600 CFM Carb "enough" for modded 460?

[panthermike]

Hello,

I started a thread earlier trying to identify the engine in Ol Yellar. Now that's cleared up(thanks everyone), I found out the Holley Carb on the truck is a 600 CFM unit. I have no idea what power the truck puts out.

It does have some mods: Edelbrock Cam, Edelbrock Intake, LT headers, and dual 3" exhaust.

I can't help but wondering if something like a 750 CFM carb might be more suitable for this motor? I'm no expert on the subject though.

 

[JustinC25]

My dad's 1965 GTO has a 400 from a 1970 Firebird, with a edelbrock performer cam, Hooker ceramic coated headers, and a edelbrock performer manifold.
It has a Holley 650 CFM Double pumper 4 barrel, and it's fine.

I'd think a 600 cfm might be a little small on a 460, but I grew up with Multi Port fuel injection. Carb's aren't my strong suit.

 

[spasm3]

It has a lot to do with what cam duration you are running.

Here is a link that you can use, it uses max rpm to as opposed to cam duration.

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

 

[spasm3]

I ran it on your engine, at a VE of .85, a top end of 5500rpm, it calculated a cfm of 622. Too much carb and you loose low rpm flow velocity.

 

[CarbonSteel]

I ran a Holley 600CFM double pumper on a highly modified Pontiac 455 in a 1980 Trans Am and it was "crisp"; no bog and ran fine through its full range. I had friends running 700 and 750CFM double pumpers on SBCs and they **almost** always bogged coming off the line. Back in the day, most folks ran what was popular and available instead of taking the time to see what was actually needed.

 

[morris]

my idea is. how big a cam is it? if its NOT a street racer the 600 carb should be fine. course i like a different brand carb. but im getting so old now it doesnt matter.

 

[Rob_Roy]

Considering the application (truck), low end response and drive-ability is more important than getting every last HP at the redline. If setup properly, it should run very well with the 600.

 

[johnnydc]

Nice engine by the way. I had a 460ci in my 1977 Lincoln mkV,and it also had a holly 600cfm. The engine was stock,and ran like a raped ape for the weight it was moving around. I miss that car. I think spasm3 has a good idea there. Check out that link to choose the right carb.

 

[OVERKILL]

It really depends on where it is meant to twist to. The heads that are on it aren't that great, so you are probably fine with a 600 or 650.

 

[Highline9]

Is it a double pumper?

 

[Scott_Tucker]

You'll low end drive ability if you go too big. You've got to ask yourself what you're going to do with the truck. For street use I personally would stick with the 600.

 

[Chris142]

a 750 would put out more high rpm hp. the 600 should be very responsive at low speeds.

 

[panthermike]

Thanks for all of the responses. To answer some questions; the cam isn't very big, mild for sure. I do believe that the carb is a double pumper.

It does have good low end grunt for sure. It does however act like it isn't getting enough fuel though, which could be a specific issue, not the necessarily the carb itself.

Maybe I should rebuild and clean it, and tune it up. Then I can go from there.

 

[Scott_Tucker]

I would recommend having it rebuild by a professional. It is not really something you can do in your garage properly. I would recommend having it checked on a gas analyzer before going further. This will let you know if the mixture is rich or lean and whether a rebuild is necessary. Your money will be better spent. Good luck finding someone that knows what they are doing in your area, they are really rare these days.

 

[panthermike]

That calculator is nice, thanks for the link. My only confusion is the part about the carb(stock vs. modified). The difference is quite a bit.

Stock-622
Modified-763

 

[Highline9]

holley carbs are easy to rebuild and tune. Make sure the linkages are working right. Full gasket kit to clean bowls. If you have a lean stumble raise the floats. I have run them alot on small and bigblock chevys. I know this is off topic but more ignition timing at low rpm helps longer duration cammed engines with pumpgas compression ratios run more responsive.

 

[SteveSRT8]

Remember no one was born with the knowledge.

Get a book. HP has some excellent manuals on Holleys. Easy to tune and definitely a DIY project if you are good with cars. Takes patience, that's why it's called "tuning".

I always used to go one size SMALLER than recommended. Your midrange response will more than make up for those couple of peak ponies you lose.

 

[Rob_Roy]

I just looked at the pictures you posted in the "identify my engine" thread - that carb looks like a model 4010 Holley.

 

[TFB1]

Originally Posted By: Scott_Tucker
I would recommend having it rebuild by a professional. It is not really something you can do in your garage properly.


Bah, I can rebuild Holleys in my sleep, besides a Ford 4100 series they don't get much easier than a Holley...

With the mild modifications it'd make more power on a 750, I would not think low speed throttle response would be greatly effected... Factory carb for 428CJ & 429CJ were 735 to 780CFM, those did breathe better than the heads you have but except for the 429SCJ, had mild cams that made high vacuum at idle...

 

[Trav]

I remember working on some old big block 429 CJ back in the 70's that had Rochester Q jets on them OEM.
IIRC they were 700 CFM give or take a little and used a dual plane manifold.

These things ran like a scalded dog but the way the CJ (not the SCJ) was set up sounds a lot like what you are running.
Maybe the aftermarket makes a spread bore manifold for the 460 or you can find one of a CJ, the ports will not quite match but it wont make a lot of difference to this engine.

That will give you the economy and low end of the Q jet with those monster secondaries for some real grunt.
Personally i would take a good Q jet over a Holley any time.