Shag's 3rd carb already? - WTF?

[cmayna]

That's right dweebs,  I just finished installing and doing a test run on Shag's 3rd Holley.

History:
1st carb - 750DP (no choke) - A major gas guzzler
2nd carb - 650DP (no choke)- Little better mileage but it was a bear to warm up in the mornings.  Besides, it was one of those shinny ones with just didn't look right for the green turd.
3rd carb - 650 vacumm secondaries with electric choke - Now this one I like !!  Hopefully I can put this carb issue away.  Test drive tomorrow to JeffTepper's abode.



 

[silverblueBP]

You should've had Duane rebuild it for you.

[B67FSTB]

IIRC  a 480cfm carb was "big" enough to suit a 289 A en D code engines with max of 6000 RPM .
Most problems , when building engines , is the fact of overcarburating.
This is a statement from " Ponycarburator" and they know their stuff IMO.
see : http://www.ponycarburetors.com/default.asp?page=calculatingcfm
So Craig , if you have the chance , try a 600cfm .Its worth trying 

[scedd]

Craig,
In my younger days i had an XA GT coupe, (an OZ Torino), 351, Hi flow 2H sig erson cam, Weiand Xcellerator, 600 Double pumper, twin point mallory dissy, toploader, 3.25 gears.
Over 11 years i mucked around with a few carbs but i always came back to that 600.
I agree that overcarbing causes more problems than anything else.
Steve

[gtscode]

Come over to my house!! I am home and want mote details I may follow your lead on this one.

[stangg]

hmmm... that looks nice.   I was getting ready to pull the trigger on a silver Holley Street Avenger 670 for my chebbie.   Aside from the color and 20 cfm difference,  I wonder if there is any major design or performance differences between the two.   I do like how the 650 you have looks more period correct.

[cmayna]

Yeah that shinny stuff was just a little too much and we all know how much we stare at our carbs on a daily basis.

 

Another reason why I went with the 650 is because it has a dual inlet which the car was already setup for that. 

But no matter what happens, these carbs are a very easy plug and play.  One day I might try a 600 but for now I want
to give this 650 a try.

[Fast68back]

Come over to my house!! I am home and want mote details I may follow your lead on this one.

Is yours done yet? I seem to recall a deadline...

[gtscode]

Thanks Craig think I'll follow your lead on this one.

[tarafied1]

I have a 770 Street Avenger on my 429 and it's 10 years old now. No problems with it. Very reliable and I averaged 16 mpg on the Power Tour with a 2.79 rear gear and no OD. I think vacuum secondaries make better street carbs because if the engine don't need it they don't open.

[cmayna]

I think vacuum secondaries make better street carbs because if the engine don't need it they don't open.

Bingo!   

[guruatbol]

That's right dweebs,  I just finished installing and doing a test run on Shag's 3rd Holley.

History:
1st carb - 750DP (no choke) - A major gas guzzler
2nd carb - 650DP (no choke)- Little better mileage but it was a bear to warm up in the mornings.  Besides, it was one of those shinny ones with just didn't look right for the green turd.
3rd carb - 650 vacumm secondaries with electric choke - Now this one I like !!  Hopefully I can put this carb issue away.  Test drive tomorrow to JeffTepper's abode.



 

Ok Craig, I have had nothing but trouble with the Holley carbs built after 1985. So I have switched to the Edlebrock and have never looked back.  For the street they are wonderful and work awesome on both Captain America and Ed.

I think if you do some searching on here and VMF you will find that Johnpro agreed with me.

Mel

[GTchris]

This is a hi-jack but, on topic.

I went with the original 650 Holley for my car but, it has an electric choke as well. I am still working on the wiring on my car and was wondering where did you tap for the choke lead?

[B67FSTB]

This is a hi-jack but, on topic.

I went with the original 650 Holley for my car but, it has an electric choke as well. I am still working on the wiring on my car and was wondering where did you tap for the choke lead?

A 12 volt source when turning the ignition key is good.
Don't take it from the plus on the ignition coil !!!!
Maybe you can take it from the trans wiring harness??
Or a seperate wire from the fusebox.

[AzPete]

The alternator connection works good.

[66benchcoupe]

Ok Craig, I have had nothing but trouble with the Holley carbs built after 1985.

http://www.barrygrant.com/

Robert

[gtscode]

Is yours done yet? I seem to recall a deadline...

Working on it!!!

[gtscode]

Well I bought the same carb from Amazon and got it yesterday!!!!

I love Amazon!

[stangg]

I got one too... got it at Advanced Auto Parts... 369.99 online,  but if you enter P20 in for a promo code, it comes down to 295.95.  Print out the order form,  and they'll match the price at the local store too. 

What brand feed line are you guys using?   It seems like there are a few choices and some don't fit right if i recall correctly...

[2ndgen]

I might be stirring up a hornet's nest here... and I do agree that it is a bad thing to over carb an engine... 

But I have a pet peeve with the combination of the carb sizing equations and the math of marketing.

If you use the supplied equations, and adjust for volumetric efficiency you will get an airflow requirement - but here is the catch - that is airflow at wide open throttle where ideally you should have close to zero manifold vacuum. Keep this in mind...

