DavidBoren

I searched and found nothing conclusive.

I'm looking for any first hand experience with the 4" crankshaft in a 3.78" bore block. Dyno graphs. Impressions. Problems. Anything, really.

I want to build one. Regardless of the small bore and small valves, the heads can be made to flow more than the stock 243's on the ls2, which is fine with me.

More airflow through smaller valves means intake velocity has increased. This would be very beneficial in conjunction with the higher piston acceleration near top dead center brought on by the longer 4" stroke.

The thicker cylinder sleeves of the small bore blocks will better handle the additional side loading that comes with the increased stroke.

Anyways, has anyone built one? Seen one? I can't find anything completed online anywhere.

I don't want to argue about the practicality of it... at all. No, the novelty of having something a little different is not worth the $2000 rotating assembly. But... BUT... testing my own ability to fail is worth every penny.

redbird555

iTrader: (14)

I don't think it would be very efficient even without the added cost. By decreasing the bore and increasing stroke you're just limiting rpm potential. Maybe not enough to notice in a street engine but it's a factor nonetheless.

The heads have small valves yes but that doesn't mean they'll be as efficient as in a larger bore.the smaller bore will still limit flow potential and still shroud the valves.

In the end the motor will run and make power but the same setup on a stock ls2 with a 4" bore and 3.66 stroke will have better longevity and walk over it

There is a very good reason engines are traditionally built with a bigger bore than stroke and why when money is no object a bigger bore is better...simply because the flow potential by not shrouding the valves is much better along with allowing the engine to rev easier

96capricemgr

iTrader: (1)

Less than a ls1 with the same heads and cam

DavidBoren

I am not trying to argue, because ultimately, I don't know ****.

But, tradition has changed. The general redesigned the age-old 5.7L with a smaller bore and longer stroke.

In theory, a longer/narrow cylinder is a better, more efficient air pump... in comparison to a shorter/fat cylinder.

And I do understand that the small bore limits flow. Every diameter of bore limits flow... you have to draw the line somewhere.

I also understand that the same ported 799's would flow even more on a larger bore. But they outflow what stock 243's flow on a 4" bore, even on the smaller bore, so I'm ok with that.

I'm not chasing ludicrous power, and I'm not going to rev it any higher than the general revs the ls7, which has the same stroke with a lower rod ratio and heavier pistons, so I'm not concerned with stroke limiting my redline.

Don't care at all about horsepower. Not at all. It's just a stupid, arbitrary number based on theoretical coal mine ponies. It's just a number.

Torque, on the other hand, is real. And increasing mechanical leverage by increasing the length of your lever, as in stroke, has to have measurable merit. And the sooner in the powerband your torque shows up, the broader and flatter that powerband will be.

Yes, increasing displacement increases torque. Fact. The small bore limits displacement, thus limiting torque. And if I cared so much about torque, I shouldn't limit displacement... But you have to draw the line somewhere.

And my line is drawn at six liters. So I want to capitalize on available torque, given my self-imposed bore/displacement restraints.

Once again, this is not an exercise in practicality. I want to test something that I, personally, think should work. This is nothing more than a test of my own ability to fail.

And if my undersquare six liter motor doesn't do better than a stock ls2... Who cares? I have a fully forged six liter LS motor... Boost will take care of the rest.

DavidBoren

But we digress. This isn't a discussion of whether or not I should build an undersquare six liter motor.

My inquiry is for the real world results of someone who already has built one.

redbird555

iTrader: (14)

In summation I don't really understand why you made this thread man no offense. You sound pretty determined to try it, that's fine but you asked for good reasons why it isn't the best idea barring cost. Well there you have it there really isn't a good reason to do it unless you want to spend a lot of money to just say you have something different that makes less power and no one will ever notice because they cant see any of it.

redtan

iTrader: (5)

You simply looking for real world results does in fact go back to the discussion of whether or not you should do it. If it's a **** poor combination then you won't have many, if any, results.

Which goes back to the discussion...it is a **** poor combination of small bore and long stroke. You are also confusing what ported heads mean, because you keep saying

When you port 243 heads you lose velocity because you increase the runner size.

