yoeddynz

Plenty of plans yet! :)

Oh man that would be good to hear.

Good heads up on grinders - especially for the folks on here with face rugs..

Yeah I can see that being the case. Its all extra resistance eh. I still have to keep reminding myself that I'll never ever get that big low grunty porsche sound from a tiny 1500 cc six cylinder engine. Even an old 2.2 porsche is going have more exhaust energy to utilise, let alone the big 3.6/4.0s. But if I can have more burble and character when just idling and cruising I'll be happy.

Thanks for the suggestions fellas. I'm constantly learning and this process is fun. Standard Goldwings run the header outputs directly into an expansion chamber and then out to the each side and the mufflers. Its very simple. You can see the box here in the centre.. and how its placed in this pic.. They actually sound pretty cool with the mufflers removed leaving only that box.(one of my fav bike fellas to watch).. https://youtube.com/shorts/-J2i6ZN7Pdk?si=Qf46nFySPSm4cwaF There's quite a few companies making X pipes/cross over pipes that replace the stock chamber. They claim all sorts of things (as usual) but mainly they are louder. My next idea is to try a bit of crossover and make a system sort of similar to like many aftermarket Porsche ones are like and have twin side exits. They usually have muffler units before this lot although some are totally muffler delete which must be ear bleedingly loud. and.. but probably not this one.. But with mufflers where I can. I have some ideas. Will order some bends from Ali. In theory it should be much quicker and easier to build.

A bit like the unequal tracts on a earlier scooby to create the off beat rumble ? But in the case of almost all Porsches and all Goldwings they have very equal systems yet still create the sound I want. I am getting closer each time though and what Ben has to say below is similar to what I'm planning next...

I've now clocked up 3200km since fitting the flat six. 1200 of those are from the weekend just past but I'll get to that in a later. First off - more exhaust box modifications. Adding that sound deadening mat around the pipe had made it too quiet and the exhaust note had lost some of its character. So I cut the box open again and removed the stuffing. This time I riveted a lid in place in case change my mind..again.. I also cut a hole in the bottom of the box and made a bolt in panel that has a folded over, wedge shaped partition splitting the main lower chamber in two. The idea is to stop the exhaust pulses from each side hitting each other and creating that hum. I don't really think it will work as such because they are pressure induced sound waves and the partition isn't a perfect seal. But it does help guide the exhaust flow up through the plate of many holes above. I didn't take pics so you'll have to picture it. So the box is sort of back to what it was like when first made but in theory better flowing. It sounds nice enough though, not droney at all, no fumes and sporty when extended. It'll have to do until I start exhaust box number 3. With that bit of exhaust fettling finished I double checked my tool box for anything extra we might need, packed the car up and cut some thick foam up to make a cradle for the UE Boom bluetooth speaker so it doesn't slide about on the parcel shelf. We headed to my mums place in Blenheim, Hannah driving convoy in the van which was filled with the last of our K11 micra bits that were getting picked up from mums by the new k11 owner the following week. She had Kevin the cat for company as mum would be baby sitting him. Pic from a stop at Pelorus bridge on the way over.. Kevin.. The drive over was great fun. I was lucky enough to almost get a clear run up the Whangamoa hill climb until I caught up to a Suzuki swift sport that was not living up to its name. For those that don't know the Whangamoa hills its a decent climb out of Nelson that's got loads of great corners where you can see well ahead. The whole road up to the saddle was resurfaced a few years ago and its a sporty drivers delight. The following day we headed south to Christchurch. Hannah had a weekend long fire fighters conference to go to. I would be free to catch up with family and friends down there. Lovely drive south with perfect weather. We've not been down the east coast for a few years and this was the first time in a very very long time we'd driven anything interesting on this road. Pics.. View from cafe stop.. Had a very nice posh hotel to stay at in Chch. Car was now plastered in fly road kill.. The next couple of days I hooned about chch city, caught up with friends. First thing Sat morning I popped in to mag and turbo and got my front wheels rebalanced as I could feel they were out slightly on smoother roads. Big thanks to @CUL8R for sorting me out there, getting the right fella (a mini loving barry) on the job. Was nice to catch up for a good old chat. The cars front end was much improved. Sunday was especially good as I managed to get some really good driving in on the Port hills and Lyttleton habour area. Good coffee, great roads, clear sunny day. I have not driven a lot of these hill roads for years and the last time at speed was in the 90s in my supercharged Mr2, brothers TVR or a bit more recently a mates WRX he lent us for a week. Great roads and luckily actually really quiet on the Sunday morning. I discovered whilst hooning through the Lyttleton tunnel that if I hit the red line in second then button right off so fuel cut activates the car does a wicked backfire. Second time back through the tunnel was hampered by someone who insisted on sitting at 40kph. Late morning whilst parked up looking at the maps on my phone six Triumph TR6 sports cars raced by. I dropped my phone and took off after them. For the next hour the convoy raced about making the most of really good hillclimbs and twisty roads. Damn it was fun. What glorious sounds! The Imp was in its element and by now I was really getting the hang of making the most of the rear engine configuration. I was bloody loving it. I just kept following them until we ended up out over in Charteris bay and they pulled into a cafe car park. They all came over to check out the Imp, wondering how I managed to keep up Lovely cars TR6's - my brother almost bought one that we'd test driven before getting his TVR. The Triumph 6 connection for me is having owned 5 TC2500s over the years. Turns out I had met one of them a coouple of years previously when they were doing a nationals meet up our way. I was invited in for lunch with them and had some good banter. Late Sunday afternoon after Hannahs conference was over we drove to Hanmer springs. Another nice Hotel and this time the Imp had company more its age.. That evening we spent several hours in the thermal springs right over the road from the hotel. Cool clear night. Tickets now include the water slides so we made the most of those too. On Monday morning we left Hanmer.. and headed back to Blenheim via Waiau.. and the inland Kaikoura road. It used to be gravel for quite a big section and I've not driven it since it's been sealed. Looking forward to the twisties but it was quite a let down. Actually very rough, lumpy and bumpy. It was not really suited to a lowered imp. Would be far more fun in a peppy Citreon or something with really supple suspension. In fact I had more fun when it was gravel. Kaikoura for lunch.. Back to Blenheim for the evening. Got to play with mums border collie puppy .. Following day it was back home. This time I was even more lucky on the Whangamoas because there was a traffic stop due to tree felling. I was at the head of the line just behind a large truck. Passed him after the lights went green and had the whole hill to myself. Fantastic. Gentle 4 wheel slides balancing that rear weight overhang on the smooth tarmac. So fun. Once home I did a final check over of the car. Needed a tiny bit of oil, 200mls, due to a small drip from the sump I have now fixed. We clocked up 1280 kms (having accounted for 3% speedo error) and across all that driving averaged 6.6L/100km or 42 MPG in old money. Of the fill ups the best was 5.9L/100km when just cruising with the traffic down the east coast, worst was 7.4 after a lot of fast driving. I'm bloody amazed. We kept re-checking the figures etc and its legit. Its just so cool that such a smooth, nippy little six can also be so thrifty. The Imp is also really comfortable (the Recaros help) on long trips too. Its the only car I have owned to date where I don't get a sore right ankle from the throttle on long runs. So I'm pretty bloody rapt with the outcome and look forwards to more road trips. Also looking forwards to cracking on some more modifications I have planned.

