back presuer

[catfish]

how nesasary is back presure in a stock 90 tbi 4.3, i want to run a strait pipe from the cross over back to behind the cab and dump it befor the axle. would my engin still run fin like thiss or whould it cose problums

any advise would be nice, espesaly from any one who has dun somthing simler. the reson i ask is my dad is giving me a lot of flack abut it and claimes it wont run right just looking for a second opinon

[RIP_K52007]

it will run fine... less mpg, but will run the same, ive done it to all my 4.3 s10's, a few just ended at the Y pipe off of the engine.

i put a glasspack on them now, sounds just as good and you get some of the MPG back

(backpressure helps "scavaging" basicly its the exhaust coming out one port, down the manifold, and when its headed out the pipe it helps pull exhaust from the next cylinder.. from what i understand)

[catfish]

good, dont caer about mpg its just a toy and im trying to put it togther as cheep as posabule

[betterbeaters]

ytou will lose bottom end power put a muffler on it!

[Kodiak450r]

idk y everyone says you will lose performance with no exhaust on it. not true and i can prove it with a dyno. i dynoed my camaro with the stock 305 when i was at school. my first run i had done nothing to the car totally stock. it made 140 hp and 190 ft lbs at the tires. engine is rated at 160/220. i installed edelbrock headers and a flowmaster exhaust as well as a exhaust cut out right after the headers. made 2 more runs 167hp and 230 ft lbs. then i ran it with the cutout open. no back pressure at all. 167hp and 228ft lbs. so i lost 2 ft lbs not ever enough to notice. don't believe me heres the dyno sheet

[catfish]

wow thanks kodiak i could never figuer out the logic behind the back pressuer is a good thery. and it is rillly reasuering to see dyno test that prove it

[RIP_K52007]

for the record i said nothing about HP or torque.. i just said MPG

[Kodiak450r]

well where you achieve HP you WILL get better economy. when my car was stock it got 15 mpg mixed city/hwy. after the free flowing exhaust it jumped to 18 mpg. that was even after putting a 600 cfm carb on it instead of the stock 400 cfm TBI. it's all about air flow. more air in+more air out= more power and to a point better economy. reason you get more power is cuz the engine doesn't have to work against it self to make the power. the technical term would be pumping losses.