Advanced Pushrod V8 for the C8 Corvette.

[dwightlooi]

The small block V8 has powered the Corvette and many other GM performance cars for decades. Among its advantages is its relatively compact size and modest weight compared to overhead cam engines of the same displacement. In fact, an aluminum small block like the LS3 can often be slightly lighter and smaller than a DOHC 32-valve engine of Teutonic pedigree boasting the same power output. Most of its advantages stems from the elimination of a pair of bulky and fat DOHC heads and its belt or chain drives. However, the small block is not without its demerits. The need to utilize a higher displacement to achieve comparable output to a state of the art DOHC powerplant means that it tends to be a little behind in economy and civility.

While a pushrod engine will never breathe as well as a well designed 4-valve OHC design, some of its disadvantages can be mitigated with technologies which can be incorporated into a push rod small block V8 but hasn't been done by GM yet. With the next Corvette being a most likely a smaller, lighter car and with Bush's new CAFE mandates filtering in over the next decade, it makes sense to produce an advanced small block which will continue to give the Japanese and the Germans a run for their money in terms of power per unit engine dimension or weight if not hp/liter.

I believe the next Corvette (C7) should be powered by a micronized 4.8 liter pushrod aluminum V8 with the following features:-

(1) Independent Continuously Variable Intake and Exhaust valve Timing (Cam-in-cam setup already used in Dodge Viper)

(2) Direct Gasoline Injection (easier to implement on a 2-valve head in fact than on a 4-valve head)

(3) Active fuel management (already proven and in service)

(4) Ionic knock detection (based on spark gap sensing)

(5) Reduced displacement (~4.8 liters)

(6) Belt-less accessory drive (water pump, A/C, alternator runs off 300,000 miles maintenance free roller chain)

(7) Continuously Variable Valve Lift (Yes, it's possible on a push rod too; see illustration below for an implementation idea)

Bore x Stroke: 94 mm x 85.6 mm

Compression Ratio: 11.8:1

Power: 360 hp @ 6200 rpm

Torque: 360 lb-ft @ 4200 rpm

Redline: 7000 rpm

The Corvette should become smaller and cut about 500 lbs off the curb weight. At 2750 lbs, power to weight ratio should be identical to the current C6 Vette. Acceleration should be similar whereas all other aspects of performance should improve due to the reduced mass. EPA numbers will be quite good too with the lower vehicular weight, direct injection and cylinder deactivation.

[loki]

interesting. you usually do come up with good articles....sometimes above peoples heads.

your CVVLS looks like it'd work, but maybe a tad fragile for the work it'll be doing...? maybe.

[dwightlooi]

interesting. you usually do come up with good articles....sometimes above peoples heads.

your CVVLS looks like it'd work, but maybe a tad fragile for the work it'll be doing...? maybe.

This is a revision which gets rid of the roller, pin and forked push rod. The concept is the same -- we are moving the point of contact between the rod and the rocker -- but the implementation is different. The effect is the same but this is perhaps more robust and "clean". It's a evolution of the same idea, very much like Toyota's VVTL-i is different in implementation but similar in it's cam switching concept as Honda's VTEC.

Instead the rod is simply flared out to a block like cross section with a cylindrical face at the tip. A spring loaded tensioner in riding the fulcrum shaft is used to keep it against the eccentric shaft when at rest. Once it gets moving the angle of the rocker's face keeps it naturally against the eccentric shaft's lobe.

This particular pairing of eccentric and tensioner size allows a variance in rocker ratio between 1.73 and 1.45. By using larger eccentric lobes and tensioners we can achieve even greater changes in rocker ratios at the expensive of greater VVT mechanism size. I think we can achieve a 1.90~1.20 variation if we want. That's literally the ability to shift between twice as docile as a typical LS engine and Winston Cup rocker ratios! And that is without any "steps" as the mechanism is continuously variable. However, NONE of the size and weigh increase in the VVT gear is the actuated valvetrain mass -- neither the eccentric or the tensioner moves up and down with the valve, rocker or pushrod so such increases in mass won't hurt high rpm performance or require higher valve spring rates.

[FUTURE_OF_GM]

The Corvette doesn't need to be smaller... Just lighter.

(If it gets smaller, I wont be able to fit in one when I'm ready to buy)

I can't wait for the small car hell that is about to be our reality. Nothing like being uncomfortable in everything you drive.

[dwightlooi]

The Corvette doesn't need to be smaller... Just lighter.

(If it gets smaller, I wont be able to fit in one when I'm ready to buy)

I can't wait for the small car hell that is about to be our reality. Nothing like being uncomfortable in everything you drive.

2850 lbs is a very ambitious goal. 400 lbs does not come easy. Going aluminum or composite this and that, and using a smaller engine, practicing better weight discipline can at best get us half way there.

The Corvette is already a very light car for a vehicle it's size and for the powerplant it packs. Really, 3250 lbs is pretty light. If you want to get significantly lighter, one of the most accessible methods is make the car smaller. Smaller car, less enveloped volume, less material overall, less weight. Having said that, the car does not have to be smaller on the inside. Instead, the rear over hang and front over hang can be trimmed significantly -- the Corvette has an abundance of the latter in particular. The other thing that can be done is to move the transmission from its current location ahead of the rear axle to behind the rear axle using a longitudal-engine, front-drive style transmission like those Audi and Subaru uses but putting it in the back and driving it with a torque tube like it is currently done. This not only improves weight distribution (the Corvette is currently slightly front heavy), it also allows the wheel base to be shortened by 6~8 inches without compromising passenger volume. Since we are talking a new transmission instead of the current breed of T6060 or 6L80Es, let's also take the opportunity to make it a 6~8 speed dual-clutch automated manual.