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Old 01-16-2013, 09:20 PM
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Confused about carbs, need help!

I've searched this forum quite a bit and I think I have a basic understanding of carbs. My confusion comes from several sources of conflicting information so I'll give all the information I can about my truck and hopefully you guys can help me figure out what changes I need to make.

I have a '61 chevy short wide that is my daily driver right now but fairly soon will be driven on the street mostly and will see a few runs down the strip several times a year during the summer months. I live in Oregon so that should give me about 4 months a year to play around, so I want it to be streetable and good fun down the strip too.

It has a 12 bolt truck open rear end with 3.08 gears, a TH350 with stage 2 shift kit and 2300 stall. I just bought my boss' old race motor and this is where it gets fun. It's a 350 bored .030 over, flat top 4 relief pistons, forged crank, h-beam rods, 2.02/1.60 valves, 1.6:1 high tensil stamped rockers, Weiand Team G single plane air gap manifold, hei dizzy with MSD module, high output coil, no vacuum advance and the lightest springs available on the centrifigul adv. so it gets full adv. right off idle, I think he said total timing was 30deg. at 3500rpm? 10.5:1 CR and the cam is a summit k1108 (specs below)


RPM Range3,400-7,000
Duration at 050 inch Lift: 244 int./254 exh
Valve Lift with Factory Rocker Arm Ratio: 0.508 int./0.533 exh.
Lobe Separation (degrees): 114
Camshaft Manufacturers Description: Rough idle, excellent high-end horsepower. Needs 10.5:1 and higher compression, 3,500+ stall, and gearing. 350+ c.i.d., bracket race cam.

He says this motor ran 450HP at 6200RPM on the Dyno with some kind of carb style fuel injection system which did not come with the motor so I need to figure out what carb will work on this motor for my application (described above) without changing anything except mayme my stall and rear end. Which brings me to another question (perhaps for another thread)?

I have a corporate 8.5" 10 bolt out of a 79 camaro with 2.41 posi that I was thinking of putting under the truck but I don't think it would hold up with that gear ratio and nobody makes a 3.08 or 3.73 gear set for the series 2 carrier so I don't know if I should change get a series 3 carrier and gear set for that rear end or for the truck 12 bolt, and will the 3.08 12 bolt open rear get me by until I save up the money for the propper rear end solution?

Thanks in advance for all help. You guys are a great wealth of knowlege and I'm somewhat new to the technical aspects of hot rodding though I do have a basic grasp on what will generally make things go faster or slower.

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Old 01-16-2013, 09:47 PM
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Confused about carbs

Someone can correct me if I'm wrong,you only need about a 750cfm carb with vacuum secondaries ,my personal preference is a Holley because of the ease of making quick adjustments.You might run into trouble with running a single plane intake with street cruising.You might also consider going with a bigger stall.I'm not sure what your truck weighs,but I would get some shorter gears and bump the stall to al least 3500 and go with a dual plane intake and a 750 cfm carb.You also want to run a vacuum advance.Hope this helps and ill be glad to try and help with your set up as much as I can
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Old 01-16-2013, 10:16 PM
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I too would use a form of 750 CFM carb. I like holleys.You could also use a quadra jet
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Old 01-16-2013, 10:26 PM
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The truck weighs about 3250lbs. Could I get away with 3000 stall and the 3.08 gears? I know I don't want to get the stall too low for the cam but I don't want to have to get too far into the pedal before the truck starts to move either. I'm used to my 2300 and even it seems a bit high for the factory spec cam that's in the 350 that's in the truck now.
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Old 01-16-2013, 10:33 PM
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Quote:
Originally Posted by CHEVILLAC View Post
I've searched this forum quite a bit and I think I have a basic understanding of carbs. My confusion comes from several sources of conflicting information so I'll give all the information I can about my truck and hopefully you guys can help me figure out what changes I need to make.

I have a '61 chevy short wide that is my daily driver right now but fairly soon will be driven on the street mostly and will see a few runs down the strip several times a year during the summer months. I live in Oregon so that should give me about 4 months a year to play around, so I want it to be streetable and good fun down the strip too.

