JoesC5

The 7.0L LS7 used in the C6 Z06 is the same physical size as the LT series engines. GM has crate engines(LSX that have 454 cu in displacement and can go to over 500 cu in) and are the same physical size as the 427 cu in LS7, or the 376 cu in engine in the C7.

JoesC5

I can't believe that you actually believe that.

Lets take my 4.125" bore and 4" stroke engine(427 CID) with 2.200" Intakes and 1.61" exhaust valves. My original heads flowed 351 CFM intake at .600 lift and 209 CFM exhaust at .600 lift. Then I installed a set of PRC265 heads with the same size valves and my flow increased 9% on the intake to 383 CFM at .600 lift and increased 12% on the exhaust to 235 CFM at .600 lift.

My horsepower increased and I didn't increase the size of my valves. I could put in a 1/4" longer stroke crankshaft In my LS7 and that 9%/12% greater flow of my PRC265 heads will feed that additional stroke, and I will definitely see a rise in horsepower, even though my valve sizes are the same as when I had the 4" stroke.

Let's take those same LS7 heads and put them on a 4.070 " bore(LS3/LT1 block) but with 2.20" intakes and a smaller1.59" exhaust. These small bore LS7 heads still flow 380 CFM intake and 230 CFM exhaust. Now drop in a 4" stroke crankshaft in place of the 3.625" crankshaft for 417 CID, It definitely will produce more horsepower than a 376 CID LS3/LT1. Like around 600 HP with the small bore but a longer stroke.

Rkreigh

absolutely correct. While it's true that unshrouding the valves does help, there is no replacement for displacement with a NA engine. 4.0 and up is still a very large bore

Ls7 heads will feed 427 and still make power with a relatvely mild cam up over 7k rpms, so a bit more stroke will increase both torq and HP as the heads flow a ton !!!

GM spend the $ on cyl head design and it delivers!!

~Josh

I actually like the fiero especially the gt body style.

Too many good cars to choose from today though. My next special car is a Lamborghini, not a Fiero or c8.

Kodiak Bear

Another absolutely correct with a couple of observations.

With all the knowledge of the small block gained over time and research, I believe that the stroke length chosen by GM was deliberate and not just a random event.

Assuming you want to keep to the small block for cost purposes, why that displacement? Durability? Durability of what? Impact of the length of connecting rods on durability? What makes that con rod length so desirable?

I speculate that the thought process was something like , "How much displacement can we get out of the small block in iron configuration and meet our durability requirements?"

I believe the length of the con rods impact on durability was the key limiting factor. But I haven't the foggiest idea what that particular length does or doesn't do for durability.

Additionally, is the forged crank shaft a "drop in" to the aluminum block?

And of course, what impact does all this have on the piston design as the 6.6 is a lower compression engine.

If you're building a lot of cranks for trucks and can just drop the crank shaft and associated con rods into the C8 engine with new pistons then there has to be a great temptation to do just that in the C8. A likely concern would be the impact on the durability at rpms higher than the truck engine.

Choices, choices. choices

Michael A

Different situation. I'm talking about everything being the same except changing the stroke. Of course, today we have better emissions equipment, the heads, intake and exhaust designed with CFD, etc.

Michael A

You are talking about completely changing the heads. Of course, it will be different.

Just change the stroke, and see what happens. You'll have more low end torque due to more displacement, and at an RPM not limited by head flow. However, on the top end, you'll have more reciprocating forces, which drops the maximum RPM, more piston side loads, and the head will still only flow the same amount. No more power.

From what I have heard, Tadge doesn't like that the current engine doesn't rev higher. Putting in a stroker is in the wrong direction to improve that.

Michael A

No, it's not "absolutely correct". The example he gave had the heads changed. Your example even changes the cam. The car companies have to meet emissions, durability, and fuel economy targets. Otherwise, they could just head over to the Chevy Performance Parts group, and sell Corvettes with crate engines.

By this reasoning I'm seeing here, Chevy didn't need to come out with a big block in the 60's. They could have just put in more and more stroke, changed heads, and changed cams on the small block. I don't recall the 400 small block being much of a powerhouse.

