hello- Will a 400 sbc work with a tbi unit in a truck that came with a 350?I think the manifold bolt pattern is different, but would it supply the fuel? Or should i change to a carb

Go to tbichips.com and email that guy to know for sure. I'd say you'd probably have to use bigger injectors, an adjustable fuel pressure regulator, and maybe a couple other mods to the TB itself. THEN, you'd probably need another chip burned for it. If you plan on any other mechanical upgrades like a cam, headers, or heads, then you need to take ALL that into consideration. Remeber that a GM TBI intake is one of the worst flowing intakes GM ever made. It may not support more cubes enough to make you happy.

It may be just as easy to ditch the computer stuff and go carb.....but it's all in what you want.

Check out Jim's performance. The link is in my signature. He can answer any questions you have. Great guy.

thanks for the help guys!

Oh my word, do yourself a huge favor and look at this page (http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_12051_762346_-1_11261). I just put this package on my 94 350 and it made a WORLD of difference. The stock intake and throttle body is so stinking restrictive for a 350, I can't imagine how a a 400 would breathe through it. This Holley TB will easily support 300HP and with the adjustable fuel pressure kit, easily 350+ (not that your motor or the stock computer will). Compared to the stock JUNK it's a vast improvement.

The Holley system is good as well as the suggestions by Knuckle and GoldenOne!

I would also suggest getting some info from the people at Turbocity,

http://www.turbocity.com/

They have some performance kits for TBI performance and also have a cool dual TBI small block set-up!

If you get rid of the stock TBI heads, the TBI can work much better and flow to more potential than many think possible! A decent cam, some compression and the required increase of fuel flow and eProm will work fo mild-to-moderate performance upgrades on a 400.

The Holley system is good as well as the suggestions by Knuckle and GoldenOne!

I would also suggest getting some info from the people at Turbocity,

http://www.turbocity.com/

They have some performance kits for TBI performance and also have a cool dual TBI small block set-up!

If you get rid of the stock TBI heads, the TBI can work much better and flow to more potential than many think possible! A decent cam, some compression and the required increase of fuel flow and eProm will work fo mild-to-moderate performance upgrades on a 400.

I agree turbo city is top notch too. It's been a few years since I dealt with them, but they were super cool and very knowledgeable.