Could anyone give some tips on this or know of any good books/websites on exhaust design, ideally rotary specific. I want to build a custom exhaust system for my 1st gen but haven\'t got a clue where to start :xconfused
Cheers
Dom
Power flow :Giggle
Only joking. errrr I heard Camskill is good. lots of the FTO people use them for custom manifolds and down pipes. I think they have a web site if not go to FTO Owners club.
Pete.
Dom, have a search on Ausrotary.com Theres a couple of usefull ones on there + we\'ve had a few discusions in the past on here with lots of links and info. There seems to be two "schools" of thought for the N/A exhausts.
Some go with a shorter collected header which meets somewhere under the drivers legs/seat area and some seem to go uncollected all the way back to the axle with multiple silencers on each system and then into one large truck sized silencer. Its basically down to what else has been done to engine, how hard you can rev it, how loud can you get away with etc. etc. A bit of a black art and I don\'t think its easy to get it spot on the first time (close enough maybee) but with a bit of DIY\'ing and rebuilding I bet you could build a decent quiet system for bugger all. (thats what I am planning)
The main part seems to be the manifold, do not skimp on this bit, get decent quality tube thick walled tube (look at the RB kits of bits for ideas), a nice thick manifold flange and try to make sure that they don\'t have too tight a bend straight out of port (2" or more was a rule of thumb I\'d heared banded about but I reckon thats probably just a diamter and a half of pipe to allow things to settle a little before the bend.
Thank you, useful stuff.
Mike, I agree it is certainly a black art and imagine it takes a lot of tinkering to get it right. I checked out the RB headers previously and was considering an unassembled header (cheaper) linked up to a Y piece collector then back through a single precilencer and then a back box of some sort. Think I\'m gonna stick to the single pipe system to keep costs down and keep things simple.
Dom
As usual Mike is right on the money...but just to confirm what he said...
I used option 1 on my mildport 12A - Short extractors/headers joining just below the drivers footwell area and then a straight pipe with a intermediate silencer and then over the diff to the rear box. It worked really well and wasn\'t too loud.
If you have a heavily ported motor deffo go for option 2 - long twin primaries with a couple of silencers merging before the diff and 3 inch over to the back box. Should flow more voulme and seems to be the go with big porting according to most people.
Headers can be brought complete from someone like racing beat or just get someone to make your own with some smooth bends and heavy walled steam pipe or similar and a tidy Y collector. Make sure whoever does it doesn\'t build the primaries too close to your floor/firewall or you\'ll end up with melted carpet and sweaty feet!! :Giggle
Thanks Mullins, good advice about the primaries not being too close to the floor/firewall, didnt think of that.
I\'ve done a fair bit of research now and have looked through some of the Ausrotary forums as Mike suggested and have found some useful info.
Regarding which option (long or short primaries) to go for, I was also under the impression that a short primary system would be better suited to a mildly modified engine. Contrary to this, Racing Beat suggest their long primary street port system "can also be used on non-ported engines with significant results". As I have quite a lot in store for the engine (EFI, porting etc) I think a long primary setup could be a good start.
Regarding headers, the Racing Beat road race headers look good but think a more gradual bend radius would help so I\'m going to fabricate the header (will probably buy the engine to header flange from RB). As for the rest of the system, this is what I\'m considering:
Tubing 2" OD (0.125" wall) running back to twin presilencers (2" ID) side by side (rather than staggered) just before the axle.
Twin over axle bends from the presilencers to a Y-piece collector (2" inlets to 2.5" outlet).
Single rear silencer 2.5" ID
All tubing mild steel, BIG bend radii wherever possible.
And if I\'ve got some money left over at the end of it all... fibreglass exhaust wrap over the header section to improve scavenging and keep intake temps down (and stop my feet burning! :flamed ).
Does anyone know of any repackable silencers or normal silencers with steel wool packing that I could use for the presilencers. For the rear silencer I\'m considering a DNX universal muffler (steel wool and high temp continuous roving fibreglass) available through the OPIE OILS website.
