How does a 5.3L engine weigh more than a 6.2L engine? Are you including the twin turbos? In that case it would have the potential to get better fuel mileage than the bigger displacement motor while making alot more power. So it would be more like tie/tie/WIN.

Not to mention the potential of that motor, without having to perform any serious mods, would be outstanding.

 

First, smaller bore means the holes in the block are smaller = more weight. They aren't going to lighten up the exterior of a block or make it physically smaller to punch smaller holes in it. 4.8's have the same exterior dimensions as 6.2's.

Second, lower displacement DOES NOT equal better fuel economy.

Lastly, putting forced induction on a 5.5 is complete waste when you can put forced induction on a 6.2 and make gobs more power.

 

Ugh...if only ricers across the world could comprehend this concept. I love how (some) people assume that a 4.8 is somehow easier to package and physically smaller than a 6.2 based on the same block.

I'm not specifically talking about anyone in this thread...

 

Well if you're going to split hairs... the classic 327ci V8 had a 4-in bore with a 3.25-in stroke which works out to ~ 326.725 cid. Yes that technically is 5.354 liters, which rounds up to 5.4, but its really a matter of semantics.

 

In theory you're correct. However we all know the real world sometimes blows those types of assumptions out of the water.

Case in point:

The classic Z/28 302 V8 had a smaller displacement than the classic SS-350 V8, (Both had a 4-in bore btw.) and despite the 350 being "rated" with more hp (295 v. 290), we all know that was actually BS and the 302 had at least 100hp more than the 350.

While bigger displacement can mean more hp, it isn't the only factor in determining performance.

 

And with the solid roller cam, high lift, and 2x4bbl crossram manifold, it probably got a lot worse fuel economy as well. Therefore lower displacement will not "always" net fuel economy gains. Just saying......I would love to have said Z/28.

 

Sure, but in today's world, GM is going to get SAE-certified net horsepower ratings on every engine, and they're going to tune each engine to a comparable level of efficiency. Crap like that just isn't going to happen two modern engines in the same engine family.

 

I know a guy that has a 68. It gets 11 MPG, according to him. Not exactly designed for fuel economy. Absolutely awesome car and I'd love to have one too.

 

Come on now... the 2x4 crossrams were extremely rare and only available in 1969. Even the 1967 MO 302's would trounce on their L48 counterparts.

 

Uh, no. It just means it's a different casting to accomodate a REPOSITIONED cylinder wall. A 4.8 doesn't use the same block as the 6.2 but just has a smaller hole cut in it. If that was the case, every smaller displacement motor could be bored out to massive diameters. The cylinder wall is generally around the same thickness in all of the different block castings. In other words, smaller bore = bigger water jacket surrounding it. Overall wall thickness is more or less the same, therefore block weight is more or less the same.

But as long as we're splitting hairs, one could argue that the pistons for the larger diameter bore are heavier, as are the larger rods, as would be the corresponding counter weights on the crank, so technically my guess is that the larger displacement motors weigh more.

 

The 302 probably still got worse mileage with a single 4bbl as well. I was extrapolating to the nth degree, point is the same.

 

Pffftt... the problem with "real world" numbers are the amount of variables that go into them. Maintenece, driving style, enviroment, and vehicle configuration can have alot of effect on that.

The only problem I see with using the EPA test is that manufacturers probably spend alot of timing figuring out how to game the system so that they can use it to thier advantage in advertising.

in both situations YMMV

 

In addition larger pistons means more weight for internal moving parts which means less efficiency. Plus larger water jackets would provide better cooling. Both of these will promote a higher redline.

My questions for the next generation is will VVT be standard and what are the rumars for the replacement A6
& M6?

 

I'd say it depends, a big bore 5.3 would have a lower piston speed compared to its small bore counterpart so piston weight might be a wash in terms of how it effects the efficiency of the engine and its ultimate engine speed.

Besides, oversquare engines favor a valve limited design like the LSx. Peak flow isn't so much the issue as it is low and mid lift flow (where multivalve engines shine in comparison).

As for max engine speed, the valvetrain is more of determining factor than the recip assembly.

 

Not necessarily any higher. The 7.0L LS7 has a higher redline than any other LS engine, despite having the largest bore and the longest stroke. It's all about the parts that make up the rotating assembly.