Boost question

[hacim]

What is the relation in boost to compresion? How many pounds of boost causes the compresion in the motor to rise?

Heres an example: If the compresion in the motor without a turbo is 9.8-1 and then you add 10 lbs of boost what does the compresion sit at with that much boost. Just curious and I dont know a whole lot about this so if I made myself look like an idiot dont flame me to bad.

[cbecker333]

Originally posted by hacim
What is the relation in boost to compresion? How many pounds of boost causes the compresion in the motor to rise?

Heres an example: If the compresion in the motor without a turbo is 9.8-1 and then you add 10 lbs of boost what does the compresion sit at with that much boost. Just curious and I dont know a whole lot about this so if I made myself look like an idiot dont flame me to bad.

You stupid idiot....j/k - I am also dumb somebody give us a detailed description or a link to a site. Thanks in advance.

[swampdonkey]

heheh I honestly can't remember...but I think since atmosphereic preasure is 14.can't rememberPSI then your static compression should be 9.8xatomphereic. SO for boost it seems you should add the LBs of boost to atmospheric and then calculate static compression.

Like this:

(10PSI+14PSI)9.8= Static compression+boost

Not certain though

[swampdonkey]

I'm going to give you a more detailed answer because my first one was kind of bad.

Atmospheric preassure= 14.7PSI (pounds per sqaure inch)

When calculating boost manifold preasure is messure in differance from atmosphereic preassure as I'm sure you already know.

For example:
When you run 10lbs of boost you have a manifold preasure of 24.7, but it is never thought of that way because we "zero" boost at 14.7. So thats why I made it a point to say boost is messured in terms of difference from absolute preassure.

Static Compression is the actually PSI inside the cylinder a TDC (top dead center)

It is calculated like this

9.8:1 is a ratio we know that each unit (1) is being compressed 9.8 times over. A unit being a full cylinder of air. We know that air was drawn in and it was at 14.7PSI becasue that is atmospheric preassure. So 14.7x9.8= 144.06 PSI is your compression at top dead center. (static compression)

To calculate boost simply add the amount of boost to atmosphereic preassure

24.7x9.8 =242.06

So static compression + boost is 242.06PSI at top dead center

[02SilverSiHB]

Originally posted by swampdonkey
I'm going to give you a more detailed answer because my first one was kind of bad.

Atmospheric preassure= 14.7PSI (pounds per sqaure inch)

When calculating boost manifold preasure is messure in differance from atmosphereic preassure as I'm sure you already know.

For example:
When you run 10lbs of boost you have a manifold preasure of 24.7, but it is never thought of that way because we "zero" boost at 14.7. So thats why I made it a point to say boost is messured in terms of difference from absolute preassure.

Static Compression is the actually PSI inside the cylinder a TDC (top dead center)

It is calculated like this

9.8:1 is a ratio we know that each unit (1) is being compressed 9.8 times over. A unit being a full cylinder of air. We know that air was drawn in and it was at 14.7PSI becasue that is atmospheric preassure. So 14.7x9.8= 144.06 PSI is your compression at top dead center. (static compression)

To calculate boost simply add the amount of boost to atmosphereic preassure

24.7x9.8 =242.06

So static compression + boost is 242.06PSI at top dead center

I was just going to say that :D

[hacim]

I understand your formula but what I really want to know is the actual compresion ratio after 10 lbs of boost has been added not the PSI. 9.8-1 plus 10 lkbs of boost equals what for the compresion ratio?

[cbecker333]

Originally posted by hacim
I understand your formula but what I really want to know is the actual compresion ratio after 10 lbs of boost has been added not the PSI. 9.8-1 plus 10 lkbs of boost equals what for the compresion ratio?

There's no change in the compression ratio, is I think what he implied - 9.8 is the factor in both equations. The cylinder still has a volume 9.8 times the volume when fully compressed. You are just starting with more pressure, before compression. That, of course means more pressure @ TDC (242 vs. 144).

[swampdonkey]

yeah the compression ratio doesn't change because the cylinders volume is still being compressed 9.8 times. If you really wanted to liken it to another compression ratio that ratio would be 16.46:1. It would be all but impossible to build a engine with compression that high. I'm not saying it couldn't be done, but it couldn't be done by one of us. Increased compression causes more tensil stress than turbocharging and is actually much harder on the engine for reasons I either don't know or have forgotten.

[95 GSR]

The most compression i've ever heard of was 16:1 on the fastest all motor crx one year ago. You might remember it , it was orange with a blue front end. But i read in a mag, a year ago, that he was running 16:1 compression ( all motor). He was doin high 10s then.

also the only sohc (all motor) crx in 10 sec club, from what i read, has 15:1 compression.

[Tekdemon]

heheheh this is the reason I like the Si over the Type-R....boosting with our lower compression ratio makes our engines more boostable =)

They probably can't run over 5 psi without serious modding to the engine while we can run a wee bit more =)

[95 GSR]

yup.. GSRs with 10:1 compression can run up to 10 psi w/o any danage. 02 SI, with 9.8, u can do 10 psi easy...
To bad for the Type R.

[hacim]

So if our motor can handle 10 lbs of boost on the stock internals then how much boost do you think you can run on the K20A2 connecting rods, head and crank. Remember the K20A2 has a 11.1-1 compression ratio. Does that mean a motor like ours with that stuff on it can obtain lets say another 5 lbs of boost without worry?

[95 GSR]

goin turbo for just 5 lbs of boost, i just dont see the piont... but sure 5lbs on a k20a2 sounds right. Most I've seen on a 98 type R is 7 lbs(race) 4lbs(street), with stock internals.

[Tekdemon]

I think he's asking if we swap in K20A2 parts into our K20A3's whether we could run 15 psi of boost(5 more than 10).

My own guess is no, since if you swap in all those parts(the head and rods and crank) you'd have just raised the compression ratio to exactly that of the K20A2 and thus you would logically be capped just like the K20A2.

For boosting the K20A3 is better since it has a lower compression ratio to start with...which makes it slower NA but once you boost you can boost more hehehe

[95 GSR]

compression wont raise if u dont change the pistons.

i dont know how stronge RSX rods are and how much hp can hold up. But even if u change to RSX, u still got to worry about your valves. U dont want to bend a valve by boosting too much