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914World.com _ 914World Garage _ megasquirt with tbi?

Posted by: tdsmoonchild Feb 21 2006, 09:38 AM

Has anyone here built a megaquirt system using aftermarket dual throttle bodies?

Posted by: Aaron Cox Feb 21 2006, 09:43 AM

you mean ITB = indiv throttle bodies?

check out JENVEY, TWM and CB performance all make an IDF style throttle body that will bolt to carb manifolds....

Posted by: DNHunt Feb 21 2006, 09:45 AM

I'm sure it's been done. I think Crash914 has but, I may be wrong. Anyway, it shouldn't be a problem. As far as I can see there are only 2 complications. One, you have to sync air flow like carbs and two, you need a throttle linkage. Both of those things are run of the mill with the carb guys.

Dave

Posted by: lapuwali Feb 21 2006, 01:44 PM

Well, you'll also have to deal with MAP issues. ITB systems generally have a highly unstable MAP signal at idle and low loads, which will require either a MAP plenum, a very small restrictor in the MAP hose, or a combination of both. Some people will tap all of the manifolds and plumb them with tees into a fuel filter, which can often stabilize the MAP reading enough for speed/density to function.

The other alternative is to use Alpha-N instead, using only the TPS as the load signal. This is often tricky to tune.

This topic (ITB with MS) is discussed pretty regularly on the MSEFI forum, so searching there should give you a lot more data to chew on. The problems are pretty much the same from engine to engine, so no need to look only at Type IV based systems.

Since Jake sells SDS with ITB throttles, he's obviously gotten it to work well. SDS has pretty much the same limitations as MS in this regard, so what works for one should work for the other.

Posted by: DNHunt Feb 21 2006, 01:49 PM

There is a provision to use a hybrid Alpha-N. I believe you can select an RPM where it switches to speed density. I think it's directed at big cams but it might work with ITBs.

Dave

Posted by: yarin Feb 21 2006, 03:02 PM

If you have the resources to machine an adapter plate I would find a 4cyl injection rack off a bike, cut it in half and bam.. you have injectors, ITBs, fuel rail, etc.. all u need is a linkage. You can find a good rack for a lot less than the other itb options. It's just a question of doing some custom work.

Posted by: crash914 Feb 22 2006, 06:37 AM

Yea, that is what I am doing...

4 throttle bodies, vacuum tied together through a filter...

I idle at a map of 50 and go to 99 very quickly.

Do a search on my screen name, I did have some pictures somewhere on my throttle bodies, etc...