Should Cadillac get its own High Compression V6?

[dwightlooi]

To keep the long story short, the GM has a new 3.6 liter V6. It's called the LFX. It'll be used in the Camaro, the CTS and everything else that currently use the 3.6 DI V6. It makes 318~323 hp / 275~278 lb-ft. As is desirable for a across the board engine, it runs on 87 Octane with 11.3:1 compression.

The question is whether Cadillac should get a "Premium" version of this powerplant. Premium as in "Premium" performance as well as "Premium" fuel. Going to 91 Octane will enable the compression ratio to go up about a point to about 12.3:1 with higher compression pistons, this alone should bump output by about 7~8% which will take you to about 340hp horses. With some minor changes to the cam profile and VVT programming one can move the torque curve slightly to the left for a total of about 12%. That makes a 100hp/liter, 360 hp engine with about 280 lb-ft of twist. Not shabby by any standard and the premium fuel recommendation is not particularly out of place on a luxury marque like Cadillac. The cost equations wouldn't change significantly since the engine is still 95% the same as its more mundane siblings and the parts that are different aren't actually more expensive.

LFX -- 91 Octane

~ 360 bhp @ 7000 rpm

~ 280 lb-ft @ 5500 rpm

[Drew Dowdell]

any way to swap the horsepower for more torque...... preferably over 300 ft/lbs?

[dwightlooi]

any way to swap the horsepower for more torque...... preferably over 300 ft/lbs?

Getting another 40 hp or even 80 hp NA is easy compared to getting another 25 lb-ft. 300 lb-ft out of 3.6 liters is about 83 lb-ft per liter. At 12:1 you are probably not going to get much above about 78 lb-ft per liter. 78 lb-ft/l is about what you get at 100% volumetric efficiency with no parasitic losses. For comparison the BMW M3 is at about 74 lb-ft per liter, the new Focus 2.0 DI is a 72.5, the Ferrari 430 is at 79. Most of these engines are operating at over 100% volumetric efficiency at their torque peaks and losing some torque to frictional losses.

[Drew Dowdell]

Well, I guess the reason I ask is that the CTS has 273 lb-ft at 5300rpm today so 75.8 ft-lb per liter. I'm not sure a bump to 280 lb-ft at 5500 rpm will feel that much different.

[Robert Hall]

Is this 'LFX' real or just more speculation?

(the acronym sounds like a plausable name for a Lexus Cayenne competitor..., LF-X).

Edited May 3, 2011 by Cubical-aka-Moltar

[Drew Dowdell]

The LFX is real

[David]

While I love the HP, I think it is crazy to have these powerful engines with wimpy torque. This is just wrong in my opinion.

[dwightlooi]

(1) LFX is the official designation; or at least it is the RPO code GM certified the motor output under when it did so with the SAE. If you want to see the report you can get it here...

http://standards.sae.org/cpgm1_12cadcts

(2) No, a bump to 280 lb-ft won't feel that much different when the car is driven moderately. However, the fact that torque doesn't falter and stays at or above 270 lb-ft all the way to 7000 rpm means that the engine feels more alive and more willing at 5500~7000 rpm. Make no mistake about it though. 280 lb-ft is not wimpy for a 3.6 liter engine. It is actually very good at 77.8 lb-ft/liter, it'll be slightly less than a full on race engine but not by much.

(3) If you want more torque you'll need more displacement, forced induction or run on something other than gasoline + air. These come with a bunch of their own baggage. The 3.6 is about as big as the current 103mm bore center HF V6 block will go. Turbos and Intercoolers are expensive, bulky, heavy and put out too much torque for the 6T75 or 6L50 transmissions. The only current GM alternative is the 6L80 which introduces two problems -- the 6L80 must shift at 6500 instead of 7000 rpm, this means a lower redline and no front drive applications. As far as Methanol-Water or Nitrous-Oxide injection... I don't even want to go there.

[smk4565]

How about their own V8?

[Drew Dowdell]

I thought they could take out cylinder sleeves to get the 3.6 mighty close to 4.0?

