Inliners International Forums General Discussion Engines Custom Marine Spec 292

I have a 20' deep V planing hull project boat that I'm planning to repower soon. I'm thinking of having custom built marine engine based on the 292 chevy 6 installed in it. Given that a marine engine has to operate in a continuous duty environment, it has to be built differently to stand up to the challenge. Getting rid of the heat and detonation are the main enemies here so you can't build anything wild and expect it to last. I'm not interested in racing. I want an engine that's happy to run reliably at 3000 RPM all day long on mid-grade gasoline. The goal is to produce as much torque as possible at a cruising RPM of 3000-3200 without burning mountains of fuel in the process.

In my view there's lots of good reasons to use the 292 inline 6 for this application which I'm sure many of you might already be aware of:

-7 main bearings instead of 5
-the undersquare bore x stroke produces lots of torque at low and mid-range RPM's
-cast iron cylinder head instead of aluminum which can be really troublesome in a marine environment
-simple gear driven camshaft
-lots of readily available marinization parts suchs as manifolds, carbs, vapour proof starters, vapour proof alternators, vapour proof distributors

I haven't yet read Leo Santucci's inline 6 manual but I plan to at some point soon. I want to be sure that any modifications to the block/head required to eliminate any possibility of hot spots and oil starvation are carried out.

I think I've done my homework so here's what I propose to have assembled:

-precision machined block and head
-forged steel crankshaft
-forged connecting rods
-forged or cast pistons (suggestions here anyone)
-clevite bearing shells

-I want to burn midgrade fuel without any possiblity of detonation under load so I believe compression should be 8.8 to 1 or slightly more or less

-fully balanced rotating assembly

-roller lifter and roller rocker valve train assembly
-stiffer valve springs
-hardened larger than stock intake/exhaust valves
-hardened valve seats
-mild port and polish of cylinder head (finished ports dimensions must match marine spec intake/exhaust manifold)
-polished and cc'd combustion chambers
-stainless steel headgasket and manifold gasket
-marine profile camshaft for maximum torque at 3000-3200 RPM with a smooth idle and proper cylinder scavenging/heat removal (is this all possible at once?)

No scrimping on vapour proof marinized parts that could result in a FATAL explosion! I believe that crusader marine still sells parts for the 250 CU. IN. chevy 6 that should bolt right up including:

-vapour proof starter
-vapour proof alternator
-crusader intake/exhaust manifold and riser
-crusader fresh water cooling system (might need a larger heat exchanger)
-oil cooler
-centrifugal advance distributor with correct advance curves and a pointless HEI
-450 CFM marine 4 bbl carb with fitted with flame arrestor (Mercruiser had this on the only marine 292 they offered for sale in 1974)

I want everything kept as simple as possible for reliability, so I'll stay away from any fuel injection and electronic engine management systems.

I'm thinking that the finished engine should produce 225 HP at 4800 RPM and about 275 ft/lbs of torque at 3000 RPM and with proper operation and maintenance should last for 2500 operating hours before needing a teardown and rebuild. Fuel consumption should be in the order of 5-6 GPH at cruising.

Excluding the marine accessories, what will it cost to build my engine at a specialty engine shop?

Have I missed or overlooked anything? Your suggestions/comments/advise/feedback are welcome.

Thanks in advance.

Your overall plan looks sound & yes, go through Leo's book too.

I would get 'flat top'* forged pistons as cast are the 'dish' type with the lower compression etc. *With the forged ones; you can choose the exact ratio (flat or with doam) you want for your project.

There have been several discussions on this, so check tech tips in the left margin.

Good luck.

First off Your going to be Pressed/hard luck doing a roller cam To run roller lifters.
as for a stainless steel head gasket??? why and again won't be easy to get. IT may?? have to be custom made. The Felpro 1025 should work just fine. bring the compression to 9-1 should help get the HP your after with a straight patteren cam NOT a dual patteren. HYD cam with around a 500 lift and a rpm band from Idle to 5000-5500
should also Keep you in a VERY good power band at 3000-3500.

The head alone will run you in the 1500-2000 dollor range.Or plus depending on the shop.

The stock crank should be fine same as the rods.
your not pushing Monster HP and your not pushing the HIGH rpm power band/range.
Ps as far as a Marine cam Check with Tom Langdon.

