touge's ae101 racecar - ‘fab it all from scratch’ project

[Rhyscar]

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. 

[Truenotch]

Hmm I don't know. The scavenging isn't necessarily done by sonic waves.

As I understand it, when a the gas pressure runs down a the pipe and out the megaphone (diffusion cone) it creates an expansion wave and the gas behind it accelerates. This creates a vacuum that heads up the pipe (negative pressure wave). I starts from the small end of the diffusion cone and works its way back up towards the exhaust port. So the positive gas pressure wave effectively "falls away" as the gas in the diffusion cone expands, which creates a draw in the exhaust port. 

In two stroke tuning, the sonic wave(s) play a key part in creating resonance, but it only works because there is no exhaust valve in the way and you can get an almost direct connection between the inlet and exhaust sides of the engine. Sonic waves can build up into multiples which is what 2 stroke tuners are trying to achieve (true resonance). 

Here's quick video that might help: 

 

And a not-so-quick one that explains the sonic vs gas pressure waves and resonance in more detail: 

 

There's another video somewhere that has good high-speed photos of the gas pressure wave entering a chamber that makes it slightly easier to understand, but I'll have to search around again to find the video. 

 

[Rhyscar]

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. 

[Rhyscar]

13 minutes ago, Rhyscar said:

There is two types of reversion. Mass flow and acoustic.  Mass flow or gas flow will have a harder time flowing upstream than down stream, down the flow will be unaffected, up the flow will be impeded by vena contracta.  In a properly designed (not too large for application) exhaust system mass flow reversion should not be a problem.  Acoustic reversion is pressure waves traveling inside your exhaust.  That same low pressure waves used for scavenging are accompanied by positive pressure waves at other rpms.  So say you have an exhaust system tuned for 6000 rpm, well this exhaust system for example might have beneficial scavenging effect from properly timed low pressure waves at 3000, 6000, and 9000rpm and have positive pressure waves traveling back to the cylinder during overlap at 1500, 4500, 7500 and 10500   If the positive pressure waves are strong enough it will actually push mixture right back up the intake manifold through the open intake valve.  The sharp edges on the pipe protruding into the AR chamber are intended to attenuate these positive pressure waves.

 

 

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

 

[Truenotch]

57 minutes ago, Rhyscar said:

 

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

 

Haha, yep, I read that last night. 

We need a dyno... 

[Rhyscar]

4 hours ago, Truenotch said:

From four stroke performance tuning

Regarding pulse tuning or acoustical tuning:

the exhaust gas is expelled from the cylinder at a velocity of between 200 and 300ft per second, but pulses or pressure waves are moving through that gas at around 1500 to 1700 ft per second.

by understanding the behaviour of these waves we can use them to improve cylinder scavenging and to increase cylinder filling with air/fuel mixture  

as the initial charge of burnt gas bursts from the cylinder into the exhaust system it creates a wave of positive pressure that travels the speed of sound through the gas to the end of the pipe. As it surges into the atmosphere, the positive wave dissipates and produces a negative pressure wave (suction wave), which returns along the exhaust pipe into the cylinder. It arrives with a certain amount of evacuation power because it’s pressure is much lower than than the cylinder pressure. The art of exhaust tuning is to determine the length and size of the exhaust pipe for this suction wave to arrive back at the cylinder during the valve overlap period.

 

So the sonic/acoustic pulses move independent of the mass flow of the exhaust and much faster.  

[Truenotch]

1 hour ago, Rhyscar said:

 

So the sonic/acoustic pulses move independent of the mass flow of the exhaust and much faster.  

Yep. And the speed of sound changes with temperature, so it's important to know the rough temperature of your pipes too. 

[Rhyscar]

Ah didn’t think about that. 

[Robbo]

On 25/06/2019 at 04:05, Rhyscar said:

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) 

Oh man, outrageous how full circle that's gone!

Cool to see you've got it back though. Last thing I saw of it was a pic of it on Facebook with a 2ZZ in it, any idea how it got into this state?

[Rhyscar]

Yeah the guy who had the 2zz in it stripped it and reshelled all the parts into a ae111 and then sold the shell. I almost bought it a 1-1.5yrs ago when it was sold that first time but we’d just bought a house and the timing wasn’t right. 

The guy I got it from just never got around to do anything with it. Came without wheels but with a few spare body parts. All the exhaust, swaybars etc are gone. 

[Rhyscar]

Been chipping away at the exhaust. Been working some big hours recently so took a few days off to reset my mental health and catch-up on some shed work. 

 

Finally finished the rear rear section of exhaust thanks to @Truenotch for helping out with another set of hands. Turned out to be a bit of a mission to fit a 3” zorst in a very tight space which required some unique solutions. 

 

So so here’s the end product which I’m very happy with. Can’t wait for it to make doorty noises! 

