carb size recommendations for dual quad 363 stroker

[F-BIRD'88]

The Edelbrock recommendation of dual 500 carbs is a good one. That combo will work really well. I've used the dual 500 cfm setup on multiple engines with excellent results.

And left POWER and torque on the table because you did not try the larger carbs.
The larger 2x4 carbs ALWAYS outperform the 2x 500's.

Some motors really like a COMBO style carb spacer. It can help equalize the air speed of the upper and lower planes of a dual plane manifold yet main the the SPLIT 180deg plenum.
Like this one..
Edelbrock carbs like Wood spacers for fuel bowl heat control.

If you search on facebook there is a guy who make up a COOL 2x4 carb spacer ADAPTER that allows
installing TWO holley 4 BBL carbs, inline on this exact Ford SB dual quad RPM manifold using the small holley fuel bowls. It is possible on the Ford.
He was smart and his 2x4 Holley to AFB dual quad spacer adapter has split 180degree plenum design.

The Edelbrock-- Carter AFB`s or AVS (thunder series) give up nothing to holley carbs on this one soo.....

[Flatheadpopup]

Jack makes a good point about knowing the customer and his expectations.

Honestly, the car will be driven only 2-3 thousand miles per year and mostly just on the weekends. I have a c-4 transmission in it now with around 3200 rpm stall converter but plan to loosen that up in the future. Not worried about it being civil, just a fun weekend toy. I seriously had considered going solid roller but backed off in fears of lifter issues on the street--plans do call for full head porting in the future and a possible swap to solid roller at that point. Right now I just want to get it running and dual quads are something I've wanted since I was a teen (closing in on 50 yrs at this point). Thanks for all the opinions/recommendations--I am taking in all the info I can and plan to use it wisely.

[tjs44]

I agree on bigger is better,the only reason I ran my 625s is I had sold off my spare pair of 750s and am too lazy to pull them off my 421 SD tunnel ram engine.Tom

[statsystems]

Anyone here remember Ollie Morris from Offenhauser? One of the single most intelligent men I've ever been able to get on the phone.

In 1982 he gave me his rule of thumb on how to select tunnel ram carbs. In fact, I think it's also published in the old Offenhauser catalogs.

He said: Whatever size carb worked the best in a single 4 application, DOUBLE it for 2x4's. That's what I've always done and it's never failed.

Too many guys under carburate in single applications. It's twice as bad with tunnel Rams.

OP, you should be using 2 750's at a minimum and learn to tune the idle circuit. You'll get the best results that way.


BTW, you should always use a custom cam when running 2x4's because it takes less cam timing to run the same RPM with a TR. Too much cam is what kill the bottom in 2x4 applications.

[wyrmrider]

getting serious I'd use two AVS over two afb's anytime

[Tuner]

To repeat this for the umpteenth time ........:::

The 750 Edelbrock is screwy because it has the same booster cluster casting as the 625 carbs.

The 750 CFM carb (and other Edelbrock AFB clones with the same primary venturi size) uses the same casting for the primary cluster as the 625 CFM carb in spite of the fact the venturi minor diameter is 5/16” or so lower in the 750 body.

This places the exit of the booster venturi 5/16” above the location of highest velocity in the main venturi air flow, the result is the “booster signal” is not obtained in the correct location and the metering is erratic, the A/F wanders rich and lean as load and RPM vary as the throttle position is changed.

Your mileage will vary.

OP, I would use 625 CFM units, unless a pair of 1850 600 CFM Holleys can be used.

[Flatheadpopup]

getting serious I'd use two AVS over two afb's anytime

Honestly, I totally get what were saying. I spent a lot of time researching intakes trying to find a proper dual quad setup that could run Holleys as I have zero experience with the Carter/Edelbrock carbs. If the Blue Thunder intake flowed to where I thought it could make the same power I would go that direction instead. Likewise, I spent a lot of time looking at the old Edelbrock FX-8 crossrams but they seem to their own set of issues (but damn they look cool). It seems like the performer air gap is the only semi modern design for what I'm doing so I kind of painted myself into a corner carb wise. I truly appreciate everyone's opinions on this as it is outside my realm of experience.

[wyrmrider]

Thanks again tuner
OP you will get new experiences no matter which carb you pick

[F-BIRD'88]

Once you start working with the afb carbs you will like them... No real need to try and use holleys on this..

The 750's drive and operate fine reguardless of the booster orientation.. They work and make more power.
And are easy to deal with..

The conp xr solid street rollers do not give issues on the street..

Do nit xompare to a race roller setup that uses huge spring prwssure and was nwver intended for street..


These solid rollers rock... Lunati has some similar purpose UDHarold SS solid street roller stuff too.

More powerfull than a hyd roller and will rev higher yet not a race only xam..

[Flatheadpopup]

Once you start working with the afb carbs you will like them... No real need to try and use holleys on this..

The 750's drive and operate fine reguardless of the booster orientation.. They work and make more power.
And are easy to deal with..

The conp xr solid street rollers do not give issues on the street..

Do nit xompare to a race roller setup that uses huge spring prwssure and was nwver intended for street..


