hey silverback

[Voodoo]

buy u a bananna if u can answer this for me. is there a equation for cubic inches vs lbs boost that u know of?? such as a chevy 350ci motor + 20 inches of boost = 570 ci?? i was wondering if there was any thing out there to help figgure this out or worth knowing. or is the variable ( head flow, valves, ect ect) to much to even have a equation??

 

[Texas Yellow Fever]

Monkey Boy can probably go way farther into this than I can, but one variable is the supercharger in question. There are 144 and 240 cubic inch superchargers, then there are 4-71, 6-71, 8-71, etc and each of them have more cubic inches. Somehow all that comes into play, but I'm not sure exactly how. It may be as simple as the 144 on top of our engine would be equal to a 649 cubic inch engine, dunno for sure, but that's always been my assumption. This may (probably is) different for the centrifical blowers too, I've only ever had roots blowers.

Basically, I'm babbling about something I know nothing about...as usual...

 

[Django]

Basically, I'm babbling about something I know nothing about...as usual...

Steve,

(Sh-h-h-h-h-h-h-h-h-h-h.......!!... I do that all the time........don't tell, ok.?)

SD

 

[fun2xlr8]

I can give you a good answer for your question. There are waaaaay too many variables. Think of adding the supercharger just like adding a bigger cam. A larger cam, just like a blower or turbo will affect your engine differently based on many variables. The biggest variables are the size of your engine and the size of the cam or blower. But many, many other, smaller details also contribute to the overall volume of air and fuel pushed into the engine. Some variable are easy to measure like valve sizes, lift, duration, fuel type, etc, but other variables like head flow numbers are signifigantly more difficult if not impossible to measure on a motor without tearing it completely down. So, in conclusion, asking if there is a way to calculate a cubic inch increase based on a blower size is sorta like asking if you can do the same thing based on a cam size. They both enable a motor to gulp more air and fuel, allowing it to run more efficiently and make greater power, but there is no across the board calculation to be had.
Think of this, an NHRA Top Fuel car makes 6000 horsepower using a 500 cubic inch engine and an 8-71 style blower. If you found a way to add an 8-71 blower to the top of one of our 500 cubic inch V-10 motors, the outcome would be significantly different. That is because off the multitude of differences(the variables) between our motors and the Top Fuel monsters. Same blower, same cubic inch size, no easy calculation.

Greg

 

[Wifey]

I can give you a good answer for your question. There are waaaaay too many variables. Think of adding the supercharger just like adding a bigger cam. A larger cam, just like a blower or turbo will affect your engine differently based on many variables. The biggest variables are the size of your engine and the size of the cam or blower. But many, many other, smaller details also contribute to the overall volume of air and fuel pushed into the engine. Some variable are easy to measure like valve sizes, lift, duration, fuel type, etc, but other variables like head flow numbers are signifigantly more difficult if not impossible to measure on a motor without tearing it completely down. So, in conclusion, asking if there is a way to calculate a cubic inch increase based on a blower size is sorta like asking if you can do the same thing based on a cam size. They both enable a motor to gulp more air and fuel, allowing it to run more efficiently and make greater power, but there is no across the board calculation to be had.
Think of this, an NHRA Top Fuel car makes 6000 horsepower using a 500 cubic inch engine and an 8-71 style blower. If you found a way to add an 8-71 blower to the top of one of our 500 cubic inch V-10 motors, the outcome would be significantly different. That is because off the multitude of differences(the variables) between our motors and the Top Fuel monsters. Same blower, same cubic inch size, no easy calculation.

Greg

Wow, sound familiar Kevin :dontknow: - I think I heard Jerry saying something verrrrrrrry similar to this last night.... - or do you remember :rock:

 

[fun2xlr8]

Wow, sound familiar Kevin :dontknow: - I think I heard Jerry saying something verrrrrrrry similar to this last night.... - or do you remember :rock:

That's funny. I swear I didn't copy. Which post was it? Gimme a link, please, I wanna see.

Greg

 

[Wifey]

That's funny. I swear I didn't copy. Which post was it? Gimme a link, please, I wanna see.

Greg

It was a verbal post via telephone - sorry, no link. It is actually hilarious, because when I read your post I had to notice the similarity in Jerry's explanation and your written version :rock:

 

[fun2xlr8]

ok, LOL. Didn't want anyone to think I was just some idiot copying someone's well thought explanation...as sometimes some poeple tend to do.

Greg

 

[Silverback]

Sorry I missed this one yesterday.

Actually Greg has given a pretty good answer. There are so many variables that a simple conversion does not exist to my knowledge.

Here is one example that usually confuses people. Take two engines of the same displacement, say 350 cubic inches. Both are boosted in some way. If one has a static compression ratio of 10 to 1 and is running a lower boost pressure, and the other has a static compression ratio of 7 to 1 and is running a higher boost pressure, but they both have equal cylinder pressures, the 7 to 1 engine will generate more HP as it has more Air/Fuel mixture in the cylinders.

Then you can get into cams, heads, headers, ...... Well you get the idea. No easy answer for this one.

Sorry.

 

[fun2xlr8]

Sorry I missed this one yesterday.

Actually Greg has given a pretty good answer. There are so many variables that a simple conversion does not exist to my knowledge.

Here is one example that usually confuses people. Take two engines of the same displacement, say 350 cubic inches. Both are boosted in some way. If one has a static compression ratio of 10 to 1 and is running a lower boost pressure, and the other has a static compression ratio of 7 to 1 and is running a higher boost pressure, but they both have equal cylinder pressures, the 7 to 1 engine will generate more HP as it has more Air/Fuel mixture in the cylinders.

Then you can get into cams, heads, headers, ...... Well you get the idea. No easy answer for this one.

Sorry.

Ok, you are right, now I AM confused my hairy friend. Just kidding. And, assuming both motors are identicle(not really possible) in every way except for the compresion ratio. Your theoreticle 7 over 1 is going to have a far more efficient and complete intake charge burn, thus making signifigantly more power due the shape of the charge when compressed. The lower compression cylinder will yield a much more round shape due to the recess in the top of the piston and the larger head chamber volume, whereas the higher compression motor will likely have a flat-top piston with nothing more than valve reliefs and a similarly flat or kidney shaped head. And that is an example of just one small variable that has a profound effect on all other parts of two otherwise identicle motors, thus making them both act completely different. So the answer when even comparing two identicle motors with as few variables as possible changed is still....."no easy explanation". That the beauty of the engine dynomometer!!!!!


Greg

 

[Wifey]

ok, LOL. Didn't want anyone to think I was just some idiot copying someone's well thought explanation...as sometimes some poeple tend to do.

Greg

They will think you are just some idiot anyways (iffen they take a notion)...

Jerry does not type, but he can sure explain ............

 

[TnVTX]

My memory ain't what it used to be...
but, if'n I remember right, when I had my Buick Turbo-T Type, it was ~30hp gain for every additional lb of boost....if'n I recollect right...