Cool plan, sounds like one heck of a solid runner!If you do not intend to go big on the bore and you keep the compresion as low as you mentioned, there is just no way you will need a bigger heat exchanger. The forged crank was only made in 63, they are hard to find and only have six counter wieghts,where as most of the cast cranks have 12.The cast cranks are kind of prefered (Leo's book covers this very well)and are plenty strong. Also a high quality harmonic balancer would round out whats sounds like one very reliable engine.

NW, contact Tom Langdon at Stovebolt for info on the marine version of the Chev 6. S

Larry/Twisted 6,

What's the practical/performance difference between the straight and dual pattern cams?

i think a dual pattern cam would help a head that has flow difficulties on either exhaust or intake. for instance a head that has poor flow on a exhaust might like more duration than intake to keep proper intake / exhaust flow ratios. i believe the ratio should be around 80%. tom

Not sure if you got a price on a forged aftermarket crank, but around 4-5 thousand should be able to get you one.
Accordong to Mike K , they do not last any longer than a stock cast unit.
In Brazil you can buy them for about 1200-1500 US dollars.
Correct me if I'm wrong Douglas.
Our resident Brazilian. Great guy!

A dual patteren cam lets more spent gasses to leave the combustion chamber as it takes on Fresh incoming fuel & air mixture. (Which is known as what is called a Over Lap) (were the intake & exhaust are open at the same time)
Where as a single pattern cam The Valves are close before the next one is opened. A Marine cam IF i remember right is basicly a single pattern cam and has a Longer/wider Power band.BUT I could very well be off on this. as I don't know much about marine cams.

Gentlemen;

I'm not familar with the latest "jargan" on cams (single/dual pattern) and "overlap" is a hard concept to explain, but I'll try.

With (high lift/long duration) cams there is a point in time between the intake and compression strokes where the intake valve has not fully closed (low speed) and some pressure is lost between cycles. As the assembly rotates there is also a point in time between the power and exhaust strokes where the exhaust valve opens slightly ahead (low speed) losing there as well.

As the engine's speed increases, the 'time' of these events lessens, because "real time" has stayed the same.

This is why compression (pressure) readings are lower with these cams and engines with them can't idle well.

At some point in real time these events become so small (higher engine speed) that they can't affect and this is where the "power curve" begins.

In marine use, the engine must idle/function @ low speed well, so I would not recommend a really "radical" camshaft etc.

Good luck.

Marine service is a completely different animal from most other uses. You've stated you'd like to get 2500 hours out of the engine, and I'd like to share a few reservations I have with some of your combination.

In my experience, longevity is reduced faster than power is increased. Getting 2500 hrs pushing a deep V is a big challenge. To get 2500 hours out of "hopped up" engine is unlikely. You'll have to decide whats more important, reliability/longevity, or a few extra knots.

Compression probably shouldn't exceed 8-1. You may find you need to fuel up somewhere that has no choice in fuel, and it may be a long trip @ 8 knots to keep it from hammering. The combustion chamber isn't known to be detonation proof.

Save the money you were thinking of spending on roller parts for the valve train. The rocker arms might last, but are not neaded in a low RPM engine, and the life of roller solid lifters at low RPM is pretty short. As failures on the water can be as bad as a failure in the air, you should keep it simple. In years past, even hydralic lifters were frowned upon. My own boat is 45 years old, and the original engines had solid lifters as do the replacements.

Forged pistons are a very good idea, and most marine engines had them. You never know when that plastic bag or piece of weed clogs the cooling intake and if you aren't staring at the gauges at that moment detonation will be the wake-up.

I'm with some of the others that a forged crank is not needed as the cast crank is very stout. My choice for a cam would be a solid lifer marine grind, although I don't think it would meet your 3K peak torque desire. I also have reservations about increasing valve size. At the RPM you are going to run, measurable power increases will be low, and as the exhaust valve depends solely on getting rid of the heat it's bathed in by transfer into the seat, the larger the valve, the hotter it'll run. Sodium cooled stems will help.