If you want to do it just because go ahead, it will definitely make power. But you won't see many results because like I mentioned it's a poor combination. On one end you bring in a long stroke demanding lots of air volume while at the other end you increase cylinder head runner size. But in the middle you bottleneck all that **** with small valves and small bore.

DavidBoren

I ran a couple calculations through the wallace racing online calculator, with both conservative and liberal flow numbers based on what I have read 799 castings can flow when worked on.

Aforementioned online calculator predicts that the ported 799's can support six liters of displacement to 7000rpms, even with conservative numbers based on flow through a 3.78" bore.

Once again, I don't know ****, I'll be the first to admit that. There's a big difference between online calculator predictions and real world performance. And the overwhelming lack of posted real world results of this combination, does speak volumes about how if it was worth doing, more people would have done it.

As for my comment on intake velocity. If stock 243's flow ~250 on a 4" bore, and west coast cylinder head stage two ported 799's flow ~265 through smaller valves, then the velocity has to have increased. The only way to get more air past smaller valves in the same amount of time is to increase the velocity.

I'm not trying to argue. I fully understand that it goes against convention. But, for whatever reason, I think it should work. In my over-opinionated and under-educated mind, regardless of valve/bore diameter, if I can meet or exceed the stock flow numbers of the ls2... then I should be able to meet or exceed the performance of the stock ls2. The one determining condition is whether or not I can meet or exceed the rpms of a stock ls2. And the online calculator predicts that those wcch stage two heads can supply enough air for more rpms than a stock ls2 redline. And there are plenty of people pushing 4" stroker motors to the 7k mark just fine, so I'm not concerned with stroke limiting my redline.

Am I wrong to assume that if displacement is similar, head flow is similar (regardless of bore/valve diameter), compression is similar, and the redline is similar... Shouldn't you be able to expect similar performance?

The only difference is that the undersquare architecture should, in theory, provide more torque earlier in the powerband. Thusly, the undersquare motor should, in theory, have a broader and flatter powerband.

And if they both have the same redline, what possibly is there to argue about with a broader and flatter powerband?

I'm still increasing displacement and head flow compared to the original small bore motor, I'm just not willing to sacrifice on the thicker cylinder sleeves because I will never be able to afford an ERL sleeved block.

Plenty of people out there paying for forged rotating assemblies in 6.0L motors, keeping the stock displacement. So the cost of the forged rotating assembly is a wash, because if you want forged steel, you have to pay for forged steel.

Who knows, it may be a turd, there's only one way to find out. And that's what makes it tantalizing and exciting... For me, at least.

redbird555

iTrader: (14)

What part of you're argument says it will work? Redtan and I explained the simply physics of why it wont make more power than a normal 6.0. Can you explain why it should? Small valves and more velocity doesn't make sense, you can put that on any motor and make more power. Putting a longer stroke on an engine wont magically make the head work better. Like redtan said porting 243's decreases velocity, but the added flow makes up for it to a point. By using a smaller bore you're choking the head. The math says it will work I understand that part but what part of your math says it will work better than a standard 6.0?'

You also keep mentioning the limitations of stock sleeves. I'm assuming you are talking about aluminum as the iron block do not use sleeves. An lq9 block is easily capable of supporting massive boost and 1k hp so you would have to stretch that limit pretty hard. if its aluminum, the stock ls2 sleeves are thicker than the earlier gen III stuff and get pushed to high 700's pretty regulalry

redbird555

iTrader: (14)

[QUOTE=DavidBoren;18959216]I ran a couple calculations through the wallace racing online calculator, with both conservative and liberal flow numbers based on what I have read 799 castings can flow when worked on.

Aforementioned online calculator predicts that the ported 799's can support six liters of displacement to 7000rpms, even with conservative numbers based on flow through a 3.78" bore.


As for my comment on intake velocity. If stock 243's flow ~250 on a 4" bore, and west coast cylinder head stage two ported 799's flow ~265 through smaller valves, then the velocity has to have increased. The only way to get more air past smaller valves in the same amount of time is to increase the velocity.

