View Full Version : Dual throttle intake??

15-05-02, 10:41 PM
What would be the effect of placing a custom large plenum chamber with dual XF throttle bodies on a N/A VL, to the standard position, running back over the head?

By opening in unison will it be detrimental to performance down low or would it be better opening in sequence?

This setup would flow some serious o2. Will Torque be affected at all, or is it overkill fullstop?

Just curious.

Peace. :D

16-05-02, 01:41 PM
XF throttles are big enough to support more HP than you can easily make out of an RB30 in NA form. So two would be overkill.

There is no real problem with having too big an opening when you are at full throttle. The problems emerge when you are at very light cruise and the throttle is only just cracked. You can probably guess that with one VL sized TB you would have to crack it open by a small amount. With two bloodyt great XF throttles, you would have to have them cracked open a much smaller amount. Possibly so small that there is no difference between what you have opened them to and closed. In that case you lose control, call it lack of fine control.

If you run them staged, then you have to be careful that they aren't biased left to right, which they will be....so you would need a taller plenum so you could mount them one over the other to keep them central...and you would get bonnet clearance problems.

If you want to go dual throttle, get two VL ones and run them in parallel....this is exactly the way a 7MGTE inlet works, go have a look at one if you haven't seen one.


16-05-02, 08:19 PM
i see were your going, but the rb30 is great cos of its torque, and with twin throttle bodies(even stock) your gonna lose most of that!

Way overkill! Take the 304 v8s, alot of guys chase down the twin tb manifold only to find they lose power(yea i know you gotta tune for them)

It would looks great but would be damn stupid, plus you computer would probably think your MAF sensor was talking shite, (or is it MAP....well if it is you wouldnt have bugger all manifold pressuer at idle, so that would stuff up the comp too)

Try finding some other ways of spoending your time/money :D


16-05-02, 09:23 PM
ta guys, thought the tourque would ide in the ass but was just curious

single XF throttle body here i come!

peace :D

16-05-02, 09:24 PM
eh words

torque and die

who's awake...

16-05-02, 09:40 PM
check out the april 2000 issue of street commos. a bloke has made a twin tb setup and although he uses an aftermarket map with no afm he has actually made a considerable amount of power (for a atmo vl) pretty simple too

16-05-02, 09:58 PM
Thanx man, i started my collection December 2000 so i will have to order a back issue.

16-05-02, 10:01 PM
shame on you. you should have them all. nah its good to see ur reading a legendary mag now. good luck with ur t/b's

17-05-02, 01:18 AM
Karl, you're not going to lose any torque at all. The same amount of torque will be there if you want it to be, all you have to do is open the twin XF throttlebodies to the same amount of 'air flow' that the VL n/a one would be. See my point now? Make sure you read and re-read GTSBoy's post, he explains the whole thing very well.

Did you know that Formula 1 and an increasing amount of production cars (nissan x-trail for one) have a throttle that is not directly actuated by the throttle cable? The throttle butterfly is opened and closed by the ECU to provide optimum torque/driveability at all times.

Back to the main topic, I think this would be and like GTSBoy said, has gotta be beneficial. Perhaps you could rig a variable cam on the throttle actuator cam so that the first 1/2 of the accelerator pedal travel opens the throttle butterflies only 1/3 of the way. This would make the throttle control greater in the ranges where you guys are suggesting torque would be lost.

17-05-02, 01:46 PM

The closest i can get to a Supra engine is pics and i can't see what you are talking about based on the pictures available from the link below: :(



17-05-02, 03:30 PM
Perhaps this loss of torque idea comes from a carby setup, where a larger carby can loose torque and low down power because the air velocity through the venturis is no longer fast enough at low revs to atomise the fuel properly.

(I've got that right haven't I? :) )

17-05-02, 03:52 PM

Yuh...although in an EFI car you will also lose torque if your manifold runners are too large diameter due to reduced gas speed blah blah blah (It's the same stuff anyway).


That is one type of 7M inlet setup. The other sort has two side by side TBs where the one in the picture has just one. The cross over pipe forks about where it starts to go over the cam cover on the driver's side...so where the picture has that HKS branded cross over, the other motor would have a Y shaped piece that goes to the two TBs. The TBs are about where you would want them to feed the three inlet runners (ie about opposite runners 2 and 5).

Keep looking, you should find one somewhere.


17-05-02, 04:58 PM
Hmmm foud this pic but its off a JZ engine, with only one tb it seems

17-05-02, 05:41 PM
Yuh...exactly that but with two TBs in between the Y and the plenum.

I knew one of the J motors had the Y but couldn't remember if it had one or two TBs, that's why I didn't mention it. Just as well too.

My mechanic has one of the 7M twin TB setups to go in his VN (on a 7M) and we were pondering the benefits of doing it to my RB20. But in the end I decided if I was going to go to the effort of cutting up and modifying th eplenum I would be better off making a proper plenum with the TB on the end so I can use shorter IC piping and keep it out of the hot part of teh engine bay for longer. Still a dream for the future tho'.


Andrew Bolt
18-05-02, 01:19 PM
Just to clear up a little confusion, the 7MGE and 2JZGE have a SINGLE large throttle body which divides into a Y and then has 2 entries into the plenum. Inside the plenum is a butterfly valve which divides the plenum in 2. This butterfly valve is activated by vacuum and electronics to open and close and hence "alters" the length of the runners so as to provide more low down torque. This system has been patented by Toyota as ACIS (Acoustic Control Intake System). However many other manufacturers have a similar setup to vary runner length and runner harmonic frequency.

By the way, 2 XF TB's will be way overkill.

18-05-02, 03:56 PM
ok then

what the total consensus is that 2 XF tb would be overkill on a atmo vl :cool:

so what would be the best path to follow?

2 smaller tb's at aimed runners 2 and 5?
One larger than XF throttle, then split in the Y fork like onthe JZ motor to enter plenum at runners 2 and 5

or will a nice Fat XF throttle body supply all the air it needs?

What is a XF tb rated for flow hp wise?

ta in advance. :D

19-05-02, 01:35 AM
Hmmm..... I have seen that 7M with two TBs on it......maybe it is a hack job. I shall have to go have another look.

But on the topic of making mods to an N/A RB30.....I wouldn't bother. The factory TB will flow enough for most mods that you can afford to make to the rest of the motor.


Andrew Bolt
19-05-02, 10:52 AM
Given that there are 2 entries into the 7MGE/2JZGE plenum, it's a very easy mod to convert to 2 throttle bodies (and I'm sure someone out there has done it), but standard they come with one TB which divides into a Y to have 2 plenum entries, and have central plenum butterfly controlled by ACIS (like in the picture in the post above).

The 7MGTE has a single throttle body and single entry into the plenum located in the middle across the top of the rocker cover, whilst the 2JZGTE has a TB located at the front of the plenum.

There is a good article on autospeed on basic plenum design, and in the Toymods tech forums there was a thread about plenum design with a few other handy links.

Cheers Dave.

19-05-02, 06:12 PM
Alright thanx again guys

i may opt for the xf throttle just to see how it goes

19-05-02, 11:31 PM
How would two XF throttle bodies be bigger/worse than having six individual throttle bodies (one for each port)?

20-05-02, 12:07 AM
hmmm, gains are there to be had...


ported manifold and ported standard tb (makes it 59mm to the xf tb's 64mm)

18% increase in power and 25% increase in torque on a VL already fitted with rampod and 2.5 inch exhaust

so the engine can make the ponies but the intake is restricting it?

in this case im thinking that the XF may be a good option.