Thought exercise: is displacement the most important

The 4.3 6 shares bore and stroke with a 350. That is 4" bore and 3.48 stroke. There were factory 350s with 2.02 intake valves, which could be put in a 4.3 head without too much difficulty. You couldn't get anything close to that in a 265. So while the 8 has a shorter stroke and should be able to spin up faster, it would take some serious black magic to get the same flow. That said, maybe the same flow isn't needed since the cylinders are lower volume? It's probably not as linear as this, but in my mind the 6 needs 1.33x the flow per cylinder for the engine to move the same air and fuel. 
Maybe the answer is irrelevant since either engine is pretty much junk for performance. Still, the comparison is interesting for me. 

All I know is 3.8 Buick's and the newer DI version from GM can hold their own.

I believe the argument should be the LT based platform v6 and v8.

barefootskater said:

I say thought exercise, but maybe someone here has access to all the engines and a dyno.  
 

anyway, dad posed the question. (gm stuff because we are cheap)
 

Which is better? 262 V6 (4.3) or 265 V8 (4.3)?

I'm thinking the V6 because the lighter rotating assembly, and room for bigger valves means it could spin faster. Maybe. 
Your thoughts?

*edit. but with the v8 you get more explosions per rotation... someone argue with me. 

The V8 will have more valve area, since IIRC it actually uses the same size valves.

Streetwiseguy said:

ProDarwin said:

Streetwiseguy said:

There is something to be said for the larger valves of the 6, but it is more than offset by the volume available through the extra two valves.  

 

I know nothing about the GM engines discussed, but in a theoretical sense with the same stroke, the available valve area would be the same.

The V8 would have more ring contact area (friction) and more cylinder wall area to lose heat to (bad for efficiency, but good for max power).

Haven't done the math, but would 8 1.75 inch valves not flow more than 6 1.94 inch valves? 

Note my comment said in a theoretical sense.

A V8 with the same displacement and stroke as a V6 with have bores that are 6/8ths the size, and valves that are 6/8ths the size.  The total valve area will be the same.

In reply to ProDarwin :

Equal valve area doesn't necessarily mean equal flow, valve stem diameter and port diameter will play a big role. Which may or may not make a huge difference since the 8 will only need 6/8 the flow per cylinder too. 
 

Im gonna change my answer to more cylinders is better, to a point. Say 12. But that also depends on displacement. 1.6l doesn't make much sense in a V8. But if the two Mazda 2.5s I've owned, I think the v6 was better than the current 4. 

Having no experience of either engine from a purely theoretical point of view...

The basic variables in the power equation are piston area, firing strokes per minute and "Brake Mean Effective Pressure" which is a big term for efficiency. Putting this into practice:

Piston area is related to capacity, if capacity is constrained then more cylinders is generally better until you start trashing the BMEP due to internal friction, airflow issues etc

Firing strokes is basically rpm although remember two strokes have twice as many firing strokes as four. As a general rule RPM is the easiest way to gain power, sometimes accompanied by spectacular failures 

BMEP is a measure, usually calculated backwards from a running engine, of efficiency. Inlet airflow, exhaust flow, mixture, friction and heat loss all affect this. 2 strokes are inherently less efficient than 4 but not as bad as 50%. BMEP  improvements are generally the most expensive to make which is why the current crop of F1 engines are so insanely priced. I believe all the teams experiment with single cylinder engines and then multiply what they have done by 6.

As an example of the "game" consider the last of the 500 Grand Prix motorcycles. The rules were pretty simple, 500cc capacity with a maximum of 4 cylinders and a limit on the number of gears. The two stroke were all but unbeatable, only Honda for reasons of their own wanted to stay 4 stroke. They calculated that a V8 at 17 to 18,000 rpm should do the job but 8 is more than 4 in every language so by overspending an unlimited budget they produced the oval piston (think sawzall though the cylinder webs) NR500 with two rods under each piston. It produced the horsepower in the end but it was peaky to the point of being unrideable (remember the gear limit) and was ultimately unsuccessful. In true manufacture tradition Honda, and probably the others, leaned all over the FIM to allow the four strokes 800cc and the rest is history.

In summary the answer to the original question is that the 8 is probably better than the 6 but some ingenuity could certainly make the 6 as powerful at the expense of unreliability.

The argument about valve area is pretty moot.  The tiny bores on the 4.3 V8 will prevent more flow than their size suggests.  Not to mention, additional friction from a greater surface area being swept.

