4k Weird Problems??

[rollake70]

hey guys this goes out to all exhaust specalists!

 

just recently got a new exhaust right changed from my standard 1

 

the new system consists of

- 2" system

- Resonator

- SuperHi Flo Catback muffler

- Sports Exhaust with 3.5" chrome dump pipe

 

the car is acting VERY weird since ive got the new exhaust, when i am driving along and then i want to plant it/flog it/foot flat down lol, it will go

put put put and the revs will go low but then the car will slowly climb and go hard??

its like theres no power or horse power but the system should be making it better not worse?

 

any help would be great, the only problem i can think of is mabey the carby needs rejetting to suit the new system but yeh ??????????????????????

[Evan G]

have you done any intake mods?

 

exhaust is free'd up. free up the intake for some more power

 

or mite be a lack of back pressure :jamie:

 

edit: lol cat back lol

Edited June 22, 2010 by Evan G

[altezzaclub]

So it dies low down but then goes hard once the revs are up??

 

What carb and cam?? Stock??

 

Sounds like a lesson in why racing cars that only run from 5000rpm upwards run enormous exhausts...

 

Oh- and what exhaust manifold??

Edited June 22, 2010 by altezzaclub

[Felix]

Adding extractors and an exhaust make a motor run leaner.

 

Has the motor got any other mods? A 2" system is to big for a standard 4k.

[rollake70]

yeh i was thinking back pressure 2 or the carby being jetted up to suit but no its as stock as a rock the 4k just the system at the moment, not sure on the manifold and yeh the 2" system is a bit big but this still shouldnt be happening?

 

yeh when you take off its like all its horse power is gone till about 3000 revs then she starts to pull??

[Evan G]

so basically no torque what so ever.

 

2 inch is huge for a 4k. at least it should have a 1.5-1.75 inch end pipe for some restriction

[rollake70]

nuh 2 " the whole way now i know its big but not enough to be doing this? what do use think

[Felix]

I think you need a fairly worked 5k to actually make use of your 2" system.

[altezzaclub]

all its horse power is gone till about 3000 revs then she starts to pull

 

I think that is exactly what I'd expect from what you've done....

 

Spend about $4grand on the motor and it will run that exhaust beautifully, porting job, high compression, balance, twin Webers, extractors..

 

But bigger jets might cover it OK.

[rollake70]

yeh i think ill get a cam grind and bigger carby hopefully ill sort the problem b4 the new engine

[RainWarriorDregs]

wait... catback?

 

4ks never had catalytic converters did they?

 

why put one in?

[ke70dave]

or mite be a lack of back pressure :jamie:

 

once again 'backpressure' has reared its ugly head into exhaust question.....

 

it is volume of air and the size of the pipe which changes the flow velocity of the gases.

 

in VERY general terms:

 

low volume of air + too little exhaust pipe = restricted gases = bad (stock exhaust)

low volume of air + small exhaust pipe = high gas velocity = good (an appropriately sized exhaust)

low volume of air + big exhaust pipe = low gas velocity = bad (what the OP may be experiencing)

higher volume of air + big exhaust pipe = high gas velocity = good (what you will get with a worked engine and an appropriately sized exhaust)

 

to the OP, did you tell the exhaust shop to put 2" on? or did he do it?

 

alternatively,

 

i was just reading about how a bigger exhaust can make a an engine run leaner, due to the fact that more air is able to get into the cylinder but the carby isnt tuned for it. so that could well be the problem also.

Edited June 23, 2010 by ke70dave