Quote:
Originally Posted by supremeefi
Quote:
Originally Posted by PTAddict
I have no experience with any of the above, although I've researched a lot and plan to add a Harrop system in my car in the next couple of years.
(ITBs present quite different challenges to the ECU in low throttle situations).
Correct. So make sure you get an ECM that will allow you to change cyl to cyl fuel trim at not only idle but other areas of the rpm range. There are only a few that allow you to do that.
Biggest advantage of a true ITB in a streetable application is the ability to use a dramatically larger cam (specifically, larger in the sense of more overlap) while still maintaining idle quality and lower RPM drivability. That's because the close proximity of the throttle blades to the intake valves creates a much smaller total intake volume that is under vacuum, and therefore a smaller volume of exhaust reversion during overlap.
That's not the only reason. You now have no dirty air, all throats are isolated from the exhaust reversion from other cylinders.
Also, an ITB is typically easy to "tune" for optimal effective runner length and thus maximum peak torque RPM.
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Hope this helps. |
Not really sure why cylinder to cylinder fuel trim would be more important in an ITB setup. It is actually easier to make each cylinder "see" the same intake tract in a properly designed ITB setup than in a conventional common plenum intake. Adjusting the individual throttle blades to be consistent is obviously very important, of course.
I have a slightly different point of view on your dirty air comment - I can easily envision a design that has big long runners with throttle blades at the very ends which will create just as much exhaust reversion as a common plenum intake. And most "street" intakes have some common vacuum channel as well. But it really isn't worth arguing - in practice ITB intakes suffer much less from exhaust reversion with big cams than conventional intakes do, and that's all people need to know to understand the advantages.