what carb would you put on this set up?

jerry S · Jun 21, 2005

I have a 351W bored .060 over, making it a 362. I currently have a holley 650 cfm dbl barrel with vac secondaries, part number 80783C. The vac secondaries are not opening up at WOT. The tuner tried re-jetting, new meters, new springs, etc, and nothing is working. His solution was to bolt them open permanently. I want to avoid that.

I currently have an auto tranny with 3.25 gears. I will be getting an AOD with 3.89 or 4.11s, [edit] lightweight flexplate [edit], and an alum drive line in the near future.

Can I put a 700 cfm double pumper on there now without overcarbing and bogging?

D.Hearne · Jun 21, 2005

If the secondaries aren't opening, there's something wrong. Try either a white or purple secondary spring. If neither works, your carb's got the vacuum passage to the sec. spring diaphram blocked. These are the two lightest springs, the white being the lightest. As for your aspirations for an aluminum flywheel and an AOD, you need to chose one or the other there. You don't use an aluminum flywheel with an automatic trans. Flywheels are for std transmissions, you need a steel flexplate for an automatic, and based on your build, it'd be wise to chose an SFI approved one at that.

grego37 · Jun 21, 2005

how do you know the secondaries arent opening?

jerry S · Jun 21, 2005

D.Hearne said:
If the secondaries aren't opening, there's something wrong. Try either a white or purple secondary spring. If neither works, your carb's got the vacuum passage to the sec. spring diaphram blocked. .

The alum flywheel is a mistype on my part. I meant light weight flex plate. My dyno tuner tried everything before settling on bolting open the secondaries. Can I use the 700 cfm double pumper ok on my set up? I figure with the 3.89s or higher, I will be revving pretty high and drinking the juice.

jerry S · Jun 21, 2005

grego37 said:
how do you know the secondaries arent opening?

From the dyno tuner. They observed this while the car was at 5500 rpm.

jikelly · Jun 21, 2005

Id say try the stuff D.Hearne suggested on your 650. If you can get it to work I'd say keep using it.

D.Hearne · Jun 21, 2005

If your tuner can't get them to open, then it's time to get another tuner. Never seen a Holley with vac. secondaries that I couldn't get them to open. There'd have to be something physically wrong with the carb for them not to open up. Sounds to me like he's trying to sell you a carb you don't need. But to answer your question, yea, that 700 will work on your motor, you might even be better off with a 750.

jerry S · Jun 21, 2005

jikelly said:
Id say try the stuff D.Hearne suggested on your 650. If you can get it to work I'd say keep using it.

The tuner tried everything, springs, jets, metering blocks with no success. I think the carb is defective or damaged. I did have two massive back fires when I started it up after installing the MSD ignition and distributor. The needles were stuck when I got it to the dyno. This was a brand new carb.

I would like to obviate the problem of vacuum secondaries and put a double pumper on there. I am just a little preoccupied about it as everything I read says to use a vac. secondary carb on an auto tranny, which I have. Will I bog with a 700 double pumper?

Dark Knight · Jun 21, 2005

how would you bolt them open ? it would be at full throttle then ... like was said above, make sure the vac passage is not plugged, and make sure there isnt something in the way stopping them from opening, gasket etc...

I sure hope they werent revving it in park or neutral to see if they were opening..

flexplates are pretty light already, doubt losing a couple ounces would make much difference

D.Hearne · Jun 21, 2005

No. it will not bog if it's tuned right AND the carb isn't too big for the motor.

D.Hearne · Jun 21, 2005

Dark Knight said:
how would you bolt them open ? it would be at full throttle then ... like was said above, make sure the vac passage is not plugged, and make sure there isnt something in the way stopping them from opening, gasket etc...

I sure hope they werent revving it in park or neutral to see if they were opening..

You can install a #10 machine screw and nut into the return linkage on a vacuum sec. Holley to make it a "poor mans" mech. secondary carb. I've done it a few times. Works better with a 50cc accellerator pump though.

jerry S · Jun 21, 2005

D.Hearne said:
If your tuner can't get them to open, then it's time to get another tuner. Never seen a Holley with vac. secondaries that I couldn't get them to open. There'd have to be something physically wrong with the carb for them not to open up. Sounds to me like he's trying to sell you a carb you don't need. But to answer your question, yea, that 700 will work on your motor, you might even be better off with a 750.

he would not be selling me the carb. I would be returning it for an exchange. I am wondering if it isn't either defective or damaged.

