Volume is volume. I still think the larger cylinder will create more pressure, unless someone can mathmetically show me how I'm wrong. Or I just have no ******* clue!

 

lol...here is a link to an illustrated version of Boyles law. Boyles law is related to TQ production VS volume (CI) but its not the only concpet thats important.
http://exploration.grc.nasa.gov/educ...ket/boyle.html

Just think in terms of a hydraulic piston. The hydraulic actualtors on a big backhoe will have a known output of work based on several parameters.
This is somewhat reversed from a motors abilty to make power but you will see how its related.

A piece of large equipment like that will have a motor driven pump that operates at a specific PSI. Many are around 3000 psi. If the actuator has a surface area of 2 square inches that the 3000 psi is apllied to (actuator surface area is like piston surface area)...that actuator will have a force of 6000 lbs it can apply (3000 psi x 2 square inches).
Doubling the size of the actuator suface area to 4 square inches...we would only need a pump that puts out 1500 psi to achieve the same forces applied (1500 psi x 4 square inches = 6000 psi)




There is alot more too it that that but thats the basics of it.

 

Another way to look at it is through the eyes of a piston manufacturer. Most pistons are designed to handle a specific pressure. I dont know exactly what that is but just say its 250 psi. Thats 250 pounds per square inch of force on that piston surface area.

on a 4 inch bore if you have 200 psi of pressure after TDC you will have 200 psi x 12.56 square inches (thats the surface area of a piston with 4" bore) thats 2512 lbs of force applied to the piston top pushing down on the rod in turn pushing on tha crank pin in turn rotating the motor.

If you increase the bore to a 4.5 inch bore you will have 15.89 square inches of piston surface area....and only require 158 psi to achive the same downward force on that piston.

Adding or subtracting nitrous will increase or decrease the cylinder pressure applied to the piston surface area.


Please dont ask how stroke gets involved...that starts getting very complicated...lol.

 

Al, guess that's a little better than my balloon story

 

Cylinder Pressure = Torque. Not HP.

 

Thats why i said
The discussion always seems to be about HP. I like to keep things abut Tq myself. Tq @ rpm. As a matter of fact...in regards to this discussion and shot size...the guys that are pushing water should be taking a hard look at thier Tq production and see where the peaks are. Those are the areas you need to be thinking about to try to preserve head gasket sealing. Lop off some peak Tq areas in exchange for more Tq in higher rpms and you will be faster and more reliable IMO.

When i start upping the shot with my RPM progressive setup I hope to make near 1000 rwhp...but only using 750 ft/lbs of Tq. That 750 ft/lbs is not excessive because the cylinder pressure required to make that Tq is not too crazy. That will roughly be a 450 shot.

 

All this talk of torque is getting boring.

Column-Average HP is what determines how fast your car is capable of going.

 

That could also be average Tq. Its all one in the same...but how to control the delivery of nitrous to achieve those optimal averages with a nitrous car seems to be the key and topic of many debates.

 

Let's take two engines that make 800HP. Let's say one is a 347 and the other is a 408. If they both make 1.4 TQ/CID (Pretty good). The 347 has to turn 8,645 RPM. The 408 only has to turn 7,358 RPM. The 347 makes 486 FT.LBS., and the 408 makes 571 FT. LBS.

Which one goes faster?

 

Well if I am understanding your question...all I can be certain from your example is that the 347 makes 486 ft/lbs at 8645 rpm to spit out the 800 hp and the 408 makes the 571 ft/lbs at 7358 to achive its 800 hp. There is not enough info about the rest of the power curves and the GEARING to pick one to be the victor. Assuming whoever put these combos together geared each car to reach the same mph at thier respective 800 rwhp....the one with the best avg tq (or hp) applied to the rear wheels down the 1/4 mile will win assuming weight, traction and aerodynamics are all the same.
If they are geared to reach the same mph at the 800 rwhp and go no further they would end up pretty close.
If you are saying they are throretical engines that make that TQ figure constantly throughout the rpm range...and they were geared to reach the same mph at thier 800 rwhp...they should tie. But if you add up the TQ at the rear wheels applied down the 1/4 they would be exactly the same due to gearing.

So really the only way i can make an assumption is to use the theoretical engine that makes constant TQ throughout the rpm range. In this case..if both identical cars had the same weight, same launch, same aero, and THE SAME GEAR TO ACHIEVE THE SAME MPH AT 800 hp (7358 rpm for the 408 and 8645 for the 347) they would end up equally as fast becase the avg TQ applied to the rear wheels would be the same.

An example the 408 makes 571 ft/lbs though a 3.90 gear = 2226.9 TQ at the axle in the 1:1 tranny gear.

The 347 makes 486 tq but uses the 4.56 rear gear it will put out 2216.7 TQ at the rear axle in the 1:1 tranny gear


I understand your use for using the 800 hp example. Its easy to talk about an 800 hp vs 800 hp. But it helps me to think about TQ at rpm to help my brain struggle to make sense of whats going on in a combo. Especially when comparing vastly different curves like a nitrous motor VS a turbo setup Really...either way you look at it...you cant make any reall assumption unless you know either the TQ or hp figure at a specific rpm over the usable range. And with the use of either of those two number the third can be found. I just like to use TQ at rpm because I can think about cylinder pressure all at the same time.

 

If the 347 makes it's torque sooner and longer it will be faster/quicker. So many variables and not enough specific info to make a good judgement call. My thinking is on line with what Al has said, and that's what I am trying to do, a linear torque curve rather than a max peak torque curve, that only looks good on paper as a peak number to show off. I am currently in the area of 500/500.
Robert

 

We've did a 350 shot for a while and never had any issues.

 

to spray a 300 or 350 do i need a standalone fuel system?

 

The 347 would be faster. Even though the peak HP is the same, the 347 can use that over a longer period in a single gear.

 

The 347 turns 15% more RPM, so it needs 15% more gear. Rear-wheel torque comes out to the exact same on both engines. If they are both in cars that weigh the same, and we assume that they both have the correct converter and chassis setup and blah blah blah, which one is faster?

 

Torque is not what makes cars fast. Horsepower is. Torque by itself doesn't matter. Torque @ RPM (Which is Horsepower, so let's just talk about it in terms of Horsepower!) is.

 

It will always be easier for a larger engine to make more average power.

 

After all...if the cars are the same weight, same launch, same everything...and have the same output of TQ applied at the wheels over the same MPH they would match each other in acceleration....in theory.

 

You keep talking about TQ....why?

 

Let's take this one step further.

Let's say I make 800HP @ 6,000 RPM and you make 800HP @ 9,000 RPM. Assuming the cars are geared properly and such, which one is faster?