CLASS RACER FORUM - View Single Post - 1957 283/270hp dual quads drag testing on a 350

wheezer · 09-04-2009, 07:17 AM

This setup is just like 1957 with 6 inch paper air cleaners.

More background, about 4 years back I called to order a set of Stahl fender exit headers. Fortunately I was able ask Jere Stahl about this dual quad setup as he had championship experience with his 56 Chevy wagon. He indicated the carbs would see a stronger vacuum signal with 350 cid and consequently higher velocity in the venturii meaning if anything it would not run lean with the needle and jet set for the mechanical camshaft specified back in '57. Well...since this setup was really a high performance option for passenger cars in 1957 the power valve booster piston spring is really-really weak in compression, meaning the weak vacuum signal of the 283 with the solid lifter cam would pull the needles down into the jets to allow low power economy and motor idle stability. So...I'm wondering if at the top of 1st gear of the T-400 the vacuum signal is strong enough to pull the needles into the economy position. Then as the motor loads and really starts making more power the vacuum signal degrades and the power piston is pushed up and giving the jets more fuel. I meant to test the k factor of those springs before I rebuilt the carbs last Spring but forgot. The other set of needles and jets I have are for the hydraulic performance camshaft from 1957 and its springs are stiffer. So I've got much more test and tuning. There are several next steps. First is to install a vacuum gauge near the tachometer.

09-04-2009, 07:17 AM	#7
wheezer Junior Member Join Date: Sep 2009 Location: Dallas/FtWorth Posts: 13 Likes: 0 Liked 0 Times in 0 Posts	Re: 1957 283/270hp dual quads drag testing on a 350 This setup is just like 1957 with 6 inch paper air cleaners. More background, about 4 years back I called to order a set of Stahl fender exit headers. Fortunately I was able ask Jere Stahl about this dual quad setup as he had championship experience with his 56 Chevy wagon. He indicated the carbs would see a stronger vacuum signal with 350 cid and consequently higher velocity in the venturii meaning if anything it would not run lean with the needle and jet set for the mechanical camshaft specified back in '57. Well...since this setup was really a high performance option for passenger cars in 1957 the power valve booster piston spring is really-really weak in compression, meaning the weak vacuum signal of the 283 with the solid lifter cam would pull the needles down into the jets to allow low power economy and motor idle stability. So...I'm wondering if at the top of 1st gear of the T-400 the vacuum signal is strong enough to pull the needles into the economy position. Then as the motor loads and really starts making more power the vacuum signal degrades and the power piston is pushed up and giving the jets more fuel. I meant to test the k factor of those springs before I rebuilt the carbs last Spring but forgot. The other set of needles and jets I have are for the hydraulic performance camshaft from 1957 and its springs are stiffer. So I've got much more test and tuning. There are several next steps. First is to install a vacuum gauge near the tachometer.