TII secondary THB mod (pros and cons).

[rotorlips]

hello all ! so, I decided to post here to get some opinions on the thb mod of removing the secondary plates . have the uim off my turbo II vert and have a great chance to remove the secondary plates if need be . so, should I or should I not ? motor is street ported, bigger turbo, front mount bla bla all the other stuff you can think of including stand alone . car runs great and is quite fast .I do have cold start hooked up but never had the thermowax valve as its a jdm valve and no port for the thermowax . no vacuum for it and no linkage going to the plates. all 5 plates move together regaurdless of temp. no idea why the jdm thb's dont have the thermowax . so, should I just leave it alone (aint broke dont fix it theory) or remove,weld the whole and go with it ...thoughts? Im listening .. thankx

[RETed]

http://fc3spro.com/TECH/HOWTO/TBM/tbm.html


-Ted

[NoDOHC]

I know of no cons, I think that it may have been installed for driveability / to protect the engine when cold.

Pros:
Slightly better throttle response,
More consistent to tune to
Pointless with no thermal wax anyway
Very minor power increase (will probably not notice)

I have none on my 4-port (stock intake manifold) and it runs fine in 20 F weather.

[FRED]

There's some small errors on this thread. To me worth mentioning an to others not worth mentioning or they would have said so. Anyway.

What makes the outer set of secondary plates ( the number two seocndary throttle valves) move is the DOUBLE THROTTLE DIAPHRAM in conjunction with the water thermo valve which is NOT the water thermowax device with the fast idle cam etc.

On a turbo thottle valve the number two secondary valves were designed to move/open slower than the number one secondary throttle valves. Driveablility thing. There is on a USA turbo throttle valve a dashpot who's plunger rides on a flat black cam and the dashpot is what makes the outer set (the number two secondary throttle plates) open a tash slower than the number one secondary throttle plates.

I find it hard to believe the JDM's have five plates and they all work together when they were built stk. But I never owned a JDM so take that for what its worth.

[rotorlips]

There's some small errors on this thread. To me worth mentioning an to others not worth mentioning or they would have said so. Anyway.

What makes the outer set of secondary plates ( the number two seocndary throttle valves) move is the DOUBLE THROTTLE DIAPHRAM in conjunction with the water thermo valve which is NOT the water thermowax device with the fast idle cam etc.

On a turbo thottle valve the number two secondary valves were designed to move/open slower than the number one secondary throttle valves. Driveablility thing. There is on a USA turbo throttle valve a dashpot who's plunger rides on a flat black cam and the dashpot is what makes the outer set (the number two secondary throttle plates) open a tash slower than the number one secondary throttle plates.

I find it hard to believe the JDM's have five plates and they all work together when they were built stk. But I never owned a JDM so take that for what its worth.

well, perhaps I worded something wrong . let me try again here . all the jdm motos I have and not one of them has the thermo valve. the fast idle/thermowax is there but no valve, no vacuum hoses and no vac diaphragm . so, its almost as to wonder why the plates are even there . perhaps if I adjusted the dashpot for the plates I could get it to open a tad slower than the others . Ill have to compare to some other stock ones I have . all the USA ones have the vac hoses and diaphragm . works with the whole cold start thing . however, I have the cold start hooked up, no valve . just debating on wether or not to take the plates out or not . full stand alone ecu and bunch of other stuff . 100% working car all ready with no issues. hmm what to do .

[RETed]

It sounds like the US-spec ones are the only ones with the thermowax - think of it as a mechanical choke for cold start.
The thermowax prevents the double throttle from opening all the way, so it keeps the fuel mixture rich by resticting intake into the engine - how an old-fashioned choke would work on a carb.
Once the coolant gets up to temp and melts the thermowax does it release the double throttle plates to fully open up.


-Ted

[rotorlips]

so, been thinking and looks like im going to remove the plates and weld up the hole . looked at some 86-91 n/a thb's and they seem to work a bit different . once the thermovalve lets the vac go, the plates stay full open all the time.seems that the 3rd gen is set up the same way . just the turbo IIs seem to have this combination of valve keeping plates closed until warm up on USA models. not sure what their purpose is on jdm motors. driveability maybe? if they are for warm up then I understand but how they help for smooth driveability I have no idea if n/a and 3rd gen stay open once fully warm . I have a stand alone ecu so I can play with the accel enrichment and decay . hmmm

[FRED]

The last time I looked the number two secondary plates do NOT stay open all the time. There is some linkage consisting of a damper.....rod and spring and a flat black cam that delay the opening of the number two secondary throttle plates.