Dark Knight said:
I sure hope they werent revving it in park or neutral to see if they were opening..

no, it was on the dyno.

10secgoal · Jun 21, 2005

Dark Knight said:
I sure hope they werent revving it in park or neutral to see if they were opening..

Probably what happened. You would think he might be able to put a vacuum to the sec. Then he could watch the open. But the motor wouldn't have to be running.

cougar694u · Jun 21, 2005

Use this formula to figure you're CFM size:

(((Max RPM/2)*Displacement)/1728)*1.1

The original formula's like this: ((Max RPM/2)*Displacement)/1728, but for naturally aspirated cars, they can reach 100% volumetric efficiency, so going 10% over is a good rule of thumb(x1.1).

Basically if you're gonna shift at 6000 RPM, then 6500 would be a good max.

(((6500/2)*362)/1728)*1.1

((3250*362)/1728)*1.1

(1176500/1728)*1.1

680.8*1.1

749

So a 750 would be the max you'll want to get if you're never gonna turn over 6500 RPM's.

I have a 950 DP on my cougar with a 351w (357 cid) and it ran better than with the 750 DP, though. Typically, going above what it shows will take away from bottom end due to lost velocity, and going below will starve the engine in higher RPM's.

grego37 · Jun 21, 2005

QUOTE:I sure hope they werent revving it in park or neutral to see if they were opening..

I was told the vac secondaries wont open unless under load (while driving)
when you say it was on the dyno, were the wheels spinning with a load on the dyno roller?

69Rcode_Mach1 · Jun 21, 2005

750 will fit your engine a lot better than a 650. I just got a Mighty Demon 750cfm, they come with mechanical secondaries and idle bleed jets and such. They are a replacement of the Holley HP series. This will allow far more tuning capabilities, you can lean or richen certain rpm ranges. Say you are stumbling down low you put in a bigger idle air bleed jet so it leans out from 0-3000 rpms and you keep the gas up top where you really need it. We have the holley version on my friends camaro and it is an amazing carb if you learn how to tune it. His is Vac secondaries though. I don't have too much experience tuning a double pumper. Shoot me a PM towards the end of next week or so all my new parts should be here and I should be able to start her up for the first time. Hopefully get a vid for the boys on stangnet too.

'69Stang · Jun 21, 2005

The Holley 700DP would be really nice on that engine. Never heard of secondaries being locked up, return it and get the 700.

jerry S · Jun 21, 2005

D.Hearne said:
No. it will not bog if it's tuned right AND the carb isn't too big for the motor.

Your answer is ambiguous and can be interpreted two ways.

1. The carb will not bog if it is tuned correctly and if it is not too big for the motor and
2. The carb will not bog if it is tune correctly. That carb is not too big for your motor.

Which did you mean?

cougar694u · Jun 21, 2005

jerry S said:
Will I bog with a 700 double pumper?

D.Hearne said:
No. it will not bog if it's tuned right AND the carb isn't too big for the motor.

jerry S said:
Your answer is ambiguous and can be interpreted two ways.

1. The carb will not bog if it is tuned correctly and if it is not too big for the motor and
2. The carb will not bog if it is tune correctly. That carb is not too big for your motor.

Which did you mean?

That could go either way. From the way it's written, it seems as though your option 1 is what he meant. I believe it's not too big for your motor. You could run a 750 and I think you'll be fine. And he's saying if it's properly tuned, it won't bog, either.

I'm running a 950 DP on an automatic and it doesn't stumble, but I played the accelerator pumps, power valves, & squirter sizes to get it tuned right.

jerry S · Jun 21, 2005

cougar694u said:
That could go either way. From the way it's written, it seems as though your option 1 is what he meant. I believe it's not too big for your motor. You could run a 750 and I think you'll be fine. And he's saying if it's properly tuned, it won't bog, either.

I'm running a 950 DP on an automatic and it doesn't stumble, but I played the accelerator pumps, power valves, & squirter sizes to get it tuned right.

I just wanted to verify as I consider D. Hearne one of the members of the Stangnet Brain Trust and his opinion carries a lot of weight with me. For you and the the rest of y'alls with DPs on your Windors, I appreciate your sharing the benefit of your own experiences with me. That counts for just as much. I wanted to make sure before I send this carb back to the US for a new one that I was on the right track with a 700 cfm dble pumper.

what carb would you put on this set up?

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