Does our Miata need individual throttle bodies? | Garage Rescue Miata

californiamilleghia said:

i love the idea of using  throttle bodies off a production car or motorbike , 

but the "brain" is a problem and  I  think beyond most of us :(

if there was an cheap Arduino type board  that could run it  maybe it be more popular , 

Even something that replaced a stock single 'smog' carb that is worn out......

I know.....dream on  !

I did it on my 924.  Used DCOE-style throttle bodies from TWM Induction and an MegaSquirt 1 w/the Extra code to also control the Ford EDIS distributorless ignition.  Used Alpha-N for tuning (leveraging TPS/RPM instead of MAP/RPM).  Worked well enough to pass emissions tests (the acceleration enrichment was a mess though, so it was a PITA to drive because I was just learning about tuning so I had a ways to go).

Its down right now because I wanted to upgrade to MegaSquirt 2 which adds more processing power and the ability to run Alpha-N blended mode where you could tune using the MAP sensor at lower engine speeds/loads, then switch to Alpha-N for higher speeds/loads.  I haven't gotten back to it in several years due to having kids and losing space in the garage to work on the car.

A buddy, Derek (he had the lambo, viper and corvette builds here), converted his 924 to ITBs off a motorcycle and was more successful out of the box due to using MS2 and having the injectors in the head.

So its completely possible.

Gonna be the turd in the punchbowl -

ITBs are cool, but just dropping in a later 1.8 will get you the same horsepower and you can tweak that for another twenty or so.  (add ITBs?)  The time and $$ you spend on ITBs just are not worth it for the horsepower.  Not sure how much the "cool" is worth.

ebay has ITBs for LS motors...

alfadriver said:

In reply to Keith Tanner :

Makes a Miata sound more like an Alfa.  :)

I see no problem with this :)

David S. Wallens said:

Good chatter. Thanks, everyone, for the interest. 

Some follow-up comments:

Need it? Who needs any of this stuff? I'm thinking pure emotion (and editorial, of course).

Keith, good point about the Link needing a MAP. Hadn't even gotten that far, but Ed and I figured we'd need to replace the ECU anyway. (And please tell me more about that set that you have stashed away. ) And what do you think about the Jenvey setups? Is that a turnkey solution? 

We've discussed bike IRTBs but Ed noted that he could feel the drivability issues from his house. (Which is not near my house as he was making a funny.)

That's the "problem" with the current setup. The engine is totally cold right now. If I turned the key, it would fire right up and then immediately set to a nice idle. No weirdness, no drivability issues--and that's with the Link, the cam gears, the lightened pulley, the aluminum flywheel, the bolt-ons, the headwork, etc., etc. Side note: The engine used to sometimes stall when returning to idle, but replacing the throttle damper seems to have totally solved that issue.

The Skunk2 intake sounds very cool but, sadly, they don't offer it for the 1.6L. Sad face. 

The Link works far better than its specifications would imply because it is coded from the ground up to be a Miata ECU. It's baked into the OS, and it makes full use of that meager hardware. But that also means a lack of flexibility to do anything weird, so it can't manage alpha-N. The problem is has with ITBs is that they run in a very narrow vacuum range and the Link has limited resolution in MAP, so it can't really distinguish between cruise and WOT. The Targa Miata ran a Hydra which is far more flexible and was able to handle the ITBs better. 

I think the Jenveys would be great on a Miata. You get the vintage look of carbs, it's really different but you can retain modern management and fuel delivery. You'd probably need a Weber adapter from Pierce and then just bolt them on. They're not turnkey because they don't include engine management. Switch to a modern Megasquirt (hello DIY Autotune!) and it could be a great solution with just the right kind of obstacles to be interesting editorially. This would also work very well for CM content, I think.

For idle, cold start, etc, just get Tom to machine a little plenum block to mount the IAC somewhere hidden and feed it vacuum lines from all four runners. Makes a world of difference in real-world driveability and that also gives you a good MAP signal.

Most of the UK crowd are using bike throttles these days, because really they're just butterflies at the end of the day. But they are also willing to accept crap driveability for character, so you do need to filter for that when looking for info.

The set on my shelf is the set that was in the dyno and talky video - some TWMs. Very nicely made with a single casting.  Not sure if you can stilll get them, I think Weber owns the brand now.

David S. Wallens said:

We've discussed bike IRTBs but Ed noted that he could feel the drivability issues from his house.

I always figured that was more a shortcoming of the tuner than the hardware.

In reply to Keith Tanner :

Thanks for the extra info. Thanks. 

Correct me if I'm wrong, but I believe Borla now owns TWM. We knew Gary at TWM. He once partied at JG's place. Did TWM made a manifold for the 1.6L?

What about the complete Jenvey kit with the intake maniold? Is it still missing anything? Still need to deal with the IAC?

And will this work with stock cams, or do we also have to go cam shopping?

Thanks. 

Driven5 said:

David S. Wallens said:

We've discussed bike IRTBs but Ed noted that he could feel the drivability issues from his house.

I always figured that was more a shortcoming of the tuner than the hardware.

He was seeing some hardware issues that he didn't like. I admit this was a few months back, so I'll have to find that conversation. 

I've already commented earlier but never been so happy to see an article asking for interest. I hope you guys land on a Jenvey kit and document it well. I'd love to add some pretty ITBs to my rotrex'd car.

My mistake, I posted earlier about the Jenvey "heritage series" bodies that are the carburetor cosplayers. I forgot they also have a bolt-on TB kit for the Miata that I believe is pretty good but more expensive than grabbing parts off a crashed bike so you don't see it as often. Still, if I were doing this I'd give it a good look. I'd still like to use the Heritage setup because it would make me laugh to have fake carbs. 

