428 build Questions need HELP

[Hunter71]

I'm building a 428CJ and I'm in the process of purchasing the parts. I'm looking at the Powermax mechcanical solid cam from Crane (344361) or (341191). I don't know if I can run this in my car because I live In California. I'm going to run Keith Black pistons .40 and Edelbrock heads. But when I'm calculating the compression ratio its in the 9:1 range. I don't know if this correct or not. My final question is my machine shop suggested to use the 850 Holley carb, but I see that most of you guys are running 750s. Need help before I spend $$$$$$$$$$$$$$$$$$$$$. Thanks, Craig

[Whaler]

I built a 68 428
went with the edelbrock package as well but opted for an Holley 850 mech double pumper manual choke
The builder said it would make more power and he recommended it .
I used the RPM cam which is hydraulic.

Just broke it in 2 weeks back

It may be a tad rich out of the box. (Jets are 78 and 80) But the jetting fun is later as I have not yet roadtested it. Its in the paint shop now. Most 428 will take over 800 cfm easy. Then depends on cam and heads.

BTW I dropped 110 pounds off the engine using the aluminum in the RPM kit

Tim

[Ron Randall]

Craig, there is an artical in this months Hot Rod mag. that will verify that you only need a 750 on a mild rebuilt 428. Over camming and carbs that are too big still seems to be a problem even will all the info available today.

Ron

[Chaplin]

Ditto on what Ron said. The other mistake (in my opinion) that people make is using a double pumper on the street. I know everyone uses double pumpers, but unless you do a lot of racing, you are much better off with vacuum secondaries. For average street driving, throttle response is better, driveability is better and mpg (I know, who cares in a cobra) is also better.


Hey Whaler, I guess Ron and I just suggested that you need to change your carb

[joea]

SO which carb do you suggest...I too am have a 428 in the works and I was leaning towards a 4150HP (mechanical secondaries)

[Chaplin]

Joea-
If you couldn't tell from my response, I'm in favor of the Holley 750 with vac. secondaries. In fact, it just so happens, that a Holley 750 with vac. secondaries is exactly what is sitting on top of my shiny new 428 that is currently sitting in my garage anxioulsy awaiting the arrival of ERA 650 to call home. BTW, I have the 4160.

All kidding aside, for the reasons I described above, I think a carb with vac. secondaries is better than the double pumper for street driving.

Mike

[joea]

My understanding is that Vac Secondaries are better for fuel economy, but Mechanical is much better for throttle response. Have you used both?

[A Snake]

I'll throw another wrinkle in to think about. First, I've used both mechanical and vacuum secondary carbs on 428 engines. The original CJ came stock with a 735 vacuum secondary carb. You have to remember that these engines were put in Galaxies and Mustangs which weighed at least 1,000# more than a Cobra.

In these two instances, the vacuum carb worked better, because the driver could not inadvertently put his foot to the floor and get a giant case of the bogs. The engine took only what it could handle, based on the vacuum signal.

Now, with a 2,300# car like your Cobra, throttle response in moving the car is very quick compared to a big Galaxie or Mustang. This simply means that it is much less likely to"over throttle" the car.

With that said, my preference is buying a "prepared" 750 cfm double pumper Holley from Barry Grant or The Carb Shop. This carb will flow like an 800, and has four corner idle which is a real blessing with a bumpy cam.

9:1 will work, but you would like 10:1 much better and still be able to use pump supreme. Using the original Med. riser 427 solid lifter cam in a 428, works like a charm. Nice chuckle in the idle and torque that will snap your neck......and that combination likes the double pumper.

If you've had a double pumper under your foot before, you know that you can feel when the secondaries are coming on. You can't gauge that with a vacuum carb and therefore actually have less control of power output. That's a big reason no racers use them on the track. The same thing applies to a few blips of the throttle on a curvy road. The last thing you need is the back half of the carb coming in right in the middle of a curve. Believe me it can happen and will.

As you get used to the car and it's power output, you're going to want tighter control of the throttle than you can get with the vacuum carb. To me they feel mushy and unpredictable. One time you stick your leg in it and the car goes like stink. The next time it makes a lot of noise and doesn't do much. Depends on air temp and density and engine temp as well as engine rpm as to when the back half begins to work.

Just a few thoughts from an old coot who's run a good many FE engines over the years....including in a Cobra.

Al

Fuel mileage? In a Cobra? Good grief! If somebody wants mileage, buy a four banger with four doors!

[Whaler]

Hi guys I agree with the above from A snake
all the reasons pointed to a double pumper with mech sec.
Go to holleys site and read the FAQ on selecting a mech or vac sec
its got cobra written all over it
light cars, manual trannys, manual control of the sec, engines where vaccuum may be low. yada yada

I may have went a little big on my builders advice but the mech secs are here to stay.

Tim

[Hunter71]

Thanks Guys for all you info. I think I'm going to get the Holley 4150 DP 850. I think A Snake explained it very well. He brought new info to the table. thanks Hunter71

[joea]

How about a 4150HP instead? Seems like a good compromise between a standard 4150 (~$400) and a "prepared" 750 cfm double pumper Holley from Barry Grant or The Carb Shop ( not sure but I assume over $1000?) The 4150 HP is about $650 and I hear Awesome reviews...Dave Braswell helped with the design

p.s. Can you send a link to the "prepared 750" you mentioned?

[clevo]

I have a 351clev with 340 rwhp, and a 580 lift crane hyd cam, and an 850 d.p. barry grant. It runs very well on street and strip. The only weird thing is it runs lean if i run aything under 80 and 88 jets in it. I think pick what you want and tune the idle circuit correctly. The only change i did, was increase the fuel restrictors in the metering blocks, so it had a good idle in drive, and dropp the jets back a bit. They have a huge 85 and 93 as standard. It revs instantly from 800 rpm......