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I was scheduled today for another round on the chassis dyno- this time to see what the final outcome was when we switched to the GM Bow-Tie Vortec single plane from the old stock replacement Performer Vortec intake manifold with these Bow-Tie Vortec cylinder heads. We found some surprises along the way. On the first pull, the graph had a very weird spike very close to the end of the pull. We were surprised to find that the secondaries were not opening up until the end. It seems the single plane produces a weaker vacuum signal then the old Performer dual -plane, thus the diaphram spring was too strong. Mind you this a Holley Street Avenger 770. No mechanical linkage here. Once that was rectified by switching to a lighter spring , we were treated to a best pull yet of 350.12 h.p. and 378.05 ft. pounds torque! Yee Haw!That was an increase from a previous of 331.71 h.p. and 363.42 ft. pounds. We never would have found this had we not witnessed the linkage on the engine. Air-fuel ratio was at 13:1, so we thought it best to leave the jetting where it was.Hopefully this explains why the car did not live up to our expectations a couple weeks ago at Pomona's quarter mile. Maybe 11's are still within reach? Hope so. Dale
 

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so Dale, do you feel that you've got it all ??? or are ya hoping for more ??? i know there's "always" more to be had... just wonderin' if yer done with the majors and are now moving on to the small tweakings ???


sounds killer ta me, a gear change in the back and you'd be even deadlier than ya are already ;)


best wishes to ya Dale :D
 

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We were surprised to find that the secondaries were not opening up until the end.
Your not alone.
Read a post the other day in the Drag racing section of some one else having the same problem.
DOES THAT MEAN YOUR RUNNING LOW 12's ON A TWO BARREL
 

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Ya know, after installing my new carb, I found out that I wasn't getting WOT either :rolleyes: I could still rotate the linkage another 1/2". My crappy bracket would bend slightly and not allow WOT.

I ordered a nice billet bracket from Jegs, but the darn thing won't give me WOT either! It's like the angle from where the cable attaches to the bracket isn't low enough to pull the linkage back completely. So, I welded a brace onto my old POS bracket and I'm finally opening up the butterflies completely.



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Dale, two secs diaphragm mods I used to do when I worked at Holley, was to change the vacuum pull area in the carb, and mod the diaphragm body for easier adjustment.

On the body, I opened up the secs diaphragm pull "hole" passage into the primary side, where the suction actually pulls the secs open. I add a brass tube with the end that inserts into the primaries cut at a 45 degree angle, with the longest section upwards. This makes for a much stronger pull on the secs diaphragm than just the hole in the side of the primary bore, and if used, also closes off the bypass vacuum hole into the secs, if present.

The second mod is to make the vacuum passage in the secs diaphragm body adjustable, instead of regulated by the secs passage ball, for more finite adjustment of the pull signal. I do this in two different ways,

1, Ford 5.0 Holleys don't use the ball in the cavity on the body, they use a starter hole of .055 to meter the vacuum pull. I make an insert with different hole sized, like changable jetting, to vary the signal to the diaphragm. This helps dial the secs in even closer than with only the springs available.

OR,

2, on the top of the diaphragm cover, I drill a hole, countersink and tap it for a mixture adjustment screw pirated from a metering block. I also install a .090 drilled insert in place of the steel ball in the diaphragm body. I use an O ring and nut to lock and seal the needle down, and adjust the needle taper into the cut oriface for adjustment of the vacuum pull signal even more finite. You have to be accurate and careful drilling the hole, as it has to be centered on the body restriction hole, and is drilled into the quick change spring cover, which is plastic.

This may sound like overkill, but it realy makes secs tip in and rate adjustment a lot easier and far more accurate than just chaning the spring.
 

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Discussion Starter #6
Dave- it all sounds very good. I forgot to add that Superior Automotive's guys took a few things "out" of the diaphram assembly (like the restrictor) but I was busy with other things and was not able to see exactly what was done, although I have trust in their abilities. On another note Dave, We may need to have you look at a re-curve on the small body HEI to better match this combo. I'll PM you with that. They liked my little "package" under that distributor cap! Dale
 
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Joe Jill has seen a couple of my conversions alredy.

Just send the dist and specs and I'll recurve it for you.

Please remember, I'm no longer in So. Cal.
 
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