V6 > V8

[SappySE107]

Im reading the 2008 engine builder magazine, and there is an article regarding GM scraping their plans to build new DOHC V8 engines for luxury cars. It was cancelled days after president bush signed into law new fuel economy standards by 2020, with the new standards coming into effect in 2011. This is what caught my attention.

"Sources say Cadillac could switch to high-powered V6s for all except for the corvette based XLR. The 2008 CTS develops 304 hp with its direct-injection V6, while the current northstar V8 engine only produces 275 hp in the 2008 DTS. A Cadillac spokeman say the V6 has become the predominant engine sold on the 2008 STS because its close in power to the V8. The V6 is about 150-200 pounds lighter."

[geoffinbc]

Well if there were 2 more cylinders on th V6 it would make even more power. I guess they just realized they can make the power they "need" from a smaller engine. I guess there is no viable market for a 500+ HP DOHC V8 in a Cadillac.

[SappySE107]

Not when fuel economy restrictions are going to be in effect soon. The V series and XLR need the most power possible but for most drivers, 304 hp with a VVT DOHC V6 seems to be sufficient The powerband is probably what really sells it.

[korbendallas68]

I though the V8 fad in non-sports cars died in the 80's.

I wonder why companies even wasted their time bring V8's back into mid-sizes? They assume that cars only need 20mpg forever? IMO I wish the law would push the minimum to around 40mpg.

V6 > V8!

[gpse3400]

Direct injection really helps alot. I totally understand why GM stopped that program though. The LSX is an engine that can do anything they want it to do 300 hp + and still have subsantiantial fuel economy though things like it's low friction valve train, DOD, and now its variable valve timing...Plus Eaton's new 4 Lobe Supercharger on the LS9 has close to the efficiency of a Turbo charger...Unless you just have to have that harder working, smaller displacement, and all those extra valves, there is no need for it. We can only drive so fast on the street before we drive right off the road.....

Other than the fancy engines they need to get the weight down on these vehicles....the New Malibu as nice as it is is over 3600lbs. That is more than my near Full size MonteCarlo. To me that is unacceptable....

[sharkey]

with the new laws out you will see more and more small displacment forced induction motors. rumor has it the base motor in the cobalts in 2010 will be a 1.4l turbo making 150hp, with the big motor still being the 2.0l turbo making 260hp. i wouldnt be surprised to even see a v6 being the norm in the new camaro, what would be so bad about a turbo v6 making, say 400hp, with the 2.0l turbo replacing the v6 as the base motor??? it would piss off the muscle car guys, but this is the wave of the future, the days of v8s in cars is done.

i predict that by 2015 the corvette will be the only gm car with a v8 in it. trucks is a different story.

[Alxsmt]

i dont see a problem with more v6s and less v8s, as long as they keep the vette, gto, camaro having v8s.. a v6 just wouldnt be right for those cars imo

1.4L cobalt? ew... im guessing that would be an 8k revver *cough* honda *cough*

[Azrael]

With trucks they'll probably keep V8's but only as diesels since there seems to be several non-fossil based sources for diesel available now.

[sharkey]

the problem with the other sources for diesel is they are just as bad if now worse emissions as diesel itself.

id guess gm will do the same thing with the 1.4l cobalt that they are doing with the 2.0l. the 2.0l is vvt and has a very small turbo, the motor is at 20lbs boost at a very low rpm, but really the turbo is maxed by around 4500rpm. this allows for good torque at a low rpm with the small motor. id guess it would be like the other 4 cyl stuff, redline at 6500. keep in mind this would be the base motor taking over for the current 2.2l ecotec.

for those that arent farmiliar with the new laws, its a 35mpg cafe rating. this means that when gm adds up all the vehicles they sell in a year and averages out the rated fuel economy, it must be better than 35mpg. the big thing here is that the trucks wich account for much of gm's sales have the largest engines and worst fuel economy. manufacturors cant take the big engines out of the trucks as they are needed for what trucks are designed for. to offset this, gm will need to downsize the motors in many of the cars so they get very good fuel economy.

if gm builds and sells as many camaros with v8s that it plans to, they would never make the 35mpg. they are going to need to come up with some potent v6 power for all the rwd cars (camaro, g8, gto) and make that the car to have, and build small numbers of v8 cars. as i said earlier, many would scoff at the idea of a v6 as the motor to have in these cars, once they figure out how easy it is to get power ofut of an already turbocharged motor i beleive it will be welcomed with open arms.

it kind of funny how history repeats itself. 74 was the end of the muscle car era because of the fuel crisis. looks like 2011 will be the end of the new muscle car era we have had for the past 10-15 years. the big thing is, today the manufacturors have the technology to downsize the motors, get the fuel economy were they need it, and keep all the power just by doing things different.

[Rhedalert]

People still have the false correlation with v8's automatically = bad economy. This was the case thru the 70's into maybe the early 80s, but lets make some comparisons:

'08 4.3 V6 Chevy Silverado WT vs '08 Silverado 4.8 V8 WT has a rated economy difference of 1 mpg. Yes, 1 mpg.

