pimpjochen

I have a 91 z28 that came with a 305. i put a 350 with 305 heads, cam, roller rockers, twin 58 throttle body, 24lb injectors, headers and 3" flowmaster exhaust. the car doesnt run right. when i give it full throttle it hesitates and wont get on it. what do i do. what could be wrong.

91RS5speed

If your still running your 305 chip thats the problem it's written to run with 19 pound injectors not 24. Your going to need a new chip before it will run right or swap the injectors.

aklim

I wouldn't put 19 pph in. You might go WOT sometime and lean it out. Switch the chip or get a custom EPROM at www.fasterproms.com and it should be fine.

What ratio of roller rocker and what cam? 305s never came with roller rockers and I believe the cam is different than the 350s. What have you done besides the twin 58 mm TB? A friend of mine tried it and went slower until he changed the plenum, runners and manifold.

Sitting Bull

test

91RS5speed

Well I saw that he was using the 305 heads so hes proboly not making that much power. I dont know what kind of cam he has but if it's not a big one the 19 pph injectors will be fine till he gets his new chip burned.

gixxer92

It's been said that the knock sensor is different betwee the 305 and the 350 motors. I ran with both the stock 86 305 and aftermarket ADS superchip for a 86 305 both preformed w/o problems.
I have a comp cams 272hr and ported heads. No real problems except for alot of retard being pulled out at WOT off idle. I just put my own modified chip in it about 2 weeks ago and haven't monitired again to see if I'm still getting the knock, pulling timing out of the advance yet. If so I am going to desensitize the knock sensor with resistors vs. buying a new one.

RedIrocZ-28

Problems in order:

A.) You have 305 heads that flow like crap to begin with on a 350 block and they are probably not helping you especially with that new cam.
2.) You have 24#/hr injectors and a stock chip that thinks they are still 19#/hr. Conclusion, they are dumping a tremendous amout of fuel into your motor.
D.) Your Throttle Body isn't helping you. You should have a 48mm or 52mm TB sitting there not a 58. A 58mm TB is unnecessary until you get near 400hp or so.

We need to know your EXACT setup including cam specs, header Primary tube diameter, Ported/non-ported TPI or heads, etc.

87irocbeast

Hi, I'm trying to do a similar swap from a 87 iroc 305 with 5 speed to a L98 from a 91 trans am with auto. Havn't completed it yet but i've done research on the subject. When going from the 305 to the 350 I found that your supposed to change 4 things, the distributer est module, the esc module the knock sensor and the chip. Along with the injectors. My problem is extended because 350s didnt come with 5 speed manual trans. So I'm trying to find out how to get a 350 chip that will work with manual trans. Any suggestions will be greatly appreciated.

Kevin91Z

The only way to get a 350 manual trans chip is to start with a 305 5-speed chip and have it custom made into a 350 manual trans chip. A Corvette chip will not work because those came with oil temp sensors, and you will get an SES light for the oil temp sensor not working. I already tried that one. A custom chip is your only solution.