It has a 12 bolt truck open rear end with 3.08 gears, a TH350 with stage 2 shift kit and 2300 stall. I just bought my boss' old race motor and this is where it gets fun. It's a 350 bored .030 over, flat top 4 relief pistons, forged crank, h-beam rods, 2.02/1.60 valves, 1.6:1 high tensil stamped rockers, Weiand Team G single plane air gap manifold, hei dizzy with MSD module, high output coil, no vacuum advance and the lightest springs available on the centrifigul adv. so it gets full adv. right off idle, I think he said total timing was 30deg. at 3500rpm? 10.5:1 CR and the cam is a summit k1108 (specs below)


RPM Range3,400-7,000
Duration at 050 inch Lift: 244 int./254 exh
Valve Lift with Factory Rocker Arm Ratio: 0.508 int./0.533 exh.
Lobe Separation (degrees): 114
Camshaft Manufacturers Description: Rough idle, excellent high-end horsepower. Needs 10.5:1 and higher compression, 3,500+ stall, and gearing. 350+ c.i.d., bracket race cam.

He says this motor ran 450HP at 6200RPM on the Dyno with some kind of carb style fuel injection system which did not come with the motor so I need to figure out what carb will work on this motor for my application (described above) without changing anything except mayme my stall and rear end. Which brings me to another question (perhaps for another thread)?

I have a corporate 8.5" 10 bolt out of a 79 camaro with 2.41 posi that I was thinking of putting under the truck but I don't think it would hold up with that gear ratio and nobody makes a 3.08 or 3.73 gear set for the series 2 carrier so I don't know if I should change get a series 3 carrier and gear set for that rear end or for the truck 12 bolt, and will the 3.08 12 bolt open rear get me by until I save up the money for the propper rear end solution?

Thanks in advance for all help. You guys are a great wealth of knowlege and I'm somewhat new to the technical aspects of hot rodding though I do have a basic grasp on what will generally make things go faster or slower.
First, what heads? You may not have enough compression ratio for that cam- or it may be too high for pump gas. You'd really like to know the exact chamber volume to take milling the heads (if it was done) into consideration.

All CR figured w/a zero deck/0.041" head gasket:

76cc heads, unmilled decks = about 9.1:1 compression ratio. Milled down to 70cc, will be about 9.7:1.

64cc heads will get you enough, just under 10.4:1, and all the CR you can use w/iron heads, if not too much.

IMO that's just too much cam unless you bring the rest of the engine in line w/it (correct CR, sufficient valve spring pressure, a higher stall converter and lower rear gears).

A 3310 could work OK, or a double pumper (650 to 750) once the stall/gears are dealt with.

The distributor needs to be set up w/a lot of initial timing and a limited amount of mechanical advance. You can use a vacuum advance limited to 10 degrees, hooked to a ported vacuum source.

The 8.5 corporate rear end is strong, but the bearings ride on the axles and are often worn and need replaced. If that's the case, upgrade the rearend to a 30 spline limited slip differential (Eaton is often recommended) and axles to match. It would be better if you posted this on the Trans/Rearend forum...

Edit- my usual calculator is misbehaving, had to edit the results.

Last edited by cobalt327; 01-16-2013 at 10:52 PM.
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Old 01-16-2013, 10:51 PM
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I think the question relating to carbs does belong here.Cobalt,Im certainly not arguing with you as you know the respect I have for your knowledge.

Its just that my opinion is: The carb fits the engine not the gear ratio. The engine is built for a purpose and the driveline is built for a purpose,not because of the others parts short comings.
good example is myself; I use a 3.50 gear ratio because that is what the car needs to perform what I want(not drag racing) My engine has a big cam that a lot of people would say"you should have 4.56 gears for that cam"

4.56 gears would not suit my purpose at all.
so I say,imo,a 750 ish cfm carb is a good choice for that engine.

