Teague On Tech: Q & A with Bob Teague July 2019

As seen in Speedboat Magazine’s July 2019 Issue.

Aftermarket Fuel Injection

Dear Bob:

I’m looking for some ideas on fuel injection. There seem to be a ton of products out there. What are the best high-performance products that are the easiest to install and most reasonably priced? Which ones will present the least amount of programming problems? Anything you could recommend for the below 500-hp build would be much appreciated. The engine is a 351 Windsor that is stroked to 408 cubic inches with 11:1 compression and full hydraulic roller. The original motor was a carbureted 302.

Matt Gleason Long Beach, CA

First of all, your compression ratio is a little on the high side for a motor if you plan to run 91 octane pump gas. With smaller cubic inch motors, you can get away with a little higher compression ratio, but 11:1 might be a little excessive in a boat under constant load. If your boat is light and you intend to run higher octane fuel, you might be OK.

There are quite a few options for injection systems out there. I think one of the best options for you if your experience is limited is one of the throttle body offerings from Holley. Their systems come with full instructions and has a self-learning feature that is easy to understand. One thing that is usually required for the self-learning feature is that you are able to install an O2 sensor in the exhaust system. This cannot be done in most cases unless you are running some type of dry tailpipes or water jacketed headers.

Choose a system that is designed for your desired horsepower and cubic inches. Many people tend to go with a higher CFM set up than they need.

Crossover Restrictor Plates

Dear Bob:

I have a 1988 MerCruiser 454 engine with the stock intake manifold and a Quadrajet carburetor. I was wondering if I should install the exhaust gas restrictor plates in one or both sides of the intake manifold gaskets. The MerCruiser manual I have doesn’t say anything more than it must use an intake gasket with an opening if it does have an automatic choke. (I boat in Arizona, so we don’t have much cold weather, but we are sure to have plenty of 100+ degree days of boating.) The old rebuilt block did not have them installed, but they also put a Gen 5 head on a Mark IV block, so I don’t trust much of what they did.

Thank you for your input!

Gary Mould Phoenix, AZ

First of all, I am concerned about installing Generation 5 heads on a Mark IV engine block. The Mark IV GM big blocks do not have enough deck sealing surface on the lifter valley side to ensure that you will not have a water leak past the head gaskets. Most aftermarket cylinder heads are designed so they can be installed on both the Mark IV and Generation 5 or 6 blocks. But if you attempt to install GM Generation 5 heads on a Mark IV block, you are likely to end up with water in your oil that is seeping past the head gaskets.

There are two basic automatic chokes used on the stock MerCruiser engines. If your engine is equipped with an electric choke that you can identify by wires connected to the side of the carburetor (usually one is purple and the other one is black), I would block off the heat riser ports because it is not desirable to have excessive heat under the carburetor. In some cases, the excessive heat can cause a vapor lock condition.

Some Quadrajet carburetors utilize a “heat stove” that consists of a bi-metal spring mounted in a metal housing that is screwed down to the intake manifold. This style of choke mechanism requires heat from the exhaust crossover to operate correctly. In most circumstances, manifolds with the heat stove type of choke actuator require that the passages are left open.

In your warmer environment, the choke is not as necessary as it is in colder environments. The only time it helps is with the first time you start the boat on a cold morning. Usually, during the day after that, there is enough heat in the motor to allow starting by just turning the ignition key.

Strange Noise

Dear Bob:

I recently purchased a used boat that’s been making a very unusual sound in the engine compartment. The sound is an occasional thud; it’s random, and not tied to engine rotation. It’s deep and can be a single thud or two thuds in a row. I haven’t been experiencing any of the typical internal engine issues. It sounds like it originates back by the bell housing. I have pulled the drive and started it, and the issue is still present. I’m just looking for some pointers because ultimately, I may have to pull the engine to dig deeper. Thank you!

Hector Gonzales Bell, CA

These strange noises are sometimes hard to find. The first thing I would check is if you have exhaust tips with the metal flappers in them. They are usually noisy and sometimes sound like a gimbal bearing is going out. If, for some reason, your engine has a misfire because of a bad spark plug wire or a crossfi re occurring in your distributor cap, it could make that thumping sound because spark is occurring at the incorrect time. I know this is a little basic, but make sure the spark plug wires are on correctly.

By removing the drive and running the engine and still having the sound, you have eliminated the possibility of it being related to the drive or gimbal bearing. I have seen cases where the drive coupler attached to the flywheel has cracked and even a bolt has come loose that attaches the coupler to the flywheel. This might be your problem, but it will require removing the engine to perform the inspection.

If it is related to a single cylinder in the engine, you can perform a simple test by running the engine at an elevated idle RPM and carefully removing one spark plug wire at a time to see if it results in a similar drop in RPM and if doing that makes the noise disappear.

If all these tests don’t find the problem, I would pull the valve covers to make sure that the valve train is intact.  Take a close look at each valve spring to make sure there is not one that is broken. Look care-fully at the inner springs.  If one of them is broken, it can “corkscrew” occasionally while the engine is running and hold a valve open.  If it is an exhaust valve that is affected, it can cause a pop or thump in the exhaust system.

I am curious to know what you find.  Good luck.

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