Good Luck

PM sent

Interesting discussion, here is my 2 cents: With the single pattern cam both the duration and the lift are exactly the same for both the intake and exhaust. Dual pattens are all freaky and complicated because the intake and exhaust can share the same duration but have different lifts, or they can have the same lifts but with different durations, or best of all, both intake and exhaust can have both different lift and duration. There is an almost infinite # of combinations with dual pattern cams so how people come up with and choose their own custom grinds is beyond me and would be interesting to to hear about.

Dan

Dear Dan;

I have sat through several "engineering" seminars over the years and most is what I call "techno-babble".

The relationship of the camshaft to the crank is the same weather stock or 'souped up'.

The main purpose of the (hi lift/long duration) cams is to get more air in and the exhaust out FASTER etc. The 'better' one can do this the more power you have.

So you can call it a pink elephant or anything, if it works good.

Greybeard is correct in that; 'hopping up' a marine engine is risky business.

Happy trails.

Thanks for all the great info. I've just returned from an enjoyable and needed weekend away.....

Sounds like a forged crank isn't needed and isn't readily available, so I'll drop that from the spec list though the ones from Brazil sound interesting enough.

Is it possible to have a billet crank custom manufactured somewhere at a reasonable cost?

As for the roller cam, I read somewhere they reduce friction which suggests some reduction in heat production. I'm sure I can source one somewhere as a custom order item. I note that Mercruiser now installs roller lifters on lot's of their newer V8 power offerings. Maybe an engine that spends it's life running at 3200 RPM isn't going to really benefit from it anyway.

I know that getting the cam profile and valve overlap specs correct is important otherwise you get too much heat buildup from the continuous duty cycle. You can still buy replacement cams for the Mercruiser 6 cylinder engines from a number of sources. Perhaps I'll simply use one of them.

Headgasket failure due to corrosion is a common problem with marine engines. That is why a stainless steel core headgasket is needed. Felpro does offer them for sale.

Any sodium filled valves that I can get my hands would be a benefit. Hopefully, I can source them in the factory spec diameters. Any suggestions on where I can source these?

Can anyone suggest a competent shop to build an engine for me. If I get the Bertram 25 I've got my eyes on at the moment, I'll need two engines, not just one.

Finally, I don't consider an engine with 8.5 or 9-1 compression together with any of the modest mods I've proposed as being seriously hopped up. Mercruiser did build a 292 marine engine for one year in 1974 and rated them at 200 HP intermittent duty and Crusader also offered them rated at 185 HP. I'll speculate for a moment that there wasen't going to be a big market to sell parts for these units and thats why they discontinued to offer them. I imagine it was easier then as it is now to sell a V-8 than it is to sell a vanilla inline 6 even thought I believe that the 6 is better suited to the job.

Using the custom (forged) pistons (+.060) will give the compression/CID you want/need with a 'mild' Hyd. lifter cam (ballanced assembly) & your stainless gasked should be enough (easy 200Hp.) You could add the 'lump ports' too. :rolleyes:

A "pleasure craft" is not fun with a blown engine, under tow.

All this 'fancy stuff' is great for the Drag Strip crowd, as their main goal is to 'shave' another half second from the ET.

NOT needed here.

Good luck.

Roller cams can be had like a dime a dozen Like shoes tee shirts For the Vthing.It's just that No body has a call(interest) for Our L6s Other then US.So nobody is making them.
The Felpro 1025 would be the head gasket your after It has the stainless steel ring.I think??
the Detrot gasket also has it But I don't know for
sure I haven't used that gasket In a VERY long
Time.

I have worked on few boats mostly Detriot Diesel and they inject huge immpossible on land amounts of fuel and still run all day and never get hot. I know that six in a row is where the simalarities between these engines end. Although the 292 does have a very respectable torque curve. I live next to Puddingstone so when I think of "hopped up" I just get a mental picture of a few 55gal drums of alcohol sitting on the end of the dock empty.

I don't know if your boat is an inboard or not, however, I sure wouldn't like to be around any gasoline that can enter any enclosed compartment.

Diesel fuel won't explode at atmospheric pressure. Diesel engines can be had in 'inline configurations.' A 4BT Cummins or 6BT should power your boat nicely. Early Dodge (non-computer) engines are plentiful and cheap and you could build a great intercooler with your free supply of cool water. Detroits are also good-a 4-53T-would do nicely, and there is lots of marine gear for them.

