i checke the vacuum gauge while accelerating my falicia up to the red mark, it ws constant at 24 from 3,000rpm to redline (7,000rpm) this tells me there is no back presure with the stock exhaust without catalyst converter, but i wonder, have any of you guys experience a real gain in power or gas economi by fitting a 2", 2 ½" or 3" exhaust ?

and in that same note, has anyone fitted there felicia with a carburator power flow conversion kit, i was thinking of building one and fitting it to my felicia but if there is no gain in performance or feel of the engine then i wont bother with it.

i cant realize how can you measure backpressure with a vacuum gauge but i experienced some performance exhaust issues

i tried several ways for tuning my exhaust a couple of years ago..

no gain in power its all about sound.. the best one is stock exhaust.

and believe me stock system makes backpressure.. with my freeflow system its very hard to climb over 120km/h, its just like some one is pulling from the back.

also lower and mid range rpms obviously lost + fuel consumption increased..

maybe additional modifications make sense with it but freeflow exhaust on stock 1.3 carburated felicia is a no-no in my experience

Edited 6 October, 200817 yr by AhmetH

i cant realize how can you measure backpressure with a vacuum gauge but i experienced some performance exhaust issues

Easy, put a vacuum gauge on a line to the manifold and notice vacuum reading, at idle (800rpm) cruise(1500-2000) and arround 3000rpm, my reading is 22-idle 24cruise and hi-revs, if you keep acelerating until you reach red line and the vacuum reading doent fall it means that there is no back presure on the engine exhaust

that means that even at redline the stock exhaust (without catalyst converter in my case) the 1.5" diameter is ok

on my 1.6 i use a standard 1.5" exhaust with a catalyst and one 18" resonator back box.

i also have a free flowing induction filter

with an open filter and only one resonator box at the back there is a noticeable differance in the power

i think its not a proper way to measure exhaust backpressure.

i dont know the amount of overlap in valve train 1.3 skoda engines

even if engine has some calculated degrees of overlap it must increase vaccum not decrease.

but you know those engines are old desing.. not high revving like honda vtec.

no reason to give valve overlap for extra intake charging.

so i think intake manifold vacuum is slightly individual from the exhaust.

may be i am wrong :confused:

Edited 6 October, 200817 yr by AhmetH

manifold depression isn't directly related to exhaust pressure. the peak vacuum reading should be somewhere near the rpm where the engine is making the most torque because theoretically that is where you have the highest volumetric efficiency. but as the ve gets less higher up the rev range the pressure in the exhaust gets higher because of the higher volume of gas flowing through it...so in a nut-shell, intake vacumm does not equal back pressure

google vacuum testing engine, you'll se a buch of pages and will notices that with a vaccum you can test basicaly everything and anything,

Knowing how to read vacuum, spark plugs and ohms in an engine is more important thant thouthans of dollars woth in equipment.