600 CFM Carb "enough" for modded 460?

[TFB1]

Originally Posted By: Trav
I remember working on some old big block 429 CJ back in the 70's that had Rochester Q jets on them OEM.
IIRC they were 700 CFM give or take a little and used a dual plane manifold.



My 1970 Muscle Parts supplement(this is a Ford publication) says the Rochester was 760 CFM, the SCJ Holley was 780 & the 428CJ/SCJ both used a Holley 735...

 

[Cujet]

Remember that the 600cfm rating is achieved at a certain differential pressure (intake manifold vacuum) . Your engine will be working hard to achieve that differential and the 600cfm flow rate That means you won't achieve maximum possible hp. Engine "bog" is not generally a factor of carb size. It's a tuning issue.

 

[Trav]

Quote:
Optional engines for the Cyclone were: a 429 cubic inch 4-barrel with dual exhaust and ram air induction called the 429 CJ (Cobra Jet) that was rated at 370 hp SAE gross (likely 305 hp SAE net) and had a 700 cfm Holly or 715 cfm Rochester Quadrajet 4 BBL carburetor, a 429 cubic inch 4-barrel with dual exhaust and ram air induction called the 429 SCJ (Super Cobra Jet) that was rated at 375 hp SAE gross (likely 335 hp SAE net) and had a 780 cfm Holley 4 BBL carburetor (it was only available with the Drag Pack option).

 

[SteveSRT8]

sorry, but almost all the 429's were dogs as delivered.

A good running 390 would eat them alive!

 

[TFB1]

Originally Posted By: Trav
Quote:
Optional engines for the Cyclone were: a 429 cubic inch 4-barrel with dual exhaust and ram air induction called the 429 CJ (Cobra Jet) that was rated at 370 hp SAE gross (likely 305 hp SAE net) and had a 700 cfm Holly or 715 cfm Rochester Quadrajet 4 BBL carburetor, a 429 cubic inch 4-barrel with dual exhaust and ram air induction called the 429 SCJ (Super Cobra Jet) that was rated at 375 hp SAE gross (likely 335 hp SAE net) and had a 780 cfm Holley 4 BBL carburetor (it was only available with the Drag Pack option).



I've had these manuals since 1971, Ford says 760, I'm not about to believe something different now...

 

[SteveSRT8]

The Rochester they speak of flows up to 800+ cfm, depends on application.

As Trav mentioned, a very good carb, but more difficult for the shade tree guy to tune properly.

 

[Trav]

I had a 69 and a 70 back in late 70's, the Q Jet was 715 CFM.
Show us the page from the manuals?
The engine was the same as the Torino with the exception of the very few Cyclones that had the BOSS 429

You don't believe Hemming either.

For 1970, there was a small, yet confusing, array of 429s available in the Torino: For starters, there was the 360hp 429 4V (four-barrel); next was the 370hp 429 Cobra with a hydraulic-lifter camshaft and 715-CFM Rochester carburetor; the 429 Cobra Jet was also rated at 370hp but had a functional ram-air scoop; finally, at the top of the heap was the Super Cobra Jet or the Drag Pack Cobra Jet, which, with a nod and a wink, was rated at 375hp. That engine had a 780 Holley, four-bolt main block, forged aluminum pistons, cap-screw connecting rods and a remote oil cooler.

 

[mechtech2]

I'd rebuild it [clean it properly with new gaskets] and reuse the 600.
85% efficiency is very good - it's high performance territory.
I doubt you are close to that.
'Spread bore' type carburetors have the best of both worlds - like a GM Quadrajet. Small primaries for cruising, and large secondaries for power when you step on it all the way.
GM offered them in 750 and 800 CFM versions. So large carb low end problems with one of those does not apply.

BTW, carbs are measured differently. 2 barrel carbs at 3" pressure drop, and 4 barrle carbs at 1.5".
Flow ratings do NOT compare between the two!

 

[TFB1]

Originally Posted By: Trav
I had a 69 and a 70 back in late 70's, the Q Jet was 715 CFM.
Show us the page from the manuals?



http://amradio.freeiz.com/turbocoupe50/429cjscj.jpg

http://amradio.freeiz.com/turbocoupe50/musclepartsindex.jpg

 

[Trav]

Okay i see it in black and white. Where are they getting 715 from? when i looked this up years ago they said 715 CFM.
Conflicting specs are never good.

 

[mechtech2]

Also read Doug Roe's excellent book on Rochester Carbs.
750 and 800 are correct.

[and Jack Benny's book on Rochester butlers!]

 

[panthermike]

Well we worked on the truck today. The original plan was to clean the carb and try to "fine tune" it. Then my BIL suggested to swap his carb to Ol' Yellar. His carb is a 625 CFM Carter AFB competition.

He just recently put this carb on his truck which has a stock 360 motor. He had mentioned that his motor seemed to "bog" a little on WOT. He felt like it was tuned well enough.

So we swapped the Carter on the truck with no adjustments(except idle speed), and wow! Truck is running great; no more stumbling, and no more pinging! I feel like the bottom and top end are better(could just feel like that because of the stumble).

I know the Holley is probably just fine, but I'll let him use it and I'll keep the Carter. He's going to rebuild and clean the Holley before installation. Should work well with his motor.

Kind of a win win for both of us. I'm stoked with how the truck is running. Next is a full tune-up, probably next weekend.

 

[G-MAN]

Originally Posted By: panthermike
So we swapped the Carter on the truck with no adjustments(except idle speed), and wow! Truck is running great; no more stumbling, and no more pinging! I feel like the bottom and top end are better(could just feel like that because of the stumble).

I know the Holley is probably just fine, but I'll let him use it and I'll keep the Carter.


Smart move, IMO. I never liked Holley carbs. My first experience was when my dad moved from our 66 New Yorker (440 with a Carter AFB) to a 69 New Yorker (440 with a Holley). The Holley on the 69 leaked at the accelerator pump from almost day one. Dad and I finally put a Carter AVS on and the engine ran better than ever. Within a year of trading that car for a 72 Imperial, we took the Holley off of it (even though it wasn't giving any problems) and put a Carter AVS on. Very noticeable difference, especially at WOT. I was always convinced that the vacuum operated secondaries on the Holleys Chrysler used never fully opened.

 

[mechtech2]

G-Man.
I also always felt uncomfortable about being the guy who never was into Holley carbs. Everyone automatically loved them. I did not.
Big deal, a bigger aftermarket carb that was jetted rich and leaked.

 

[morris]

TO:G-MAN the holly on a chrysler 440 is NOT the same as over the counter holly, it was junk. thats why carter sold so many over counter AFBs, AVSs. you can have your hollys. the idea of holding fuel in a carb with gaskets is STUPID.

 

[panthermike]

Really liking the Carter so far. Got a little worried this morning when the truck stalled on me. Turns out the coil wire came unplugged

.

Had to do a little tuning; after a short drive the truck would idle way low and stall. Increased the idle speed and it's been good after 20 miles of driving.

Now my BIL is not sure he wants the Holley. I told him I'll sell it and give him the money. That way I can keep the Carter and he can get an Edelbrock or whatever he wants.

Truck is running super strong though. I think the Holley had a few things going against it; out of tune, really dirty, sticky linkages, and probably could use a rebuild.