Now for the marketing math... every carb manufacturer I know measures CFM for 4 barrel carbs at 1.5 inches of vacuum for historical reasons. If your car has 1.5 inches of vacuum at wide open throttle your carburetor is acting as a restriction! If you do the math, you will find that a 800 CFM carb measured at 1.5 inches of vacuum is really about a 630 CFM carb at 0 inches of vacuum.

If you go by the supplied equations above and do not account for the "marketing" flow numbers, I guarantee you are leaving power on the table. 

I'm not saying that it is good to over carb an engine and I admit most street cars don't see prolonged wide open throttle operation; but if you are going to use equations, be sure all the terms match...

Good luck,
-Rory

[cmayna]

What brand feed line are you guys using?   It seems like there are a few choices and some don't fit right if i recall correctly...

I tried a Mr. Gasket and the fitment into the inlets of the carb sucked big time.  I found a Holley back when I started out with the 750 and have kepted it.  The one I'm using is 3/8" since my entire fuel line is of that diameter.  I assume Holley makes a 5/16 for those that require it.

 

[tarafied1]

I might be stirring up a hornet's nest here... and I do agree that it is a bad thing to over carb an engine... 

But I have a pet peeve with the combination of the carb sizing equations and the math of marketing.

If you use the supplied equations, and adjust for volumetric efficiency you will get an airflow requirement - but here is the catch - that is airflow at wide open throttle where ideally you should have close to zero manifold vacuum. Keep this in mind...

Now for the marketing math... every carb manufacturer I know measures CFM for 4 barrel carbs at 1.5 inches of vacuum for historical reasons. If your car has 1.5 inches of vacuum at wide open throttle your carburetor is acting as a restriction! If you do the math, you will find that a 800 CFM carb measured at 1.5 inches of vacuum is really about a 630 CFM carb at 0 inches of vacuum.

If you go by the supplied equations above and do not account for the "marketing" flow numbers, I guarantee you are leaving power on the table. 

I'm not saying that it is good to over carb an engine and I admit most street cars don't see prolonged wide open throttle operation; but if you are going to use equations, be sure all the terms match...

Good luck,
-Rory

very good info, thanks!

[Opentracker]

From a guy with a lot of carbs and a lot of cars.

A small carb will pull the car across the intersection quick.

A large carb will pull the car down the highway quick.

Small carbs have better throttle response and idler better.

Large carbs don't idle as well and use more gas.

I've put carbs from 390cfm up to 950cfm on the same motor. The small carbs work great around town but don't pull hard on the highway. The larger carbs suck around town but work great on the highway. Something around 600-700 works the best overall IMO on a Cleveland for a street driven car.

I have a NASCAR racing 390 on the Mule and it works great for doing burnouts and getting around the villiage here. It doesn't pull worth a darn in 4th gear though.

[2ndgen]

From a guy with a lot of carbs and a lot of cars.

A small carb will pull the car across the intersection quick.

A large carb will pull the car down the highway quick.

Small carbs have better throttle response and idler better.

Large carbs don't idle as well and use more gas.

I've put carbs from 390cfm up to 950cfm on the same motor. The small carbs work great around town but don't pull hard on the highway. The larger carbs suck around town but work great on the highway. Something around 600-700 works the best overall IMO on a Cleveland for a street driven car.

I have a NASCAR racing 390 on the Mule and it works great for doing burnouts and getting around the villiage here. It doesn't pull worth a darn in 4th gear though.

I agree 100%.

And for street driven cars, erring on the small side is the right answer (obviously to a point - you can definitely go too small too).

I just wanted to point out part of the reason why the carb sizing equations give "small" numbers compared to what the dyno/track  proves to make the most power.

Finally, as with just about anything else on a modified car, if you just slap a carb on and do not tune it you learn little about the true requirements...

If a untuned 600 runs better than an untuned 750 on your car, it does not mean that a tuned 600 will run better than a tuned 750 on the exact same car.

Good luck,
-Rory

[180 Out]

The '70 Cougar 351C with FMX auto, and 3.00 9", when I sold it late last year, I had owned it for 12 years. One of the first things I did was to put a 600 cfm, electric choke Edelbrock Performer on it and had no regrets.  I used an "RV" level cam (112 LDA, .484"/.512" lift, 204/214 duration at .050"). This combo would pull hard to 5000 rpm and top out at 5500. It might have pulled another 500 rpm with more carb, but at 5500 rpm it was doing 130 mph, which was fast enough for me. Because of its weight problem it also wouldn't win any drag races, but it was a fun and reliable daily driver.

One thing I wanted to mention, if you want good cold start performance make sure the heat riser is functional. The heat riser is the hole in the middle of the intake side of the heads, which corresponds to a passage that runs from one side of the intake to the other, directly underneath the carb. You can see the heat risers on each of the heads standing  vertically in this pic:



The function of this system is to heat up the carb as quickly as possible. The whole purpose of the choke system is to deal with the inability of cold fuel to atomize.  If you have no choke and your heat riser is also not functional, cold start driveability suffers a double-whammy.  Ask me how I know.