ITB project, Honda VFR 800 ITBs Options

[kevin311]

I've been running Megasquirt II for a while now on my 71 1.7 with the stock D-jet components and it has been running well. But everything is looking tired in the engine bay and I am planning on taking out the engine to clean everything up and install SS fuel lines.

Then I remembered seeing a video youtube with an australian guy reviewing his 914 and he mentioned having GSXR ITBs on his car. Sounds like a fun project to me so I started researching and think I have found an even better solution.

The throttle bodies I found are from a 2001 Honda VFR800. The bike is a V4 so the TBs and fuel rails are already split into pairs, and have a linkage that connects both. They have 37mm throats, and came with the throttle position sensor, fuel pressure regulator , injectors and and all the wiring and connectors. Also the brackets on the sides already have a tab for throttle cable.

The injectors are high impedance so I wont have to run PWM on Megasquirt anymore and hopefully can get an even finer tune.
I'm also thinking about switching the PCs for 96mm, but I think that will wait until later, but you never know this started out as an engine cleaning...

The only things I need to figure out are the flow rate of the injectors, where I'm going to hook up the IAT sensor, and will need to build a vacuum plenum. Also these injectors run at 36 psi, can the stock fuel pump handle that or do I need to look for another solution?

Here are some pics, check out how close the spacing is for weber manifolds.
Please excuse the dirt. I still haven't cleaned them up.

This is gonna be fun. (IMG:style_emoticons/default/beerchug.gif)

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[monkeyboy]

If so, you had about 1.75" of throttle plate. Less actually I think. You will now have 5.8"+ throttle plate area without increasing anything else to use that volume.

With a four-banger, you don't get one cylinder drawing from the plenum at a time. So the throttle body only has to pass enough air to fill one cylinder.

With independent throttle bodies, you only ever have the one cylinder pulling air through a single throttle body. So it needs to be able to pass enough air to fill a single cylinder...

This is one of the reasons why you do not go way, way up in throttle body size when you use a single plenum. Or conversely, why you do not have to drop to little pencil-sized throttle bores on an ITB setup.

Of course, nothing is ever that simple, especially where airflow is concerned. But we do know that 40mm throttle bodies work reasonably on a 1.7 liter 914 engine if they are carbs. So it probably won't be horrible with an EFI setup. Worth a try, certainly! (Especially since it isn't my time and money. (IMG:style_emoticons/default/wink.gif) ) And the cool factor is way up there, too.

--DD

Right Dave, but I think the 40mm ITB's will probably be a lot. Don't forget that those 40mm carburetors are necked down, usually to 28mm, at the venturi. No venturi in throttle bodies.

Plus with the vents and everything else in there...

From what I have read around, you can usually get twice as much airflow from a TB than a carb of the same bore size since the TB has an unimpeded airflow.