225 Modified Slant

-
2

2-66 Cudas

Well-Known Member
Joined
Jan 18, 2010
Messages
400
Reaction score
7
Location
West Newton, PA
I picked up a "Modified" 225, it came with a Clifford 4bbl. intake, a pair of headers (2 3 port) mated to an 833 4 spd. I was told the head was shaved and it has larger valves and had a 650 Holley when it was installed in a 68 Dodge short wheelbase van. Supposedly gave Camaros and Mustangs a good go from red light to redlight. Anyone else think a 650 is a bit much. Comments. I am currently preparing a 66 Valiant 100 post car to drop it in - no chrome - sinister looking! Just wanna know what size carb you slant Gurus suggest.
 
I dunno, I'd run it the way it is 1st, it's already set up that way. Yes it sounds big, but We don't know exactly whats inside, leave it be & run it....

Wait, HAD a 650 holley?, where is the carb now again????
 
Last edited:
Yes it seems your 66 valiant would be sinister at that, a real sleeper. Since nothing is really known about the internals, maybe for decent street ability I'd stick with a Holly 390 CFM 2 bbl. 650???
What is a sleeper is my 70 Dodge Challenger w/ the 225 /6, 904 on the floor. Go-Mango Orange, Black interior. Nothing over the top, mopar elect. Ign. , Super 6 set-up, Hooker headers 3 into 1,real dual exhaust 2.25" w/ H pipe, glasspacks. Open element air cleaner K&N, Accel coil. The addition of the dual scooped hood and T/A ducktail rear spoiler is a nod to it's performance heritage at a glance.
 
Looks like we are on the same page. I'm doing an Offy manifold with a Holley 390, Oregon cam, Dual Dutra duals, also with head shaved and bigger valves, along with some porting work and an 833 OD. All going into my 66 Valiant 100 post. How about some photos of your build? I'd be interested to see what you think of your combination.

And as feedback, I'm a relative noob when it comes to figuring out what parts work with other parts in a /6, but all I've heard and read about indicates a Holley 650 is a whole lot of carb for your application.
 
Yeah it is too big. Even a 390 is probably more than the slanty can make maximum use of.
But that doesn't mean you can't run a 650. It kindof depends on the combo.
With 4.10s in the back, and a 3.09 low;it might be fine.
With 2.76s and a 2.66 low, maybe not so much.
If the van is driveable on the primaries, that is to say easily controlled by the gas pedal, and not overly sensitive to throttle opening,and if it is free from bogs or hesitations, and is jettable; then drive it.
In most applications, the primaries alone of a 650 would be large enough to pass enough air for the NA slanty's needs, up to around 5000 rpm. The primary thing that suffers with a too big carb, is low-speed driveability.
A vacuum secondary would be a better choice.
That's why the 318 can accept a big TQ, with the big primaries. The 1.5 primaries are about the same as a regular 2bbl, so for most of the time the teener doesn't even know there is a 4bbl on it. And both the rate of secondary opening, and the amount of that opening are adjustable, to size that carb to almost any engine.
 
Last edited:
I guess it should also be pointed out that a 4bbl often adds only about 10% power to the engine on a streeter. And contributes very little to the making of torque, below the torque peak.
So if you build a 200hp slanty, you can expect 20hp at peak output. The 4bbl power will build from just measurable before the torque peak, to maximum at the power peak, and then it will help to sustain the power a bit longer over the top.So even tho the secondaries double the butterfly area, the airflow volume through the primaries reduces as the secondaries open. So if your engine can only inhale 300cfm,then,whether you have a 390cfm carb or a 500, or a 650 will not make it go any faster.
But, you might ask; if it can pull all of those 300 thru the primaries,what is the point of even having secondaries?
>Well, for one thing Smaller primaries make the engine more driveable. The signal thru the boosters is sharper and is faster to be activated, requiring less band-aiding from the accelerator pump.
If the primaries get to be too big, then every little movement of the gas pedal produces a large throttle change and the engine gets to be jumpy.
If the primaries are too small, then they might be always opening far enough to activate the secondaries, and smooth acceleration gets to be tricky.
There is a formula to help you size your engines needs. It looks like this;horsepower times RPM divided by 3450.
So in the above example 200hp x 4800/3450= 278 cfm. If you have an automatic and have to rev it 15% higher to put down the maximum average hp, then the revs will go to 5500, and the required cfms will be 200x5500/3450=319cfm. Typically these are minimums.
>A small 4bbl is better than maxing out a big 2bbl. Why? Cuz the smaller butterflies of the 4bbl are more driveable at normal rpms. They will be less jumpy, and require less pumpshot to cover sags. And just maybe you can tune the primaries a hair leaner for a bit better gas mileage, and fatten up the secondaries a hair,to average it out.

EDIT
If you put that 650 on your slanty that only can pull 319, then it will be a 319. I guess that is what I was trying to say
 
Last edited:
Just out of curiosity....anyone know the CFM of a typical Carter BBD? Say a late 60s 318 carb. Was the super 6 carb basically the same rating?

P.S. The carb on my 1973 rotary-engined Mazda was the smallest, cutest 4 barrel I've ever seen.
 
I have a SS on my 1980 Volare. 1.44" throttles/ 3.257 total sq inches. These are the same as a Holley 390, but the 390 has twice as many,so;totals 651sq inches,and 100% more area.
>The Holley650 has 1.688 throttles, for a total of 8.95 sq inches, or 37.5% larger than the 390,and 275% larger than the SS!!
>I would sooner have two or three of those SS carbs on my slanty, than a 4bbl. They have very small hi-velocity venturis with, IIRC, dual boosters per hole. They are very small tho.Yeah I think a 6-pac of SSers would be nice; a SuperSix-Pac!. that would total 9.77sq inches. OK, that might be crazy...

The thing to remember about comparing 2bbls to 4 bbls, is that they are rated differently, and even if I had the numbers, I have forgotten the conversion factors.

I think a slanty would like a staged 2bbl, with a small front and a big rear vacuum operated dump. Like half a Thermoquad,lol. I have seen a staged 2bbl once,but I forget what on.
 
Last edited:
You must log in or register to reply here.
-

Back
Top