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Discussion Starter · #1 ·
OK here we go.

A statement was made to me recently that got me thinking. And the validity of the statement has been backed up by reputable folks.

"When turbocharging an engine, cubic inches are insignificant"

When I really thought about this. It seems that if a given engine can "process" all of the air a turbo puts out it will make that much power.

Most turbos come with a HP rating. This is based off of how much air they produce.

The person that made the statement to me is making 3,000 HP with a 4 cylinder engine.

Lets see how the deep thinkers feel about this.
 

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steelcomp was here
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An engine is only an air pump before anything else.
How much air it processes (mixed with fuel, of course) will determine it's power output. 1 cyl, 5 cyl's, 12 cyl's- doesn't matter.
 

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Discussion Starter · #5 ·
Thanks Scott

The amount of power that is ultimately output by the engine will be determined by how much of that power the engine and power adder took back from what was produced.
 

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steelcomp was here
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Thanks Scott

The amount of power that is ultimately output by the engine will be determined by how much of that power the engine and power adder took back from what was produced.
That's true. How ever the power is distributed, it's still determined by how much air and fuel the engine can process either through natural or artificial means.
 

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OK here we go.

A statement was made to me recently that got me thinking. And the validity of the statement has been backed up by reputable folks.

"When turbocharging an engine, cubic inches are insignificant"

When I really thought about this. It seems that if a given engine can "process" all of the air a turbo puts out it will make that much power.

Most turbos come with a HP rating. This is based off of how much air they produce.

The person that made the statement to me is making 3,000 HP with a 4 cylinder engine.

Lets see how the deep thinkers feel about this.
I believe your guy is correct(unless carried to the far extremes). The larger cid just gives you quicker spooling/TQ and usually comes along with a stronger foundation to build on.
In a turbocharged deal I certainly wouldnt trade good geometry--rod x stroke ratio, and meat between the cylinders for more cid. jmo.


Supposedly been a 4 cyl make 4000hp.
 

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Or Seth, either one
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OK here we go.

A statement was made to me recently that got me thinking. And the validity of the statement has been backed up by reputable folks.

"When turbocharging an engine, cubic inches are insignificant"

When I really thought about this. It seems that if a given engine can "process" all of the air a turbo puts out it will make that much power.

Most turbos come with a HP rating. This is based off of how much air they produce.

The person that made the statement to me is making 3,000 HP with a 4 cylinder engine.

Lets see how the deep thinkers feel about this.
If detonation is of no concern, absolutely. As long as an engine wouldn't hydro lock on the fuel (assuming it's liquid). I suppose you could stuff as much air in cylinder, as much as the compressor/s are capable of anyway.

However, the point always arises that once that limit is reached a larger cid would still make more under the same conditions.

Good point for the thought factor, but otherwise it's the same age old undeniable fact that there's no replacement...
 

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Discussion Starter · #9 ·
If detonation is of no concern, absolutely. As long as an engine wouldn't hydro lock on the fuel (assuming it's liquid). I suppose you could stuff as much air in cylinder, as much as the compressor/s are capable of anyway.

However, the point always arises that once that limit is reached a larger cid would still make more under the same conditions.

Good point for the thought factor, but otherwise it's the same age old undeniable fact that there's no replacement...
The key word in bold. :)
 

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Discussion Starter · #10 ·
It will have to be thought of as fluid in motion. The entire process into and out of the engine. Not necessarily one cycle of one cylinder.
 

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Or Seth, either one
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Most turbos come with a HP rating. This is based off of how much air they produce.
Just a little food for thought. I'm pretty sure what limits the mass flow of a compressor is directly related to it's inducer diameter.
 

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Highaboosta
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Bob GN7 made the point a couple years ago that would be valid here.
What % of the cylinder are you going to fill with your turbo or blower boost ?
If your pumping 30# boost to it the cylinder is certainly not going to see that whole charge when at 7000 rpm the entire intake stroke only takes .017 sec.

