×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

supercharger relativity?

supercharger relativity?

supercharger relativity?

(OP)
If you take a large supercharged engine and make it smaller, but all other components remain the same(heads, supercharger,etc), will the reduction in power be relative to a n.a. engine? Or because of the constant displacement supercharger, will the increase in cylinder pressure compensate for the lack of cubes?

RE: supercharger relativity?

In theory the increase in cylinder pressure will compensate, as the same mass of air is being pumped if it is truely a 100% efficient positive displacement pump, but as the smaller engine will accept less volume of air at the same rpm, the manifold pressure will go up, which will cause more leakage past the blower, so a little less air (depending on clearances) will be pumped.

Presumeing it's a Roots blower, the air leaking past the rotors will be heated by shear, and by conduction from the rotors which will be heated by friction, so the new charge will contain some preheated air as well as ambient, further increasing pressure and/or reducing density.

Also, to pump the same mass of air to a higher pressure will absorb more power to drive the blower, so the sacrificial losses will increase.

On the other end, depending on how you changed the capacity, piston speeds might be reduced, so there might be less losses in the inertia of the reciprocating parts, and less drag from the rings. If the bore is decreased, the rings will be shorter and the pistons lighter again, thereby also reducung inertia and friction.

Bottom line, it's a whole lot of compromises, and all we can do is try to pick the optimum compromise. The  knowledge gained by observing successfull examples is a good guide as to how the various pros and cons ballance out

 

Regards
pat

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources