Numerical comparison
 

Attached is a graph of the comparative wall loading as a percentage of the combustion force on the piston and the loading on the crankshaft at each degree of rotation. It represents a common 4.250” stroke comparing 6.385”_6.535”_and 6.700” center to center rod lengths.

As seen the crank loading is so close that the three curves are indistinguishable in the overlay. The wall loading variance moves from 0 to a peak of less than 3 percent variance at 90º, back to 0.
Mean piston speed of the three iterations is 2833.33 for all.

Max piston velocity is

6.385”_4690 FPM

6.535”_4680.3 FPM

6.700”_ 4669.66 FPM

That is a variance of .4 of 1% (4 tenths of 1%)

Rod angle

6.385”_19.44º

6.583”_18.98º

6.700”_18.49º

That is a variance of less than (.95) 1º degree.

Now an interesting trade off presents itself when weighing the downsides of raising your decks anywhere from .400” (10.2”) to 1.835” (11.635”)

Bob

Steve,
The 572”/804 HP presented by Brian is an outstanding 4.375”, short deck package that is fully capable of eclipsing the 850 mark. The heads are prepped by Tony Mamo (Mamoized) of AFR and fully capable of moving enough air to support your goals with more cam, vacuum and a revised induction package.

If you’re going 10.2” and 4.500”, Wette Vette has that covered.
598 CID
Dart 355 heads and tunnel ram by Darin Morgan
A true 10.82:1 compression ratio runs on pump gas 93 octane.
10” vacuum
34º total timing
150º water at 24 PSI
More to follow.

Bob

I'm just trying to learn here, would the graph look any different using the 4.75 crank in a 10.2 block ?

Gary,
The comparison is meant to illustrate the sum of change (or lack thereof) based on rod center to center dimensions in a given (stroke) engine displacement. I can plot any 3, what are we looking at? A 4.750” with what rod c to c? Better yet, we can start a new thread keeping the OP’s on track.

Bob

The side loading deal is a non issue. When I choose a long rod, it's usually to move the pin up the piston, which makes a more stable, and lighter piston, and also to keep the piston from being pulled out of the bottom of the bore, which does accelerate skirt wear. I mostly use a 4.375 stroke, and don't see any additional bore or skirt wear between that and say a 4.5" stroke combo with a 6.535, or 6.7 rod. When I get a chance I'll take some pics of the bottom of the pistons on a 4.750, 4.500, and 4.3750 stroke engine so you can see the difference in how far out of the bore the piston gets yanked with the various strokes.

Other benefits of a shorter stroke are: reduced windage, reduced reciprocating weight, reduced pumping losses, and less frictional losses. On the tall deck deals, I believe Bob could help explain the compromises in regard to line of sight on the induction side, bore stability, and valve train stability.
You're up Bob. :)

Just wondering how to calculate the side wall load difference between your 4.25 crank example and a 4.75 crank with 6.635, 6.535 rod. Thanks

all these years i thought that the stroke controled piston speed at a given rpm and also dwell time,it looks by the info bob posted that rod length makes almost 0 difference.

Excellent information. I know every builder has a few favorite combinations when it comes to bore/stroke/rod length. What is yours, as far as a marine endurance build?

Also, at what point does your liking of a raised pin height, become a worry with forced induction, or does it?

So what are you saying?

im saying that rod length has no real difference in piston speed from a measurable difference.a few feet per second when you are talking about thousands of feet per second is not going to matter,but i did learn something,and that is that rod length can change piston speed ever so slightly.

Gotcha. It was some interesting information. I've always gone with "stick the longest rod possible in the motor" and still try to have a decent ring package... I think that philosophy is starting to change now to as I've heard the pro stock guys are decking the heck out of their blocks and running very short rods. I still think for an endurance motor it is better to go with a longer rod.

i 100% agree with that.

My friends at Diamond Racing did exactly that along with EXTENSIVE cyl head work, running 7500 RPM Custom pistons (made by Diamond) and did they ever sound scary on the dyno!! I'm still running those cyl heads on my 502s now. but mild short block set ups for reliability as I eluded to in past posts. Haxby's N/A set up sounds sweet!! should make Tinks Daytona fly.

