If this was 1954 then I would say that kinda of makes sense. However we as enthusiasts have seen manufacturers, engine builders and other enthusiasts go through said "experiments" for 6 decades now of the Chevy small block OHV architecture and all of its iterations. There's a reason why you don't really see small bore/long stroke motors (at least in the SBC/LS/LT world) like what you are building. And there's a reason why GM keeps increasing the bore size in the LS1->LS2->LS3 without really going too different in the stroke department.

Right now, what you're trying to do is nothing new or groundbreaking. It's just repeating something that has been kicked off even the backburner of most people to the point that today you don't see any real examples of such a build. There's a reason for that...and it's not because 3.78" bore blocks and 4" cranks are not readily available to the public.

I applaud you for trying something different just so you can say you have a rare engine combo that noone else has, and if you like to fund out of your own pocket yet another build of said performance then power to you.

 

No they don't, I've owned multiple sets of each. A 799 head is the exact same as a 243 just cast at a different plant. The intakes are 2.02 and the exhausts are 1.57 plain and simple. An 862 5.3 head has smaller valves but those flow worse than a 799/243 head until they are ported...even then a ported 243 will kick its ***.

Also the stock cranks in ls motors can take 1000hp so idk what the fascination with a forged crank is. If you want to forge something go with pistons and rods

 

The first statement is not necessarily true...That has a lot to do with the shape of a combustion chamber in the head some are suited better to larger bores. So thats a dangeros blanket statement.

I dont think anyone here has even brought up a money thing...All we're saying is that it wont be as efficient as a normal engine of the same cubic inches. I would actually like to build that engine or a 4.125 bore with a 3.62 stroke. The difference with that is like stated you will be sweeping less of the cylinder wall which is good for oil consumption among other things.

Next is that engine will love to rev up over 8k with a supporting valvetrain. It will be a tad weak down low but will come alive in the top rpm which is ok for a sports car geared accordingly. It will also have a massive bore which will let you run any head you want. That goes back to that whole deal about un-shrouding valves with a larger bore and PROMOTING head flow. That engine with a set of Mamo 215's jesel rocker system, and forged rods and pistons would be a monster at 8500 rpm NA or even better with BOOST.

On the other hand the engine you want to build will be rpm limited because it has a long stroke and tiny bores which for you doesnt matter to much but if you're going to make this comparison it has to be noted. Next as I said your tiny bores will choke a ported 243/799 head a 4.125 bore will work well with any head.

Its actually no question why thats a better option than this

 

Just for the sake of mental masturbation, I want to dive a little deeper into the friction aspect of this.

Correct me if I'm wrong, please.

To find the total ring surface area, it's circumference multiplied by the height of the rings. Ring dimensions are usually given in millimeters, so I'm going to use "mm" for the math, and convert to inches at the end.

And a standard 1.5/1.5/3mm ring pack will be used for this example.

3.78x25.4=96 (bore in millimeters)
3.14x96=301.48 (circumference in millimeters)
301.48x6=1808.87 (surface area in millimeters)
1808.87/25.4=71.22 (surface area in inches)

Same math, using a 4", or 101.6mm, bore results in a total surface area of 75.63sq/in.

Now we take the total ring surface area multiplied by the stroke:

@ 1rpm:
71.22x(4x2)=569.76
75.63x(3.6x2)553.61

It's less than a 4% difference.

 

So more friction = better?

 

No. More friction is not better.

But 4% difference is damn near negligible.

Definitely not enough to say it will be the deal breaker for whether or not an undersquare six liter motor is a worthwhile endeavor.

 

Not sure how you came to that conclusion. He is saying that the total ring surface area between the two bores is 4% different.

 

Just build it and let us know how it works out. While I believe the same as the others, I'd still be curious to see how it works out.

 

And therefore friction is increased with increased total ring surface area of the longer stroke. Seems like OP already made up his mind on the subject and just wants to justify his reasoning, however flawed that reasoning might be.

So be it, OP just post up some dyno sheets when the build is complete to silence the haters!

 

I haven't exactly made up my mind. Not at all. I just haven't been shown anything conclusive to turn me away from the idea.

I absolutely knew that friction would increase. But everything I see, read, and hear leads me to believe that the difference is negligible.

