The_7

whats the difference between a half bridge and full bridge? is the only difference the port after the bridge is smaller? do any of you have a half bridge as a daily driver?

D3rELiC

i'll run a full bridge in a weekend car, on a carbed s5 13b

The_7

full bridge carbed 13B....

but what is a half bridge?

The_7

also, when does the real torque kick in, i heard somewhere that it starts to make good levels at 6000rpm for a full bridge, is this true? also, when does the volumetric efficiency start to drop off with a full bridge?

inittab

Correct me if I'm wrong but I believe that a full-bridge is where both the primary and secondary ports are bridged. A half-bridge is only on the secondaries.

12abridgeport

Half-bridge is having only two bridges instead of four. It could be two on primary or two on secondary, i've seen both setups.

The real tourque kicks in at different times for all briges depending on overlap, and style of porting. But usually it is around 6k or even higher of it's really big.

Half-bridge is very streetable compared to a full bridge, you can actually still idle around 1k and eat a little less fuel.

The_7

whats the power difference between half and full? like, 12bridgeport, how much power do u have now, and what do you think you would have if it was half bridged? also, i was thinking and im having trouble imaginine why a bridgeport uses so much gas. i know that the intake is diluted with some of the exhuast gas because of the port overlap. so the intake gets less fuel each time because the exhuast takes up space and heats up the mixture. so it has to idle higher but even tho its at a higher rpm it uses the same amount of gas because it takes in less each intake stroke than a normal porting...so why does it use so much?

12abridgeport

Honestly i have no idea how much power i'm making right now because i haven't even brocken in the new motor yet. But 230-250 rwhp is possible but that varies a lot with different setups.

The reason BP eats so much gas is due to a much bigger surfice area that the a/f mixture is sucked in the motor, it doesn't really have anything to do with the exhaust in the mixture.

The_7

but how is the gas wasted? even tho it comes in through a bigger port doesnt most of it still get burned?

mwatson184

With overlap some of the intake mixture blows straight through the exhaust port.

-Marques

The_7

i thought the pressure of the exhuast gasses prevented that and that it was the other way around with the exhaust diluting the intake...

12abridgeport

I've never heard of intake mixture going through the exhaust

That is correct, most of the gas does get burned...that is exactly why at low engine speed there is just not enough velocity for all of the burned gas to escape, thus going back into the intake again. After i went DFIS with MSD it rumbles even more now because it burnes more fuel.

DriveFast7

iTrader: (1)

half bridge hp would be half the increase the bridge provides over a streetport. seeing that a bridgeport has the primary ports streetported, then 4 extra eyebrows are cut in, making the bridges.

rototiller1

You use more fuel because the temptation, to put your foot to the floor, is overwelming. If two cars weigh the same and you drive them the same. Then the one modded to make more hp, should get better mileage
all things equal , such as carb, headers

The_7

i still dont understand why this drops the gas milage

Tom

I would assume that if do a 1/2 bridge say on the secondaries, your primaries are going to be street ported, not stock. You've added intake duration (letting in more air/fuel per combustion cycle) to the motor. In order to feed this increased appetite for fuel, you top off this motor with an aftermarket or modified carb and fuel pump capable of sending gobs more fuel at higher volumetric rates.
So now you have multiplied your HP by about 2x (100% or so) and assuming you drive it like the way it should be driven (spanked like a naughty little monkey) you've netted yourself one gas guzzlin sportscar and a guaranteed Holiday card from Prince Faud of some oil producing sand encrusted flyspeck nation in the Middle-East. Happy Motoring!!

The_7

well i understand that higher accel equals more fuel but i thought that the mpg is lower in the lower rpms than it is up high in the power band. isnt this true? what causes it?

The_7

bump

dr0x

Just idling at 1700rpm will use quite a bit more fuel than 800.

The_7

so the only reason bridgeports get bad city gas mileage is because they have to idle higher in order to keep from stalling?