Maxt

I once wrote a whole page diatribe on the subject on here, but that was before the "hack" ..

No comparison between a decent bridge and the streetport in terms of spool and midrange, I have gone from a large streetport to bridgeport with the same turbo, and dropped the spool time by 1500 rpm..If you think a sp spools a turbo fast , next time try a BP, currently my latest turbo is running a 1.0 a/r q trim undivided turbine, I can build 12 psi in first gear, the streetport wouldn't do that with a p trim divided turbine...maxt

BLUE TII

What was your intake opening degrees on the streetport Maxt?



What kind of tires are you running that you can put 12psi to the ground in 1st gear???

93BlackFD

a lot of cars can have the "brap brap brap" if you run them too rich



also, overlap will cause lots of exhaust gasses to go into your LIM/UIM, i had the half bridges setup and can attest to this



it makes throttle response/tipin really hard to get properly set, and idle is hard to get A/C to run

spooliNrx7

I thought it would be just the opposite of this?? If the exhaust is being pushed out by the rotor and also being sucked out by the low pressure in the exhaust manifold, wouldnt that help out the intake of air in the sense of creating a low pressure in the chamber during that overlap period would help suck more air in faster??

heretic

At idle you're still going to have a fairly high pressure drop between the chamber and the intake manifold.



The "brap" is from each rotor firing three times and missing three times. Three chambers per rotor, a coincidence? When it's misfiring the pressure differential is lower in each chamber vs. the intake port when the chamber swings past the port, no residual exhaust gases, you see. So when each non-firing chamber swings past, it doesn't have the exhaust gas contamination to creep into the intake port (to be drawn in later after overlap is completed). So it gets a more or less "full" charge, or at least one strong enough to make a nice bang, and you get three "firing" chambers. Which then have enough residual exhaust gas pressure, etc, and the bridgey goes "brap brap brap" while the stockport goes "hmmm".



You can also see the reason why the exhaust system's efficiency plays a role in how well the engine idle's (or doesn't).



Furthermore, you can tell the idle speed just by counting braps per second. 1500rpm is a common enough idle speed, which at 25rps is a hair over 8 rotor revolutions per second, making at slightly over 4bps (braps per second). Try it, it's fun for the whole family.

spooliNrx7

Heretic:



What do you mean firing and missing 3 times?



Also, yesterday I was at a friends place tooling around in the shop looking at a 13b-rew that had a half bridge done to it. I was playing around with a rotor, housing and an iron and I now see why the bp has that brap noise from the bridge opening up so early with the exhaust still open, compared to the secondary port which is just starting to open while the exhaust is just clsoing. I then looked at it in a sesne that there was no bridge and saw that you dont get much overlap with a large streetport.



It's all making sense now