I know that this has probably been a fairly common topic, but I am looking for some advice.
I have an 89 IROC (L03-T5) which is pretty tired. I am looking to rebuild/replace the engine. I can't bring myself to bebuild the 305 and was hoping to install a 350. In consideration of keeping the TPI, it looks like I may need to look to replace the heads. I have heard that the stock L03 heads on a 350 will raise the compression level too much. Any advice on a reccomended short block. I would like to buy a new short block from GM performance. Any reccomendation on heads that can run with this block and the stock TPI and roller cam.
I am looking for some moderate upgrades in performance, but nothing too radical.
The main motivation to go to the 350 is it just doesn't seem to make sense to put a rebuilt 305 back in.
Thanks for any help here.

 

Search on crate engines, 350 H.O., zz4.

Go to Jegs or summit online and look at the crate engines from chevy.

 

chevy's are pancake pistons. If you raise the compression by doing the swap, get a thicker metal gasket for under the heads. The little bit you gain over 8 cylenders may be enough to lower the compression to where you need it.

 

If I were to do it all over again.Get the zz4 shortblock slap in the gm 845 cam. zz4 is to mild and hot cam is a little wild for my taste. It is a great compromise between low-end torque and top-end horsepower. Then I would top it of with fastburn heads and roller rockers. The stock tpi unit will need an aftermarket baseplate and runners to get the full potential of that motor.Just my two cents.Should make about 400hp if the tpi can flow.

 

First, welcome aboard TGO.

Second, let's clear up some things. An LO3 engine has TBI - throttle body injection - not TPI - tuned port injection. LO3's and their 350 siblings, LO5's, have swirl port heads, which are fine for the respective engines as delivered, but poor if you want more. GM Goodwrench engines have these same heads, so watch what you're getting when looking for a GM engine.

Now, as to the advice you've received so far: Feel free to ignore most of it. But, you can use the 350 HO, you'll just have to find a Vortec-specific intake manifold to work with your TBI. The ZZ4 has a slightly different bolt pattern - actually different bolt angle on the center two intake manifold mount bolts on each side - but your current intake or aftermarket replacements can be made to work with it.

What you really need to know is that increasing the displacement will play havoc with your TBI tuning. Go over to the TBI forum and read the stickies there on the topic. Doable, but not simply a matter of bolting in a 350.

 

Didn't realize it was TBI.Sorry.

 

Thanks for the advice so far. It sounds like my "assumption" that the engine was a L03 is incorrect. It is definitley Tuned Port Injection (TPI), not Throttle Body Injection (TBI). It looks like it is engine code LB9? Will the increase in displacement cause "issues" with the TPI engine controls? I have read that I can order a new Prom set to accomodate the 350 with a 5 spd?
What I am hoping is that I can simply order a new GM Prformance short block with a roller cam, and have the heads rebuilt.
Thanks again for the advise/info.