Anybody tried double D-jet air boxes and TB before?

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/Lars S

Mine's a little different than what your picture shows.
I made my own plenums.
1911cc with two 1.7L TBs.

We have a racer out here running 4 diet throttle bodies

Oh that's more professional!
Mine is also a 1911cc, havn't started it yet, any D-jet tuning tips to make double TB's work?


/Lars S

Wideband AFM and set up the MPS so you can make adjustments using the info on Brad Anders' site.
You'll need to modify the bypass screws to close further since there are now two. Otherwise you won't get the idle down low enough.

Thanks!
I thought of making the linkage so that one TB is fully closed until 2/3 throttle like a 2 step carb. After 2/3 throttle resistance will be added to the CHT for enrichment.
Up till 2/3 hopefully good MPG (IMG:style_emoticons/default/smile.gif) .


/Lars S

I made mine so both are at the same opening at all times.
Being so far apart and only joined with a small hose, making them progressive isn't an option but it might work with your setup.
The only downside I've noticed is a sensitivity to slight input changes at very light throttle settings.

I'm not sure but I think you may want to cut the cyl 1/2 runners so they are the same length as your 3/4 runners, you could then use the cutoff section of the runner to connect the 1/2 TB manifold to the 3/4 TB manifold?

This should make your setup and flow to each cylinder bank more even. The way it is right now I would expect cylinders 3/4 to have higher flow than 1/2 (even if the 3/4 TB is closed and 1/2 TB wide open CYL 3/4 would still have the 3/4 TB manifold acting like an air reservoir while 1/2 would have to pull their air all the way through full length runners from the 1/2 TB manifold.)

I don't have fuel injection on my Type IV but from an even flow perspective that should make things easier, neat project though

So what do you gain with Double Throttle Bodies and Two Plenums?

I can understand that if I bumped the Stock Displacement of a 2.0, I'd get higher vacuum at the same RPM (making no changes to valve and cams). I'm assuming that this higher vacuum gets out of the range of the MAP sensor so the computer doensnt' get signal to send MORE gas?

If I split the airflow into two seperate throttle bodies, I can see how Pressure-Drop or Vacuum would be reduced quite a bit for the same airflow since I'm flowing only to 2 cylinders.

Is this the idea?

I am in love with this hack.
Please explain why and the benefits.

I just see twin turbos, but please don't get side tracked on that.

Rich

To be honest - I dont know yet. This is an experiment I set up, could not resist to make it since I had all the stuff and it is a super easy modification (so far).
The Engine is a 1911cc with standard 1,7 heads and std 1,7 D-jet, not started with the double arrangement yet. Its a street car, Im not looking for race performance.

The theory is thet the larger displacement needs more air (and fuel) and hopefully the two 1,7 airboxes and TB's and can give some more air. Fiddeling with the MPS, CHT and fuel pressure will bring more fuel. I may have used a single 2,0 TB with manifolds instead if I had one.



Yes lower vacuum sensed by the MPS means more fuel as far as I understand.


/Lars S

Yes the arrangement is not balanced (yet). It was wery handy to use the original brackets for the left plenum so that one is in its original position. However it would not be to complicated to make the installation almost symmetrical.


/Lars S

Why not split two plenums down the middle at the seams, and weld the two half pieces together to make one plenum with two throttle body openings?

It would be simpler, and the intake runner lengths would not change.

More volume in the plenum is part of this solution.
So adding that volume with two plenum a is one way of doing that.

I am still curious as to why someone would do this?

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More cc's needs more air.

/Lars s

Yes one combined plenum sounds like a good idea!

/Lars S

Neat idea, but I don't see any benefit in your case. The small increase in displacement, maintaining the same long restrictive intake runners, and I assume the stock fi cam make it a fun science experiment that will probably be a pita to tune with little to no benefit.

Thanks,
Im afraid you might be right but I can't resist to do it.


/Lars S

If you move each TB close to the heads like you have on the 3/4 Cyl side the shorter runner and closer TB may help out?