Power slot in an model a engine?

Johan Ottosen

Johan Ottosen

Junior Member
Hi everyone.
I saw a Ford v8 engine beeing machined on youtube. They made a groove between the cylinder and valves - a so called Perfoemance Slot. They said that i Pulled mutch better from this. Is there any merrit to this and is this aplicable to the Model A?

Johan Ottosen
Toudor early 1929
 

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I believe in the old days of hotrodding they called that "relieving". It was supposed to add power to hopped-up V-8 blocks. Like the Beach Boy song "Little Deuce Coupe" goes: "She's ported and relieved and she's stroked and bored."
Marshall
 
Y-Blockhead -
In my life at various times I've been "relieved", I've been "stroked" and I've been "bored". But I have never, ever been "ported". :)

Marshall
 
That won't help on a Model A. The V8 has a much smaller combustion chamber, especially with hi-compression heads and the relief helps the mixture squeeze around the corner and into the cylinder. Also the valves are angled on the V8 creating more of a shelf that can be ground away. Some V8 people dispute the benefit of relieving but either way it won't help your A. :)
 
The valves in an A sit up more flush with the block deck so there is nothing really to relieve in the block. Much more beneficial to make sure the head is open around those "big" valves that you instaled to unshroud them ��
 
I think in the early days of the post WWII hot rodding era, it was an ego thing to be able to brag that one's "mill" (engine) was "relieved". 'Didn't impress those who really knew engines, but it bowled over the non-automotive types, who didn't know what the heck "relieving" meant. I also read that relieving was finally recognized as not being cost-effective or created any significant additional horsepower, and sometimes it actually decreased the engine's performance. But it sure sings when you say: "She's ported and relieved." Come to think of it, that could also apply to several girls I used to date. :)
Marshall
 
Relieving a model A block will definitely help if you are building a flathead configuration for all out racing. You need to lower the transfer area in the head to match. It all has to do with flame front speed and distance travel.
This is also one reason why a deep relief in a V8 makes it go faster.

Not much help on a wimp street engine.
 
It doesn’t help to thin out the deck which is o-2-thin to begin with
Getting the valves up high out of the seats makes more sense and flow
Chamber design is crucial for performance

J
 
Ford generally only relieved the truck engines and like the photo in post #1, it was just a basic straight cut relief. Racers took it to an art form.
 
johnneilson said:
It doesn’t help to thin out the deck which is o-2-thin to begin with
Getting the valves up high out of the seats makes more sense and flow
Chamber design is crucial for performance

J
Click to expand...

You just machine the deck away in the relief area and weld in a steel plate at the same time you weld in the tubing for 4 intake ports.

The old full width and full depth all the way works best.

I was going to try moving the valves and cam closer to the cylinders but never got around to it after I switched to V8's..

I also had plans for combining pieces of an Olds quad 4 and a model B block so it still qualified as a vintage block but had all the attributes of the quad 4.
 
Head design has everything to do with power. Two heads with the same compression ratio but with different chamber design will perform differently. The intake air has to get past the valves and then down into the cylinder in the smoothest way. And the squish area has to create the most turbulence for ignition without creating a dead pocket or a chilled area. Racing flat heads are the best examples to follow. Relieving the block, in my opinion, is not going to gain much for a Model A engine. It is better to create a smooth path for the air in the head. The intake air already has some momentum upwards as it exits the valve.
 
nkaminar said:
Head design has everything to do with power. Two heads with the same compression ratio but with different chamber design will perform differently. The intake air has to get past the valves and then down into the cylinder in the smoothest way. And the squish area has to create the most turbulence for ignition without creating a dead pocket or a chilled area. Racing flat heads are the best examples to follow. Relieving the block, in my opinion, is not going to gain much for a Model A engine. It is better to create a smooth path for the air in the head. The intake air already has some momentum upwards as it exits the valve.
Click to expand...

We gained more by lowering the transfer area and making the relief deeper.

A good example of one of these engines was several years ago a FLATHEAD B engine won top eliminator in the vintage 4 cylinder dragster class at the Antique Nationals 2 years in a row. The OHV engines just couldn't do it.
 
Pete said:
We gained more by lowering the transfer area and making the relief deeper.

A good example of one of these engines was several years ago a FLATHEAD B engine won top eliminator in the vintage 4 cylinder dragster class at the Antique Nationals 2 years in a row. The OHV engines just couldn't do it.
Click to expand...

Was that B still using the siamesed intake ports? Just wondering how far you can go with the shared intakes on a serious motor. Thanks. :)
 
Flathead said:
Was that B still using the siamesed intake ports? Just wondering how far you can go with the shared intakes on a serious motor. Thanks. :)
Click to expand...

It had 4 intake ports.

While welded in tubing was the first way tried for that, a much easier and better way was found later by hogging the whole area between the ports out and attaching a divider plate to the header plate.
Ended up with considerably larger port.
 
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