GM 3.5L V6-Catching up with the imports?

[IAMCANADIAN]

Well it isn't like it will be the most powerful FWD car out there though with the LS4 in the Impala SS and Grand Prix GXP. Which I hear that with the Grand Prix GXP, the mods GM made to to GXP did help reduce the amount of Torque steer. So I am sure GM could do the same mods to whatever car that might have the 275 HP 3900.

That's true, it's not impossible to control, but it's not impossible to have a bit of torque steer either. I'd like to see that car in production though. It would really be a great addition to the G6 lineup. I'd even like to see this engine in the Grand Prix.

[ImpalaLTZ]

What exactly did they do to the 3.5 to increase the hp?

[FightingChance]

Any car that recommends premium fuel but will accept regular will automatically retard ignition timing when regular grade fuel is introduced, and HP will fall. Quoted HP numbers are definately assuming premium is used.

[Michael_S]

Any car that recommends premium fuel but will accept regular will automatically retard ignition timing when regular grade fuel is introduced, and HP will fall. Quoted HP numbers are definately assuming premium is used.

Starting earlier this year, the Society of Automotive Engineers (SAE) released a new standard for measuring horsepower. Under the old standard, if a car manual recommended premium they measured horsepower with premium. Under the new standard, if the manual only recommends premium they still test with regular. They only test with premium now if the manual states that premium is required.

The 268 horsepower rating of the Camry is with 87 octane fuel. I believe every car listed in grumbles' post has been tested under the new standard. I don't believe any list premium as required, so they all make those figures on regular.

[importedtuna]

I agree w/this. Power/mpg should be really all that matters. I wouldn't care whether it's a 3.3L or 3.9L.

Only Hondaheads really care about HP/Liter, as far as I can tell. Power and fuel economy are all that matters, especially if the engine is a naturally compact design like GM's pushrod.

[importedtuna]

What exactly did they do to the 3.5 to increase the hp?

Variable Valve Timing, a few other things. The 3500 that was in the Malibu is closer to the 3400, and the 3.5LVVT is more like the 3900 engine.

The LZ4 3500 is an OHV engine based off of the 3.9 L LZ9 V6. It was introduced for the 2006 model year in the Chevrolet Impala and Monte Carlo. It includes continuously variable valve timing on both intake and exhaust valves. It has a cast iron block and aluminum heads. Output is 211 hp (156.5 kW) at 5800 RPM and 214 ft·lbf (298 N·m) at 4000 RPM. Bore is 99mm, stroke is 76mm for a displacement of 3510cc. Horsepower rating changed for the 2007 model year to Horsepower: 224 @ 5800 rpm and Torque: 220 @ 4000 rpm.

http://en.wikipedia.org/wiki/GM_High_Value_engine

[Michael_S]

You can't have your cake and eat it too. When the pushrod engines get 3+ valve heads, their fuel economy edge will probably go down the toilette. The reason that typical DOHC engines get worse fuel economy, is because they can breath in more air, so the ECU can pump in more fuel, to get more power. You effectively achieve similar ends, as using a bigger displacement engine.

The 3900 is already a big displacement engine. Giving it 3 valve heads will make it breath like an even bigger engine. DOHC engines don't get worse fuel economy simply because they have an extra camshaft or two.

If you have more power, you can make your gearing taller so the engine runs at lower RPMs when you aren't racing. That can offset the fact that it breathes better and make the net change to fuel economy small.

The Impala SS V8 and Impala LTZ have identical transmission gearing, but the V8 has a 2.93 final drive while the LTZ has a 3.29. GM takes advantage of the V8's massive low end torque to give it taller gearing.

[FightingChance]

Starting earlier this year, the Society of Automotive Engineers (SAE) released a new standard for measuring horsepower...

I stand corrected and am enlightened.

I don't think I understand, then, unless some of these engines now make even more horsepower than stated when using premium fuel. (this being the only factual reason to use premium fuel.)

[ImpalaLTZ]

Wait though, I don't understand, the 3.5 had VVT in 2006, so what made them increase the hp from 211 to 224 in 2007?

