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Old 11-08-2012, 01:29 PM
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boat engine for truck.

i have a marine vortec 5.7 i am slowly overhauling to a low end torque roller 355 for my s-10. that is the overlying future goal. for now currently i have a 1984 305 from a boat (im a boat guy). the intake manifold has the exhaust crossover blocked. will this be a problem for summer driving only? fuel mileage is a concern obviusly. im sure the carburetor curcuits will need attention for street driving and will accept suggestions but i do know tuning trial and error will dictate the whole scheme of carburetion. the engine is rated at 230 Hp. i plan on using the mercruiser alternator and distributor and brain box. basically works like an msd box but set up for 8 degrees base timing and 33 degrees all in at 4000.(this timing is ok for cold running engines like 130* or less) the heads are marine 434 castings. they are 1.84.1.50's i am wondering if some exhaust port cleanup, 1.5/8" headers and a .015" shim head gasket would boost that number of 230Hp, or better yet bring the torque curve to a lower rpm. also i have a holly street dominator intake manifold number 300-38 that has the exhaust crossover. would this be a better manifold? im looking for low rpm power, torque, everything down low. should i degree the cam, maybe 1.6 rockers for the exhaust side... im looking for fuel mileage long range boat towing with an 89 s-10 stock 700R4. looking for the best economy/power low end torque on a 305 with the parts i have untill the 355 is done. also i have tinkered with the ideah of the 350 vortec heads on the 305 block bored .030, with summit pistons and .030 decked on the heads, with retro roller cam, roller rockers, and high vollume oil pump. manual valve bodies in the transmission and spread bore Q-jet. 160 thermostate, and marine computer timing would make a fuel saving s-10 sound just trick! if yall could let me know if im on the right track or enlighten me as to how to make fuel mileage and torque work for me. im not looking for a 10 second truck. not even lookin for a 20 second truck. looking for sound quality and low end torque and fuel mileage or best medium.

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Last edited by s-10again!; 11-08-2012 at 01:39 PM.
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Old 11-08-2012, 02:11 PM
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Fastest running truck in reverse as some marine engines are reverse rotation.
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Old 11-08-2012, 02:29 PM
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Only boats with twins have 1 reverse rotation engine..

Exh crossover will only make a cold hesitation with a carb. Once it's warm, it will run great. As far as low end torque, the marine engine will be perfect for it.
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Old 11-08-2012, 06:04 PM
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how are you going to run water through the exhaust manifolds? joking. why are you using the marine ignition?
Seriously,if you want torque and mileage with no need for a lot of horse power,the 305 is the way to go. high velocity heads with moderate flow,more emphasis on all the ports being equal flow. and,,, fuel injection on a street master as apposed to street dominator.good ignition is also importand with both mechanical and vacuum advance or better computer controlled ignition to match fuel injection
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Old 11-08-2012, 07:45 PM
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Quote:
Originally Posted by s-10again! View Post
i have a marine vortec 5.7 i am slowly overhauling to a low end torque roller 355 for my s-10. that is the overlying future goal. for now currently i have a 1984 305 from a boat (im a boat guy). the intake manifold has the exhaust crossover blocked. will this be a problem for summer driving only? fuel mileage is a concern obviusly. im sure the carburetor curcuits will need attention for street driving and will accept suggestions but i do know tuning trial and error will dictate the whole scheme of carburetion. the engine is rated at 230 Hp. i plan on using the mercruiser alternator and distributor and brain box. basically works like an msd box but set up for 8 degrees base timing and 33 degrees all in at 4000.(this timing is ok for cold running engines like 130* or less) the heads are marine 434 castings. they are 1.84.1.50's i am wondering if some exhaust port cleanup, 1.5/8" headers and a .015" shim head gasket would boost that number of 230Hp, or better yet bring the torque curve to a lower rpm. also i have a holly street dominator intake manifold number 300-38 that has the exhaust crossover. would this be a better manifold? im looking for low rpm power, torque, everything down low. should i degree the cam, maybe 1.6 rockers for the exhaust side... im looking for fuel mileage long range boat towing with an 89 s-10 stock 700R4. looking for the best economy/power low end torque on a 305 with the parts i have untill the 355 is done. also i have tinkered with the ideah of the 350 vortec heads on the 305 block bored .030, with summit pistons and .030 decked on the heads, with retro roller cam, roller rockers, and high vollume oil pump. manual valve bodies in the transmission and spread bore Q-jet. 160 thermostate, and marine computer timing would make a fuel saving s-10 sound just trick! if yall could let me know if im on the right track or enlighten me as to how to make fuel mileage and torque work for me. im not looking for a 10 second truck. not even lookin for a 20 second truck. looking for sound quality and low end torque and fuel mileage or best medium.
A small runner dual plane intake w/a Q-jet would give you great low end response and as good of mileage as you're going to get using a carb. If the engine has a Q-jet (I believe it should) it can be recalibrated as needed for mileage and performance and the intake reused.