Hopefully it wont be too loud!
Merlin Motorsport do repackable universal silencers as do a lot of the kit car places.
for header design, since you\'re building from scratch, maybe you should check out a place called SDJ Racing (or something to that effect - i positive about the SDJ-part, but not-so-sure about the Racing-part). anyway, all the hardcore racers on my side of the pond say that their design is better than Racing Beat\'s when it comes to performance. what i\'ve "read" into those comments is that they make more power than Racing Beat, but promote more noise on the street.
i honestly can\'t remember if they had pics on their site, but it\'s worth a look. i visited there once and never went back because they are expensive as hell - about $600 each. until i build an actual dedicated race car, i can\'t justify the price of that over the Racing Beat system i already have (about $750 for the entire system). however, it costs you nothing if you want to "borrow" their design. :)
as far as the rest of your system, you should check out ausrotary, as suggested before. i prefer running systems that remain uncollected until the rear end, but i\'ve run collected systems in the past. regardless what people say, size does matter! bigger is NOT always better. so consider that in your final decisions. one thing that doesn\'t change though is the thicker the tubing, the better - for sound control. forget fancy, shiny metals unless you care about looks, too. mild steel works just fine - just get it thick.
that\'s about all i can think of for now. please show your progress and results.
Cheers Diabolical, managed to find a few pics of the headers by SDJ. The company is SDJ Motorsport, although it seems pics and info on the headers is pretty thin on the ground.
Had a thought last night whilst driving south on the M5. Trying to keep the cost of the system down, so want to keep things as simple as possible so multiple bends and welds on the header (as seen on the SDJ headers) is out of the question. Furthermore, simple is often better. So what I was thinking was identical headers (i.e. the same bend radii and tube lengths for both primaries) over the first stage of the exhaust to behind the main engine bay bulkhead. The design of these headers could theoretcially be very simple but they would be of unequal length when collected. Rather than contort the headers to match their length over the first stage of the exhaust (i.e. the header) I reckon it would be far simpler to match the length of the primaries over the centre stage of the exhaust (i.e. below the floorpan/chassis). This could be easily achieved by running the exhaust from the front rotor straight back, and incorporating a bend of suitable size in the rear rotor exhaust such that lengths are equal at the stage where they hit the presilencers/collector around the axle area.
The disadvantage of this type of system is that it would be resticted to a long primary configuration. A collector straight after the headers would not work as the headers would be of unequal length at this stage.
Dom
no worries, man. :D glad you were able to use something i said. keep us updated.
on a side note: i suppose what you proposed for your new idea would work, but i\'m not sure how well. i freely admit that i\'m a bit leary at the inequality in length. the design you\'re considering reminds me of PaceSetter too much, i guess and i\'m not very fond of them. however, the mere fact that you\'re building your own is respectable and i recognize that.
yet another idea ... you could work really hard on the header and make it equal length and just collect into a larger diameter, like MindTrain does/did. their collector was 2.5" if i recall correctly. then you could just run 2.5" (or whatever you choose) back as a collected system, it\'ll probably shift your torque curve a bit, but i think you\'d get a decent balance between flow and noise control. just my thoughts ... sorry. :)
Thanks again Diabolical, your comments are very useful. I\'ve got the car booked into a local garage for some repairs this week so i\'m going to take some dimensions and photos of the underside of the car when its up on the lift, specifically the clearance between the exhaust ports on the engine and the steering/bodywork to see how much space i\'ve got for the header.
Working on the car is very difficult at the moment as I\'m living away from home so dont have access to any of my tools. Taking a week off over the summer to get this sorted though so i\'ll hopefully have some progress pics up soon (will start a new thread and list everything I\'ve learnt along the way).
Took the 1st gen up the 1/4 mile at Rotorstock III on Sunday. First time up the strip and had a great time. Was interesting to see what she\'d do with no mods whatsoever. Got a 17.6 overall on my second run (0.6 sec reaction time) without any weight removed from the car. Not bad for an oldy! :cool