Neither one is a great performance option.  I detest small bore engines.  It means that pretty much anything you do is a waste of money in the hp/dollar war.  The old wive's tale of "long stroke makes more torque" is complete BS and has been disproved with every single dyno test ever done in history.  Displacement makes torque.  The only reason long-stroke/small bore engines are torquey is because that's all they can do.  They are destined to be low-rpm grunt motors because they can't breathe.

If you threw the same exact mild parts and head flows at a Buick 455 (4.31 x 3.9") and an Olds 455 (4.126 x 4.25) they would make the same torque and the same power at the same RPMs.  The main difference is if you started throwing performance parts at them, the Olds would run out of breath first, and you'd be limited to lower RPMs because of the piston speeds and rotating weight.  Getting a small bore, long stroke engine to be a true performer means deep pockets and lots of engineering to overcome the small bores.  Big bore means throw parts at it.

There is a fair aftermarket for the V6.  There is next to zero aftermarket for the V8.  Sure, there are plenty of aftermarket SBC and LT1 parts that would fit the V8, but unless you want 7:1 compression you can't really use the good heads.

At least consider the fact that the V8 is all the weight of a monster cast iron SBC or LT1 with only 4.3L of wheeze-tastic inside of it.  Why do a 600-lb engine with only 4.3L when that same 600 lbs could have 7L?

In reply to Curtis73 (Forum Supporter) :

Yeah I thought I was doing well, slightly above average at 6.6L until I saw some of those websites they talk about. 

To throw a wrench in this with regards to heads... the Bucsh cup cars made a switch to V6's at one point. You could get 18* aluminum 2.02 heads for the 4.3 block with 210cc intake ports IIRC. IT's been a long time since I looked into it. I was going to go that route with a truck I had. Because of the bore size I think the potential for power is going to go to the V6.

The other thing is, are we talking baby LT1 4.3 or original 265 SBC because those are two completely different beasts. 

In reply to bobzilla :

The original 265. But this was meant to be more of a thought exercise than an argument between a wobbly v6 and an anemic v8. 

I ask because I wanted to swap the Baby LT1 into my 2000 Sonoma. And then put 4.3 badges on it

In reply to bobzilla :

It's the wheezing epa pos 265 from the early 80's.

Curtis73 (Forum Supporter) said:

The argument about valve area is pretty moot.  The tiny bores on the 4.3 V8 will prevent more flow than their size suggests.  Not to mention, additional friction from a greater surface area being swept.

Neither one is a great performance option.  I detest small bore engines.  It means that pretty much anything you do is a waste of money in the hp/dollar war.  The old wive's tale of "long stroke makes more torque" is complete BS and has been disproved with every single dyno test ever done in history.  Displacement makes torque.  The only reason long-stroke/small bore engines are torquey is because that's all they can do.  They are destined to be low-rpm grunt motors because they can't breathe.

If you threw the same exact mild parts and head flows at a Buick 455 (4.31 x 3.9") and an Olds 455 (4.126 x 4.25) they would make the same torque and the same power at the same RPMs.  The main difference is if you started throwing performance parts at them, the Olds would run out of breath first, and you'd be limited to lower RPMs because of the piston speeds and rotating weight.  Getting a small bore, long stroke engine to be a true performer means deep pockets and lots of engineering to overcome the small bores.  Big bore means throw parts at it.

There is a fair aftermarket for the V6.  There is next to zero aftermarket for the V8.  Sure, there are plenty of aftermarket SBC and LT1 parts that would fit the V8, but unless you want 7:1 compression you can't really use the good heads.

At least consider the fact that the V8 is all the weight of a monster cast iron SBC or LT1 with only 4.3L of wheeze-tastic inside of it.  Why do a 600-lb engine with only 4.3L when that same 600 lbs could have 7L?

