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Older 360 replacement

Phil's

New member
Hello, and thank you in advance. I'm seriously considering purchasing a boat with a 20 plus year old Chrysler 360 inboard. It is tired, and I'm also looking for better fuel efficiency, as I understand the 360 is a thirsty engine. I'm not a speed demon, so even a 318 would be a possibility( EFI available?), if the existing trans works. Are there any other options I should consider? I know switching to GM 350 or 305 with EFI is possible, but that definitely means a new trans, and very likely, other alterations in the installation. What do you think?
 
My 360's is 36 years old and run like a champ. Almost bullet proof. I like the simplicity of them. Maybe do a re-manufactured block on the tired one.
 
Going to GM block would not require a transmission change. The bell housing of GM will bolt onto your existing trans. I'm guessing you have velvet drive 71's or 72s
 
Thanks for both responses- definitely valid alternatives. I will go with the remanufactured 360, or change to a GM engine, after weighing the pros and cons of each choice. Thanks.
 
I too run old 360s and they are great engines. Where gas mileage is concerned, they are as good (or bad) as a Chevy. Finally, going to a smaller engine (318) will not necessarily improve gas mileage. Hard to believe, but hard working, underpowered boats burn more gas. (For example: Those over powered, noisy "go fast" boats get fabulous gas mileage IF driven carefully.)

Jeff
 
I too run old 360s and they are great engines. Where gas mileage is concerned, they are as good (or bad) as a Chevy. Finally, going to a smaller engine (318) will not necessarily improve gas mileage. Hard to believe, but hard working, underpowered boats burn more gas. (For example: Those over powered, noisy "go fast" boats get fabulous gas mileage IF driven carefully.)

Jeff

I hear you Jeff, regarding no fuel savings on an underpowered boat. Seems as though the 360 is a tough animal, and that's always a plus for a marine application. I think I'll stay with that engine( remanufactured), unless parts, eg. manifolds, fresh water cooling parts, etc., are tough to find.
 
................ I'm not a speed demon, so even a 318 would be a possibility( EFI available?), if the existing trans works. Are there any other options I should consider?
I know switching to GM 350 or 305 with EFI is possible, but that definitely means a new trans, and very likely, other alterations in the installation. What do you think?

Going to GM block would not require a transmission change. The bell housing of GM will bolt onto your existing trans. I'm guessing you have velvet drive 71's or 72s
I agree with westirmax.
With the Borg Warner flywheel covers (of which you now have), any transmission that is Borg Warner capable, will work as long as the ratio is correct for the engine. Borg Warner pattern is Borg Warner pattern thoughout the industry....... and should place the transmissions where they were.



................ I'm not a speed demon, so even a 318 would be a possibility( EFI available?), if the existing trans works. Are there any other options I should consider?
Yes!
If you go with the SBC 5.7L, have a good quench effect built into the cylinder head combustion chamber area.
The Wedge style combustion chambers offer a quench surface that is seldom taken advantage of. Don't settle for the typical GM style full dished pistons that GM provides and that most re-builders provide. :mad: :mad:
You'll do much better with a piston profile that mirrors the quench surface of the cylinder head.
A good quench dimension for the Marine engine is in the neighborhood of .038" to .040".
Any good piston supplier can provide the correct profile for you... and most any good machine shop will know just what/how to do this.

The Q/E will not only offer more torque, with the Q/E also comes a more efficient engine in terms of less fuel burn.
This is Fact..... not Speculation.

I'm not as familiar with the Chrysler 318/360 engines...... but I'm thinking that if you stay with the Chrysler 318/360s, that these also offer a wedge style combustion chamber, of which means that a good Q/E can also be built into the Chrsyler Marine engine.


BTW, if you get that Deer-in-the-headlights-look when you mention "Quench Effect", find another machine shop!
 

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  • Chrysler 318 360 cylinder head quench .jpg
    Chrysler 318 360 cylinder head quench .jpg
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Rick- Thanks for the education. I looked into a bit, and see the point of building mechanical octane into the engine with the correct pistons. Seems like flat tops, or something similar is the way to go. Very, very interesting. I will follow up with your suggestion. Thank you so much!! Phil
 
Phil, you'd need to know the cylinder head's combustion chamber volume (plus bore/stroke) before deciding on a piston profile.
Flat tops may work...... or you may need dished piston....... but the key is the deck area of the piston in that it "mirror" the cylinder head's quench surface best it can.