These solid rollers rock... Lunati has some similar purpose UDHarold SS solid street roller stuff too.

More powerfull than a hyd roller and will rev higher yet not a race only xam..

Would you lean toward the AVS line of carbs or the traditional AFB? It looks like the AVS is available in a 650 or a 800 cfm designation. I like the idea of being able to easily adjust the secondary. I was originally going to run a 830 cfm Holley on the Super Victor--do you think two of the 800 AVS carbs would be overkill for a dual quad application? It sounds like a lot of cfm until you start breaking things down with the dual carb/dual plane intake deal.

Thanks for the insight on the solid roller cams too. With the dart block and good rotating assembly I'm not afraid to spin it a bit.

[Tuner]

The 750's drive and operate fine reguardless of the booster orientation....

No, they don't. You need to use a WBO2 and actually drive one, instead of just fantasize about it. You obviously never have, because if you had, you wouldn't say they "operate fine", because they don't. If you perchance ever do use a WBO2 on one you will find the 750 cannot deliver anything but a wandering, oscillating, A/F with any change of throttle position in the part throttle range. The A/F can swing from near the lean limit to plug fouling rich with a small change of throttle position, change it again another similar increment and watch the A/F swing back to lean. Because of the high booster exit they simply do not function as a 'normal' carburetor. No production engine carburetor was ever manufactured with such a screwy deal as raising the booster 5/16" above the vena contracta, it never happened because it doesn't work.

[statsystems]

The 750's drive and operate fine reguardless of the booster orientation....

No, they don't. You need to use a WBO2 and actually drive one, instead of just fantasize about it. You obviously never have, because if you had, you wouldn't say they "operate fine", because they don't. If you perchance ever do use a WBO2 on one you will find the 750 cannot deliver anything but a wandering, oscillating, A/F with any change of throttle position in the part throttle range. The A/F can swing from near the lean limit to plug fouling rich with a small change of throttle position, change it again another similar increment and watch the A/F swing back to lean. Because of the high booster exit they simply do not function as a 'normal' carburetor. No production engine carburetor was ever manufactured with such a screwy deal as raising the booster 5/16" above the vena contracta, it never happened because it doesn't work.

I remember a Comp engine that was right about 680-685 HP at 9000 or so. They were fighting an issue in the gear changes (5speed car) and they were working like dogs on the clutch/shocks/IC...everything.

They sent the carbs to someone (I think it was Cubic but I no longer remember who did it) and they just moved the booster in the Venturi. Exact same power and torque curves on the dyno. In the car....a different story. It was .15 quicker. The gear change issue went away.

So booster placement is a BIG deal.

[Flatheadpopup]

To repeat this for the umpteenth time ........:::

The 750 Edelbrock is screwy because it has the same booster cluster casting as the 625 carbs.

The 750 CFM carb (and other Edelbrock AFB clones with the same primary venturi size) uses the same casting for the primary cluster as the 625 CFM carb in spite of the fact the venturi minor diameter is 5/16” or so lower in the 750 body.

This places the exit of the booster venturi 5/16” above the location of highest velocity in the main venturi air flow, the result is the “booster signal” is not obtained in the correct location and the metering is erratic, the A/F wanders rich and lean as load and RPM vary as the throttle position is changed.

Your mileage will vary.

OP, I would use 625 CFM units, unless a pair of 1850 600 CFM Holleys can be used.

Tuner, looking at these carbs online I see that edelbrock doesn't offer a 625 cfm like carter did, just a 600--can I assume that this is the same carb with a different designation given to it when manufacturer changed? What are your feelings on the standard performer carb vs the AVS? Is it worth the extra ~$100 dollars between the two carbs to go with the AVS?

Once again, I really have to thank you guys. I know I am full of questions, I just want to get this right the first time around. Thanks

Tony

[Tuner]

Yes, I should have said 600 .... 600/625 or whatever ?? whoever calls that size of AFB. To me they will always be the Carter AFB, whether Federal Mogul, Edelbrock, or what else whoever else calls them. it's an artifact of how long I've been doing carbs.

The regular AFB (as in not AVS) will work fine. You want the 1405 version with manual choke, and hope they come with the secondary booster clusters with small main air bleeds and open main well tubes. Otherwise, if they come with the goofy boosters with the .073" MAB and the main well tubes with the .073" "pinch" hole in the bottom of tube, you will need to modify them so they can be jetted rich enough for WOT. There are some good threads about tuning these carbs here in SpeedTalk.

The other carburetor lottery ticket you need is the one for having same size idle tube in each primary booster cluster.

It is a given that nobody brings a good running carb to be fixed, so describing these issues is a result of seeing the problem carbs, which isn't to say they are all like that. However, the lop sided idle jet has been common in the Edelbrock/Weber carbs.

Whatever origin of the AFB type carbs, they run fine when they are set up to mimic the '60s era production carbs, but it takes some work. No matter what carb or carbs you start with, expect to do some tuning.

[tjs44]

FYI,I always run original Carter AFBs.Been lucky enough to have them or able to find them.Tom