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#1
11-28-2006, 11:51 PM
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carby help
My setup
318 with mopar P4452992 .474/.474 cam 3200 stally stage2 904 reworked heads with 1.96/1.6 vales weiand manafold duel exhaust/pacemaker extractors 3.23rear end (Aussie CL Charger) Am currently using a 600cfm holley but its leaking from several places and is just running like crap (bogs down up top a bit) slightly sluggish of the line too. Was working fairly good for a while until it started to leak. I want to replace this carb with a new carb (brand new) just wondering what you guys suggest. Im still thinking of going with a 670 street avenger but some people suggest the edelbrock 600 or the 750 carbs. What do you guys suggest? 
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#2
11-29-2006, 12:56 AM
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#3
11-29-2006, 01:39 PM
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Which Weiand is that? If it is the spreadbore intake, I like the T-Q over the Rochester myself. If you can find a electric choke model, your in great shape. Easy on with a single wire for the choke. The Rochester is an idea. They do make'em new.
On your idea of a 670 avenger, it might be a bit much cfm wise for a street driver. But doable. A 750 is to much and a waste of time and cfm on that engine and build. The Edelbrock @ 600 cfm is just replaceing one style of carb with another , cfm wise. I really think 650 is the limit while looking at the build specs.
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#4
11-29-2006, 07:33 PM
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k16, you might be well advised to try a proper rebuild of your existing Holley if you're into doing that sort of thing. Get a manual to walk you through it. Save $$ as well. But if you want to replace it as you mentioned, and you have a SPREADBORE Weiand you might go with the Rochester as they're available new from Edelbrock. As for TQ's sure if you can get them in Oz, otherwise not easy to deal with. I think some (years?)International trucks came with the electric-choke type. Mopar TQs all had the divorced-choke set-up and you need the factory manifold for that.
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#5
12-01-2006, 12:54 AM
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#6
12-01-2006, 10:09 PM
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You could consider an AVS for a 383.....easy to tune.
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#7
12-02-2006, 01:11 AM
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Remember that the rule of thumb for carbs is your cubic inches times two equals what your carby cfm should be+-. 318x2=636. A 600 Holley is perfect(if you ask me,but I run Holleys only and have never bought a brand new one),but I would fatten up the jets to 66's,or 68's.
Rebuild it. Check your manifold vacuum at an idle. If it is below 8,run a 5.5 power valve and take out the 6.5. Learn to tune it in. Study up on it.  It will save you a lot of talking and money. For years now,Holleys were all you'd ever see at the strip(with the big boys-12 seconds and under) and there's a reason for that.
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#8
12-02-2006, 08:05 PM
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#9
12-02-2006, 08:41 PM
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Reason for that (IMHO) would be that Holley and the clones are the only ones to provide product and do the marketing for high-power, full-race aplications. Edelbrock (nee Carter) develops and markets product for the street/strip folks. That's my theory for this week. What's yours?
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#10
12-02-2006, 08:50 PM
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I remember a pro stock Camaro with dual 1000cfm TQ's and a tunnel ram on it back in '69 or so.
Was it Dick Harrel?
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#11
12-04-2006, 10:26 AM
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Quote:
C.I.D. x R.P.M. / 3456= CFM
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#12
12-04-2006, 10:43 AM
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Quote:
Quote:
(John Lennon) Quote:
That would do the trick
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#13
12-04-2006, 02:54 PM
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There's a problem with the C.I.D. x R.P.M. / 3456= CFM formula for a race car. Well, not with the formula itself, mathematically it is correct, at least once you also multiply the result by the volumetric efficiency of the engine. The problem arises when you attempt to select a carb based on the results. If you use the CFM rating given, and buy a carb with that rating, you will need to generate 1.5 inches of manifold vacuum in order to obtain that flow. Oops, sorry. You just lost your race. Your carb is too small! Why? Because at 1.5 inches of vacuum, you are restricting your engine from achieving maxiumum volumetric efficiency. You do need the amount of flow the formula predicted (once you have also adjusted for V.E. as well), but you need to get it at 1 inch of vacuum or less. So how do you calculate that? By using the square root of the ratio between the vacuum used to rate the carb, and the desired vacuum at which you wish to generate the required flow. Let's use an example to clarify:
The formula says that at 100% V.E. and 6000 RPM, your 318 needs 552 CFM. You have determined that you can have no more than 1 inch of vacuum in order to achieve 100% V.E. (we can go into how to do that in a different thread), so the ratio of rated vacuum to desired vacuum is 1.5 / 1, or 1.5. The square root of 1.5 is 1.225, so you multiply that by the rated CFM. 1.225 * 552 = 676 CFM. Even a little more than the Old Guy Racer rule of thumb, actually. But pretty close (am I an old guy already? Funny, I don't feel old, most days anyway! Maybe Shaun is an old guy.) If you wanted to keep vacuum below .75, the required carb would need to flow an advertised 780 CFM. Keep in mind that this is for maximum performance only. For acceptable street behavior, you wouldn't want a carb that big.) Or would you? That's the great thing about vacuum secondary carbs (or "air demand secondaries" to be technically correct, as was pointed out in another thread.) You can go big, and still maintain streetability, especially with a spread-bore design like the Thermoquad. I personally prefer Holleys, but it is hard to deny the bolt-on-and-go ease of the Carter-style carbs. So what does that mean I am recommending to k16charger? Well, ah, um... I guess I was just babbling! The point is though, if you go with a Carter-style carb, go bigger than 600.
