Firebird is gutless turd-pig. Help!
 

Why is my Firebird such a gutless turd? 1969 Firebird, 400 ( .030 over), M-20, 3:73 rear. Engine has strong, even compression, #62 heads, long branch manifolds, Gardner stock-type exhaust, stock 1969 intake, correct 1969 M/T recalibrated Quadrajet, Summit 2802 cam, 1.65 rockers, DUI HEI with 24 degrees @ 3000, Delco 44R plugs gapped to .050 (as per DUI instructions). Runs cool even in 90 degree weather. Total timing is/has been 32, 34 and 36 degrees while trying to find the sweet spot. Still looking for it. Sadly, it pulls about as hard as the Saginaw 3-speed V6 ’81 Malibu I had as a kid. None of that pushed-into-the-seat power I have had with previous cars. It’s embarrassing. What am I missing? Could this still be some kind of timing/ignition problem? Slipping balancer? Is the quadrajet insufficient? Way too mild a cam? Has Greta Thunberg put a curse on me? I’m stumped.

Maybe find a good chassis dyno shop around you and run it out?Tom

That should be a strong running engine. Describe how you calculated 32,34,36 total timing vs 24 degrees at 3k rpm - this is way too low. Initial timing + mechanical advance should be around 34-36 degrees and if using vacuum advance another ~10 degrees at light load. I would certainly verify the balancer hasn’t slipped. Was cam degrees-in? What is the history of the engine?

I would want to see 34* timing at 3000 if not sooner. Maybe the 24* is a typo? Anyway, the combo looks good. You say stock type exhaust. What size pipes and what mufflers? This could be a restriction. Any sign of a fuel starvation issue? Stock pump with in tank pickup/sock?

No disrespect intended, but that Gardner style exhaust could be a choke point. I know I had one and loved the sound, but taking mine off got me probably 30 hp. I had a 66 GTO that i dynoed on a chassis dyno and it made 209 hp at the wheel. I took off the Gardner exhaust and stock manifolds, added Ram Air manifolds and went to a 2.5 inch exhaust, and from a stock cam to a Crower 60916 and re dynoed at 270 hp. It's something to look at.

Watch this. https://www.youtube.com/watch?v=eLceqIoTMvo

You may want to check cam lift. Years ago they had trouble with those cams being soft. I put one in an engine and it didn't even make it thru the break in on my test stand. Replaced with another brand and it fixed the problem. I won't buy that brand again. Just saying.

I've got the same engine, 400, 62 heads, 2802 cam, 1.5 rockers. RPM intake, QF 750 double pumper, headers, 2.5 exhaust, magnaflow mufflers dumped. 35* at 3000. Loose converter and 3.25 gears with true-trac. Thing will absolutely fly, easily breaks the tires loose, fairly strong for an old worn engine. My hat is off to whoever built the thing like 30 years ago. I did the 2802 swap, replaced a 1980s Crane 284HIT cam and valvesprings that was in it. Makes 13" of vacuum at 900 .

I suspect the exhaust, the carb and the 1.65 rockers are the issue, in that order. The engine wants to breathe, and likes the gas. I suspect the stock exhaust is choking it, and the engine wants more accel pump shot and a different opening rate on the secondary flaps. Maybe the secondaries aren't really opening? The 1.65s may be hurting the low end, and are overkill for stock port 62s and that cam.

A wideband O2 sensor will tell the tale.

Thanks. The 1.65 rockers are a late addition. Started throwing parts at it after I ran out of other ideas. Had same issues with the 1.5s. Carb is recalibrated and secondaries work as they should. A double pumper is tempting though. Consensus seems to be exhaust. Didn’t even cross my mind but it makes a lot of sense since I’ve been over everything else multiple times. It’s on it’s 2nd cam, new rockers, 3rd distributor, 2nd carb, etc.
the exhaust has resonators and a transversal. Maybe I’ll give a different exhaust a shot in the spring.

