Our S650 HP compared to the C8.

[LouG]

Stroke doesn't affect torque any differently than bore. It's a common myth. All that matters is cubic inches.

It absolutely does. An undersquare engine has a longer crank throw than an oversquare engine of the same capacity.
The longer throw equates to more twisting leverage on the crank which = greater torque especially at low revs.

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[Junkyard Dog]

It absolutely does. An undersquare engine has a longer crank throw than an oversquare engine of the same capacity.
The longer throw equates to more twisting leverage on the crank which = greater torque especially at low revs.

Smaller piston area offsets the leverage.

 

[Junkyard Dog]

Stroking an engine does result in more torque, but the cubic inches are no longer equal. In fact, many times the stroker crank is installed with an overbore for even more cubic inches. Lots more torque and power.

There are other issues with a small bore, of course, shrouding of the valves and less cylinder head flow for the intake valve being one.

 

[LouG]

Smaller piston area offsets the leverage.

Not in practice.
Back when undersquare engines were common, and oil tchnology/metallurgy didn't allow them to spin out like an oversquare engine, they were considerably torquier at low revs, less powerful at their top end due to a lower rev limit.
I'm comparing British engines of the period, BMC 4's compared to, say, a Ford Anglia or many Italian small 4's.

 

[robvas]

It absolutely does. An undersquare engine has a longer crank throw than an oversquare engine of the same capacity.
The longer throw equates to more twisting leverage on the crank which = greater torque especially at low revs.

I understand that the 'math' is there but in the real world it doesn't really make a lick of difference.

Go get a dyno sheet and prove it. Both engines have to have the same displacement, compression ratio, cams, and the same heads. Only difference can be bore/stroke. Going to make the same powercurve.

 

[Junkyard Dog]

Not in practice.
Back when undersquare engines were common, and oil tchnology/metallurgy didn't allow them to spin out like an oversquare engine, they were considerably torquier at low revs, less powerful at their top end due to a lower rev limit.
I'm comparing British engines of the period, BMC 4's compared to, say, a Ford Anglia or many Italian small 4's.

They typically came with smaller port sizes in the heads, e.g., Pontiac's heads v. Chevrolet big block rectangular port heads. The former made a large amount of torque at a lower rpm but ran out of breath at the high end.

Pontiac 455 had 4.21" stroke, Chevrolet 454 had 4" stroke, but the real story of the torque curve was in the cylinder heads.

I don't know anything about British engines, so I cannot discuss them, sorry.

 

[LouG]

They typically came with smaller port sizes in the heads, e.g., Pontiac's heads v. Chevrolet big block rectangular port heads. The former made a large amount of torque at a lower rpm but ran out of breath at the high end.

Pontiac 455 had 4.21" stroke, Chevrolet 454 had 4" stroke, but the real story of the torque curve was in the cylinder heads.

I don't know anything about British engines, so I cannot discuss them, sorry.

The basics are much the same. But modifying British stuff when new was uncommon. That was left to we poor teenagers when the cars got a bit of age on them.

 

[Kevi]

I'd say the big problem with base mustang vs base c8 is more the difference in tire size and axle ratio vs engine power.

255/40 on 8.5" wide rims and 3.15 final drive vs 305/30 on 11" wide rims and 4.89 final drive.

Small wonder why a c8 destroys a stock GT in the 1/4 mile. The stock GT is nowhere near optimal for putting power down to the pavement. That's why they want to sell you a 5k "performance pack" that really should come on the base GT. Instead the base GT gets ecoboost tires and axles.

 

[Neggytive]

Yeah, my last electric car was capable of a scaled up 400 kmh.
The problem was, I couldn't sit in it, it ran in a slot, and I didn't have a licence, I was 13.
I don't consider EV's to be cars, fast fridges maybe.

Have you ever driven one?

Nothing accelerates like an electric vehicle, the torque curve is flat, at maximum power from second one and will put a smile on your face.

