Thoughts on my engine build

I am building 2 408 Cu In 360 Magnum based motrs for my 27' Magnum marine sedan. THe specs are as follows:

5.9 Magnum blocks
Engine Quest Iron Magnum replacement heads W 2.02 I 1.62 E valves
Icon 983 Forged step dish pistons with a 27 CC dish
Scat Cast Iron 4" stroke cranks
Scat I beam connecting rods
Hughes Engines Hydraulic roller cams 217/227 duration at .050 114 lobe separation .539/.555 lift
Edelbrock Performer RPM Air Gap intakes
Mallory Marine unilite distributors
1985 up Chrysler marine center rise exhaust manifolds / risers thru hull exhaust
Closed cooling for the blocks
Crank mounted raw water pump


I assembled my short blocks and the quench dome is .001 in the hole.

Cometic makes head gaskets in .040,.045,.051,.056, and .060 thicknesses
my compression ratio looks like this:

.040 gasket 9.406 static 8.179 dynamic
.045 gasket 9.318 static 8.056 dynamic
.051 gasket 9.215 static 7.968 dynamic
.056 gasket 9.131 static 7.897 dynamic
.060 gasket 9.065 static 7.841 dynamic

Trying to balance quench and compression ratio, Most marinas around here have 91 Octane Alchohol free fuel

MM, I don't claim to know the Chrysler 5.9L engines. I am much more familiar with the GM SBC.
However, the two do share some similarities in that they both incorporate a "Wedge" style combustion chamber...... of which lends it'self to a Q/E if the build is done correctly.

Here are a few images that I created some time back. Perhaps they will be useful..... perhaps not.

BTW...... if one of these is to be a RH REVERSE Rotation Engine...... watch the wrist pin offset and the crankshaft seals.

Have fun!

RicardoMarine said:

MM, I don't claim to know the Chrysler 5.9L engines. I am much more familiar with the GM SBC.
However, the two do share some similarities in that they both incorporate a "Wedge" style combustion chamber...... of which lends it'self to a Q/E if the build is done correctly.

Here are a few images that I created some time back. Perhaps they will be useful..... perhaps not.

BTW...... if one of these is to be a RH REVERSE Rotation Engine...... watch the wrist pin offset and the crankshaft seals.

Have fun!

Click to expand...

Rick, I was hoping you would respond. I am running Volvo SP-A drives currently. With the future plans upgrading to DP-X drives so both of my engines are standard rotation. My combustion chambers look like this



Which thickness of head gasket above would you recommend? I was leaning towards the .045 or .051. But want to make sure I retain quench with my step dome Pistons. In my case the dome is .001 down the hole at TDC so the thickness of the gasket will essentially by my quench dimension.

This is the piston



The quench dome is .001 below the deck

My question is, would a 9.3 to 1 motor with .046 quench be less prone to detonation than a 9.2 to 1 motor with .052 of quench? Or should I just go with .041 of quench and the 9.4 to 1 Fuel availability for my is at least 89 octane but mostly 91 running on the great lakes or at sea level.

.............................

murfman said:

Rick, I was hoping you would respond. I am running Volvo SP-A drives currently. With the future plans upgrading to DP-X drives
FYI...... the DP-X is not interchangeable with the SP-A drives.


so both of my engines are standard rotation.
Correct........ Volvo Penta has never use a RH Reverse Rotation Engine.


My combustion chambers look like this



Which thickness of head gasket above would you recommend?
I would not be able to recommend a compressed head gasket thickness until all values and/or dimensions become known.



I was leaning towards the .045 or .051.
I can only suggest that with the 5.7L SBC (3.480" stroke) that a Quench dimension of .038" appears to be ideal.

Keep in mind that this is the SUM of the piston deck height and compressed head gasket thickness.
While these are low relatively RPM Marine Engines, your stroke has been increased, and may cause the need for increasing the Quench dimension tad bit.


But want to make sure I retain quench with my step dome Pistons.

Forgive me, but I have never before heard of these being called a "Step Dome" piston.
If these were for a SBC, we would call them a LCQ (low compression quench) piston or a Reverse Dome quench style.


In my case the dome is .001 down the hole at TDC so the thickness of the gasket will essentially by my quench dimension.
In that case, you would be correct! However, that is getting quite thick for a head gasket!!!!!

Click to expand...

RicardoMarine said:

.............................

Click to expand...

This is the drive I plan on eventually run



it is still based off the Aquamatic architecture

The "Step Dome" is what UEM (Manufacturer of Keith Black Hypereutectic and Icon forged Pistons) calls this piston design.

A standard Felpro MLS head gasket for a small block Chrysler is .047 thick. Cometic actually makes gaskets all the way up to .120 thick!!!

Im going to go with the .045 head gasket giving me a 9.318 to 1 static compression

You have hit the jackpot on the quench, more than .O40 lessens the effect, the idea is to tolerate more compression. .045 is working backwards. You could open the chamber at the spark plug end for a couple CC's if that would make you feel better. You've got a lot of time, effort, and $$ invested in your project. It would be a lot of work to tear down the motors to reduce the C/R by less than a tenth, put one together and run it on a dyno and see how it goes with a .040. I'll bet it will be fine. If it rattles like crazy for want of an additional .005" I'd be surprised.

........................

murfman said:

This is the drive I plan on eventually run

View attachment 14612

it is still based off the Aquamatic architecture
Yes..... these incorporate main suspension fork and pivot tube geometry. Much better than a Gimbal Suspension system and with far fewer issues.

The "Step Dome" is what UEM (Manufacturer of Keith Black Hypereutectic and Icon forged Pistons) calls this piston design.
Ah!

A standard Felpro MLS head gasket for a small block Chrysler is .047 thick. Cometic actually makes gaskets all the way up to .120 thick!!!
Keep in mind that your concern is the "compressed" thickness!

Im going to go with the .045 head gasket giving me a 9.318 to 1 static compression
If a good Quench is established, you can go a bit more!

Click to expand...

mcomm said:

You have hit the jackpot on the quench, more than .O40 lessens the effect, the idea is to tolerate more compression.
Not necessarily!
The idea behind a good Q/E is to eliminate Detonation Potential that in turn allows us to throw more Ignition TA at the cylinder, which in turn allows for a better LPCP.
LPCP is ultimately controlled by spark lead.
LPCP should ideally be around 12 to 14 degrees ATDC.


.045 is working backwards. You could open the chamber at the spark plug end for a couple CC's if that would make you feel better.
Because there is no effective quench area at this side of the piston, I would agree.
However, if you were to do this, you would decrease the piston dish volume as to accommodate the larger chamber.

You've got a lot of time, effort, and $$ invested in your project. It would be a lot of work to tear down the motors to reduce the C/R by less than a tenth, put one together and run it on a dyno and see how it goes with a .040. I'll bet it will be fine. If it rattles like crazy for want of an additional .005" I'd be surprised.
I don't necessarily disagree...... but because of his increased stroke dimension, his Quench area may need to be a tad bit greater.
I'm not sure what I'd do.

Click to expand...