View Full Version : 2x4 intake

09-08-2004, 11:11 AM
Starting to put together some ideas for a EFI system and was wondering if anyone has used a 2x4 intake manifold. I know it would have to be a system that would to be some what peiced together but what would be needed exactly what company would be easiest to adapt? Also I would think the wow factor when popping the hood would be pretty cool. Thanks Jon Keller

09-08-2004, 12:21 PM
A Holley Stealthram is a tunnel ram base that was re-cast with injector bungs. It would be really cool if a regular tunnel ram top still bolts to it. I'm positive one could be adapted. You could run dual throttle bodies up top and a Holley Commander 950 to run the system.


09-08-2004, 02:35 PM
I think a crossram style manifold with two throttle bodies would be pretty trick too...but then again i ate paint chips when i was younger

09-08-2004, 02:53 PM
the crossram intake would be really cool even just with carbs but it would be a little hard running fuel rails I would think, maybe a tunnel ram with short runners so hood clearance issues wouldn't be to bad any ideas on a manifold?

09-08-2004, 06:13 PM
the MSD prostreet chevy has a similar set-up, its on the 55 that is testing their coil per cylinder system. Its been in all the new msd magazine advetisments. i don't think it was a tunnel ram though.

09-08-2004, 09:09 PM
I've seen the dual throttle body in a magazine before. I think it was an issue of Super Chevy.

Fuelie Fan
09-09-2004, 08:14 AM
It wouldn't be too hard.

Holley sells 4bbl throttle bodies without fuel rails, just an in and an out. You could plumb it one of two ways:
1. Allow each throttle body it's own regulator. You would tee the supply line, one to each throttle body, then tee the returns back together
2. Gut the regulator in the first throttle body, and run it in series.

Approach #2 was used by GM (Remember the Cross-Fire?!?!?), except I think they had a damper in the first throttle body. It's cleaner and less complicated, and probably all that's required.

With a 2 4bbl TBI's, you'd have 8 injectors, so you would size them pretty much exactly as if you were doing a MPFI setup. The smallest available TBI injector, to my knowledge, is 31 lb/hr, which would be perfect for around 400 hp. If you've got less, you may run in to idle instability. Doesn't seem like too many people on this website have less than that though. :0

Be sure to batch the injectors in a split fashion, ie pair two from one throttle body with two from the other. Otherwise you'll run into distribution problems.

Idle control could be an issue, since you'd only have an IAC on one of the two throttle bodies. I think a generous plenum size will cover this up, though. Shouldn't be a big deal.

09-09-2004, 08:44 AM
The Weiand 2x4 tunnel ram top, part number 1913, will bolt right up to a StealthRam base. You would have to fab something up for the throttle linkage. Fuel rails, injectors, ECU, and just about everything else you will need can come from Holley as well.

You can use 2 of the 1000cfm throttle bodies and just use the IAC from one of the throttle bodies.


09-09-2004, 09:57 AM
Thanks for the input Andrew. Do you think 2000cfm would be to much? I have always been told for EFI the more cfm the better. the plan for the engine is a 427ci small block.

09-09-2004, 11:28 AM
if you do end up doing this, take lots of pics. I'd love to see something like this.

09-09-2004, 11:37 AM
With a bit of imagination, you can use oddball intakes and do so fairly cheaply. My intake started off as a tunnel ram lower and I'm using twin Honda throttle bodies because they were free, reasonably sized, and had a 0-5V TPS signal that my FAST ECM could recognize. I didn't have a lid for mine or I would've probably adapted it; instead, I made a sheet metal and billet flange and lid for it with tube inlets in front (more convenient for a turbo motor).

You could use two of nearly any EFI throttle body with adapter plates to bolt them to a carb baseplate. One of the Mopar mags even had an article where they used the bottom of a carb for the throttle body, with a carb spacer forming the "air horn" above the throttle blades. It's just easier to use EFI throttle bodies because you get an existing TPS and IAC in most cases. :)

DB Z28
09-09-2004, 11:43 AM
Mercury Marine also has one on their small block they used a edelbrock victor ram it was casted buy them with the mercruiser name on it. they had that out in the 80s have one pictured on next cars here Dale Buerger 79. have one was going to use with a supercharger. but not going to use it now.

09-09-2004, 11:46 AM
Turbo City was working on a dual TBI setup that would be pretty cool on a crossram manifold instead of a tunnel ram. Check out Dual TBI (http://www.cfm-tech.com/CompleteTBISystems.htm)

09-10-2004, 04:15 AM
You should be OK with 2000CFM total. With EFI the CFM ratings are not nearly as critical as they are for a carburator.


09-10-2004, 06:20 AM

Any idea why they cast that base with such a small intake port? Probably to help with the torque since it's replacing a TPI on a lot of applications.

I just wished they had a little more meat there; Don's car has intake ports with a #1206 Fel Pro gasket; they literally extend beyond the outside of the casting! We're trying a smaller gasket and hoping we can get it to seal.


09-10-2004, 08:03 AM
Mercury Marine also has one on their small block they used a edelbrock victor ram it was casted buy them with the mercruiser name on it.
These intakes also have an IAC that is seperate from the throttle body. The one I have has the throttle body cast into the front of the lid with the IAC at the rear of the manifold.

Fuelie Fan
09-10-2004, 11:33 AM
There is a point of diminishing returns of throttle body sizing. As the throttle bodies get larger, the amount of throttle body opening to achieve 100 MAP gets smaller. So, whereas with 750cfm at 2000 RPM it takes maybe 50-60% throttle to achieve full load, with 2000cfm on a small block it will now take only 30% (all total guess numbers for illustration purposes only). In other words, you'll end up with "binary" or "on-off" throttle feel. This obviously also makes acceleration enrichment calibration very difficult. You won't make any more power than you would with 1000 cfm. As for low end torque, well technically the cam and intake should dictate that. Recall we're not relying on air velocity through venturis for fuel supply any more so low speeds through the throttle body are not nearly as important. May have only very minor torque losses, again plenum size plays into this.

It's certianly doable, though if you don't have to have the look of actually having 4 barrels in your throttle body, I would recommend using two stock GM 305/350 Throttle bodies and then just making an adaptor plate. This will give you just about 1000cfm total, and they come stock with 45 lb/hr injectors which would be a very good start for 350 hp or so, and you can always upgrade to 55 lb/hr or even 80's or 90's if you need. Hidden below an air cleaner nobody would know the difference. Just an option for those looking for the low-buck version.

Edit: Oops I think I just unknowingly recommended exactly what Turbo City has on their webpage. Surprising, becuase the one time I saw some of their work I wasn't too impressed.