I'm in the process of attempting to build a turbo 292 with a MegaSquirt EFI, and am at a point where a re-thiink of my design assumptions is warranted.
I've spent the last several months attempting to fabricate an intake manifold, and have just thrown the fourth one away when pressure testing revealed that it is one giant leak.
Here are the assumptions that have driven me to the point of drooling idiocy:
1. That because an intercooler is planned, draw-through is not a viable option.
2. That because the rebuilt 292 I'm using is equipped with the heavy stock-type pistons, it will have zero tolerance for running lean under boost.
3. That I should concentrate on a TBI system rather than port injection due to charge robbing, especially when under boost.
4. That because of the relatively long intake manifold, multiple throttle bodies would equalize flow paths and reduce any tendency for poor mixture distribution.
5. That although dual-quad intakes are available which could mount a pair of TBI, the requirements for multiple 90 degree airflow turns make these manifolds relatively inefficient.
6. That in order to minimize the number of airflow directional changes, I should base the intake design on side-draft throttle bodies.
Based on the above assumptions, I've purchased a set of four motorcycle individual throttle bodies of 46 mm bore. They conveniently split into two pair; I had considered buying another set so I could use three pair, but figured I was at the point of diminishing returns.
The manifold I designed is a side draft configuration with two pairs of TB spread far enough to slightly bias for the outer ports since the center is fed from two sources, and is bent up at a 45 degree angle to space the manifold farther away from the turbo and exhaust manifold. I had planned to equip each TB with two injectors; one upstream of the throttle plate like the usual GM tbi, and one downstream for supplemental fuel during high-flow periods.
I've learned that when one is but a rank neophyte at welding aluminum, that complex projects are contraindicated. The manifold could probably be saved by a pro, but the cost would exceed the price of a purchased manifold.
I expect that the simplest and most cost-effective path forward would be to slap a pair of GM tbi on a dual-quad intake and call it done. This would likely perform only adequately, and would not be at all unique.
I could re-fabricate the intake and have a pro weld it, but it would be likely too costly for my meager purse. I could re-fabricate the intake out of steel or stainless, materials that I cold handle somewhat more competently. This would be unique, but would the (putative) performance increase justify the trouble?
I could also fabricate three individual port runners, each mounting a tbi, linked by cross-over tubes. These would likely be simple enough that even I could handle the fabrication. And, if the runner bent up at an angle like the existing design, the tbi could mount at that angle for a pseudo side draft configuration, which would seem to be relatively efficient.
Obviously, there are countless other possibilities such as port injection, those non-electronic fuel mixers, what ever they're called, and so on. Before my wife has to go through my garage and remove all sharp objects, a bit of a reality check would be a help.
