1975 SRV 220 Overnighter Hard Top - Anybody know the Top Speed?

[mitchvon]

Agreed. I beleive, judgeing from the motor mounts this is a stringer set up.

I considered pulling the powertrain and replacing it with a 350 MPI V8 and Bravo III drive. total cost about 3-4 X the purschase price for the boat and trailer. The dual axle trailer came without lights or brakes. I bought and installed a new hydraulic actuator, 4 new rotors and disc brakes, new tires and wheels then wired it and installed lights to be safe and legal. All worked fine when I pulled her out in Brinnon and pulled her up to Port Angeles.

351 GT40 heads have larger combustion and valves for better flow and are realatively inexpnsive. Ford used them on the Explorer from 92-01 so getting them from a wreching yard and letting a machinist rebiuid them is typically less sweat and labor then an exngine swap. Typically provides a increase of 20-30% hp and I can re-use the 302 manifold as the angle is from the block. The GT40 heads take a larger bolt diameter but there are there are inserts available to use original bolts. There are also some marine fuel injection kits available as well for improved fuel efficiency. Then of course there are a litany of prop choices. If money were no object I'd consider a toroidal propeller, google Sharrow Marine, whose performance shows some impressive numbers. Lastly if I wanted to get nuts, I could rig her with hydrafoils but I'd need a longer shaft outdrive.
I'll see how she runs after some lower cost improvements.

 

[DaveKamp]

Your 'boat info' description says "1 engine OMC/Ford 302 V8 with a 2 barrel carb"
I don't think you have an OMC.

This is an OMC 'stringer drive' typical of what would be behind a V8 of the mid '70's era Sea Ray:

The drive's thrust does NOT go into the transom, it goes into the engine, which is secured to the stringers, hence the term 'stringer drive'. OMC used a variety of GM and Ford engines throughout their production, including the Buick 225 V6.

The stringer drive coupled the engine's output to the drive through a pair of 'drive knuckles', one inline with the crankshaft, the other in line with the upper gearset, and the knuckle's centerline pivoted on-axis with the knuckles. The concept worked, but the knuckles did wear divots intot the knuckles, as visible in this picture:

This is a MerCruiser R/MR that would typically be found behind a 1976 SeaRay 22:

Someone fitted this one with a plastic 'whale tail' by Doel-Fin. Advertised to make miracle improvements in basically EVERY aspect of performance, it was most effective at generating sales revenue and fouling with seaweed. Imagine it's not there, and gain fuel economy and speed. For what it WOULD improve at low speed, one could install a pair of trim tabs and do much, much better.

The MerCruiser R/MR/Alpha series, and their bigger brother Bravo, and the earlier high-power TR/TRS drives all mounted securely to the transom, decoupling the reaction load from the engine, hence, also from the stringers.

They all used a double-cardan joint between the drive and engine coupler:

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I am absolutely, positively certain that no matter WHAT you do to your current engine's cylinder heads, that it will NOT overcome whatever problem is limiting your ability to exceed 3000rpm. You're NOT going to get any improvement by changing the heads, for one basic reason: The head flow of the WORST 302 head, at 3000rpm, is NOT RESTRICTIVE. On ANY MerCruiser drive system, You won't find the flow limits of the factory heads. The factory iron heads will breathe fine to above 5000, but the MerCruiser R/MR DRIVE cannot spin above 5000rpm- it will melt it's upper gears.

The breathing limitation of a MerCruiser 188, and any OTHERs of the era (the 888, 233, etc) is the log-style exhaust manifold, the riser elbows, the Y-pipe combining the two risers, the passage through transom plate, then through the drive housing and out the exhaust hub.

But IF you were to change the heads, convert to through-hull (wet) exhaust, and put on EFI, you'll still have the same situation- SOMETHING is keeping the engine from breaking 3000rpm.

You COULD have an improper prop pitch. You MIGHT have a case where the drive you have, was accidentally fitted with the wrong gear ratio at the factory. It might be that your boat's prior drive used that same prop and a LOWER gear ratio... as it was not uncommon for manufacturers to build up boats and request an OPTIONAL lower ratio. Your hull with a 1.65:1 or even 1.84:1 ratio, swinging a large diameter, higher pitch prop would perform well with a lower power engine such as the 188.

The gear ratio is USUALLY stamped on the port side of the upper gear housing to the left of the serial number:

You MIGHT have a situation where the throttle handle, or the throttle linkage at the engine is getting hung up on something. You might have improper timing due to spark advance or point cam wear.

My gut says it's something simple. The 22ft hull, with windshield and roof in the wind, drive fully down, It should come up on plane at about 20 by 3500rpm, and once up and flat, start trimming up, it will lift to the first chine, and top out around 28-30mph at about 4400rpm.



Going to a counter-rotating double prop system will certainly do a good job at adding unnecessary weight to the transom and emptying your boat wallet... if you're considering all that, and the spiral prop, then you should really consider having an entirely new hull made, and move your SRV's hull brand plates carefully removed and fitted to the new hull with solid gold sheet-metal screws...

 

[DaveKamp]

But i guess if you're serious about the hydrofoils, nix the I/O altogether and drop in a GE T58 and a surfacing prop. that'll save you lots of weight and eliminate mechanical complexity.

 

[mitchvon]

The sterndrive appears to be a Mercruiser from your photo. No numberes on either side nor on the stern.

GE T58? either that or a couple of JATO packs to get up on plane quicker.

