bayyum
Well-Known Member
i would go with 750 if i were you, 650 is better for modified motors, and you said you were running stock
650 or 750 cfm. carb??
- Thread starter 74scamp360
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74scamp360
Junior Member
stock for now, the whole point is is that it's not going to be stock for long and i don't wanna buy another carb. after i do some work to it. I've got a 318 thermoquad which i believe is an 850, i'm not really interested in using it though so...
stroked 340
Banned
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I think you have that backwards 650 would be more suited for a stock motor..750 for a modified one..:-D
74scamp360
Junior Member
ok, so who out there has used a 650 edelbrock on a stock or modified 360?? i know that there must be some out there. what did you think of it? ever race it? if so how does the carb. work. I just wanna get it right the first time and now i see people saying in other forums that a 650 will not do if the car is going to be raced?? I won't be at the track every weekend but when i am there i want it to work properly and not being starved for gas. Thanks again guys your input is appretiated!!
dgc333
Well-Known Member
If the carb is set up correctly it won't be starved for gas regardless of what size you have. The worest case you can expect is the carb presents a slight restriction and will make a couple of horsepower less than a 750 and the car will be 0.1 sec slower.
Do your self a favor and size the carb for what the majority of your driving will be.
Do your self a favor and size the carb for what the majority of your driving will be.
Hey 74 You could call this fella, JESSE he very easy to talk to and set me up good as far Im concerned Not cheap tho. Had a DEMON 650 before this not gona run it down, but like this new HOLLEY better. My opinion D http://bing.search.sympatico.ca/?q=BIGS PERFORMANCE&mkt=en-ca&setLang=en-CA
74scamp360
Junior Member
dgc333. thanks a lot for the tip, that helps a lot and like i said the majority will be street driven with a little fun track time so i think i'll go for the 650. thanks again
dougie800, thanks for the tip, i wish i had more to spend on a carb. but unfortunaly i'm on a fairly strict budget.
dougie800, thanks for the tip, i wish i had more to spend on a carb. but unfortunaly i'm on a fairly strict budget.
larryo340
Member
My 340 never idled good and just didn't feel right with the Holley 750 DP mechanical secondaries then I put on a speed Demon 750 DP mechanical secondaries without choke, and the car never ran so good. The Demon ran great right out of the box.
Im just repeatitng what was told by reputable builders to me! Guy that built my 340 said about my Speed Demon "Get rid of IT". Fella from Engine shop Told me the "FUEL curve Is Horrible on them, make same top end power on Dyno as A HOLLEY but the way up is where the fall short" Which really doesn't matter If your If like me and not a big time Racer. But did find My car ran better with the Holley. I had a 650 Holley Before the 650 Demon, then went to a 750 Bigs Holley glad I did. Just my experience and what Ive been told. To bad just sold My Speed Demon for $200.00 on kigijii few months ago, D
MopaR&D
Nerd Member
I think a 650 Edelbrock AVS is a good choice; the adjustable secondary air door will allow you to fine-tune it more as you upgrade the engine. I've ran an Edelbrock 600 AFB on my 318 and it worked great (even got 1.5-2 MPG better than my ThermoQuad). ThermoQuads are great too but you'll need to do a LOT of tuning to get one to run any better than a "new" Edelbrock, and you'll probably have to re-do all of the jetting and settings on the carb once you add a cam and other stuff.
74scamp360
Junior Member
ya like i said above i do have a thermoquad but am just not interested in using it really, it's just easier to buy a new one plus by the time i spend some money making the thermoquad decent, it would just be more worthwhile buying a new one. Thanks again guys!!
dgc333
Well-Known Member
You can't compare a Thermoquad spread bore carb too a square bore carb. The primaries are tiny and the secondaries never fully open on a stock or mildyly modified motor. Those big carbs worked only because of the small primaries.
dgc333
Well-Known Member
A bigger carb will not make more power if the engine can't use the capacity the carb has and a 360 turning no more than 6000 rpm just can't use all the capacity of a 750. You can certainly can tune the carb so it will run but you will give up throttle response compared to a smaller carb.
mullinax95
Well-Known Member
CFM......cubic feet per minute, a measurement of the velocity at which air flows into or out of a space. I was talking air not fuel... the fuel can be adjusted.
I'm not going to argue with you on this. Run the small carb I really don't care. I would take the larger carb (750) on a 408 come race night everytime. Don't believe everything you read.
http://www.forabodiesonly.com/mopar/showthread.php?t=75159&highlight=carb
Galactic_eyes
Well-Known Member
I have a Eddy 600cfm on my slightly moded 360 with my total timing set at 36 degrees. I have great idle with excellent throttle response. The 600cfm seems to be a good match for my application. Which is an Airgap intake, Crane cam and the heads have been cleaned up. The block also has been bored .30. All of this going to TTI headers and X-pipe.
