Bulldozer
free ice cream sandwiches
Lol
Carb question
- Thread starter ramman7284
- Start date
-
cubic inch x 2 . if it don't reach the next 50 go down to the smaller carb. for high rpm HP. go to the next larger. 318 +318 = 636 - 36 = 600 cfm. dual plane/ med. cam. single plane with larger cam use 650 cfm. Always worked for me
ramman7284
Well-Known Member
Hmm I guess I'll have to see what I come up with i might end up goin with a Holley cause in a since I like the way it looks and since its got great throttle response I'm falling more that way cause I love being thrown into the back of the seat
Still learning here
was I wrong or just off? (I know I was just genralizing) Up to this point I've only been a 4bbl,cam and header kind of guy nothing bigger than a 650 carb/340cam, my 273 gonna be my 1st full build.
Still learning here
273;
In an ideal setting ......... 1Hg. is max and zero is right. So to say your "just off" is OK in a good way. Above, I quoted Rick in his method. I also use this method. It is a general way of getting you there. Some will trash it as being to basic and maybe even barbaric LOL! But, it'll work. For a general purpose.
In the 318's math above, this works. Do note you can get away with a 500 cfm carb. It'll also start to pull a few Hg.'s at WOT. This indicates a carb slightly under sized. This is not a bad thing. But a indicator that a larger carb could/can provide more power/performance.
Setting #1;
IF I was building a 318 for mileage with stock manifolds, a 500 could get the nod, I myself would do a 600. It would get the nod for service.
#2. Replacement carb, slight performance enhancement over stock? A 600 would go to work. This carb/engine combo could still be on a stock engine or one with the basic bolt on parts and a cam. Even increased compression.
#3 When the build starts to get hot, a 650 should be employed. Things like a Hyd. cam above 236 @ 050, ported heads, headers, increase stall and 3.91 gears.
These are general settings. Things like increased cam size, manual tranny and higher gear ratios can have the CFM go up 50 cfm. A drag car, a Duster lets say, can use a 750 to 800 on a 318. You'll have to consider that the engine lives on the top end of the RPM scale and should have a weight under 2800 as a min.
What you'll find in your build is once your done. You can try other size carbs and each will have a slightly different effect on, well, basicly everything! Going slightly smaller will increase throttle response and could help mileage. Going larger will decrease throttle response while allowing more top end power. Mileage may drop if you can not tune it well. The bigger the carb (On your mill) the harder it will be to get mileage and a good running engine. The butterflies are to large, open to fast, even if care is taken with the right foot, it becomes difficult.
The signal to the carb weakens and fuel metering become hard to deal with. This is why most times a smaller carb is the one to choose. Better to error on the small side. And yes that means puling a Hg. or two is not the end of the world. Loosing it all together is bad.
You can also couple up the HP level of the engine to a carb size. This also must be done with the intended use of the engine as well as the cars weight, gear ratio and stall, etc.....
The OE Poster said 400 HP. For a 360 small block, a 650 will do for the street. A 750 would be a better choice since the engine is probably one that is a bit cammed with increase compression with the basic bolt on's. Bowl ported heads are possible for this. As stock heads would require a good bit of cam for 400HP.
He wants a cam to cover both bases. Well, a 650 would do it. I'll bet blindly that the 650 on the 360 will pull 1.3 or better Hg.'s.
I myself would purchase 2 carbs, 1 for each engine. Then, once done with them, sell them, roll the money over into the next build..
lmao...
green1
Well-Known Member
Rumble nailed it. Per theory, a stock 350 does best with a 500. Now change the engine- more cam, more flow, needs more cfm. But, over-carb: the vacuum signal to the carb changes, affecting the metering. This screws your whole world up. The carb doesn't know what to do.
This goes back to us installing cams, and putting bigger carbs on. Yeah, got a cam. The idle and total advance now has to be changed. The carb? probably too big. The solution? drill holes in the primaries, replace the power valve.
Yes, get the hg( more $, but it works), get vacuum up, with timing once you learn a vacuum gauge, you forget about a rpm gauge.