That's a tough question. Every single build is a bunch of compromises, strength for weight, average power for peak, component quality for budget, compression for octane, etc. Even a completely optimized build is full of compromises. On the rod length / pin height deal for a forced induction marine app, absolutely, crown thickness, depth to top ring land and overall ring pack dimensions take priority. With newer piston technology and design though, it is possible to push the limits a little more. I never used to build blown 4.375 short deck combo's with anything but a 6.385 rod but, now with better piston/ring design and quality, I've had good luck with a 1.07" compression height for low boost (10# ish), so I can run a 6.535 rod if I want. To sort of answer your question; I prefer shorter stroke, short deck, big bore combos most of the time for marine blower app's. You really don't need anything bigger then a 540 - 557" deal to make 1000 - 1300ish hp

I was talking with a buddy about this yesterday. I had said, that in this day and age, I would be just fine running a short stroke large bore engine in a blower app. We have access to great cylinder heads, great valvetrain parts, fabulous choices in superchargers, intercoolers, off the shelf parts, etc. Its not to say the big stroke stuff doesn't work, just not sure its the route I personally would go for a marine supercharged setup.

I almost bought some real short stroke shortblocks a couple years ago I thought were cool. A friend of mine had them, they were 3.875 stroke, merlin blocks, callies magnum cranks, oliver rods, 4.560 bore. I thought they would make some nice little high revving engines. They were long rodded, with big domes. I just couldn't tear two nice new setups apart to make the changes I would have needed to make them work, so I left them alone. I thought the 3.875 stroke was pretty odd when I first looked at them.

That TR motor RM posted up looks sweet!!:party-smiley-004:

Badazz!! It's a freakin work of art..

So if instead I went with a supercharger.
Lets say I buy a blower, intercooler and FAST fuel injection that I can put on my existing 509engine, 10 to 1 compression, crane 741? hyd. roller cam, pistons are zero decked, Pro 1 heads that were reworked by Jim Valakeo.
Thinking with the compression I should be safe to run E85 even with the blower.
Later I build a new bottom end that can handle much more HP and bolt my heads, blower and fuel injection to it.
Will the FAST fuel injection system work well with a blower and E85?
What blower would you suggest?

M3 procharger all the way with that kinda motor. I've never ran e85 but I can tell you from being around alot of blown alcohol motors that alcohol does not get along with aluminum. If you let it sit in an aluminum pan it will eat a hole through it. I'd be afraid of it eating a hole in gas tank. And the fact that its gonna use alot more fuel also...

Been running E85 for a couple years now, no problems eating up anything. With the right map sensor and proper tuning the Fast will do anything you want.

I have had a piece of aluminum sitting in a cup of e85 for a year now testing this theory. Absolutely no effect on the aluminum thus far.......?

He may be thinking of Methanol rather than Ethanol for corrosion. You will use about 32% more fuel when running E85 vs Gas, but at $3.50 a gallon it seems to be worth it.

Good to know. Like I said no experience with e85. Does it become corrosive after combustion?

Just throwing an idea out there. What if you were to strip down your current shortblock. Install some blower pistons. Grab that B&M 420 in the classifieds with the whipple intercooler for 2500 bucks, run your 741 cam and valako prepped pro 1 heads. On 92 octane, 8psi, you should have no issues making 900HP. Total cost, under 5 grand. That blower is a smoking deal. The intercooler is prob worth what he wants for the whole setup.

http://www.offshoreonly.com/classifi...o54277-en.html

2500. is a smokin deal,900 hp that will go 3 to 4 hundred hours before needing a refresh.imo this is much smarter than a n/a engine making 900 hp from a cost and maintenance standpoint.

Air packer on her (god rest his soul) had that exact combo. 900hp at 6000

that is an insane deal. I would make sure the blower is tight and send it to the blower shop for seals, bearings and strips for about another ~$500 investment and peace of mind.

