Info on 165hp 250ci in line 6 cyl.

[Step Up]

So I have this 1974 20 foot Sceptre it has the original 6 in it. I want this boat for a run about only. So I was thinking pull the 6 and go 5.7 or 5.0 but then I was thinking why. I am not building a race boat. But I would like to spruce it up the 6 a bit. Have any of you beefed up a 6 before? As well any one know the average WOT of a 20 I/o with the 6

[77SceptreOB]

I had that engine in one of my past boats (1977 Stingray) and loved it. Very dependable and easy to work on.

Jim

[wattaway2]

The old Chevy inline 6 is a reliable piece . There many parts available Clifford made intake manifolds 6=8 cams and such a lil research will bring a wealth of info. Contact the manufacturers for there advice on combinations for marine work ignition systems -going to a updated pointless design making spark more reliable . Exhast would likely be the hardest hop up design to find but I'd bet there's something out there. In the end it's just a air pump more in and more out = more power but it must work as a combination!

[Terry England]

Originally Posted by Step Up

So I have this 1974 20 foot Sceptre it has the original 6 in it. I want this boat for a run about only. So I was thinking pull the 6 and go 5.7 or 5.0 but then I was thinking why. I am not building a race boat. But I would like to spruce it up the 6 a bit. Have any of you beefed up a 6 before? As well any one know the average WOT of a 20 I/o with the 6

I think they are probably one of the best sterndrive power-plants ever put together. Formula and Bertram put "pairs" of them in hundreds of boats and Cigarette used a pair them some of their "fishing" 28's. A single manifold and elbow cut down on the maintainance costs and they seldom developed enough torque to destroy a type one Mercruiser. You could "squeeze" two in an 8' beam hull and still change the starter motors without pulling the engine. They were part of the "Iron Duke" Chevy family of engines. When Mercruiser started using the 302 Ford block "888 Mercruiser" (V-8 - 188 HP) they became a little more popular in a single engine application than the inline six. Still there are many functioning today with marginal mechanics keeping them going.
Pontiac used that 250 CI block and built an aluminum Single overhead cam version with better carb's and put some in Firebirds and their LaMans' or Tempests. That very light motor would make 250 HP, I think out of the box.
I believe you would see something north of 40 MPH with one in a 20' Sceptre. (The 4 cylinder Mercruiser powered SeaFaris would go about 36 MPH) What a great "low budget" Ski Boat. Pelican knows about these motors and drives, maybe he'll chime in.

[Fr. Frank]

Originally Posted by Terry England

...
Pontiac used that 250 CI block and built an aluminum Single overhead cam version with better carb's and put some in Firebirds and their LaMans' or Tempests. That very light motor would make 250 HP, I think out of the box.

Mercruiser DID make a 250hp version of this motor for racing purposes. It was called, strangely enough, the 250/250. used through-hull exhaust and was coupled with the M/R drive. Carburetor was a marinized Rochester Quadrajet, but I don't know what the cfm rating was.

I've only seen two boats with this power setup.
John Allmand made a 19' back in 1968 for the offshore racing circuit (yes, intended to compete with the 21' SeaCraft), that was powered with a single 250hp 250ci motor. I don't think he ever finished a major race. We had this boat collecting dust in the boat barn, and I only saw it taken down once for someone to take photos of it.

Formula made the '69-70 23' with twin 250hp 250ci I-6 Mercruisers and they too, were, in fact, rated at 250hp each. Top speed was in the high 50mph range. We got one of these in at Waterway Marina in Palm Beach Gardens back in '84 with a bad motor, and we sent it across the street to Frank Brown Marine. As I recall, they gave it a new long-block because the motor had ingested water through the exhaust. I recall one of the mechanics saying he got it up to 58 mph during "testing".

[Step Up]

Terry England is this the Terry England that lives in Seminole Florida ? I think I would be happy with 40 knots this is going to be a run about as I have boat to fish from. The hull restoration will beat up my budget so keeping the power cost to a min. would be a good thing. The 6 that is in the boat turns but has sat for many years so a total rebuild is a must. Ty for the info

[Terry England]

Originally Posted by Step Up

Terry England is this the Terry England that lives in Seminole Florida ?......

That Depends on if I owe you money or not -
If I don't owe you money, then still I don't know anything about jumping cars at the railroad track crossing on 78 Avenue, Skiing the Narrows before Hamlin's Landing or Robyn Dalton. I don't know anything about racing Soap Box Derby cars down the hill south south of SHS on Vonn Road or Penny Chetham either. That was the other "Terry England" and NOT ME!
If I do owe you money than Terry England is just my "Nom De Plume" and my real name is Lee Pearce and I'm a bailiff with PCSO at the County jail.
Step Up, how would you know about that other scoundrel, vagabond, pirate and derelict who uses my alias? It's embarrassing!!!

[Bushwacker]

Originally Posted by Step Up

. . . So I was thinking pull the 6 and go 5.7 or 5.0 but then I was thinking why. I am not building a race boat. . .

One potential issue with a V-8 or even a V-6, is clearance in the engine box. The 20' Sceptre that Strick redid originally came with a V-8, which he pulled and replaced with a bracketed outboard. I remember Strick commenting that clearance in the engine box was very tight, such that even changing plugs was a chore, let alone trying to change exhaust manifolds, risers or starter! Big difference in maintainability between a V engine and the I-6!

That said, the 3.8L GM V-6/Mercruiser seems to be a nice package, as I remember a Seafari advertised for sale with that package which was reportedly a 50 mph rig! Although the I-6 is probably heavier than the V-6, I think your CG would be further forward with the I-6, which would make it ride better!

[FLexpat]

Originally Posted by Step Up

So I have this 1974 20 foot Sceptre it has the original 6 in it. I want this boat for a run about only. So I was thinking pull the 6 and go 5.7 or 5.0 but then I was thinking why. I am not building a race boat. But I would like to spruce it up the 6 a bit.

I put a 5.7 in a 20 Bertram that originally had a 165 in it - with the 5.7 it was fast but I REALLY wished I had left the lighter/smaller motor in it; changing plugs was awful and usually involved blood, it didn't self bail at the dock, trimming it was hard, and it 'wandered' at idle with all that weight aft.
The only way to get more power is to move more air through. I am pretty sure 292 I6 block is the same as the 250 with a taller deck and longer stroke - it was a truck engine. I know they made marine versions that were about 200HP. You could also port and polish the head and if it is FW cooled you could go to a good aluminum intake manifold. A good roller cam in all that and you would be up well north of 200HP. It would be a project for sure.

[jtharmo]

California Bill has you covered.

https://www.amazon.com/gp/aw/d/19311...SGHRCZ8Y4X79R8

In the early-mid 50's the Chevy I6's were a staple of amateur drag racing and land speed cars. They were more efficient then the flat-heads and OHV V8's were new and not readily available in junkyards I imagine. I would have to think there is a lot of performance cross-over. And think of the cool names, "6 Pack", "Six-Shooter", etc. I say be different and proud of it.