Whos running a mechanical secondary carb on their BBB455 street machine

My 455 had a 4011 series 650 holley on it and I recently acquired a Holley 850 double pumper but it has mechanical secondaries. All I keep reading about is unless I plan to drag it I need to stay with vacuum. I don't plan to always drag it but I do plan on running hard. Anyone else have a carb with mechanical secondaries that can shed some light on how it runs for you street driving?

 

If you tune it to your engine,it should run just fine. The "double pumper" feature only kicks in when you kick it passed about 40-60% throttle,or put it to the floor,and after the initial pushing it to the floor,the "pumpers" are basically done,unless you let let off and punch it again.

With a Holley double pumper mechcanical secondary carb,the squirters(or pumpers) for the secondaries are there because they aren't depending on vacuum to open the secondary butterflies. And w/o any vacuum to pull gas in,there would be a gaint bog until the the ventri gets the signal for gas to flow.

Just like a vacuum secondary carb,there is a squirter on the primary circuit too.Because even on a vacuum secondary carb,the primary circuit uses a "pumper" to squirt gas in as the pedal is being pressed until the pressure difference makes gas flow though the primary circuit. So basically the "pumpers" are so the engine doesn't bog when the throttle opens,and are done until the throttle is closed and opens again.

Properly tuned,a Holley 850 double pumper should run great on a street driven 455. I'm not running one on a 455,but my 65 Impala with a sbc 383 has a Holley 850 double pumper on it,and it runs great!(granted its a little big for that engine,but I got a great deal on it) And the mileage posted is with that carb on it. For "normal" part throttle driving there shouldn't be any issues if it is tuned to your combo.You wouldn't even be able to tell the difference with "normal" driving between a VS,or a MS carb,until you smash the gas pedal.


The double pumper is a great design,with a whole lot of tuning options,that are fairly easy once you learn about how to do them. If you have the carb,I say,try it you'll like it.

The only problem I have using that carb is trying to get traction with my 3.07:1 12 bolt posi,with my 700R4 in 1st gear trying to launch at the track with drag radials,some times it breaks loose if I start with the RPM to high.(LOL,its kind of a heavy car) The traction was actually worse when I disconnected the secondaries to see how it would run that way.(it made too much low end torque w/o the secondaries opening)

Have some fun,goodluck.

 

Thanks for the post, that clears up a good amount. All I kept reading was unless I was dragging or running a manual trans a mechanical was a no go. I haven't really looked at the carb all that much, gonna throw a rebuild kit in it to be safe but couldn't pass up the price. Since it isn't a vacuum secondary does the PCV valve need to blocked off coming off the intake? I didn't even look to see if there are ports or not for the hose. I'm not to familiar with these carbs but learn fairly quick when it comes to metering and tuning them however.

 

You will need the PCV regardless of carb choice.

If the double-pumper dosnt have a port, youll have to hook it to a vacuum port on the intake.

A D-P Holley can be a little trickier to tune than a V-S carb, but it is very doable.

If they didnt work, they wouldnt still be a top selling carb after 40+ years:Brow:

 

Tuned correctly it will be very responsive.Probably has 30cc pumps and 31 squirters.Generally,depending on engine mods and converter, these will have to be changed.50cc squirters will need to be used,and the squirters to 35 plus.Just play with it till there isn't any hesitation and is crisp.sometimes the cams operating the pumps also should be changed to fine tune it.We've done lots of 850-950 and after some tuning they run great.
good luck
gary

 

I'm with the above; I'm running an early Barry Grant Silver Claw carb (Holley 4150 copy), mechanical secondaries. What's been said about tuning accelerator pump volume, cams and squirters is essential. The carbs tend to be more forgiving going to WOT from idle or part throttle if higher torque converter stall speeds are used. A tight converter coupled with good traction can make mechanical secondaries more difficult to tune for drivability.

Devon

 

Great info, thanks guys! It does have a 50cc accel pump on there, as for the squirters I forgot to ask. It came off a nicely worked 396 so hopefully the squirters were prob changed as well just need to see what size if so.

