Flathead V8 Problem

[Ol' Ron]

If you have a stock 8BA engine then you can't use the stock distributor. The carbs should have stock power valves. To prove a point, Remove one carb and block off the base. Engine should rune OK under all conditions. If not, you have other problems

 

[Sid]

This is fine if you are using progressive linkage. However I do not recommend this kind of setup. Run both carbs with straight linkage.

The info. I gave was for straight linkage. I also think you need a pretty wicked flatty to run power valves in both carbs. That's why you block off one power valve on multiple carb. set-ups.

 

[flatjack9]

Don't agree at all.

 

[estout81]

I run power valves in both my carburetors. Runs well.

 

[Tinker]

Run 3.5s power valves in a dual 94 with all in dump. chevy conversion distributor. just my opinion.






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[Flathead Fever]

do you have those little air filters with the paper element remove them & try it

Richard is right. I had brand new ones change my idle speed. If they can restrict it at an idle imagine what they do at road speeds. You can try driving it without them (if you have those).

 

[Flathead Fever]

He says the advance is working but I wonder how he knows. If it is advancing the curve may not be right.

Frank asked how you check total advance. You use an "adjustable" timing light and a hand operated vacuum pump.

Disclosure I'm not a flathead guru. I know enough to hold a conversation but I'm not an expert. I was a professional mechanic so I know how things work. There is nothing magical about a flathead (except the sound)

Something I like to do is try to get "car people" to understand how these systems work. You can't work on them if you "don't" understand how they work! Most car people" think they know but they don't really understand what is happening. A lot of the "paid" mechanics don't know either, especially in hot rod shops and antique auto restoration shops. They are restorers (I use that loosely) they are diagnostic mechanics. The problem with your engine could be either fuel of ignition, which you already know. For now I'm going to discuss the ignition.

Checking advance, you check the mechanical advance with the vacuum advance line disconnect and plugged. Then you compare the mechanical advance to the rpm. You can watch it move with a timing light. You compare it against the factory specifications up to the point you reach maximum mechanical advance. This is done while your looking at the pulley's timing mark while you turn the dial on the timing light which moves timing mark back to your base timing. Then you read the degrees on the timing light and you can tell how much advance you have. You have not changed the actual timing but changed when the timing light flashes. The dial on the light tells you how many degrees in crankshaft rotation you have altered the flash.

The mechanical advance can become stuck or the springs get can get weak causing it to advance to fast. You will able see all of this with your adjustable timing light.

Next the vacuum advance. At an "idle" you apply vacuum to your advance with your hand pump until it reaches maximum advance. You do not want the rpm above idle because then the mechanical advance will start to kick in and you only want to see the vacuum advance reading. Move the dial on the timing light just like you did before and this will tell you what the vacuum advance is capable of. The combined base timing, mechanical advance and vacuum advance will give you your total advance. Do "not" buy a timing light unless it has a way to measure advance. I just picked up a really nice one in the box at an estate sale, dirt cheap. The new ones are digital with buttons instead of the dial.

Lets talk about that vacuum advance on a '49 to '53 flathead and any other engine equipped with one. Not the earlier 59A style distributer, that is a vacuum brake system and works completely opposite the way the later flatheads work.

The vacuum advance does not work the way most people think it does. Even most mechanics don't know since everything is computer controlled now. It was not designed for a high performance engine. A good example is the Ford 289 engine. All the 289s came with a mechanical and a vacuum advance distributor "except" for the factory hipo 289, 427 side oilers and few others. They only have a mechanical advance, why would the engineers have done that? The vacuum advance is not there to make more power its there to prevent detonation under a heavy load like climbing a hill. Going up a hill you have your foot mashed to the floor so the maximum amount of air and fuel is being drawn into the cylinder but the RPM is not very high as engine is being bogged down. If it were to receive the maximum ignition advance at the same time the mixture would detonate, "engine knock" because the engine is rotating to slowly to receive the spark that early.

To prevent detonation they installed the vacuum advance. Now you need to understand how engine vacuum works. At Idle vacuum is high because the throttle plate is closed. The engine is sucking against the bottom of that plate. If you hook a vacuum gauge to a port "below" the throttle plate (manifold vacuum) it will give you a high vacuum reading on a engine with good compression and a stock camshaft. As you open the plate the vacuum begins to drop because you are reducing the restriction. A partially open throttle plate would be typically be when you were cruising down the road. The vacuum advance receives its vacuum signal from "above" the throttle plate (venturi vacuum), because we don't want it advancing at idle which it would if it was connected to a vacuum source located below the throttle plate. As that throttle plate opens there is now vacuum above the plate which is sent to the vacuum advance which advances the timing. You now get better power and better gas mileage because the increased timing produces more pressure on the top of the piston. That is why when you advance the timing at idle the rpm goes up, more pressure (weight) is pushing down on the piston so it moves faster.

Your cruising a long and now you reach that hill and the engine starts to lug down. You push the pedal to the floor. The throttle plate is now wide open. There is no restriction and vacuum drops to zero. There is no longer a strong enough vacuum signal to operate the vacuum advance and timing retards. Retarding the spark, making it happen "later" reduces the pressure on the piston and prevents detonation. These engineers were no dummies. That was a brilliant idea!

On a hot rod engine we do not want the timing to retard when we mash the pedal to the floor. We want to create the most pressure on the top of that piston as we possibly can without blowing a hole through it, more pressure more power. So we run a mechanical "advance only" distributer that can produce the most advance the engine can take without detonating. Detonation causes a loss of horsepower. We prevent the detonation by using higher octane fuel which burns "slower" than low octane fuel. The low octane fuel (regular gas) actually has more power than high octane fuel but not as much power as a high compression engine, with advanced timing running on high octane fuel. That's the trade off.

Your actually reducing power when you put high octane fuel into an engine designed to use regular gas. Not only does the high octane gas have less energy it changes the timing of your engine. It burns slower so the maximum pressure will not be achieved when the piston is at Top Dead Center.

Even after the 8BA flatheads came out in 1949 hot rodders continued to use the older flatheads with the mechanical only advance distributers. They could not create as much power with 8BAs vacuum advance style distributers. It took a little while for the aftermarket industry to make a mechanical only distributer for these later flatheads. You will here a lot of old-timers swear by a 59A engine There is no way they will use an 8BA engine. Its not because the block was any stronger. It had to do with those late model distributors. Those guys that tried to make power with them still hate them to this day(my 88 year old dry lakes racer neighbor).

One of the things you can try is to remove the vacuum advance line from the advance unit and plug it. Then hook up your hand operated pump with a long enough hose to reach inside the car. Then you can apply what ever vacuum you want, at any rpm or load to your distributer just to see what it does. Do this kind playing around with stuff. Its not going to make since reading about. It will stick in your head forever once you put your hands on it.

Another thing, a lot of vacuum advance are adjustable but I don't know about flatheads? When you remove the hose you can stick an Allen wrench in that vacuum port and adjust the advance limit.

 

[tubman]

I have purchased two "Advance" type timing lights and neither worked properly. Just a heads up.