Carb selection help, please ?

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'70_Duster_340

'70_Duster_340

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I don't know the duration and lift of the cam in the '70 Duster 340, but it's a direct connection purple shaft ... It's bored .30 over ..The heads are pretty stock except for heavy duty valve springs, and now has hooker headers w/ a 2 1/2" exhaust system ...

The Carter AVS seems to be my trouble now, after installing a new tank and pump ... I'm thinking of buying a Holley street avenger carb for it and am not sure about what size to get ... The Holley carb selector gadget on their website says anywhere between 650 and 770 CFM ...

I want to choose the right carb ... Suggestions anyone ??

Thanks a lot !
 
Your probably bestter off with the 670. You said preety stock. This leads me to ASSUME iron intake and exhaust manifolds.

(EDIT! I just realized headers. I still stay with what I wrote. You'll be happier with somthing a tad small rather than a tad large.)

Well, we'll need the rest of the info of the car starting with the drivers intentions. (Knowing the cam would be a big big help)

Pure street or street strip.

Weight of car
tranny
stall converter (If it applies w/an automatic trans of course)
Gear ratio
tire size
 
Hey Rob ... Thanks

I'm guessing the car is right around 3000 lbs. I gutted it right down some time ago and don't plan on putting everything back ..

The trans is a 727 w/ a Cheetah turbo action valve body, reverse pattern, manual shift with no gear braking in 1st .. stock converter

14" tires on stock ralye wheels ... 3:91 rear end .. stock intake

Planning on probably more strip than street, but still want to keep it driveable on the street ...

I wish I could find the papers on the cam, but I've had this car since I was a kid..bought it in 1978... and had the motor built a couple years later when I blew it up .. The memory isn't what it used to be !! :(

Kenny
 
NIce, long time owner.

The wheel size would be 225/70/14? Rim size alone means nuts. He he he.

I'd still wonder about the cam. Ummm, heads are stock minus springs?

MoPar used to recomend there 292/.509 cam with non-ported heads IIRC. That cam could be large(ish?)
I'd still stay with the 670 Holley. Plenty of cfm for ethier. The larger carb can make it muddy down low even with the 3.91's.
 
Yea, I have 2 kids, 18 and 23 who can't believe I bought the Duster a week after my 21st birthday back in 1978 !! .. It had 78K on the odometer and 84K on it now ... The engine was built in 1980 or so... The guy who built it for me is still building engines so now that I (almost) have the car to the point where I can drive it, I'm gonna stop down and see what he remembers about it..I'm pretty sure the heavy duty springs are all that were done to the heads...I remember I was working down near Norwalk, CT back in those days, and there was a Chrysler dealer that had alot of direct connection stuff.. I'd stop in week to week and stock up on parts as I could afford it, and then brought them all to the builder .. I think I paid something like $700 for his labor ... (probably couldn't do heads for that, these days)

205/70/14's on the front and 205/60/14's on the rear ... Thanks for pointing out my numbnuttedness !! :mrgreen:

So while I'm still feeling stupid, when you say "muddy down low" I'm guessing that means you think it'll bog down alot at launch ? I wouldn't want that for sure ...

The stock AVS seemed to do the trick pretty well, but it won't idle for crap and every now and then she's totally flat accelerating... won't start hot, etc.. I think it's probably all gummed up from sitting around so much.. Do you know what the CFM's are on that stock Carter ??
 
A rebuild kit for that AVS isn't that expensive. Carbs are really easy to rebuild. Some spray carb cleaner, compressed air, small scrub brush or toothbrush, etc. Those AVS's were my favorite chrysler carb. If you need to replace it, try the Edelbrock Thunder Series. They're AVS carbs.
 
I like the AVS myself.

Muddy feeling down low. Not bog. But when you hit the gas, it has a sluggish response. Not snappy. Smaller carbs have higher velocity and this helps atomize the fuel for a better burn. Large carbs on small motors are best suited for HI RPM.

According to the old Carter tech line, they told me 630 cfm for the small Carter AVS. Dons right about the rebuild kits. Cheap. Cleaning the carb is the battle. Blow it out with air after soaking.
 
I might give rebuilding a shot, even though carburetors always intimidated the **** out of me ... I suppose I don't have a whole lot to lose. I just wish I understood carbs a little better.

Don, you like the Edlebrock over the Holley street avenger ?
 
FWIW, I have a 360 that is right around 370 HP. I have had 600, 670, 725 and 750 cfm vacuum secondary carbs on it.

The 725 and 750 have a noticeable advantage above 4500 rpm compared to the 600. BUT, below 3500 rpm the 600 has a huge advantage in throttle response and driveability over the 725 and 750. FWIW, the car with the 600 has run a best of 13.7 @ 102 with a very traction limited 2.2 sec 60' so the 600 wasn't hurting performance much. The trap speed and 60' time suggest that that I easily have a low 13 second car if I sort out the traction issues.

