Q45 throttle body is NOT a 90mm!
 

I thought id make it clear for people that the vh45de (Q45) throttle body is not a 90mm throttle body. i have measured more that one the inlet measure's at 83mm. The the size of the blade is 80mm people NOT 90mm. Tired of seeing false information being thrown out there.

From researching the forum the stock FD is equivalent to an 83mm so a q45 throttle body might actually be a down grade.

i took pictures of the measurements ill post them up soon.

isn't it 90mm on the outside so you can use a 3.5" coupler?

either way, 7mm on a throttle body on a forced induction car doesn't make much of a difference.

And i'm not sure if anyone can say its a downgrade over stock, the 3 hole stock design vs. a single opening throttle body needs flow analysis to determine which is better, regardless of any difference in overall surface area.

But either way people are crunching number using 90mm as the measurement to use. we measure throttle bodies by the size of the blade not the outer diameter. 10mm difference is the difference between the fd being smaller and bigger. but yes a flow analysis would be the way to go as well.

Here are the pics i promised. One is from he inlet after it concaves is and the other is the blade or throttle body butterfly.

Uhh dude, you want the one from the vh41de. I used to own a 1997 model q45.

i just read somewhere that the vh41 used a 75mm throttle body....? i beleive also that 97 and up Q45s have the cruise control or traction control built in the throttle body which is why they arent used in the tuner world. Though i may be mistaken. From many visits to the junkyard i remember that 97+ models looked different from what everyone uses. Which the Vh41 was offered in 97+ models.

I think to support my memory lol a smaller TB would have probably been done if they reduced the displacement as well. not a whole lot of info on this out there. But indeed the TB that everyone seems to be claiming a 90mm actually tapers down to a 80mm buttlerfly :nod:

Never had a problem running a Q45 Throttle body in my R33 GTST with RB30 bottom end and a RB26 Head. As far as i can recall that TB had the cruise part built in but i just didnt use it, never caused me any problems. Can add that i ran twin BW turbos and a max boost of 1.7bar. BUT it was 90mm outside.
http://www1.garaget.org/gallery/arch...668_xpltrp.jpg

Nice ride :), also in the works of helping a friend build his rb25, he is also using the Q45 tb, but remember a Q45 tb would be considered to be an upgrade in almost any piston powered car, considered they come from factory with smaller than 80mm tb(you get what i meen). But for an FD whose tb has more surface area though 3 hole design i wonder if it is worthy of spending time and money for this.(as in for an FD)

david.fryklind : the throttle body your using is the correct one, i was refering to the vh41de 97-01 tb, ill post a pic of one so you know what im talking about.

lets get a mathimatical example borrowed from Bumpstart

Originally Posted by bumpstart
some basic tech -

multiple throttles may be set up to allow staged throttle ( as in rx7 )
smaller multiple throttles of same area to a large single
may prove more responsive to throttle changes
due to inherent more liner airflow response to tip in throttle movements off idle
( especially in petrol and liquid fuel cars when air velocity is critical )

IE
in a big single TB, a small throttle movement down low can amount to a large change in surface area, and drop in airspeed
- hence mazdas trick to use a single 45mm bore for its primary in rx7
then staged 2 x 45mm secondary, with delay till after that critical throttle position

some direct comparisons of the various common import and aussie TB sizes

will update as i go

top to bottom

circle area =
pi x radius squared


42mm x 4
3.14 x ( 21 x 21 )= 1385 mm2 each
1385 x 4
= 5540 mm2 4 x 42 mm
( bike quads , also aftermarket )

stock FD- 45mm x 1 + ( 50mm x 2 )
3.14 x ( 22.5 x 22.5 ) = 1590 mm2
+
[ 3.14 x ( 25 x 25 ) x 2 ] = 3926mm2
= 5516 mm2 staged throttle body, 1 x 45mm, 2 x 50mm
( suspect cosmo RE also similar )

stock FC- 45 mm x 3
3.14 x ( 22.5 x 22.5 ) = 1590 mm2 each
1590 x 3
= 4770 mm2 staged throttle body, 3 x 45 mm
( s4 and s5 rx7, NA and turbo )


OK so if we use 80mm => 3.14x(40x40) = 5024mm2

5516mm2-5024mm2 = 492mm2 of a difference between both. Now considering the 3 hole design should flow less(but higher velocity) , can the 80mm make up the difference?? Also think about FD pulse charge intake manifold design, wouldnt a single 80mm blade drop the air speed in low throttle input making the design of the manifold less efficient in vacumm?

With all these questions in my head i consider is it even worth it? i opted for big bore FD TB. :)