Tinker,

Below is a table of the most commonly used stroke/rod combinations currently in use in BBC marine applications. The rod angle is calculated at max.

The 4.375”, short deck carries only .6 º (six tenths of one degree) more rod angle than your basic 540 short deck and less than .5º (one half of one degree) of the 4.375” Mercury Marine Bulldog Tall deck. It actually has a better rod angle than the tall deck 598 package with a 6.535” rod.

The graph below charts normal force on crankshaft and side-wall loading as a percentage of the
combustion force on the piston. The blue trace represents the 4.375” stroke 6.385” rod combination. The orange trace represents the very popular 4.500” stroke 6.700” rod 598 tall deck engines frequently used in 1200 HP + marine forced induction applications. You need to look closely as the overlays are close enough to appear as one line.

Why is this important?

Reduced friction and windage

A more direct line of sight to the back of the intake to the plenum

The biggie is a massive reduction in pushrod length, eliminating compliance and energy storage in the pushrod. That reduction allows for an opportunity to find huge gains in stabilizing the dynamic mass of the valve train, one of the biggest challenges in a marine endurance application.

The 4.375’ short deck provides the opportunity to exploit displacements from 557 CID-582 CID. I know Haxby, Orlandi, and MER use the combination and stand behind it as they would any other application.


Stroke____Rod____Rod Angle___Engine

4.250”____6.385”___19.44 º___540 Short deck

4.375”____6.385____20.03 º___557 Short Deck

4.500”____6.535”___20.14 º___598 Tall deck

4.500”____6.700”___19.62 º___598 Tall

4.375”____6.535”___19.55 º___Merc Bulldog

4.750”____6.700”___20.76 º___632 Tall


Bob

bob, just for laughs, where do 454 and 427 with stock length rods fall in that list? since that is obviously the most commonly used crank-rod combo. maybe throw in 400 small block with their short oem rods as mr goodwrench himself considered them ok for use...

I have never built a stroker - Learned something new today. I didn't think about the 1/8 inch - kept thinking it would pop the piston 1/4 inch out of the bore not 1/8 inch.
Talked to Dave Wesseldyke today. He said it wouldn't be worth it for the $. If I could get to 750 HP I was going to look into it.
I am just going to do the cosmetic work and the extension box. And run the engine the way it is now until I get the 598 built.
I even looked into getting a newer hull that wouldn't need as much work. Still might do this option. Have a call into a guy.
Thanks for the info guys.

Rod ratio at the OEM level is a pertinent design element. That is the only period you have to alter the engine architecture to a desired spec. See the LS2 rod angle below. It reflects the lowest angle of any of the compared platforms. At the design level, that is not an accident.

Once that architecture is in place, chasing rod ratio will yield little in quantified gains using aftermarket components. Going up in pushrod length .400” is a huge penalty for a perceived gain of .6 (tenths) of a degree gained by increasing rod length. The only necessity in going to a taller deck is when you can no longer physically package the stroke, rod length, and pin placement into the 9.800” platform

Stroke____Rod____Rod Angle___Engine

3.480”____5.700”___17.77 º___SBC 350

3.750”____5.700”___19.20 º___SBC 383

3.750”____6.000”___18.20 º___SBC 383

3.750”____5.565”___19.69 º___SBC 400

3.760”____6.135”___17.84 º___427 Short

4.000”____6.135”___19.02 º___454 Short

3.622”____6.098”___17.28 º___6.2 LS


Bob

OK - SO I guess I accelerate the 598 project. Starting to order parts. I am planning on using a crank trigger to control the spark. Whose ignition control would you use. does anyone make an ignition control that will do coil on plug ignition control. Can you use something like the FAST system but not use the fuel injection?
What distributor would you run if it is only distributing the spark? Or if I can use the FAST system do I need one with a cam sensor? I was looking at the Daytona sensors control.

If you want CNP you need a cam sensor. One engine or two? At this point why not efi? CNP is good move. MSD 7al2plus is as good as you can get on the reliability side. Daytona sensors I think is good but no experience with it. I would never use any of the 7digatal MSD boxes in a boat 30 minutes in my boat an craped out.

Not that you were asking, but a 598 would not be my first choice for a M4 Procharged deal. Also, I would strongly recommend not using a carb at that power level in a boat, especially if you're going to the trouble of CNP ignition, as Apache mentioned.

My first choice for efi would be holley dominator can do CNP and has self learn. What do you use?

6500+ RPM M4 procharged engine?

I'd also skip the 598, long stroke, 4.600 bore, tall deck setup. I'd rather go with a std deck , 4.25 or 4.375 stroke, smaller bore out of the box (for rebuild purposes).

EFI on that setup hands down. A M4 procharged 557 with the right heads, will make more power than you'd ever need in a smaller single engine cat.

The engines I just took apart were 4.375 and the cylinders looked like chit....thought it was rod angle, but then again there were many issues there...