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#14
12-04-2006, 07:14 PM
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Good post 72
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#15
12-04-2006, 09:17 PM
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How about the edelbrock 650cfm thunder series? They seem cheaper here then the street avenger ($595 for the avenger $490 for the edelbrock)
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#16
12-04-2006, 09:31 PM
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Stick with a 600 Holley and tune it in. They will flow 650 cfm's(or close),no mumbo jumbo.
You will do very good to get 85% Volumetric Efficiency,no matter what you do,or where you live,unless you are very good. Point is,the old way works best. But by all means,if you think you can get a 750 to run better than a 600,on a little engine-go for it. 
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#17
12-05-2006, 09:42 AM
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Hell I used a 450 vac. sec. carb. on a 360 because it was what I had. 72, I totally understand what you are saying but at the same time you really need to make sure that when you are using the math, you actually put the true info that you are going to turn the motor and figure you v.e. as you said. I forgot that step. Even if you leave it it will put you pretty close to what it would want. I don't beleive in the cid x 2 method is all that I am saying.
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#18
12-05-2006, 01:37 PM
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Remember that the CID X 2 method is a rough rule of thumb for racing, not for the average street vehicle. I prefer the formulas because they are more accurate. They are also much more critical if you are using mechanical secondaries, which in my opinion only belong on race cars, or street cars that see more racing than cruising and are otherwise set up to handle the extra airflow. My point was that there is a lot more to figuring the right carb than just using a rule of thumb, or even a very precise formula. That's why I strongly recommend vacuum secondaries for street cars, because they are more forgiving of mistakes.
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#19
12-05-2006, 02:04 PM
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#20
12-05-2006, 02:39 PM
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#22
12-05-2006, 09:40 PM
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Here's food for thought....
 -Your manifold has alot to do with how many cfm's you can,or should have(along with head flow,cam,exhaust and cubes). I've ran many hot 318's and never did any better with a 3310 vs. a 1850. But with my last build,my 440,I broke in the cam and ran(for a hundred miles,or so) a 3310,on top of the ole Torker mani. It ran very well. I had 76 jets in it,or 74's(can't remember) and had a 50 cc pump squirting through .045 shooters and the weak spring in the seconds.  Well,I knew,by the crude formula and by what I have in the 440,that I would benefit from more carb(cfms). So I bought an 850 Double Squirter. Meanwhile,I bought a Team G mani,with the 4150 flange. I put the 3310 on it and she didn't want to run. I fattened up the jets and she ran better,but still like %#@*. I borrowed a race setup 4779 from my buddy and at WOT,she was really getting the air/fuel thing right.  So,when I got the 850 DP,guess what? She ran even better. Opening her up is TOO much fun. Poor ricers. So,remember what I learned. It's not just your cam,head flow,exhaust and cubes. It's your mani,too. I still think you will do fine with a 600-1850. Fatten her up to about 70 jets and fiddle with the shooters and run that weak spring-maybe cut one down. Good Luck, Shaun
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#23
12-06-2006, 10:50 AM
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#24
12-07-2006, 06:29 PM
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Ill throw in a graph out of Vizard's book on Carbs. It takes the cam duration into effect to help estimate the VE of a motor and how it related to a correction factor. The different numbers on the graph represent level of modification, 6 and 5 are stock and street, then it goes down into exotic heads and carburetion so #5 would be a good reference.
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#25
12-10-2006, 10:32 PM
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Pissed off
Decided to get my current carb rebuilt. Took it to a local carb rebuilder (has a good rep),
Paid the $200 he wanted to rebuld it and picked it up the next day after work his shop is now closed for xmas car was parked outside. Started the car and it ran like shit. Carb isnt leaking and look good he has fitted a fuel rail. There is a loud knocking sound kinda like a bad lifter coming from the drivers side and a fairly loud whisleing noise comeing from near the carb. Car backfires and stugles to rev past 500rpm on idle. I Still drove it home as i had no choise only 1k up the road so not too bad. Cant take it back and $200 bucks later it runs like its been flogged to death. Took the carb off and tryed another carb and it ran a bit better still has the knocking sound and that whistling sound (air leak my mate says) Will be looking at filing a complaint with fair trading commission after xmas ....sign I hate this shit!! So much for crusing in xmas
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#26
12-11-2006, 12:05 AM
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#27
12-11-2006, 04:24 PM
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Pissed off is right!! However, I got a feeling your problem isn't the carb, especially since you tried another with little improvement. Big air leak somewhere? Crossed plug wires? buggered-up cam timing (slipped timing chain)? I'm not much help but I'd be looking at other possibilities.
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#28
12-11-2006, 08:49 PM
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Whistling is throttle shaft or extremly lean condition due to vacuum leak.
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#29
12-17-2006, 01:44 AM
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Got it runing a bit better now seemed to be a electrical problem. Weak spark made it idle rough also fitted new coil/plug and leads made it run a bit better.
Whislting was due to the replacement gasket. Was told to use a thicker gasket and that solved that whisling noise. Carb I'm still not happy as its started to leak again out of the same place the power value Also had a exhuast leak. Fixed that When buying a new carby whats best a manual or electric choke? Whats the pros and cons of each? (Im gona buy the 670!)
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#30
12-17-2006, 04:32 PM
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Personally I prefer an electric choke but I get winter here also. Manual is fine as long as one remembers to shut it off. One could rig an indicator light to remind one, but one could rig an electric choke about as easily. I'm pretty sure either Holley or Edelbrock chokes are simple to set-up so use whatever works for you.
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