Sorry, I was not clear. I meant 24 degrees mechanical with the 10-12 degrees initial. So, 34-36 degrees total @3000.

If you’re not sure if the balancer has slipped or not giving you inaccurate timing readings you could use a piston stop that replaces the number one spark plug and verify TDC.

Of simply replace the balancer if it’s old anyway.

Regarding the exhaust, honestly how bad could it possibly be? A copy of an original HO or Ram Air exhaust has to be better than the standard 400 system that used log exhaust manifolds. I had a 1969 400 4-speed Firebird with the standard 330 hp 400 and it ran just fine with the original factory exhaust, it sure didn’t feel like a slug I can tell you that.

The long branch exhaust should have 2-1/4” headpipes, a standard system only has 2” headpipes.

If you still think the exhaust is too restrictive then take the headpipes loose and run it without the exhaust hooked up, that’ll tell you right away.

Double pumper Holley carb would not be an improvement, just diminished fuel efficiency.

I'm running 16* base timing, 19* advance bushing, timing all in by 3100 or so. Another 11 degrees on vacuum advance. I run 93 octane E10 gas. Throw more base timing at it, reduce mechanical advance and see what it does.

I'm a Q-jet guy, the QF750 came with this car. Having tuned both, I do like how easy it is to get a holley apart. It's also nice to not depend on a thimble's worth of gas in the bowl with a cheap mechanical fuel pump. It's taken a LOT of work to lean it out to where it gets decent mileage. I suspect it wouldn't be as much fun if it didn't have a 3500 stall converter. A double pumper is bog city if the engine doesn't have the converter or gears to revv freely.

I agree that it seems unlikely that it's the exhaust alone. My stock RAIII ran as you'd expect it to with a basic factory style Gardner exhaust system. Your engine combo seems a bit better than a RAIII so it should run better than you describe with a Gardner exhaust..

Sounds like your timing is not horrible either. Sure, maybe it could be better, but it shouldn't be causing a major problem.

I'd be thinking more about the carb. I just had two different Quadrajets both built by "experts" that had serious problems. One was as simple as the secondary air door tensioner installation/adjustment. But even though it was a "simple" problem, the motor ran like total crap until it was fixed.

If not something like that, then maybe something worse. Hopefully not.

Agree about your Quadrajet.

Who recalibrated it?

May be time to question that work and try another carb guy like Ray Klemm (worked with Cliff Ruggles) or Shaker455:https://forums.maxperformanceinc.com...r.php?u=140343

No mention of AFR, you can be real lean or super fat and missing 40hp etc right there, I'll assume the plugs don't read black so you're not super rich.

You have not stated what was done to your #62 heads to allow them to work with the 488" exh valve lift of the 2802 Cam.

Even if you have changed valve springs to allow the use of 1.65 rockers there is not enough stock valve installed height to work with the . 488" lift no less the .536" Exh lift, or even the .516" lift the intakes will have with the 1.65 ratio rockers.

Have you checked your valvetrain geometry with the 1.5 rockers no less the 1.65 rockers to see if you need different lenght push Rods?

Are you getting full throttle when the pedal is on the floor?

Will the motor out of gear and with wide open throttle buzz right up to 5400 with no back firing?

I would start out with a vacuum gauge and do basic tune up troubleshooting. Increase the timing while watching the vacuum gauge. Let us know what kind of readings you are getting.

What is the cranking compression? Was the camshaft degreed? Did you confirm that the balancer is accurate during cam install? Does your carb have a secondary lockout?

A late addition of 1.65 rockers?

tells me the heads were not prepared for them correctly.

Good point in the above!
I forgot to mention that 1.65 rockers can be dropped on any factory cam other then the RA4 cam without running into push rod to guide hole clearance issues, but once your into higher lift non factory cams that can change.
In short you may have push rods rubbing on the rocker stud side of the guide hole.