 

The engine is actually a surprisingly small part of the factors that will influence the accelerator pump tuning...the car's weight, gearing and stall play big roles. Regardless of what's already been done to it, plan to go through the tuning process all over again. You might find one or both of these two items invaluable:

http://www.summitracing.com/parts/hly-36-182
http://www.summitracing.com/parts/hly-36-184

Devon

 

I run a 1000 cfm Race Demon and would never go back to a vacuum secondary carb. If I were to down-size, I would go back to a Q-Jet.

Even in a very mild combo, I personally would prefer mechanical to vacuum secondaries...but that is me.

 

If you have an manual transmission it's perfect.

 

I run a Holley 950HP carb. No problems once you get it in-tune with your engine. That means idle, power valve, air bleeds, and jetting, and getting the secondary blades in just the right position on the slot that's in the body.

 

I prolly have 50-60K miles on BigRed over 15 years with a double-pumper of some sort. LOTS of highway cruising ... blasting on the street ... running at the track = never a problem

 

Is there a book avaialble that would help me know how to tune my Holley 850?

Any recommendations?

 

First off you made a good decision getting rid of the 650 holley. WAY to small !!! For me I used to think the same thing. After an engine rebuild and various modifications, I'm running a 1000 hp holley. Yes with mechanical secondaries. I'll never go back to the old 750 vacuum sec holley I used before. The throttle response is quick and it drives just fine on the street. It's a good carb for the street and the strip. Follow the people on this site and they'll take care of you. They'll steer you in the right direction. We need all the respect we can get. Too many Ford, Mopar, and Chebby guys out there with advice that doesn't always work for our Buicks. John B.

 

I have a 850 DB ran it for years soon to upgrade to 950 CFM Carburetor or F.A.S.T EFI Not sure which way to go..

 

I'm running one on my 430'ed 72 Riv. The car starts after the first couple revolutions everytime, even in the cold thanks to the electric choke i added; it responds and runs just fine at part throttle and it runs like a raped ape up top, but it needs tuned for my combo for better part throttle response and better fuel economy. Whoever had it before me put 82 jets on the primaries and secondaries so it's pig rich all the time. I also think a 50 shot for both is probably too much as well so I will be chaning that as well. To properly tune any carb be prepared to spend some time and money to get it right. I'm not looking forward to it, but I know in the end the results will be worth it.
Read this two part article and go from there: http://www.amosauto.com/Articles/General/Tech/tuning-holley-four-barrel-carbs

 

http://www.amazon.com/Holley-Carbur...e=UTF8&qid=1358432296&sr=1-11&keywords=holley
http://www.amazon.com/Holly-Carbure...ie=UTF8&qid=1358432296&sr=1-3&keywords=holley
http://www.amazon.com/Holley-Carbur...ie=UTF8&qid=1358432296&sr=1-2&keywords=holley

Devon

 

Somewhat off topic but you added an eletric choke? My 650 has an electri choke on it, do you know if I can swap it over to this 850?

 

If both of your carbs are 4150 series then yes.

 

Been a while and haven't had much time to really work on the car. I got the carb all hooked up, internals clean, fresh gas, etc and it fired right up. I am having a horrible stutter leaving the idle circuit and think I may have tracked it down but need some input on how to fix. It has 50cc pumps on both ends and I have adjusted them according to Holley's site. After letting it warm up the it seemed ok working the throttle linkage by hand and had nice response. Once I use the gas pedal and hit it quick it was almost cutting out again and then it happened, a nice poof and a flame flew out the carb and actually had some excess fuel burning which i put out. I noticed the accel pump at the front of the carb will not return all the way back to its starting position. It seems to be the actual linkage getting stuck. I am going to have to pull it apart again and see whats going on so could this be the culprit to the blow back I got or is there still something I am missing that is obvious?

I had a 650 on here before and didn't have this issue so I do not believe its timing, switch of a plug wire etc.

82 primary jets
84 secondary
50cc pumps 35 squirters
red pump cam
Choke disconnected