far it works great. Played with Holleys and Edelbrock/Carter AFBs. I was looking at the Vortec stuff and can get them fairly cheap but don't think I really need them jsut to play for another year till I get something else. Also I think they had just put a replacement truck cam as the cam and lifters were new when I switched them over. I'd like to switch to the comp cams 256h if any one thinks it would be worth it?
Also, yes I reatained all the marine spec parts off the old motor. No auto parts on here except for the flywheel and freeze plugs. The boat is freash water as well.
The hull and transom are solid as a rock and the boat over all is in great shape minus the teak being weathered, vinyl a little dirty, and the gel coat needing shined up.
This site has been a lot of help on gaining knowledge in a fairly unfamiliar territory so far. Thanks in advance for any advice offered.
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