The big block was born for a reason.

JoesC5

The lifters on the AFM is what is limiting the RPM to 6,500 on the current engine. They are heavier than the normal lifter. On the LT1, the camshaft even has different shape ramps on the cylinders for the 4 AFM cylinders vs the other 4 cylinders to slow down the opening/closing speed of the lifter. Even though the LT1 is a 6.2L, same as the LS3, it was designed as a torquer engine, and has smaller intake valves than the LS3, even though the cylinder block bore is the same. Increasing the stroke so the engine is .4L larger in displacement has nothing to do with the 6,500 RPM restriction.

The LS7 was tested to 8,000 RPM even though it has a 7,000 redline. Heads do make a difference. My example is what can be accomplished by improving the head design to increase the flow without having to go to bigger valves as you claimed was necessary to feed a longer stroke LT1 engine. I also gave you an example of actually increasing the valve sizes by installing the LS7 heads on the small bore engine. Oh, and the C7R uses a LS7 as an engine(block and heads) even though it has a smaller bore than the LS7 used in the C6 Z06. They reduced the block's bore diameter, as well as the stroke, to get the engine down to 5.5L(to meet the rules) but used the LS7 heads with it's larger vales(and ports) to get horsepower at higher RPM's.

When designing an engine all the engine's components are designed to complement each other. There is nothing to suggest that GM only changed the stroke on the 6.6L engine without changing anything else(such as the heads). As I pointed out, on my LS7, it's easy to get more airflow without increasing the valve size. With my new heads with larger ports but the same size valves, I can increase my stroke by a 1/4" and my heads would supply enough air(9% more on the intake and 12% more on the exhaust) to support the increase in the engine's displacement.

Rkreigh

LS7 heads flow way better, show me a stock BB head as delivered and unported that flows 380 cfm as delivered???

LS7 engines meet emissions and fuel economy targets just fine.

If chevy had the big displacement LSX motors in the 60s the BB would look like a boat anchor and would have gone the way of the 409 and the flat head. Technology marches on.

Don't get me wrong, I love a good modded BB chevy and still have a couple in pieces.

But the modern stuff is so much better. The new ZR1 modded just cracked 8s with a stock bottom end. Not too shabby.

with the new engines you get much improved ports and big displacement in a small and light package that puts out improved power and efficiency in comparison to the old Rat.

I'll take those new ti valves from the factory too as well as the ti connecting rods. New tolerances are WAY better too.

wish my old Rat had the block strength and 6 bolt bottom end back in in the early 70s

GM has indeed gotten smarter than the 60s technology don't you think?

Dominic Sorresso

Have we landed on whether or not this “new” LT2 motor comes w 1 or 2 cams “in block”?

QKSLVRZ

Much better heads.

84 4+3

Well the 400 was like only used in mostly trucks and regular sedans so... But all the big block was was a scaled up small block too lol. It works.

kozmic

Wait... and this is a legit question... Pontiac made a 5.2 Fiero? Or was this a typo, and you meant 2.5?

I never knew of a 5.2 Fiero, and if they did make one, that must have been a badass little car for its time!

RapidC84B

The leaked build sheet shows the LT2 as 6.2 liters.

Kodiak Bear

A few shops made some bucks putting Cadillac Northstar engines in Fieros, The 4.6 lt version. 300hp As I recall, it could be modified to 375hp. But you need to check it out as I'm working from memory.

Kodiak Bear

Makes sense. But without all the product specs we don't know what the intention was. The best part of the 6.2 is that it should be reliable as it is a continuation and should have taken the minimum dollar investment to develop so more dollars could be directed toward the change to mid-rear.

Donuts

it’s what I’ve been trying to tell everyone this whole time

Donuts

Isn’t Ford bringing back the 460 ?

Michael A

I am not sure what to make of this, because you are mixing up so many parts and engines. The LS7 had titanium rods, and the LS3 has powered metal. There is a bit of difference there. I don't know where you are getting your information that the bottom end of a stroked LS3 will hold up to 6500 rpm without some upgrades unless you built and dynoed it, or you have inside information from GM.