HoffDaddy

Does anybody port their engines without changing the port opening timing? I was thinking that opening the port earlier would do more harm than good because it is decreasing the exhaust scavenging. Other than that I'd want to move as much air as possible and the port can be open as long as I can with out changing exhaust scavenging. Just for this example the exhaust port would remain mostly the same. How much can you bridgeport, or j-port if possible, without opening the port much earlier? Idle would be the only time I'm ok with the overlap, but almost as soon as it's off idle I'd like it to run perfectly smooth.

peejay

That makes zero sense. The point of a bridge port is that it is the only way you are able to open the port earlier. Conversely, it is impossible to make a bridge port that does not open at least 70-80 degrees earlier than a stock port.

Opening the port early is what increases exhaust scavenging in the first place. It's how the ports work. Actual airflow through the port when the full face is open is not very significant until you get into the J-port range, the big benefit is exposing the intake port to the vacuum created by the exhaust to start it/keep it moving forward.

j9fd3s

iTrader: (3)

my friend did a bridge port back in the day that would have been called a big J bridge, so it was way into the water jacket, but with timing as mild as he could. it worked really well, with a holley carb, it did 230rwhp and it would get 26mpg on the freeway, it was his DD for years.

i would suggest that a 230rwhp 26mpg rotary is possible, but you will be totally bonkers after a while.

HoffDaddy

That does make sense and I didn't think about that. The idea of porting without much change to the timing just popped in my head. As j9fd3s said it is obviously doable.

That is really cool, I do want to try it sometime. I understand now what changing the timing will do, but I see that you also don't have to and you get a different result. Very interesting .

j9fd3s

iTrader: (3)

just to be clear the timing on my friends bridge was way different from stock, and pretty radical, but it just was less timing than the normal monster bridge port template, but with the same size port as the monster bridge. it had a brap brap idle, but it had mufflers, and was street friendly

peejay

Eh, my engine is almost a carbon copy of the bridge ports Mazda was running in Group A in the early 80s, and it's pretty street friendly, and has mufflers and stuff too.

HoffDaddy

Gotcha.