Long stroke engines can't breathe?  In 1948 Jaguar came out with the in line six. It has a 4.7 inch stroke. Maybe you aren't familiar with a Jaguar but it is a true Hemi head ( DOHC ) they produced that same engine  for 47 years. Won the 24 hours of LeMans 5 times . Used in everything from little economy sedans ( 2.4 ) liters to Tank engines ( 4.7 ) liters. for decades the queen drove around, Er, was driven around in cars powered with it.*
 The famous Hudson Hornet was also a long stroke engine, Duesenburg was a long stroke engine. And in 2932 the SJ version made 265 horsepower when Ford was struggling to make 80. 
Finally both Caterpillar and Cummins produce very respectable horsepower run as high as a million miles have a very long stroke  ( and 4 valves per cylinder ) 

Finally we are talking about small block Chevy, there are sprint car engines out there with 4 inch stroke

* When Jaguar reversed the bore stroke ratio and went to a 3&1/2 bore with a 2&3/4 stroke in the all aluminum V12 the engine weighed within 30 pounds of the Cast Iron six.  Though Six was designed in WW2 and the V12 in the 1960's in the same car the V12 made 24 more horsepower than six even though the V12 was 1100cc's bigger  

In reply to frenchyd :

I didn't gather that he was saying long strokes are bad, but that small bores are bad. Of course a long stroke means a heavier rotating assembly, and the requisite taller deck means a heavier block too. 

In reply to Ranger50 :

No, or not exactly. The original small block from the 50s. That is if I have my history correct. 

In reply to frenchyd :

Breath and stroke aren't what I was talking about.  The OP was talking about two of the same displacement engines; one with a small bore and one with a big bore.  Given the same displacement (as a big generalization), a 4.3L that gets its displacement from small bore/long stroke will run out of breath before the same 4.3L that gets it's displacement with big bore/short stroke.  In a street application where you're never going to go big, it's a bit academic, but it's just physics.  Getting the Olds 455 to breathe like the Buick 455 in my above example will take a lot more engineering and a bigger wallet.

Also, since force is squared with velocity, adding 10% to the stroke means potentially doubling the inertial forces on the rotating assembly.  Getting an engine to hold together and not launch the pistons into the heads requires more weight, stronger materials, and can become a point of diminishing returns.   For a performance application, I will always choose the big bore/short stroke version.  For a street beast, I just go big.  Like 500ci is a good start :)

barefootskater said:

I say thought exercise, but maybe someone here has access to all the engines and a dyno.  
anyway, dad posed the question. (gm stuff because we are cheap)
Which is better? 262 V6 (4.3) or 265 V8 (4.3)?

I'm thinking the V6 because the lighter rotating assembly, and room for bigger valves means it could spin faster. Maybe. 
Your thoughts?

*edit. but with the v8 you get more explosions per rotation... someone argue with me. 

But the v6 has heavier pistons per cylinder, thus limiting RPM compared to the V8.  All else being equal.

500cc / cyl is about optimal for combustion FWIW.

I tried plugging 90deg V engines into the game Automation, and all else being equal it seemed to think that the V6 would be lighter and make more power due to a higher knock threshold.  V8 would be much smoother though.

In reply to red_stapler :

That depends on several things. What is the intended use? Rpm range? Expected (required) power output. Fir 500cc/cyl, it's easy to have a square piston setup (86mm x 86mm) which tends to give a good all around package and allows for good parts sharing if you only want to have one piston mold for your 2L I4 and your 3L V6.

That said, 500cc can be made many ways, but few are as advantageous as the example above.

But it's moot anyway, since the engines were talking about are measured in freedom inches. 'Murica!

In reply to noddaz :

I've since changed my answer. It would be interesting to see the exact weight of each rotating assembly though. I bet it's not that different. 

In reply to Curtis73 (Forum Supporter) :

I LIKE BIG BLOCKS AND I CAN NOT LIE. 

noddaz said:

barefootskater said:

I say thought exercise, but maybe someone here has access to all the engines and a dyno.  
anyway, dad posed the question. (gm stuff because we are cheap)
Which is better? 262 V6 (4.3) or 265 V8 (4.3)?

I'm thinking the V6 because the lighter rotating assembly, and room for bigger valves means it could spin faster. Maybe. 
Your thoughts?

*edit. but with the v8 you get more explosions per rotation... someone argue with me. 

But the v6 has heavier pistons per cylinder, thus limiting RPM compared to the V8.  All else being equal.

Not necessarily.  If the V6 has a shorter stroke, the extra weight is more than offset by the lower velocity.

barefootskater said:

In reply to Curtis73 (Forum Supporter) :

I LIKE BIG BLOCKS AND I CAN NOT LIE. 

You other brothers can't deny.  When a girl drives up with an itty bitty race and a big block in your face you get sprung.

I drive a vehicle with a 1.6 liter engine. Ill show myself the door.

In reply to dxman92 :

Yeah but is it a 4cyl normie, or a V10 That idles at 4K RPM? Because one is good, the other is legendary.