Then work on carb. An example, and I will get my butt kicked for this statement; 440, mild cam, 9.0; Eddy 1405 and 1406, ran out of rods and jets ever made, trying to make your eyes stop burning. Non-tunable.
Holley- dis-connect the secondaries. Put aroun, and nail it- read plugs, and adjust accell pump. Hook secondaries, full run. read plugs.
If you feel/hear the secs come in. that was a bog. Need bigger jets on sec, or during the transition, need secs to start later.
And still idle load-up? underneath the secs is a screw, open up the secs more.
First time I tried to tune an Eddy, loved the "no gas on manifold" But Eddy doesn't make the parts to fine tune. Back to the old Holley stuff.
This goes back to us installing cams, and putting bigger carbs on. Yeah, got a cam. The idle and total advance now has to be changed. The carb? probably too big. The solution? drill holes in the primaries, replace the power valve.
Yes, get the hg( more $, but it works), get vacuum up, with timing once you learn a vacuum gauge, you forget about a rpm gauge.
Then work on carb. An example, and I will get my butt kicked for this statement; 440, mild cam, 9.0; Eddy 1405 and 1406, ran out of rods and jets ever made, trying to make your eyes stop burning. Non-tunable.
Holley- dis-connect the secondaries. Put aroun, and nail it- read plugs, and adjust accell pump. Hook secondaries, full run. read plugs.
If you feel/hear the secs come in. that was a bog. Need bigger jets on sec, or during the transition, need secs to start later.
And still idle load-up? underneath the secs is a screw, open up the secs more.
First time I tried to tune an Eddy, loved the "no gas on manifold" But Eddy doesn't make the parts to fine tune. Back to the old Holley stuff.
ramman7284
Well-Known Member
Well looks like I'm buyin a new carb I've tryed to save this one but it just doesn't want to cooperate at all
67dartgtgo
Well-Known Member
ramman7284, you don't say what your running for a transmition or if your car's a 4 speed but Demon carb has been bought out by holley and their new line "street demon" carb is def making some impact. 625 cfm may be what you looking for in a vacuum secondary automatic tranny.
www.demoncarbs.com
Very innovative. I have the 625cfm polymer on my 360/300 crate with a 727, vacuum secondary. Car goes like a raped ape. Very easy to set up with a vacuum gage, and flapper adjustment easy as pie.
www.demoncarbs.com
Very innovative. I have the 625cfm polymer on my 360/300 crate with a 727, vacuum secondary. Car goes like a raped ape. Very easy to set up with a vacuum gage, and flapper adjustment easy as pie.
moparperformance70
New Member
do your self a favor and stay away from edelbrock carbs. if your gonna go the afb style go on ebay and find a 625 carter afb competition series, theyre bullet proof but they stopped making them about 8 years ago but guys still have them new in the box for sale.
i personally would get a base plate for the holley you have; theyre so versital and easy to work on. it will work good on a 318 and a 360 if your not gonna turn anything over 6000 rpm.
put in a 68 jet in the front and a 74 in the rear with about a 7.5 power valve and that 318 will be happy. bump it to a 71 and 78 when you go to a 360, if you need a little more flow just get a quick fuel center body it
thats my thoughts
i personally would get a base plate for the holley you have; theyre so versital and easy to work on. it will work good on a 318 and a 360 if your not gonna turn anything over 6000 rpm.
put in a 68 jet in the front and a 74 in the rear with about a 7.5 power valve and that 318 will be happy. bump it to a 71 and 78 when you go to a 360, if you need a little more flow just get a quick fuel center body it
thats my thoughts
65Val
Average Length Member
...that's, 'cause being a Holley, you're ALWAYS workin' on 'em!....
I prefer Holleys, but I have a 625 carter afb competion series that came on my duster.
This carter carb is about maintenance free as they get.
My duster sits for months at a time, just pull the choke, pump it once and it idles nice and smooth, even when starting at 30 deg F temperatures.
Fixing you holley would be cheaper......
ramman7284
Well-Known Member
Right now I have a 727 in it but I do want to covert it back to a standard hopefully. 6spd but probably end up doin a 5spd and I just bought a 600 Holley dp the 4776
-