So it is gasoline only for you?

Diesels can make power and incredible amounts of torque

Steam was used to power cars at one time too.

Natural Gas? Propane? Hydrogen, Alcohol?

Turbines?

There are many ways to get a wheel to spin.

 

[Neggytive]

Its really all to do with air flow. DOHC allows a more controlled air flow at a greater valve angle, along with less losses across the entire pushrod system.

As much as I love pushrods, they're sort of shit at higher rpms. Theres a lot of tricky engineering to make all the components stay sync'd up and correctly tensioned when there's as many joints and as much distance traveled as those rods and buckets. Can't have slop in the system.

Its why you see a lot of pushrod motors typically make greater torque figures down low than DOHC motors. They maximize what they can do well while sacrificing that which they do not. By keeping rpms lower, manufacturers choose to sacrifice higher end power gains and focus on lower end grunt. More stroke typically means more torque, but also means a lower rpm ceiling before the entire rotating assembly decides to eat itself apart. Thats the simplest way I can really think to put it without getting into the wacky world of physics regarding 2 vs 4 valves, etc (much of which I have forgotten, its just so much stuff).

Then once you start getting into flat plane cranks, its a whole different ballgame with airflow and scavenging.

Just looking at the specs, the smaller 5.5 liter LT7 actually has a greater bore size than the 6.2liter LT2, however the stroke is far shorter. Whilst I presumed the LT7's bore would be larger than its stroke (obviously), I didn't expect it to be that much, surpassing the LT2. Its not that going smaller is the reason that the LT7 makes so much power as much as the fact that the smaller size is a biproduct of a different way of extracting/making higher power figures. It seems like the only real reason the 5.5 is 'smaller' is because the stroke is so much shorter. Its just less rotating mass overall, if that makes sense. They could've easily kept the stroke and made the bore bigger, but it would've been adding lots of weight, making it harder to rev higher. Its easier to take the weight away.

LT2 (OHV):
Bore 103.25 mm
Stroke 92 mm

LT7 (DOHC):
Bore 104.25 mm
Stroke 80 mm.

Tl;dr - OHV's add mechanical complexity that is not present in DOHC. The greater simplicity of a DOHC allows it to better exploit higher RPM's, which can negate the need for longer strokes. The lack of a longer stroke, however, typically robs them of low end torque.

Thats my 2 cents, if anyone disagrees, please feel free to correct me. I could be off base for all I know, but I'm very much just spitballing what makes sense to me.

Then we start getting into the world of square, under square, over square, not something that really gets discussed in cars, but in the V Twin world it does constantly

Bore less than stroke, bore same as stroke, bore greater than stroke.... all 3 have their own peculiar ways of making power. Each has it's advantages depending on where you are trying to make peak power

 

[Cz_Ziemniak]

Then we start getting into the world of square, under square, over square, not something that really gets discussed in cars, but in the V Twin world it does constantly

Bore less than stroke, bore same as stroke, bore greater than stroke.... all 3 have their own peculiar ways of making power. Each has it's advantages depending on where you are trying to make peak power

What surprised me is that the LT2 is oversquare, not what I expected.

 

[GripTime]

People fixate too much on HP when comparing cars. There is so much more to it, like torque, weight, and gears. The Camaro was a much more fair comparison.

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People complained that the turbo lag in the STI was too much. However I loved it because it just made the car fun to drive when that boost hit, you had to time it! There is so much more to it and also what you like in a DD or a weekend car. I prefer to have cars that behave differently.

 

[Danee]

GM does make a 670hp 5.5l

 

[robvas]

I'd say the big problem with base mustang vs base c8 is more the difference in tire size and axle ratio vs engine power.

255/40 on 8.5" wide rims and 3.15 final drive vs 305/30 on 11" wide rims and 4.89 final drive.

Now compare the trans ratios in the C8 to the 10R80

 

[MegaMan]

I think the sound of the 5.0 Coyote smokes the sound produced by the C8!

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