Need help with carburetor

[TheMADHATTER661]

I bought this engine from craigslist it's a 1969 camaro ss 350 engine with chevy 400 head what carb should I put 750 cfm or 600cfm the summit racing  carb is the one I'm looking at by the way 

[Miles]

http://www.thecarburetorshop.com/Carburetorsizeselection.htm

[Michael]

While helpful, that site results in a carb selection that's very conservative, especially for a light car with a manual transmission.

 

More specific to Mad Hatter's question... how does one arrive at a 350 engine with heads from a 400?  That seems like a mismatch, to say the least.  Also, it's odd that somebody would remove an engine from a 1969 Camaro and sell it separately, given how these vehicles have become so valuable in "numbers matching" guise.  Something here is incongruous, or at least, merits further research... before worrying about optimal carb selection.

[Miles]

Try the math as a starting point.

[Miles]

Looks like a drive by question.

[Michael]

On 8/28/2019 at 6:28 PM, Miles said:

Looks like a drive by question.

Indeed.  I was fondly hoping for a discussion on carburetor flow-rating vs. mixture-velocity, and how to size carburetors for various engine operating conditions, displacement, volumetric efficiency,....   So, feeling jilted, I did a site-wide search on "Holley".  Most hits were in the for-sale sections.  The first serious link was this one: <https://forums.hybridz.org/topic/417-is-a-750-edelbrock-too-much-for-my-setup/?tab=comments#comment-2819> ... where the original question was asked in 2001, then renewed earlier this summer by the same fellow who started this thread, then answered by you, and then... crickets.

 

But what really broke my heart was a quip in the aforementioned thread, where somebody said, "Hey, this is a Datsun forum, so if you have a Chevy question, why don't you go to a Chevy forum"?  Well, as the kids say these days, WTF?  This forum began with the specific purpose of tech-support/discussion on swapping Chevy engines into Datsun bodies, as a rebellion against Datsun purism.  And now it seems that we've gone full-circle.

 

Then I checked the FAQs.  Lots of topics on fuel-injection, and some on Mikuni or Weber carbs.  But nothing on Holley, Carter, Edelbrock, or any of their knock-offs or cousins.  Does anybody know how to change jets anymore?  Or to set the float-level?  Or even care? 

[calZ]

1 hour ago, Michael said:

But what really broke my heart was a quip in the aforementioned thread, where somebody said, "Hey, this is a Datsun forum, so if you have a Chevy question, why don't you go to a Chevy forum"?  Well, as the kids say these days, WTF?  This forum began with the specific purpose of tech-support/discussion on swapping Chevy engines into Datsun bodies, as a rebellion against Datsun purism.  And now it seems that we've gone full-circle.

 

I assume the quip you're referring to was my message. I assure you, I'm far from a Datsun purist and was not trying to chase him away. It was pretty obvious the person had gotten to the thread via a Google search, and he had not yet gotten a reply. I was simply letting him know that it's possible someone might have an answer, but that if he's looking for something quick and guaranteed it would be more likely found at a Chevy forum. I wasn't saying GTFO, but rather trying to help him get an answer as quickly as possible. **** me for trying to help, I guess. 

[Miles]

While Hybridz has a lot of good information from some very gifted mechanics/builders, I have found over the years that I needed to augment Hybridz searches with other automotive web sites.  I reasoned that my hybrid 240z with Chevy engine,  and parts from other Japanese cars,  was really just another hot rod with issues that all hot rodders run into. So I started looking at hot rod, Corvette, Camaro, Toyota, 240SX, Nismo etc websites for ideas and information. For example, My Holley 570 Street Avenger carb was indicating a stumble and lean sag at low speed cruise. I found the solution on a hot rod website.

 

I have also purchased or down loaded manuals, manufacturer instructions, factory service manuals etc for every component used in my build project. Many of the manufacturers supplement their installation manuals with videos on YouTube.

 

 

[Miles]

2 hours ago, calZ said:

 

I assume the quip you're referring to was my message. I assure you, I'm far from a Datsun purist and was not trying to chase him away. It was pretty obvious the person had gotten to the thread via a Google search, and he had not yet gotten a reply. I was simply letting him know that it's possible someone might have an answer, but that if he's looking for something quick and guaranteed it would be more likely found at a Chevy forum. I wasn't saying GTFO, but rather trying to help him get an answer as quickly as possible. **** me for trying to help, I guess. 

 

CalZ was just pointing out a fact - this is a Datsun site with a mix of Ford, Chevy, racers, etc members.

 

[jhm]

Excellent point, Miles.  I have always found NastyZ28 to be a good source for high performance SBC and BBC engines.  H.A.M.B. Is another good one I've gotten useful info from.

[Miles]

Here is a handy carb calculator:

 

http://www.gtsparkplugs.com/CarbCFMCalc.html

[JMortensen]

My $.02, people make too big a deal out of the size.

I think you can make a pretty wide variety of sizes work. Some stock car classes run 500 CFM carbs. Sure, it hurts performance, but they still run pretty well. Vizard in his book has 350s running 850 carbs, and goes to great lengths to modify the boosters to get the right size fuel droplets to correctly atomize at part throttle preventing stumbles on accel. 

I have a 5.3, used the calculator, figured out I wanted a 750 with annular boosters to follow Vizard's lead. tube80z says he's got a 650 with downleg boosters and 4 hours run time on it, makes me a deal. SOLD. Never looked back. Car hauls ass.

[Michael]

On 9/12/2019 at 3:51 PM, JMortensen said:

My $.02, people make too big a deal out of the size.

I think you can make a pretty wide variety of sizes work. Some stock car classes run 500 CFM carbs. Sure, it hurts performance, but they still run pretty well. Vizard in his book has 350s running 850 carbs, and goes to great lengths to modify the boosters to get the right size fuel droplets to correctly atomize at part throttle preventing stumbles on accel. 

I have a 5.3, used the calculator, figured out I wanted a 750 with annular boosters to follow Vizard's lead. tube80z says he's got a 650 with downleg boosters and 4 hours run time on it, makes me a deal. SOLD. Never looked back. Car hauls ass.

 

That's why the bigger issue is correctly tuning the carb that one already has (or one that's approximately correct), rather than optimally sizing one, based on volumetric flow-rate formulas.  Indeed, the trouble is how to learn how to disassemble the thing, what the various parts do, how to swap them out (or whether even to bother), and how the whole collection works together.  That's hard to get from a book, even one that's a thorough as Vizard's books.  This is where we need testaments of first-hand knowledge.

 

Let me offer a practical example.  For reasons beyond the scope of this thread, my own car has been sitting for about 3 years.  Every few weeks I hit the starter, to turn over the engine to (perhaps) circulate some lubrication, or at least to preclude the rings from seizing.  But I've not started it.  Yes, there are ample checklists for how to resuscitate a long-dormant car. Drain this, add fresh that.  But... what about the carb?  Should the bowls be disassembled and the gaskets renewed?  No?  Any other gaskets?  Rubber O-rings at the float adjustment bolts?  And so forth.  This is practical carburetor knowledge, that's hard to find in a book, or you-tube, or even a "normal" car forum.

[JMortensen]

Agreed! For sure practical knowledge is useful. I'd look hard at the needles and seats after that period of time. Don't want them sticking in either direction. Outside of that, I'd probably just pull the bowls and metering blocks and visually inspect the fuel passages and make sure nothing is clogged up with varnish, just blow everything out with some carb cleaner and reassemble. Mine use reusable bowl/block gaskets, worth the extra couple bucks if you don't have them, because you'll need gaskets to reassemble anyway.