marcus_booth

Hey guys so i just rebuilt my 305 tbi and put new l98 corvette heads on, a .45,.46 lift cam, exaust headers, took off the exaust air pump (the emissions thing) and replaced the clutch. I started it and it wont idle, it just sits at 500 rpm for a bit then dies, when i test drove it it had nearly no power, i floored the gas and it very very slowly crept up the rpm. I think it could be a sensor not working, ive checked the MAP sensor, O2 sensor and the knock sensor they all work. I dont know what it could be, next i will be putting the valve cover to tbi pcv valve on. Any other suggestions to get my car running at least normal again?

mk1431

If I'm not missing something you put 350 heads on a 305? there's about .25 inch bore size difference. I think you compression went to s**t. 350=4.00 bore 305=3.73 bore
Are they the aluminum corvette 350 heads that were 58 CC? only one that MIGHT work
Also the valves maybe too large for the 305 maybe hitting
Other things to consider is chamber size, intake runner size

marcus_booth

They are the aluminum heads, i already checked the valves they clear with a little to spare and my compression should acutally have gone up because its a smaller combustion chamber than stock. As for the intake runner what are things to consider? It should be fine no matter the runner size right?

mk1431

depends on port velocity,overly large port can hurt power. Increasing the size may increase the flow but the port velocity will drop. this will hurt the output more than the flow increases the output. Everything has to match or at least be very very close to for a motor to run at top efficiency. just trying to help. If your confident that the stuff you put on are made to work together(you probably wouldn't have started this thread) then start by doing a compression test with a tester and see what your compression is then pull your sparkplugs see what they are telling you.Start diagnosing and find out where your problem are you getting too much fuel not enough air or vice versa... this is all basic stuff when building an engine. good luck to you. this is a great way to learn about your motor so take it as learning and don't get discouraged you'll find it im sure. plus you have other people on here smarter than me and hopefully they'll chime in to help.

sofakingdom

iTrader: (1)

Lotta things can go wrong in a swap like that.

The problem ISN'T the heads themselves. Whether they're "the best possible" choice for the situation at hand is of course debatable; but the symptoms you describe aren't due to them being SO wrong that they're hopeless.

Same for the fuel curve; the box-stock one might not be "right" or "perfect", but just changing the heads didn't yoink the engine so far out into the ozone that the stock tune is SO completely wrong that it's causing the behavior you describe.

First thing I'd look at, after finishing assembling the engine (yes, you should put the WHOLE THING back together COMPLETELY before even TRYING to start it, let alone driving it around half-a$$ed and expecting it to work right), is the static ignition timing. Put down "light", ignore "mark", close "book", and forget about "spec" for the time being. Loosen the bolt and advance it. ALOT. I'd suggest, start by rotating the dist body counterclockwise about 30°. Don't argue, don't "but... but... but..." anything, just do it.