The Ford Barn

goodcar · 12-13-2022, 06:21 PM

Quote:

Originally Posted by Smokedtires

Hello all, I bought my 30 Roadster last June and put almost 600 miles on it before putting away for winter. I'm interested in more torque for hill climbs while keeping everything appearing stock.

My question is, should the Zenith's jets be increased in size to accommodate the higher compression? Any other considerations to go with the new head? Currently it is restored with everything in stock form.

Thanks, looking forward to hearing from the pros here.

If this hasn't already been done, timing needs to be set 20-25 BTDC vs TDC to keep from beating engine to death at higher speeds. It took me quite a while to learn this. All the hullabaloo about HC heads, not much about changing the timing.

alexiskai · 12-13-2022, 06:26 PM

Quote:

Originally Posted by goodcar

If this hasn't already been done, timing needs to be set 20-25 BTDC vs TDC to keep from beating engine to death at higher speeds. It took me quite a while to learn this. All the hullabaloo about HC heads, not much about changing the timing.

Be more specific - are you suggesting setting the initial timing to 20 degrees BTDC?

goodcar · 12-14-2022, 12:04 AM

Quote:

Originally Posted by alexiskai

Be more specific - are you suggesting setting the initial timing to 20 degrees BTDC?

Yes. Suggest you read post #23, he says 35 BTDC. I think he is more knowledgeable about this than I am. My car with a 5.5 ran fine at TDC until I got over about 30 mph. Then it started hammering. After a lot of research, I learned that timing needed to fire BTDC. I also used the NuRex timing light.

I think this also explains why some people have a problem until they discover that they have a timing cover from a B engine which fires BTDC.

goodcar · 12-14-2022, 12:12 AM

Quote:

Originally Posted by goodcar

Yes. Suggest you read post #23, he says 35 BTDC. I think he is more knowledgeable about this than I am. My car with a 5.5 ran fine at TDC until I got over about 30 mph. Then it started hammering. After a lot of research, I learned that timing needed to fire BTDC. I also used the NuRex timing light.

I think this also explains why some people have a problem until they discover that they have a timing cover from a B engine which fires BTDC.

Correction: read post #7 not 23.

alexiskai · 12-14-2022, 12:56 AM

There are two important timing settings on the Model A manual timing system: the initial timing and the total timing. The initial timing is the timing you get when the spark lever is all the way up on the quadrant, i.e., fully retarded. The default setting for the A is 0°, meaning TDC. The default setting for the B is 19°. Since this figure is a positive number, it should be understood to signify 19° BTDC.

Although the default initial timing for the A is 0°, this default was chosen to make it easier to hand crank the engine, or to start it in extreme cold conditions with the straight-weight oil available at the time. Most stock A engines in good shape will start with initial timing as high as 25°. This was demonstrated by Nu-Rex years ago. However, it is useful to retain a low initial timing to give the driver room to back the timing off when under load.

The total timing is the timing you get when the spark lever is as far down on the quadrant as you are willing to move it. This is the maximum amount of spark advance available to the engine. For an A engine where the initial timing is 0° and the spark lever is set at 9:00, this is usually about 30° (again, BTDC).

Most HC heads decrease the optimal advance at any given point on the torque curve in comparison to the stock head. The most important effect of this is to reduce the total timing. Usually this ends up being around 22-28°. If you exceed the optimal total timing, you get knock.

Drivers tend to accommodate this in one of two ways: either they reduce the range through which they adjust the spark lever, or they adjust the initial timing so that it goes below 0°, e.g., -8° (negative numbers signify ATDC timing).

When you refer to post #7, the author is talking about his setup in which he set the initial timing to 0° and the total timing to 28°, not 35°.

Bill G · 12-14-2022, 01:56 AM

Sponsored Links (Register now to hide all advertisements)

I made no changes to the carburetor when going to the 5.5 head. I actually get better mileage with the HC head and as everyone says, quite a bit less advance is needed.

