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Exhaust Question.

  
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Exhaust Question.

 
coppingers coppingers
New User | Posts: 4 | Joined: 06/14
Posted: 06/11/14
10:41 PM

What I've got is exhaust boost related question centered around a roots blower. I know of the advantages of or turbos, centrifugal s, but I'm centered around the roots..

In my crazy world to understanding boost: There a 3 sides of boost..
1) Pressure in the intake manifold
2) Pressure in the cylinder
3) Pressure in the exhaust manifold

Cylinder is the only area where control is beyond physical abilities. Example pressure cylinder of 10# is just that how to change it open any valves (intake/exhaust) and now you're referencing intake/exhaust manifolds..

Concerning intake manifolds with a roots blower, hard to control but generally there is none because it's part of the roots design.

Whats left is the exhaust: I view this as fast as you can get it out the better. I believe the larger the exhaust primary to the collector the better..

What is your thoughts?  

wayne712222 wayne712222
User | Posts: 121 | Joined: 10/13
Posted: 06/12/14
09:04 AM

wow... and i don't know if i can get you a DECENT answer..  

#1.   pressure in the intake manifold.. with a roots type supercharger..

pressure is adjustable.. with drive sprocket ratio changes..  also with other things like rotor to case clearances. some of the newer designs actually have a bypass valve that opens to bypass the supercharger somehow.. i know the ford superchargers had something like this.. i have not really studied how it worked..  probably does not apply to anything you are doing..

#2.. pressure in the cylinder.. has to do with #1 , cam grind selection and cam/crank phasing. and if you have adjustable valve timing on your engine..

#3. lets blow this out the tail pipe..

a whole bunch of stuff here.. max operating RPM. and how often are you going to be operating the engine anywhere near there..  or is this going to be a street cruiser motor that needs to operate at 900 rpms to 3500 with a few seconds of higher engine speeds for passing and removing tread depth from the rear tires.

if you are going to be operating the engine at wide open throttle for an 1/8 or a 1/4 mile at a time..  or even land speed racing operation where you will be at part throttle but slowly increasing over the mile or more to wide open throttle.. you will want a big primary tube diameter.. and big collector..

if you are going to street drive this..  you will want something slightly less.. than max size..  what size you actually end up with also depends on 1 and 2..

cylinder scavenging is one thing the primary size to collector size and shape come into effect..  if you have over sized primary and collectors.. you may not have enough scavenging effect and might even get into the brraaapppp.. of reversion pulses slamming into the next exhaust event..    you might want to look into some anti version devices. but with a roots type supercharger?? are they going to help or hurt..

you may want to dive into one of the books listed here..

http://books.google.com.au/books/about/The_Scientific_Design_of_Exhaust_and_Int.html?id=oIZTAAAAMAAJ&redir_esc=y

here are some other ways around the world.


Megaphonebaffle Zpsfd73fcaa

Passive Anti Reversion Chamber Zps6eee70cf

Antireversioninserts Zpsf2256d28

and these are aircraft versions.. for P51 large scale flying replicas

Mustangaircraftantireversionexhaust Zpsdd762fbb

burns stainless and others create merge collectors to speed up the exhaust flow thru the collector to increase scavenging.. recall that at higher speeds there is still expanding flame in these pinched areas..

Kiwienginneringxk120exhaust Zpsf97257e6 1

here is something i drew up for a friend with a non boosted hot honda..

his exhaust was way raspy.. like somebody pounding on a really big tin can that had tears in the surface..  

016060A4 B4d9 4F15 Bd08 64E547dace6a Zps07f8bae4

i ask him to have several sizes and lengths made up..  the first one he tried he picked up 10 Horsepower increasing from 265 to 275 with that one change.. and it no longer sounds like a raspy honda.. it sounds like a healthy big block chevy now..  

coppingers coppingers
New User | Posts: 4 | Joined: 06/14
Posted: 06/17/14
07:55 PM

First Thanks !! This information is always good to know.. Future builds ect..

May I ask a question:
Since I'm centering around a roost blower..  Isn't low end torque what these types of superchargers are known for ?  Is there ever anything as too much torque being the trouble ?  

coppingers coppingers
New User | Posts: 4 | Joined: 06/14
Posted: 06/17/14
07:55 PM

First Thanks !! This information is always good to know.. Future builds ect..

May I ask a question:
Since I'm centering around a roost blower..  Isn't low end torque what these types of superchargers are known for ?  Is there ever anything as too much torque being the trouble ?  

wayne712222 wayne712222
User | Posts: 121 | Joined: 10/13
Posted: 06/17/14
10:38 PM

roots type of super chargers were designed to operate on LOW RPM diesel engines..  where they might max out the RPMs at 2300 RPM..  power range from 1500 to 2300.. perhaps not even that high..

there are so many variables and i am not a super charged engine specialist..

type in supercharger or supercharged into the search window above right.. see what you find.. you will want to pull down  the new search window in the middle to allow you to search all the magazines..  click the PHOTOs tab off to the right.. it will narrow down some of the search results so you can page thru looking for super charged motor builds.

one thing..  carbs sitting ontop of a super charger need to be either modified.. or ordered as special super charger carbs..  as the power valve will be hooked up to the intake manifold pressure instead of the top of the blower..  you will also want to monitor this vacuum connection with a vacuum/boost gauge.. so you know what vacuum the power valves are being exposed to.  

coppingers coppingers
New User | Posts: 4 | Joined: 06/14
Posted: 06/18/14
06:24 AM

Cool -Thanks I'll will head off in this direction. Carburetors and fuel injection has come along way since I've started this project (2004).

Technology has caught me in a good way.. I've got the new F.A.S.T. 2.0 throttle body that flows for 1200hp N/A with a XFI 2.0 ECU - CompCams (FAST) provided a solution that will work along with their distributor and the new (CraneCams venture) spark box..  

Anyway I'm hoping Car Craft will do another test of similar before I get on the road, the magazine provides a lot of good starting tips and steps.