I'm confused as to what I'll need to do once I get it running. I have a 1983 Cross Fire Z28 with the original 305 still in it.

Here is what I've done so far:

Ported the stock heads...I have the Renegade manifold which I ported paying special attention to the ports for cylinders 6 and 8 which required some work since the EGR passage is routed below them and there was extra material cast into the port area which would have restricted airflow. I'm also installing 1.6 ratio rockers and new valve springs and push rods.

On the exhaust side I got Hooker shorty headers and off road Y-pipe ans well as a Flowmaster American Thunder exhaust system.

My question is...with all of the extra air flow I have created, how will I know if I'll need more fuel? Will the stock 305 injectors work? What about a fuel pump? What about the ECM...will it need to be upgraded? I heard so many different things that I'm getting confused.

Any help? Thanks!

 

you can always get a wideband installed and see what you need to do.

 

We have a chassis dyno here at school and a wide band O2 sensor. We're starting to put the engine back together, so it will be a little while. I have my stock throttle bodies ready to be rebuilt, but I have a feeling they won't provide the fuel necessary for the added airflow.

 

well I have the corvette crossfire throttle body's with the DCS spring so you could adjust the fuel pressure. They are 350 injectors and should supply you with enough fuel.

 

how's the car running?

 

Well, not good. I installed the throttle bodies I got from you and it has issues. Idle is fine but it stumbles and bogs down in low to mid range rpm. I tried putting my stock 305 injectors back in to see what happens, but I'm not sure it fixed it. Fuel pressure is at about 12.5 to 13 pounds. It seems like it's getting too much fuel yet. I thought of backing down the fuel pressure and see what happens. Do you have any suggestions?

 

what's the wideband telling you? Did you install the 350 prom? Did you try to synchronize the throttle bodies? It could be the injectors are way to big for your stock cam and heads. Try the wideband first and see how rich it is.

 

We did a couple of pulls on the dyno yesterday and it was very disappointing...110 HP and 163 lbs of torque. We had the wide band hooked up to it and and I think it had read about 10.5 at the richest. It had a bad stumble. I didn't installed the 350 prom. Can I install that with my 305? I wasn't sure My heads have been ported, but we didn't go to extremes, just cleaned the casting up...nothing to resize the ports. I didn't sync the throttle bodies. It was idling too fast when we first ran the engine and we found the front throttle bodies was not coming back to rest on the idle set screw, so we adjusted the idle screw on the back one and the idle speed came down.

 

Also when you set your timing did you do it with the ecu wire disconnected.

 

10.5 is way too rich. 110 hp is way down. check your timing and get that fuel way down. You want it no more than 12 at wot

 

I'm not sure that dyno is all the accurate, but the one instructor insists it is. That's why I put my stock injectors back in. What is the size difference in the 305 to the 350 injector? I'll try driving it tomorrow and if it's still giving me problems I'll try adjusting fuel pressure and go from there. I need to be able to drive it back to my garage where I keep it from here at school in Blairsville, which is about 3 hours.

 

I would stick to the 305 injectors for now. recheck your timing with the power wire disconnected. the ecu should get it to run right. unless the throttle bodies are not in sync.

 

I set the timing yesterday to the stock spec for the engine. The emissions label under the hood says base timing with the wire disconnected is 6 degrees. The only problem is my class is over and I don't have a place to work on the car here. I thought the throttle bodies were in sync.

 

they were in sync when they were installed on my engine but maybe they moved when I unbolted them from the top plate. never know just throwing some ideas your way. 6 degrees seems low. did you try to bump it up to 10 or 12 to see what happens could lean it out.

 

Maybe it does need more timing since I changed the manifold and ported the heads. I also installed 1.6 rockers which I was told would giving me about .030" more lift. I also replaced the valve springs and push rods.

 

Any codes showing up? A bad coolant sensor will make it go rich also.

 

No code...no check engine light. I replaced the coolant temp sensor, so that's not it.

 

Since you are using a stock 305 cam, stick with 305 ECM and injectors. Also stick with factory 13 psi fuel pressure setting.

You really should get a dealer service manual. It has all of the procedures for setting the TBs - doing it correctly is very important. If everything is in good condition, your engine should have a good idle.

Leave timing at factory spec, the ECM controls timing and takes the 6* initial setting into account when calculating timing. If you change too many things at once, you will be chasing your tail figuring out what to do.

I think you need to get all of the TB settings in order first. Then work on other stuff.

 

I do have a dealer service manual. Hopefully other things I have done haven't affected the way it runs. I ported the heads, but didn't do anything to enlarge the ports. The main focus was to remove the roughness...I did do some work in the bowl area of the intake side and gasket matched the area where it meets the head. I installed 1.6 rockers and replace the valve spring and pushrods.

The throttle bodies that are on the engine now have been modified the make fuel pressure and idle speed adjustable. I installed my injector in those throttle bodies. I'm thinking of putting my old throttle bodies back on since they are unmodified and the engine ran fine with those and I'm sure they were in sync...then I'd know where I was at.

 

How did you the throttle bodies adjustable?

 

You have to cut the weld on the adjustment screw. Also there are plugs on the throttle bodies that can be prayed off inside are adjustment screws.

 

I was looking into this earlier tonight, and I'm not sure I understand. What's the difference between CFI and TBI? Looks like about the same setup, but I know there has to be a difference. Does it have to do with the shape of the intake passages?

 

crossfire injection is just a name GM came up with for The system using twin independent TBIs on a crossram intake manifold-Single TBI used on many 2.5"iron duke"starting in '82 uses basicly the same TBIs as CFI,except 1-11/16 bore instead of 1-13/16 bores on CFI.

 

CFI is Cross Fire Injection, which is a form of throttle body injection or TBI. It uses two single bore throttle bodies which were used on GM's 2.5L engines. The throttle bodies are arranged to where one sits closer to the right side of the engine closer to the front and the other sits on the left side closer to the back of the engine. The throttle body on the right was suppose to feed the left bank of cylinders and vise versa....hence the name Cross Fire Injection.

 

Ok, so the shape of the intake is a factor. That's kind of what I thought. As I looked at pictures, it looked like the passages "crossed" in relation to the 2 tb's.

 

Going to keep an eye on this thread as I may end up referencing back to it. I'm rebuilding a 305 to go back under my CFI and changing maybe to vortec/hooker headers. Not sold yet on Renegade and as of this moment.

 

You can't just play with the idle settings like that. You need to sync them with a water manometer. It will stumble and run like crap until you get that done. Make sure you are running the proper size injectors as well.

 

my 83 ta with 305ci V8 CFI made 176 HP and 257 TQ at the rear wheels. During all 3 dyno runs. You need to balance the tbis with a water manometer and reach 6 inches if water.

 

bump

 

those are some pretty healthy dyno #s in reply 28-better than the original flywheel rating -getting close to getting the renegade on? I might do a few tweaks to my crossfire this yearrobably upgrade the fuel pump again as the one I installed about 6 yrs ago seems to be losing pressure...might put my SLP headers back on too(edelbrock TES on now)