I absolutely knew that the small bore limits head flow. But everything I see, read, and hear concludes that regardless of bore and valve diameter, my proposed undersquare six liter still receives more air than the stock ls2.

I absolutely knew that the increased stroke would limit my redline. But everything I see, read, and hear leaves me with the impression that I will still be able to reach 7000rpms.

The ONLY thing I am concerned with, is the smaller piston surface area in the combustion chamber effecting the amount of pressure transferred to the crank.

With my limited understanding of how this works, I think the pressure should actually increase, working in my favor.

Same amount of fuel and air, being ignited under the same amount of compression, should produce a set amount of force. The same amount of force being applied to a smaller surface, should, in theory, raise the pressure applied to the crank... Right?

PS. For comparison purposes, the ls7, has 77.72sq/in of ring surface area, and is 621.72 @ 1rpm... Even with the same stroke, "my" proposed undersquare six liter is experiencing a full 10% less friction than the ls7.

 

You are focusing solely on piston ring surface area related friction while ignoring MANY other variables.....read this article and let the last sentence sink in: http://rehermorrison.com/tech-talk-5...ich-is-better/
There are much more cost-effective ways to tailor an engine’s torque curve than to use a long stroke crank and small bore block. The intake manifold, cylinder head runner volume, and camshaft timing all have a much more significant impact on the torque curve than the stroke – and are much easier and less expensive to change.

 

Quite contraire, actually. I am not concerned with the piston ring friction, at all. I've done that math before I started this thread. I already knew it was a miniscule difference. Someone else brought it up and I provided the rest of the math to show that the increased friction is actually nothing to worry about.

What I am caught up on, is Pressure = force / area... And if reducing the area of the piston actually increases pressure to the crank. The same amount of fuel, with the same octane rating, mixed with the same amount of air, being ignited under the same amount of compression should, in theory, produce the same amount of force.

The same amount of force applied to a smaller area INCREASES pressure. More pressure on the crank should, in theory, translate into more torque... I think.

Can anyone explain/prove/disprove this for me?

PS. Thanks for the article/link. I will absolutely have to look into the whole distance, in degrees after top dead center, between when peak cylinder pressure is reached compared to when the rod is perpendicular to the crank. The article stated that peak cylinder pressure happens around 30ATDC and the crank isn't perpendicular until 80ATDC, so I need to study up on the effects this has on efficiency, and what changes to the length of stroke does in regards to increasing or decreasing efficiency in this case.

 

I still think you should go for it.

 

Interesting idea, I applaud the originality. I have a 396 block and have looked at putting a 454 crank in it, sort of the same idea. You can buy pistons for the swap. They pick up tq but not much HP over a 396. The Chevy 307 was sort of the same concept which was never a common performance build platform. The long stroke makes great TQ but the bore makes for a rev friendly HP. I think the 359 would make a great truck motor but the cost of the rotating assembly would make this unattractive. I'll still tune in to see results.

 

Of course, because you're comparing a ported head to a stock head. But do the same on the regular 4x3.622 6 liter and you're going to once again be behind. So all that just to match or slightly beat the stock 6 liter airflow?

Curious to see how this combination works, but seems alotta work and money for something not as efficient as say a combination with a bigger bore.

 

Thank you for the encouragement. I really want to build this, for sure. Right now I'm just researching. I'm a broke-*** college student with a family, looking for a house to buy. Not that anyone gives a ****. Lol.

Anyways, the location of peak pressure, apparently known as the LPP, is actually closer to 15ATDC, according to an article from contactmagazine, I just read.

So if peak pressure occurs at 15ATDC, and is decreasing continuously after that. And the rod isn't perpendicular to the crank until 80ATDC. Then you have 65 degrees of rotation between those two events.

The only way to reduce this gap, that I know of, is to lower the rod ratio. Lower rod ratio architecture brings the point where the crank and rod are perpendicular closer to 70ATDC.

And what is a byproduct of increasing stroke with a set deck height? Shorter rods. So it looks like the undersquare architecture actually should promote efficiency, in this regard.

Can anyone elaborate on this, or tell me why that is right or wrong?

