DREYKO

ok the car is an 88 n/a
the engine is a s5 n/a

as you all know the aux ports and vdi on the s5 are operated differently than on the s4 motors. so rather than clutter up my engine bay with lots of switches pumps or solenoids i think i may just swap the s4 intake manifolds on to it and run off of back pressure.

so first off, will i have enough back pressure to do that? my setup is pacesetter header, to bonez high flow cat, to borla dual muffler cat back.

and secondly will I lose any decent amount of power? im under the impression the s5's increse in power is from the rotors, the intake just flows better for its increased redline.

now i do not have a s4 block to compare against so are there any major differences in the lower intake to block mating ports?

thanks guys

Icemark

The larger runners of the S4 intake will probably net you some better low end, but tend to run out of steam around 6000 RPM when compared to the S5 ones.

Actually it is not back pressure that activates the ports, but rather exhaust gas velocity. If there is insufficient exhaust velocity (too big of exhaust pipe for the engine is the most common reason) then there won't be enough to open the ports, and you will need to either use a air pump or some other method of actuating.

The S5 HP increase is based on a combination of things, part of it is the peak RPM efficiency (when compared to a S4 non turbo), part of it is from higher compression, part of it is from reduced weight, part is from the higher speed ECU... so just changing one thing won't make a huge difference, and besides the peak torque is almost the same regardless of series (138 vs 140 ft/lbs).

DREYKO

so my next question is the exhaust velocity part, im pulling that from the aux tube that exits the cat correct?

farberio

iTrader: (7)

Correct.