When you consider what % of the cylinder you fill with your compressed A/F mixture at high RPM it is logical to conclude that it is going to fill a small displacement cylinder to a higher % than a large displacement cylinder.
Especially with 2 intake valves per cylinder.

And that's why those old John Deere tractor 2 cylinder motors were never used for racing :)sphss
 

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Or Seth, either one
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Bob GN7 made the point a couple years ago that would be valid here.
What % of the cylinder are you going to fill with your turbo or blower boost ?
If your pumping 30# boost to it the cylinder is certainly not going to see that whole charge when at 7000 rpm the entire intake stroke only takes .017 sec.

When you consider what % of the cylinder you fill with your compressed A/F mixture at high RPM it is logical to conclude that it is going to fill a small displacement cylinder to a higher % than a large displacement cylinder.
Especially with 2 intake valves per cylinder.

And that's why those old John Deere tractor 2 cylinder motors were never used for racing :)sphss
Now there's a good point to discuss. :))THumbsUp:))THumbsUp

You could certainly cam and head an engine to achieve peak volumetric efficiency at 7000rpm. It is possible to fill a cylinder of any size to 100% or even more at that rpm and in the given time available, if the cam and intake/exhaust ports support it. I know it's not anything you didn't know already and that your point was aimed toward an engine that makes peak hp at 7k, not peak Tq at 7k. Just say'n.

The other point that exists between the lines of your post is; could boost be elevated until the cylinder is "full" again? The answer is no. Once past peak VE in the powerband the engine will not have the time to fill to the point that it's effective pressure is equal to the pressure in the manifold. But in another sense, the answer is yes. A cylinder could be filled to the same desired effective pressure with elevated manifold pressure. Desired pressure would most likely be just below the threshold of detonation, but still wouldn't be equal to manifold pressure. In this way, peak torque should be able to be carried throughout the remainder of the powerband, as long as the compressor can keep up with the increasing pressure and mass flow demands to offset the decreasing VE. At the point the compressor can no longer keep up, torque should sharply nose over.

I haven't heard much of this strategy being used intentionally yet, but have noticed it's effects in the results achieved by many.
 

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Discussion Starter · #16 ·
Torque is directly related to complete cylinder filling.

One fact to remember once the engine reaches the point of incomplete cylinder filling due to the time it has to do so. The greater number of power strokes per minute make up for it. When that maximum is reached power will no longer increase.

When you consider what % of the cylinder you fill with your compressed A/F mixture at high RPM it is logical to conclude that it is going to fill a small displacement cylinder to a higher % than a large displacement cylinder.
Agreed but it is still a % compared to a %
 

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mo balls than $cents$
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In my experience a small ci motor spools wayyyy faster than a large ci deal given both having ideal turbs in place for a 7krpm range goal. a pancake air compressor is gna fill faster than a big ingersol with a 30g tank. the small c.i. sees load quicker and more brutally at the hit. hard to explain till ass is in the seat and have felt both tuned properly.
 

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This is one of the better reads on here in awhile! Keep in mind when all you turbo guys are comparing knowledge that if you don't agree then one of you is WRONG! :)UnsureLol:stir: carry on
 

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In my experience a small ci motor spools wayyyy faster than a large ci deal given both having ideal turbs in place for a 7krpm range goal. a pancake air compressor is gna fill faster than a big ingersol with a 30g tank. the small c.i. sees load quicker and more brutally at the hit. hard to explain till ass is in the seat and have felt both tuned properly.
Wouldn't that all depend on how much load there was in getting to the 7000 rpm?
 

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steelcomp was here
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My thought on why smaller engines respond better to boost is this: I think bore dia. plays more into this than just displacement. The flame front and burning gasses have to expand laterally (following the path of least resistance) before they begin to push the piston down. The sooner they hit the cyl wall, the sooner they start pushing the piston. In a NA deal, we're concerned with VE and bigger bore = better breathing and better VE but when you can exceed 100% VE long before any NA engine would, that bigger bore IMO begins to be a negative instead of a positive.
 
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