carb size recommendations for dual quad 363 stroker

[TAG]

Oh................those terrible Edel carbs.......

If this was meant for me; i use edelbrocks and wouldnt change. Just out of curiosity, since ive never found out how much carb spacing dual holleys actually need.

[andyf]

Update to my original post. I eventually went with two Edelbrock 1405 600cfm carbs for this engine. This last week it finally all came together and was run in on the engine dyno. It churned out a max of 490hp at 6400rpm and 465 torque at 4900. Eventually I'll get it re-cammed to better suit the dual quads as this cam was spec'd for a single plane intake but overall I am really happy with this outcome. I just wanted to thank everyone for their suggestions.

Tony

That is good power for that engine, sounds like the dual 600 carbs worked just fine. I've used the dual 500 carbs on a few different engines and they work really well too. At your power level I bet the dual 500's would've worked just fine on the dyno and they might even run a tad better on the street. Smaller is often better when working with dual carbs on a street engine.

[F-BIRD'88]

This is flat out not true unless the engine is very LOW power near stock. If you want real power from a modern street high performance high rise RPM Dual Quad system use 2 big carbs on it.
The 600+ cfm carbs always outperform the small 500 cfm carbs.
The new edelbrockn 650 cfm AVS2 w/Annular boosters carbs are very good..

Do not choke it with small cfm carbs. It has to breath deep to go fast.
The 500 cfm carbs are for the T Bucket cruiser set.
With low power near stock engines.
On a high output engine 2x750 carbs is none too much.
The newest 800 cfm AVS2 thunder carbs with improved Annular style primary boosters do not bolt on directly as is because the secondary throttles are BIG 1-3/4". Again on a high output engine these are none too big.
Requires carb flange mods or carb spacers to mount.

Do not equate these hi power capable Dual Quad hi rise systems with the old school low rise dual quads of the 50's 60's era on relative low perf oem engines.

All the real deal Big power Dual Quad muscle car engines like the 409-425 hp 427 425 hp fe , Hemi, Max Wedge etc etc engines used 2x 600 cfm + carbs.

Remember the 650-800 AVS2 carbs are fully adjustable secondary throttle rate. You can dial in the secondaries progressive opening action, for any application.
Do not use single 4 bbl carb thinking.
In your case on your capable 363w you would have given up at least 10 hp and some torque with smaller carbs.

Never drove a dyno down a race track or down the street.

[MadBill]

...
Never drove a dyno down a race track or down the street.

I have. OEMs use them all the time. Many others too.
https://www.taylordyno.com/products/tow ... gJHyPD_BwE

[tjs44]

3705 Max wedge carbs are 750 AFBs I believe.Your right the 409s were 625s along with the 421 pontiac AFBs.I have been running 2-4s since 1962 and have always picked up HP with larger carbs.My experience has always been with factory AFBs.Never had good luck with street driving the E AFBs but they do race well.FWIW,Tom

[F-BIRD'88]

I have had to do more tuning on a eddy 600 cfm afb than had to do to a 750 1407 edfy carb to get it right.
And, the 750 is ALWAYS more powerfull.
The 750 only needed minor chabges to get it right fir each different engine/car/.
The 600's did work ok once dialed in...
The recent new 650 AVS2 and now 800 AVS2 Carbs seem very promising. The price is right.
The 500's seem to run fine but never as much power as the larger carbs are.

[F-BIRD'88]

I wish Edelbrock would offer the different booster clusters and secondary air doors as service parts, to allow more advanced end users/ tuners/ racers to fine tune them for their race car.
More people would use their carbs, which means MORE Sales. $$$$

[Little Mouse]

Might be interesting to put the new 750 street demon on a dual manifold. seems like edlebrock carb a disadvantage to a holley with it only having any idle adjustment on the primaries, with big cams cant be good.

[F-BIRD'88]

The primary side idle system only of the Edelbrock carbs is not as much of a issue as the dificulty in changing the iidle circuit metering orrifices in the booster cluster EASILY.

Edelbrock needs to come out with a "Victor Jr." Racer/Tuner friendly version of these carbs. Or tuner friendly service parts.
With tunable swapable fuel metering orrifices.

Yes the 4 corner idle is nice nice. The Street Demon 750 carbs with the "Google valve secondaries" are very interesting. Especialy for multi carb applications.

[F-BIRD'88]

Might be interesting to put the new 750 street demon on a dual manifold. seems like edlebrock carb a disadvantage to a holley with it only having any idle adjustment on the primaries, with big cams cant be good.

One way of tuning tweeking the idle and idle front rear bias on a Edelbrock carb is to adjust +/- the air flow rate (internal orrifice) of the PCV valve. This both tweeks the overall idle fuel curve but also tweeks the front rear BIAS of the idle fuel pattern.
Very effective. IMHO a must do on tuning dual quad setups. There is a lot you can do and should do by playing with the pcv valve. You can move it from rear to front too. Use on both carbs (shared flow) or only on 1 carb as required. It is a critical tuning element that does not involve drilling on your carb.

When tuning do all evaluation with the air cleaner installed. Ya it matters quite a bit.

[Little Mouse]

What is a pc valve dont do those. Lol

[F-BIRD'88]

What is a pc valve dont do those. Lol

Thats why you have problems tuning carbs.
99% of carbs are designed and calibrated to use a pcv valve. If you eliminate that then You create more issues than you solve. On a race only engine you need not put the pcv valve in the valve cover. But when you just eliminate it you screw up the whole idle circuit, including throttle idle position , T slot exposure at idle idle/off idle afr balance etc etc.
Use the pcv valve to your tuning advantage.
Instead of drilling this drilling that and the other, that you don't really under stand and cannot do accuratly, easily.
95% of that carb drilling yada yada yada is not nessessary.

[F-BIRD'88]

F-Bird,
I found that last night while I was perusing. Good call, yep a bit pricey but a good investment.

Thanks for the link(think it was you)
http://forums.ihpartsamerica.com/attach ... 1243874727

Is there an off the shelf part number for that?

I believe there is a napa number for these. May be a Fram number for this too.
I believe they were used on the old 60 65 era big block FE engines like in the Galaxie. 390-406-427 of the era.
I belive some old Chryslers used that style of screw together servicable pcv valve too.
Some one a lot smarter than me , will know.

[Little Mouse]

The pcv valve that vents the engine dont use it carb wont work.. Huum.

[Little Mouse]

The pcv valve that vents the engine dont use it carb wont work.. Huum. Started putting carbs on cars 1969 never drilled on a carb. Even in the days when holleys had little adjustment to them, using 265 .050 cam with 3.36 highway gear i never even had a need to drill the throttle plates. You can get away with a lot on duel plane with big carbs. That said street cars get kept at 3500/4000 rpm 90 percent of the time. Bigger carbs do not payoff like that. The bigger the engine the more it masks that the carb is to big. The manifold is going to be the restriction problem in comparison to what modern heads flow today, throwing on a bigger carb wont fix that. OP picked the right carbs for his size engine.