GM inline 6 versus 302/188 ford

[pugsley]

Hi, this may seem like a very odd question but after searching extensively, I can not find a clear answer. I have an old classic 74 22' sea ray that needs repowered. For numerous reasons I do not want another 302 ford or to rebuild the one I have...but it is rebuildable.
In researching the production and as listed here on iboats, the boat originally came with a variety of engines beginning with the 250/ inline 6 as well as the 188 and up from there. Personally, I think the GM 250 6 is one of the great ones. I have had these engines in boats and work trucks from the 1970s on. The trucks ran until the bodies fell off. Same with the boats. They had as much power as I ever wanted.
I have a pristine 250 rebuild and outdrive that I was going to put in a smaller boat. I know that most would consider this underpowered for a 22' boat yet the boat was available with one. I'm old, don't give a damn about speed, water sports, or anything but cruising small inland lakes here in Indiana. Plus, the "admiral" won't let me run over 30 mph in any boat. I have read many opinions. So, for example, I have a 140 hp in a 19' Glastron cuddy which goes 42 mph (gps) with 4 people. (admiral threw a fit) I don't consider it "underpowered" at all.
This sea ray weighs 3400 lbs. I appreciate an opinion on whether the 250 inline 6 would work for my needs which is simply to get up on plane and cruise. Thanks

 

[Bondo]

Re: GM inline 6 versus 302/188 ford

I have a pristine 250 rebuild and outdrive that I was going to put in a smaller boat.

Ayuh,... So long as you have the COMPLETE driveline to swap, 'n can handle glassin' in a front motor mount, 'n lengthin' the motorbox,...

Sure,... Go for it,....

 

[pugsley]

Re: GM inline 6 versus 302/188 ford

Have complete driveline. No stranger to glass and mounts. have not measured but will take your word for it, but the box is huge. PO said with 188 he ran 30+. Wondering how the 165 hp will compare to 188? Boat is in incredible condition for its age but the motor has to come out one way or another. Drilled core samples and found zero water or rat. Despite the condition, I'm reluctant to dump thousands into a repower, particularly when I just had the 250 rebuilt. Also, iboats is the only source I have found that states the SRV was availble with the 250/6, but I know that a lot of 70s boat came with it, bigger than this one. How will the 188 and 165 compare performance wise. Thanks for your response and I realize that I am asking for "educated speculation."

 

[Bondo]

Re: GM inline 6 versus 302/188 ford

How will the 188 and 165 compare performance wise. and I realize that I am asking for "educated speculation."

Ayuh,.... 'bout 23hp Different....

 

[kilowatts]

Re: GM inline 6 versus 302/188 ford

Hi Guys:

As I'm a big fan of the inline 6 any response from me is likely to be biased in their favor! However, in my opinion you'll do just fine providing you're not expecting a speed demon. The first thing you'll notice is better fuel consumption. As Bond-o said though, you'll have to get a new drive line, front motor mounts and box to go with the swap. They are longer and higher than a V8 engine but much easier to work on.
good luck.

kilowatts

 

[erie_guy]

Re: GM inline 6 versus 302/188 ford

Pugsley,

I owned a Merc 188, 302 ford powered 19' Lund fiberglass bowrider for about 20 years without any serious problems. It was a good engine, but I often wished I had the ford 351 windsor or cleveland blocks instead of the 302. I believe they are the same size engines but have a larger cylinder bore.

After about 4 years of ownership, I cracked the 302 block and had to rebuild. I purchased a 302 "bare block" from Ford and swapped all the engine guts and accessories. We used it for another 15 years before I sold it and move to a larger boat.

You might check with a marine engine rebuilder to learn if the 302 and 351 blocks can swap accessories such as exhaust/intake manifolds, alternator, engine coupler, etc. I would repower/rebuilld it as the 351 and enjoy the added torque that comes with more cubes. HP would probably increase as well.

Just my .02.

erie_guy
Port Clinton, OH

 

[bruceb58]

Re: GM inline 6 versus 302/188 ford

I would stick with a 302 and not switch to the inline 6. You will be underpowered depending on conditions. If its just you on the boat with one other passenger at sea level, it might work. With other conditions, might be tough to get on plane. You will be working the 6 harder than the 8 and your fuel mileage could actually be worse.

 

[pugsley]

Re: GM inline 6 versus 302/188 ford

Thanks. I was hoping others would chime in. I ama a strong believer, through experience, in the 250/6. I just didn't know how it would perform in this size boat but my gut instinct tells me it will suit me. I have no need or desire for speed. On the ford, I know thqt it was also a very good engine. In my area and among friends, I know local dirt track car racers. Almost all use a 250 chevy. The others use a 302 block. While they are not marine mechanics, they are true motorheads and know these engines well.

