46MM ITB Throttle Bodies
 

Would 46mm throttle bodies be too small for a 6 port stock port 13B? I work at a place that works on snowmobiles, and I have access to a cheap set of throttle bodies, the 800/1000 Arctic Cat 2 strokes use twin 46MM throttle bodies, these have a fuel rail and injectors that I can use as secondaries, TPS, they are spigot mount though, so that will need something custom.

Here is a picture:

https://cimg0.ibsrv.net/gimg/www.rx7...0f79d285b2.jpg


800 Arctic Cat Throttle Bodies

Also, I was planning on using the upper intake that bolts onto the stock 6 port lower, that way I can retain the port actuators. I have them on manual control, this engine is in a B2200, and I like to close them when I am using it as a truck or pulling a trailer for the extra torque. I know most people seem to like the 50MM, but would these 46MM work, or would they be too small? I am OK sacrificing a bit of top end for something resembling torque.

Here is the manifold:

https://cimg0.ibsrv.net/gimg/www.rx7...98ae71f16a.jpg

I am already running an Adaptronic ECU, so I have the ECU to control it.

The M1000s are 50mm, or at least the ones I picked up off ebay are, and that's a nice size. The 46mm ones should still work pretty well for a stock or streetport. The fuel rail should be modified to not be returnless though. I think the injectors (in the M1000 TB I have anyway) are something like 7-800cc/min too, which is good enough to run without the stock primary injectors.

Shameless self promotion, but check out https://www.rx7club.com/naturally-as...sting-1079605/ It got stalled due to my buying a house not too long after the last post, which put a slight dent in my free time.

I may be converting my car to returnless. There are some significant advantages to running a returnless fuel system.

It's not very expensive, either. I'm already set up for a GM 3/8" quick-disconnect fuel filter. (I use a pair of 8mm plastic to 3/8" quick-disconnect fittings and clamp the rubber hose right onto the fitting instead of using nylon). A fuel filter for, say, a 2002 Corvette will plug right in, and has a 58psi fuel pressure regulator built in. And they are CHEAP, i think the last one I bought was $20 or so.

What advantages? I'd always thought that there might be a risk of hot restart issues from cooking the fuel, but I've not looked into it much. Would make things really simple, as the red Denso injectors in the Arctic Cat TBs (or the style I have anyway) are rated at something like 850cc/min and are even high impedance.

I might see if I have an FC LIM/UIM gasket to model from - it kinda looks like a RB style elbow going to snowmobile TBs might be an interesting intermediate step to doing my straight shot manifold.

Hot restart issues aren't so bad as you'd think. If the fuel gets hot enough that it will boil at 58psi then you have bigger issues (like finding the fire extinguisher :) ).

The main thing I like is that the fuel in the tank should stay a lot cooler. Which is a lot of the reason why the OEMs did it.

Having a constant pressure differential across the injectors makes things easy for old school EFI but pretty much anything modern-ish can compensate for the variable pressure drop with a fixed fuel pressure. And you get higher effective pressure at low manifold pressure, which should in theory translate to better atomization.

Huh. That's a good point. One less line to run, too.