bottlefed125

i have a 350 bored .030 over with 10-1 flat top pistons, 75cc heads, performer rpm intake, msd drop in coil in a hei dist., the cam is a 535 lift with 310 duration, dynagear gear drive with 5 degrees of retard. I was wondering if the Holley 650cfm vacume secondary carb is to small for the engine and what size carb i should run. Could i run an 850 with mech secondaries on a cam like that or is that to much? everyone put some info in on this, every bit of info is appreciated.

cc 82Z-28

iTrader: (7)

Unless you're going for a race motor, I would go for the 650 or the 750, I would stay from the 850, you would not be happy with one, too much carb. Are you running an automatic trans? If so, and the cam you're using isn't too radical, you could probably use a carb of mech. or vacumn secondaries. I have a 355 with about 9:7:1 compression and aluminum heads. I run the 670 Holley avenger on top of an Edelbrock air gap rpm manifold. It runs great withno hesitation or bogs and flat out runs. I use an MSD 6-A box with a new high performance HEI dist. Accel 300+ wires and Hedman headers. Just my opinion, and I'm sure you'll get lots of them.

GASGZLR

I am a firm believer in the equation for required MINIMUM CFM. it is this I think:

CFM= 85% VE (Volumetric Efficiency) x [(CID x MAX RPM) divided by 3456]

A 355 small block with 85% VE at 6500 RPM needs a MINUMUM of 567.5 CFM

So yeah, the 650 would work fine, and there is gonna be a lot of people trying to tell you to run a 750 or 850 but it is over kill. My motor is a .040 over 350 that runs at 91% VE at 5800 RPM and I saw NO decrease in power when I took off a 750 and put a 600 on it. In fact it is WAY more responsive and the 600 is tuned optimum and is still 8% leaned out,but do to my elevation of 5500 feet. A HUGE carb will just run sluggish and use gas unless it is a pure race car that has a 3500+ stall.

five7kid

iTrader: (14)

The chart on this link http://www.holley.com/HiOctn/TechSer...fo/TI-225.html will tell you how big of a mechanical secondary carb you can run. It doesn't depend upon the cam, it depends upon your stall speed (the cam will dicate proper stall speed, if you want to get into the powerband from a dead stop).

Two other points:
1) For performance, stay away from vacuum secondaries. Unless you consider towing "performance".
2) I agree that the smallest carb that will feed your engine is the best choice. I've gone over this topic in other posts relative to my 750VS vs. 650DP vs. 750DP experience last summer on a 396 that revs to 5800 RPMs. Bottom line is 650 is big enough for it.

bottlefed125

i am running a 3500 stall actually, it does seem to run a little rich...what jets should i run? and should i go to mechanical secondaries? When i rev the car up it doesnt seem to open the secondaries. it has plenty of vaccume when its about 2000 rpm, do you think the carb isnt getting enough vaccume in the beginning to open it right away?

five7kid

iTrader: (14)

The vacuum secondaries aren't opened by engine vacuum. They are opened by a vacuum created in the primary venturi. You will never see them open by blipping the throttle in the driveway - the engine has to be under load.

See http://www.holley.com/HiOctn/TechSer...fo/TI-223.html for explanation.

bottlefed125

according to the site about what size carb is recomended i should be running about an 800-900cfm carb, that sounds like a bit much, i might attempt to put a 770 on it with mechanicle secondaries but im not sure...what do you think?

five7kid

iTrader: (14)

It's not telling you what size you should run, but what size you can run.

AJ_92RS

Yes. You obviously missed this part...

bottlefed125

i saw that aj but if i got to small ill choke the engine cause it cant get enough air...

five7kid

iTrader: (14)

Chose the minimum size by the formula.

Chose the maximum size by the chart on the Mechanical Secondaries page.

There will be a huge range inbetween. If you're running a 3500 stall, it is more than huge. Minimum 650, maximum around 1100. For driveability, go to the small side. For drag racing power, go to the large side (I really doubt a 1050 Dominator is called for, though).

An example of too much carb: Back in the 70's, I had a SBC 302 clone, LT-1 solid cam & 2.02/1.60 heads, original Torquer single-plane intake, with a 1100 stall Powerglide. Draw a line on the chart, and they don't make a mechanical secondary carb small enough. I had a 600 DP on it, flooring it from a stop produced instant bog. Get the RPMs up above 1500 when you floored it (which is on the chart), it was still a dog but at least it didn't die.

On the other hand, when I put a 780 CFM VS on it, it could be floored from a stop - although it still didn't have any power until RPMs got above 2500...

In your case, vacuum secondaries are completely uncalled for.

bottlefed125

i think im going to be purchasing a 770 demon mechanical secondaries anyone have any luck with this carb?

Air_Adam

Thats probably a good size for a 350... as in streetable, but still kinda on the big side. I'd use a 650 for just about any street-driven engine up to 400ci or so myself.

Barry85Iroc

770 should be ok. Mine works fine......once I got the jets straightened out. Get a jet kit. You'll have to play with it.

bottlefed125

i have a complete holley jet kit so ill fiddle with it when i get around to it...my ex wrecked her camaro so im building her a new car from an empty shell up so it kinda set my car aside...been working on it non-stop for 2 weeks and the weeks before that i was working on tearing her old one apart so im pretty beat right now and i have a long way to go to have the car done by the deadline on april 15th