In any intake system there are two main conditions you are dealing with, resonant frequency changes of the inlet tract under a wide range of engine speeds and the inertia of the gas column in the inlet tract. Air has weight!
For every positive increase in cylinder pressure from wave motion there will be a corresponding decrease at some other rpm. Nothing is free in pulse tuning you will usually encounter two major positive and two negative pressure harmonics if running up to 8000 rpm depending on camshaft timing. If you tried for a node at the choke this would be fine on a single speed engine but as our engines are required to work over a wide range this node position would be constantly changing. On the dyno last week, we tried back to back ramp ups of different length ram tubes and all had noticeably different performance curves. The best length was a surprise to me and the dyno operator as it worked well at low engine speeds and also at high engine speeds. In the middle it had enough inertia to overcome the negative pulse created and increased air fuel ratio, that was so noticeable with the shortest ram tubes. To do any meaningful work on ram tube lengths, you need to consider the cylinder head as a system. Inlet, Camshaft and Exhaust all parts of that system. During the cam overlap period the negative wave produced by the slug of exhaust gases has an effect on the tuned desirable tuned length as well. The majority of benefits from longer ram tubes do not come from pulse tuning. Rather the main benefit is from the inertia of the column of gas that is contained in the system. This slug of gas is moving at approx 100 m/sec at WOT. This column should be at least 1.2 times the volume of the cylinder being fed by the inlet tract so a complete cylinder fill is always fully contained in the tract or mixture stand off can occur at WOT and the mixture gets diluted and dissipated over the inner guard etc and larger jets have to be used to compensate for the screw up in the pulses. There is considerable benefit to be had from port shaping to create a vortex in the throat area just before the valve and by directing the charge into the cylinder to help cylinder filling Its worth noting that you have approximately 4 milli-seconds to fill the cylinder at 8000 rpm My 20 cents worth of opinion. Cheers, Feral Errol Get Serious tm<http://www.datrats.com.au/> -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Robert Charles Scealy Sent: Wednesday, June 25, 2003 4:26 PM To: [EMAIL PROTECTED] Subject: Re: 40mm weber ram tubes Maybe you could get some difference if you made the distance from the port to the choke equal to the tuned length from the choke to the bellmouth exit, then you would have some chance of setting up a harmonic standing wave, with a node at the choke? Like if you pick a guitar string, and then place your finger over the exact centre of the string, you still get some of the sound? On Wed, 25 Jun 2003, David Andrews wrote: > Guys, what you are talking about is the RAM effect which occurs as > follows: > > When the intake valve opens, an expansion wave travels up the intake > runner. When it reaches THE FIRST JUNCTION, it is reflected back as a > compression wave. The RAM effect is using the compression wave to > compress the air into the cylinder just as the intake valve closes again. > It is apparently possible to achieve Volumetric Efficiencies above 100% > (for a specific rev range obviously). > What Kris said was correct, longer is for low end, shorter is for top > end: > > http://www.grapeaperacing.com/GrapeApeRacing/tech/intaketuned.cfm > > But if you actually plus the numbers in, you're not talking 1.5 inches. > You're talking more like 15 inches. The link above has some formulas for > working it out. But the important thing to note is that it won't make > fuck all difference on a car with carbies because the first junction > (where the reflection happens) is at the `out' side of the carby, not the > inlet side. > > However, using bellmouth shapes does increase the airflow into the carby > by reducing the turbulence around the opening. But the length of this > will have a negilible impact on the overall VE of the engine. > Regards, > > Dave > > > >>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<< > > On 25/06/03, 14:31:24, Richard Webb <[EMAIL PROTECTED]> wrote > regarding Re: 40mm weber ram tubes: > > > > I found a pic of some on that race car that someone sent to the list > > recently.... > > > http://www.race-cars.com/carsales/other/1054143781/1054143781ph.jpg > > > They are tiny?? and the eggcups wouldnt need any extending.. I guess > > they are after high end. Isnt there a stainless bowl or cup or > > something I can modify... :) > > > ----- Original Message ----- > > From: "Kristian Walsham" > > Date: Wednesday, June 25, 2003 2:09 pm > > Subject: Re: 40mm weber ram tubes > > > > A long one will better suit low to midrange torque and power while > > > a short > > > one will produce more mid to top end. > > > I think most short ones are about 1.5 inches long while longer > > > ones are > > > about 2-2.5 inches