I hear you loud and clear on the explosion risks connected to inboard gasoline engines on boats. As with many things in life, It is a risk I am willing to accept.

The weight of a marinized 6BT would likely sink my boat and the total cost of a new sterndrive to handle that kind of torque would more than completely empty my wallet.

Low RPM diesels don't mate up well with planing hull vessels. In order to get the proper propellor speed you can't use any reduction in the drive line. That requires major retrofits in order to install larger shafts etc. to handle the stress. Diesels also cost BIG BIG money to fix when they break.

High RPM diesels don't seem to stand up either with lot's of problems due to corrosion, cracked cylinder heads and WHY. These units also cost lot's of money to fix when they break as well.

There are lots of folks who have collectively spent many many millions of dollars trying to find the perfect diesel power solution for their Bertram 25's , 28's and 31's to no avail.

In my view, the using the 292 is an overlooked and novel lower cost approach to the problem of powering a Bertram 20 (single) or Bertram 25 (twin) balancing cost, installed weight, performance and fuel economy.

Don't know if you found the external pieces you were looking for, but this might be a cheap and easy way to get them....

http://cgi.ebay.com/ebaymotors/OMC-165hp...1QQcmdZViewItem

Hi, Northwester,

After reading your post and the various replies to it, I think there is one option that you might have missed. That option is water injection. If you're attempting to control detonation, there is no better solution. In the 1970's, I had a Chevelle El Camino with a big block Chevy V-8 in it and somewhere in the neighborhood of 11 or 11.5 to 1 compression. By 1976 or so, there was no gasoline available at any gas station that would not detonate fiercely as soon as I started the motor, and I wound up parking the El Camino for most of a year because I was afraid of ruining the motor and didn't have the money at that point to do a complete rebuild with lower compression pistons. Around 1979 I heard about someone marketing an aftermarket water injection setup that was supposed to control detonation. It was made by one of the main aftermarket speed equipment companies (although now I don't remember which one)and didn't cost a fortune, so I bought one and installed it on the El Camino. It worked to perfection. I still had to run premium fuel, but the detonation was completely gone.

I still don't remember the name of the company who made my water injection, but when I put "water injection" in the search field on eBay, I usually get a few hits on NOS Holley or Edelbrock water injection units produced in the late 70's for the exact problem that I had. Recently I have done a bit more research and found that although Holley and Edelbrock no longer make water injection systems, there are companies whose entire product line is water injection kits and parts. Coolingmist is one of them, and they make kits for both turbocharged and normally aspirated engines. The normally aspirated setup sells for about $200 US, so they're definitely affordable, and judging from their literature, they're also better quality than the old Holley and Edelbrock units.

You can run distilled water, and I have heard from people who should know about these things, that you can also use windshield washer fluid in them with no problems. Besides controlling detonation in an engine, they also keep it cleaner internally due to a sort of natural steam cleaning of the cylinder head and piston crown when the engine is running, so you don't get the normal carbon buildup. You can do a search for Coolingmist, but I think their website is www.coolingmist.com if you want to try looking at it. If that address isn't right, just do a google on Coolingmist and you'll have it.

As far as the rest of you engine project goes, it sounds like you've done your homework well. Except for maybe the roller cam idea. A flat tappet cam will work just fine for what you want the engine to do. Roller cams are generally meant for high rpm engines, which you apparently don't need or want in your boat. I think probably an RV type of cam with a power band from 2000-5000 rpm would be just the thing for your boat motor.
Good luck with the project. It sounds like fun.

I am running twin 292's in my boat right now. You don't need to build anything above stock for your engines to run reliably for 2500 hours. My boat is a little bigger than the 25 Bertram and a little heavier, but not much. I run my boat on regular gas and cruise it at 3200 RPM's. The biggest killer of a marine engine is ROT. It will likely take 10 years or more for you to get 2500 hours on your boat, and that is if your use it every weekend of the year for 10 years. Sitting in the marine environment is the killer.

You WILL burn more fuel than you are hoping for. I have 2-barrel carbs on my engines and burn ~8 GPH per engine at 3200 RPM's. My speed is ~30 mph.

Any other info I can provide, let me know.

Water injection, very novel. I'm going to explore water injection sytems a little further. How long does a typical tank of water last?? 1 hour, 4 hours?

