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mke
mke Dork
10/23/21 8:30 a.m.
Pete. (l33t FS) said:
mke said:

I'll add this, unlike with carbs there is very little downside to a TB that is bigger than needed.  The bigger the TB the harder is it to get a smooth off idle transition and it theory it could cost HP because there is more air mass in the intake track to accelerate so velocity should in theory decreases.  In practice though the stuff I've tried or seen tried what happens is the hp goes up as TB size goes up until a bigger TB no longer helps....I've never seen the hp start coming back down, not to say it couldn't, but I've not seen it. 

  That is still an eight valve head.  He described the intake as having "only" 55mm throttle bodies. 

That is, 55mm per cylinder.

I'm not familar with that application but  mine are 54mm because they were the biggest I could get for relatively little money ($50 each) and are costing about 0.5-1% on the flow bench so 55 or 56 would have been my preference if available. There is a company doing a 58mm conversion on them I saw...for another 300 each!  so that is not happening sad  I did cut the side of the shafts flat which added about 2% or so iirc to get me to were I am.

Mine are off a ducati 749/999 (well 6 actually) so 375-500cc per TB from the factory and I'm at about 450cc and that sizing seems about spot on with big valves and a high flowing port....its really hp/cyl whic is really flow/cyl that you're trying to match, no idea how that translates to a roary though?  Anyway,  the stock 308 or TR head flow about 60% of what I have now and on those 44mm from a zx14 or hayabusa seemed about right and I helped a couple guys install them on their 308s, one a 4V, one a 2V, both heads flow exactly the same stock btw, the 4v just needs less cam for the same hp numbers so better for pollution regs I guess.  Anyway, these are 3 liter V8s making a little south of 300hp so pretty much the same as a 1.6 or 1.8liter 4 making up to about 150hp and 150hp is right about what those bikes made stock so again everything kind of matches up to the expectation.  A smaller but higher output engine is generally more sensitive to small flow changes so something that works well on a big V8 making 50hp/cylinder is probably too small on a little 4 banger making the same 50hp/cyl. So were it me, I'd be looking for an option right around 44mm for an application like this (miata) I think.

Last thought is a TB flows better and a carb of the same size...a TB is an empty tube, a carb has stuff mucking up the air flow so when you see people switch from carbs to efi and pick up hp its usually that they had carbs that were too small and replaced with the same size TB, which is effectively bigger so they added the flow they needed, at least this is true for race engine.  On street engines you really don't have a choice but to run the carbs a bit smaller than optimal hp wise as that is the only way to keep the bottom and midrange working well and that is were street engine live 99% of the time so you just have to get that working right.  With EFI and TBs, that is basically a non-issue so I err on the large size if unsure and use a nice progressive throttle pedal linkage to give good throttle position control at small openings where a small change in throttle position makes a big airflow change so its easy to drive around town. 

With DBW so common getting a progression you like just means changing numbers in a table, not not reworking linkages.  This is how the table I use on the frankenferrari...you see the lower left the pedal move a lot for small changes in the TBs then on the upper right the TBs are moving much quick where there is a much smaller % flow change from a % position change.  at idle with the pedal full up the TBs are at 6%...this was high idle on a not well running engine so real idle will probably be say 4% but 6 for now....then when the pedal is at 20% the tbs are at 10%, so only a 4% change and that seemed about right playing with it in the garage...very progressive because that small position change will more than double air flow into the engine.  As I said in my 1st post, its the small things like this that can be really frustrating about ITB setups when you get them wrong.  ITBs are wonderful when they are right, but getting them right, especially on a street car, often takes a bit of patience.

 

 

accordionfolder
accordionfolder SuperDork
10/24/21 9:26 a.m.

You guys want a great deal on my Wossner 12:1 1.6 pistons and REALLY make it scream? These came with an engine I bought and I'm probably never going to use them...

David S. Wallens
David S. Wallens Editorial Director
10/24/21 9:33 a.m.

In reply to accordionfolder :

Please show yourself out. I mean, What more can you tell us about them? smiley

captdownshift (Forum Supporter)
captdownshift (Forum Supporter) MegaDork
10/24/21 10:02 a.m.

12:1, cams,  E85 and ITBs would make for a properly spicy fun setup. 

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
10/24/21 11:15 a.m.

In reply to mke :

Ever look under the hood of a 2.3l OHC powered Ford?  That, on steroids.

Esslinger made quite a name for themselves building fast Lima based engines.  I say "based" because they make their own heads and blocks, including tall deck blocks for the 3l+ engines.  Bring a styrofoam cooler full of money. 

