carb size recommendations for dual quad 363 stroker

[Flatheadpopup]

I'm putting together a 363 (common 4.125 bore, 3.4 stroke, 5.4 rod setup) Ford for my 65 Mustang and am seriously considering going the dual quad route (I've got a super victor on the shelf if this doesn't work out). The car is going to be mainly street driven with a little track time for my own entertainment. I'm looking at getting the Edelbrock 7535 performer rpm air-gap dual quad intake but am stumped as to carb sizing. I know Edelbrock recommends two of their 500 cfm carbs but I'm not convinced that this would be best for my up-sized combo. Since there are some individuals on this site with lots of experience in the realm of multiple carbs I pose this question to you: What size/model carbs do you guys think I would be best off running? Keep in mind I am stuck with the edelbrock/afb style carbs when running this manifold. Here are a few specs if it helps:

363 cubic inch
Dart block, forged crank and rods, wiseco flat tops
10.75-11:1 compression (need heads cc'd still)
unported Edelbrock Victor Jr heads with an upgraded spring package
custom hydraulic roller 239/250 duration at .050 with .587/.579 lift on a 112 lobe separation--hoping to make max hp somewhere around 6300-6500 rpm
c4 transmission -- stall yet to be determined
3.89 gears and a 26" tire

Thanks in advance for the help

[tjs44]

I ran a pair of 625 AFBs on a 366 street Pontiac engine.Ran fine.Tom

[Flatheadpopup]

Thanks Tom, I appreciate the input. I've been considering the 600's or maybe even a couple of 750's as I've read some older posts where Joe Sherman has had good luck with them in dual quad applications. I don't want to over carb this thing but I certainly don't want to restrict it either--which I am afraid the 500 cfm carbs might just do.

Tony

[mag2555]

Edelbrock knows just what they are doing in calling for 500 cfm Carbs!

A 600 cfm Carb is a great pick for making up to 390 to 400 hp out of a non race motor, so two 500 cfm Carbs is over kill , but the vacuum secondary's save the day!
What these low rise 2-4 bbl Manifolds need is atleast a 1/2" 4 hole spacer to get the throttle blades up out of the plenum and from being the restriction that they are in that regard, especially in regards to the throttle blades hanging in the shallow side of each Plenum.

[KOLI11]

I knew this marine mechanic. He was a gun marine mechanic and mainly did ski boat engine rebuilds. He swears by running dual quad as he had found that it had the best of both worlds, low end and top end. He use to use 600 mostly and found they run smoothly and efficient as he would say. If I was you I would run dual 500. Beleive me, the engine will suck what it needs. However, it has been proven that holleys make more power. Although, the driveability of edelbrock is amazing. I have got one in my ski boat, and have not touch the mixtures in the last 4 years and starts first shot. That is a plus one for me.

[BigBlocksOnTop2]

Dual plane intake has the divider and that effectively cuts the carburetor flow in two. Each plenum see only half the carb. You can get away with a large carb.I have 395 in . Windsor that's warmed over pretty good. Weiand Stealth with the outer four runners heavily ported. Short side plenum ported heavy too. Divider intact. Street manners pretty good for 249 degrees at .050 and 110 lobe center. Big single plane intake equals no street manners. I would like myself to try the dual quad dual plane intake on my combo....I think it would like it.

[Flatheadpopup]

Thanks guys, lots of food for thought. As configured my engine should make around 475 hp according to what I come up with using the engine pro and pipemax programs. Any other opinions on this subject? Probably have about a week before I pull the trigger and order something. Thanks again.

Tony

[wyrmrider]

I just relocated my TQ stash into one of those truck pick up trash cans- full
so I'd probably use two TQ's vac secs are nice

[PackardV8]

Will this be simultaneous or progressive linkage? They'll all work. The vacuum secondaries are pretty idiot-proof. Studebaker put two 625 CFMs on a 304.5"; sucked gas like a trash pump, but no driveability problems. The 500s will be better for 99.9% of your driving. Larger will be better the .1% at the end of the longest straight on the track.

Has anyone see a back-to-back dyno comparison of the above-mentioned Air Gap 2X4 over the Super Victor? The tests I read in the past showed the older design 2X4 cost a bunch of horsepower.

[Flatheadpopup]

Will this be simultaneous or progressive linkage? They'll all work. The vacuum secondaries are pretty idiot-proof. Studebaker put two 625 CFMs on a 304.5"; sucked gas like a trash pump, but no driveability problems. The 500s will be better for 99.9% of your driving. Larger will be better the .1% at the end of the longest straight on the track.

Has anyone see a back-to-back dyno comparison of the above-mentioned Air Gap 2X4 over the Super Victor? The tests I read in the past showed the older design 2X4 cost a bunch of horsepower.

I haven't decided on which way to run the linkage yet. At first I was thinking 1 to 1 but I have read some stuff that makes me think it would be worth trying progressive first.