 

TEN percent less distance traveled is hardly negligible, even if the surface contact area is more due to the larger bore.
All four rod throws which hold the heaviest part of each connecting rod also travel TEN percent further distance with each revolution....#bearing speed
The rod to stroke ratio falls from 1.68 (6.098"/3.622) to 1.53 (6.125"/4)
rod angularity does affect skirt friction as well as piston rock on directional change.
Guess what happens to the piston rings when a larger piston to wall clearance forged slug rocks on directional change.....????
You guessed it, rings flutter and unseat during the ever so important first fifteen degrees of power stroke.......less snap sealed up pressing down means more getting past and into the crankcase
Ring seal is amazingly important to the internal combustion engine. This is why racing classes that allow dry sump oiling systems and/or crankcase evac systems usually pick up anywhere from 20-50 flywheel horsepower by reducing the crankcase pressure (creating vacuum) in order to not flutter the rings. This is why builders as well as GM have been gapping the second ring larger in order to reduce the inter ring pressure which can flutter and unseat the primary ring sooner in the power stroke. This is why any good engine shop will load and lug an engine on the dyno brake during break in just to build heat and pressure force the ring moly into the cross hatch finish....AGAIN because ring seal makes power !!!!!
I'm not saying your combo won't make good power/torque. A set of Mamo ported 862s and a decent 230 cam would be a tire fryer for sure, however the laws of physics will undoubtedly dictate that the more efficient/less friction engine will have a lower Brake Specific Fuel Consumption number which means that it will produce more average power throughout the entire power band.

 

This is a bit off. A shorter rod increases side loading on the piston(friction/skirt & bore wear) and makes the direction of force less parallel to the force on the crank. All bad things. The longest rod you can run is ALWAYS better. The options are shorter piston height or a taller deck. I know in the past Tony Mamo has suggest a 6.2" rod to a number of folks over the 6.125"/6.098" rod for these exact reasons.

If you note in the article he(Mr. Reher) says the pressure drops off drastically not decreasing continuously(sounds like evenly) as you say. Moving the ideal angle of torque 10* does not justify the tradeoffs.

 

All excellent points. Thank you for a good technical response. These are the answers I am looking for.

As for lowering the rod ratio to shorten the gap between LPP and where the crank and rod are perpendicular... I was merely bringing it up as the only way I have heard to move where the rod is perpendicular. I, fully understand the merits of a higher rod ratio, and, personally, prefer to have the highest rod ratio possible. But in regards to lessening the gap between LPP and where the crank and rod is perpendicular, I don't know of any other way, except lowering the rod ratio. As was previously mentioned, the trade off is not worth it. Higher rod ratio trumps the smaller gap between those two events, for sure.

The stroker kit I want to use does have 6.125" rods, K1 forged, and a 4" forged K1 crank. Still only gives me a 1.53 rod ratio, which isn't stellar, but it's still better (or at least higher) than the GM factory ls7 rod ratio.

For what it's worth, wiseco's forged pistons for this kit have a special designed skirt to provide stability, and not stick out of the shorter sleeves of the small bore blocks.

Also note, that a set of mamo-fied MMS205 AFR heads and an equally mamo-fied Fast RT 102/102 will be added with the turbo. To my knowledge, Tony isn't quite finished with his dedicated small bore 205's, so I have a little bit of time to stash some pennies away.

When I get the MMS205's for the undersquare six liter motor, the WCCH stage two 5.3 heads will either find their way back on to a 327 with a d1 centri blower, or a 4.8 with some adapters from third-gen and an lsa blower.

PS. I absolutely do understand that the smaller intake runner of the mamo 205's would be WAY better than the wcch stage two heads, especially before the turbo when it's still naturally aspirated. And if his heads are available when I get around to building this, which I'm sure they will be, then I will probably skip the wcch heads for the six liter motor altogether, and go straight to the mamo-fied 205's and Fast set-up, even before I even start adding a turbo. I plan to run it naturally aspirated for a year or two before adding the turbo.

 

Side note:

Can Tony Mamo port a Holley high ram intake?

I found a pretty slick air to water intercooler that is designed to sandwich between the base and lid of the Holley intake.

I would actually really like to go with the Holley intake on the 359, because that intake is just too sexy.

Might have to use the mid-rise intake, because the intercooler adds 2" of height, and I don't want a big stupid cowl hood on my S10.

Have I mentioned that this abomination of an undersquare LSx is going in a 3000# S10?

Why? Because I hate tires, that's why.