I'd recommend adapting the IAC for any application. It's something that people don't always do because it's more stuff in the engine bay (for the wire tuck crowd) or because it involves complexity/cost. But it's the right way to do it. 

Right, TWM is now Borla. And I think Pierce is under the same umbrella which may make things easier. My TWM setup has a very nice mechanism for the throttles.

Do the cams need to be tuned for ITBs? That sounds like a great story idea :) My ITB 1.6 had Web Camshaft 505s which I loved - streetable but operatic at the top end. Throw in some valve springs, a bit of compression and rev it to 8000 or so :)

I'd be interested in a thorough article. Specifically setup, tuning,  dyno and tune comparison between open stacks and common plenum, and of course all the problems along the way.

In reply to Keith Tanner :

WRT cams, w/o a real plenum, you could increase overlap to help midrange, too- and not hurt idle as much.  Kind of the other direction of increasing the engine speed.  And also differentiating whether this is for a street car to increase the sound/feel vs. going for power.  That would be an interesting comparison that can be done on a dyno with adjustable cams.

In reply to Keith Tanner :

I do hear you on fake carbs. Hmmm, more info to digest. And, yes, lots of potential editorial fodder. 

I had a Web camshaft in my Rabbit GTI. Sadly, you can no longer simply Google "Web cam" these days....

alfadriver said:

In reply to Keith Tanner :

WRT cams, w/o a real plenum, you could increase overlap to help midrange, too- and not hurt idle as much.  Kind of the other direction of increasing the engine speed.  And also differentiating whether this is for a street car to increase the sound/feel vs. going for power.  That would be an interesting comparison that can be done on a dyno with adjustable cams.

This can do some weird stuff at idle, as the fuel can come flying out of the stacks and all over the place at idle (and I have seen this). We ended up having to dial it back out, so the engine bay didn't get covered. 

I have seen ITB both make and lose power and torque compared to plenum/single throttle. Generally the ones with the best mids were on the small-ish side and had great response but lost some top end. The ones that made the best top end seemed a bit lazy in the mids to drive but looked good on the dyno. The guys making big power in the drag setups are using pretty big throttles and an airbox fwiw.

David S. Wallens said:

In reply to Keith Tanner :

Thanks for the extra info. Thanks. 

Correct me if I'm wrong, but I believe Borla now owns TWM. We knew Gary at TWM. He once partied at JG's place. Did TWM made a manifold for the 1.6L?

What about the complete Jenvey kit with the intake maniold? Is it still missing anything? Still need to deal with the IAC?

And will this work with stock cams, or do we also have to go cam shopping?

Thanks. 

TWM makes/made DCOE, DCNF and similar IrTB replacements.  That's what I used on my 924.  The only issue I had was that once they were warmed up they liked to stick slightly just above idle so they wouldn't always idle down.  This was a common problem with some of them apparently.

I used a poor-man's variable cam timing pulley (Franco automatically adjusting cam gear) along with a slightly higher lift cam and longer trumpets to help retain some midrange power.  Ultimately, the 44mm bores were just too big for my engine due to the lack of decent compression ratio.  With IrTB's you can get away with slightly smaller sizes than the carbs due to the lack of chokes.

Hard to believe these pics are from 2010!

One other thing for editorial: you can tune the powerband by varying the length of the bolt-on velocity stacks. Not hugely, but you can see it on the dyno. It's pretty cool to see. That's why the 787B rotary had an adjustable length intake.

In short, yes. It wants individual throttle bodies. That being said, you're still going to want some kind of plenum. For all the reasons above but also intake air temperature unless you plan on having the air horns sticking through the hood. My RX7 runs an IDA-style throttle body (not quite "individual throttle bodies) and before I made my plenum I could easily see 140F and higher intake air temperatures and since it was pulling in hot air from under the hood going faster didn't really improve things. After adding the air box and running a tube to a filter located in the airstream my IATs are never much more than 10F above ambient. Maybe it's a rotary thing but I also haven't really had any issues using MAP-based tuning. I'll admit my car's tune isn't 100% but I'm not sure alpha-N will fix that. Going to play around with it this Fall/Winter to see if there's any improvement.

EDIT: Pictures. Because posts are worthless without them.

Oh pics. Hard to argue. 

How do you deal with no accelerator pumps ?

My old vw bug did not have one and it had a BIG flat spot off idle.......

In reply to Keith Tanner :

Here's a guy methodically testing stack lengths (and soup cans) on a 4AGE.

Yes, it does.

When do you start?

californiamilleghia said:

How do you deal with no accelerator pumps ?

My old vw bug did not have one and it had a BIG flat spot off idle.......

They are created by the software, its called Acceleration Enrichment and its actually kinda fun to tune.  Once you get the hang of it.  After tuning cold start and the general fuel table, accel enrichment is a bit of dark art but it is where the engine really comes alive.

David, 

If you want to confuse some viewer, see if you can find a SPICA airbox.  Then you will have to find a cool air source, but heads would tilt a little in confusion seeing that.  There are some Alfa people near you that probably has a spare or two.

In reply to frenchyd :

So the guy constantly selling the V-12 love is complaining about added complexity? 

Do it!

Ooooo I'm really going to throw gasoline on the fire, yes to ITBs but only if you use a slide valve  throttle rather than butterfly type.

The flat slide carbs on my Datsun make a glorious intake roar.