Just a thought which may or may not work (and could end up looking ugly..) but can you fit tiny nylon balance tubes between each bank?

No real opposition to the side exit. From the very beginning of starting this conversion I just always had the picture of this setup having the twin centre exits and I prefer the look of them But fumage Quite keen on seeing what two corner exits might be like with regards to the airflow wisking away the fumes.

I sort wish I had started that way! I have spent more time making exhausts than actually driving it. God knows how much of my life this thing has taken actually. But this is oldschool And its fun.

yeah aware of that. But even if I extend them quite far out its still going to be an issue I believe. But they are bolt on units so I can certainly try longer ones in the future. Its a problem many Hillman Imp owners have had due to the not so fantastic sealing quality of the rear opening windows etc and all the owners who have gone to side exit exhausts fix the issue. The power of the low pressure zone is strong in this car The other day I went for a hoon after the council mower man had cut the verges around the bay. I got home and the engine bay was full of cut grass! All sucked up and through the vented engine cover

You're probably not wrong. I actually copied the flowmaster muffler design for the Datsun A12 and apart from it now rotting out because made of zinctec its a good sounding muffler.. I took the Imp for a good thrashing this evening up the up the Riwaka hill, over and back. Caned it heaps and its interesting how the exhaust note changes as the muffler gets some real heat in it. Worked the brakes hard and the front pads are properly bedded back in (but will be replaced anyway) Got home and straight out with the temp gun. Front brakes perfectly matched in temp, rears only about 3 degrees out side to side. Really good to see. I'm still going to design another muffler setup because its a fun thing to do. Got some ideas on how to modify the original one for better sound too - although I'll never be able to design away the fume problem from its centre exits so it'll never be good for summertime windows down cruising.

Oh also - for @Roman and anyone else who likes graphs.. check out the wall of text and graphs that Bill Verberg loads up on this thread I found in my searches... http://forums.pelicanparts.com/porsche-911-technical-forum/592353-mid-engine-exhaust-design.html

Yep .. "This time I filled the cavity around the perforated tube. I'm hoping it might quell some of the 'hollow cackle reverberation' sounds" Edit - I've just realised the build thread is missing a photo I took of me adding packing into the chamber with the perforated tube.

I'll check that out but I think the headers are fine because it sounded pretty bloody cool when bench testing, both without mufflers and with some in place. But was probably too loud and not the most practical packaging They are the two mufflers that came with the engine. It did have a small balance tube installed between the original headers. The jury is out about balance tubes on flat sixes. From what I have absorbed they are not needed at all for performance gains but can help for a certain sound. My current exhaust box effectively has a balance chamber but as I have noted this is possibly the cause of the resonance. The previous exhaust box had none of that type of resonance but being a straight through it suffered from the drone sound I pretty much got rid of using the J pipes. But to me it sounds just like a straight six until around 4000 rpm. Engine with just the old mufflers loosely sat in place over the ends of the headers... Same setup at idle. Sounds exactly like I want... I'm trying to design another setup that has these two mufflers or similar (because I have actually given these to a biker mate) mounted across the back, with an exit out each side sort of like this