Tips on tuning new street avenger

[TimDart]

Ihave a new 670 Holley Street Avenger recently fitted. Ran nicely out of the box, but felt a touch lean so I upped the primary mains from 65 to 68. I also swapped in a light spring to bring the vacs in earlier.

on the highway, the car runs smooth and strong, but at around 4000rpm up she really takes off/ the difference is really noticable in acceleration compared to below 4K.
Any tips on how to get more of this power out of the carb below 3K?

My combo is
360, 9.5.1 comp,
XE268 cam
iron heads with stock valves, valve job and light porting
340 manifolds + 2.5 TTI exhaust
Air Gap manifold
3.55 gear
timing is 18 initial , 30 @ 3000rpm

 

[Nick M.]

Sounds like the secondaries are opening too early, causes a lack of power then a rush of acceleration once the engines demand for air/fuel more closely matches what the secondaries are providing

 

[TimDart]

Thanks, that was mentioned to me in conversation on Sunday. I have a range of springs, so i'll experiment with those first.

 

[dgc333]

That surge in power you feel with a vacuum secondary carb is actually a bog that is the result of the secondaries opening to soon/to fast. The way to select the proper spring is to start with a stiff one and keep going lighter until you get that surge then go back one size.

The rpm range in which the engine makes power is a function of the combination of parts you are using. Getting the carb dialed in will improve the power over the entire rpm range but will not appreciably change the shape of the power curve.

FWIW, I have a 360 with a 670 and XE268 cam and mine has an appreciable increase in power past 3500 rpm too. I think you find that is the nature of the combo.

 

[ramcharger]

I agree with everything that dgc333 said. To get a little you've got to give a little. High rpm power comes at the expense of low rpm torque.

You could mess with your timing a bit and that might help. I would shoot for 32-34 total all in by 2500 rpm but leave your initial timing alone.

I also agree that the secondary spring might be too light.

 

[TimDart]

thanks guys, thats interesting to know.
I'lltest as you suggest and get back in a few days.