The blocked heat crossover probably won't be a problem, but it's easy enough to open one or both sides if needed by using different gaskets, as I believe the stock intake should be equipped w/a crossover- but I'm not a marine teckkie so this might not be correct.

A better advance curve could be set up using an analog HEI distributor w/mechanical and vacuum advance. You want the initial advance higher than 8 degrees and the total advance higher and in sooner than 4K rpm, plus you want to use a vacuum advance if mileage is the least bit important to you.

My thoughts are to build the 305 as cheaply as possible using the existing parts- or parts that can be used later on the 350, and focus your money and efforts on getting the 350 dialed in to your liking.

But the 305 might be enough for the application. In that case I'd be looking into a set of L30 Vortec heads that were used on the 305. More on the L30 305 Vortec heads at Post 478. As I'm betting you already know, the Vortec heads also require center bolt valve covers, a Vortec-specific intake, and either self aligning rocker arms or installing screw in rocker arm studs and guide plates to use non self aligning rockers.

Adding long tube headers and a dual exhaust system w/low restriction in mind will always help. Cold outside air to the carb, too.

Whether or not the marine cam (even w/1.6 exhaust rockers) has the specs that would be best for the truck I can't say, but there are hundreds of grinds to choose from if the cam needs attention.

Good luck.
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Old 11-08-2012, 10:46 PM
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My 351w Ford on my ski boat is reverse rotation, so not only twin powered ones have one running reverse rotation. I know it has nothing to do with yours unless your going to Ford power it...GROSS! Just saying


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Old 11-09-2012, 10:34 AM
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ok so i was going to use the computer timing from the marine but your saying vacume advance would be the ticket. that i understand because of the vacume would dictate how much timing im needing instead of adding timing by rpm. that makes perfect sense. dunno how i didnt see that working for me. then i could switch that distributor over to the 355 also. as for the reverse rotation, usually only twin screw vessels come with one reverse rotation engine because of the centrifigal force would cause the boat to turn. most mercruisers are standard chevy blocks and heads with cams designed for high cylinder pressure and almost no valve overlap. if a marine cam with wet exhaust had valve overlap you could/would experience water reverberation and hydrolock the engine or blow a piston rod through the block. marine intake manifolds are supposedly the best gm factory intakes for performance. but the crossovers are true blocked. there is no provisions for them on these manifolds from GM. im a boat guy, i really really wanna stay away from fuel injection. and yes this engine and most all other mercruiser engines are equipped with quadrajet carbs.i played with a marine holley before, i didnt like it. also the l30 heads are a good ideah becasue the 355 has the vortec heads and i already have the intake for those heads. thank you for that link cobalt327 that was alot of info that was enlightening. but i am on the right track. boat engines are definately beast in trucks and cars. car and truck engines in boats are sluggish untill they blow apart. it has to be a timing or cam thing. i know the timing has to be 8* base and 33* all in by 4000 on a boat. also the mercruiser ignition is very hot! 75,000 volts hot. thats pretty good damn ignition so i thought. wonder if thats the marine trick. i tried to set a boat up without the computer and used springs and weights to set the timing curve and the engine would diesel BAD! it would overheat at wot untill i reset the max at 26* then it was a total slug. marine parts in boats only. if i were to get you gentlemen some cam specs would you be able to tell me if degreeing the cam 4* with a indexable timing gear would gain me some down low? i have a mercruiser bible around here somewhere and its got my cam specs in there. also if i were to put all new lifters in, would i need a new cam? do you think some lobelife zinc stuff would help the new lifters mate to the cam? i wiped a cam before by putting one new lifter in my 94 Z71! i dont know if i should have put something besides assembly lube on the lifter tappet or if a new lifter on an old cam is a blatant NO-NO. i do know that the lifters have to ride the grind perfectly and i always check by hand that the lifters are spinning whene i rotate the engine. if a put new lifters and they all spin, am i good? id like to use the old cam but i mixed the lifters, there dun.

by the way guys thank you for all your insight. ill be around a while and ill have many many more questions. this 355 will be my third completely overhauled engine and im still very green behind the ears but the first two engines that i build start to finish are running strong and one of them has 190 hours and 375hp and its in my wellcraft nova speed boat so im a little egotistical about that but i am by no means knowledgeable, but im a smart and ambitious shoprat and quickly becoming obsessed with this chevy sbc stuff. also bonuts, i absolutly would never install a ford product where a gm peice was origionally. it was funny though, i see the humor. fords and dodges can park in my driveway but if its foreign you walk down the driveway to my house lol.

