before my cat back the gas pedal felt stiffer, now its easier to push. but thats not the problem, thats just something that may go along with it, this is kind of hard to explain. when i take off from a stop, not jumping on it hard i mean normal, when i hit the pedal it takes off slow, then i have to hit it harder to get it to move up to speed, after that point in time maybe like 10 mph it starts to act normal. Is this the comp readdjusting itself to the new flow? also its a 3" intermediate pipe, which personally i think is too much for a 305 but thats the only size the hooker one came in. Thanks.

 

Sounds like you have an off idle stumble, Your motor is moving more air once you crack open the throttle. Your ecm is speed density which means it only measure manifold vacume to determine airflow, so it doesn't know your moving more air through the engine now. SO thats where your lean stumble came from.

Your ecm, probably won't learn that out. Only way to really fix it is to learn to burn chips and change it in your chip. You'll need to change the electronic version of the pump shot.

Don't worry about the 3" pipe it won't hurt it.

 

it definitely feels like it has more power but that stumble is pretty annoying, it wont hurt anything will it. I plan on getting rid of the motor anyways i guess, so i can just toss all the computer stuff anways right? Since im probably going to run either a mechanical fuel injection or carb. Any help is appreciated.

 

The stumble shouldn't hurt anyhing, I'm sure over the long haul it could eventually burn a piston, but like you said your yanking the engine soon.

When you yank the FI be prepared for worse drivability and fuel economy. FI has no match when it comes to throttle response and fuel milage. Except when you mod the motor and don't tell the ecm abou it. I would leave the mechanical injection to the circle track guys, it was only designed to run well at wide open throttle. It won't run well in a street car at all. As for carbs I love holley's my girle friend has one on her monte and the throttle response is amazing for a carb. Fuel milage is a little lacking but it's silky smooth. I ran a eldelbrock (carter is the same thing) when I first started fiddling with my car. I will have to say this is the easiest carb to learn to tune on. It doesn't quite have the throttle response of the holley, but it is more adjustable. I was able to get 19 mpg out of it on the highway. My suggestion to you is to start out with a carb and learn to tune it really well, eventually your going to realize the limitations of the carb and want more, then you'll be ready to learn how to tune factory GM FI setups. Then you'll have complete control over your engine.

 

This'll do better in the exaust forum.

Edit: doh! Didnt read down far enough in the thread. This is more of a tuning issue then an exaust issue.

 

The exaust system you have has more flow. Its probably just going lean on tip in. The 3" exaust is fine for your application. If you mate that up with some good 1 5/8 in primary headers then you should be good to go.

After that, its time for tuning.

 

ok what do you think of those universal fuel injection kits from holley, i think there all throttle body injection, ive seen a 670 cfm one and a 900 cfm one. Also how can this burn a piston, im kinda freaked out about that now.

 

Running lean tends to burn up pistons. Don't worry about it your lean stumble isn't enough to hurt anything. The holley systems are ok, They are great for the average joe who wants to plug it in and have minimal fuss. Performance wise they work, but the stock GM ecm is much more complicated therefore much more refined. I just can't hack the 4 digit pricing on those systems when I know I can burn chips for less then 150 bucks and use ecm's that cost 80 bucks at the local parts store, and 20 bucks at the local salvage yard.

 

Quit with the auto tune answer. It's a frickin catback for crying out loud.

 

He mentioned yanking the FI and going with carb / holley FI / mechanical injection. So I gave him my opinion on each. Don't see where that was out of line.

 

A less high performance exhaust, if working properly, will lean out the engine a little bit. Headers do the same thing. It exactly what they are supposed to do. Its called scavenging. If you had it running on the ragged-edge before, it probably now is too lean. If you have EFI, it should be able to compensate for this, but a carb or mechanical injection won't, it must be recalibrated for it (ie. richened up).

 

it was running really ragged before because i had holes in the pipe that rotted totally through, so with new echaust it should be better, i hope.

 

I said ragged-edge... as in right at the limit of igntion timing, air/fuel mixture, etc...

 

AHAHAHAHAHA......i walk outside tonight and there is the ups guy standing there with my new 80 series flowmaster im ike uhhhhhhhhhhhhhhhhhhhhhhhh give it to me now before i kill you. Awesome cant wait to put it on.

 

ummmm oh yeah, about that burn a piston thing will i be ok if i just raise the fuel pressure to accomodate for the increased flow, or will an aftermarket chip work? i was wondering because its gonna be early spring before my new motor goes in,This tbi thing is getting alittle to complicated, im just gonna run a big block with a carb in the spring. Or can convert from tbi to mass air flow? And whats a pump shot?