Quadrajet gasket - decisions, decisions

I'm doing some tuning on my 455 with quadrajet and want to pick up some extra gaskets for the carb to intake. Below is a pic of the gasket that came with the carb and also the manifold which is an Eddy Performer that, I believe has had the divider between the left and right side cut out. The carb is from a '71 Buick 455 and is 7041240.

So, which gasket should I use and does it pay to use a steel spacer also? The heads are also aluminum TAs. Based on the staining on the current gasket, I'm thinking I might should use an open gasket type. There are so many options like these:

http://quadrajetparts.com/quadrajet-base-gaskets-c-128_25_37.html

 

Absolutely use an open-type gasket on that intake manifold. You don't want unsupported areas of a gasket to be ingested once the material deteriorates. Looks like that hasn't happened yet with the current gasket, good to see! If you wish, you could also trim the existing gasket away from the area above the plenum to accomplish the same thing.

The results of using a spacer or not, type (four-hole or open) and height is going to be more a matter of experimentation than anything else, but with the relatively mild cam and the rest of the package, a four hole spacer might be a good first try, in my opinion. If you go for it, use the four-hole gasket between carb and spacer, and the open gasket between spacer and manifold.

Devon

 

Thanks, I thought an open gasket might be best. As for the spacer, I was thinking of the thin steel spacer more for heat dissipation than height. Since I will run the stock cold air factory air cleaner most of the time, I don't want to raise the air cleaner up too far off the support bracket for fear of bending the thing. So, how about a thin SS spacer in between the two regular gaskets (one 4 hole and one open)?

 

Contact Ken at everyday performance and get a carb gasket from him. He sells a thick gasket that works very well. Metal is a good conductor of heat and not a good option to isolate heat off the carb.

 

Just saw a pic of an original Performer and noted that my manifold has been modified (by a previous owner) by having the center divider cut to expose both sides to each other. Was this a good idea and what affect does it have on performance, if any?

Unmodified Performer

 

I see. If you used an open gasket, the plenum would also have had access to the primaries as well, I believe. Interesting.

 

A small "notch" or open gasket is all that is required on a dual plane intake manifold. If/when you start cutting down too much of the divider, or using open spacers, stacking open gaskets, etc, you can really hurt power. We've done considerable dyno testing with dual plane intakes, spacers, modified dividers, and gaskets. You can actually KILL mid-range power cutting the divider down too far, and you can also induce a "stumble/hesitation/bog" into the engine when you go quickly to full throttle with these sort of modifications. I've lost count of how many times I've made insert dividers where some well meaning soul has cut down or machined most of or all of the divider out of a stock, Performer or Performer RPM intake......FWIW.

I also see folks causing themselves great expense, grief, and frustration trying to run 1" or taller spacers on basically "stock" or mildly modified engines. 99 percent of these efforts are a complete waste of time/funds. I've seen Pure Stock NHRA SA cars run nearly into 10's with one gasket sitting on a stock factory intake. I've also seen folks at the track running mid 15's with a 2" spacer on a stock intake and the carb sticking up thru a big hole in the hood!.......Cliff

 

Thanks for chiming in, Cliff. I always enjoy your comments and experiences. Hopefully my setup won't cost too much power as I'm not wanting to remove the manifold to remove the cut-out. So far, my engine has no hesitations and seat of the pants power through out the range seems fine. Or course, I don't have any time slips to compare with. As for spacers, I learned a long time ago that they don't do anything but raise the carb up too high to run the stock air cleaner. I don't like them.

 

On several occasions I've back to back tested intakes and spacers at the track. For spacers, we tested 4 different ones. Fully open 1", fully divided 1", semi-open 1", and 4 hole 1".

For all testing the 4 hole was the worst, followed closely by the fully open spacer. It "felt" OK on the street, but down everyplace a the track. The fully open was nearly as bad, and KILLED 60' times. The fully divided was very good and the semi-open ran the fastest everyplace.
The semi-open is simply divided at the primaries and open between the secondaries. Then we ran no spacer at all and a thick open gasket under the carb.



The quickest for all runs in ET was no spacer at all. The highest MPH was with the semi-open spacer. It gave up just enough 60 time that it ran .02-.03 slower in ET than no spacer at all.
This testing was done on my last 455 right at 500hp/585tq and the intake used was a stock intake opened up under the carb to the same basic size/shape as an Edelbrock Performer or RPM. At that time the car was running mid-11's around 116-118mph.

With this in mind, I see folks using all sorts of different set-ups under the carb, most on engines making considerably less power, and expecting half a second or so improvement at the track.

I would also add here that a fully open spacer worked very poorly on my intake as it put a stumble/hesitation/bog into the deal on the starting line that we could NOT tune out. It hurt power and 60 times quite a bit, then finally straightened out and pulled pretty hard in the upper mid-range and top end.

When you take into consideration the cobbling often involved with spacers, linkage, choke hardware, hood clearance, custom fabricating air cleaners, etc, in most cases its best just to use the stock parts and save yourself the work and expense which more times than not will result in very minimal if any gains anyplaceFWIWCliff

 

Thanks, Cliff. I've decided to just leave well enough alone as this is a 95% street car. I'll just live with the cut-out in the intake and will use an open gasket to match up with the intake. No spacer but, do you like the .250 (regular gasket is .125) insulating gaskets with the phenolic inserts in the bolt holes? I've got aluminum heads and intake but, maybe keeping some more heat away from the carb is a good thing? Your thoughts?

 

I like and use the 1/4" thick gaskets. You need some insulation from the heat on hot shut-downs with this new fuel.....Cliff