My 87 iroc tested lean at the smog check, but my check engine light is not on. The light has come on for other codes,and iv'e fixed and cleared them. I thought the light comes on when running lean or rich. Any one know about this. The car is running fine except it tends to have a slight surge at around 1500 rpms. Tipical for running lean.

 

I am assuming that was post cat? You would need to know your A/F pre cat to know exactly what you engine's A/F ratio is. Then tune from there.

Easy causes of lean condition is a bad fuel filter, regulator or a pump that is on it's way out. I'd check your fuel pressure and make sure it's up to spec to start with.

 

what fuel system does the car have? if it was a 305 and now a 350 and you used the same fuel system it will need to be reprogrammed or the correct injectors installed. if all that was already done then also check for a vacuum leak or egr problem.

 

I think I know why it's running lean, just wondering why its not throwing a code for lean o2 reading.

 

Yea I swaped the 305 to a 350 and used the 21lb injectors. Everything else is still the same. Just used the block, heads and injectors for the 350. The 305's were 19lb.

 

I thought that since the 305 and 350 used the same ecm, that the injector pulse width would be similar. thats why I used the 350 injectors. I know the chips have diferent #'s. Was just trying to avoid burning a custom chip. On another subject: How close can you get to the max lift on valve springs. My springs max is 500. Would 492 be to close on my cam?

 

seems close but i always check with a pair of solid lifters.

 

Yea, I'm trying to decide on using 1.60 ratio or 1.52 ratio roller tip rockers. My cam with 1.50 rockers has a lift of 459. If i go with 1.60 they will raise it to somewhere around 489 to 492.

 

Same ECM, different prom. You want the 350 prom is you are running the larger injectors.

What heads/springs are you running?
As for lift, it depends on how your springs are rated. is .500 where the coil bind is? Usually the max lift rating is withb .030 safety margin, if that is the case then running it right up to .500 is fine, if they are not rated with a safety margin you are definitely pushing it close to breaking one.

 

yea I used the 22 lb inectors from the 350. And I'm not sure if it is bind on the springs. I got them off ebay and the ad said max lift was 500. If I use 1.5 on the intake and 1.6 on the exhaust, will that work well. I have a square cam at 210 duration @ .050. everybody says that off set cams work better. watcha think?

 

Split pattern cams are dependent on your power goals and you heads. Longer exhaust duration can be used to make up for an exhaust port that doesn't flow as well or for better scavenging of the combustion chamber. I am not a cam expert by any means though. Just what I have been told and read.

 

The heads are stock L98 heads from a 91 trans am. I just had them rebuilt and put the 500 max lift springs and a three angle grind on the valves.

 

Did you pin the studs or go w/ screw in studs? I haven't experienced it but i have read enough about studs pulling out that I am not going to swap my ZZ4 cam without pinning the studs.

The L98 heads aren't known for there chamber effeciency or stellar exhaust ports, I'd definitely go with a split pattern cam. This is a somewhat popular cam for mild TPI motors.

http://www.summitracing.com/parts/CCA-08-302-8/

I think I saw one for sale in the classifieds too.

 

The cam is already in. its a 210 x 210 duration @ .050 and a 459int x 459 exh. The lobe sep. is 112. I'm putting roller tip rockers on and was trying to decide on 1.52 ratio all the way or get 1.50\1.60 split set. Watcha think?