Throttle body opening size

[GEM930]

I'm in the process of swapping my 0-320 for an 0-360 and have a question I'm hoping those more knowledgeable than myself might be able to help me with. I installed an electronic fuel injection system on the old engine and was using a throttle body I made from a Datsun 240z throttle body. The intake size is 52mm and lined up perfectly with the intake hole on the bottom of the sump. The sump intake hole on the 360 is 60mm but looks like it has been machined larger forming a smooth down to a 53mm hole where it enter the interior of the sump. I'm guessing the old 52mm throttle body is large enough for the new engine, (only being 1mm smaller then the ultimate intake diameter) however I'm concerned about the "step" the air is going to see when it enters the system (going from a 52 mm opening to a 60mm opening). As a side note, the fuel is not injected until about midway up the intake tubes. Is this step up in size something I should be concerned about? Is there any reason to fabricate another 60mm throttle body?

Thanks

GEM

[rv7charlie]

I doubt that Lyc did a very good job in matching everything up, but you could still do better. The step will be pretty turbulent, & make the flow even worse.

I think that some of the old Ford 302 (5L) intakes were pretty close to 60 mm. I've got a couple that came with my alt engine stuff; I'll try to find them tomorrow & measure for you. They are very easy to convert, & very cheap, too.

Or, you could machine a dual tapered cone & proseal it into the intake...

:-)

Charlie

[rocketbob]

I've heard of guys putting the sump on a mill, and using a boring bar enlarge the throat to the larger diameter. I'm going to be doing this myself in the not-too-distant future.

[GEM930]

So two votes for larger tb... I knew that was probably going to be the case, but I was really hoping not to have to do this again. I got lucky with the mounting holes only needing to be slightly enlarged to fit the lycoming bolt pattern with the 240 tb.