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Just updating the thread. I decided to go with the Dorito adapter + the Bosch 82mm DBW Throttle Body. I haven’t been able to test anything yet but will update when I do. I really like the way it looks and the Bosch throttle body isn’t insanely large.
Will update with more pics when its in the engine bay and also after its tuned.
For the Pedal, I'm using an Rx8 pedal and making a custom adapter in solid words for it. Testing a few different designs before I send out to get it CNC'd.
I was also having issues finding an adapter that would let me bolt the rx8 pedal to the Rx7, so decided to make my own and trying to make it sit at the exact position of the stock pedal.
Just updating the thread. I decided to go with the Dorito adapter + the Bosch 82mm DBW Throttle Body. I haven’t been able to test anything yet but will update when I do. I really like the way it looks and the Bosch throttle body isn’t insanely large.
Will update with more pics when its in the engine bay and also after its tuned.
For the Pedal, I'm using an Rx8 pedal and making a custom adapter in solid words for it. Testing a few different designs before I send out to get it CNC'd.
I was also having issues finding an adapter that would let me bolt the rx8 pedal to the Rx7, so decided to make my own and trying to make it sit at the exact position of the stock pedal.
Looks like a nice setup! I'm also using an RX8 pedal, with a mounting adapter that my car's PO fabricated. When you design your pedal mount, I'd be interested in seeing the end result. I would advise designing in some fore & aft, and side-to-side adjustment into it, so the pedal position can be precisely set just how you like it. Mine is fixed, and though I got used to it, my pedal position sits a bit too high for my liking. Been thinking of switching to something like this Z-precision adjustable mount that uses a GM pedal: https://www.zprecision.com/product/r...pedal-mount-v3
If you come up with a good adjustable design for the RX8 pedal, perhaps we can get the CNC shop to do a small group buy!
Since the Aussies seem to be further along the DBW journey than stateside, I ultimately decided to pair the Dorito adapter with a 82mm Bosch TB. I selected a souped up version from these folks (86mm rated at 1100 max CFM):
Additionally, they make a really nice pedal controller, which modifies the voltage signal being sent to the ECU for optimizing overall throttle response under a variety of different driving preferences. Even wout a modified TB, this control module seems to be a very practical upgrade when going DBW.
Note: I'm using a GM pedal paired with the Z Precision mounting adapter to round out things. Project conversion is currently underway so no real-world experiences to offer just yet.
Finally have my DBW setup all sorted out. For my setup, the LS3 throttle body would have been the better fit over the LSA. The extra height of the LSA throttle body makes contact with my strut bar. Here are a few pictures as well as the pedal pinout that worked for me.
Additionally, they make a really nice pedal controller, which modifies the voltage signal being sent to the ECU for optimizing overall throttle response under a variety of different driving preferences. Even wout a modified TB, this control module seems to be a very practical upgrade when going DBW.
Yes I am, again there are RX8s with REW turbo engines making 550+ whp without issue using the RX8 TB and adapter on the REW UIM. Including the one I own.
Clearly you didn’t understand how TBs are even rated. If a TB flows 1,000 cfm at 28” vacuum, what do you think it flows with 1+ Bar boost pressure on it? You likely have much larger losses in your system than a 70mm TB would create at 600 whp. Which you likely don’t even have.
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Originally Posted by mr2peak
Here's the thing: you had a 70mm throttle body on your RX8. It was free. It works for you. I'm happy for you bro, enjoy it. But that doesn't mean it's efficient or in any way the better choice for most people.
<snipping out all the blah-blah-blah>
actually the thing is all explained well in the video linked below, starting about the 7:15 time stamp relative to throttle body size selection:
it’s stated that a 70mm ID TB is adequate for 800 - 1000 reciprocating piston engine HP = 600 - 750 rotary engine HP. Along with explanations on why it’s better not to oversize the TB, especially on a street vehicle.
So it might be worth watching the entire video to gain a better understanding overall and try to avoid the bigger = better quicksand trap wrt induction systems. So enjoy it bro, because educating and expanding your mind is a beautiful thing …
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it just depends what it actually flows, being an early 1990ish OE emission TB compared to what is available today - you’re making an assumption that for the same area it has the equivalent flow rate. Does it?
There are two 50mm and one 52mm dia blades on the OE TB? That’s 152mm of blade and shaft thickness across the center. An 82mm TB only has 82mm of center blockage fir shaft & blade.
look at it this way, if it’s too big you’re hurting yourself at both ends and overall too
an oversized TB is going to dump more air at very low blade angles, making low speed control less defined, especially as a single blade compared to a multi-blade with a delayed-progressive secondary blade setup.
and at some point on the other end at maximum engine air flow performance, an oversize throttle body is capable of supplying more air than the engine can ingest, i.e. (just grabbing a theoretical % number to make a point) if the engine is reaching max flow use at 60% blade opening, then the remaining 40% is essentially dead pedal.