Like everyone has said, It depends on what you are going to do with your car. My car sees mostly street use with some track time.
Like everyone has said, It depends on what you are going to do with your car. My car sees mostly street use with some track time.
1wild&crazyguy
Banned
750 dbl pmpr= controlled cfm by right foot.
750 Vac secondary=cfm controlled by foot spring against vacuum.
750 Vac secondary=cfm controlled by foot spring against vacuum.
MopaR&D
Nerd Member
Wait a second... Are we talking about a 360, or a 408 here???
dgc333
Well-Known Member
CFM is volume of air not velocity.
We are talking about a 360 not a 408 and we are talking about a street car that might go to the track once in awhile. I will take a carb that will give me the best response in the rpm range I am going to use it the majority of the time and for a 360 that won't see the high side of 6000 rpm that is something in the 650 to 700 range.
74scamp360
Junior Member
i was talking about a 360 but someone got talking about a stroker 408???
Thanks for the tip Galactic eyes your build and usage sounds nearly identical to what i will be using and it sounds like you've had good luck with it. thanks again!!
Thanks for the tip Galactic eyes your build and usage sounds nearly identical to what i will be using and it sounds like you've had good luck with it. thanks again!!
mullinax95
Well-Known Member
I just copied and pasted the CFM info from here. It was the first one that I clicked on because I was curious of the definition myself as I goggled it.
http://homerepair.about.com/od/termsaf/g/cfm.htm
That was my fault about the 408.. I should have said 5.7/6.1 as you mentioned not 408.... I don't know where I got it.
Tell you what 74scamp360 after rereading the post you need to take dgc33 advise run the carb he recommends.
Galactic_eyes
Well-Known Member
No problem. I have thought about going to a 750cfm but, like the saying,"why fix it if it's not broken." At the track my Duster gets in the high 13's. That is with a 321 gear. I'm sure I could drop my time a little with a higher gear.
Jay_340
Moparologist
How is your carb set up if you don't mind me asking? The 360 in my Duster sounds fairly close to yours, but with the 600 Eddy AFB I have, it has a nasty ping when it gets up in the revs. I have a 650 Holley double pumper that turns the car into an powerhouse, though the AFB is much easier to drive.
BJR Racing
Well-Known Member
IMO I think that you need to tell us what you have in mind for a cam and what amount of head work you plan on having done and is the compression ratio staying the same or is it going to be increased? I don't ever run anything smaller than a 750 VS carb on the street, and alot larger than that on the track. In order for anyone to tell you exactly what carb you really need is a shot in the dark until we know a few things as I mentioned above, as they all have effects on the carb. A 360 that I did with mild head work and a XE284 cam and a Torker II intake and shorty headders needed a minimum of 750 cfm's and we ended up using a 830 cfm carb. Throttle response was great and crisp as you would ever need one. We tried smaller carbs and they were flat just above 5,000 rpms, because they just couldn't flow enough air to satisify the engines needs.
If this is going to be a street only engine and less than 5,000 RPM's 98% of the time then I might consider a 650, but don't expect any big power from the engine. And as I stated before this would be in stock form only, without any considerations for improvements. But from what you stated that you have intentions of modifing your engine then I wouldn't even consider anything smaller than a 750 VS. In fact Holley recommends this for there street avenger carbs,
570 cfm's for 300 HP
670 cfm's for 300-400 HP
770 cfm's for 400 + HP
870 cfm's for 500 + HP
you can get anyone of these with electric choke. A buddy of mine had a 670 on a stock 454 and had problems pulling hills with a trailer behind him. This is in a Chevy Dually, he stated that he was getting 10 MPG with it but couldn't keep up with traffic on the interstate when a hill came up. Then I loaned him my race 780 cfm carb VS and he said man what a difference. Sure his gas mileage dropped but it was because of his right foot. He told me that he no longer had to keep his foot on the floor to pull the trailer, and that when pulling the trailer that he could pull hills at half throttle. He said that he could do 70 mph and it not back off at hills. And the engine was only turning just over 3,000 rpm's.
So my point being that reguardless of engine size a VS 750 is one of the best all around carbs for the street and power and IMO I would use a 770 street avenger. You have to look at it this way also, that your only running the engine on the primary front 2 BBL's most of the time, and if the engine needs more then this can be adjusted by the secondary diaphram springs for when you want it to come in. But it's a simple change.
On my 322 engine with 302 heads I don't run anything smaller than a 750 and in the last few weeks I have had a 9375 1050 Dominator on it, that a friend of mine was having problems with on his 540 BBC engine. I cured the problems with it and he told me to run it so I did. The result was that without dejetting it that it ran just as fast as the 750 did but believe me there was alot left in the engine with this carb on it. Had I been able to tune it to the engine it was on. I would say that with this carb on the little 318 .030 over that it would have run 1/8 mile times equal to low low 11's on 87 octane gas in a 3,330 lbs duster.
