They do not show this part in the summit site it may have been discontinued. The part summit shows is #63-1 instead of the part Derek shows(63-11). It also looks different and is 43.00$ This adjustable part will do the trick. In my Holley book they show the standard spring in the secondaries which is plain in color starts to open at 2240 rpm and is not fully open until 8160 rpm, the yellow spring will start to open the secondaries at 1635 rpm and will be fully open at 5750 rpm, the purple spring will start to open at 1915 rpm and is fully open at 6950 rpm. At least the adjustable one will work in between these numbers. An air cleaner causes an earlier opening in all cases. The cfm formula for a carb sizing is cfm= rpm x cid (over) 2 x 1728 x volumetric efficiency = .9 (90%) This comes out to be a 600 to 700 cfm carb for a heavy car. The SP intake takes away fuel from adjacent cylinders in the firing order, in ours it is 5&7, this is because it is open. We may only need a 600 dbl pumper for this SP intake and going against all of what everyone said in the past regarding the DP intakes, which many said and proved on the dyno that a 950 carb produced more hp than a 650 carb. We may have to rethink this intake and in the Holley book these intakes run from 3500 to 8000 rpm. The Holley spread bore is said to outperform the Q-Jet and get better gas mileage. There's another cog in the wheel for you all. Proven in the Holley carb book done on a Chevy, this is with the stock manifold. and you thought this was going to be easy. Now don't you all wish the heads would have been done first?
Just skimming this part of the thread here... Might not be any difference in the various carbs' potential near the top of the powerband. I'd definitely be concerned with torque in the mid range and shift recovery rpms. Mild engines are very sensitive to this with single plane intakes, esp. in heavy beasts. Smaller carb sounds like a good idea.
I've never seen a Holley get better gas mileage than a Q jet. Even in spreadbore configuration the Holley primaries are bigger. I also said heads first.
I've got a 750 holley ultra DP electric choke carb I picked up from ethan ( I think ) awhile back - looks very nice . will have to check and see if I've already gone through that . if so then it should be back to oem spec parts , cleaned and passage ways blown out . I think I had to bush the choke shaft end holes to use the choke parts he sent - seems to work fine . if you would like to try 'er out no risk let me know . money back if not needed . just can't beat 'er up though . crap ! - won't let me upload that file pic . e-mail me at deadmanscurve@stny.rr.com and I can try that way - if interested . I think it is a holley #76750 . black billet base n block version . can go to summit web and search #HLY-0-76750BK to check pics n info . and as a side note - yeah those quick fuel adjustable vac sec assy's look interesting . bought a couple of e-bay brand new for less than $20.00 each . got one mounted on a #3310 milled choke 750 that I just got done doing a little while ago . even better than the quick flip lid version holley has on their newer carbs . edit : also in process of putting together a street avenger 870 . electric choke . but its a vac secondary carb . just thinkin , options .
I got this from my Holley book. This was done on a small Block Chevy, this might be different with a Buick. The Buick has more torque than the Chevy so this may work even better here. Ok, if you go by Gary's idea that a 2 bbl on the 300 gets more torque than the 4 bbl in the low end of the rpm scale this same idea may be the same for the Holley spread bore compared to the Q-Jet. Since the primaries are somewhat bigger in the Holley Spreadbore this would mean that you would NOT HAVE TO OPEN the primaries as far as with the Q-Jet. This would translate into more torque in the engine and would automatically let the engine get better gas mileage. The car is heavy and if you have small primaries you have to open those more to get the same amount of power in the LOW end as compared to the same type carb with a slightly larger primary. No one here has ever used one so how would any one know? I just happen to have one and I used it a long time ago and it did work well on the stock intake. It would definitely smoke the daylights off the right rear back in the day. A lot harder than what the 2bbl would do. Any one here ever use a Thermoquad? I did, Where is the thinking out of the box at? How about a Carter AFB? Did that too. The Carter gave me 365 HP with the TA 510 cam and the Holley 750 Dbl Pumper gave me 395 HP on the engine dyno which would you use. I never went back and tried the different carbs I had I put them on the shelf Maybe I need to get them all out and rebuild them and try them. I know a heck of a lot more now on carbs than I did back in the 80's. The Holley book suggests no more than a 700 carb with 600 being the best starting safe point. Todays food for thought.
