Frank Acampora
Supreme Mariner
- Joined
- Jan 19, 2007
- Messages
- 12,004
Here is something interesting for all you Chrysler and early Force four cylinder engine owners.
In an experiment to reduce fouling of plugs at idle I changed the oil recirculation system. It was a very minor modification.
Chrysler and early Force 4 cylinder engines recirculated excess oil and fuel puddled in the crankcase to the number one and three cylinders. They used two tubes that screwed into a hole in the bypass covers. These tubes protruded through the covers into the top bypass port of these cylinders. Thin hoses connected the cylinder drains to these tubes.
I removed the tubes and replaced the bypass covers with ones that were not drilled and tapped for them. I bought a 1/16 X27 NPT tap and drilled and tapped the manifolds. The lower manifold was drilled and tapped on the starter side just behind the carb mounting bolt. The upper manifold had a boss on the opposite side and that boss, which is used to mount the throttle cam on the lower manifold, was also drilled and tapped behind the carb mounting bolt.
The recirculating tubes were screwed into these holes and the bottom one was shortened a bit so it reached to the center of the reed plate. The top tube was approximately the correct length. Cylinder drains were reconnected to these tubes. My reasoning was that the excess oil would be recirculated through the rotating parts of the engine rather than being simply burned and this was the easiest place to do it.
NOW: The most interesting part. Yesterday I took the boat out for a test. Immediately upon starting I noticed some dramatic differences.
1. Choking in fast idle position started the engine immediately but fast idle was at 3,000 RPM instead of 15-1800 as usual for this engine.
2. Regular idle was at 1500 RPM instead of the usual 700-750. I found it necessary to lower the idle with the idle stop screw before shifting the engine into gear.
3. Top speed was 500 RPM higher. Unfortunately, I did not take my GPS and the speedometer does not work, but the tachometer does not lie. This engine went from 4,500 to 5,000-5050 RPM.
4. During acceleration from a hole shot after idling, the engine loads up and runs rough for a second or two until it clears itself out. Then it goes like a bat out of hell. I'll take that as a trade for 500 RPM in a New York second.
5. It did not appear to degrade the idle in any way. The engine ran rock solid at 700-750 RPM for at least 5 minutes.
Total cost? 20 bucks for a 1/16 X 27 NPT tap through Mc Master-Carr.
At first I thought the increased idle was due to additional air being pulled into the manifolds through the recirculating system. However, the hole in the tubes is only 1/16 inch and could not leak enough air to cause this. My second theory is that the oil and fuel recirculated into the intake manifolds seals the reeds better for less blow-back. Thus: more air/fuel mixture is inducted and pumped to the cylinders, generating more horsepower. Cheaper than hi-performance reeds too!
Now, mind you: This was on my Chrysler 140 which has been ported, has a 2 to 1 lower unit, and the exhaust is vented a bit. This engine is swinging a Michigan cupped 13 x 19 pitch prop behind a 21 foot cuddy. If you try it on a stock engine, you may not get such dramatic results.
In an experiment to reduce fouling of plugs at idle I changed the oil recirculation system. It was a very minor modification.
Chrysler and early Force 4 cylinder engines recirculated excess oil and fuel puddled in the crankcase to the number one and three cylinders. They used two tubes that screwed into a hole in the bypass covers. These tubes protruded through the covers into the top bypass port of these cylinders. Thin hoses connected the cylinder drains to these tubes.
I removed the tubes and replaced the bypass covers with ones that were not drilled and tapped for them. I bought a 1/16 X27 NPT tap and drilled and tapped the manifolds. The lower manifold was drilled and tapped on the starter side just behind the carb mounting bolt. The upper manifold had a boss on the opposite side and that boss, which is used to mount the throttle cam on the lower manifold, was also drilled and tapped behind the carb mounting bolt.
The recirculating tubes were screwed into these holes and the bottom one was shortened a bit so it reached to the center of the reed plate. The top tube was approximately the correct length. Cylinder drains were reconnected to these tubes. My reasoning was that the excess oil would be recirculated through the rotating parts of the engine rather than being simply burned and this was the easiest place to do it.
NOW: The most interesting part. Yesterday I took the boat out for a test. Immediately upon starting I noticed some dramatic differences.
1. Choking in fast idle position started the engine immediately but fast idle was at 3,000 RPM instead of 15-1800 as usual for this engine.
2. Regular idle was at 1500 RPM instead of the usual 700-750. I found it necessary to lower the idle with the idle stop screw before shifting the engine into gear.
3. Top speed was 500 RPM higher. Unfortunately, I did not take my GPS and the speedometer does not work, but the tachometer does not lie. This engine went from 4,500 to 5,000-5050 RPM.
4. During acceleration from a hole shot after idling, the engine loads up and runs rough for a second or two until it clears itself out. Then it goes like a bat out of hell. I'll take that as a trade for 500 RPM in a New York second.
5. It did not appear to degrade the idle in any way. The engine ran rock solid at 700-750 RPM for at least 5 minutes.
Total cost? 20 bucks for a 1/16 X 27 NPT tap through Mc Master-Carr.
At first I thought the increased idle was due to additional air being pulled into the manifolds through the recirculating system. However, the hole in the tubes is only 1/16 inch and could not leak enough air to cause this. My second theory is that the oil and fuel recirculated into the intake manifolds seals the reeds better for less blow-back. Thus: more air/fuel mixture is inducted and pumped to the cylinders, generating more horsepower. Cheaper than hi-performance reeds too!
Now, mind you: This was on my Chrysler 140 which has been ported, has a 2 to 1 lower unit, and the exhaust is vented a bit. This engine is swinging a Michigan cupped 13 x 19 pitch prop behind a 21 foot cuddy. If you try it on a stock engine, you may not get such dramatic results.