For the SBC, this could be a D-dish, Reverse Dome or a LCQ piston....... and for the 5.7L with 76cc chambers, the flat tops work out to be ok.
Not sure about the 318/360!

Next will be the piston deck clearance and the compressed head gasket thickness.
The sum of tese two dimensions give us our quench dimension.


.
 
The 360 is an excellent engine for a boat and may actually be better for the tougher marine demands. Here in the midwest, we have a racing class for dirt track that has a 360 ci limit and 9:1 compression max on a single 4 barrel carb. The guys that spend the extra money to build the Mopars over the 350 Chevs, continue to do very well. We have produced 410 hp and 430 lbs of torque from the 360's but they are a bit more expensive to build. Best years are the black motors around mid 80's and usually out of an RV. RV blocks, like marine blocks are selected with minimal core shift to ensure consistency in cyl wall thickness and overall casting integrity. This is very important when running a cruiser for hours and hours at 4000 + rpm. In a typical automotive application your cruising rpm is 2000 to 2500. The 360 also has a larger lifter bore which allows more aggressive cam lobes. The 4 barrel intakes have generous port size and good rise which help flows at higher rpm. I built a Chev 327 for my Chris Craft ski boat, but that is a rocket and not designed for cruising. Good luck and be sure to continue your research, you'll be happy with the end results. Ricardo knows his stuff. Regards, Tim
 
Phil, I failed to mention that with a good tight quench dimension, we can go up a few points on the static compression ratio without further risk of detonation! This is achieved by reducing the piston's dish volume a tad bit.
You can use an "on-line" static compression ratio calculator and play with the numbers!
You'd need to have your known values in hand: bore, stroke, combustion chamber volume...., etc.

Also, your total ignition advance (at the full-in rpm) can be increased some, placing the LPCP closer to where it needs to be for more torque.



.
 
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Thanks Rick, and Tim. Your technical knowledge really helps me. This boat has a modified V hull, that being a "warped" hull shape that gradually transitions, instead of a pure constant deadrise pure planning hull. She will plane, but not over 25 mph, and that would be at WOT. I would imagine I'll cruise at 18-20 mph, at 2/3 throttle. Hopefully, relatively efficiently. Again, thanks. Phil
 
thanks for the chart- seems torque flattens out at 33-3400 rpm so running higher doesn't get you any more, so tuning your prop for 42-4400 WOT would be about right. interesting. I run 3100 all day long with a WOT of 46-4800 thinking i could use a bit more pitch. Since engine is throwing its most torque right about where i'm running.( slightly above) might pay big to run at 3400 with a bigger wheel?
 
Phil, at the risk of being the Quench NAZI here........ I'll offer this to you.
As mentioned, this engine also uses a wedge shaped combustion chamber, and is capable of a quench design.

Torque is what we want... and is all about LPCP.
LPCP = location of peak cylinder pressure.

Most engineers will agree that LPCP should be near 12 to 14 degrees ATDC. Gas or Diesel... Hot Rod, lawn mower, tractor, go cart, car, truck or even an airplane piston type engine....., it makes no difference.
Thisis when the combusted gasses are at their most expanded value, and have their greatest leverage advantage over the crankshaft throw. This is what makes torque.

Aside from proper compression, correct F/A, and all other aspects, Igntion advance has the last word in LPCP.

Marine Engine loads are quite different from that of Automotive.
When a Quench Effect is light or non-existant, Marine Engineers hold back TA (total advance) as to avoid Marine Engine "ignition induced Detonation".

When the Ignition TA is held back, so is LPCP held back.
LPCP that should be 12/14 degrees ATDC, may end up being 16/17 degrees ATDC.
A lazy LPCP makes for less torque and leaves some performance on the table.

As said earlier... ignition advance has the last word in LPCP.

Give this engine a good Q/E, and the ignition lead can be increased with little to no risk of Detonation potential.


Again... I'm not a Chrysler Marine engine expert at all. My experience is mainly with the SBC both auto and marine.
However, the Q/E is nothing new to the Chrysler Wedge Head boys in the auto world.



.
 
