Rhyscar

That’s interesting. Here is the dyno sheet for the 20v. Is flywheel kw the tuner works on a 16kw drivetrain loss for this car. Hopefully the data is useful. The best engine we had was about 12.5:1. over that it’s diminishing returns over that. Below graph is 13.5:1 but hasn’t really run reliably with that setup. Also found header design for reference

Have you seen this? https://thumpertalk.com/forums/topic/1075515-megabomb-header-explanation/

4 stroke is the same where you want to have that negative pressure wave reach the valve For the small amount of time where they are both open to draw through more intake charge (scavenging) The trick is to make sure the valve is closed before the vacuum sonic wave stops (length of expansion chamber determines your window) to prevent reversion pushing spent gases back into the chamber. I think we are both on the same wavelength... the 4-stroke application has a lot smaller rewards than 2 stroke but is still worth chasing.

Nah not hytechs we got them acoustically designed by Harris pipes in Chch then built them ourselves. This was a about 5 years ago before I had learnt anything about this stuff. Agree that hytechs are the best for Honda’s and so cheap too.

This is where reversion (has particles moving) is different to the sonic scavenging wave returning back into the intake chamber during valve overlap. There are gains in the 10-15% range to be had for doing it right from what I can see. In a motorbike situation you don’t need a reverse cone as it is open to atmosphere but in a car where you have an exhaust attached it reflects the high power part of the sonic wave back up the header system essentially isolating it from the following mufflers/exhaust.

Yeah it is a black hole indeed. Interesting data about the megaphones. Looks very weighted towards v8 collector sizes though! The book describes them as tail pipes and has similar data around 7-10deg angle and lengths. There isn’t much about the angle of the reverse cone but my understanding is the steeper the angle determines the sonic power reflected and over what rev range. I suspect picking something in the middle of the recommended angles (similar to dads expansion chamber) is the way to go unless you are doing all the calcs and can test 2-3 designs.

Yeah the step is the way to go. From what I’ve been reading they broaden your torque range by a good 500rpm. I think it would be worth doing a bit more work on the collector and the restriction straight after Which sets up the scavenging effect. here are the headers on dads car they were good for 140kw but is suspect they are a bit small for the 150 it’s now making. In hindsight we should have gone to 4-1 design as the range it makes power in has so many more variables such as cams and intake than just the header design and you want them to compliment each other slightly offset not all line up in the same spot. Making power is like building momentum (I.e. area under the graph) Keen to see how far this thing can go 150kw is a lot. What compression are you running? I’ll see if I can pull out a dyno graph of the old mans 20v. Edit: @Truenotchafter reading those articles in my build thread I realised my understanding of reversion vs scavenging effect was wrong. I always understood them to be the same thing but they are quite different. the reversion wave (exhuast particles) travels at approx 300ft/s (this may change depending on cylinder/header sizes and compression) and the scavenging wave (sonic) travels at 1540ft/s (this is a number a smart old Barry once told me to use with expansion chamber distance from exhaust valves) I guess the trick is to set up the lengths so you don’t end up with a flat spot caused by reversion but still get the benefits of the scavenging. I wonder if the reversion chambers would effect the scavenging wave too?

Yeah that’s it sorry. Maybe they needed to be longer? Agree it will be interesting to see once it’s all together with the new intake. What’s your goal max torque rev range you are aiming for?

Going back a few posts here but do you think the 6000rpm flatspot has more to do with the lengths than the diameter of the tubes?

Oh thanks I dont so much os browsing these day I’ll take a look.

Thanks Markku. Yeah agree it’s the first time I’ve really seen it all together and it blew me away how low it was and how unlike a teenagers-first-car spec it is. Very motivating. In other news I’ve been doing some reading of this book that arrived. Interesting read even though some of the data/engines are old it’s still very relevant. Interestingly after a bit of ready I’m leaning towards a 4-1 stepped header instead of a 4-2-1. Not as much info on expansion chamber design as I’d hoped though. They damaged the book in transit so I’ve got a replacement on the way if you want it?

