OzVMX Forum

Clubroom => Tech Talk => Topic started by: shelpi on February 14, 2012, 05:25:24 pm

Title: Expansion chamber design
Post by: shelpi on February 14, 2012, 05:25:24 pm

Hi, i want to make a set of chambers for a suzuki T series Pre 68 motocross out fit/ sidecar, can you please help with the design for a good set of chambers that gives lots of power over all rpm range's :o would like to be able to calculate length and diameter of the header, divergent cone, belly , convergent cone and stinger muffler  :) have sheet metal roller and Blairs formula but im not real brite with maths  :'( .
 but can lift heavy things. cheers

Title: Re: Expansion chamber design
Post by: lukeb1961 on February 14, 2012, 09:05:29 pm

get this http://www.iwt.com.au/mota.htm

Title: Re: Expansion chamber design
Post by: Lozza on February 14, 2012, 09:28:26 pm

Quote from: shelpi on February 14, 2012, 05:25:24 pm

can you please help with the design for a good set of chambers that gives lots of power over all rpm range's :o would like to be able to calculate length and diameter of the header, divergent cone, belly , convergent cone and stinger muffler  :) have sheet metal roller and Blairs formula but im not real brite with maths  :'( .
 but can lift heavy things. cheers

Don't we all and how heavy is your wallet  ;D
Some advice the first 5 pipes will be complete shit, then start to improve about the 10th pipe will be pretty good. At that stage you will have spend 8 to 10 times the amount you could have bought one for. Blair's formula is complete crap anyway, there are many cheap online pipe calculators that will give very poor results.
Failing that you stump up and purchase MOTA which is an engine simulator.

Title: Re: Expansion chamber design
Post by: Curly3 on February 14, 2012, 09:35:44 pm

I read on with interest because I want to build my own set of Chambers for a T20 Flattracker.

Title: Re: Expansion chamber design
Post by: Freakshow on February 14, 2012, 10:13:13 pm

Pete come see me at Ians, or we can suss out the ones on the speedway T500.  you will need to figure out how much space you have to work with and suss all that out first.  Some times the perfect pipe is 2 m long, that wont happen so you have to adjust sizes and shapes to keep it in context and working.  you also need to figure out where you want your power spread.

Title: Re: Expansion chamber design
Post by: cyclegod on February 14, 2012, 11:21:55 pm

Quote from: SlideRulz on February 14, 2012, 09:35:44 pm

I read on with interest because I want to build my own set of Chambers for a T20 Flattracker.

You can buy a kit here...

http://www.swarbrick-racing.co.uk/early.php

Title: Re: Expansion chamber design
Post by: shelpi on February 16, 2012, 11:31:11 am

Hi, thanks everyone, Kerry that will be grate  ;), the motor im useing is a T20 with T350 pistons and carbs  ::), i spoke to T Otto and the brainy act came up with some impressive ideas  8), so far me knows there is a 1500 rpm power range that starts at approx 6000 rpm and acceptable torque curve starts at 5000 rpm, and all dead before 5000 rpm  :'(, so im going for a mid range power setting  :-\  so for mid range short fat chamber and for top end long and skinny  ??? apparently the first divergent cone length and diameter is where max performance carictor change occurs and if you raise the exhaust port you will move the powerband to higher rpm's, those pressure waves are makeing me crazy  :P so what diameter and length should they all be (cones)  ??? hopefully we will be able to ascertain a simple, cheap a accurate way to calculate chambers for pre reed valve donks and layman's like me, expansion chambers for dummies.
please keep all information comeing, the biiterness of poor quality remains long after the sweetness of low price.

Title: Re: Expansion chamber design
Post by: Freakshow on February 16, 2012, 01:33:39 pm

GEt me the port timings of the barrel and i can get ian to shove em in the Computer and print out the cones for you onto paper.  trace the cones and weld away ....  failing that Thurday nights at the shop im usually down there and we can ask then.

Title: Re: Expansion chamber design
Post by: shelpi on February 16, 2012, 04:00:37 pm

 ;D thanks Freaky, have sent ya a email,  ;)

Title: Re: Expansion chamber design
Post by: Freakshow on February 16, 2012, 05:07:27 pm

Stupid Question but is there any reason for using a 250cc and not a T500cc ? seems a bit small for an Outfit to scamble ?

Title: Re: Expansion chamber design
Post by: Lozza on February 16, 2012, 07:05:17 pm

The program Ian uses is here (where it says 'download here')
http://www.iwt.com.au/MOTA.HTM

Title: Re: Expansion chamber design
Post by: mike1948 on February 17, 2012, 12:29:35 pm

Know of any people in the Brisbane area who can make up an expansion chamber, if I supply the dimensions?
Any recomendations pls?

Title: Re: Expansion chamber design
Post by: shelpi on February 17, 2012, 06:45:57 pm

thanks mucho grassy, correct me if Iam wrong but  the T500 can only qualify for pre75 not pre 68  ??? plus me only has a T20 with T350 piston and carbies, but if I am wrong  :-\ has anybody got a T500 donk they want to throw my way  :-*

Title: Re: Expansion chamber design
Post by: shelpi on February 17, 2012, 06:56:53 pm

thanks lozza spoke to the guy that has MOTA but the engine mechanical and port data is not on the program so back to square one.

thanks mike1948, I can make chambers but am to simple to do calculations so it has bin recommended tostart with RD400 chambers see what the performance charictures are in real time and start fiddleing, these chamber's are makeing me thirsty