Standard valley pan to blocked crossover *PROBLEM*

[Stringbender]

Will try an keep this short. I replaced my valley pan with the felpro version with the crossover blocked. After thinking I must have a massive vacum leak at the pan on the passenger side (blowing air sound, blackened all plugs on that side, struggling to run above idle). Im convinced my problem is actually blocking that crossover. Has anyone ever had a problem changing to this type of pan? If not what is WRONG with my head?
Details: 68 383,452 heads, Edelbrock performer
Will provide more, including why I'm convinced it's restricted exhaust if needed,thanks

[5wndwcpe]

Nope. I run that pan all the time.  Try covering the carburetor with your hand with the car running.  If the idle goes up, then it's definitely a vacuum leak.

Did you use the paper gaskets or any sealant around the ports ?

Was it a new valley pan or used ?

Did you check the alignment of the bolt holes before you torqued the fasteners ?

[BSB67]

Nope. I run that pan all the time.  Try covering the carburetor with your hand with the car running.  If the idle goes up, then it's definitely a vacuum leak.

Did you use the paper gaskets or any sealant around the ports ?

This, probably.

If you have exhaust manifolds, first check that the passenger side manifold exhaust valve is open or working freely.   If it is, the blocked crossover is not your problem, it's your installation.

[Stringbender]

Thank you for replying! Yes it was a brand new pan. The old one had been installed (by who knows) with no gaskets. The car ran fine with that one an showed no signs of a vacuum leak. The FIRST time I tried all four gaskets with copper spray(Rtv on ends and small dab in each corner). That time it ran the worst would barely idle. Ran it less than a minute. Pulled intake checked the alignment. It looked good, added a small amount of Rtv around ports. Fired it up same result. After finding the plug problem, I removed the top gaskets. Now it idled fine, but would hear the rush of air as soon as It came off the iddle circuit, an would struggle to run. Drove it a short ways, tested for vacuum leak (spray/hand over carb etc) finding nothing. This time when I pulled the Intake I could see the area around crossover pushed up slightly on the passenger side. I removed the pan noting a discoloration on it at the crossover on that same side. Reinstalled using no gaskets just the pan an a small amount of Rtv. Completely tore apart the carb cleaned it out (Eddy Avs2 650). Fired it up SAME result. Starts and idles Great, can find zero sign of a vacuum leak at idle. Infact hooking up a vacuum gauge to it my needle has never been so steady. Oh no stock manifolds, unknown brand headers. Since I'm stuck at home today I'm gonna pull the intake an cut out the blockage on that side of the pan, an will post my findings. Appreciate any ideas if I'm not on the right road here. Thank you

[Stringbender]

Forgot to add, I do have the Eddy adapter plate and gaskets installed (spread bore intake to square bore carb). So it's not a vacuum leak when secondaries are engaged. Thanks

[b5blue]

Gaskets are available in several thickness to compensate for block being decked/heads milled. Things that move sealing away from intake mating face. (Intake bolt holes can get a slight misalignment.)

[Stringbender]

Thanks Blue, the bolts did start easier without the gaskets. Not sure of thickness they were the ones that came with the felpro kit. Seemed to be sealed just fine with the old pan and no gaskets. Seals fine at idle with this pan an no gaskets as well. I replaced the pan because it looked very old an ugly.

[Stringbender]

Cut the crossover "block off" out this morning put it back together. Cars back to running Fantastic!? Hopefully one the engine guru's can explain this. Hopefully this post may save a guy from doing the same job 5 TIMES as well!

[cdr]

Nope. I run that pan all the time.  Try covering the carburetor with your hand with the car running.  If the idle goes up, then it's definitely a vacuum leak.

Did you use the paper gaskets or any sealant around the ports ?

This, probably.

If you have exhaust manifolds, first check that the passenger side manifold exhaust valve is open or working freely.   If it is, the blocked crossover is not your problem, it's your installation.

If it runs good now it is because of this^^^^^^^  Russ nailed it !!!!

[Stringbender]

I'm running Headers. That makes perfect sense if manifolds though!

[5wndwcpe]

The only other thing I can think of is the exhaust crossover was leaking between the gaskets/pan to the intake port(s).

The crossover only serves to heat the intake for quicker warm ups.  The gas essentially pulses with each valve event through the manifold.  Other than a negligible amount of scavenging, it shouldn't affect the way the car runs, blocked or otherwise.

[BSB67]

Nope. I run that pan all the time.  Try covering the carburetor with your hand with the car running.  If the idle goes up, then it's definitely a vacuum leak.

Did you use the paper gaskets or any sealant around the ports ?

This, probably.

If you have exhaust manifolds, first check that the passenger side manifold exhaust valve is open or working freely.   If it is, the blocked crossover is not your problem, it's your installation.

If it runs good now it is because of this^^^^^^^  Russ nailed it !!!!

And even if it doesn't.   

[cdr]

it could have no H pipe & one of the mufflers is collapsed inside.  

[Stringbender]

Didn't even THINK of an obstruction in that muffler. I do NOT have an H or X pipe. That's really got me thinking. I feel like some are implying I just botched the install the first 4 times. Which is fine I know there's guys with a wide range of "skill" on this site. If it had been just the first 1 or 2 times I wouldn't put it past myself to somehow fail to get a good seal. I appreciate ALL you guys who have given it some thought and chimed in.

[BSB67]

it could have no H pipe & one of the mufflers is collapsed inside.  

And it is not uncommon for a muffler to collapse internally.

[Stringbender]

Haha I really hope that's the issue. The car came with an older set of flowmasters which are fine. Personally I don't prefer the chambered muffler sound on these cars as much as a straight through. So I've been itching to replace them. May have found a Reason to. Other than this one neighbor I have. Who I suspect is actually just jealous unfortunately. That even though he's never said "Hello" or Anything else to me. Will occasionally open his front door and holler out complaints about how loud the car is. Then duck back inside before I can respond. Haven't been willing to make any changes for HIM, but WILL if the mufflers to blame. Will test for a restriction an report back. Thanks

[c00nhunterjoe]

The exhaust crossover port is tiny compared to the 4 exhaust ports on the head. If the car went from "not running" to "back to running fantastic" simply by poking a hole in the crossover........