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Discussion Starter #1
I live at 5,500 feet and have attempted to make my 650 Holley double pumper work well. I did lean it out two main jet sizes which in theory should work for 4,000 ft. Better a little rich than lean with a new engine I always say. I used a stock 65 power valve when I rebuilt the carb that came in the kit. After a normal street run I look at the plugs and they are darkish tan but darker on one side of the porcelan than the other. When the car is cold and not warmed up it can hesitate as expected under 1/4 throttle. When warmed up it runs ok. At full throttle it runs well but that's not where you run on the street most of the time.

My question is should I be running a different power valve at 5,500 feet. I know engines have 2-3 in hg less vacuum at idle here by Denver since there is less air pressure. In the interest of clean running and economy should I be using like a 55 or lower PV? Has anyone played around with this.

Of course there isn't a secondary PV, it's plugged. The car idles with 15 in hg and the needle valves are about 1 1/2 turns out for best vacuum and idle. I run a modest Lunati 60101 cam for good street torque. Right now I run Comp Cams 1.6 rockers on the exhaust but will switch them over to the intakes after the engine is broken in to see if it likes it.

Anyway, if you have been here and suceeded with clean running, reasonable economy and good spark plug color, let me know what you have tried.

Thanks
 

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FWIW when I drove to Reno NV for Hot August Nights one year in my 70 nova I had a 750 holley DP that had close to stock jetting and PV for driving around near sea level. Now Reno is over 6,000ft elevation so I noticed when I got over 4,000ft the car was lugging going over the hills. I had to pull over and drop the jets all around 6 jet sizes so the car would run. Weather was over 90 degs too. I also readjusted my A/F mix screws, bumped up the timing and idle speed a bit. Ran ok but not like it did at sea level. Drove back home and had to stop again at 2,000 feet and put jet back in it cuz it was surging really bad.

The color you see on the porcelain is fuel splash. I don't know if you can totally get rid of that. Maybe once you get the jetting/timing down it may decrease it some. Just my .02:D
 

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Discussion Starter #4
bigger number power valve may help

higher number power valve, 8.5 or 10.5,, maybe add 1/4 turn to the idle mixture screw too
After my thread, I found a Holley carb rule: 1/2 your idle vacuum level for the power valve. So now it idles at 15 in hg so a 7.5 power valve would let it get rich sooner and I may be able to go one more jet leaner on the primaries. That may clean up my plugs a little. I'd rather they were light tan.
Thanks for the input, I'll give it a try.
 

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i think

in a street car , the best way is to put the vacume gage ( yeah get a 8 ft piece of vacume line ) in the car with a friend reading it at light load , cruising conditions.

Once i had a 71 ss 350 , torker intake with a 600 DP ,,, it liked gas alot so i took it down 2 sizes in the primary , and it stumbled a lil on acceleration from steady state cruising RPM's,, thinking back , if i would have raised the power valve , so it would do its function earlier ,, i might have been able to get the best of both worlds

DP carbs are set up for a more radical set up and race conditions ,, not highway ,,, but they can be manipulated to do well in both worlds
 
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