Yup. If I has a single engine boat, i'd have bought it already just for the intercooler. Problem is if I buy that one, I'd have to get real lucky and find another used whipple intercooler, or bite the bullet and buy a new one, and they are pricey. :(

I was going to start a thread myself on this topic. I'm looking to upgrade to a bigger boat and I want a minimum of 800hp ea and would like to stay away from a blower. I was considering a 572 with some custom heads, 10:1 compression, tunnel ram, solid cam, and lightning headers. I didn't consider dry sump although I have thought about using extractors to reduce crankcase pressure or even a vacuum pump. I currently have a 524 running just shy of 700 with a hydraulic roller cam at .623/.612 lift and 242/252 duration at .050". It took every bit of tweaking to get that, I know the stretch to 800 and still have drive ability is going to be tough, but I really like the rumpity rump of a big cam. I checked out AFR's heads, I currently have the 315's, while AFR makes a bigger port, they don't flow more than the 315 until they hit .700 lift and they all flow worse below .500. Anybody have any recommendations on heads that flow really well from .200 to .700?

Haxby, some of the new throttle bodies say they will support 900hp but require 9" of vacuum to function properly. I have been thinking about using throttle bodies on a tunnel ram to make more power through more complete atomization. What are your thoughts?

Blower with small boost is better on the drive train. Easier to make Horsepower. Mild Boost engines last along time. Mercury has been spinning blowers for years and they have the R&D to prove it. Just easier to make reliable, cost effective horsepower. Seems like once you go above 700HP NA, its time to start Blowing

Here is a video link of the dyno run for the engine I built for my personal boat.

http://www.youtube.com/watch?v=1deXRs-g51g

598 with AFR 335 heads,9.8:1 compression, hydraulic roller cam, Dart tunnel ram with 4 x 2bbl throttle bodies, efi w/mefi3 ecm.
It's been running great for several years. Idles at 800 RPM and very well mannered. I believe targeting much more HP than this you'd give up a lot of durability and drivability staying naturally aspirated.

Bob Lloyd
Full Throttle Marine

Just curious but what are the supercat merc motor specs? I know they ran!!!

Those 315's are a great head. A combo like the one Brian Orlandi posted will give you 800+ and very good reliability and is still a fairly docile engine. With a cam from Marinekinetics, there's no problem running the EFI as well. The systems that say they require 9" of vacuum at idle, are usually very entry level, and allow limited user input/tuning. They need a strong enough vacuum signal for the computer to self learn at idle and part throttle. With the Holley system, it is not an issue at all. You could certainly run two throttle bodies on a tunnell ram, or for not a whole lot more you could step up to an MPI set up. If your goal is only 800hp, then a properly ported and set up single four barrel manifold and 2000cfm throttle body will do the job nicely. Bob Madara can get you the engine specs, and I can set you up with a tune for it.

Everything today is blamed on ethanol and most problems have nothing to do with it.

Nice work Bob! That thing must make crazy torque.
Love the custom throttle body setup, bet ya spent a couple hours figuring out that linkage. Do you run a big hat on it, or individual flame arresters?

haxbypeed - After doing some thinking I think the best thing to do is go supercharged. Most people feel the Procharger I the way to go. If I go with a supercharger what would you suggest? My thoughts are to buy one that will be able to feed a 1000 + HP engine that will work on my existing 509 until I build the new short block. My 509 has 10 to 1 compression and I was thinking about running it on E85. Could I run E85 at 10 to 1 and run 7 lbs boost???

That'll work. I agree, to make 1000 reliable HP with a 509 you'll need a centrifugal SC or a turbo, with the centri being much cheaper and easier to do. I'd go with an M3sc, It'll make 1000hp now, and support up to 1200 if you upgrade to a 540 down the road. The M3 along with your compression will make a ton of torque in the midrange.

+1, Now that there is some good advice!

Any chance the M4sc might be better for future HP, http://www.procharger.com/marine/M_tech_specs.shtml

The M4 takes quite a bit more power to turn then the M3. I don't usually upgrade to the M4 unless I'm looking for 1250+HP