2GR Gutting ACIS? - MR2 Owners Club Message Board
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post #1 of 15 (permalink) Old July 29th, 2019, 11:00 Thread Starter
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2GR Gutting ACIS?

As you might have guessed from my head porting thread, I'm looking for more low cost / low effort ways to squeeze a little more out of a stock 2GR. Not that I'm dis-satisfied with the power, but I just can't leave well enough alone. And once I start wondering if something *might* make a difference, I want to know for sure!

So, any thoughts on what if anything might result from completely gutting the ACIS system and plenum divider?

We know the ACIS system as-is helps torque in the mid range (~2800-4300 rpm):


If I am understanding the system correctly, with the ACIS flapper closed the manifold is divided in half horizontally nearly to the throttle body, with half of the runners taking off from each half of the manifold. When the flapper opens these two cavities are connected, allowing all of the runners to draw from an effectively larger plenum, and with reduced runner length.

But here's the thing. The flap is actually quite small relative to the rest of the manifold. From looking in through the throttle body, I would say maybe an inch wide by a few inches long, and it only opens about 45. So while opening it might have a decent effect on intake resonance, any flow exchange that might be trying to happen between the two halves of the plenum will be pretty restricted still.

What I'm considering trying is getting another #2 manifold, cutting the ACIS actuator out of it, grinding out the divider to make one open plenum, and then sealing up the ACIS hole with a block-off plate. Might be necessary to cut a hole in the bottom as well for access, but a little sheet metal, some sealant, and a few pop rivets should take care of that and not be visible when done.

Thoughts?
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Last edited by Alex W; July 29th, 2019 at 11:15.
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post #2 of 15 (permalink) Old July 29th, 2019, 17:51
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I am really curious to hear what comes of this. I suspect you won't get a noticeable difference but this is one of those things you simply don't know until you try it.

It would also be interesting to play with intake pipe length while talking about cheap gain possibilities.

beyond that it would be neat to design a higher ratio rocker to get more lift without a cam regrind but the cost would probably end up being higher than just getting regrinds.
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post #3 of 15 (permalink) Old August 2nd, 2019, 09:48 Thread Starter
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Yeah, worth a try I think. I wouldn't have thought there was a worth while difference between the stock manifolds until I tested it.

Looking at the dyno graph above and doing a little extrapolation, it looks like if the ACIS was held shut all the way to redline there would be a huge loss (looks like it would be down about 10ft-lb at peak torque, and probably a lot more at high RPM). So if opening that small flap causes that sort of gain, it seems plausible that opening it up further could be worth something as well.

New manifold is supposed to arrive on Monday.


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post #4 of 15 (permalink) Old August 2nd, 2019, 16:47
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While you're in there i'd love to get some inside pictures if you're willing to post them.
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post #5 of 15 (permalink) Old August 2nd, 2019, 21:11
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Any thoughts in trying to 3D print a larger plenum and epoxying/bolting it together (I'd assume it'd be done in like 2-3 pretty big pieces at a minimum)?

Or a fabricated aluminum manifold, but I feel like on an NA application you could make a PETG plenum easily work and be pretty easy to print. Nylon or ABS would be a little stronger at higher temps, but harder to print large stuff at good tolerances.

I would think the worst case loading would be sitting in traffic with everything super heatsoaked, but the plenum should probably still stay below about 160 F, and PETG is strong enough to probably get her done. You could always wrap the finished piece in fiberglass/carbon fiber and you'd easily have enough strength then.

Gutting the stocker is definitely the easy button tho'.
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post #6 of 15 (permalink) Old August 5th, 2019, 19:38 Thread Starter
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While you're in there i'd love to get some inside pictures if you're willing to post them.
Of course.

















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post #7 of 15 (permalink) Old August 5th, 2019, 19:40
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Thank you for posting the pictures.