This engine failed due to rusted manifolds. Had water in the oil and on top of the pistons. Head gaskets appear fine. They availabuility of marine parts for the ford is the reason I don't want to replace it. Did some checking and can only find questionable parts. I'm retired. While I'm always buying and selling boats, this will likely be my last for personal use. Probably going to go with the 250. I have 2 complete drivelines that were pulled from an old sea ray. One is a fresh rebuild. Thanks for the advice

 

[HT32BSX115]

Re: GM inline 6 versus 302/188 ford

I would stick with a 302 and not switch to the inline 6. You will be underpowered.

Howdy,


I had a 66 model 18' boat that came new with a 150 Mercruiser(230 cu-in GM 6). When I sold it it was 39 years old and still ran good.

I'll agree that all the GM 6's are pretty much bullet-proof and will run for "ever"......but they're NOT real power-houses.....

I'm with Bruce......that boat is probably going to be a underpowered with a 250.......(as some expert here once said......."There's no substitute for CU-Inches")

If you want to do a little updating, and get an engine that will be supportable for years to come AND since you will probably need to replace manifolds and risers anyway...........(I wouldn't put "old risers/manifolds on any "new" engine), You might also consider finding a GM350 engine and flywheel housing etc as required, and switch it over.

I found my complete 454/Bravo setup on Craigslist........

Since I did mine, I have seen all combinations of engines, drives, new & used etc there.....



Good luck,



Rick

 

[pugsley]

Re: GM inline 6 versus 302/188 ford

I was posting while bruce58 was. That was the real question i.e whether the boat would plane out with the 250 or have significant performance problems. As bondo replied, a "23 Hp" difference. Well, If a 188 hp will plane out (about 20 mph) and run past 30, then I see no reason why 165 wouldn't get the boat up. But, its a hell of a lot of work to find out. I've read lots on the topic of power on this site. One post had charts etc which seemed very realistic in that it takes about 80 hp to get a boat this size on plane.If thats the case, and from owning numerous boats, that sounds right to me. But if I knew, I wouldn't have to ask.
Searay hulls are purported to very well designed. I guess the question is, how does YOUR classic cruiser perform with a 250 inline 6. I know plenty of them were made up to 25 feet in the 70s. Thanks again

 

[kilowatts]

Re: GM inline 6 versus 302/188 ford

Hi Guys:

I have a 21.5 ft Grew/Slickcraft, 1976 vintage; Deep v hull with 6" reverse chines, very heavy for its size; the boat has the original inline six with a Doel Fin on the outdrive; clean bottom and engine in top shape. My boat will plane at a very low speed due to the reverse chines and the fin. I cruise around 3200 RPM at 26-28mph by GPS; the engine likes this speed. I can go around 35mph at WOT of 4200 RPM but I only do that a couple of times a year to blow out the cobwebs. I boat in the Fraser River, the lakes and the Pacific Ocean where my speed is governed by the state of the tide and weather conditions. I have never had a problem with the power of the engine or with performance of the boat. I have a friend who has a very similar boat with a V8 of the same vintage and I keep up with him without a problem but I use a lot less gas and my engine is a lot easier to work on.
I hope this will be of some help.

kilowatts

 

[bruceb58]

Re: GM inline 6 versus 302/188 ford

I had the straight six in a 20' boat back in the 70s. It was a dog with that motor when you were fully loaded.

 

[ziggy]

Re: GM inline 6 versus 302/188 ford

got me a 165hp L6 in my 19' aristocraft. works just dandy. but it's a pretty light boat + 2'' shorter than yours.
with my base load + 2 people, i jump on plane very fast and achive 41-42 mph @ wot. 19p alum. prop. 3 people, still ok. 4 i start to not come out of the hole as fast. 5 and she starts to be a dog. never done 6 which is max cap. of my boat.

that said. keep in mind that an underpowered boat could be dangerous in certain situations.

good luck in your decision...

 

[pugsley]

Re: GM inline 6 versus 302/188 ford

Just as in kilowatts reply, my needs are dictated by personal needs and the waters I boat in. Hull design is clearly a factor. His slickcraft is of similar classic "overbuilt" construction i.e very heavy but with reverse chines and his use of a doel fin. The SRV is not as much of a deep V as the Slickcraft and purported to be designed to get up on plane easily. This boat has bennett trim tabs which will surely help with lift.

I keep returning to 45Autos post "Boat Performance Secrets - How Speed, Acceleration and Efficiency Works!" http://forums.iboats.com/showthread.php?t=225803h. The chart "Power Required vs Power Available" seems to be a great explanation and the difference between what is required to get a boat on plane and the remaing power available for acceleration. While there are numerous factors, I equate this with my big V8 in my Ford truck. Its great for pulling, but I will never use the availble Hp unless I want to pull a trailer 100 mph down a highway. Cold day in hell. Same with the boat. Like kilowatts, we like to cruise in the 25 mph range.

