Easy way to add HP?

[olddog]

The flatter the torque curve (the closer the torque is to a flat line) over say 2500 to 5500 rpm, the more predictable and therefore the easier the car is to handle. If all you're interested in is drag racing (idle or full throttle), this isn't important. If you are driving around twisty roads and are not a trained race driver, then the flat torque is very important. Possibly life saving important.

That said stay away from centrifugal blowers. They make almost no pressure at low rpm.

I think if I was in your shoes, I would sell the engine if you can get anywhere near what you said. Those heads make more power than the stock factory heads, but not much more. The E303 cam sounds good and that is about all it does. The only thing I would use out of that engine is the Block, and lifters.

Go 347 stroker. Spring for a boss block or aftermarket if you can afford it. Better oiling and stronger. For a couple hundred more you can go to a 4.125" bore and get some more CID and un-shroud the valves. Put good heads on it. The heads make the engine. Don't screw up a perfectly good engine with a junk intake. Match the cam up to everything else.

Talk with Brent Lykins or Craft Racing, whichever you are closer to.

[moore_rb]

Originally Posted by olddog

That said stay away from centrifugal blowers. They make almost no pressure at low rpm.

This is an accurate point when applied to the older style belt-driven hair dryers (which "feel" a lot like turbos as they spool up); but the latest crank drive blowers out there now are able to start adding boost as low as 1500RPM...

[olddog]

Originally Posted by moore_rb

This is an accurate point when applied to the older style belt-driven hair dryers (which "feel" a lot like turbos as they spool up); but the latest crank drive blowers out there now are able to start adding boost as low as 1500RPM...

They can angle the blades and make improvements, but a true centrifugal blower, the pressure output is proportional to the tip speed of the blades. The relationship is typically pretty close to: pressure equals tip speed squared. Since it is difficult to fit a 3 foot diameter blower in a car, they end up with a small diameter and a planetary gear set spinning the wheel up to 80,000 rpm to make pressure. At low rpm the boost is very low, with little increase in boost for a 1000 rpm motor increase. At high rpm, boost is high, and a large increase in boost for a 1000 rpm motor increase. Torque is proportional to boost, and boost increases with the rpm squared. This gives a very steep increase in torque over the rpm range, until the engine pumping efficiency starts dropping off rapidly. Once that point is reached, the centrifugal blower and engine combine to flatten the torque out for a while.

Multi stage compressors wheels exist in industry, but I have never seen them in an auto application. The pressure is still proportional to rpm, but not as steep. These need a good deal of application design and cannot handle a lot of variable changes, as they can get into vibration harmonics and destroy themselves. I don't see these going into auto applications, but I get surprised all the time. I just doubt that there is any centrifugal blower that doesn't have a steep rpm to pressure curve. Physics doesn't change much.

Now change to the roots bower, or better, a screw compressor and they are positive displacement blowers. You pretty much get the same boost pressure (thus torque) at all rpms.

So let's assume your engine NA has 300 ft-lb torque from 2500 - 4500 rpm and then it starts dropping off to say 250 ft-lb at 6000 rpm. With a centrifugal blower you may get 350 ft-lb at 2500 rpm at 2.5 psi boost. At 4500 rpm you are likely at 8.4 psi and 470 ft-lb. At 6000 rpm you are likely at 15 psi and 500 ft-lb. Some of that torque would be consumed by the blower belt, but that's more work than I wanted to put into this, so I am ignoring those losses.

In comparison if you used a positive displacement compressor at 15 psi boost (again ignore power robbed to drive the blower) you would double the torque everywhere. So cruising down the road and pulling up a mountain at 2500 rpm the positive displacement would would have about 600 ft-lb of torque available, where the centrifugal would only have 350 ft-lb available (only 50 more than the engine had normally aspirated). Sure drop two gears and rev it up to 6000 rpm, they both have the same torque, but every place below that, the positive displacement wins hands down.

I hate a different torque at every rpm. So you come out of the first turn at 2500 rpm smash it to the floor and get a modest 350 ft-lb of torque. Yea this is fun. The next corner you are at 4500 rpm and smash the throttle, expecting the same fun, only the engine pumps out 470 ft-lb of torque. The tires break loose on a corner, in a 90 inch wheel base car, and you are dead.

With the centrifugal smash it in first gear, and your tires will hold to the ground until the rpms come up. If you do not back off the throttle before the tires break loose they will rapidly go up in smoke. To keep the tires from breaking loose, you have to continually back off the throttle, as the rpms increase to keep the tires hooked. Same thing in every gear. Not for me.

[moore_rb]

Originally Posted by olddog

They can angle the blades and make improvements, but a true centrifugal blower, the pressure output is proportional to the tip speed of the blades. The relationship is typically pretty close to: pressure equals tip speed squared. Since it is difficult to fit a 3 foot diameter blower in a car, they end up with a small diameter and a planetary gear set spinning the wheel up to 80,000 rpm to make pressure. At low rpm the boost is very low, with little increase in boost for a 1000 rpm motor increase. At high rpm, boost is high, and a large increase in boost for a 1000 rpm motor increase. Torque is proportional to boost, and boost increases with the rpm squared. This gives a very steep increase in torque over the rpm range, until the engine pumping efficiency starts dropping off rapidly. Once that point is reached, the centrifugal blower and engine combine to flatten the torque out for a while.

