1.6 Rocker Ratio Cause Rough Idle?
 

I am planning out the last set of modifications to my 1989 GTA 5.0 litre TPI engine. Recently, a rebuilt 5.0 litre engine from GM was installed with a Comp Cam installed. Here are the specifications:

Gross Value Lift: (intake) .48 (exhaust) .487
Duration at 0.50: (intake) 206 (exhaust) 212
Lobe Lift: (intake) .3200 (exhaust) .3250

Lobe Separation: 110.0

When I had my mechanic install the cam I knew little about cams other than what I was taught in high school shop (many years ago) about what lift and duration were. I have since learned a lot more from this and other websites. What I wanted, at the time, was a cam that would give me some more power and still idle well without affecting fuel economy too much. It seems to do that in spite of the LSA being a little bit low. With what I have learned I may have gone for a slightly more aggressive cam. However, this cam is not too bad for what I wanted. I also had Hedman Hedders installed, the catalytic converters removed and a Walker Dynomax Super Turbo muffler installed so the engine breaths much better now. I plan on porting the plenum, runners, inlet to the stock manifold and port matching the gaskets. Installing a Holley AFPR and Ford Motor Racing 19lbs/hr fuel injectors. Installing a 160 degree thermostat and a switch to turn the second fan on sooner. Then getting a better PROM chip burnt.

My question is will 1.6 ratio roller rockers help? They would raise gross value lift to the low .5’s. Will they affect idling? Comp Cams makes Magnum and Pro Magnum rocker arms. Thanks for everyone’s advise here I have learned a lot from everyone. I only wished I had found this information source sooner.

Just off the top of my head, you might not be able to go with the 1.6 rockers without changing your springs. Something tells me your going to need to do that if you wanna go that high. Plus, if these are stock heads, when you do the mods you might not see that much of an improvement since the 305 heads "might" be holding you back. Just something else to think about.

um.. i could be wrong.. but from what i hear.. 110 lobe is a no no on TPI cars.. you needa 112 minimum

Like was said above your stock springs may very well bind up with that lift even with the 1.5 rockers. You can have your heads modified to accept the higher lift. Talk to your mechanic.

Back to your question. I doubt if the 1.6 rockers will effect your idle. Allen

Yeah, pretty sure it is that lobe seperation. Surprised you can get it to run without some major tuning.

Thanks for your comments. Everyone here is very helpful and knowledgeable. Yes it was a stock rebuilt replacement long block from GM so the heads are stock as would be the springs. I will discuss it with my mechanic; however, it appears that 1.6 rockers may not be a good idea. If I find otherwise I will share my experiences on this project.

After hearing from everyone on this site it appears that the consensus is that that the LSA is just under the minimum of 112, which I will discuss with my mechanic. My mechanic has either advanced or retarded the timing, I can't remember which. I contacted Comp Cams and posted my results on another thread. The company representative noticed that the cam was a little different than he would have chosen, but that it could be compensated for when a new PROM chip is burnt. The car idles very well and has tons of acceleration for what is in it. Again thanks for all your comments.