My jets/metering rod question answered

[John_S]

A few weeks ago, I had mentioned about being confused by some of specs on the Weber carbs, found in the service manual. The main one was "Why was the secondary jets on the 350 Mag so much leaner than the L model specs?". Well, the confussion was generated by my belief that all the 4brl Webers on Mercruiser SBC's and V6, were of the 600/625cfm. Turns out that the ones used by 350 mags and LX's are of the 750cfm. This shouldn't be too surprising, since the q-jet they replaced where 750cfm.<br /><br />I was rebuilding a 9770 from a 350 Mag Ski, and seeing that all four butterfly's are the same size, and compared them to the Edelbrock 1409/600cfm where the primaries are slightly smaller than the secondaries. Also see this: http://buickperformance.com/carter.htm Given that, the 97XX models should be 750cfm, while the 96XX models are the 600/625cfm. The 97XX were also used on the big block chevy mercruisers.<br /><br />Anyway, just in case anyone else was confused.

 

[MGallik]

Re: My jets/metering rod question answered

Thats interesting John. Hmm, do I need to rethink the jetting on my 9666 S or replace it with a 97xx? I would think 625 cfm would be all the 5.7 can use anyway.

 

[Bondo]

Re: My jets/metering rod question answered

Ayuh,.........Very Interesting Link...... I Learned something here today........<br /><br />I thought this Spreadbore looking, Squarebore carb I've got here was a 750cfm.........<br />I'm Glad it's the 625cfm...... That's Perfect for the 383cid it's going on.........<br /><br />sx,<br />I don't think you'd Want a 750.... 350s only move 500something feet @ 5000rpms.........<br /><br />I was worried about a weak vacuum at lower rpms.........<br /><br />That makes My Favorite Carb. Look even Better........<br />Small Primaries,.......... No Wonder My fuel mileage is so Great.................

 

[MGallik]

Re: My jets/metering rod question answered

My thoughs all along have been to build a "stock" 350 Mag. I see now that the 625 will probably be a better choice overall.

 

[John_S]

Re: My jets/metering rod question answered

Theoreticly, you shouldn't even need a 600cfm for the 5.7L. The 600 on stock mercruiser V6s should be major overkill, too. Also many a sbc have come with 750. I was surprised that the 350 mag had a high-rise manifold, as well. That high rise, theoreticly, wouldn't have much benefit to an engine that is 5000 rpms or less, either. Who said it had to make sense? ;-)

 

[MGallik]

Re: My jets/metering rod question answered

I though about that too and, in passing, figured it might help soften the bottom end punch of the 5.7 a bit to make life easier on the Alpha.<br /><br />I have a hotted up 350 in a full sized Blazer that can hit pretty hard.<br /><br />Then again, it probably doesn't make all that much difference. Most big gains take system wide changes.

 

[John_S]

Re: My jets/metering rod question answered

1900sx,<br /><br />Not sure about our '96 and '97 Alpha 1 gen II drives, but the current models are sold with 300hp Mag engines and would imagine the current vortec engines have more torque at lower rpms than our engine/heads.