[dwightlooi]

I thought they could take out cylinder sleeves to get the 3.6 mighty close to 4.0?

The current bore is 94mm, the bore centers are 103mm. That's 9mm between in the walls between the cylinders. You can probably shave it to 8mm or even 7mm. The HF V6 also has a rather short deck so you can't really stroke it much without the rods getting overly short and side loads getting rather high -- which is bad for durability and bad for fuel economy. I mean, yes, you CAN change the bore centers and redefine the crank to deck height, but that'll basically be a clean sheet engine.

Let's shave it to the limit and go with a 96mm bore. That's say 96mm x 85.6mm which gets you to 3717 cc. But it'll require major changes to the engine's block and liners. Maybe going to an sleeveless aluminum block which then requires a silicon impregnated alloy block or a Teflon-Ferrous plasma coating because aluminum-on-aluminum has very high friction coefficients. It's definitely more than higher compression pistons and a revised cam grind. And, at the end of the day, you have to ask if 3717 cc is really worth it.

[dwightlooi]

How about their own V8?

A way to do it will be to build a 60 deg V8 of 4.8 liters using the HF V6 architecture. You can build it on the same lines, they'll used the same pistons, rods, valvetrain parts, etc. A balance shaft can be used to smooth out the 60 deg configuration (ala Volvo's Yyamaha built 4.4 V8). It'll be a DOHC 32v engine making about 420~430 hp.

But, again, such a V8 will be a heck of a lot more work and money than a variant of the LFX V6 with different pistons and a cam grinds.

[smk4565]

How about their own V8?

A way to do it will be to build a 60 deg V8 of 4.8 liters using the HF V6 architecture. You can build it on the same lines, they'll used the same pistons, rods, valvetrain parts, etc. A balance shaft can be used to smooth out the 60 deg configuration (ala Volvo's Yyamaha built 4.4 V8). It'll be a DOHC 32v engine making about 420~430 hp.

But, again, such a V8 will be a heck of a lot more work and money than a variant of the LFX V6 with different pistons and a cam grinds.

What about a 90 degree V8 from scratch, or by using blocks of the 2.0, 2.4 or 2.5 liter ecotecs? The Germans seem to come up with a new V8 every other month, Cadillac had the Northstar for 18 years and now nothing.

[CanadianBacon94]

How about their own V8?

A way to do it will be to build a 60 deg V8 of 4.8 liters using the HF V6 architecture. You can build it on the same lines, they'll used the same pistons, rods, valvetrain parts, etc. A balance shaft can be used to smooth out the 60 deg configuration (ala Volvo's Yyamaha built 4.4 V8). It'll be a DOHC 32v engine making about 420~430 hp.

But, again, such a V8 will be a heck of a lot more work and money than a variant of the LFX V6 with different pistons and a cam grinds.

What about a 90 degree V8 from scratch, or by using blocks of the 2.0, 2.4 or 2.5 liter ecotecs? The Germans seem to come up with a new V8 every other month, Cadillac had the Northstar for 18 years and now nothing.

other than the LS's

what if GM made a seperate displacement for cadillac?

EDIT: acually if they could fuse those ecotechs tegethor it might not be that bad an idea

Edited May 5, 2011 by CanadianBacon94

[Drew Dowdell]

How about their own V8?

A way to do it will be to build a 60 deg V8 of 4.8 liters using the HF V6 architecture. You can build it on the same lines, they'll used the same pistons, rods, valvetrain parts, etc. A balance shaft can be used to smooth out the 60 deg configuration (ala Volvo's Yyamaha built 4.4 V8). It'll be a DOHC 32v engine making about 420~430 hp.

But, again, such a V8 will be a heck of a lot more work and money than a variant of the LFX V6 with different pistons and a cam grinds.

What about a 90 degree V8 from scratch, or by using blocks of the 2.0, 2.4 or 2.5 liter ecotecs? The Germans seem to come up with a new V8 every other month, Cadillac had the Northstar for 18 years and now nothing.

No, they just have better marketing departments.