I guess I look at carbs differently than most do, I don't like to put the minimum cfm carb on a engine but rather I allow a couple of hundred cfm's more. And this usually is seen in the time slips at the track. If more airflow didn't or doesn't make more power then why did they put Q-Jet carbs on the 231 V-6 engine that Buick ran in there Grand National Cars. I had one of these cars without the turbo and it ran very well, and in stock trim could smoke the tires. The main thing here is to use what ever carb that you want, it's your car/engine and you have to live with what ever you choose. But I know what I would do. And this is comming from someone that has built many different engines and for different purposes and what they required to make them work well.
Oh ok 1 more, my 318 that I had in a 4,000 lbs truck was getting 17 mpg without a OD and it was a 750 VS holley. This was a stock 318 engine and a 727 transmission. And it passed 04' emissions better than the new cars did. It was a 3310-1 and had 78 and 84 jets in it with a 6.5 PV and the air bleeds were 72 and 32 idle and power, with the idle mixture screws turned out 1 turn. The engine had 20" of vacuume.
If this is going to be a street only engine and less than 5,000 RPM's 98% of the time then I might consider a 650, but don't expect any big power from the engine. And as I stated before this would be in stock form only, without any considerations for improvements. But from what you stated that you have intentions of modifing your engine then I wouldn't even consider anything smaller than a 750 VS. In fact Holley recommends this for there street avenger carbs,
570 cfm's for 300 HP
670 cfm's for 300-400 HP
770 cfm's for 400 + HP
870 cfm's for 500 + HP
you can get anyone of these with electric choke. A buddy of mine had a 670 on a stock 454 and had problems pulling hills with a trailer behind him. This is in a Chevy Dually, he stated that he was getting 10 MPG with it but couldn't keep up with traffic on the interstate when a hill came up. Then I loaned him my race 780 cfm carb VS and he said man what a difference. Sure his gas mileage dropped but it was because of his right foot. He told me that he no longer had to keep his foot on the floor to pull the trailer, and that when pulling the trailer that he could pull hills at half throttle. He said that he could do 70 mph and it not back off at hills. And the engine was only turning just over 3,000 rpm's.
So my point being that reguardless of engine size a VS 750 is one of the best all around carbs for the street and power and IMO I would use a 770 street avenger. You have to look at it this way also, that your only running the engine on the primary front 2 BBL's most of the time, and if the engine needs more then this can be adjusted by the secondary diaphram springs for when you want it to come in. But it's a simple change.
On my 322 engine with 302 heads I don't run anything smaller than a 750 and in the last few weeks I have had a 9375 1050 Dominator on it, that a friend of mine was having problems with on his 540 BBC engine. I cured the problems with it and he told me to run it so I did. The result was that without dejetting it that it ran just as fast as the 750 did but believe me there was alot left in the engine with this carb on it. Had I been able to tune it to the engine it was on. I would say that with this carb on the little 318 .030 over that it would have run 1/8 mile times equal to low low 11's on 87 octane gas in a 3,330 lbs duster.
I guess I look at carbs differently than most do, I don't like to put the minimum cfm carb on a engine but rather I allow a couple of hundred cfm's more. And this usually is seen in the time slips at the track. If more airflow didn't or doesn't make more power then why did they put Q-Jet carbs on the 231 V-6 engine that Buick ran in there Grand National Cars. I had one of these cars without the turbo and it ran very well, and in stock trim could smoke the tires. The main thing here is to use what ever carb that you want, it's your car/engine and you have to live with what ever you choose. But I know what I would do. And this is comming from someone that has built many different engines and for different purposes and what they required to make them work well.
Oh ok 1 more, my 318 that I had in a 4,000 lbs truck was getting 17 mpg without a OD and it was a 750 VS holley. This was a stock 318 engine and a 727 transmission. And it passed 04' emissions better than the new cars did. It was a 3310-1 and had 78 and 84 jets in it with a 6.5 PV and the air bleeds were 72 and 32 idle and power, with the idle mixture screws turned out 1 turn. The engine had 20" of vacuume.
Galactic_eyes
Well-Known Member
As far as I know nothing has been done to it. The 360 had a Thermoquad that the previous could not get to act right. He had pulled the 600 off of his Montecarlo. It's been on there ever since.
What octane gas are you using? If I use anything less than 93 it will ping like a mother.
A friend of mine has a 650 DP that we were going to try on my car but we didn't have the bracket for the TV cable going to the trans.
1wild&crazyguy
Banned
You know...I heard that if you get in your car and fire it up, while it's already warmed up, and it don't start unless you give a squirt or 2, the carbs too small.fwiw
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