Not long after the HC head, I blew through an old fiber timing gear. Some have said it could have been due to the higher compression, which I struggle to quite buy into. Others say it is just that it was coincidence. At any rate, I replaced the chewed up fiber gear with an aluminum.

katy · 12-14-2022, 10:33 AM

Quote:

My question is, should the Zenith's jets be increased in size to accommodate the higher compression?

No, the jets are sized to the amount of air going through the carburetor, If you increase jet size it'll be too rich a mixture.

jack backer · 12-14-2022, 11:18 AM

The 5.5 is the only performance head designed by Ford engineering. For model A engine performance increases compression and fuel top the list, the engine can handle in excess of 100 psi compression pressure, stock is 65 psi compression pressure.. fuel? The zenith follows about half the CFM of the engine.. a single Holley 94 or Stromberg 97 downdraft carburetor matches the engine flow almost perfectly.

A performance model A engine is more of what made the stock engine fun to drive, Torque rises with performance improvements.

12-14-2022, 12:56 AM	#25
alexiskai Senior Member Join Date: Apr 2018 Location: Mebane NC Posts: 2,356	Re: 5.5 Snyder head, what else is needed or recommended? There are two important timing settings on the Model A manual timing system: the initial timing and the total timing. The initial timing is the timing you get when the spark lever is all the way up on the quadrant, i.e., fully retarded. The default setting for the A is 0°, meaning TDC. The default setting for the B is 19°. Since this figure is a positive number, it should be understood to signify 19° BTDC. Although the default initial timing for the A is 0°, this default was chosen to make it easier to hand crank the engine, or to start it in extreme cold conditions with the straight-weight oil available at the time. Most stock A engines in good shape will start with initial timing as high as 25°. This was demonstrated by Nu-Rex years ago. However, it is useful to retain a low initial timing to give the driver room to back the timing off when under load. The total timing is the timing you get when the spark lever is as far down on the quadrant as you are willing to move it. This is the maximum amount of spark advance available to the engine. For an A engine where the initial timing is 0° and the spark lever is set at 9:00, this is usually about 30° (again, BTDC). Most HC heads decrease the optimal advance at any given point on the torque curve in comparison to the stock head. The most important effect of this is to reduce the total timing. Usually this ends up being around 22-28°. If you exceed the optimal total timing, you get knock. Drivers tend to accommodate this in one of two ways: either they reduce the range through which they adjust the spark lever, or they adjust the initial timing so that it goes below 0°, e.g., -8° (negative numbers signify ATDC timing). When you refer to post #7, the author is talking about his setup in which he set the initial timing to 0° and the total timing to 28°, not 35°.

12-14-2022, 01:56 AM	#26
Bill G Senior Member Join Date: Jun 2017 Location: Walla Walla, WA Posts: 1,045	Re: 5.5 Snyder head, what else is needed or recommended? Sponsored Links (Register now to hide all advertisements) I made no changes to the carburetor when going to the 5.5 head. I actually get better mileage with the HC head and as everyone says, quite a bit less advance is needed. Not long after the HC head, I blew through an old fiber timing gear. Some have said it could have been due to the higher compression, which I struggle to quite buy into. Others say it is just that it was coincidence. At any rate, I replaced the chewed up fiber gear with an aluminum.

12-14-2022, 11:18 AM	#28
jack backer BANNED Join Date: Mar 2022 Location: Chenango Bridge NY Posts: 433	Re: 5.5 Snyder head, what else is needed or recommended? The 5.5 is the only performance head designed by Ford engineering. For model A engine performance increases compression and fuel top the list, the engine can handle in excess of 100 psi compression pressure, stock is 65 psi compression pressure.. fuel? The zenith follows about half the CFM of the engine.. a single Holley 94 or Stromberg 97 downdraft carburetor matches the engine flow almost perfectly. A performance model A engine is more of what made the stock engine fun to drive, Torque rises with performance improvements.