Well its time... the ol 360 is pooping out and im done pumping money into it so time for a all new engine. What size carb do you think will work best on the 445? I was thinking a holley street avenger 770? The guys at survival motorsports thought that was sufficient but wanted to double check.

 

Those guys know their chit....

For a street motor, even a 445FE stroker, 770cfm is more than adequate...

Were this is a street/race motor that will only see a lot of time @WOT i'd consider at least 850cfm.

 

Thanks Montana. Ok so im in debate over hydrolic flat or solid flat cam now because a roller motor is way to expensive for me to do at this time.... Now on another web forum barry actually said he recommends a 750 db pumper.... That just spells SUCKISH GAS MILEAGE to me. Not that a 445 isn't already going to be bad but still. So will a 870 cfm street avenger by holley equal a 750 db pumper or what?

I want power but not 2mpg


Barry ""
I do a lot of them with a basic downleg booster 750 double pumper. Tom is spot on with the peak power comment - we see about 10HP more with the bigger carb, but teh smaller stuff is better from a driving and transient perspective. I have not run the 830 annular, but it should be very good, and will give one a try soon.

Cheap vacuum secondary 750 carbs with straight leg boosters are down at least 20HP compared to the good ones...
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I wouldn't recommend a double pumper on a street motor...

I prefer vacuum secondaries... unless mpg is of no concern and you're gonna race this motor....

In that case, yea, a double pumper is fine.

It comes down to your intended usage.....

 

Its my daily driver to college and back and to the girlfriends house etc. But I plan on the occasional towing, some off roading, and want to race my buddies at the track so im thinking db pumper is overboard. So I cant decide if I need that 770 or id be better of with a 870...

 

Even a 650 can be adequate on a 445 stroker, until you wind it up, then it starts to fall flat...

I'd highly recommend the 770, plenty of cfm when you do see 5,000 and above rpms....

Again, it all comes down to what you wanna do with this motor...

 

I live in southern california, but I would hit up a company like PC carb for a custom built + tuned model.

If you send them a $100 core 750 vs for about $350 on the rebuild you'll practically have no tuning to do. Compared to a 770 that you'll need to adjust based on your motors needs.

 

Honestly what would the difference be between putting a 770 on or a 870?

 

If they're both vacuum operated not much.....but the 870 you're referring to has mechanical secondaries.....it'll suck gas like no body's business.

 

Holley Performance Products 870 CFM Four Barrel Carburetor 0-80870

says vacuum. So would mpg be about the same?

 

Depends how easy you are on the "fast pedal"

What kinda vacuum are you drawing at idle? 18-21? or 10-14?

 

No idea because we haven't figured the cam out yet. But we will be going to hydro boost breaks cuz Schneider cams says vacume will be below normal. So im assuming that means low vacuum. It ill be a mild cam. Just hot enough for some oomf but don't want to loose towing capability. (im open on suggestions for cam lift and duration and all)

 

What are your build specs? C/R? expected HP? are you using Barry's parts?

 

Barrys 445 stroker kit. Edelbrock heads. Edelbrock rpm intake. Barry said with the stock heads I was going to use I could look for about 470 hp and well over 520 pounds of torque.... Now that I just got a sed of edelbrock heads with the cj valves and all I assume id get closer to the 500hp mark.

 

I am not a carb expert so take it for what it is worth.

I was running a 670 cfm Street Avenger on what I thought was a 400 cu in motor, but once I tore it down learned that it was only a 351 cu in. The carb, once I had tuned it, ran wonderful with great throttle response on the street.

I am now in the process of building a 437 cu in stroker out of it. I used one of the online VE/CFM calculators to find a ballpark figure to work with for carb size, which ended up being around 630-640 cfm at 100% VE at 5,000 rpm. When I was talking to T. Meyer putting my engine package together I asked his recommendation on carb size and he said to run a 750 cfm.

I started looking at carbs and liked the QFT SS series carbs for the features I got at the price point. The only problem is, they only have a 735 cfm and 780 cfm carb in the 750 range so I called up QFT and explained my build and goals. I explained to the tech that I wanted good throttle response, but at the same time I didn't want to leave anything on the table by going with too small a carb and gave him the figure I got out of the VE/CFM calculation. The tech recommended the 735 cfm carb to me stating that it was going to be a better option to run on the street due to the fact that it was flowing about 680 cfm on the front end, close to the CFM number calculated. I ended up purchasing the 735 cfm carb.

Unfortunately, I am still waiting on custom parts from Tim so I cannot give any insight into whether or not it was the right choice or not on a running motor, but I figured I would give you a little information on my thought process for selecting a carb and maybe it would help you select yours.

PS - The QFT carbs are a nice looking unit.

Street Carburetor 735 CFM VS