KMatch

If you own one and haven't tuned it, you're missing horsepower if you own a light car with a smaller engine! I've found this out first hand. I've been looking for lost horsepower in my build and doing the research I found some interesting reading. It appears the SA series is set up conservatively on the secondaries without a lot of hoopla in the paperwork other than a couple of springs and some basic info written in a yawning manner. For instance, I my research I found my 570 is rated for a 350 running over 8k rpms just to allow the secondaries to open fully! My healthy 302 only revs to 6000, so after doing the math I ordered a secondary tuning kit and must say, without even comparing times or using the paperclip to monitor secondary opening, the first spring change I made was DRASTIC! So, do yourself a favor and don't live with it out of the box. Or better yet, leave it alone and come race me!

There's a basic heads up for the ones of you who didn't take the time to make it right - as I did for months...

67mustang302

Or just get a mechanical and not mess around with springs.

boogerschnot

Agreed.. the yellow spring did wonders for me. I pull about 19 inches of vac. At idle. I also adjusted my accelerator pump linkage and that made a great improvement in parkinglot situations.

KMatch

Really? You'd still bolt it on without tuning? It still defeats the purpose. Many buying the SAs want to bolt-n-go and even at this simplistic level, you won't get the performance it's capable of without hitting the high end of Holley's intended specs. Much less with an improperly tuned DP. Back on topic, we're discussing vac secondaries.

kalli

have a DP as well, so therefore I don;'t need to swap springs either. But that bolt and go is _never_ true for any carb.
In your case it did wonders when you added a lighter spring and I guess in most cars (no matter what engine) this will make for a nicer tune (power develops more brute rather than slowly in). Again a difference if you drive stick or not. I believe with stick this effect is a lot more drastic than when you drive a stockish auto.
yes the street avengers will drive on every car if half decent matched, but to make power you _have_ to adjust at least: jetting, idle speed/mixture, povervalve, accellerator pump cam and linkage. that's kinda the bare minimum.

I'm happy for you though that you found power with such a simple change, though :-) I guess you're driving a stick with 3.5+:1 gearing if it makes such a difference.
if I order a carb for a stick then I buy a double pumper, no matter what anyone else might say. just my opinion though

MonsterBilly

maybe this thread can help me. I have a 670 street avenger on my 66. i came as a top end kit from summit with a lunati 61003 cam and a stealth intake. I am also running a t5 with 3.73 gears. i have always thought that there should be a little more from my engine.

I am however running mech secondaries.

anyone have any tuning tips for me? Should i get a A/F ratio guage?

1slow67

Sounds like your carb is too big. My dad and I both have an edelbrock 600cfm carb on our engines.

I have a 302, weiand intake, HEI, midlength headers, T5, and 3.00 rear gears.

He has a corvette 350, edelbrock performance HCI kit, full length headers, 700R4 tranny, and I believe 3.55 gears.

67mustang302

Mechanical > vacuum when it comes to tuning for performance. More control, and the throttle responds to your foot.

With vacuum the throttle responds partly to your foot, and partly to the CAR(not just the engine). A heavier car, with taller tires, taller gears, taller trans gearing, tighter converter etc will need a stiffer spring. Lighter car, smaller tires, more gear etc will need less spring.

BUT, the reality is even the best tuned vacuum secondary leaves power on the table because you still have to control the rate of secondary opening to compensate for a lack of accelerator pump.

Vacuums are better for most auto cars and people not looking to extract every bit of power and response from a carb(which can be time consuming and expensive).

KMatch

You guys who spend the time to test spark plug gaps for horsepower are totally missing the point of this thread. The whole point is for those who were mislead to believe the vacuum secondary carb was a bolt-n-go solution are missing a BIG chunk of power if they don't do the simplest of tests. My tuning has already gone way beyond this as well, but the secondary tuning is so easy to take for granted and many won't even know they just bolted on an expensive 2 barrel carb if they don't look into it. The mechanical versus vacuum debate can be dealt with elsewhere along with flip-flops as a weight reduction over Nikes for better ETs. Keeping it simple...

KMatch

If you're running stock heads, that's your limiting factor. And unless you're turning well past 6500, the 670 is too much carb and its potential will never show.