I have a Maxton Rollerskate that is in despirate need of more power. It currently has a 12A SP and the carb doesn't work in the turns. This makes for very disappointing results and I need to seriously upgrade stuff. I really hate turbos so that is out and my street port has virtually no bottom end power. I've gotten a 13B 4 port with stock ports, I have also started to aquire fuel injection parts and I've got a carb being rebuilt and modded by Cobrastng but I don't see anyway to get enough power and in a wide enough power band without breaking new (for me) ground. In reading some threads by some of the well known first gen racers a street port won't cut it. A P port is way too much work so that leaves me with a bridge port as the "best" option.
Has anyone got some kind of instructions they know of on how to do a small bridgeport? I can go with a professionally built engine but the cost is likely to be very high and I'm trying to become more of a hands on guy and build my own. So any advice would be appreciated.

 

Assuming the ports are untouched, I just mark the whole area with a Sharpie, set my dial calipers to 6mm, and scribe a line to mark the bridge.

If it's used housings, there should already be a mark from where the coolant seal and/or rotor housing edge were. You want to open the eyebrow out to the rotor housing edge at a minimum, but no closer than 1mm at the VERY tightest to the coolant seal. THAT is only if you want to make a relieved-housing engine. '86-up engines can't go this large because it undercuts the coolant seal groove.

Anyway, I then just go in there with a 1/8" carbide (Dremel) at kind of an angle. My previous engines all had ~32mm high eyebrows, now I'm just going for full port runner height.

6mm is a starting point. The bridge width I shoot for is 5.1-5.0mm, and it's the last part of the port that I do. The MFR bridge port speced out a 4.5mm wide bridge but I have always done 5mm with no problems. (The MFR eyebrow is 7.5mm wide, incidentally)

Don't thin the bridge's underside, and do port the runner closer in before the eyebrow. You don't want to make the bridge weak but you do want to allow the air to want to go through the eyebrow instead of the main port.

Disclaimer: I have never purchased a bridge template from anybody. Much of this info was out already online that I went by when I made my first bridge port. Therefore, I'm not infringing on anybody's intellectual property. I am still learning, but I make engines that don't blow up due to seals falling into ports. I note with interested that when I found a copy of the MFR port outline, it's VERY similar to what I've been doing, just with a deeper eyebrow.

 

Thanks peejay for the info. In doing some research on this, it seems like a good idea to get someone to build me a motor. The possibility of screwing everything up seems huge.