243's and 799's are the same head they both have the same valves the wcch heads flow more because the runners have been hogged out. You will not gain velocity by porting the runners out larger and keeping the same size valves. Again it goes back to the smaller bore will inhibit flow of the heads whereas a larger bore will promote it. So no you will not have the same flow with the smaller bore thus it will not make the same power.
I'm not trying to argue. I fully understand that it goes against convention. But, for whatever reason, I think it should work. In my over-opinionated and under-educated mind, regardless of valve/bore diameter, if I can meet or exceed the stock flow numbers of the ls2...
But it wont because the heads are being choked by a smaller bore

Am I wrong to assume that if displacement is similar, head flow is similar (regardless of bore/valve diameter), compression is similar, and the redline is similar... Shouldn't you be able to expect similar performance?

Head flow will not be similar see above.
The only difference is that the undersquare architecture should, in theory, provide more torque earlier in the powerband. Thusly, the undersquare motor should, in theory, have a broader and flatter powerband.

And if they both have the same redline, what possibly is there to argue about with a broader and flatter powerband?
QUOTE]
Also you cant compare flow numbers from different companies. Every flow bench will read differently, just because a ported 799 head flows 310cfm on a 4" bore on one bench may mean it only flows 295 on another.

DavidBoren

I have no empirical evidence to support that my proposed undersquare six liter motor will beat a stock ls2.

None.

I am basing this on my limited understanding of how all of this works. To me, there is absolutely no reason for "my" motor to not match the ls2. Same displacement/compression/head flow/rpms... only thing that changes is architecture of the rotating assembly.

Why wouldn't it match the ls2?

And not to be overly blunt about it, but I know and understand that if I put the wcch stage two heads on a larger bore, that they would flow even more than they do on a 3.78" bore. That's not the question. It's not in any way related to my inquiry.

I am comparing what bone stock 243's flow on a 4" bore, to what the wcch stage two heads flow on a 3.78" bore. And, in this exact comparison, the stage two ported heads flow a greater volume of air than the 243's... Even despite having smaller valves and being on a smaller bore.

And to me, more air means more power. It was even mentioned earlier that to increase torque, you need to increase the amount of air being compressed. And "my" combination does that, when compared to a stock ls2.

I see absolutely nothing holding me back from at least matching a stock ls2. I can meet or exceed the:
Displacement,
Compression,
Airflow,
And the rpms.

If I end up with just bone stock ls2 performance, in a much more expensive undersquare forged six liter, so what?

I'm not trying to beat the ls2, necessarily. It's just my basis of comparison. It's par, if you will. I, personally, feel I can beat it. No real data to support that, though.

Other than the head flow numbers. More air means I can use more fuel, and in theory, make more power.

I don't know why everyone is so caught up on the small bore size. Who cares? It literally doesn't matter, at all, whatsoever... The end result, despite the smaller valves and smaller bore, is that the wcch stage two heads still provide more air than the stock ls2 receives through its heads.

If "my" six liter motor has better flowing heads than the next six liter motor, I would imagine that my potential for power production is greater.

The stock ls2 having bigger valves and a larger bore literally means nothing if all of that combined still flows less than "my" small valves/bore.

The only thing I have to worry about is meeting or exceeding the stock ls2 redline. And I have read about plenty of success stories using the 4" crankshaft, spinning as high as any stock ls2, so no worries there. And all the calculations I can work through says/predicts that the head flow provided by the wcch stage two heads is enough to support six liters of displacement up to 6800-7100rpms... which is more than the stock ls2.

Yes, the same mods would probably yield better results if done to a stock ls2. But that's not what this discussion is about.

I had this same discussion on the lat-g forums, and the only thing that they brought up that concerns me is the surface area of the piston, and how that effects the equation for force applied to the crank. I'm still not completely sure if I understand that correctly, so I didn't bring it up earlier.

redbird555

iTrader: (14)

where are you getting the smaller valves? a 243 stock head an a 799 or 243 wcch head have the exact same size valves. But to answer your question, yes if you put a stock 243 on an ls2 or a ported one on a 3.78 bore engine of course the ported combo will make more power. Its not that much of a hinderance BUT why would you do that? Its not a fair comparison put the same heads on the same engine and do the compare, in that case the small bore engine will make less power.