I use my boats any chance I can get. My last boat received 400 hrs use in 2 years. Dockside ROT is a big problem for sure. I will be keeping this one at home on a trailer and flushing with freshwater following any use and fogging the engine when it's layed up for any period.

I'm working in Imperial gallons for fuel consumption. So 8 US GPH = 6.5 Imp GPH. Your boat is heavier and your running it a little harder so I think I'm still in the ballpark at projecting 5.5 Imp GPH fuel consumption per engine.

I'm rethinking specs for engine based on the great information everyone has provided. Thanks! I'll start a new thread with the new specs for discussion.

To that end, I'm reconsidering my position on fuel injection and engine management systems. An integrated engine management/fuel injection system would allow me to eliminate the distributor and replace with individual coil-near-plug ignition. I would also be able to replace mechanical fuel pump with an electric one and exchange the carb with a throttle body injection unit. Couple all of this with a knock sensor and I could raise the compression to 9-1 and have fully programmable control of fuel flow rates and ignition advance curve. Bad load of fuel, no problem, the system will look after the engine and ensure no detonation. This should improve fuel economy as well.

Having stood on my head and suffered some of the worst motion sickness of my life in the Haro Srait trying to solve an engine problem, I take my hat off to anyone who wants to load their boat down with engine electronics.

I quess it's like driving a new car, if the engine quits, don't bother opening the hood, 'cause there's nothing you can do but call AAA. I quess if the engine quits on your boat you need not bother opening the hatch. Call the Coast Guard.

I still have points in the engines in my boat, and carry spare points, condensers, rotors and caps, extra plug wires, fuel filters, carb kit, fuel pump, water pump impellors, and the tools to repair. I can't imagine what one would do out in the Haro or Georgia Straits and something in the electronics takes a dump. Stuff only seems to quit when the wind's blowing 30-40 and and the tops are blowing off the waves into your face. Salt water everywhere...and electrical connections don't like it.

Don't get me wrong. I applaud the use of the six. They take up less floor space in the boat, can be very reliable. My thoughts about a boat out in the Salt is to keep it simple. KISS !!!
I lived on the Strait of Juan de Fuca and have run boats to Alaska. I personally wouldn't trade off reliability or the ability to service for a couple knots of speed.

Good Luck

Greybeard is right-on with keeping it simple. I do have electronic ignition on my engines, but I do still have the mechanical fuel pumps. All that electricity in that enclosed compartment with those 2 hot engines and 160 gallons of gasoline under the floor. Sea-sickness gets a whole new meaning when you are upside down with your head between 2 hot motors trying to fix a problem in 6 foot seas also.

I live and boat in South Louisiana in the Gulf Of Mexico.

One other thing that may need to be considered is the air intake temperature. It will be up to 20- 30 degrees higher than ambient due to the enclosed engine box. Don't know if that makes a difference or not, I am still learning an awful lot about engines in general.

Generally, a tank of water for a water injection system is about half a US gallon in size and is supposed to last for about as long as a tank of gasoline does, or about 300 miles. The reason for this is because underhood space in automobiles is limited on one hand, and probably to remind the driver to refill the water tank when he fuels up on the other hand. However, on a boat I would think you could use any size tank that was practical to install and connect it to the pump for the water injection. If you decide to try water injection, one other thing that you will probably want to do is to add a bit of denatured alcohol to the water, not to add any more power, but to retard algae growth in the water tank. I would think that a 5 gallon gas can or water can would work pretty well for a water injection tank and would give you several hours' worth of running time. That's just a wild ass guess on my part, but any water injection system that you buy should come with directions that tell you number of untits per hour that the system will consume. And I suppose as a last resort if there isn't information about water consumption included in the instructions, call the company and ask them.

I also am a firm believer in the KISS system, but I do think that using a Pertronix ignition system instead of points would be a good idea. Again, it doesn't cost a whole lot, has one moving part, is all contained under the distributor cap, and uses a magnetic Hall-effect trigger to fire the coil, which is about as foolproof as you can get with electronic ignitions. I have one of these on a 1968 Mustang, and I love it. Takes about 15 minutes to install and never needs adjustment after that. Hope some of this helps give you some ideas or answer questions.