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Sirs,
I'm finally able to sort out a cam swap I did in my 86 firebird. I found a once used 260H Comp Cam for 40$, and replaced the peanut cam and the stock timing chain (that had slack in it from the 130K highway miles on the car).
So far, the idle quality isn't bad. I'm still able to idle at 600 rpms. Granted I still do have on the stock exhaust. As soon as I deal with the 700r4, I'm planning to replace the Oem exhaust with headers and 3" single exhaust. I will see about posting a video on the car idling with this cam. The only other change I did was an Edelbrock 2101 intake, and 50k volt coil and performance distributor module, and cap and rotor, Taylor thunderbolt 50 wires, and gapping the NKGs to .055s. I can't wait to break her in next week on the hwy. I've got a long list of stuff to do here. Even a 3.42 gear and posi swap.
I ran a 270h old comp grind back in the day in an lg4 with headers and S/r 305 Torquer heads and other items and it performed nicely and still had pretty good manners.
Since it was an 83 it had a very limited ECU but needless to say it went in the trash along with the stock camshaft and a 750 double pumper holley was fitted at that time. It ran hard for what it was and put away a lot of cars back then!
I broke in the cam today. Car refused to go above 60mph. All vacuum lines and ports were plugged. I'm a bitt puzzled. I'm wondering if the stock exhaust system is limiting the power. Any thoughts? I was able to get the bird to kick down to 3k rpm on the highway, but it would do no more than 60 mph.
The stock exhaust, in good condition, will be a restriction, but not THAT much of one. If it has the stock converter, and if it has collapsed inside, then it would cause this problem. Otherwise, your issue lies elsewhere.
Modern converters use a ceramic honeycomb core, that is coated with precious metals.
That ceramic core (sometimes referred to as a brick) is fairly robust. But, they can fracture and collapse. Physical damage, backfiring, excess heat...these can all lead to damage of the converter. Here's one that has collapsed.
Here's one that has become plugged with contaminants.
Here's one that broke apart inside. The pieces blew back into the muffler.
Modern converters use a ceramic honeycomb core, that is coated with precious metals.
That ceramic core (sometimes referred to as a brick) is fairly robust. But, they can fracture and collapse. Physical damage, backfiring, excess heat...these can all lead to damage of the converter. Here's one that has collapsed.
Here's one that has become plugged with contaminants.
Here's one that broke apart inside. The pieces blew back into the muffler.
I think you get the idea.
Fortunately, today. I had stopped by a exhaust shop and talked with them on replacing the stock exhaust in 2 weeks, with a 2.5" from the manifolds into a 3" single cat. Your reply makes sense. The old lady had taken great care of the car, but did'nt have the money to repair the cars problems in the end. I'm going to attack the exhaust, and see if that caused the car problem.
Last edited by w41duvernay; 09-25-2016 at 08:24 AM.
Exhaust is just one possibility. And there are ways to test if this is bad. Pressure gauges, or dropping the exhaust for a short test drive. Your exhaust shop should be able to do this for you if you'd like.
It would be disappointing to spend $$$ on a new system, and not have it run any better do to some other issue.
Dyno,
I'm better this is a correct anaylsis. This car does run capped up. I even had some trouble getting back up the hill where I live after an hour of driving on the interstate. With the 260 cam, this thing should be running hard. I was going to replace the exhaust anyway.
08-22-2016, 10:46 PM