My point is why would you spend thousands to equal a stock ls2? Put a forged rotating assembly in an ls2 block. In the end the difference wouldn't be much at all in cost, I understand the want to be different but it just doesn't make sense here. Put those wcch heads on a 4" bore and it would be much better than a 3.78 bore and blow a stock ls2 away instead of just equaling it

96capricemgr

iTrader: (1)

While you are going this far with the poor ideas why don't you find a copy of Comp's cam selection software and let that finish wasting your money on more of the wrong parts for you.
Hell in another thread a few months ago someone was arguing displacement makes torque not stroke and was looking to use a big bore short stroke to make torque

Those who want to get into baseless benchracing can argue whatever they want. In the end the blind quest for displacement is the most expensive way to get a low level of return on your HP dollar. Even using a larger bore and letting the head breath, stroking is the most expensive HP you can buy.

Years ago with the Gen2 LT1s I donated an L99(4.3l Caprice version of the LT1) crank and rods to a guy who assembled it with stock LT1 pistons in a LT1 block, the rods were longer so the piston was the right height with this combo. Guy really knew what he was doing and built this 302 LT1, basically admitted it didn't do anything he hoped it would. He hoped it would get better mileage and didn't, and was a turd on the strip, he tried to tow with it and it hunted gears relentlessly. But at least his mistake was cheap, he paid the $50 to ship the rotating assembly, maybe something to press the pistons and then it was gaskets.

Benchrace whatever angle you want, but there is a reason nobody has stepped up with an example. The platform is old, if it worked somebody would have tried it and reported it.

DavidBoren

Wow. I didn't mean to offend anyone proposing that I want to build an undersquare motor. Opinions seem to be very heated on this topic.

And the 799's on the small bore have a 1.89" intake valve, compared to the stock ls2 intake valve of 2.00"... That's where I figured that velocity has to increase. Even the stage two ported heads from wcch, have a 1.95" intake valve... Still smaller than an ls2 intake valve.

Anyways, I set the bar pretty low, just trying to match Gm's ls2, considering I'm probably going to stick a t6 s480 on it anyways. But if I can reinvent something that the general spent millions of dollars researching and developing, I think I can call that a success... Given that making an undersquare six liter motor is such a waste of money. If my waste of money can remotely match the general's corvette engine, I will be happy with that.

I see that same waste of money argument with 383 builds. Why waste your money, get a 408. But the 4" bore is still a restriction, don't waste your money on a 408, get a 427. But there's still more bore available, step up to the 4.17" bore, and a super deck, and 6 bolt heads... Blah blah blah. Like I already said, I will never be able to afford an ERL sleeved block. I am not chasing ludicrous power. You have to draw the line somewhere. And the thicker cylinder sleeves of the small bore blocks comforts me. So, I will do what I think the best possible small bore engine can be.

It's literally just something I think should work and want to try, I don't know why that would make anyone seem so upset.

At the end of the day, I will still have a fully forged six liter LSx. That's not ever a bad thing, is it?

A.R. Shale Targa

iTrader: (2)

You're completely overlooking one small yet meaningful detail.....
Approximately 60% of an air pumps rotating friction is from ring travel...
Each crankshaft revolution causes a 4" stroke piston to travel 8 inches (top to bottom and back up again)
Times 8 pistons is 64 inches or 5.3 feet...
At a modest 6600 rpms (110 revolutions/sec.) your proposed peanut bore combo will be trying to overcome the ring friction of nearly two football fields each second (583 ft.)
It's called parasitic frictional losses
I don't give two ***** what valves you have in what castings ported by Moses himself, brand XYZ cam, thick liners....blah blah blah
FACT....it will have to kick the pistons harder in order to overcome it's own geometric inneficiencies
IMO....go right ahead and do it, it's your money and honestly I'd like to see you try it just for whatever reason, but speaking from experience here.....an S480 don't need any crank stroke to make a thousand horses AND a thousand foot pounds.....