A couple of thoughts: Dual plane intakes make better use of larger carbs because they help offset the fact that there's less plenum to work with (and why adding a 4 hole spacer tends to help offset the size of carb needed); smaller carbs on single planes for those same engines/combinations (usually mild-moderate) aid with velocity/fuel charge quality with the larger plenum. The SP3 seems to differ from traditional single planes in the sense that the runners are designed to work well with the 350's runners (tall and narrow). Using an out of the box SP3 with a smaller Holley double pump (650 CFM) is probably the best combination for engines with power ranges between 2000-6000 RPM (trying to keep a long story short as to why). Putting a Qjet on the SP3 will have mixed results, depending on the combination, but it would probably work best with a higher-end/higher RPM engine, opposite of how it behaves on a dual plane (the stock dual plane especially). Remember the Qjet will open its secondaries depending on air demand of engine. On a dual plane, this typically happens more gradual and the size of the secondaries add to plenum volume, which the dual plane needs. This is also why a large 2 barrel carb like the Rochester 2g does so well on a stock dual plane intake, especially the Buick 350, which has very long runners due to the width of the intake. On a single plane intake, air demand is high and so secondaries open up quicker and at lower RPMs, kills velocity with a large plenum underneath it. By the time the air/fuel reaches the runners, the charge quality is less atomized, and I wouldn't be surprised if there was some fuel settling on the bottom of the plenum and runners this way. Don't forget reversion. This will exacerbate the fuel charge problem even further, with the charge moving back and forth under the carb... Coupled with the fact that the Holley DP is square bore, aids in even fuel/air distribution all around the plenum at full throttle, and with the secondary accelerator pump, acts like 2 large 2 barrel carbs sitting side-by-side. It's actually the perfect carb for this intake, second only to fuel injection! Low-mid range would be superb, and top end as well, even with the smaller CFM carb. Why? Because of increased plenum draw on the carb, making it act like a larger carb than what it is. Let me explain: there's a trick circle track racers use on their 2 barrel carbs in the 2 barrel racing class. This trick is to open the plenum up underneath the carb, then use a tapered spacer that is wider on the bottom than it is on the top, acting like a type of venturi vacuum to draw harder on the 2 barrel carb. The science behind it is the carb thinks the engine is at a higher RPM than it is, so delivers more fuel/air. Same principle with a smaller 4 barrel carb on a single plane intake. So what you end up with is good power across the entire RPM band. My semantics may be a bit off in a couple places in this post, so anyone with a better description to explain please feel free to correct me or add to it. Gary
What you said right here Gary makes me think that the intake Should Not be cut out for a Q-Jet. 2 2bbl carb is the key word here. Maybe it should only be opened up on the port matching from top to bottom to help keep the velocity up. Then put one of those Wilson tapered 4 hole spacers on it with my K&N Flo-Control air cleaner.
This is VERY enlightening, educational, AND interesting! The more I read, the more sense its all starting to make, air flow, squarebore, spreadbore. A square bore carb seems to make sense, 4 equal size holes centrally located above the plenum, verses 2 smaller, and two WAY larger holes, the fueling would seem uneven. Im not bashing my Q-Jet, Ken did an awesome job, and it kicks ass on the Stage 1 Hope a Holley kicks ass on my SP3 after I smooth and contour the rear runners:laugh:
I think you can turn that vac sec into a double pumper with some extra parts...I think. There may be some passages in the main body missing and it might not work. Hove to start to look in my Holley book. might be time to reread that sucker.
I read all this and wonder if anybody reads what I say regarding the 350. I wonder if the info comes across in a different language or maybe people can't read. I have tried carbs up to 1000 cfm on the s/p. best response the engine has given me is with a 650 d/p and the others are now sitting on the shelf. another carb that would be interesting to try is a c&s aerosol 2bbl carb. they make them up to 950cfm. I think it would be good. only issue is $$$$. sheesh.....
