70MM Throttle body upgrade, opinions.
 

I've looked high and low about all of this information and read pretty much every relevant looking thread I could find. Why don't more people use the 70mm throttle body from BEGI?

https://www.miataturbo.net/attachmen...ine=1461121820

Throttle Body. 70 mm.Polished.

I know everyone has seen my motor and hates it/me but I have some down time after my crank pulley shit the bed so I was looking into this. It (other than my head) seems to be the last restriction in my intake system. Would opening this up not help the manifold flow more air sooner and at high RPM? I have the BEGI intake manifold and 2.5" IC piping and made over 400hp @28psi. I know a lot of people asking aren't really candidates for any kind of gains with a larger TB but maybe I am?

Is there any disadvantage to this vs the Skunk2? I run no IACV or any of that stuff, it's all been blocked/deleted on my stock TB. The only thing it doesn't have is an idle screw, so that kind of sucks. Anyways, it's a cheaper option and I don't need any of the factory stuff.

So pros/cons?

Edit, it's going on this

http://i271.photobucket.com/albums/j...D5F48CBACF.jpg

Pros:
Flange might match better on the outside and look slightly better

Cons:
Loss of some part throttle modulation

the two setups i drove with 70mm TBs were very twitchy, but i think it most had to do with the bad linkage. Not enough spring-back on the cable since the TBs were for old shitty american cars.

I thought that BEGI piece looked a lot like the chinese 75mm for American cars.
New 75mm Throttle Body Direct Bolt Fit for Mustang 4 6L 2V Ford 1996 2004 | eBay
https://www.miataturbo.net/attachmen...ine=1461156368

I'm using a stock Mustang 5.0 65mm throttle body and the return spring is very weak compared to the stock Miata TB. I added a second return cable/spring to remedy that.
https://www.miataturbo.net/attachmen...ine=1461156368

TurboTim mentioned a particular mustang TB that played well.

Wasn't soviet running the stock throttle body and stock NA intake manifold? If you've got problems making more than 400whp at 28 psi, it probably isn't the throttle body holding you back.

Ok, dug through your old posts and.... I think I found the problem. You're running a 1.6L with a GT2867? I think making 400whp is a pretty good accomplishment with that turbo.

I will try to look up what Mustang TB I have and use on my Begi IM. It is probably the one TurboTim played with.

I think he's just assuming that it's a bottle neck at his power level.

I doubt it.

But since you don't need any of the OEM stuff then might as well try this out.

but I agree with the guys - there are much cheaper options available for you

One other thing that occurred to me is that people running squaretop plus 99+ head on a 1.8L aren't seeing more than tiny gains from big throttle and porting. We are talking about a head/intake combo that flows 50-100 percent better than a stock 1.6L. If there was flow to be gained at the throttle, you think the 1.8L guys would see it.

I don't see how putting a giant throttle on a 1.6 head/intake is going to be remotely useful. The 1.6L has so many flaws in terms of flow restriction and the throttle isn't close to being the worst of them. I think the 400whp result says more about the high efficiency of the GT series and the miracle working power of E85 than anything else.

the way he uses his car he should probably get away from the stock tb throttle screws anyway tho.

Go for a billet S90 70mm... 10 times better than a Skunk2. It has idle adjustment, room to mount a honda Tps and map sensor and there are heaps of good 3-4 bar map sensors out there for decent prices.

As for low throttle modulation... who needs that?

It's a turbocharged application, the stock throttle body is not a restriction at those power levels.

Yes but restrictive or not, the main reason to replace the stock throttle body is for insurance against shaft failure taking out an expensive built engine. I personally would not bother with throttle body from Skunk2 as they all have major design flaws. The S90 that I am recommending is a good balanced option in terms of quality and cost... There is even a 55mm S90 for those wanting to keep close to stock sizing.

from tim:

Yep that one. Flange geometry drawing below.

https://www.miataturbo.net/attachmen...1&d=1461242693

I've seen design flaws of the S2 part brought up a few times now, specifically what problems have you seen?

design flaws don't necessarily mean problems, even though some can become it. I think some were already mentioned in the "other" thread

Can you point to said "other" thread?

Does the epoxy mod not work anymore? Or is it just considered a bandaid?

Band-aid

One small problem: S90 does not make a Miata throttle body. The Skunk2 has issues, yes, but they are all easily rectified with a little knowledge and 5 minutes of preparation before installation. I broke a throttle return spring on an early production part, but I've had absolutely no issues with the replacement Skunk2 TB on Rover over the last ~5 years.

I love how this is some kind of closely guarded secret...

I know S90 doesn't make one for miata's but I have to change my flange regardless because it's a 1.6L car, so nothing is going to just bolt on for me. So if it's a DSM throttle or a 70mm from BEGI or a S2 I don't think it will fit on the current 1.6 flange.

Also, Did you guys test between a 52-65-70 mm TB as far as power gains? I was thinking maybe with my manifold and turbo setup I might see some benefits some where as far as power goes.

:facepalm:

no matter how you re-phrase the same silly question, the answer remains

you know what you should test with?

a higher flowing engine.

I was just curious what all people tried out there and if there were any results. If not, I'll just throw the stock one back on for the moment before going through all the trouble of re engineering my whole manifold/throttle body/swirl pot/car, just to fit a stronger throttle shaft.

but you see, that's a concern for your car: the shaft on the stocker will likely break at some point, especially the way you use the car. if you cracked your manifold several times, the tb shaft will likely not last too much longer and can take out your engine as it goes.

this is not as much of an issue for a street car.

you just need to understand that its a reliability mod, not a power mod. not for your engine

Issues are:
Sticky throttle is common... I think due to the next point
Movement in the throttle plate when partially open (ie sideways movement in the bearings)
Throttle return spring is too weak (ie return force) and the locating tag can break off
Idle adjustment screw doesn't offer enough idle adjustment so you have to use the throttle stop. (which also changes TPS)
Throttle stop bolt can come loose unless you loctite it or put on a better locking nut, or do it up very tight.

On the non Miata throttle bodies:
TPS locating tab is held on by the tiniest of screws. High reving motors can vibrate it loose.

Not all the above issues effect every throttle body. Some are fine and have no issues out of the box, but all the above are fairly common if you search. There is a good reason the Skunk2 products are referred too as Junk2 on the Honda forums. The Miata specific Skunk2 throttle body is actually one of their better throttle bodies...

I wouldn't worry about throttle modulation with a 70mm. That's all we run on the K series cars, or 74mm, and they all feel fine. Domestic guys have been running 90mm+ forever.

Edit: I can also vouch for Skunk2 throttle bodies. That's all we use, and I assume their Miata piece is similar quality.