Bends weren’t quite tight enough so had to cut them up to make them tighter. Luckily the band saw and linisher made this task a dream leaving a nice flat surface to get some mint welds on;

 

In order to get it fitting tight with no movement I over engineered the shit out of the mounting 

rear mount had double rubber mounts inside the chassis rail for max stealth  

 

Rear of muffler had this swanky mount to the subframe 

 

and under the subframe i added this rubber to keep it from hitting the subframe mainly as it’s only got 5mm  clearance.   

 

Been working on building collectors for headers today also. Bit of a head fuck trying to work out how to construct these from the measurements I had but got there in the end.

 

So I’ve decided to go with a Venturi style merge collector and a 4-2-1 header design mainly for packaging reasons. The idea is the gas speed increases momentarily accelerating it through the merge and it also amplifies the any acoustic resonance that we may or may not be able to create with the expansion chamber (standby for @Roman science in near future)...

End product just looks like two bits of stainless welded together...

 

Used a bit of card to make a template to get the angles right for the two halves

They actually have a small plate/baffle welded in to restrict the area where the two flows merge. Normally (depends on merge angle) the area almost doubles which slows the gas flow and worst case can cause reversion at certain rpms. 

Welds came out pretty good with no purging only a few small spots of penetration that I’ve mostly been able to get rid of. Smashed through almost a whole d-bottle doing this and the exhaust though!

 

heres the rough plan with my headers;

My primaries are 41id stepping up to 44id then this Venturi is 47id before stepping up 56id secondaries and another 51id Venturi and tapering up to the expansion chamber. But that’s about as far as I’ve got sorted at this stage more to come on that next time...

[Truenotch]

Good progress! 

Venturi collectors look like a cool idea. I've never seen inside one before. 

[Rhyscar]

Yeah it’s  interesting that you may never be able to tell what collector style it is from the outside or even looking down the end of the pipe. 

 

Need some bends in an assortment of sizes for the next step of header making.

Does anybody on here have a trade account with Autobend that I could use for a box of beersies? 

[Rhyscar]

I have a bit of a tight spot at the end of my tunnel/fuel tank that required a tight bend. And I was being cheap so I bought some pie cuts from nzpiecuts on Facebook. showed up the next day A+ service! 

Turned out awesome no purging and bugger all penetration. Oh yeah and I over engineered the shit outa another exhaust mount.. I’ll post a pic of the finished product a bit later in the week! 

 

Full disclaimer I’ve got very limited fabrication skills I am a project manager who sits at a desk all day long. But I’ve been super enjoying making cool stuff so I thought I’d give an expansion chamber a go to test a few theories.

 

Patterned it with the help of youtube

I don’t have any rollers so just decided to use my small folder. 

 

due to there being 12 folds per half each fold is 180/12 = 15deg which is bloody hard at the best of times so I made a gauge so I could check on my progress as I went..

 

turned out not too bad got a bit of beating to do to get the seams to line up and make it round but not a bad start! 

 

[Rhyscar]

So finally got off my ass and finished this expansion chamber and my exhaust. 

I ended up rolling the belly section and rear cone of the expansion chamber. Should have done this for the front half too it was tricky but turned out way nicer! 

 

and gave it a polish up

 

finished the tunnel end end of my exhaust off too. It’s a pretty tight gap to fit through hence the pie cuts and stupid amount of mounts

 

heres the whole system complete just waiting to build headers and order a Flexi and I’ll be able to install it for good  

 

 

still trying to to find some 41mm od bends for the headers so might need to find something else to sort in the mean time! 

 

 

[AllTorque]

What’s the theory behind using an expansion chamber?

[Rhyscar]

Still a bit of a work in progress we haven’t proven our theory fully but here’s what I’m basing it on;

scavenging can be done 2 ways. 

Mass flow/inertia - header lengths, pipe sizes and mass airflow velocities helping scavenge airflow out of other cylinders. The key to this is keeping velocities up and preventing reversion so the pressure differential always wants to empty the cylinder. 

Acoustic - expansion chamber is to reflect the sonic wave that is generated when the valve opens. The expanding of the wave into the chamber causes a reflected negative wave that if it is tuned to the right length can reach the valve on the next cycle of the cylinder. 

 

This is based on 2 stroke theory which is well proven. Every example I’ve seen of one being used the car has made a lot more power than expected so just trying to figure it out for myself.

@Roman has some fancy gadgetry to hopefully measure and prove all this at some stage. 

[Rhyscar]

Its been a few years since an update. Phew covid sucked. This will be mostly pictures so if you have any questions about stuff I have/haven't done ask away. 

If you want more updates check out instagram account https://www.instagram.com/garage_rfab/ 

 

Nick added to the rollcage. New harness bar and general improvements to increase the safety. New side intrusion, rear brace and strut tower connections

[Rhyscar]

New wheels showed up. Went to 17" for max tuck. Car also got painted earlier this year. Went for a replica colour based on Tom's racing colour. 

 

 

 

[Rhyscar]

Fabricated a v-mounted dual-pass radiator