Exidous

iTrader: (11)

I'm looking to do the exact opposite down the road. Biggest bore I can on a normal 3.622" stroke. It will be somewhere around 400-404ci. There is a reason so many race engines go big bore tiny stroke(NASCAR/F1/Indy/LMP). The more sq in area on the piston the more effectively the cylinder pressure can move the piston.

What you are proposing can absolutely be done but for the exact same overall ci a bigger bore will make more power.

What would be interesting is to see two motors. Identical in every way except bore and stroke. Same ci on both. One big stroke and one big bore. I'm 100% certain the big bore will have more area under the curve.

MuhThugga

This kind of reminds me of those ~330 strokers people did with 305 blocks and a 400 crank. OP, while it is a different generation of engine, you could look up the results people got with those 305-based stroker engines and compare them to the results people got with 331 engines (327 bored .030" over). That would give you an idea on the powerband differences between the over- and under-square motors, and what to expect with this setup.

Take a factory 5.3 and compare it to a 6.0 with a 4.8 crank. That's about as close as you'll get to that comparison.

redtan

iTrader: (5)

You keep thinking that simply installing a smaller valve will somehow magically increase velocity throughout the head, even after significantly opening up the rest of the runner. Then on top of that you put it all with a small bore.

All you're doing there is having a whole bunch of lazily moving air getting slammed into a tight area and then trying to squeeze it all into a small opening.

You only increase the velocity right at the valve and entrace to the chamber, which may be worth something...but 90% of the other time the air will be moving slower due to the larger ports.

Think of a garden hose by putting your thumb over the nozzle...yes the water sprays faster from then on but the water behind that moving through the hose does not actually speed up just because you decided to put your thumb there, it remains the same. And by installing an even larger hose diameter behind the nozzle all you're doing is slowing the water down nullifiying any action you may be providing by holding your thumb over the nozzle.

If you want truly increased velocity everywhere then you need a small very efficient runner, not a hogged out one that most ported OEM castings are. Those go from 210cc runner to high 220s even 230s. That in no means increases efficiency and velocity, then you go a step further by making the valve opening even smaller. Why do you think all these aftermarket castings for small bores are in the 205-215 range? Because it keeps velocity up.

You installing a 230cc head on a 1.95" valve and 3.78" bore is going the wrong direction.

Exidous

iTrader: (11)

It's important to note that the purpose of "matched" velocity through the port and valve is scavenging. You are using the pulses, weight and atmospheric pressure of the air behind the valve to help push air past the valve. It's not suction pulling air in. It's the atmospheric pressure being higher than the cylinder pressure. Said atmo pressure is pushing air in. A hogged out port will slow the air killing its momentum.

It's kind of like cooling some thing off. You don't make it cold, you remove energy/heat.

DavidBoren

A 3.6" crank still travels the pistons 538 feet @ 6600rpms, so I'm really not adding that much more friction, maybe 10%... Unless frictional loss is exponential...?

Plus, the smaller piston has less ring surface area interacting with the cylinder walls to create friction.

And the flame will propagate through the smaller bore combustion chamber more efficiently than a larger bore. The smaller bore has less surface area to steal heat from the combustion chamber to the cooling system. Maybe some of the small bore's better burn characteristics will make up for the extra friction.

I don't know. I don't. And I definitely do not mean to sound like I know everything. I appreciate the concern of everyone who is worried that I may waste my money building this, if I do. Nothing is set in stone at this point.

I, personally, would do nothing but encourage people to try new things. Sure, bring up the shortcomings, and give fair warning, but don't cast your petty judgement as to whether or not it will be a waste of money. That's not for you to decide.

Trying new things, building **** that shouldn't work, making mistakes, going against tradition... It's how this industry progresses. I would think that everyone would be rather encouraging if for no other reason than to just see one be built, with real empirical evidence and results.

And if it's a turd, then you would have this wonderful, shining example of failure to bring up next time someone like me asks a question like this.

If I was asking about building an oversquare 353, with a 3.3" crank in a 4.125" bore block, there would be an equal outcry about me wasting my money. I know this because I have seen it, on this site, for that matter.