Ask Away! with Jeff Smith: Will My New EFI System Work With My Setup?

(Image/Jeff Smith)

I just bought the EZ-EFI and I’m still waiting for delivery. I have a 455 Pontiac. For the last couple of days, I’ve been reading up on it (should’ve done that first) and it doesn’t sound like it’s going to work for me.

The only thing the salesman said is that it will work is as long as you have a minimum of 9-10 inches of manifold vacuum. That’s where I’m at so I figured it would be okay. Since then, I’ve read it doesn’t work well with manual transmissions or any kind of road racing. I’ve also heard that cams cut on a 110 lobe separation don’t work. I fall in all of those categories. I hate to return it without even trying it but if I’m to believe what everyone says, it just won’t work on my car. 

I’m running a .030 over 455 (462), 10.7:1 compression ratio, lightly ported Edelbrock RPM heads, a 232/241 at 0.050, 110-degree LSA Lunati Voodoo cam, and a M20 Muncie 4-speed trans.

What’s your opinion? Will it work? 

Robert

We pulled this question from a previous post because the answer was—as usual—going to be a bit longer than a simple yes or no. We will assume that this gentleman is purchasing a FAST EZ-EFI 2.0 throttle body system. The statement made by his sales guy is correct. Most of the throttle body systems, including the EZ-EFI 2.0, are designed for milder engines with streetable camshafts that are not too radical. Engines that idle in the range of 9 to 10 inches of manifold vacuum are right on the edge.

Let’s get into what this really means, which also relates to his question about his camshaft and the statement that this EFI won’t work with cams with 110-degree lobe separation angles. If you understand how camshafts work, that statement about 110-degree LSA cams is incorrect. It’s important to understand why.

The Camshaft — A Few Degrees Can Make a Difference

Let’s deal with the camshaft question first. If we increase the duration of either the intake or the exhaust lobes (or both) on a camshaft this means the valves open sooner and close later. Now, if we maintain the same lobe separation angle (defined at the number of degrees between the intake and exhaust lobe centerlines) but add intake and/or exhaust duration, this means the duration of overlap will increase.

I did a quick bit of research with three cam cards I have in my files. All three are hydraulic rollers and all three have the same 110-degree lobe separation angle. But all three have different duration numbers. The 281/283 cam had 59 degrees of overlap, the 282/288 cam had 65 degrees of overlap and the 294/300 cam had 77 degrees of overlap. The more overlap, the lower the intake manifold vacuum will be because both valves are open at the same time – pushing exhaust gas back up into the intake manifold. Yet all three of these cams have the same 110-degree lobe separation angle. So you can see that the statement that an EFI package won’t work with a 110-degree LSA cam is not based in fact. It means the person voicing these works does not understand how camshafts work.

The reason we look at idle intake manifold vacuum is that at 10 inches or more of vacuum, the engine will run with a decent amount of idle quality. As the idle vacuum drops, this indicates the presence of increased levels of exhaust gas dilution from valve overlap. This exhaust gas won’t burn a second time so the idle quality suffers and generally we attempt to compensate with a richer air-fuel mixture. You say your manifold vacuum is around 9 to 10 inches of manifold vacuum. It’s possible that your current carburetor and ignition system state of tune is such that you might be able to improve those numbers slightly, which will help the off-idle performance of the EZ-EFI throttle body fuel injection.

It’s entirely possible that by adding a couple of degrees of initial timing and careful idle mixture adjustments, you could improve the idle quality of your big-block to 11 or 12 inches of manifold vacuum. The 10.7:1 compression also helps with idle quality. These factors point in the direction that an EZ-EFI 2.0 throttle body system will work for your application.

Tuning for the Four-Speed Transmission

The four-speed transmission adds a bit more to the tuning requirements since this will be a more dramatic load dump on the engine when you engage the clutch fully from a full stop. For example, the first thing we would recommend is if you do not have a vacuum advance style ignition, then this would be a great time to add one. The EZ-EFI 2.0 can control the ignition as well, but let’s stick with a mechanical advance system for this discussion.

Taking advantage of vacuum advance offers the ability to create load-based timing advance that isn’t possible with a simple mechanical advance curve. Mechanical advance is strictly controlled by rpm. With vacuum advance, we can add timing as the throttle is first opened as you are engaging the clutch. This helps the engine compensate for the major load put on it at low speed. Often, the addition of even just four or five degrees can really make an appreciable difference in terms of drivability. This may not seem like a big deal, but trust us, this is extremely important if you drive the car on the street. There’s nothing more annoying than an engine that stumbles right off idle.

You Must Have Proper Fuel Delivery

A big part of converting to EFI means adding a proper fuel delivery system. This is something that many enthusiasts seem to drop the ball on. You must make sure your system has the proper fuel pressure, and the best way to do this is with a full return, in-tank pump delivery system. There are multiple systems available. Yes, they’re more difficult to install and more expensive, but if you’re not willing to do that then I suggest you stay with the carburetor. Trying to “cheat” an EFI system with a cobbled-up fuel delivery system will only create frustration. My guess is that a good percentage of people with EFI problems are really suffering from an inadequate fuel delivery system.

You also mentioned road racing but I’m guessing this is still a street engine. The advantages to any EFI system is that you can more easily control the air-fuel ratio for your engine over a much wider range of operating conditions—idle, light part throttle, heavy part throttle and, of course, side-open throttle (WOT). Out-of-the-box carburetors do an okay job at WOT, but need plenty of specialized tuning to optimize the idle, midrange, and WOT numbers. With an EFI system, you can call out the idle, cruise, and WOT numbers with a couple of key strokes and let the system tune itself to those numbers. That’s a great advantage.

Most installers merely pick some numbers that sound good, or even leave the default numbers in place and drive the car. It’s possible with some smart tuning, the EFI system will outperform the carburetor. We’ve all read responses from people who have had unacceptable results—but at least the ones that I’ve become involved with all had outside mechanical issues that affected the EFI system, and yet, the EFI was still to blame.