1275 Exhaust Design

[chrisryder]

Greetings!

I have myself a hankering for some daft exhaust making. (well i've got some ideas floating around).

I'm studying Motorsport Engineering but we haven't done anything on exhaust design yet, not sure what the folk on here know regards ideal silencer sizes. I know tube size is complex, as a small diameter increases speed of flow, but restricts volume. and larger diameter improves flow but reduces speed making the flow more likely to change direction. I think i'd use an off the shelf LCB manifold such as the Falcon or Maniflow one so that wouldn't be an issue, and i'd have to get the front silencer the right size dependant on the outlet from the manifold. Maniflow do larger bore manifold for 1275 engines in a Minor so i'm tempted by that.

I quite like the idea/look of twin pipes out the back, always looks that little bit more awesome to me, oh and a nice noise wouldn't go a miss either.
[frame][/frame]
i've just thrown that together in Paint in a few seconds, the split would ofcourse be symetrical as opposed to offset like that. I have seen something similar on a pale yellow convertible but the split was just a hole cut in the side of the tube, with another tube welded on. can't see the flow going round that corner when it can just go straight on.

I've got plentifull access to all diameters of stainless tube and can mandrill bend most diameters too so i'm going for 'ideal design' and i'll make it as best i can after!

Can someone enlighten me as to the ideal silencer size, change in pipe diameter after the split (if it's got to change) and tell me what you've got on your minor and how well it works!

[PSL184]

I like that design. Use 1.75" dia pipe and a couple of RC40's out the back and it should be good. JLH sell all the straights and bends etc to make up your own design.... http://www.jlhmorrisminors.co.uk/store/ ... t&catId=25

[chrisryder]

will bend it myself, don't fancy welding together a million curves and straights!

silencers are tricky as they need to be short enough to get a good radius from over the back axle. They also can't be too wide as there is limited space around the fuel tank.

i may also struggle as the minor this is destined for has angle tele shocks at the back so i need to find a good route for the pipes that wont get in the way!

[MarkyB]

Do some practice welding pipe before you start in earnest, it's quite tricky to get a gas tight seal.

Also consider how much weight you will be adding, albeit low down, silencers can be quite heavy.

[chrisryder]

will be welding as little as possible really. i'd rather have joints to make it easier to fit/maintain/impove.

and i am removing weight in other areas

[hotrodder13]

i was going to do this and jst left it with one stright through silncer and no back box, what you can do is, keep it a single pipe till after the over axel bend and then stick a t piece on then go behind the fuel tank (save a few bits of pipe)

[chrisryder]

was thinking of splitting futher back that in my drawing, but was also thinking that i could have the front silencer going straight out into 2 pipes, but that would require me finding a silencer the right size with the right size twin outlets (bit of a hard task?)

i've seen the T-piece idea, but if you're suggesting you come in from the bottom of the T and go left and right to each silencer, that would be 2 nice big right angles to go through. unless i get/make a nice curvy Y type joint. that would help with the problem of my tele's getting in the way!

[cmea]

A few years ago I bought a tuned 1098 4dr with no silencers just 2 cherry bombs( reg VPR849 - I wonder if she is still around). Sounded great (a bit loud) but went absolutely fantastic (could do a ton - apparently! ). Didn't do any flow checks on it but it was a very good set up. Not sure how you would go about proving / testing the flow rate / back-pressure / performance for your set up short of using a dyno.
For your project you really need to read / refer to David Vizards "Tuning the A-series engine". A must for any A-series tweak-er . I trust that you are sorting/replacing the carb and inlet manifold as well.
JLH does some good flexi exhaust pipes / tubes for the DIY-er - this would help in some of the bends - but remember bends = in an exhaust.

[chrisryder]

I've got the good book, i've got an off the shelf setup on my 1098 minor (in my sig) which seems to flow well and sounds pretty tasty actually. it just doesnt look all that fancy (really want twin pipes ).

at my uni we have engine dynos and bench flow meters, but it's only an engine dyno not a chassis dyno, and it's a lot of work getting an engine and everything connected and sensor-ed up. doubt i would get a full exhaust system on the flow bench too!

it'd be easy to buy an off the shelf system for the 1275 engine that'll be going into my 2-door project, but i'm wanting to make that one a little more personal, and use it as a mobile CV

the midget engine i've got came with a HIF38 (think it's a 38 anyway) on a Titan heated (just incase BMC is reading this, i'll make it only heated in winter ) inlet manifold. and i'll be taking the head off as the gasket is weeping, so i'll be modding the head while it's off.

i dont mind the exhaust being loud, so long as it's only at high rpm, it's having a 5 speed (my only concession to weight!), 3.9 diff and slightly oversized wheels, so the revs should be lowish on the m'way. the best thing i have found with my off the shelf system on my 4-door is that at low revs it's nice n quiet, until you want it to be a snorter and then she wakes up!

[hotrodder13]

mines 1.3/4 with one cherry bomb and its stupidly loud on idle

[chrisryder]

get a video on facebook.... pleeeeeeeeez whenever u can hehe.

i have thought about cherry bombs, saw 2 for £25 each at a show last month...

[Mogwai]

You can just see the exhaust in my sig pic. its a twin box maniflow one consisting of two round silencers toward the rear

[chrisryder]

the maniflow system is a bit pricey but a good system apparently.

i'm looking to do something a little more individual though, anyone can buy parts off the shelf, i want to have a talking point

[hotrodder13]

i baught all my bends and made the whole system, the manifold if a lot more free flowing then a maniflow one and looks better

[chrisryder]

got a pic or two hotrodder?

[hotrodder13]

only one i got il take sum of the whole system 2moro[frame][/frame]

[ratrodmog]

the manifold if a lot more free flowing then a maniflow one and looks better

Not too sure about that dude. I was under the impression that Maniflow made the best flowing manifolds for these engines. I never did a flow test on mine before it was removed but I did polish the ports to aid the flow as well. I may be proved wrong though.

[hotrodder13]

il get a pik up of my y piece 2moro it looks so much better plus mine was more then half the price of a fully polished one

[ratrodmog]

I think you may have misunderstood mate. When I said about polishing the ports I was referring to inside the tube mouth at the head end to smooth out the welds and aid the flow of air. The easier the gasses can escape from the engine the smoother the power will be. I couldn't care less what the manifold looked like as it was wrapped in heat wrap. Out of interest who manufacture the manifold you are using and is it stainless as mine was mild steel.

[hotrodder13]

me and my dad made it and yes i did port and polish it along with the cylider head and it is stainless so i could polish it to be on show,