600CFM to 670CFM worth the effort?

[PRH]

I can understand where the 670SA has developed a rep for being lean at WOT.
I’ve only run one on an engine on the dyno, and this was a very mild 455 Poncho making about 325hp…….mid-16’s A/F ratio at WOT.
A swap to one of the shop carbs showed normal A/F ratios, so no weird carb requirements from the engine.
The 670 had stock jetting.

There is a shop in town with a chassis dyno that tested quite a few cars running 670SA’s…….most(all?) of which were somewhere between “pretty lean” to “abort the pull” lean.
Some were cured with jets, others got different carbs.

I’ve seen/heard enough stories about unhappy customers running them to where I can’t imagine recommending one.

 

[Slantsix64]

I can understand where the 670SA has developed a rep for being lean at WOT.
I’ve only run one on an engine on the dyno, and this was a very mild 455 Poncho making about 325hp…….mid-16’s A/F ratio at WOT.
A swap to one of the shop carbs showed normal A/F ratios, so no weird carb requirements from the engine.
The 670 had stock jetting.

There is a shop in town with a chassis dyno that tested quite a few cars running 670SA’s…….most(all?) of which were somewhere between “pretty lean” to “abort the pull” lean.
Some were cured with jets, others got different carbs.

I’ve seen/heard enough stories about unhappy customers running them to where I can’t imagine recommending one.

Is it just the jetting? I see they come with 65 jets in the primary which should be more 68 or 70 for that size of Carb.

I have also heard the issue is in the meter in block itself which is specific to the SA670CFM. Where the idle circuit is too lean, and it created a bog from Wot at idle.

I’m guessing the IFRs are tiny and cannot be removed\swapped this is why everyone drills them out.

 

[Killer6]

I can understand where the 670SA has developed a rep for being lean at WOT.
I’ve only run one on an engine on the dyno, and this was a very mild 455 Poncho making about 325hp…….mid-16’s A/F ratio at WOT.
A swap to one of the shop carbs showed normal A/F ratios, so no weird carb requirements from the engine.
The 670 had stock jetting.

There is a shop in town with a chassis dyno that tested quite a few cars running 670SA’s…….most(all?) of which were somewhere between “pretty lean” to “abort the pull” lean.
Some were cured with jets, others got different carbs.

I’ve seen/heard enough stories about unhappy customers running them to where I can’t imagine recommending one.

Hmmm, quick question, heat/no heat to the intake crossover?? And were the floats on or not when it was 1st fired/warmed up?? Unless those WP SBC heads had far superior BSFC#'s, and they did run best on 25° total timing....so that's possible, I must've got the only 'right' SA670 in the world........

 

[PRH]

You’re quoting my post, but that post is based on a test session with a Pontiac 455, not a SBC.
Obviously I would have verified the float settings, and that engine had factory heads(which have heat for the crossover from two ports per side), and a std performer that wasn’t blocked.
Also as mentioned, the shop carb was showing normal A/F ratios.

The main reason I even tested that engine was because the owner wasn’t happy with the results from the builders dyno test(which were much lower than the numbers he and the builder had outlined for the build), and I was hired to “fix” it.
I wanted my own baseline numbers, so I tested it before I took anything apart.
The numbers from my testing were even lower than what the builders numbers were.

Edit- I see now the SBC you’re referring to was the one you tested.

I’m not saying a SA670 can’t work perfect on something, I’m just saying that every conversation I’ve had about them, and my one personal dyno experience with them is that “lean” does seem to be a common theme.

My quick and easy test for trying to see if a carb is even “close” or not, is to install a “known good” one.
In that test, the SA670 was 3-4 points lean.
The known good one was fine.
(“Usually” I start the testing with one of my known good carbs, but since this engine was fresh off another dyno, with the SA670 being used for that test, I figured it was “good to go”)

Since it was not going to be suitable(imo) for the desired final result(500hp), I just replaced the carb with something I felt would be better suited to the build(Holley 4781).

 

[Dart Frog]

Well has the op tested it yet? Easy enough to know the answer takes about a half hour at the most. I wish more of my questions with that straightforward.

 

[mopowers]

I can't see how a SA670 would out perform a run of the mill 1850 600VS. The throttle bores and venturis are the exact same size as one another. You gotta take the cfm "ratings" with a grain of salt in my opinion.

Well has the op tested it yet? Easy enough to know the answer takes about a half hour at the most. I wish more of my questions with that straightforward.

Looks like the OP picked up a 3310 instead (post #23). Good move in my opinion.

 

[Killer6]

You’re quoting my post, but that post is based on a test session with a Pontiac 455, not a SBC.
Obviously I would have verified the float settings, and that engine had factory heads(which have heat for the crossover from two ports per side), and a std performer that wasn’t blocked.
Also as mentioned, the shop carb was showing normal A/F ratios.

The main reason I even tested that engine was because the owner wasn’t happy with the results from the builders dyno test(which were much lower than the numbers he and the builder had outlined for the build), and I was hired to “fix” it.
I wanted my own baseline numbers, so I tested it before I took anything apart.
The numbers from my testing were even lower than what the builders numbers were.

Edit- I see now the SBC you’re referring to was the one you tested.

I’m not saying a SA670 can’t work perfect on something, I’m just saying that every conversation I’ve had about them, and my one personal dyno experience with them is that “lean” does seem to be a common theme.

My quick and easy test for trying to see if a carb is even “close” or not, is to install a “known good” one.
In that test, the SA670 was 3-4 points lean.
The known good one was fine.
(“Usually” I start the testing with one of my known good carbs, but since this engine was fresh off another dyno, with the SA670 being used for that test, I figured it was “good to go”)

Since it was not going to be suitable(imo) for the desired final result(500hp), I just replaced the carb with something I felt would be better suited to the build(Holley 4781).

Thx for the feedback. Yeah, that's pretty lean for a heated aluminum intake, & a carb that small/cid.