hey guys I have a 5-speed car and I have heard that vacum secoundaries are no good for stick cars. Now I have also heard that by putting on a holley my car woudl be alot quicker. Now is any of this true and if so woudl a 670 street avenger be good on my motor rigth now and if i change to vortecs in the future? thanks

 

Demand-type secondaries, such as the Edelbrock/AFB, q-jet, and Holley/Demon VS, have to "recover" after each shift. But, a double pumper will return to full open as soon as you mash it again after a shift.

Not that the other type of carbs are "no good", just not as good.

Personally, I won't have a VS/demand-type secondary carb on anything not used for towing or not requiring the system for emissions purposes ever again.

 

I have a 670cfm holley street avenger...Im tinkering with the idea of getting a 650 double pumper...not sure tho.

The holley 670cfm street avenger seems to be a decent carb. Ive got in tuned in pretty good with my setup. However I have never tried a mechanical secondary carb before...I may someday.

 

ok well i have a 750 with mechanical secoundaires on my motor rigth now and its an edelbrock. Now say I buy some vortec heads that can take the lift of my cam and put them on using an edelbrcok performer rpm vortec intake and the same cam i have or possibly an XE274. Now would a holley 650 double pumper be good for the setup or would my edelbrock be better for it? Also if the 650 isn't enought would uping the holley to a 750 net me much gain over the edel?? thanks guys

 

I think a 670cfm street avenger or a 650cfm holley double pumper would do very good. I have heard edelbrocks don't make as much power but I doubt its that big of deal. Most people on here are gonna say "get a 750 double pumper". You don't need its. Whats the point of putting a 750cfm carb on a motor then having to go 10 steps down on jets so you can run the 750 on a stock 305?? I don't know why people do that.

 

You need to understand that you do not have "mechanical secondaries". You have a throttle body with secondary throttle blades that are opened mechanically, but there is still a flap above the secondary throttle blades that are opened based on demand.

You can probably produce the same peak HP numbers with an Edelbrock that you can with the same CFM Holley. And, a 750 on a 305 is overkill in most cases. However, there is more to "speed" than peak HP, and jetting to get the right mixture ratio should be done regardless of CFM.

What can be said without fear of contradiction is that a properly tuned DP carb will make the car quicker than a similarly properly tuned demand-secondary type carb. Over-carburation is the main issue with the DP, and Holley has a chart to help you avoid that.

Back to the original question, though: none of the discussion between my first response and this one even addressed it.

 

I never said anythign about a 305, I am talking about my 350. no affense but who cares about 305s lol

 

The quote got fouled up. My apologies, I fixed it. (Some people do care about 305's - and over-do it. )

Anyway, definately go for the double pumper. The chart on this page http://www.holley.com/HiOctn/TechSer...fo/TI-225.html shows the RPMs you need to be above when you floor it for a given engine and carb size to avoid bog. A 650 will allow that from about 1000 RPMs, a 750 will have to be above 1500 or so. The peak power difference will be minor, because flow is more likely restricted by some other engine factor than it will be by the carb. That's what the CFM=CID x maxRPM/3456 formula tells you.

 

That's what I'm running, and I can't hook the biatch up! Need some DOT's!

 

Hey Barry have you ever run your setup?? Cause I have the same cam, edelbrock 750, and performer RPM intake but with stock heads. I am saving for vortecs and just wondering what kinda numbers I will be looking forward to. thanks

 

Ther is a very eay way to overcome and eliminate any airdoor or secondary throttle shift transition lag.
Keep your right foot to the floor while shifting.

Just lift your foot slightly off WOT during the shift.
The throttles will remain fully open during the shift.
So will the Edelbrock air door.
Once you've mastered this "speed shifting" technique, don't be suprised if you find your vacuum/volocity valve controled secondary carb now outperforms even a sharpely tuned double pumper on a 4 or 5speed car.
You can also mount a block of wood under the clutch pedal to limit how far it travels when depressed. You only need to depress the clutch just far enough to take the power load off the trans during the shift. Any further clutch pedal travel during the shift wastes time.
that will really speed up your shift time.

Now which is quicker?

You will retain the smooth operation of a vacuum sec carb as well.

If you have a rev limiter all the better. Set the rev limit and you can go nuts power shifting it and not worry about overreving 'er if you happen to miss a shift at WOT.

Try it.... .......at your own risk... Your skill level may vary....

 

On street tires (i.e. NOT hooked up) I ran a 9.11 in the 1\8th at 77.9 MPH. The rear end broke loose when I banged second. There is a guy who posted here who's got basically my motor and his car is hooked up that ran an 11.98 in the quarter on motor only. so GET THOSE VORTECS, and and soon as I get some street slicks, I'll be in the 12's.