well I know that u should get low comp pistions for forced induction cause ur pushing so much air in and u dont wanna blow the engine w/ too much comp, right? well if u have an N/A motor with really high comp, isnt that the same thing?????????

 

Yes.

There's only so much you can compress the mixture before it blows up uncontrollably. If you've got 11:1 compression, it might be fine NA although right on the edge. If you then boost this engine 14psi, your end compression will be 22:1. That's over the edge.


[Modified by Lsos, 2:58 PM 12/26/2002]

 

so why do peope turbo when all u have to do is get better compression and if u get that, there is no lag to deal with

 

By bumping up compression you can at most gain about a 10% increase in power before pump gas gives up.

By turbocharging, 50% increases are the norm, 100% aren't uncommon, and I've heard of 500%+

 

also the lower the compression, the more space there is for air and fuel to mix. Think of it as more air space for the combustion to take place, resulting in more ammounts of combustion........

 

I'll give a little bit on why one turbo's an engine. To a first order, not accounting for pumping losses the number of air molecules in the cylinder is proportional to (Pressure in the cylinder in absolute units like PSIA * Volume of the cylinder)/(R the gas constant 53.3 for english units * Temperature in degrees Rankine [degrees F + 460])

or in equation: n=PV/(RT)

If I boost by 1 bar or 1 atm, P doubles from 14.7 psia to about 29.4 psia so I have double the air and hence double the oxygen in that cylinder. That allows me to throw in double the fuel! More fuel, more BTU's, more cylinder pressure. More cylinder pressure more torque!

You can also see why one wants to intercool to reduce the charge temperature or part of what you gain in pressure you loose in temperature effects.

There is much more to the thermodynamics that I won't go into, but this gives you a little thumbnail of why boost increases the density of the air charge to generate more torque when adequately fueled.

Regards,
BigMoose

the usual disclaimer....bla bla air isn't a perfect gas, its a mixture ...... etc. etc.

 

just out of curiousity, how did you determine that, and how would someone make it possible to run 10:1 compression with 18 psi, some guy at vertex motorsports told me he was doing that but it sounds a little wack to me...

 

[/QUOTE]just out of curiousity, how did you determine that, and how would someone make it possible to run 10:1 compression with 18 psi, some guy at vertex motorsports told me he was doing that but it sounds a little wack to me...[/QUOTE]

its possible. extremely high et or exhaust temperatures. it all depends on how strong the internals and sleeves are. if he works at a motorsports company he most likely has resleaved the block to be able to acheive that amount of boost

 

You can retard the timing to keep from detonating. You lose power this way though.

This statement doesn't really hold much water. The higher the compression, the more efficient the combustion process (that's why diesels are more efficient than gasoline engines). The lower the compression, generally the crappier the combustion. Giving air and fuel "space to mix" isn't really going to help anything.

 

you can make high compression turbo setups with proper tuning