[Paul78Zephyr]

Hi all,
What are the opinions here on vacuum vs mechanical secondaries for a 100 percent street driven engine. I have a 1978 Mercury Zephyr with a 1989 Mustang 5.0L HO converted to carb. Currently I am running a Holley 0-1850 600 cfm vacuum secondary carb. The engine is 100 percent stock except for an Edelbrock Performer (not Performer RPM) manifold, and Duraspark dist with MSD 6A. T-5 manual trans and 3.27:1 Traction-Loc 8.8. The engine rarely sees over 5000 RPM. I want good low end response. The engine runs very well, but Ive never been sure the carb I have is the best street performance option.

Paul

_________________
1978 Mercury Zephyr 4-dr / Holley 600 vac sec carbed 1989 5.0L HO with Edelbrock Performer intake / MSD-6A / T-5 / 8.8" rear 3.27:1 / Mustang 5.0L brakes, suspension, steering / Dual exhaust / Mustang 10 hole wheels / P225/60R15 Goodyear Eagle TR

<font size=-1>[ This Message was edited by: Paul78Zephyr on 4/23/06 11:44pm ]</font>

 

[mstngjoe]

IMO, the only time a mech secondary would be a better choice is if you're racing.

All other things being equal, the mech secondary should make for a quicker e.t. by avoiding the secondary opening lag you find in the vacuum actuated secondary.

In most cases you can also get away with a slightly larger carb when using vac secondaries. Especially with a dual plane intake.

 

[71hotrodpinto]

Vacuum secondary for the street. Especially with your needs.
The need for a mech secondary in reality is just for racing. Some have success in thier applications on the street ,but ive heard more issues against using them than for them.
And as far as the bog issue with vacuum sec , thats only an issue when its out of tune. A properly adjusted spring will not have any bog or "RUSH" when they open. The transition will be seamless.
On the issue of your carb, you might want to check out the Edelbrock performer (500cfm)or maybe the Holley Avenger (570cfm)series. They are much better driving carbs than the ol 1850.
good luck!

 

[DrStang]

I've driven Mech secondary carbs on the street for 25 years, the racing only application is false. I enjoy the fact that my secondaries are opening mechanically and the bog that some mention is usually just a linkage or pump adjustment to correct. Relying on a vacuum to open my secondaries is an uncertainty IMO. The mech sec carbs are a nice option on the street and having 2 extra barrels instantly at the press of the accelerator is a greta way to go.

 

[mstngjoe]

On 2006-04-23 09:08, 71hotrodpinto wrote:
And as far as the bog issue with vacuum sec , thats only an issue when its out of tune. A properly adjusted spring will not have any bog or "RUSH" when they open. The transition will be seamless.

I would agree that a "bog" would indicate inproper adjustment.

However, the vacuum secondary is dependent on engine demand before opening. Whereas the mech secondary opens based strictly on the linkage.

The mech secondary doesn't have to "wait"....that's why the e.t. should be better.

For a street car a vac secondary makes good sense.

 

[mstngjoe]

On 2006-04-23 09:27, DrStang wrote:
... the racing only application is false.

Who said that?

 

[mustangboy]

On 2006-04-23 09:33, mstngjoe wrote:

On 2006-04-23 09:27, DrStang wrote:
... the racing only application is false.

Who said that?

71hotrodpinto said that..........I'll add my 2 cents worth by saying my car seems a little smoother to drive with a 3310 VS holley on the street but its quicker with my 650 DP.

_________________

1968 mustang 306,stock ported heads,650 Holley DP,weiand Xcellerator intake, Comp cams Magnum 292,[email protected] and 518L,heddman headers,4speed with a 4.11 detroit locker.13.69 at 101 mph.

<font size=-1>[ This Message was edited by: frdnut on 4/24/06 12:41am ]</font>

 

[dacofa]

Vac and play with the secondary spring tension to get it where it works right for you.

 

[mstngjoe]

OK....see it now.

I thought he thought I said it.

The 3310 is a great street carb.

I used a Holley 750HP (0-82750) vac secondary on my 331 and it ran fantastic.

Also had a DP on for awhile......loved the gas.

 

[mstngjoe]

Here's a pretty good article:

http://www.chevyhiperformance.com/techarticles/83798/index.html

Note the "Sidebar" articles about the track times and vac vs. mech secondary performance.

 

[Blue Fastback]

A properly adjusted vacuum secondary for street use. Most guys dont try to adjust the secondary spring for the fastest opening which should be done for best performance. The vacuum secondarries are better on gas with a street vehicle.

 

[Motorhead]

Vacuum secondaries are for people who don't know how to give the engine the proper amount of throttle and just like to mash their foot to the floor and let the carb do all the brain work. I think vacuum secondaries are OK when you've got an automatic transmission, but with a manual I wouldn't even consider running a vacuum secondary.

 

[wildosvt01_OLD]

I don't know why I see so many people stating the 1850 is a POS?

Ive run them and my buddy runs one on his worked over 302 and straight loves it (13.6 e.t.). I never had a problem with them.


:edit: FWIW! I'm not saying a DP is bad. We just swapped out a POS edebrock 600 for a 650 DP spreadbore

..




_________________
1965 Galaxie Fastback-351C 2v/C4 with a 3.50 posi

1973 Gran Torino Sport (sold)

2004 Cobra
2004 Marauder

<font size=-1>[ This Message was edited by: wildosvt01 on 4/24/06 8:13am ]</font>

 

[F15Falcon]

I have a 700 Holley DP on my '64 Galaxie with a 2V 351 C and a 4 speed, and a 750 Holley DP on my '70 Mach I with a 4V 351 C and a 5 speed and I drive them on the street alot with no problems, and the gas mileage is not bad on either. Is there anything else besides a double pumper?

 

[quickshift]

My personal preference is a DP. I can feel the resistance in the pedal as the sec's open,allowing me to adjust my economy or "fun" factor as necessary.
Just to add confusion to DP vs VAC,.....68 shellbyGT350,306HP,725 holley with VAC sec's.....go figure.

<font size=-1>[ This Message was edited by: quickshift on 4/24/06 10:52am ]</font>

 

[mikes82GT]

AND, To further confuse the issue: square bore vs. spread bore. I feel the spreadbore is better on the street.

 

[ujt389]

I like DP's, and I run a 650 DP on my 67 mustang with a 302 and no problems on the street.

 

[71hotrodpinto]

Ok well after reading all that i have to ask;
Why would this guy, who asked the question in the first place, run a mech sec Race carb on his stock 302?? especially after stating that the engine Rarely sees over 5000rpms?
Sometimes i think that we can get off on a tangent too easily...

 

[Motorhead]

Because he has a manual transmission and a light car... and mechanical secondary does not equal "race carb"... I'd say it's more of a "fun carb"

_________________
'86 Bronco fullsize, 460, E4OD
'85 Ranger, 340hp 289, T5

<font size=-1>[ This Message was edited by: Motorhead on 4/24/06 12:56pm ]</font>

 

[BLACK65FORDFALCON]

The guy that started this thread is running a VS carb, Not a DP. I also wouldn't classify a 650DP as a full out race carb, Definately more of a fun carb to me as well.