long. You would have to design it around engine > > > bay space > > > and the type of cam you are using. > > > > > > Kris. > > > ----- Original Message ----- > > > From: "Richard Webb" > > > To: > > > Sent: Wednesday, June 25, 2003 1:48 PM > > > Subject: Re: 40mm weber ram tubes > > > > > > > > > > I know this has been discussed before but how long (idealy) > > > should the > > > > ram tubes be? Also how the hell do you join stainless steal? The > > > > article says use tig welder... or hose clamp? Any ideas, because > > > I dont > > > > have a welder... > > > > > > > > ----- Original Message ----- > > > > From: David Andrews > > > > Date: Wednesday, June 25, 2003 1:21 pm > > > > Subject: Re: 40mm weber ram tubes > > > > > > > > > If twas me: i'd be going from 47 (45 by moi) down to the 40 > > > with a > > > > > nice > > > > > cone rolled up by your local stainless shop. I'm doing the same > > > > > thing, > > > > > albeit longer, for my custom intake manifold. > > > > > > > > > > Dave > > > > > > > > > > >>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<< > > > > > > > > > > On 25/06/03, 15:36:55, Richard Webb wrote > > > > > regarding Re: 40mm weber ram tubes: > > > > > > > > > > > > > > > > Yeah just got the article, 47mm diamater isnt going to work too > > > > > well on > > > > > 40mm > > > > > > webbers. I'll have a look with one of them see what I can make. > > > > > > > > > > > I dunno how that Jullian Edgar guy comes up with 1/2 that > > > > > stuff.... hes a > > > > > > total car nerd :) > > > > > > ----- Original Message ----- > > > > > > From: "E Smith" > > > > > > To: > > > > > > Sent: Tuesday, June 24, 2003 5:11 AM > > > > > > Subject: RE: 40mm weber ram tubes > > > > > > > > > > > > > > > > Dave, > > > > > > Youve been reading Autospeed :-) > > > > > > > > > > > Cheers, > > > > > > Feral Errol > > > > > > Get Serious tm<" target="l">" > > > target="l">http://www.datrats.com.au/>> > > > > > > > > > > > > > > > > > -----Original Message----- > > > > > > From: [EMAIL PROTECTED] > > > > > > [mailto:[EMAIL PROTECTED] Behalf Of David > > > > > Andrews> Sent: Tuesday, June 24, 2003 2:42 PM > > > > > > To: [EMAIL PROTECTED] > > > > > > Subject: Re: 40mm weber ram tubes > > > > > > > > > > > > > > > > You may be able to make your own out of some egg holders from > > > > > > Safeway/Woolworths. They're $1.85 each here, perfect bellmouth > > > > > shape. ID > > > > > > of 44mm. Regards, > > > > > > > > > > > Dave > > > > > > > > > > > >>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<< > > > > > > > > > > > On 24/06/03, 14:01:59, "Kristian Walsham" wrote > > > > > > regarding Re: 40mm weber ram tubes: > > > > > > > > > > > > > > > > > You could try Four Plus Performance in Brisbane ( i don`t > > > have the > > > > > > number) , > > > > > > > or Autosport in Vermont, Datrally in Cheltenam. > > > > > > > > > > > > I know i had a few spare somewhere, i will have to look. > > > > > > > > > > > > Kris. > > > > > > > ----- Original Message ----- > > > > > > > From: "Richard Webb" > > > > > > > To: > > > > > > > Sent: Tuesday, June 24, 2003 1:39 PM > > > > > > > Subject: 40mm weber ram tubes > > > > > > > > > > > > > > > > > > Hi guys, > > > > > > > > > > > > > > > > Can anyone tell me where abouts I might be able to get some > > > > > weber ram > > > > > > > > tubes/pods/trumpets (whatever you call them). The guy at > > > > > unifilter> > > thaught he had some but doesnt anymore! Now I've > > > > > rang up a few places > > > > > > > > and they are telling me no one makes them anymore??? > > > > > > > > > > > > > > > > Im in melbourne and would be interested in any info on > > > where to > > > > > > > > purchase them. > > > > > > > > > > > > > > > > Thanks in advance, > > > > > > > > > > > > > > > > Richard > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > --membersozdat------------------------------------------------- > > > ---- > > > > > -- > > > > > OZDAT Mailing List Please Note:- > > > > > Send (un)subscribe requests to [EMAIL PROTECTED] > > > > > Send submissions to [EMAIL PROTECTED] > > > > > No unauthorised redistribution of this email > > > > > http://www.ozdat.com/ozdatonline/index.htm > > > > > http://www.ozdat.com/ozdatonline/listindex.html > > > > > http://www.mail-archive.com/[EMAIL PROTECTED]/ > > > > > --------------------------------------------------------------- > > > ---- > > > > > -- > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > --membersozdat----------------------------------------------------- > > > -- > > > OZDAT Mailing List Please Note:- > > > Send (un)subscribe requests to [EMAIL PROTECTED] > > > Send submissions to [EMAIL PROTECTED] > > > No unauthorised redistribution of this email > > > http://www.ozdat.com/ozdatonline/index.htm > > > http://www.ozdat.com/ozdatonline/listindex.html > > > http://www.mail-archive.com/[EMAIL PROTECTED]/ > > > ------------------------------------------------------------------- > > > -- > > > > > > > --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/[EMAIL PROTECTED]/ ---------------------------------------------------------------------