Multi stage compressors wheels exist in industry, but I have never seen them in an auto application. The pressure is still proportional to rpm, but not as steep. These need a good deal of application design and cannot handle a lot of variable changes, as they can get into vibration harmonics and destroy themselves. I don't see these going into auto applications, but I get surprised all the time. I just doubt that there is any centrifugal blower that doesn't have a steep rpm to pressure curve. Physics doesn't change much.

Now change to the roots bower, or better, a screw compressor and they are positive displacement blowers. You pretty much get the same boost pressure (thus torque) at all rpms.

So let's assume your engine NA has 300 ft-lb torque from 2500 - 4500 rpm and then it starts dropping off to say 250 ft-lb at 6000 rpm. With a centrifugal blower you may get 350 ft-lb at 2500 rpm at 2.5 psi boost. At 4500 rpm you are likely at 8.4 psi and 470 ft-lb. At 6000 rpm you are likely at 15 psi and 500 ft-lb. Some of that torque would be consumed by the blower belt, but that's more work than I wanted to put into this, so I am ignoring those losses.

In comparison if you used a positive displacement compressor at 15 psi boost (again ignore power robbed to drive the blower) you would double the torque everywhere. So cruising down the road and pulling up a mountain at 2500 rpm the positive displacement would would have about 600 ft-lb of torque available, where the centrifugal would only have 350 ft-lb available (only 50 more than the engine had normally aspirated). Sure drop two gears and rev it up to 6000 rpm, they both have the same torque, but every place below that, the positive displacement wins hands down.

I hate a different torque at every rpm. So you come out of the first turn at 2500 rpm smash it to the floor and get a modest 350 ft-lb of torque. Yea this is fun. The next corner you are at 4500 rpm and smash the throttle, expecting the same fun, only the engine pumps out 470 ft-lb of torque. The tires break loose on a corner, in a 90 inch wheel base car, and you are dead.

With the centrifugal smash it in first gear, and your tires will hold to the ground until the rpms come up. If you do not back off the throttle before the tires break loose they will rapidly go up in smoke. To keep the tires from breaking loose, you have to continually back off the throttle, as the rpms increase to keep the tires hooked. Same thing in every gear. Not for me.

We're still not talking about the same thing... You are still hammering on fixed ratio, belt driven superchargers... and I don't disagree with anything you wrote (yes, I read your WHOLE post )

However, what if the ratio of engine RPM to compressor RPM wasn't fixed? what if you could vary the impeller speed and set the boost level wherever you wanted it, at almost any RPM? What if your blower could be PROGRAMMED to work with a MAP sensor, and a variable speed transmission, to deliver more boost at lower engine RPMs, and less boost at higher RPMs in order to provide a nice, broad, flat torque curve...?

Yes, you sure can....

https://www.procharger.com/procharger-i1

[olddog]

Originally Posted by moore_rb

We're still not talking about the same thing... You are still hammering on fixed ratio, belt driven superchargers... and I don't disagree with anything you wrote (yes, I read your WHOLE post )

However, what if the ratio of engine RPM to compressor RPM wasn't fixed? what if you could vary the impeller speed and set the boost level wherever you wanted it, at almost any RPM? What if your blower could be PROGRAMMED to work with a MAP sensor, and a variable speed transmission, to deliver more boost at lower engine RPMs, and less boost at higher RPMs in order to provide a nice, broad, flat torque curve...?

Yes, you sure can....

https://www.procharger.com/procharger-i1

Wow I am behind the times. I read where one of the German car companies were experimenting with a continuous variable drive design on a positive displacement blower. If memory serves they were shooting for no throttle plate. Quite a few years back.

Ok now that I am up to date, yes that would work as you described.

Thanks for the link and explanation.

[MKS427]

Originally Posted by moore_rb

We're still not talking about the same thing... You are still hammering on fixed ratio, belt driven superchargers... and I don't disagree with anything you wrote (yes, I read your WHOLE post )

However, what if the ratio of engine RPM to compressor RPM wasn't fixed? what if you could vary the impeller speed and set the boost level wherever you wanted it, at almost any RPM? What if your blower could be PROGRAMMED to work with a MAP sensor, and a variable speed transmission, to deliver more boost at lower engine RPMs, and less boost at higher RPMs in order to provide a nice, broad, flat torque curve...?

Yes, you sure can....

https://www.procharger.com/procharger-i1

WOW, Impressive numbers on the Coyote! That could easily be 580 TQ at the crank.
I originally suggested a centrifugal, because I am not aware of a screw type for a 302 Windsor, that won’t pop up through the hood (bonnet).