So overall, it ends up being less defined relative to the gas pedal input. Sure, with a DBW setup you can electronically try to compensate for that, but ultimately it comes down to how well defined you want it to be relative to the pedal input.
My own thought is that a 4-barrel DBW TB with progressive secondary and a manifold to match having all four port runners being separated from each other should be considered
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Well, either way I'm moving the a Bosch 82mm throttle body, my LSA throttle is giving us trouble and the Bosch parameters are more available. I LSA throttle I have is very possibly not a genuine part..
If you're gonna deal with 4 throttle bodies, better make it a 4 rotor peripheral port with adjustable length trumpets.. at least that's tried and true
The key to most DBW conversions is finding the optimum balance of CFM throughput (bigger is better) vs throttle response (smaller is preferred). You obviously don't want to limit or choke the turbo you're running. But an oversized TB will adversely affect throttle response and or make low speed rpm/map tuning difficult to manage.
Ultimately, I chose the 82mm Bosch TB to pair w my EFR 8374 turbo. And my tuner did indicate to me that it was a challenge to tune (as was anticipated). But I'm guessing the 74mm version Bosch offers may even be a better choice since throttle response & overall smoothness during acceleration are bigger motivations than ultimate HP for me. That said, I can't recall if there was a suitable adapter going from 82-74mm for the FD application when I went down the DBW rabbit hole. Additionally, there is only so much real estate available before you reach that sharp bend of the intake piping in our compact engine bays. Trying to fit another adapter could perhaps get dicey(?).
The adaptor isn't the best, but an air tool and some time on the intake and adaptor will be fine.
I have a turblown DBW intake coming eventually, and it looks like that will be an 82mm native part. So, might as well make that change now rather than later.
You can use the stock rew uim secondary throttle together with a single blade dbw and a suitable control method to keep the secondaries closed until just before the secondary injectors come online... Best of both worlds
Whats the pedal feel of a dbw from a cable driven? Big difference?
It's completely configurable. Mine was setup remotely to get the car on the road and there was a bit of "lag" with the pedal initially. The pedal is not completely linear, which is not intuitive and really hard to get perfect without feeling it. Once my tuner had my car in person, it was just a few minutes to get it perfect.
There was a low mileage, looks near new 70mm RX8 DBW TB sitting on RX8Club for $50 shipped, but I think somebody just bought it
which they’re commonly used on RX8 REW turbo swaps in the 550+whp range without issue and there also being REW UIM adaptors readily available for it.
but my recent bumping of this thread came from mrspeak challenging me in such a snarky way previously that 70mm is too small. Which I chose to walk away at the time knowing there was a proper time to respond. So in the Plasmaman intake discussion linked further above from a High Performance Academy video, they state that 70-74mm is a good size for 1000 piston hp. Which equates to over 700 rotary HP wrt equivalent flow between the two engine types
Honestly though, if I had a 700+hp potential rotary engine I’d probably choose an 82mm size, but am confident recommending the 70mm RX8 TB for under 575 whp.
apparently he doesn’t understand how a 4-barrel TB works either 🤔
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If you want to run a smaller than stock throttle body for double stock HP, go ahead I guess.
I was at the track this weekend for a test and tune session for my friends FD, getting it prepped for the PT Maxnitron GT series (wheel to wheel racing, not time attack). It’s an 8374 turbo with a 90mm throttle body. We have Bosch 82mm at the shop, but 90mm is better here. We are swapping out the RW 90 for an LS DBW 90.
Another one of the team cars has the outright H pattern transmission lap record at this track (Bira). Faster than anything else without a sequential. These guys know what they are doing.
I'm not sure why there is so much tension. It's pretty much proven that the 70 is going to be fine. Likewise, it's also proven a 90 works fantastic and does not lose velocity as some would think. 82 is probably the sweet spot but who cares. They all work great! Main issue, as always, is setting it up correctly in a particular ECU.
If you want to run a smaller than stock throttle body for double stock HP, go ahead I guess.
making an assumption using generic flow rates:
50mm TB = ~260 cfm
52mm TB = ~280 cfm
FD3 TB = (1) 52mm + (2) 50mm = ~800 cfm
70mm TB = ~800 cfm
However, my bet is that the OE FD TB flows less than an OE RX8 70mm TB.
never mind that most FD’s are running intake manifolds with a total runner diameter area that equates to not just less flow area than an 82mm TB, but also considerably longer length that equates to much more total flow restriction than a short TB length. Or that the total area of smaller multiple diameters has to be larger than a single diameter area to have the same flow rating. As I keep trying to patiently explain to you.
but if you want to keep asserting that shooting-from-the-hip guesses are indisputable facts, while laughing and mocking other people like they’re less informed than you are, then go ahead and do that.
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11-02-23, 07:33 AM