You know, after seeing the insides i have a suspicion that this will help the top end a few horses. I'm guessing only 5hp or so but i think you'll see something. Probably a bit of low end loss also.
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post #8 of 15 (permalink) Old August 6th, 2019, 00:29
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Did you radius the edges of all the internally wetted areas? Even something like a 1/8" radius helps a lot to prevent flow separation at higher Reynolds numbers.
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post #9 of 15 (permalink) Old August 6th, 2019, 00:30
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Oh, and is there room on the plenum close-out to make the plenum volume larger? Basically bump it out to where it just clears the engine? That should shift power up a slight bit.
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post #10 of 15 (permalink) Old August 6th, 2019, 07:52 Thread Starter
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Did you radius the edges of all the internally wetted areas? Even something like a 1/8" radius helps a lot to prevent flow separation at higher Reynolds numbers.
A little, and I will try to do a bit more with some sand paper before I close it up. I also think I will try deburring the edges with a torch, I think that should smooth things out nicely (the plastic melts and flows pretty readily).

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Oh, and is there room on the plenum close-out to make the plenum volume larger? Basically bump it out to where it just clears the engine? That should shift power up a slight bit.
Maybe a little, but there isn't a whole lot of room to the valve cover. And it would be a lot trickier than just a flat closeout. The plenum volume will be increasing a bit regardless just because of all the stuff that was removed, and the area at the end that was the ACIS actuator adds a bit as well.


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post #11 of 15 (permalink) Old August 6th, 2019, 07:57 Thread Starter
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oops


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post #12 of 15 (permalink) Old August 8th, 2019, 07:37 Thread Starter
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Well, this turned out to be one of those "Toyota knows what they are doing" things. Preliminary testing based on MAF readings show exactly the same mid range loss as with the ACIS unplugged, and zero top end gain. If anything, it lost a couple of g/s at the top end, but it's hard to pick 1g/s out of the noise on a log of MAF readings.

A little surprising, it looked like it should make a difference! Maybe it would if something else was changed? Could be that the stock manifold is ideal for a motor with stock cams and as you do other things to increase flow the manifold would become a restriction.


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post #13 of 15 (permalink) Old August 8th, 2019, 07:53
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Alex, I really appreciate you trying this kind of stuff to see if there is anything there. It would really be awesome to get that last 10hp to get to that magic 300rwhp.

According to DDPR, the thing holding us back from that last 10-20hp is longer primary exhaust runners. According to the online calculators the current runners are the right size to make peak power near 7500RPM and if they were to be about 10" longer we'd move that peak power down to 6500RPM or so which would be more appropriate for the current cams. Maybe that's why my headers/tune responds so well to those MWR cams because they move the peak power to that 7500RPM range and everything is in sync then?

Maybe with those the slightly shorter runner setup due to opening the ACIS valve and the plastic around it would make a difference there?
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post #14 of 15 (permalink) Old August 8th, 2019, 08:16 Thread Starter
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Yeah, that's what I'm wondering. And yes, I was really hoping for a cheap way to break that 300 number! I'm not going to throw it away, if I ever get cams I might test it again just in case it helps once other things are flowing better. Longer exhaust runners might be nice, but man that would be a pain in the ass to package.

You say the headers respond well to the cams... have you seen a dyno with the cams yet? I'm really hoping Mike Reed will dyno his car...

I will say one thing, that ACIS module is a brick! For the "every ounce counts" weight savers out there, the ported manifold was 1.8lb lighter than the stock one (most of that being the ACIS).
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post #15 of 15 (permalink) Old August 8th, 2019, 08:40
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Im not 100% sure its my headers but the whole configuration, changing only the cams responds very well to MWRs stage 1 cams. essentially the horsepower rolloff moves from 6500 to 7500. it only gives a touch more peak power but makes the power band way wider giving you a bunch more area under the curve when accelerating. I don't have a dyno sheet to point to right now but yeah, Mike should be posting some soon-ish.
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