I have two manifolds if anyone is interested in buying the

 

In regards to this topic, what manifold setup would be the best for Acceleration? DCOE would allow for longer runners and result in more low end correct?

Reason being, I am currently piecing my ITB seut up together and the only thing I am wavering on is to go DCOE, IDA, or just custom.

 

That depends entirely on the manifold. There are very long DCOE manifolds that wrap up and over the engine, and there are very short DCOE manifolds that put the carburetor next to the engine (Lake Cities style, I believe Atkins produces them now)

My favorite is the short dual DCOE manifold that TWM used to sell. The runners were very short and had next to no bends in them. And, apparently, a pair of 40s would have good drivability but flow more than a 48 IDA. That is assuming that you'd only put 40s on it...

 

the IDA is basically the same as a DCOE, its just that one is horizontal (the O) and one is a downdraft. the D stands for doppio, or double. C i think means it has a choke.

so the big difference is the intake length you end up with, IDA is in the middle, and DCOE can be short or long.

so you need to do some thinking about where you want your powerband to be, and what parts you have already selected (porting, etc). just for fun, the S4 efi is 500mm from trochoid to throttle plate, the peripheral port stuff is either 400mm or 370mm depending, and the Rx8 has 3 lengths, the shortest being around 300mm

 

Thanks for the insight! As acceleration down low would be the focus, I am definitely searching for a mid range rpm band (anywhere from 3k to 6k) .This is of course being an S4 with a moderate streetport, I am thinking of running a Star Mazda manifold with Hayabusa throttle bodies (50mm I believe).

 

Bump! I found a company that manufactures quality itb setups for a very nice price! That being said, would a 45 mm be too small for a street/small bridge build?

 

Not if there were four of them. If only two then I'd like to see 51mm at a minimum.

 

dang. They do offer a 48mm but they dont currently produce any 48mm air horns or extension tubes. for reference, this is the site : www.racehead.com.au

 

If you're looking to source just the velocity stacks, Gene Berg in Orange, CA has then to match IDA covers. They're nice and thick machined parts, not spun. They have two lengths.

 

The guy I have spoken with, Rama, has been a great help so far. He indicated that 45mms would flow fine for this type of setup. His reasoning was that larger bodies are usually selected for carb set ups due to the smaller venturi. Itbs dont have them and flow considerably more air. Also with the lenght of my intake manifold and setup, this should effectively move the power band down to around 8k.

edit: he did contact me back and stated that I could get some custom 48mm if my heart was really set on them. (which it kind of is)

 

Have you checked with Pierce Manifolds in Gilroy? 48mm is such a common size for these that I can't believe someone doesn't have a complete setup in stock.

 

my 44mm works, it doesnt make crazy power but its got torque peak down low with plenty of mid range umph. Sure if I had the right carb it would unlock a good amount of HP but that costs money.

 

Peejay, for the sake of clarity, i think i recall reading somewhere that it's the "E" that references the choke - DCO vs. DCOE.

 

if you poke around VW speed shops, you should be able to find them. in my quest to find air horns for my 50s, i come across 48s. so much so, that i'm tempted to just get some 48s.

 

So I now have my itb setup and will post pictures this evening. I do have a question that maybe RotaryEvolution or someone of similar expertise could answer. The manifold and itbs I have do not have any injector holes milled, leaving the placement of them up to me. As the motor is stock port now and will only see a streetport, what would the optimal injector placement be? should I mill the manifold after the itbs or try an mount them further upstream on my throttle body spacers?

 

Optimum injector placement is-

Primary injectors- stock primary ports in center housing (if applicable to engine) and as close to port as possible.

Secondary injectors- above the air horns in "shower configuration".

Primary and secondary injectors do not correspond to primary and secondary ports.
- It would be optimal for each runner to have a primary injector as close to the port as possible for very fast transient response and a secondary shower injector for increased charge density at WOT.

 

Mazda's R26B sae paper goes into injector placement a little.

they found that the closer the injector was to the engine, the more responsive the engine was on transients (on and off throttle), also fuel consumption went down, so they picked an injector location close to the engine.

they do mention peak power was slightly better with the higher up placement, but when they went from 13J to R26B the injectors moved closer and not further

 

Thanks! This is the info I was looking for. I was aware about the top end matter of things but unaware of the movement closer relevant to the engine. This actually works out better in my favor as it will make placement of the secondary fuel rail much easier for me.

 

"nice"

-John "Hannibal" Smith

 

Now that that is sorted out.... anyone got some links for a Weber DCOE fuel rail? ; p

 

This is really interesting to me as I have the primary injectors set in the center housings and the secondaries way out in the TB's. I have great throttle response and after converting to alpha N, great throttle transitions. I just need to see if the mileage is better than before.

Cool when theory reflects reality.

Eric

 

The stock FC primary fuel rail should fit fine, as long as you dump the pulsation damper. That was the only interference i found when using the RB dco upper manifold on my S4 lower with the primary rail in place

 

they didn't try one of each, but in theory, having the stock primary, and then the secondary way out there, should have the benefits of both..

 

With my setup, I don't think there will be clearance issues for the primary rail. I did intend on running staged injection to keep it similar to the stock fuel system. Plus, I don't wish to run huge A** primaries alone on a simple stock/ soon to be streetport. Hence, I am searching for a standard size fuel rail for DCOE style itbs (that don't cost a fortune).

Also, pictures as promised!

 

In that case, you will likely have to fab up your own standoff assembly, and either have a rail made or go super old school and attach individual fuel lines to each injector. When embarking on my itb build I intended on running staged injectors, with my secondaries in a standoff form like you're intending as well. I built the air box and the standoff tower and cut down a MK3 supra fuel rail (the injector spread on the supra is just a little narrower that the barrel spread of my weber. Ultimately, for simplicity and minimalism, I decided to just run a single pair of 1000cc injectors in the stock primary spot