Randall & ARC Chamber

[dadbif]

I wonder if an inter cooler with guts knocked out, or similar, would have the same effect.

[cat]

Isn't it 90% nonsense though? An air box of many kinds would serve a purpose in reducing turbulence in the air which is about to go down the breathing hole;
but otherwise we're into 2 stroke resonance territory I think. That's mostlyl about tuning the space so that after the last time a valve closes, the shockwave back out of the inlet is bounced back so that it's a positive pressure reaching the *next* intake valve JUST as it's opening.
Anything other than that is just some shiny prarrie canoe isn't it?
We'd probably be better off looking at velocity stacks of some kind.
At the worst case of course you might build a nice resonance that leave the valves opening to a pressure of LESS than atmospheric for extra low power lols.
This is all babble and I have no real idea what I'm talking about obviously.

[dadbif]

I thought it was exhaust back pressure that had that effect on two strokes??

[cat]

it's both ends, two strokes pull fuel in on the exhaust stroke and for best performance pull it right through into the exhaust, the back pressure blows it back and ideally the hole in the cylinder closes on the interface between the good and the bad air. Makes sure all the bad is out and limits detonation in the exhaust, probably.
Again, what the prarrie canoee do I know about any of it?

You want both ends working though, extraction on a tuned exhaust makes the low pressure from the tail end of one runner crawl back up the exhaust runner of the one that's just about to exhaust.
combine the in pressure with the out vacuum and you can get a lot more *stuff* through your bang parts... your half way to a turbo.
Again, I know almost nothing about fluid dynamics.

[wannabe]

Aug 6, 2018 17:56:52 GMT cat said:

it's both ends, two strokes pull fuel in on the exhaust stroke and for best performance pull it right through into the exhaust, the back pressure blows it back and ideally the hole in the cylinder closes on the interface between the good and the bad air. Makes sure all the bad is out and limits detonation in the exhaust, probably.
Again, what the prarrie canoee do I know about any of it?

You want both ends working though, extraction on a tuned exhaust makes the low pressure from the tail end of one runner crawl back up the exhaust runner of the one that's just about to exhaust.
combine the in pressure with the out vacuum and you can get a lot more *stuff* through your bang parts... your half way to a turbo.
Again, I know almost nothing about fluid dynamics.

I never knew that.

Is that why two-stroke bikes generally stink (because they are not perfectly tuned)? lol

[schercheeroo]

If you're a masochist or suffer from insomnia you could check out this video on pressure waves in fluids;

[cat]

2 strokes also stink because they use the waste oil system and burn some of it.
With most systems you can't change one thing in isolation ever :/

[scottydugg]

This is lifted from my build thread but I finally got it fitted:
"Feedback on the new arrangement, it’s changed the exhaust tone marginally and it’s certainly smoother lower in the rev range. Is it faster I hear you cry? Maybe, it feels it, but whether that’s the alignment inspiring confidence or the ARC I’m not sure. Is it worth picking one up cheap? Yes it is.
Fitted the Ford washer jets, very misty a worthwhile mod"
MX5 08/18 by Scott Reid, on Flickr
MX5 08/18 by Scott Reid, on Flickr

It's certainly had a positive effect, it's not introduced flat spots and it does feel smoother down low, where before it was slightly jerky.

If picked up for a decent price, I don't see any negatives against fitting one.

Eventually I'd like to get the car RR'd, so if I do I'll be sure to put information in here