 

Not all that different from what guys who rally Volvos do with redblock engines where class rules limit them to stock engine architecture and number of valves.

accordionfolder
accordionfolder SuperDork
10/24/21 4:50 p.m.
David S. Wallens said:

In reply to accordionfolder :

Please show yourself out. I mean, What more can you tell us about them? smiley

Lol, not much to say! I was hoping for 150obo + shipping. They're 500 new, and these are bnib. I think they'd make a super neat build especially with the availability of e85, just not enough time!

 

**Edit, apparently 650 new.

https://www.vividracing.com/wossner-16l-785mm-121-pistons-mazda-miata-19901993-p-132253.html

 

 

Keith Tanner
Keith Tanner MegaDork
10/25/21 8:46 a.m.

"while you're in there...."

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
10/25/21 8:58 a.m.

In reply to Keith Tanner :

2 years and $30,000 later, the car is so upgraded that it is sold at a huge loss and a bone stock NA is purchased because it's more pleasant to drive, look forward to spending time behind the wheel instead of dreading it.

Paul_VR6 (Forum Supporter)
Paul_VR6 (Forum Supporter) SuperDork
10/25/21 9:42 a.m.
Pete. (l33t FS) said:

In reply to Keith Tanner :

2 years and $30,000 later, the car is so upgraded that it is sold at a huge loss and a bone stock NA is purchased because it's more pleasant to drive, look forward to spending time behind the wheel instead of dreading it.

Every project.

accordionfolder
accordionfolder SuperDork
10/25/21 9:50 a.m.
Pete. (l33t FS) said:

In reply to Keith Tanner :

2 years and $30,000 later, the car is so upgraded that it is sold at a huge loss and a bone stock NA is purchased because it's more pleasant to drive, look forward to spending time behind the wheel instead of dreading it.

Stock 1.6 cars are fantastic for the road, but on track or autoX ... Man they're incredibly slow. Good character, but literally ~6 seconds a lap to a stock VVT engine at NCM, same tires and setup. I drove one for a whole season in 2020 and loved it, but even 141 whp from my VVT car might as well be a rocket ship compared to it.

Rodan
Rodan SuperDork
10/25/21 9:07 p.m.

In reply to accordionfolder :

I can vouch for this.  Compared to a worn out 1.6, a stock VVT 1.8 at ~140hp is a LOT of fun.  But it's still not really fast... wink

wspohn
wspohn SuperDork
10/26/21 9:55 a.m.
DeadSkunk (Warren) said:

Wanna screw with people? Put four SU carbs on it with the pistons locked up in place so that they're just throttle bodies.........

SU sort of did that themselves (I owned a pair of these).

David S. Wallens
David S. Wallens Editorial Director
10/27/21 11:18 a.m.

One thing I do like about the Miata's current setup: It uses pump fuel and, as a result, I can fuel up anywhere. It doesn't have a huge tank, and on the highway the engine turns about 4500 rpm. Being able to fill up anywhere has been nice. (I know, think about the editorial....)

californiamilleghia
californiamilleghia UltraDork
10/27/21 12:00 p.m.

In reply to wspohn :

the 2 barrels are cool , how rare are they and what did they come on ?

Thanks

wspohn
wspohn SuperDork
10/28/21 11:48 a.m.
californiamilleghia said:

In reply to wspohn :

the 2 barrels are cool , how rare are they and what did they come on ?

Thanks

The DU6 carbs were very rare back in the day. They used them on the Lotus FPF engines (used in F1 cars), Cooper Monacos, briefly experimentally in MGA Twin Cam factory racers, and the Triumph TRS Le Mans cars.

Very, very rare for many years, they are now being reproduced for Jaguars etc. at pretty eye-watering prices.  I played around with them a bit as I was setting up an MGA Twin Cam for racing, but I decided (wisely, I think) to go with the more easily tunable 45 DCOE Webers, just as the factory had done.  

Should have hung them on the wall as garage trophies but sold them to someone who was restoring one of the TRS cars.

captdownshift (Forum Supporter)
captdownshift (Forum Supporter) MegaDork
10/30/21 10:53 a.m.

ITBs and bear wheels so that the induction noise from the ITBs can be referenced as the growl of the bear. Or you can go panda with it and turn a bamboo shift knob. There is 3D printing filament that is made from bamboo as well for some questionable theme ideas. Such as a bamboo printed pi dash surround, bamboo spoiler risers, etc. 

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