I’m building a street/strip style 430 buick. I plan on running a Holley 850 mech secondaries double pumper (because it’s what I have) and i’d Like to know what you guys might think I should run for jets and power valve size. Here are some basics on the engine. 69’430 Match ported heads 9:1 compression 282/494 (roughly) cam Edelbrock aluminum intake TA full length headers. Any advise would really be great! Thank you
You did not post up the weight of the car , but at 3600 lb or greater unless your running atleast 4.11 gears out back that 850 Carb will be a poor Pick to run with! There two ways you can go in my book, ( 1) send that Carb out and have it converted over to high gain boosters and ball park calibrated for your motor ( expensive!) or (2) turn up a used rebuildable 750 to 780 cfm vacuum secondary Carb and run that.
yes , i would kind of agree with stevem . but look at your REALISTIC drive style . if it's 50/50 street strip ( nice weekend runner and strip visits , not going to work every day ) with high 3 or lo 4 gears the 850 is worth a try for sure especially if it's sitting on your bench anyway . the 750 ( probably a #3310 he's talking about , old cfm rating was 780 ) is a good basic flexible big block carb that's been around a long time , no surprises , vac secondary so a little more forgiving as far as "tune" and might run a little cleaner in cruiser mode . and if you add a better vac sec set up and rear metering block kit instead of the rear plate it gives you some advantages . proform makes a HP style body for those , done 1 or 2 of those . I would be tempted to redo the 850 , stock specs as a start up point , see how it goes and how you like it . edit : just thinkin' - a really good running 650DP ? never know ! might be a good fit .
Thanks guys. I probably should have mentioned that this is a 4speed car. As I had understood it, mechanical secondaries are are best for manual trans applications.
sorta correct - lightweight car , manual trans , engine mod's , gears . but I always add that with a mod'd automatic and careful converter selection probably fine in same style car . hell , just have two carbs to use - only takes about 15 minutes to change 'em out . just make sure the fuel inlet setup is the same and similar vac hoses , linkage etc for a quick easy swap . and have some extra base gaskets handy . and not a bad idea to try out some dif style/height carb spacers .
I have seen a 650 Holley with 455 cid under it make 420 hp with better drivablity everywhere below 5300 rpm then what a 750 Holley could do! Stock heads and or a non maxed out stocker street / strip race rebuild will be very hard pressed to make 400 hp and you need atleast a 600 cfm Carb with 430 cid to make that 400 hp. Yes , with a 650 cfm Carb and 430 to 455 cid to feed the hp curve will nose over very fast above 5000 rpm, but then again the motor does not spend much time up there except near the end of a 1/4 mile pass depending on your gearing out back.
Thanks for the advice guys. I'll run it and see what she does and report back if I ended up going with a smaller carb.
Running it is fine , but you need to find a a way to A/B it with a smaller Carb! Even if you can borrow something like a buddy's 600 cfm Cater or Edelbrock AFB would be a good test. One thing to do first is to confirm that the Holley has 6.5" power valves in both ends!
If you go to holley.com and search around ( tech info ) there will be a list of carb numbers with specs next to them for jetting , nozzle size , power valve # , etc . If you can't find it let me know and I will get specs for you from my Holley info . edit : was out in shop so wrote down some info : there are at least 9 variations but all are about the same spec wise . it will at least give you a "ballpark" and if something is way off it's a clue that someone's been in there guessing/adjusting before . needle n seats - #504 ( .110 ) fr jets - 80 rr jets - 78 ( older versions are 80 ) power valve - 6.5 ( front n rear ) front nozzle - 31 rear nozzle - 31 front pump - 30cc rear pump - 50cc dash-1 and dash-2 versions are 2 corner idle , newer should be 4 corner idle . if incorrect then someone has swapped something . also if it was 2 corner oem just throwing a dif rear block with idle screws is not going to make it a 4 corner system . dif in the base plate assy .
Do you need a choke? What I would use is a AED 750 modified with Substack and 1/2" or 1" 4 hole spacer, it would let you more options to tune. A 850 would work, but I think more complicated to tune. If you want a 850, I would recommend one with stepped downleg or better Annular booster. Best mix would Annular on the primary and stepped downleg on the secondary side. I think the best carb for your application is a 850 / 900 cfm vac secondary like a speed Demon or QuickFuel Q Series (no choke) /Super Street Series (with choke). The vacuum side is adjustable, they come with or without choke. They can react quick for race and slow for the street and you get only the cfm you need in this situation. The old DP is a good carb, but not easy to tune if you want more than only change the mains. I had one before I bought the AED. What a difference when you want to fine tune. I'm using an Innovate O2 sensor for the tuning. You can try this one: Put an old carb on it or borrow one. Connect a vacuum gauge to manifold vacuum, make a pass on the track or safe street where you can go WOT. The lowest vacuum reading counts, less than 1" is too big, more than 1.5" is too small. After that you will know better which size you go.
