Go Green
A. Kotecki, via CarCraft.com: Will the E85 "green" carb you used awhile back have any benefit on the 6.0L engine you just built with L92 heads?
This is the E85 carburetor we used on the Magnuson-supercharged 355ci small-block on E85 fuel that made 601 hp. It is a 750-cfm carb and is available right now from Quick Fuel (PN Q750-E85, $625.00)
Jeff Smith: We just love getting questions about our E85 stories because it tells us that you guys are really paying attention. The E85 green carb in question here is the Quick Fuel carburetor specifically designed to meter E85 fuel. We used E85 on the Magnuson supercharged 355ci small-block Chevy in the February issue ("E85 Solution"), where our little Mouse motor made 601 hp at 10 psi with a 9.4:1 compression ratio. To bring everybody up to speed, E85 is 85 percent grain alcohol mixed with 15 percent gasoline and offers an excellent 105 octane rating. The trick to using E85 is a carburetor modified to handle an increase of roughly 25 to 30 percent more fuel. This is why Quick Fuel decided to build a special E85 carburetor-many standard carbs are not designed to handle this great an increase in fuel volume.
So now we can jump over to the LQ4 6.0L (364ci) engine we tested in the May issue, where we bolted on a set of L92 aluminum factory heads and a carbureted intake manifold along with an aggressive Comp Cams XR281HR hydraulic roller camshaft. This amazing 364ci Gen III engine cranked out 551 hp at 6,800 rpm in this configuration at around 9.4:1 compression, which is on the low side, especially for a cam this size. The advantage of using the Quick Fuel carb and E85 on this engine is not so much what the fuel would do with the engine in its current configuration as much as what the fuel offers in terms of potential. As we stated earlier, E85 is a 105-octane fuel that can be purchased in most places for equal to or less than the price of 87-octane pump gas. If we wanted to configure this 6.0L to run exclusively on E85, then the first step would be to get rid of the stock pistons and jump into a set of forged aftermarket pistons to raise the static compression ratio. It's possible to bump the compression to 10.0:1 with a flat-top piston with a 4.030-inch bore and stock 3.62-inch stroke, but this really doesn't take advantage of the E85 octane. Domed pistons will certainly do the job, and most piston companies like Diamond, JE, and others make a domed version for this configuration. We researched the Diamond piston catalog and found a 10cc domed piston for a 4.030-inch-bore Gen III package that would be worth 11.6:1 compression, and if we mill the heads down from 70cc to 62cc, it would bump the compression to 12.9:1. Don't let that scare you, because with 105 octane and the cooling effect of the alcohol-based fuel this motor would make some serious power.
CC Quickies
Please stop mounting phony brake rotors behind your wheels. We'd rather see real drum brakes than fake rotors.
The rule of thumb for compression is roughly 3 percent gain in power for every 1 point of increase in compression. Moving from 9.4:1 to 12.9:1 would be an increase of 3.5 points, which equals roughly 10.5 percent. Round that down to 10 percent and we're talking about 600 hp with an equal or greater increase in torque throughout the entire power curve, because compression adds power everywhere. Another good reason to swap the pistons, even if you only pump the compression to 11.0:1, is that these power and rpm levels are pushing the limit of stock cast pistons. Our ex-GM engineer pal Mark McPhail tells us that the early LQ4 pressed wristpin pistons could fail at these engine speeds. Later LQ4 and LQ9 engines after roughly 2002 come with floating pins and are of a stronger design, though still cast.
The downside to building a 12.5:1-compression engine is that it's destined to always run on E85 or race gas. But it appears that E85 availability is on the rise across the U.S. Right now it is still most easily found in the corn-producing midwestern states, but with all of E85's green advantages-especially as a renewable resource of fuel-expect that you will be able to find E85 in an increasing number of places all over this great country of ours.