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Thanks Rick. Your shared knowledge will be utilized to properly repower this boat to is maximum efficiency. I get the impression that many, if not most engines are running less efficiently than they could be. Again thanks, I will utilize your technical advice.
 
I get the impression that many, if not most engines are running less efficiently than they could be.
Yes, and not necessarily due to tuning or ____!

Phil, quick and short story... but not necessarily pertaining to Chrysler engines.

Previous to the early 70s, GM's SBC used a piston profile that offered a quench..... even back to the first GM 265 cu in V-8.
These little engines actually produced decent power.

Then in the early 70's, our government demanded stronger emmision control measures.
So GM (in the Chevrolet scene) came up with the full dished piston as to reduce emmissions that were being demanded of the car makers.
This idea worked OK to lower the emmissions for cars and trucks.

Since the gasoline Marine Engine is basically a modified auto engine, GM just continued with this piston, and the marinizers fell for it. :rolleyes:
The Marine Engineers now needed to figure out how to avoid detonation issues.
The fix: hold back ignition advance.

This actually helped GM in that it reduced the load on the engine, giving it a slightly longer life in the Marine environment.
But at the same time, it prevented this engine from developing it's potential.

Here's what this piston looks like.
(I put the red cross-out line through it a few years ago! ;) )

attachment.php


The above GM full dished piston has a very small quench band around the perimeter only, and cannot create a true quench effect.



The correct piston should "mirror" the cylinder head's full quench surface, similar to this piston profile below.

product_thumb.php

This is such an easy and relatively inexpensive piston profile to obtain, it amazes me that people can't see the advantages and use it.

Good quench = less detonation potential.
Good quench = a point or two increase in the Static C/R.
Good quench = proven better fuel economy.


I've built quite a few SBCs over the years, and have never used the GM style pistons.
You can bet that the Chrysler Wedge Head boys understand this.

End of story! :D



.
 
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Rick- Thanks for posting the picture of a piston with a profile that maximizes the Quench. I also appreciate the information regarding ignition advance. Is there any danger in advancing the ignition too much when running some of the time at low RPM's? For instance when trolling for fish?
 
Rick- Thanks for posting the picture of a piston with a profile that maximizes the Quench. I also appreciate the information regarding ignition advance. Is there any danger in advancing the ignition too much when running some of the time at low RPM's? For instance when trolling for fish?
Typically not at low RPM...... but perhaps the question would be.... why?

The OEM ignition advance curve is designed to be progressive throughout the RPM range.... starting with NO EST or Mechanical advance until RPM begins to increase up to the Full-In RPM (of which is our TA... total advance).

I'm still puzzled as to why we cannot find an OEM Chrysler Marine Corp ignition advance curve!
The guys here have looked and looked........, but apparently all we can find are the automotive curves.
They've found the Marine Engine BASE/Initial advance.... but no progressive or TA info.
I even contacted one of the ignition system manufacturers.... and they aren't clear on this for the Chrysler Marine.

To my knowledge, Merc, Volvo Penta, Crusader, PCM, Indmar, etc, all offer us this info.




.
 
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Going to GM block would not require a transmission change. The bell housing of GM will bolt onto your existing trans. I'm guessing you have velvet drive 71's or 72s

My PennYan Explorer came with a 318 block out of boat and B-W transmission. Will the bell housing bolt up to a 340 or 360?

I read this thread and others, like the idea of greater low end torque, not a go-fast guy, so greater horsepower is just a bonus, the motor just won't have to work as hard to do what it does. Had thought about doing a stroker kit on a 318, but just finding a 340 or 360 if it's compatible with the bell housing would be easier.

Thanks!
 
This may not be an issue at all with marine applications.
I can tell you that in the car world that the left engine mount (bracket I believe) is different between the 273-318 LA's and the 340-360 LA's.

Suggest you take good pictures of the currently installed mounts before you change things.
 
318LA are internally balanced and 360LA are externally balanced, so flex plates/flywheels and vibration dampner/harmonic balancer do not swap.
 
318LA are internally balanced and 360LA are externally balanced, so flex plates/flywheels and vibration dampner/harmonic balancer do not swap.

Castle Cape -- but those parts are available, right? Would the bell housing swap between a 318 and a 360?
Thanks for your reply and info.
Nuts, we all are
 
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