Swap inline 6cyl to v8

[GarageGuy42]

I have been considering swapping inline chev 6cyl. to a v8 in a pristine 74 mark twain 19'. has anyone attempted this and what is involved as far as the outdrive and any transom adapters. I'm trying to achieve a go fast and the 6 banger isn't getting it. Any useful info will be appreciated.

 

[DJ]

Re: Swap inline 6cyl to v8

Garageguy42,<br /><br />I have assisted in replacing a four cyl. to the inline six like you have, but not to a V-8.<br /><br />If my memory serves me, that drive was OK for lower hp. V-8's, (305 cid). The 350 cid. tended to overpower it and cause failures.<br /><br />Your biggest challenge is going to be with the engine mounts to the stringers.<br /><br />Otherwise, I believe a v-8 will bolt up to the bell housing.

 

[f_inscreenname]

Re: Swap inline 6cyl to v8

The best thing to do is find a motor that came out a boat and rebuild it. There is so many little things you will need to swap out exhust mans,cooling system........I have done 2 ground up restores that were "go fasts". Swaping out motors for larger,getting everything to work. If you dont drink you need to start.

 

[MGuckin]

Re: Swap inline 6cyl to v8

GarageGuy4,<br />Have you given any thought to working with what you have? Don't know whether you already have the v8 or not. Granted you will definately get more power from more cubes in a stock configuration. You might be surprised what you can get out of a modified 6 banger. If bottom end is tight and heads are good, you could add a descent cam & lifters, a descent intake and a carb and a set of headers for about a 40% increase in power. Advantages: Don't have to remove the motor, no weight increase, don't have to buy another motor, definate overall performance increase, 3 hour job, shock other boaters with your little old six banger smokin em. Disadvantage: Use more fuel, make more noise, may put strain on drive components, take about a week to get parts and cost about a grand for parts.<br />Just a thought,<br />Mike <br />

 

[GarageGuy42]

Re: Swap inline 6cyl to v8

Mike<br />Have considered using what I have, But I haven't been able to find anyone that has ever beefed a six cyl before,What lift cam, best carb cfm etc. Also I haven't been able to locate a supplier for thru the hull exhaust, manifolds etc.<br />I put in a Jasper short block in about 10 yrs ago and I know it doesn't have more than 10-15 hours on it so I reasonably certain the bottom end is ok and the pistons are .30 over. The reason for the Jasper is it wasn't winterized properly. Split Block. If you have anymore info, please send it my way. Thanks <br />GG42

 

[MGuckin]

Re: Swap inline 6cyl to v8

GG42,<br />I would go with a 2 barrel as opposed to a 4 barrel but something around a 500 cfm holley, but not with a stock cam or intake, too much fuel. Need low to - mid-range cam, you won't be running high rpm unless you want to build a drag boat. 6 bangers like to run low rpms. As far as exhaust is concerned, you want power or quiet? Run drag tubes and dump it in the air! You could also use street rod type headers (shorties) and make your own pipes and fittings to connect to your existing exit location. Any exhaust shop should be able to make that. If you are running wet exhaust loose it, too much back pressure. I like projects like this. Too bad you aren't closer to me. Try here for available parts. Good tech support and advise. Keep me posted or email me at mikehomeservice@aol.com <br />Mike<br /> http://www.cliffordperformance.com/home.htm

 

[GarageGuy42]

Re: Swap inline 6cyl to v8

Mike<br />I appreciate the input you have given me and checked out the site. They have my info and am waiting for a reply. I don't want to get real radical about the upgrade. The manifold is really the only thing I am concerned about. All it is used for is poker runs (lake bar hopping quickly) and screwing around. In other words, make noise and go fast. I know 6's aren't rev monsters and it runs 4k at wot now at about 45mph on a good day. I got a PWC that will do 65mph last year and now I am getting the need for speed with more than just 2 people on board.<br />I could upgrade this for $3500 and get 70 more hp,and do 85-90 mph but the wife would squell like a pig under a gate. I'm just going to take what I can get and be glad I got it.<br />Anyway, many thanks for the info. I will let you know the outcome.<br />GG42

 

[ODDD1]

Re: Swap inline 6cyl to v8

Drystacking the exhaust on a straight six, in an old Twain???? Got my laugh for today!

 

[DJ]

Re: Swap inline 6cyl to v8

GarageGuy,<br /><br />That old GM six will protest loudly at anything much over 4300 rpm.<br /><br />I too gota laugh out of drystacking a six. It'll kind of sound like these "buzz bombs" that the teenagers drive around now. You know the Civics, and Accords and the like with "coffee can" mufflers.

 

[MGuckin]

Re: Swap inline 6cyl to v8

I didn't say it sound good, just run stronger.