carbs

[dodge440]

hey guys, what is a good carb to use on a street driven 500 hp 500 inch bb and 727 auto?
I know gearing and a lot of other stuff help selection, but just in general terms.
I went from a 1050 holley to a 850 BG mighty demon, not happy with that change, but now I see the holley HP 750 flowing 830, holley 950 hp, and Proform 750 - 950 etc, and the holley online selector says 850 with vacuum secondaries.
Is there an "ideal" carb for a street driven crate motor?

[rumblefish360]

Well, I would not go smaller than a 750. The engine is just plain old large. Of course, like you said, alot depends on gearing, stall converter, car weight, intended useage of the car.

In example, if it were just to cruise around in and the gear ratio wasn't to high, like a low 3.xx, a 750 would be OK to use. Not great. A little short on the upper midrange and top end. But with 3.23/3.55's, your not trying to do 140 down the Hwy. If you were, then more cfm's would be due, LOL.
But this would be my idea of a street driven set up. No need to go big on the carb. The smaller carb would actually be very crisp and snappy.

A 950 + carb would do very very well in a lighter car and higher stall and gears. It would allow the engine to really sing up top. Like this engine in a Duster with mid 4.xx series gears and decent converter. This would really be a great runner.
This wold be my idea of a street strip like ride. The carb would have to be dialed in well and the gear ratio wold make it feel snappy rather than a smaller carb with high velocity through it.

[thatwasfunny]

830 chokeless race carb w/annular boosters or 950 if your in it all the time.

[rumblefish360]

Originally Posted by thatwasfunny

830 chokeless race carb w/annular boosters

For a street ride? A Chokeless carb? Well, as a New Yorker, seeing how the weather can be chilly, I'd opted for a choke, to at least be swaped in and out for the weather changes. Not that thatwasfunny's choice is wrong bad or otherwise, it's just my view and what I would opt for. A choke.

[valiant64]

I doubt he really will need to use a choke in Australia. What do you have for rear gears & converter stall speed? If it's a street only car, I think you'll be better off with either a vacuum secondary Holley or air valve secondary carb like either the big Carter AFB/AVS or Thermoquad since you're using an auto trans. But regardless, I'd say something in the 850-950 cfm range would work fine.

[DartGT66]

I live in Finland, and haven't needed a choke in my holleys either. And about 1/2 of the year itäs pretty cold in here. Actually, the manual chokes have never even worked for me. Automatics are a different story, since they have the vacuum system to open the air flap when the engine can use the air, but the manual choke really "chokes" the engine.

For a 500, you propably start seeing a power gain after about 5000 rpm using a bigger carb than a 750.

[dodge440]

Thanks for the replies guys. My gear ratio is 3.9 and the stall is 3000 rpm.
The cam is good to 6000. The 850 Demon seems to lay down over 5000, but then fouls the plugs when cruising around town, so much so that it couldn't pull the skin off a custard.
As for the weather here, we have just had record length heatwaves, and I have problems keeping the car cool, so no need for a choke. Never seen snow here either..

[thatwasfunny]

Check the your vacuum reading ,if auto-in gear w/foot on brake,
If manual- neutral what ever the reading is install a power valve rated 4inch less than what you have for a reading-see the power valve could be open all the time which will do like you are saying along with other things.
If after doinfg this you get a stumble off idle then you need to increase you shooter size probably somewhere around 42 especially with 3000 stall remember to use the pump cam holley recommends in relation with shooter size . Now if the jetting is on or close then you might wanna put a higher heat range plug in it so it will clean it self better.
Regardless you probably need to install new plugs to get an accurate read [if yours are fouled like you say.
Tell us what cam is in it.

[crisser]

This should be a good carb for 500 CID. The 4 corner idle should help with any chokeless issues. http://www.holley.com/0-80513-1.asp

[dodge440]

The power valve is good, standard 65, I changed it just in case it was faulty.
I did go to colder plugs than I had with the 1050, mainly because that was a race carb, and ran rich no matter what. The cam is a MP solid cam, 284 deg .528" lift, heads ported stage 6 etc
I checked out the above holley link, maybe a little too radical..???

[thatwasfunny]

Ok let me get what your saying , so you did check your vacuum at idle and it indicated that you need a 6.5? I say go hotter on the plugs if they are fouling unless you get detonation.
What jets are you running and what shooter size?
Demon's are, from what I know/experienced are a little lean out of the box.
What kind of timing do you run?
BTW that cam is a bitchin piece.

[crisser]

Originally Posted by dodge440

I checked out the above holley link, maybe a little too radical..???

Remember, the HP series is rated higher than the old Holleys. That carb has the same size venturis and baseplate as the old 850. So, it`s like a modern 850. A 500 cube engine is large, even if it had a small cam, it`s got a big appetite.

[dodge440]

I am running #85 primary and #93 secondary jets, 31 shooter. all of which is straight out of the box.I have opened up the high speed air bleed to .033. This was all done on a chassis dyno.
Timing is 14 deg at idle, all up 34 deg.
There's not a lot of strokers around here so not a lot of tuning knowledge.
The holley link took me to a 1000cfm race carb, that's why I said it was a bit too radical.

[crisser]

Originally Posted by dodge440

I am running #85 primary and #93 secondary jets, 31 shooter. all of which is straight out of the box.I have opened up the high speed air bleed to .033. This was all done on a chassis dyno.
Timing is 14 deg at idle, all up 34 deg.
There's not a lot of strokers around here so not a lot of tuning knowledge.
The holley link took me to a 1000cfm race carb, that's why I said it was a bit too radical.

What carb is this on? What is the idle vacumn? And, does it have a rear PV?

[dodge440]

BG 850 Mighty Demon, idle vacuum 12psi, no rear pv

[crisser]

So the problem is what? Rich at low speed and flat above 5000? And was it flat above 5000 before you changed the high bleed?

[dodge440]

yes, rich at low speed, flat over 5000, and was flat before we changed the bleed. The above was the reason I had the carb tuned. The 1050 ran rich right thru, which is a reason why I need a street carb, but which one.
BG says the mighty demon range is for radical cam/race motors, so maybe this is a cause of the richness down low. I cruise this car, we don't have a drag strip here.
I run MSD ignition, so no probs with the spark.

[crisser]

I see that carb comes with a 038 idle feed restrictor. Might want to go down to 035. But first, check that the transfer slots are not exposed too much. They should look square and not long. Use the "idle eze" to set idle speed and not the throttle plate screw. That`s why they added the idle-eze. On the high speed flatness, is it going rich or lean?

[dodge440]

the transfer slots are fine, the idle was set with the idle-eze.
the carb runs slightly on the rich side over 5000 rpm on the dyno, I have an autometer air ratio meter in the car, and that also shows slightly on the rich side on higher rev range.

[thatwasfunny]

What's the A/F meter read @ wot 5000 rpm-up 12.1?