I just recently purchased a 670 Street Avenger and this has to be the closest to a plug and play carb I have ever had. The only thing besides setting the idle speed I have done with it is play with secondary springs. Jets, idle mixture, accel pump are all as spot on as I can get it with a dyno.

From a performance standpoint I can't feel the difference in top end compared to the 725 or 750 and it has all the throttle response and driveability down low of the 600. Plus it gets 5 mpg more around town compared to the 725 or 750 and about 2.5 more than the 600.

If your car is primarily a street driven vehicle you will be much happier with the 670 compared to the 770 IMHO.
 
Ask Jesse at Bigs Performance in Altoona, Wisconsin. He did a Holley carb for my 67 Satellite with a 440. It really ran good with his carb. Jesse is very helpful. Bigs phone number is 715-835-3726
 
Thanks for all the input guys, I appreciate it .. I'm mulling over options and reading all I can, and of course using the input I've found here more than anything ...

Dave, that 670 avenger sounds almost perfect for what I want ..I really wanna keep that low end snap ... I've also got a good deal on the table for an Eddy that's nearly new, so lots to consider over the weekend ...

Thanks again for all the replies, you guys rock !!

Kenny
 
I decided to go with the Holley Street Avenger 670 ... Shopped around quite a bit and the best price I found was from all places, Amazon.com ... $320 w/ free shipping ... I'll let you guys know how she runs .. I'm sure I'm gonna need some tips tuning it (if I have to) but maybe I'll get lucky and it'll be good right out of the box ...

thanks,

Kenny
 
Best of luck with it Kenny. I think you'll like it alot. Take your time tuning, one step (Change) at a time. Drive it warmed up and for a few miles before you change it around again.
 
I don't claim to be an expert on this, but I'll tell you my experience. I have a built 360 in my '62 Valiant with "J" heads and 10.5:1 compression. I started out with an Edelbrock Performer RPM square-bore manifold and a Barry Grant Speed Demon 670 CFM (square-bore) carb. I didn't like the way it ran. Then I switched over to an Edelbrock Performer spread-bore manifold and a ThermoQuad off an Olds "W" car (I don't know the CFM rating of that carburetor). I like the way it runs with the spread-bore manifold and carb a lot better than the square-bore. IMHO, there was a reason why the factory equipped these cars with spread-bore: that's what they were designed for.
 
Bill Crowell said:
I don't claim to be an expert on this, but I'll tell you my experience. I have a built 360 in my '62 Valiant with "J" heads and 10.5:1 compression. I started out with an Edelbrock Performer RPM square-bore manifold and a Barry Grant Speed Demon 670 CFM (square-bore) carb. I didn't like the way it ran. Then I switched over to an Edelbrock Performer spread-bore manifold and a ThermoQuad off an Olds "W" car (I don't know the CFM rating of that carburetor). I like the way it runs with the spread-bore manifold and carb a lot better than the square-bore. IMHO, there was a reason why the factory equipped these cars with spread-bore: that's what they were designed for.
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I wish I could tell you guys exactly how the Holley is performing, but until I resolve my brake booster problem all I can do is rev it up in the garage :banghead: .... She sure seems to be wide awake now, and can't wait to get her out on the road ... Wish my floor wasn't in such good shape, or I might just cut a huge hole in it and make a Flintstone machine :smile:
 
Hey Bill. Welcome aboard.

Posted by Bill;

a ThermoQuad off an Olds "W" car (I don't know the CFM rating of that carburetor). I like the way it runs with the spread-bore manifold and carb a lot better than the square-bore. IMHO,
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GM's came with a Rochester. Very similar in a manor. The vacuum secondary carbs are very good for the street and when these carbs are dialed in right, there real good.

there was a reason why the factory equipped these cars with spread-bore: that's what they were designed for.
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There an emissions carb and designed to be as such. Nothing more.
However, there was talk between the auto makers and the carb makers. They all wondered out loud near each other and said something like,...

Auto guy talking to another auto guy....

"Damn, we need this carb to perform super in our super stock class. Do you think it'll have enuff CFM to run?"

Carb guy..."I think I can make some adjustments"

Auto guy...."I hope it can whooop *** from a dead stop and wide open throttle."

Carb guy...."I think I can make it work."

Auto guy..."I hope they can make tuning kits for the track guys."

Carb guy...''I think we can do that. You know, we make things happen."

LOL
 
"GM's came with a Rochester."

No. You are failing to distinguish between standard GM fare and the Olds "W" cars, which came with a TQ because the large, spread-bore secondaries gave better performance than an equivalent square-bore carb.

"There (sic; "they're) an emissions carb and designed to be as such. Nothing more."

No. You are failing to distinguish between an early TQ and a late one. The early TQs were no more of an emissions carb than any other carb of that era, and they were used on some very high-performance vehicles. Late TQs were definitely emissions carbs with an electric bowl vent, non-adjustable idle jets, etc. Early TQs gave excellent performance due to their huge secondaries.
 
