650 holley a good replacement

Got to be careful you're not confusing a carb that's not tuned properly for a carb that's too big. although in this case I would agree the 850 is too big for a standard displacement 351C motor in a mild state of tune.

I would recommend a Holley carb in the 700 to 750 cfm range. The 600s & 650s will trade off a little bit on top for a little more signal at the bottom.

The carb & ignition have to be tuned properly for your motor to run without flat spots through out the rpm range. Having made that warning, I've seen the 750 Holley work on Cleveland motors in states of tune from mild to wild; from 300 bhp to 500 bhp. The Cleveland is not a small block Chevy, it likes a much bigger carb. This recommendation is as old as the Cleveland motor itself.

There are several choices of Holley in that size, vacuum secondaries or double pumpers, manual chokes or electric chokes, street avengers, HP series, street tuned HP series, standard series.

cowboy from hell

I just completely rebuilt the Holley 4778-2 700CFM double pumper that came on my car, including jetting it to original Holley specs. I bolted it on this morning, gave it a coarse tuning (float level, idle mixture), and headed off to work.

Wow, what a difference! No gasoline smell, no run-on, reliable return to idle, nice throttle response, and the car even sounds better.

I have an appointment booked for some dyno time at 11:00am on Saturday March 17th. I'm going to use that to get the carburetor finely tuned, including:

- idle mixture and idle throttle opening
- primary & secondary main jets
- primary power valve vacuum rating and PVCR sizing
- primary & secondary accelerator pump cams
- primary & secondary squirter nozzle sizes

By juggling all this, the end result should be exactly the right amount of fuel and air available for combustion at all times, and a VERY responsive engine. Fuel economy should be improved, too.

Until my dyno day we won't know for sure, but my guess is that 700CFM is quite appropriate for my somewhat upgraded engine. I happen to already have a double pumper, but if I was buying a new Holley I would go for a Street Avenger 770CFM with vacuum secondaries (actually I want quad Webers).

The beauty of the vacuum secondaries is that you can somewhat oversize the carburetor, and not cause problems. If your engine cannot use 770CFM, the secondaries won't open all the way, so the mixture etc. will still be correct. On a mechanical secondary (double pumper) carb, to get that effect you have to convince the driver to lift his foot slightly. (I'd bet on the vacuum secondaries.)

Surely a sign of someone who knows holleys well; intent on optimizing the PVCR(PVCO)s

quote:

Originally posted by PartTimeAdult:
Surely a sign of someone who knows holleys well; intent on optimizing the PVCR(PVCO)s

Well, a month ago all I knew was how to spell "Holley", but there is lots of good Holley information out there to get saturated in.

I have John Passini's Weber tuning books, and have studied them carefully. Pretty well everything translates to Holleys, except that the means of adjusting are different. Air bleeds, emulsion tubes and PVCRs are exotic tweaking using drill bits on a Holley, but on Webers these are as easy to change as Holley main jets.

I'm kinda hoping the oxygen sensor says everything is perfect, so I don't have to do anything except read the horsepower graph.

This 750 has to be a best buy in Holley carbs, look at the features. I bolted one on my stockish rebuilt Cleveland with Performer manifold and ignition mods, reduced the size of the stock primary jets 1 size. For my application, it worked great. Instant throttle response, very pleased.

http://cgi.ebay.com/ebaymotors/Holley-0-82751-750-CFM-S...QQrdZ1QQcmdZViewItem

quote:

Originally posted by johnk:
This 750 has to be a best buy in Holley carbs, look at the features. I bolted one on my stockish rebuilt Cleveland with Performer manifold and ignition mods, reduced the size of the stock primary jets 1 size. For my application, it worked great. Instant throttle response, very pleased.

http://cgi.ebay.com/ebaymotors/Holley-0-82751-750-CFM-S...QQrdZ1QQcmdZViewItem

That does look like a nice carburetor; I like the adjustable air bleeds, though you would need dyno time to make use of their adjustability.

I agree on the 770 Street Avenger. I bought one and am very happy. The carb was put on out of the box and required very little tuning. It was installed with some other updates and dyno'd at the time of installation. (How do you spell dynod? maybe dinoed? )My cleveland is a mild build w/330 RWHP. I was shooting for a broad and flat torque curve.