That's why those parts EXIST on a USA turboII thorttle body.

You'll get no argument from me that on a NON TURBO engine the number two secondary throttle plates stay WIDE OPEN after the engine warms up. NOT so on a TURBOII car for the USA.

A jpg of a USA body is attached that I stole off the web. Pay no attention to the red arrows. To the left you can see the flat black cam that the piston of the damper rides on. Black cam is just to the left of the bottom 12mm wrench size nut..............the damper is the gold round object in the left bottom of the picture.......the rod and spring with 8mm wrench size nut are to the left and in the middle left of the picture.

The cam.......rod and spring....damper cause the number two secondary plates to open slower than the number one secondary plates for Driveablility purposes and this happens long after the engine is fully warmed up.

If the double throttle diaphram is installed and if the water is still cold.......the number two secondary stay fully closed and the black cam etc play no part whatsoever til the engine gets hot.

[Garfinkles Motor Works]

Remove them for better flow and weld the holes not JBweld .I have done a couple and many for 3rd gens . Plus you can port the casting for better flow, reshaping or porting the casting is easer if you remove the plates and shafts.I also replace the round headed screws with counter sink screws to get them out of the air flow .You must counter sink the shaft to do this . Good skill to you .

[FRED]

The jpg attached are of a JDM throttle body, but is a series five.

First jpg shows the flat black cam, damper, rod and spring that control the number two secondary plates.

Second jpg of the JDM throttle body show the number two secondary plates shut which is normal til the pedal is stepped on fully and then they are supposed to ( on a stk car) open after the number one secondary plates and primary plates open.

And yes, no double throttle diaphram is shown for the JDM.

Thats what a stk JDM throttle body should look like for a turboII.

[FRED]

And I might add that the outer set of secondary throttle plates can come in handy especially on a series four non turbo engine converted to turbo. If one uses the stk turbo on that configuration and deletes the twin scroll......the car will bogg down and have less torque than a non turbo engine til you get the rpms up over three grand. But if you run a vacuum line to the double throttle diaphram the outer set will stay closed til you virtually get into boost, thereby increasing the low end torque. Makes the thing driveable in the neighborhood when just going to the store to do shopping i.e. normal drive situations. Thanks to a kiwi named Bumpstart for that idea.

[FRED]

A fellow from Aus who goes under the name BUMPSTART, added these words about the configuration of JDM turboII throttle bodies:

************************************************** ***********

later JDM still has the wax cam,, just lacks the vacuum thermoswitch and double throttle dash pot that holds off secondary operation when cold

warm,, the throttle delays work all the time ,, following behind the main throttle plate movement
and is set via the dashpot which adds drag to a black plastic bob weight

these are found on N318 updates and also on s5 n370 ,, though there is trivial differences in the two TBs and they are not exactly the same
( mainly TPS differences,, but s5 TB also requires a shorter mounting stud on the bottom of the pattern to the UIM )




early s4 t2 ( jap and aus ) have a wax cam ,, and a thermoswitch ,, and a double throttle diaphragm which allows vacuum to hold out secondary delay operation when cold

- but as above,, the secondary delay throttles always follow behind the movement of the primary throttle
they are never locked in the open position
and,, in mazda words,, is provided to prevent a lean condition during rapid acceleration

these TB's are less common,, but are obvious to ID from the added vacuum can that is working on the delay mechs

i seek these TB's out,,, clever use of the vacuum delay , hooking it to primary runner vacuum ,, amounts to boost / load demand secondaries ,, something akin to the way the secondaries work on the old nikki carb

[rotorlips]

all welded up . going to put it all back together and see what happens . I was removing the pulsation damper and stock fpr so figure perhaps this may be a great time for the mod. not that I had a problem before but seeing so many the the stock dampers fail I figured why not . the aeromotive fpr will now be the only dedicated regulator for fuel . thankx for all the input .

[FRED]

Another JDM turboII throttle body. I'd no idea this version existed. No flat black cam but has the spring/rod for the outer set of plates and seemingly a diaphram of sorts that is triangular in shape with a black vent on its side.

This is just FYI and nothing more or less.