I read what you say Johnny. It's reassuring to me that my thoughts coincide with yours, since you have a lot of experience to offer here. It tells me I'm on the right track and makes me feel more confident sharing my thoughts. You're one of the first people to pioneer with this engine, so I think people listen more than you may think. If I may be so bold though, I think the 2 barrel idea is best suited for dual plane intakes; same reason for Qjet and larger bore (higher CFM) carbs. We already know smaller throttle blades and venturi are needed for a single plane. I see where you're going with it though. The thinking is more centralized air/fuel distribution. The Holley DP is about as close as one can get without port fuel injection. UNLESS you're talking major RPMs, then you'll need larger and maybe that 2 barrel idea is suitable. I posted a video on another thread with a 320 CID engine turning 8100 RPM and making 527 hp with a frickin 2 barrel... Gary
You would need a new main body and a new throttle base because the vacuum secondary main body doesn't have the squirter channels in the secondaries and the throttle base plate doesn't have the secondary squirter arm and I think the rear metering block is also different. If you get a base, main body and rear metering block all the rest of the pieces should work, http://www.ebay.com/sch/i.html?_odk...y.TRS0&_nkw=650+carburator+main+body&_sacat=0 Here are some base plates; http://www.ebay.com/sch/i.html?_odk...50+DP+carburator+throttle+base+plate&_sacat=0 And here are some metering blocks; http://www.ebay.com/sch/i.html?_odk...holley+DP+carburator+metering+blocks&_sacat=0 If you do a more extensive search you can probably find the parts needed to convert a vacuum secondary carb to a double pumper for less $$? I found and bought a brand new 850 double pumper base plate for $50 from eBay which would work for a 650 main body, it just gives a few more CFM that way but will work just as good as an actual 650 base plate. What you don't want to do is use a 650 base plate with an 850 main body, I don't think that won't work so good? I have seen dp main bodies for under $100 before, so $150 plus maybe the $39.99 metering blocks and PRESTO that 750 CFM vacuum secondary car is a 650 DP!! GL Derek
Looks like theres tons of options! My head is spinning here LOL:eek2: Im starting with replacing my fuel pump (Airtex, new this April) I called TA, for one of the good 350 pumps, they're out, and no more coming in I found an NOS AC Delco pump on e-bay, ordered that, 39.00 Another question, on the Holley carbs, are the fuel inlet lines the same dimension (inlet to inlet for the front and rear bowls) for 650/750 and vac sec and DP's? Reason I ask, I want to use the same braided -6AN line from my pump to my carb for all my carbs Im going to accumulate, LOL. My Q-Jet is set up for this, and I want to set up my Holley 750 vac. sec. same way, AND eventually a 650 DP, and Nicks carb he said I could try, this way I can swap carbs at the track in a few minutes without having to jack around with different pump to carb lines. I don't like rubber hose, ESPECIALLY for fuel, and the close proximity to the engine fan, and distributor/electrical.
To get a good deal just wait until someone like me gets tired of their present setup and sells really good stuff for a lot less than they paid for it. ou:
A > converting a vac sec carb to dbl pump is probably not gonna be worthwhile or cost effective . start out close and make small changes and upgrades instead of big steps . B > fuel inlet spacing is 8"+ on vac carbs , 9"+ on dbl pump carbs due to the addition of rear metering blocks . vac carbs with rear block kit would be the same as a DP . dominators are bigger . look over the holley style fittings that screw into bowl , I've seen some 5/16" versions , most are 3/8" . C > mark I have one spare buick 350 carter strip mechanical pump left ( had 3 , new one on my car , one used one went to ohio a little while ago for a fuel pressure problem , still have a good lookin used one left ) . can't remember the part number right off - something something 650 I think , i'll check . grabbed the one new one that jegs had left over a few years ago . no more that I've seen out there . if you would like to try that let me know . may want to run a regulator with that ? D > good read . the 2bbl and plenum ideas are interesting . but remember the holley primarys are open by themselves until approx. 30% and then the secondaries start to kick in so not that much dif than a q-jet except for the staggered bore sizes . maybe the extra plenum draw fools the q-jet as far as a vac signal where the mechanical secondaries would be as set . am I thinkin correctly there ? maybe why some have good luck with the 850DP carbs on the SP 455's ? edit : checked , pump part# is #M60650 . that was on new box . so either that or #60650 . 8 psi . 120 gph , 1/4" NPT inlets - info per box .
Mark, I wonder if You can use one of Robb Mc's pumps with a 350 arm on it? http://www.robbmcperformance.com/products/buick550.html
Mark, didn't your car pick up MPH when you leaned out the secondary rods? If so, that sure doesn't seem to point to a fuel supply problem. Have you considered going back to the Stage 1 intake and throwing a 100 or 150 shot of NO2 on it? Fun and streetable!