Been chipping away at this even though work has been crazy busy the last few months. Competed the front passenger tub and headlight tubeframe. Have left the inner quarter panel for now due to: a) I didn’t like what I did on the drivers side and need to change it and b) I couldn’t figure out the best solution here so will move on and come back to it when I find more enlightenment. So so much room for activities up front. Airbox is guna be huge!! so I bought my old road car back as a rolling shell that I sold to @Robbo a few years ago. I know it’s a tidy shell and still certed etc. don’t know what I’m guna do with it yet but for now it will sit in a shed at the farm just need an engine so may slap it together for something like 24hrs of lemons or other endurance racing event/get it back on the road and do some doorts or just keep it for when I eventually write off this shell (it will probably happen one day) Had a real lol moment when the strop broke and it rolled off the back of the trailer in the middle of Rotorua! Haha it came with a fibreglass bumper the same as the one I have for the racecar, spare facelift side skirts and most importantly a bumper support so I can mount the racecar one without more fab work woohoo! result is the front end is together for good now. Going to be challenging to drive anywhere on the road at this height (not a bad problem to have) while waiting on more materials for the exhaust I started ironing out my fuel supply pipework. Have used 1/2” stainless tube as an alternative to braided lines as I hate smelly fuel lines inside the car and the ID of 1/2” is the equivalent of -12an or something stupid so will be plenty big enough. Made some fuel line clamps lamps from some Ali I had lying around. Very happy with the result. any recommendations on fuel pump/filter to use? Want something reliable with a no-bleed back feature so I can run two pumps in parallel. Dont need much flow approx 200lph will be ok I think (need to check calcs) I’ve seen too many fuel pump failures at the track or beginning of stages that stop people completing events. Not going to take that risk.

Those are cool how do you buy one/how much are they? These projects always take way longer than expected. If it wasn’t a good winter project to chip away at I should have just paid the money and bought one in hindsight... thabks kimjon I’ll give it a go!

Solved one of the first world problems we have with our outdoor furniture lately. After browsing mitre 10/Bunnings and not finding any decent quality options that aren’t $500+ made me decide to build one instead. https://photos.app.goo.gl/hY6EvVE2qRRJ448H7 Built a frame then stained some ply and slapped it on the outside. https://photos.app.goo.gl/dYM4WfYmcDWqi9d79 Came up pretty sweet. Now my cushions stay dry when I want to use them https://photos.app.goo.gl/g2e2k7eh5bdaUNUx6 Edit: how do you embed/upload multiple pics? I’ve been struggling along only adding 2 pics to each of my posts to fit under the size limit but surely there’s a better way!?? thanks in advance!

love these things. Well done to you sir. Continue winning at life.

Yeah there were a few too many weetbix to bother keeping it. Got plenty of material that needs to go to Tenfive’s for the next bonfire!

Sweet little project for the day to make more useable work and storage space in the shed. Had an old kitchen unit just taking up space and holding the toolbox up. Wasn’t very useable had a warped soggy mdf top on it. I had a lot of extra bits and pieces jammed into other corners of the shed that needed a home and weren’t very well stored Picked up some offcuts of ply off a friend and made a new bench top for it. The ply was 12mm so decided to double thickness it with the help of some no more nails.. By the time I pulled the old top off half of it was rotten and junk so rebuilt it with some old wood I had lying around. Quick trip to Bunnings and got some storage bins for like $7ea to fit into the shelves as deep drawers. Pretty happy with the result and didn’t really cost me anything. Feels like a successful Sunday project!

Thanks @cletus much appreciated!

Just wanting to check what I can do to my seam above my wheel in cert world. I have enough clearance (just) for full compression without it touching but just wanting to be doubly sure I can’t damage the tyre on a big compression. This is being built to do jumps on targa.. A double seam like this provides quite a lot of strength to a sheet metal folding so I’m not sure if I can cut it back then stitch weld a doubler over the gap or something similar? In the past ive bashed seams like this flat but that doesn’t seem like the right thing to do either.

Yeah I’m liking the white on white option I think.

Added a few more braces to the mounting without trying to make it too strong so frontal impact etc isn’t effected too much. Has some movement so I’m sure will rattle with solid engine mounts but shouldn’t effect night driving too much Hopefully saving some weight too I’ve cut heaps of shit out of the front end and not a lot going back in.. got oil cooler mounted and will start ducting that when I convert my shed back to Ali after I’ve finished all this mild steel fab. Any opinions on what colour/coating these headlight mounts should be?? They unbolt so I can remanufacture when I crash it/bend it. a) zinc passivated like subframes b) powdercoat white c) powdercoat gunmetal grey d) other options?? Im 76.9% sure engine bay will be painted white. Tossing up gunmetal cause it looks tidy but like the idea of the carpet matching the drapes etc.

so much room for activity at full lock. Time for some caster you say?? I’m really trying not to talk myself into making some bottom arms for this...

Today’s progress. Headlight 95% mounted