[importedtuna]

Oh that. Well the Impala still has 211hp. I think its more about the application of that engine in the Aura, and by extension the G6 and Malibu. Maybe they could wring more power out of it in those cars without negatively impacting fuel economy due to their being lighter weight cars? Or fuel economy was less important than in the Impala? Kinda like how the 3800 in the Lucerne only gets 190-something horsepower but got 205 in some other cars with the 3800 in the past.

[a_v_s]

If you have more power, you can make your gearing taller so the engine runs at lower RPMs when you aren't racing. That can offset the fact that it breathes better and make the net change to fuel economy small.

The Impala SS V8 and Impala LTZ have identical transmission gearing, but the V8 has a 2.93 final drive while the LTZ has a 3.29. GM takes advantage of the V8's massive low end torque to give it taller gearing.

I was referring to V6 engines. An earlier claim was made that a 3900 with multivalve heads would get better fuel economy and power than a similarly sized DOHC engine. This wouldn't necessarily be the case. There is nothing magical about DOHC that robs you of fuel economy. It's just simple physics of burning more fuel because of better aspiration. There is no reason why a 3.9 litre V6 with 3 valve heads, can use taller gearing compared to a 3.6 litre DOHC engine with multivalve heads. V8's yes, but not when we're talking about V6 engines with displacement differences of 0.3 litres.

[ImpalaLTZ]

Oh I thought I remember reading somewhere they upgraded something...but I could be wrong.

Oh that. Well the Impala still has 211hp. I think its more about the application of that engine in the Aura, and by extension the G6 and Malibu. Maybe they could wring more power out of it in those cars without negatively impacting fuel economy due to their being lighter weight cars? Or fuel economy was less important than in the Impala? Kinda like how the 3800 in the Lucerne only gets 190-something horsepower but got 205 in some other cars with the 3800 in the past.

[Titanic]

The 3.5L is not catching up to any of the important import competitors.

If we're going to talk about the 3.5L in terms of power and economy, let's take a look at the 2007 G6 lineup to see how it stacks up against a variety of different motors (OHC and OHV) in the same car.

2.4L I4: 169hp/162tq 23/33mpg
3.5L V6: 224hp/220tq 20/28mpg (Pontiac.com lists hwy at 30, 29, and 28)
3.9L V6: 240hp/240tq 18/27mpg (6spd manual)
3.6L V6: 252hp/251tq 20/28mpg (6spd auto)

So, for a gain of nearly 30hp and over 30 lb-ft of torque, the DOHC V6 will match the 3.5L OHV V6 in fuel economy. The 6-speed auto isn't the complete reason for that.

[Squachy]

I stand corrected and am enlightened.

I don't think I understand, then, unless some of these engines now make even more horsepower than stated when using premium fuel. (this being the only factual reason to use premium fuel.)

Engines that were made to run on 87 octane wont benefit anything going to premium (maybe like 1-2 horsepower gain and/or smoother operation).

Engines that were made to run on premium, but CAN run on regular without issue WILL lose power but wont have issues. (Power will decrease quite a bit. maybe around 5-10hp)

Engines that were made to run on premium, but REQUIRE premium will have issues dropping to the lower octane fuel. (hard knocking, pinging, all that bad stuff).

[Xenon]

The 3.5L is not catching up to any of the important import competitors.

If we're going to talk about the 3.5L in terms of power and economy, let's take a look at the 2007 G6 lineup to see how it stacks up against a variety of different motors (OHC and OHV) in the same car.

2.4L I4: 169hp/162tq 23/33mpg
3.5L V6: 224hp/220tq 20/28mpg (Pontiac.com lists hwy at 30, 29, and 28)
3.9L V6: 240hp/240tq 18/27mpg (6spd manual)
3.6L V6: 252hp/251tq 20/28mpg (6spd auto)

So, for a gain of nearly 30hp and over 30 lb-ft of torque, the DOHC V6 will match the 3.5L OHV V6 in fuel economy. The 6-speed auto isn't the complete reason for that.

So whats the point of the 3.5L? If it produces less power and gets the same fuel economy of the 3.6,wouldnt that make it an inferior engine?