Q&A

Ask Away! with Jeff Smith: Upgrading Fuel Injectors for Better Performance in an LT1-Equipped Chevy Camaro

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What would be the best injector for my 1995 Camaro? The idea is to get higher performance. Would I have to change fuel pump also? Thanks.

P.B.

It’s a common misconception that installing larger injectors on an EFI engine will make more power. This is not necessarily true. Assuming that the manufacturer equipped the engine with sufficient size injectors, adding larger injectors will not improve power. Before we get too deep into this, let’s review some internal combustion engine basics.

Understanding the Air/Fuel Mix

All internal combustion gasoline engines operate the same way. The cylinder captures a given amount of air in the cylinder during the intake stroke. In a carbureted engine, the fuel is mixed with the incoming air in a given air-fuel ratio that will produce power. If the air-fuel ratio is excessively rich or lean, the engine will make less power than with a proper air-fuel ratio.

In a port fuel injected engine like yours, fuel is mixed downstream, but still before the air reaches the intake valve and into the cylinder. The manufacturer will make sure the injector is properly sized to supply sufficient fuel to make the rated horsepower. Adding a larger injector is a little bit like adding bigger jets to a carburetor that is already jetting properly.

Adding more fuel does not increase power.

Calculating Engine Power Potential Based on Injector Size

Let’s look at what stock injectors are in your engine and we can estimate power based on that fuel flow. Our research indicates that the stock injectors for the 1990s-era Chevy LT1 engine were 24 pounds per hour (lbs./hr.). This number by itself isn’t really that enlightening. But we can do some quick math to estimate power. Most current gasoline engines will use somewhere between 0.45 and 0.5 pounds of fuel per horsepower per hour. This is called a brake specific fuel consumption number (BSFC). So if we multiply your 24 lbs./hr. injectors by 8 injectors, we come up with 192 lbs./hr. total fuel delivery.

Now we divide the 192 lbs./hr. by a BSFC number of 0.45 to determine the horsepower potential the engine has based on fuel delivery:

 192 / 0.45 = 426 horsepower.

This is the potential power your engine could make based on fuel delivery. Since your engine is rated at only 275 hp, clearly there is plenty of fuel delivery potential existing with your current stock injectors. This means that adding larger injectors will not help horsepower. That would only occur if your engine was already making in excess of 420 hp.

To be fair, most recommendations for injectors request that the injector only run at roughly 90 percent capacity. There are several reasons for this that we don’t have the space to explain here. But even multiplying 426 x 0.9 = 384 hp, which is still 100-plus horsepower more than your engine is making.

Building Power in a Stock LT1 Engine

Let’s assume that you want to modify your engine with a mild improvement that will make more power. The way to do that is to create a situation where the engine captures more air in the cylinders. Mixed with the proper ratio of fuel, the engine will make more power. Increasing airflow can be accomplished literally in hundreds of different ways. You can increase the compression, change the cylinder heads to increase the airflow, change the cam timing, add a better intake manifold, add a set of headers, a mix of all of these ideas, and so on. Or you could possibly add a supercharger.

The key would be to identify the biggest restriction to engine breathing in your Camaro. Assuming your engine is in fact the LT1 350 V8, you have a wealth of options. The basic 275 horsepower 350 cubic inch LT1 is blessed with decent compression and cylinder heads, so the basic configuration offers potential to increase airflow.

The simplest moves would be to minimize the biggest restrictions with simple modifications like a higher airflow intake system or perhaps a cat-back exhaust system that will reduce exhaust backpressure. If the exhaust system and muffler are restrictive, the engine has to exert power in order to push the exhaust out. Relieving this pressure with a high performance muffler and exhaust piping will add power by reducing the extra work the engine has to perform. This is generally a great place to start on these kinds of engines.

A Smart Camshaft Upgrade for the Chevy LT1

While these small improvements may help increase airflow, these mods will not require larger injectors. A change such as adding a slightly longer duration camshaft with more valve lift will certainly help and then perhaps larger injectors may be necessary but you may be surprised at how much power you can add without having to add larger injectors. As our math indicates, you can add perhaps as much as 100 hp before your injectors reach maximum capacity.

One place that can help wake the engine up is with a cam change. The factory LT4 engines that appeared in 1996 and 1997 used a much stronger camshaft. The advantage is that this is a factory available camshaft that can add some significant power. Chevrolet Performance offers what it calls the LT4 HOT cam (NAL-24502586) that can deliver improved performance. We’ve listed its camshaft specs in the chart at the bottom of this post. This is a great street cam that offers a major gain in power while still retaining mild street operation characteristics.

This should also be accompanied with better valve springs and that would also offer the opportunity to add better valve guide seals to reduce oil consumption. This does not necessarily demand that the engine be removed from the car, but it will require some specialized tools, knowledge, and experience to swap the cam in the car while reusing the stock lifters.

Of course, there is a wealth of other cam companies that can offer similar cams with very similar timing that you might also consider. It’s probably a good idea to not exceed these duration numbers just to keep the engine mild enough for everyday street driving. Also note that this cam is ground on a 112 degree lobe separation angle (LSA) while many aftermarket cams are ground with a narrower 110 LSA. The tighter 110 degree LSA generally makes the idle a little rougher but also adds mid-range torque.

Your LT1 Performance Recipe

A combination of a good cat-back exhaust system (retaining the catalytic converter of course), the LT4 Hot Cam and rocker arm swap, a less restrictive air intake system, and new ignition components for the Opti-Spark ignition should be worth some substantial power while still retaining most of the Camaro’s street manners.

LT4 Hot Cam Specs

LT4 CamshaftDuration @ 0.050"Valve LiftLSA
Intake2810.492"112°
Exhaust2280.492"112°

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