twin throttle body vn v6

[6cylpwr]

im thinking of having a go at modifying a stock vn v6 intake manifold to take two stock throttle bodies on the top, and blocking the back section off. ill get some dodgy pics up of what i mean when i get a chance, just wondering if any computer work/tuning will be needed to run two throttle bodies, and two airflow meters or can it be map based with the pressure sensor after the throttle bodies?

[Andrew426]

Your car already has a map sensor - so there isnt really all that much to do. You will need to adjust your kickdown cable but thats about it (i think).

I was planning on making the same setup when I was doing my aluminium welding tickets, but everyone around here wants $60+ for a series 2 manifold so i deemed it too expensive and a waste of time.

Also, on a completely stock engine you wont see the full benefit of a twin TB manifold. You really want a cam and full exhaust to go with it.

Should be a good project though - post pics when you are done. I am especially interested in how you are gonna duct it. I wasnt gonna bother with ducts for mine. I was just gonna chuck a couple of foam filters on top, cut a couple of holes in my bonnet and modify a grp A style scoop to work as a cowl induction scoop.

[6cylpwr]

Your car already has a map sensor - so there isnt really all that much to do. You will need to adjust your kickdown cable but thats about it (i think).

i thought it did, just wasnt sure, i just remember this morning that it didnt have an airflow meter anywhere between the filter and tb. can you tell me which sensor it is and where?

I was planning on making the same setup when I was doing my aluminium welding tickets, but everyone around here wants $60+ for a series 2 manifold so i deemed it too expensive and a waste of time.

i already have a manifold to do the work too, i bought the vn with a stuffed engine that had done 250,000ks. went to speeds holden spares and bought another engine with 166,000ks for $100. so now i have heaps of spares if something breaks, or i want to try modify something myself.

Also, on a completely stock engine you wont see the full benefit of a twin TB manifold. You really want a cam and full exhaust to go with it.

cant say it wouldnt be cool though

Should be a good project though - post pics when you are done. I am especially interested in how you are gonna duct it. I wasnt gonna bother with ducts for mine. I was just gonna chuck a couple of foam filters on top, cut a couple of holes in my bonnet and modify a grp A style scoop to work as a cowl induction scoop.

i had pretty much the same idea about ducting as you, except i wasnt entirely sure if i wanted a scoop on the bonnet...i was thinking just have the throttle bodies poking through the bonnet with a filter a bit like this covering both of them.
E-3514 - K&N Replacement Filters, Custom Air Filter
should be a good learning experience for me. i wont be doing the welding, but i'll probably give porting and polishing a go, as well as making sure all the runners have roughly equal flow from the throttle bodies...how am i gonna be able to check that?

[Zuicider]

tried the two throttle bodies out the top need to cut the bonnet to suit right through the middle of the frame. even with the intake machined right down

[voxbox]

As andrew said, there's probably not a great deal of point in doing it, other than showing it can be done. You may find you actually lose low-end torque due to reduced airspeed of the in-coming air(this is why alot of engines run either variable-length intake runners or staged opening of throttle butterflies). It shouldn't be an issue for the MAP/MAT sensors tho, provided they still take their pickups from the plenum.

If you were to go forced induction, or high-compression N/A with big cams and huge valve lift, having dual TBs would be greatly advantageous.

*deposits 2c*

[Andrew426]

What you could do is use a series 2 intake manifold instead, which (iv heard - never had one apart to look) have the intake runners an inch longer. This could help make up for your lost torque.

Also, you could try going with 40mm throttlebodies instead of the (60mm?) stock ones to keep the air velocity up.

[VT-565]

Another tip would be to check out the VL & VN Group A twin throttle set ups, they have a smaller, delayed second throttle for use with WOT.

[immortality]

the twin TB's mounted straight on top has been done on a stockish engine and the guy claims good results. was a member on this site, i think he's on the other commodore site also. i believe MACE ENGINEERING GROUP PRODUCTS do a variation of that with a new plenum top that has the twin TB's hanging of the side much like the grp A manifolds and there is another company that has also developed something similar and are claiming 230kw/165rwkw on a built engine with their manifold.