'08 Chevy midsize Colorado I-5 vs Full size Silverado 4.8 has an ecomony difference of 2-3mpg depending on trim level.

'08 GMC Envoy 4x4 4.2L I-6 15 city/21 hwy. '08 GMC Yukon 4x4 4.8L V8 16 city/21 hwy, yes you heard that right. A V8 making more power and torque in a bigger 1000 lb heavier truck getting BETTER economy in the city, and equal on the highway.

And to top it off, my Camaro averages 21-22mpg on my work commute. My Olds is 23-24MPG in the same driving conditions.


I would like to think fuel economy is influenced more by (and not limited to) engine internal friction, efficiency, drivetrain gearing, resistance, and weight. Car companies need to address THESE issues if they want to see some real MPG increases. Just like having a V6 in a big truck did jack shit for fuel economy, you'll see similar outcomes if they do that to other vehicles.

Now the LS based engines DO have the best of many worlds, even looking at it in basic form. I can't fathom this big DOHC V8 with all the extra weight and internal friction from the valvetrain getting any better fuel economy than the LSx. Play around with the LSx platform for a fraction of the cost and get a better outcome. This is probably why they scrapped the Caddy V8 idea, it would only hurt them in this situation.

[Joseph Upson]

The current trend I've noticed is that cars are getting heavier and heavier, you can bet every time you look up the specs on a car that is being recognized for its increased horsepower rating that more times than not it is heavier than the previous version with a lower hp rating, most sports cars being the exception. Manufacturers are yielding to the potential of smaller engines that sip gas under normal conditions and work like big engines with the help of turbos.

At the same time 6 speed semi automatic transmissions are providing room for closer ratio gears to make smaller engines more effective at getting the newer sleds up to speed quicker, reducing the need for low end high torque V8s.

Contrary to the old clechae' "There's no replacement for displacement", yes there is, simply put, a smaller turbocharged engine will likely be more efficient operating at 100 hp on the HWY with the ability to produce 300 hp on tap, than the same car with a naturally aspirated V8 rated at 300 hp and only capable of running at a minimum of say 130 hp on the HWY under the same conditions due to all 8 cylinders firing. Even if cylinder select were added, it would be on and off continuously because running on 4 cylinders might drop it below the minimum power level needed to hold speed at some points. And then there's the additional weight and space consumption. Smaller engines mean more cabin space or smaller cars without reducing cabin space.

They probably will not put a turbo on the 3.6L because they don't have a car that needs the kind of power that would result from as little as 7 psi, with respect to the V8 engine already allotted for it.

[Superdave]

my 5.3 LSX based Sllverado gets about 13 MPG in the city and over 25 on the highway..


GM had the answer to the fuel economy back in the 90's, too bad the EPA made them disable it. This summer i'll be enabling LCM in my Z24 and testing to see if i can get 30+ MPG on the highway. Last year i got about 15 on the highway

[Joseph Upson]

my 5.3 LSX based Sllverado gets about 13 MPG in the city and over 25 on the highway..


GM had the answer to the fuel economy back in the 90's, too bad the EPA made them disable it. This summer i'll be enabling LCM in my Z24 and testing to see if i can get 30+ MPG on the highway. Last year i got about 15 on the highway

I figure with the oil squirters one should be able to run a higher than stoich default AFR like maybe 15.5 instead of 14.7 in addition to lean mode and maybe run a little lower thermostat opening temp. Some of the 3800 SC Fieros are getting 30 + hwy, I'm hoping to get 35 with the 6 spd.

[ForcedFirebird]

I figure with the oil squirters one should be able to run a higher than stoich default AFR like maybe 15.5 instead of 14.7 in addition to lean mode and maybe run a little lower thermostat opening temp. Some of the 3800 SC Fieros are getting 30 + hwy, I'm hoping to get 35 with the 6 spd.

Wouldn't you have to squirt all the cylinders for that to work properly? The 3500 only squirts #5 and #6.

[sharkey]

you can already run 16:1 afr during cruise, i did that with my cavy with no ill effects. manufacturors wont do it because when you run that lean you drive up the NOx and it wont meet emmission standards in that catagory.

there is no replacment for displacment. that only applies to performance, never was stated to go along with fuel economy.

sure a truck with an underpowered v6 wont get get better fuel economy, you need x hp to move them weather its comming from 6 or 8 cylenders. trucks will always need v8s, you cant make a v6 make torque for hauling loads, a v6 truck will never get good fuel economy.

caddy killed off the new dohc motor because of this new law. they are not going ot be using an ls based engine (aside from the xlr), they are all going to v6s.

so why have a turbo v6 making say 400hp in the new camaro when you have a v8 making the same??? my question is why have a v8 making 400hp when you can have a v6 making the same??? they will never meet the targets if they flog a whole pile of v8 cars out. same deal with the g8, why bother with a v8 in it??? its a car, sure it may weigh close to 4000lbs, but with the 6 speed auto and a turbo v6, thats more than plenty of power.

the rest of the world has been downsizing the engines, its time for the US to catch up.