Chaps,

I'm going to make my own manifolds / downpipes etc as space dictates some odd shapes.

Anyone have any recommendations as to what tube diameter I should use of downpipes/collectors etc. I'm thinking of 1.5" for d/pipes and 2.5" from collectors to silencers.

Thanks very much

Simon

To be honest, unless you are worried about the last 'nth of performance, any sensibly designed manifold will probably out-perform a standard cast jobbie. It's hard to give recommendations on pipe sizes/lengths, really we would need to know type of engine, cc, state of tune etc, etc, and even then it would only be a guesstimate, as small differences in design can make big changes to power characteristics. The only tip that may be worth bearing in mind is that it is good practise to try and get all the manifold pipe lengths the same. This will make the engine a lot easier to set up for fueling and ignition timing requirements.

Stu,

Engine is a standard Rover V8 (from a P6), but (one day!!) may swap cam / carbs.

Appreciate about pipe lengths being equal.

Going by OE manifold, I reckon Primaries of (as little as) 1"/1.25" dia would be OK, given that gasflow will be improved. Holes in manifold are only about that big, just square - will have to measure ce soir to confirm.

Want to run 2" system down both sides of car, through something like Cherry Bombs.

ATB

Simon

Are you going to use ready-made flanges, pipes, bends etc from Demon Tweeks etc? If so, that will dictate the size of the pipes. As you say, no point in having the manifold pipes any bigger than the exhaust ports

John

Simon, from what you describe your system plans sound good. It can be beneficial to go slightly bigger on the manifold compared to the ports for a couple of reasons. Firstly, it creates a step, which doesnt affect flow of gas from the engine any discernable amount, but what it does do is prevent reverse flow, and may increase bottom end power slightly, especially with a higher lift cam with large overlap. The other point is if you do decide that the head could do with porting, then the exhaust is already sized up!

HTH Stu.

Simon: If you're not planning on tuning the old P6 lump at present, a fair bit of gain can be had from a decent exhaust system on the standard motor. I've built quite a few systems for the Rover engine, standard, and in various states of tune (see my mid-engined Beetle photos in the Photos section under Rorty).
Standard diameter or smaller primaries (generally speaking) will give more torque, but as the Locost is a light car, you needn't worry about that.
I would aim for a 4-2-1 system, as it will give improved bottom and mid range, and combined with 1 1/2" primaries, will give a healthy top end too.
The Rover heads are reknowned for being asthmatic, and there isn't an awfull lot you can do with them (they can be ported to some degree, and there are aftermarket heads with better designed ports and leaders).
I would make the primaries about 900mm long (longer will increase lower rpm power, which isn't necessary if you stick to 4-2-1, and shorter than 900 will increase the higher rpm power).
The secondaries would be best at about 300 long X 1 7/8" diameter, finishing in 2 1/4" tube for the rest of the system. Cherry Bombs or similar will be fine too.
One more sleep!

heres what you want:
http://www.billzilla.org/engexhaust.htm

written buy an aussie whos done a bit of racing in his time. knows his stuff. look around the rest of his site in the cars and tech section....... itll make you want to power your locost with a 4age engine, he loves it and shows why.

John,

Had a look at DT site. Is it my imagination or does the link to the online catalogue not work. Just get taken to catalogue order form!!

Was intending to buy some tube and sheet, and make whole lot myself (using flanges from original manifolds or make). If DT prices for flanges etc are similar to Custom Chrome, it'll be cheaper to buy a tube bender!!

Stu, correct me if I misunderstood, but by deliberately leaving in a step (ie by welding round tube to the original flanges (with "square holes"), I'll be doing myself a favour - less work for me, and the benefits you describe.

Rorty, four metres of tubing within my engine compartment (each side) should be fun to do. Tech question following a read from Finlays suggested site concerning the 4-2-1. Which ports to pair off?

Re space - appreciate that paired primaries will link in engine bay, will need both to exit bay before joining secondaries!

Last (?) question. Any recommended tube gauge - 18/20swg or thinner

Thanks for your help/suggestions, chaps

ATB

Simon

Yep, seems too easy dunnit? But the step is the right way round, i.e. small to big, so exhaust flow will not be impaired too a measurable degree.

Hi Simon

I work for a tube bending company making exhaust pipes etc, If you get stuck for tube/bends give me a shout.

Billy,

Thanks for the offer - will be worth remembering.

Have a good one.

ATB

Simon