carb size recommendations for dual quad 363 stroker

[F-BIRD'88]

My first thought was "thermoquad" when I looked at the Street Demons. After reading up a little bit I find them somewhat intriguing. I'll definitely take a better look at them and see what people are saying. Its always good to have alternatives, even if I don't end up going in that direction.

Yup apparently the primary jets and rods in it are thermoquad type and the sec jetting is standard holley jets.

There is a feature in HotRod.com online on the Street Demon carb.
Interesting stuff.

Secondary air door rate adjusts the same way a Carter/eddy AVS carb air door does.

[F-BIRD'88]

This is the Wagnar Adjustable PCV valve.
http://mewagner.com/

See I am not the only one thats clued into the importance of the right PCV valve
for your carbed engine , so it runs right.

If your motor is non stock,,, cammed up etc there is a good chance you need
a different or modified PCV valve flow rate.

Save yourself a lot of BS trying to re engineer your carb, pretending you are a carb drilling happy, carb guru etc and get the PCV valve right.

[In-Tech]

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?

[F-BIRD'88]

no idea on the part number on that stuff.

If a "Fixed Orrifice" style PCV valve is suitable for your engine.
Sometimes big cammed low manifld vacuum engines like this)

Then you can hack a simple GM LS motor truck motor replacement Fixed orrifice
PCV valve to change the "Fixed" flow rate YET keep the critical NESSESSARY
one way anti backfire valve function in it, so you don't get a carb back fire
going into the engine crank case. That could get ugly.

This is how you get the (adjustable) added idle air flow bypass air
to let a cammed up motor idle with correct throttle T slot position at idle
so the idle and off idle circuit fuel metering works as designed.
No need to drill carb throttle blades.

AT WOT:
Having a slight negative relative pressure in the crank case
ALSO lets the engine piston rings SEAL BETTER to make MORE POWER
much like the benefit of a engine crank case vacuum pump or pan-a-vac- on racing engines.
Ya that PCV system is a Speed secret, when its working right.

At idle, and at part throttle, the system creates a Cross flow flow thru accross the opposing valve covers to ventilate the crank case. The other opposing valve cover needs a FILTERED and oil baffled Vent.

As soon as you change the camshaft, you also change the manifold vacuum rate
to the PCV valve. Got 2 carbs, 2x4's.... may need a different or modified PCV valve flow rate.

Now you can make street carbs work right on that pesky tunnel ram,
so it runs sweet on the street and makes great power.
This is a critical part of getting that right.

[F-BIRD'88]

There is nothing saying you can't create a 2 stage or 3 stage
multi flow rate controled PCV system using more than one PCV valve and electronic
or simpler Solenoid control based on vacuum signal and throttle position
and rpm. Could even have a feed back circuit reading real time crank case relative pressure/vacuum.

[F-BIRD'88]

OP: When you got 2 x big ass 750cfm carbs feeding the motor you don't need
the typical hot rod single holley 4 bbl carb thinking like cutting off the choke horn for more air flow.
It's just not really nessessary and doesn't pay off. Better off to keep the chokes
and use them to good effect on a street car.
Easy to hook up a simple manual choke cable. It also controls the fast idle
throttle system, nice for start up rpm control for those STREET solid roller lifters
that like oiling at (increased idle speed during warm up) when warming up the motor.
There is a reason for all this stuff. use it to your benefit.

[Flatheadpopup]

OP: When you got 2 x big ass 750cfm carbs feeding the motor you don't need
the typical hot rod single holley 4 bbl carb thinking like cutting off the choke horn for more air flow.
It's just not really nessessary and doesn't pay off. Better off to keep the chokes
and use them to good effect on a street car.
Easy to hook up a simple manual choke cable. It also controls the fast idle
throttle system, nice for start up rpm control for those STREET solid roller lifters
that like oiling at (increased idle speed during warm up) when warming up the motor.
There is a reason for all this stuff. use it to your benefit.

Makes sense to me. Thanks for the in depth advice. If everything goes as planned I will be making a sizable parts order tomorrow.

[F-BIRD'88]

You could even try the 2x4 carbs on a carb adapter, on your Super VIC single plane intake.
(BDS 4-71 type carb adapters)(you need a single and dual)

Get the 2 carbs dialed in and I bet the single Holley 4bbl carb stays on the shelf collecting dust.

Fast cars have 2 carbs ..... "Dual Quads"

[Flatheadpopup]

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

[Flatheadpopup]

Cell phone pics of dyno readout. For some reason my camera was freaking out and I kept getting the banding in the pics.

[F-BIRD'88]

On the dyno tests were the carbs bolted right on the intake or did you try some spacers under the carbs?
Joe Sherman used to get extra horsepower using various spacers on these dual quad rpm air gap engines.
He had dialed in quite a few on his dyno for his customers.. Gave me a few tips for my 406 sbc.

[F-BIRD'88]

490 hp from 363 cid. Nice job.

[Flatheadpopup]

I had the divided 1/2" edelbrock wood spacers under the carbs when it dyno'd. The heads were milled to a true 58cc putting me at 10.7 compression, so it is a pump gas motor. There is more power to be had when I get the heads ported and cam optimized but for now I am really happy.

[TAG]

Loosely related; whats the length of 1850 600cfm Holley? Impossible to find. Trying to determine if two of them fits next to each other on weird Offenhauser 8 3/15" carb spacing. Thanks.
From the picture on first pages, looks like they dont take that much space.

[Geoff2]

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