Oldsmobiles came with Thermo-Quads! Noooooo way!
I'd like to see some ref's and for surely pictures if you got'em.

I do have to admit this one real fast, the first T-Q's were race carbs. On the production line for the first years they came on MoPars, they were not of a smog design, but not race ethier. You said this;
no more of an emissions carb than any other carb of that era,
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I couldn't agree more.
So, yep! I failed there. LOL!

I have a few on the shelf. There just waiting for an engine. He he he.

Oh, thanks for the spelling correction. Your not going to be the new guy to follow me around and correct me to high heaven are ya? You'll be busy!
 
Weren't Rochester carbs a spread bore design too? For sure they use the same air door design on the secondaries as a TQ.

Also, according to Wikpedia they switch from 3 2bbls to a Rochester Quadra Jet in 1967 for the W30 option.
 
Update;

I got the brake booster so now I've been able to road test the car ... Been doing small tweaks here and there and this is where I'm at ....

If I power brake to about 1500-2000 rpm's and mash it to the floor, she seems to get right up and run strong to 6200-6400 rpm's, but if I'm driving along at say 30 mph and mash it, there's a stumble or hesitation, and then she puts ya back in the seat ....

The avenger came w/ 3 springs for the secondaries .. I tried both the lighter and heavier but not much of a difference....

I should also state that I did a compression test this week, and 6 holes were right around 135psi, #6 was at 115, but #7 was only 85psi... I squirted some oil in the cylinder but stayed at 85 so I'm thinking valve guide or stuck valve or something in the head ??? Also, can't get the car to idle for **** at a stop light with the brakes on ... need to keep the idle pretty high to avoid stalling....

thoughts ?? help??

Kenny
 

Try advancing the initial timing some. That should help with the stalling in gear.
 
dgc333 said:
Try advancing the initial timing some. That should help with the stalling in gear.
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Hi Dave ...Thanks.... I've tried the timing all over the place.. seems it runs best when it's advanced so far that the vacuum advance hose off the distributor is nearly crushed into the manifold...I have no idea what the timing of this thing should be so it's always been by ear, holding the throttle around 3,000 rpm's and feeling for that sweet spot...

Kenny
 
'70_Duster_340 said:
Update;

If I power brake to about 1500-2000 rpm's and mash it to the floor, she seems to get right up and run strong to 6200-6400 rpm's, but if I'm driving along at say 30 mph and mash it, there's a stumble or hesitation, and then she puts ya back in the seat ....
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It could be worn plugs or not enuff pump shot.

The avenger came w/ 3 springs for the secondaries .. I tried both the lighter and heavier but not much of a difference....
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You'll probably need the track to see any difference if you can't see/feel it.

I should also state that I did a compression test this week, and 6 holes were right around 135psi, #6 was at 115, but #7 was only 85psi... I squirted some oil in the cylinder but stayed at 85 so I'm thinking valve guide or stuck valve or something in the head ???
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It's worth a check. What about a worn out cylinder, bad rings/ broken rings?


Also, can't get the car to idle for **** at a stop light with the brakes on ... need to keep the idle pretty high to avoid stalling....
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WHat is your vacuum reading at idle? Where is or how is your distributor set up and timed? Did you dial in the cam? How far open is the butterflies of the carb? Check choke setting?



Kenny
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Good luck with this. It's not easy figuring this out via the net.
 
Thanks for the suggestions Rob, I hope to get some time to tinker with it some more before the roads get too crappy ... 2" of slushy snow today !! I did do a vacuum test a couple weeks ago but can't remember the #'s, only that it was a little low ...

The plugs, wires, rotor, cap and electronic box are all new .. The cam would have been dialed in when I had it re-built, right ? The timing is a pain in the butt.. The distributor is in the rear, and the only way she seems to wanna run is by turning it to the left (standing on the drivers side) until the vacuum advance hose just touches and slightly bends on the intake manifold...

It's a little frustrating, but it's also cool to tinker with this car again after leaving it sit for the most part, for the past 25 years ... I'm planning on pulling the motor and trans out this Winter and will at least have the heads re-done, and hopefully do a little body work and re-paint it .. It's a fun project and can't wait to get it up to the track in Lebanon next year ...

Kenny
 
The cam would have been dialed in when I had it re-built, right ?
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No. Unless it is itemized and payed for. A dot to dot alignment should be OK.

The distributor is in the rear, and the only way she seems to wanna run is by turning it to the left (standing on the drivers side) until the vacuum advance hose just touches and slightly bends on the intake manifold...
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Not enuff room huh? Pick up the distributor and move it one tooth over so it will give you a little extra room.

Lebanon next year ...
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Where are you? Might see you there. E-town is closest to me. I wonder about it time wise as compared to the other track in N.J. straight out from N.Y. instead of turning south in N.J.

I tried to make E-town Saturday past and it took 3 hours to arrive to late to get in. Leaving late is a death kiss some days. Amount of racers is the other half. I couldn't go Sunday, the last day.
Oh well, next year, March 2.
 
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