Our lakes are Corp of Engineers reservoirs. All have "Warning; Underwater Hazards" signs posted. Anyone who ignores these is a fool. The levels are constantly changing and a few feet can and does get people hurt every year. No way would we put our grandchildren or anyone else on a tube or ski's behind a boat on these waters. Yet they are nice reservoirs good for relaxation and sometimes good fishing. The two we frequent have aprox 10 miles of cruising waters, and rest are idle zones. Going 40 MPH or more makes no sense in this case.However, Lake Michigan is only an hour and a half away.

I appreciate the inputs and opinions. I have not decided whether to try the 250/6. I like vintage things and enjoy restorations. But I may repower with a modern V8. If I try the 250 I'll post the results. Any other opinions would be greatly appreciated. Based on 45Autos post (recommended) and kilowatts experience with the slickcraft, the 250 should suit my personal needs even if its a "dog" for acceleration past 30 or so. Thanks again

 

[kilowatts]

Re: GM inline 6 versus 302/188 ford

Hi Pugsley:

Please click the following link for a previous thread I started on the inline six torque curve. http://forums.iboats.com/showthread.php?t=455778
From it, other posts and my own experience I'm convinced that I have the ideal setup. Let me know what you think.

kilowatts

 

[pugsley]

Re: GM inline 6 versus 302/188 ford

Thanks kilowatts. In the other referenced post "Power required vs Power Available" torque is referenced but not specified. But power reequired is clearly the torque band rather than available hp at wide open throttle. You mentioned that your boat will plane at a very low speed which seems to paralell my thinking that the differnce of 23 HP... meaning potential developed hp.... should be relatively insignificant except for additional acceleration way beyond my wants or needs. So the torque band seems to be the most important factor. It would be very interesting to see a comparison between the 188 and 165.
While I am not a mechanic, I have had a wrench in my hands since I was old enough to hold one. Regardless, I know a lot about efficiency and practicality. I spent a great deal of my working life as an industrial electrician/electrical contractor. (kilowatts?) So I understand potential and developed HP very well. A motor is a motor whether powered by gasoline or electricity. But with an electric motor all operational parameters are generally readily available. Not so with boat hulls and apparently unreleased camshaft specs etc.
Many posts refer to this engine as a "torque monster" and "workhorse" etc. I agree. My stock car/ dirt track racing friends also do. They could run anything, yet most use the 250...because of its torque.
I have two of these motors and drivelines which were pulled from a huge boat that went to the crusher. I had no idea of what I would do with them. Then I found this old boat in a barn in northern Indiana, under a tarp no less. I won't tell what I paid for it, but it was relatively nothing. Even the gel coat barely needs buffing. The interior is near perfect.
In looking at the torque curve from the post, along with your input, I am leaning heavily towards trying it. Clearly, that is the only way to tell given all the unknown factors. I've owned boats for decades. In every case, I would cruise at 2500 to 3k rpm, regardless of available power. I think that I can do this in this boat witha 250/6. If so it will save me a ton of money and I will have a spare engine.
I certainly appreciate your and everyone else's input and will let you know how I come out.

 

[kilowatts]

Re: GM inline 6 versus 302/188 ford

Hi Guys:

My last name is Watts, hence kilowatts! It seemed amusing at the time,eh? My son, a sound engineer, has a company called Megawatts Sound Inc. which I thought was really appropriate.
If memory serves, when you draw a vertical line on the graph for the 165 the most available power and torque are at about 3200RPM so it seems to me just about perfect for my boat. I wouldn't like to hazard a guess for someone else's boat but given similar characteristics it seems one could expect similar performance.

kilowatts

 

[bruceb58]

Re: GM inline 6 versus 302/188 ford

If memory serves, when you draw a vertical line on the graph for the 165 the most available power and torque are at about 3200RPM

Curious, how are you figuring that?

Bottom line, HP is derived exactly from torque and RPM.

 

[pugsley]

Re: GM inline 6 versus 302/188 ford

I would have laid $ that you were a brother electrican lol. " most available power and torque are at about 3200RPM." If the graph is anywhere near correct, then I should be in good shape. It makes sense to me based on the way I usually handle a throttle + similar characteristics should equal similar performance. Doesn't mean that it will but it nonetheless makes sense. Based on the graph and 45 Auto's post stating that it takes roughly 80 hp to get a 3 to 4000 lb boat on plane, then its worth a shot. I was considering pulling everything out (302) and sending out for magnafluxing etc. Nah. I can put the 250 in and put it on the water and see. Its not like I'm going out of pocket for something that might not work. I measured and the bilge area has plenty of room. Making a box is nothing for me. I have a complete woodshop. I'll keep you posted. Thank you again

kilowatts

 

[bruceb58]

Re: GM inline 6 versus 302/188 ford

Curious, I am assuming you ran the boat with the 302 in it. How did it perform? Did you feel you had a lot of reserve there so that you didn't need full throttle to get up on plane?

I had a friend years ago that had your boat witht the V8 and it was a bear to get up on plane with 4 people and gear. Of course this was at a couple thousand feet elevation.