Roman's 4GR V6 Toyota Carina

[Roman]

Because it's easier than doing any actual work on the car.
 thought I'd ask chatgpt what it thinks about exhaust design, with regards to preserving the high pitch of the engine that is currently getting nuked.
I was expecting it to trot out the usual stuff "make a 6-1 exhaust manifold" "fit an x pipe and an H pipe and a Z pipe" 

However it had some surprising suggestions. When I queried its sources it had some actual university studies etc to back up its findings.
I'm trying to have an exhaust that primarily makes zoomy noises in the 300-500hz sort of range.
The main things it stressed was that muffler length/shape/type/position are all critical for not destroying frequencies in this range.
Which is not something I've ever even thought about.

It says any oval muffler, (like I'm currently using)  is off the cards.
Mufflers must be round shaped to best preserve the pulses, and larger body diameter the better (better noise absorption with no downsides) 

It says aim for a straight through mufflers with no internal louvres.
A front resonator about 600mm past extractors around 180-200mm long.
Then a rear muffler, also straight through and circular with no louvres that is approx 300mm long. 
The first resonator near the extractors gets rid of all of the ear piecing high hz screeching noises.
Then the larger mufflers at the back do the bulk of the sound reduction without killing the pitch.

Surprisingly it also suggested that any addition of an X pipe or an H pipe will ruin how this works. 
So either it's scheme is fairly holistic and all needs to work together as one. Or it's fundamentally misunderstood what I'm aiming for. Haha.
It suggests keeping the banks totally separate which I found interesting as that's contrary to what seems to usually sound good.
Also a straight cut exhaust tip with no flare or rolled end. 

I asked it whether I'd be better off running both banks into an LFA style rear muffler box.
It said that this will achieve largely the same sound as that. But with less trial and error to get the box volume correct for an LFA style setup.
I'm guessing it will be a bunch louder though...

There's a huge amount of online real life evidence that points towards an x pipe making a motor like this sound way better. 
So ordinarily I'd just go straight for that.
However the reason I'll give this setup a chance is that keeping the banks separate for starters makes prototyping it exceptionally easy. 
There arent really any downsides to giving it a go, apart from a few extra hours. 
But it will scratch the itch to know whether or not chatgpts exhaust design suggestions are valid.
It's now made me curious about what sort of muffler lengths people have been using. 300mm max seems kinda short.

This is a before/after of what I'm going to do for starters
(before probably finding that chatgpt is full of crap and I end up fitting an X pipe)

[Roman]

Ethrottle fix 

I bought some different ethrottle motors that have a higher ratio gearbox on the front. So it can only move slower, but has better holding torque. 
So far so good, still really snappy on throttle. 
But now it only needs between 10-20% duty cycle to hold the throttle at any position. Previously at some points was near 50%. 
I changed the bracket design so rather than being single piece. 
They're two separate ones which slide onto a carbon fiber shaft. 
So there are no issues with the centers being off.



Works well, I have had it on a test mode all afternoon spamming throttle open and closed a whole bunch. 
I've also got the Toyota TPSs mounted on properly now, and its much much much better.
I've now got super aggressive PID settings and it's all working great.

Exhaust stuff

For the exhaust revisions, first thing was cutting off the extension part of my manifolds, and putting a V band on.
So they're easier to get in and out of the car, and also a lot easier to get test sections off and on.
A lot of people warned me about warping the flanges, so did it with the other half bolted on and slowly stitched around it while letting it cool a bit.
Seems good so far.



The next step  was to do some open header limmy bashing to make sure the neighbors horses are awake.

Will be interesting to do the same test once the 2-1 section is on there. For science, of course.

I am just going straight to making a 2-1 section instead of the chatgpt suggested dual 3-1 scheme. 
Like it would be interesting to see if it works but my patience is wearing thin for exhaust stuff at the moment.
Watching the video of the Stratos with the discrete 3-1 pipes vs the 6-1 and its absolutely no contest. The 6-1 sounds wild by comparison.
I will still be taking onboard its suggestions about muffler type/length/etc.

I started making a shallower angle 2-1 section. With about a 12 deg angle this time instead of about 45 deg. 
I've not had much luck trying to do cuts like this on the right angle and line, so printed a template that showed where to cut but also the angle to hold the grinder up against. 
Worked pretty good. 



It was a real bastard trying to weld up the gap in the middle though. It will probably still leak right at the top. haha. 




Then my next problem is trying to get the 2-1 section equal.
So one bank is further back than the other, adding to this is that my manifold design is different each side. So the collectors are at different distances back. 

The Vband on each of these bolts on to the collector, then I marked where the pipes line up with the gearbox crossmember.
So I can get an idea of the difference.



So I need to squeeze about 140mm into one side prior to the 2-1 merge. 
Will take a bit of stuffing around. But hopefully worth it.

Injector issues

Something else that is annoying after reviewing things from the drags. 
My injectors are at 96% duty at 9750rpm. 
So absolutely completely out of injector. 
"They say" you should aim to not exceed 85% duty cycle. 
I'm now getting to 85% at only 7500rpm.
So definitely need new injectors now.