As far as direct comparisons I did find an article with a very similar setup to mine. The Super Victor did make more peak power by about 20 horses using a 800 cfm carb vs two 500s on the dual quad intake. I'm not sure how to attach a link to the article here but if you google Ron Burgundy 363 manifold test you'll see it right away. They actually test a performer, performer rpm air gap, victor jr, air gap dual quad and a super victor on the same engine. Interesting results that make me think the dual quad might actually work pretty well for what I want.

Tony

[statsystems]

I just relocated my TQ stash into one of those truck pick up trash cans- full
so I'd probably use two TQ's vac secs are nice

PM Sent to wyrmrider.

[F-BIRD'88]

You will get a lot of mis information on this.

EG if a 750 is fine then 2x500's must be all it needs. etc etc.

If you want the most power use big cfm carbs on it. 2x750.
The 2x 750 carbs DO NOT over crabeurate. They are progr3essive ith air demand based secondaries.
The larger carbs always more more power in dual quad applications than the 500's do.

Ya it will run good withn the 500's on it but it will MAKE MORE POWER AND TORQUE
with larger 2x750 carbs on it. Ya it needs these larger carbs.

2x600's will make more power than 2x500's too.

Do not pick carbs by cfm size based on some CFM flow rule formula that is BS.
This does not work on Dual quad or any 2x4 induction set up.

The dyno will prove this and the 750 carbs will run just as sweet as any other.
It will not be over carbed.
Joe Sherman gets good dyno tested power gains by working with various carb spacers.
You are not limited to just trying open spacers for more power.
If you want the crisp low rpm throttle response and low rpm torque of a true dual plane with split
180deg plenum try a split carb spacer pair.
Open spacers may degrade the very low end or may need specific different tuning setup,
But they have been shown to make more top end power.
Small cfm carbs will limit top end power on this intake.

The cam is small.. The cam that is best on a dual plane is going to be different than the best single plane cam is going to be.
A little bigger cam allows the dual plane dual quad to breathe deep and make MORE power on the top end
The 180deg split plenum keeps the big torque and low end response even with a bigger cam.
If you only pick a cam based for the VIC JR single plane YOU WILL LEAVE POWER on the table
taht you could get using the RIGHT CAM for this dual plane dual quad manifold.
It will be DIFFERENT.
DO NOT UNDER CAM or undr CARB it. LET IT breath DEEP.

You will need to dial in the jetting and dyno testing is best.
Then final in car jetting adjustment is advised. Road testing Drag testing
but dyno testing will really help you dial it in.
BRING JETS AND RODS AND SPACERS.
The 2x500's are for the T bucket set. near stock motors "cruisers and show cars.
If you want to get serious and match the power of the VIC JR use 2x BIG CARBS on your dual quad
.

The progresive secondary air control and the progressive front rear carb throttle linkage
and the split 180deg "dual plane" plenum ENSURE it will have very strong throttle responce
while makeing big power and torque when you hammer it.
The engine idles on both carbs equally but it "drives mostly on the rear "primary" carb until you get further into the throttle, then they all open progressivly and thy will open all the way.

[F-BIRD'88]

If you really want this thing to HONK on the street use one of the COMP XR mechanical street rollers.
Even the off the shelf part numbers will out perform that HYD roller cam and getting a custom grind version of these powerfull Solid street roller street cams is a phone call away.
They are not noisey to drive and are not difficult to keep in lash adjustment.
and will out perform that cam by a worthwhile margin.
THey work great on these RPM Dual QUAD air gap induction setups.
These are not racing roller cams. They run GREAT on the street and make MORE POWER.
With aluminum heads I like setting the valve lash COLD a good bit tighter than the cam car HOT spec.
It opens up a bit as the motor gets up to running temp.
They are near quiet at idle .. often QUIETER than many pesky hyd rollers are.
and out perform the hyd rollers without the hyd roller lifter noise.
Why? because they re not playing games with the hyd bleed rate and valving trying to cheat physics.
trying to avoid pump up/bleed down/////

[andyf]

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.

[PackardV8]

Your opinions and results may vary. We'll agree with everything F-BIRD'88 suggested above, if one knows the customer very well.

The car is going to be mainly street driven

granted, maybe OP is a hard core guy willing to make some hard tradeoffs of civility and ease of operation for max power. He didn't say how many days and how many miles of street driving, but more than fifty years of this have led me to undercam and undercarburet mainly street driven cars.

"It just doesn't want to idle slow"

"It just doesn't pull right off idle."

"Shouldn't it get more than 8 MPG?"

"Yeah, I said I wanted that bad-azz lope at idle, but it's maybe too much."

"When I get all eight open, then drop back to idle, it changes every time."

"Yes, you told me the 2x4s need stronger throttle return springs, but that gets tiring on the highway."

"When the converter goes into lockup on the highway at 1800 RPMs, it seems like it's fighting the cam."

"That high stall converter just feels weird. I'm not sure I like the way it drives in traffic."

"It smells up the garage. My wife says it can't stay in there."

One hard-and-fast rule - every build gets a wideband O2 sensor on both sides. After all those years tuning carbs, with the first direct readout O2, I learned how much I didn't know.