[Andrew426]

In the time I spent looking into this, I did come to the conclusion that two TBs mounted pointing straight up is the best way of doing it. ****ing around with secondaries and side mounted TBs leads to all kinds of flow issues, with uneven flow and certain cylinders leaning out at different throttle positions.

If you have the money to invest (and I mean a LOT of money) there are definitely better ways of doing it - but for the average guy in his garage playing around with spare bits, I do think this is the only way to do it.

[greenfoam]

You can easily make the high speed flow go better into the rear Cylinders with a little bit of grinding, I done that on my Lexcen, so there's no really need to go crazy with twin throttles

[immortality]

You can easily make the high speed flow go better into the rear Cylinders with a little bit of grinding, I done that on my Lexcen, so there's no really need to go crazy with twin throttles

i might give mine a quick tikle with the rotary tool. any advice on what particular area's i need to look at. i was mainly gonna clean up casting marks

[greenfoam]

Yeah on the first two (rear cylinders) where the bend goes in the manifold you can cut back all that area of the manifold and even into the bend pieace if you want, just so there's a nicer blended entry into those rear cylinders, just don't go too far down on the flange face so it still seals but you can go silly through the rest of the thickness of the flange. If that makes any sense I hope so. Not sure if theres any gains there really but it must all add up in the end

[immortality]

Yeah on the first two (rear cylinders) where the bend goes in the manifold you can cut back all that area of the manifold and even into the bend pieace if you want, just so there's a nicer blended entry into those rear cylinders, just don't go too far down on the flange face so it still seals but you can go silly through the rest of the thickness of the flange. If that makes any sense I hope so. Not sure if theres any gains there really but it must all add up in the end

cheers, thats what i figured, clean up the short raduis turn into the rear runners and remove any sharp edges that destroy a nice laminar airflow and create turbulance

[6cylpwr]

when it comes time to hook all this up, im gonna take a punt and say i only need 1 tps and 1 iac valve plugged in? the other ones can just be there but not plugged in?

[immortality]

when it comes time to hook all this up, im gonna take a punt and say i only need 1 tps and 1 iac valve plugged in? the other ones can just be there but not plugged in?

yep. but you need to make sure the 2nd IAC is fully closed. use the TPS on the 2nd TB as you need to make a linkage between the 2 TB's. you'll also need to block the vac ports on the 2nd TB

[Andrew426]

when it comes time to hook all this up, im gonna take a punt and say i only need 1 tps and 1 iac valve plugged in? the other ones can just be there but not plugged in?

Pretty simple really, as immortality said, link the two together then block up any holes that you wont be using.

I would steer away from grinding internal bits out of your intake manifold though. turbulent air entering the cylinder may seem a bad thing in theory, but it helps move the air/fuel mixture around - you can actually lose power by doing this.

[immortality]

I would steer away from grinding internal bits out of your intake manifold though. turbulent air entering the cylinder may seem a bad thing in theory, but it helps move the air/fuel mixture around - you can actually lose power by doing this.

what your talking about is swirl and is different to turbulance. the problem with the buick manifold is that the air distribution in the manifold isn't that great for the rear cylinders as the air has to perform a nasty turn to get into the rear runners. holdens answer to this was the plastic bellmouth in the s2 motors. creating swirl is as easy as porting the bowl/intake runners with some biase towards the long side which the air naturally flows down and then around the valve. for a efi engine with the injectors just before the heads good fuel atomisation comes down to the injectors/fuel pressure

[greenfoam]

The only time you need turbulance in a manifold would be in a carby car and even then you don't really want it but it does help keep the fuel from a carby suspendend in the air. No point when your injecting a mist straight into the port. The bellmouth actually is suppose to help smooth out the idle by helping the front cylinders get some air at low speed. It only makes things worse for the rear two at speed and they are the real problem anyway, but they wanted a good idle, I don't think they cared too much about top end. And you wont loose any torque putting twin throttles on it because the velocity through the runners and head ports will still be exactly the same as it was before. But I still can see it really making any gain. The best thing would be to cut the manifold off at the base and make proper runners and two plenums, one for each bank of the motor but that's a big job