the 13/16 comes from a 94 del sol si.
can it be done?

 

found an answer that a 15/16 will fit. it doesn't say if the lines need bending.

 

BrakeExpert doesn't seem to think that changing the booster is necessary if you've matched the Master Cylinder:

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BrakeExpert &raquo;</TD></TR><TR><TD CLASS="quote">Brake Booster
Upgrading your brake booster to the Integra (or maybe other) sized one has the only drawback of pushing the MC forward, so the hardlines aren't going to be in the same place as they were. So bending hardlines may be in order. What a bigger booster does is the same thing as increasing the pedal length, it increases the force on the MC linearly. Like it may may push on it 40% harder or so at any given point. So this basically makes your foot do less work. This is for people who have a really soft foot and want to make their car brake 'harder'. This can be done, but given the weight of the civic chassis, if you use the right sized MC with its paired caliper, no upgrade to the booster is necessary. It gets to the point where its just personal preference.</TD></TR></TABLE>

https://honda-tech.com/zerothread/1811368

 

thanks. also found this https://honda-tech.com/zerothread?id=364783.
46100-sh4-a11 is a direct bolt on, no need to change anything.

 

go to autozone and get one for a 1991 honda civic ex sedan with a 1.5 engine.i just got on for like $45 and it fits with no mods

 

is it 15/16?

 

yes it's 15/16 i know cause i've done it.

 

thanks

 

The 46100-SH4-A11 and 91 Civic EX (4-door) brake master cylinders are one and the same.

You may also want to check this thread out:
https://honda-tech.com/zerothread/928201

As for using other brake MC/booster combos, you may need to replace the hard lines going from the MC to proportioning valve. ELFATHER on K20a.org makes custom brake lines.

I believe a lot of these MC's take a 1/8 NPT fitting.