Last edited by s-10again!; 11-09-2012 at 10:49 AM. Reason: edited to say thank you all for helping
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Old 11-09-2012, 11:03 AM
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You pick up things quick! I foresee good things for your career in engine building if this thread and your previous builds are any indication.

I believe if you could find the cam specs, an educated guess could be made as to what advancing the cam would give you. It will increase the dynamic compression ratio (DCR), for one thing. The added cylinder pressure at low rpm will help power at low rpm and can increase the vacuum as well. The thing to watch out for is gaining too much DCR, which could cause detonation or the need for more octane.

What you do not want to have to do is lower the max power timing to prevent detonation. That just murders power and mileage. Much better to build the engine w/a tight quench and the correct compression ratio for the cam. That way you can use max power timing w/o detonation and reap all the benefits that gives you.

You might get something from this page on selecting cams. There are additional links under Resources at the bottom of the page, too.
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Old 11-09-2012, 11:39 AM
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Just some quick thought on using a marine engine in a road vehicle.
The ignition timing on a marine engine is not as complicated as it is on a road vehicle.
A boat engine you generally put a propeller on to allow WOT RPM to be within a small range, and essentially, it is like having only one gear. After that initial set up with the proper propeller, any part throttle operation pretty much goes to one RPM, and one manifold vacuum. For example, 1/4 throttle, will always be 2000 RPM, with 15"of vacuum.
With a road vehicle, depending on what gear you are in, 1/4 throttle could be 4500 RPM in first gear, and a high vacuum, or 1750 RPM, in top gear, and a pretty low vacuum.
In fact, some outboard engines do not have vacuum or centrifugal ignition advance. The advance is purely mechanical, connected to the throttle linkage.
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Old 11-09-2012, 07:13 PM
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boat engines and air craft engines both operate at or near full throttle for extended amounts of times.In both cases the engines are designed and built to be most efficient at those throttle settings. Automotive engines are rarely operated a full throttle for any length of time. With boats/aircraft durability is the most important issue in particular the bearings need to be the most important parts to deal with. In the case of bearings,the thrust part of the bearing surface has to be correct for durability. Props produce thrust that crank bearings dont like. The subaru boxer engine has better bearing surfaces as it is a design from an aircraft engine.

to say a boat engine is better than an automotive engine? I think you like the tuning better. A 5.7 is still a 5.7 in a plane,in a boat,in a car,in a train,,,,
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Old 11-09-2012, 10:07 PM
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All of the boats I have seen and worked on the propeller thrust is not applied to the engine crankshaft.
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Old 11-10-2012, 04:13 AM
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All of the boats I have seen and worked on the propeller thrust is not applied to the engine crankshaft.
Wondered about that myself but I am not a boat guy at all, so figured there was something to it I didn't know.
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Old 11-10-2012, 06:55 AM
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All of the boats I have seen and worked on the propeller thrust is not applied to the engine crankshaft.
Many older style boats were direct drive with no transmission. Point the boat where you want it. Turn the key and go.
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Old 11-10-2012, 07:02 AM
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Many older style boats were direct drive with no transmission. Point the boat where you want it. Turn the key and go.
No neutral or reverse? Shut it off every time you wanted to hold position? That is some funky boat.
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Old 11-10-2012, 07:39 AM
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Some of them used a 'kitchen rudder' which uses 2 doors that close to direct the water the other way for reverse.

Cracker box is the most common direct drive boat known. Originally race boats, gained popularity as pleasure boats with the ability to go fast early on. Even tow skiers.
There are other 'jet boat' type hull's ( mostly tunnels ) that are primarially used in jet boats but sometimes got direct drive V drives with no transmission because more HP is used with a prop, rather than a jet.

Last edited by matt167; 11-10-2012 at 07:46 AM.
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