With my old intake, I was only getting to 80% duty right at the limiter. Only 68% duty cycle at 7500. So a big difference.



These are around 330cc at the fuel pressure I'm running, and so its chugging down about 1.7 litres per minute at full steam.
Annoyingly the BMW V10 uses a non standard injector length, and has a longer than usual pintle on the front. 
So it might be a bit of a pain finding some bigger injectors.
But need to figure it out.
Not the worst problem in the world to have? As it means the engine should actually be making some alright power now.


Gearbox issues 

I pulled my other gearbox out as it wasnt shifting properly, and the problem would happen even when the motor was off. 
When putting the factory 3S bellhousing back on, the old gearbox now works fine. 
So I'm thinking there are a few possible issues... 

1. When using a rubberband to hold the reverse fork thing on, this could be causing the issue. Maybe. 

2. The weight of motor and gearbox is flexing the bellhousing because I've got no bolts around the bottom. Will test this by jacking it up by the center and see if anything changes.

3. The bellhousing welding warped the front casing slightly. 
apparently it takes hardly anything, to pull the shift forks or front bearings out of alignment and cause issues. 

4. Something else. 

Will pull the motor and gearbox back out once I've finished with exhaust stuff, and do some more testing. Hopefully there's an easy-ish fix, but it was interesting to see that the factory bellhousing back on, fixed the problem.

[Roman]

Slow progress on the exhaust, but I've manage to cobble together a 2-1 section that is nearly equal (Still needs about 75mm more, on the wiggly side) 



After the 2-1 join it'll revert back to a single 3" pipe and a single barrel muffler for now.
Here's a neighbor's horses awakeness test with the 2-1 mostly finished. 
 

I think I've cured the 3 cyl sound at least. 
So its a good starting point, can hopefully fine tune it from there without having to stuff around with that part anymore.
Will just have a single 3" pipe from there back, and a single barrel shaped muffler.

Theennnnnnnnn
I need to get some air filters on at some point. 
Now that I know what the runner length is going to be, more or less. can plan an airbox.
After an extensive amount of fucking around with test prints and so on, have got an airbox shape sorted.

I'm thinking the red backing plate bits will be alloy plate (less the radius shown) then can hopefully get a nice hidden detail with cap screws coming in from the back (rather than studs)



It took 30 something hours to print the two parts, not including the 2x failed attempts due to powercuts.



I was initially planning to just print PLA and then wrap in carbon.
But, I think I'll try make some proper molds this time and try get a nice surface finish. 
Then maybe just wet layup on the inside. not sure yet.
Just get this bit finished first.
Sanding sucks.



Please ignore the fact that I say this is about fitting air filters, yet have no obvious way to fit an air filter to this so far. 
 

[Roman]

Alright, so had to pause on the airbox stuff because my ethrottle motor shit itself again. 
As I'm not sure how new system would work they might clash with airboxes.
However, I found some similar motors to my existing ones. But from RS components instead of aliexpress.

They have motors of similar design to the ones I'm using, but they better list the specs including max current.
My existing motors are rated to 1.2 amps, where as ethrottle will push out around 2 amps at max. 
So I found some replacements that are rated to 2.8 amps. So fingers crossed thats going to fix the problem.

Next  thing, is that my motor still sounds quite rough and not very "v6 smooth" kinda thing. 
I've been wondering if the small amount of imbalance in 2-1 section is the cause, and if so, how I could test that. 
Since my engine has VVT on the exhaust side, I can adjust the timing of when the exhaust valves open. Usually all at once, but if I unplug one side. 
then I can move the opening/closing timing and see if it eliminates the imbalance.

I am guessing there are only a few degrees of imbalance, but I can swing it by around 40 crank degrees which is huge.
So I did this, and the motor seemed really insensitive to it.
Apart from starting to glug when you retarded the cam too far. 
So is something else wrong?
I unplughed all of the coilpacks 1 by 1 while the motor idled. It turns out that cylinder 1 and cylinder 6 both have bad coilpacks.
So I replace these, and now the motor is back to firing up near first crank instead of taking ages. Then also sounds a bit different.

So here is were we are at with the 2-1 section finished, and a 300mm long straight through muffler stuffed on the back for testing. But all coilpacks working ha.
There's no pipe length after the muffler itself at this point.
 

Doesnt sound particularly pleasing to the ear and its also still god awful loud. 
Howeverrrrrrrr  its making the right sort of noises to start with, that can be beaten into shape so that's good. 

So I think the 2-1 section is good now. So I can work on beating the rest of it into shape from here. 

This is the plan roughly: 




The two main ways I can adjust it a bit are with muffler dimensions and adding a helmholtz/branch resonator. 
Adjusting the muffler controls the high pitch stuff, and overall volume of the system. 




Adjusting a branch resonator can eliminate an annoying drone or idle noise.




There's a program called Audacity that is a free download, than can show you a frequency plot but also do a bunch of other stuff. 
So looking at a plot from this can give you an idea of which frequency you need to eliminate if wanting to do a branch resonator.






But what is also handy is that you can use the graphic equalizer in the program to eliminate that frequency first and then play the noise back.
So you can see what sort of change it would make before committing to it.