Both days I took her out to break in the drive I was in Hood Canal sailing from Pleasant Harbor in Brinnon up to Dabob Bay Near Quilicene and back. Maybe 3-6 knot breeze if that. Seas were flat and calm. Would have good for water skiing. I had to open the front hatch as there didn't seem to be much of a breeze and I was need some air to flow though the helm area as sun was quite warm. It was late August.

Best I can tell notes writen on the Merruiser Seervice Manual "Outdrive Mercruiser 888- Serial # 4227910" I plugged it into SEI"s website and the recommend replace gear ratio looks to be 1:47

 

[DaveKamp]

Yes, that's a MerCruiser R-series drive system, with a Sierra marine replacement drive.

I haven't seen any recently, but many years ago I installed an SEI replacement drive, and it had the gear ratio numbers stamped on the drive upper.

The manual will say that the STANDARD gear ratio for your drive is 1.47:1... and with the 22's weight and the 302's torque curve, it would have been fitted with a 11" pitch prop, 4,400rpm at 28mph under 10% slip. I don't think the 302 would ever manage that under the 22 with that wind drag.

Your BOAT may have been fitted with a drive that had OPTIONAL ratio of 1.65, or 1.98, in which case, it would have had a higher-pitch prop.

Going to a 1.65:1 ratio means you could go up to a 13pitch, 4400rpm, 10% slip at 29mph.
Going with a 1.98:1 ratio, 4400rpm, 10% slip on a 15" pitch, you're at 28.5rpm.

1.65:1 and 1.98:1 were ALL OPTIONAL RATIOS for the 188.

If you find NO OTHER obvious problems, and you're still stuck at 3000rpm, and your prop is 15" pitch or greater, then the problem is that your replacement drive has 'standard' 1.47 gears, when the ORIGINAL drive had Optional 1.98 or 1.65:1.

The MOST COMMON props used on the R/MR drive series was 15,17,19, and 21. 11, 13, 23, 25 were very uncommon, the lower being on workboats and houseboats (frequently twin engines, and having significantly more blade surface) and the higher were on very light runabouts with considerable horsepower-to-weigh ratios. Typically, the 23 and up were cleavers (like mine).

You didn't note your prop pitch or diameter, you just noted 20kts at 3000rpm.

To get that, with a 1.47:1 ratio, you'd need a 13pitch prop at 9% slip, or a 15pitch at 20% slip. If you're not on plane, 20% slip would be totally plausible. The 9" slip at that velocity not so plausible.

What IS your current prop pitch?

 

[mitchvon]

The prop was a little hard to read but ìt looks ĺike it's a 15 inch prop with a 17 pitch.

 

[DaveKamp]

Okay, so 3000rpm with 1.5:1 drive ratio, 17" pitch and 10% prop slip, you SHOULD be going 29mph.
With that combination, at WOT of 4400rpm, you'd be at 38mph.

If you're only making 23mph with that combo at 3000rpm, your slip MUST be almost 29%, which means you have incredible drag...

Or the tachometer is wrong, and your ignition timing is off... and there's a whole lotta something ELSE holding you back.

I really do NOT think that the 188 has the amount of area under the torque curve to push you to 4400 with that combination.

So there's one other possibility- that your tachometer indication is wrong. Since it's a dwell-sensitive device, if your point cam is worn, that changes dwell, and causes timing advance to drift.

put a timing light on it, and check see if the mechanical advance IS advancing.

 

[Lazy Daze]

Mitch, there's been a lot of interesting talk throughout this thread... but have you taken the boat back out and tried trimming up higher, yet?

 

[mitchvon]

Dave,
"If you're only making 23mph with that combo at 3000rpm, your slip MUST be almost 29%, which means you have incredible drag..."

I agree. The bottom was never painted and after runing the first 5 hour I/O break inn the boat sat in the slip for a week. When I returned there was substantial growth. In my youth I would have jumped in the water and cleaned the hull with a 3m scouring paid. No wetsuit and 50 degree water I attempted to clean off as much as I could with a long handled nylon brush.

When I hauled her out power sprayed the bottom there was a few barnacles in their early stages on the bottom. I have sinced fully cleaned the bottom and and about to paint on antifouling

That, new plugs, plug leads, a new coil and sacking the old points for electronic ingnition, should help me realize a significant improvement.

I'll keep all posted on the final outcome once I re-launch

Okay, so 3000rpm with 1.5:1 drive ratio, 17" pitch and 10% prop slip, you SHOULD be going 29mph.
With that combination, at WOT of 4400rpm, you'd be at 38mph.

If you're only making 23mph with that combo at 3000rpm, your slip MUST be almost 29%, which means you have incredible drag...

Or the tachometer is wrong, and your ignition timing is off... and there's a whole lotta something ELSE holding you back.

I really do NOT think that the 188 has the amount of area under the torque curve to push you to 4400 with that combination.

So there's one other possibility- that your tachometer indication is wrong. Since it's a dwell-sensitive device, if your point cam is worn, that changes dwell, and causes timing advance to drift.

put a timing light on it, and check see if the mechanical advance IS advancing.

 

[mitchvon]

Mitch, there's been a lot of interesting talk throughout this thread... but have you taken the boat back out and tried trimming up higher, yet?

Hi LD,

Getting ready too re-launch later this month after some serious maintenance. I'll update this thread on the final outcome.

 

[Drifter22ft]

I have a 74 220 srv with the ford302 something to keep in mine is the haul is thicker than the newer one even just a couple years newer was a lot lighter boat. Have had mine for over ten years and it runs great but also slow but I bought a boat to be on the water not flying and it’s on the water. Enjoy the old girl you will get a lot of looks