Vacuum vs mechanical secondaries on street engine

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





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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>

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.
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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!
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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.
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<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
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.

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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.
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<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2006-04-23 09:27, DrStang wrote:
... the racing only application is false. </BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

Who said that?
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<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2006-04-23 09:33, mstngjoe wrote:
<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2006-04-23 09:27, DrStang wrote:
... the racing only application is false. </BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

Who said that?

</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>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.

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1968 mustang 306,stock ported heads,650 Holley DP,weiand Xcellerator intake, Comp cams Magnum 292,244dur@050 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>

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

OK....see it now. [img]/forums/images/smiles/icon_smile.gif[/img] I thought he thought I said it. [img]/forums/images/smiles/icon_wink.gif[/img]

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. [img]/forums/images/smiles/icon_rolleyes.gif[/img]
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Here's a pretty good article:

http://www.chevyhiperformance.com/te...798/index.html

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


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