I would at least remove the rear power valve and make the change up in jets by about 6-8 and start there. Depending on your idle vacuum, the 6.5 may be too high for the front. I have run carbs with no power valves, but they were radical cam engines that idle vacuum didn't really exist anyway.
Need them carb guys and opinions
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It already has a block off with 90s I was gonna try a 6.5 back there with the same jets as the front, so the front will have 82s with a 6.5 power valve and so would the back .My vacuum is 13-14ish I have to drive it with the vacuum gauge see what wants
Greetings 39F & all; Since I haven't run a BB since the early 70's my advice could be dated?? For a reference, GM BB's with Holley's a 360 HP, 375 HP, 425 HP (L-72), 430 HP (L-88) & 450 - 465 HP. So lets look at the L-72 for starters. 780 CFM Vac secondary. What was the factory jetting? 70 Pri with 6.5 Pv & 76 Sec No PV. Next an L-88 had a 855 CFM Double Pump Pri 76 L - 72 R with a 6.5 Pv & the secondary 82 L - 78 R. They were cross jetted. If we go back to my oldest Holley book (late 60's) it states that if you're not running a rear PV 6 to 8 Jet sizes larger will be required to keep A/F mix balanced. My newer books say 8 to 10 jets sizes larger with no Pv. And from what I've learned the newer book is more accurate. Now your compression is less than all the previously mentioned engines as they were 11 to 1 & 12 to 1 examples with large rectangle port heads & solid lifter cams. So if ya want my opinion get a 750 or 780 Vac secondary Holley try 70 Pri with a 6.5 PV & 78 or79 Secondary jets without PV. The reason a don't want a secondary PV is as you accelerate fuel is pulled away from the metering block rendering the PV unreliable for consistent fuel flow. That's why secondary jets have extension on them (to pull fuel from the back end of the float bowl). Good luck Ole' Bob.
My motor used to have (026) rectangles with close to 13-1 635 lift 288 duration at .050 cam ,strip dominator with the same carb and it didn't run as well as my buddy's 1050 he let me try out on it world of difference ,but since I took the compression out ,small cam , smaller ovals on it , I did try a 3310 Holley on it the other day and lost alot in the top end it feels like , 850 pulls alot longer and hits harder too ,a friend got a 850 HP carb he's gonna let me try out if it works better I'm buying from him , I was up in the air about running a rear power valve I got more fuel then I'll ever need to keep it fe'd well just seems as running the rear one should be more street friendly with better fuel economy not that I'm really worried about it that tho lol . Fuel system includes aeromotive A1000 pump ,Holly billet fuel reg., -10 supply ,into a larger fuel log ,into a -8 line . Goal is once car is in tuned fairly well I plan on hooking the plate back up for 100 shot to start with and work my way upbit no sense in having more when everything else isn't right yet
compression and cam have nothing to do with the cfm required. The displacement and rpm is needed to figure out what the engine needs.
It's not too often that you get to try an upgraded carb for free and then also having the option to buy it if you like it at a great price.
Why isn't it on there yet?
Why isn't it on there yet?
Yea CFM calculator says 778 for street and 1010 for race applications that's 427 CI and 7500 rpm
Haha yeah he works alot different hour then I do and the PA weather has been limiting me lately you know 19 degrees one day and 50 the next , hopefully I can get it by Friday supposed to be 50 again ,get it bring the jet kit and go make some passes
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