Will that truck make a fast pass at the drags?
different question
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Old 01-16-2013, 10:56 PM
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3000 stall speed and 3.08 = a big disappointment. The stall you can get by with but the rear gear will make the acceleration poor.
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Old 01-16-2013, 10:58 PM
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Quote:
Originally Posted by vinniekq2 View Post
I think the question relating to carbs does belong here.
Who said it didn't. If you think the gear ratio/stall speed doesn't matter when using a double pumper, I got news... the average Joe ain't gonna like dealing w/a DP carb, a tight TC and high gears.
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Old 01-16-2013, 11:04 PM
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U can use this for your 373 gear in a 2 series carrier.. Mr. Gasket Ring Gear Spacers 908A - SummitRacing.com
...not the strongest, but I used a spacer in my G-body wagon with a stick and fairly healthy 355 after I broke the stock gear, and the new one lived and I'm hard on my junk.
YouTube
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Old 01-16-2013, 11:09 PM
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Quote:
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Who said it didn't. If you think the gear ratio/stall speed doesn't matter when using a double pumper, I got news... the average Joe ain't gonna like dealing w/a DP carb, a tight TC and high gears.
3800# b-body, 2600 stall, OK it had 411's but went from a 650VS to a 750DP and it picked up 2tenths, and was a ton stronger on the street with none of the perceived pitfalls. If its set up right, it can work beautifully.
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Old 01-16-2013, 11:17 PM
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Quote:
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3000 stall speed and 3.08 = a big disappointment. The stall you can get by with but the rear gear will make the acceleration poor.
3.08 gear ratio is not a good gear for launching,true. From 25 MPH up,whats the difference from the 3.08 guy accellerating in low gear and the 3.73 guy accelerating in second gear?

At 60 MPH,in my car,using a 950 double pumper,I can yard the secondaries wfo with out bog or hesitation.In fifth gear my over all gear ratio is 2.87.
I have 5 gears so it makes more sense to go down a gear and use 1/2 throttle.
just saying,if the carb works,it should work at all RPMs
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Old 01-16-2013, 11:18 PM
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Quote:
Originally Posted by CHEVILLAC View Post
I've searched this forum quite a bit and I think I have a basic understanding of carbs. My confusion comes from several sources of conflicting information so I'll give all the information I can about my truck and hopefully you guys can help me figure out what changes I need to make.

I have a '61 chevy short wide that is my daily driver right now but fairly soon will be driven on the street mostly and will see a few runs down the strip several times a year during the summer months. I live in Oregon so that should give me about 4 months a year to play around, so I want it to be streetable and good fun down the strip too.

It has a 12 bolt truck open rear end with 3.08 gears, a TH350 with stage 2 shift kit and 2300 stall. I just bought my boss' old race motor and this is where it gets fun. It's a 350 bored .030 over, flat top 4 relief pistons, forged crank, h-beam rods, 2.02/1.60 valves, 1.6:1 high tensil stamped rockers, Weiand Team G single plane air gap manifold, hei dizzy with MSD module, high output coil, no vacuum advance and the lightest springs available on the centrifigul adv. so it gets full adv. right off idle, I think he said total timing was 30deg. at 3500rpm? 10.5:1 CR and the cam is a summit k1108 (specs below)


RPM Range3,400-7,000
Duration at 050 inch Lift: 244 int./254 exh
Valve Lift with Factory Rocker Arm Ratio: 0.508 int./0.533 exh.
Lobe Separation (degrees): 114
Camshaft Manufacturers Description: Rough idle, excellent high-end horsepower. Needs 10.5:1 and higher compression, 3,500+ stall, and gearing. 350+ c.i.d., bracket race cam.

He says this motor ran 450HP at 6200RPM on the Dyno with some kind of carb style fuel injection system which did not come with the motor so I need to figure out what carb will work on this motor for my application (described above) without changing anything except mayme my stall and rear end. Which brings me to another question (perhaps for another thread)?

I have a corporate 8.5" 10 bolt out of a 79 camaro with 2.41 posi that I was thinking of putting under the truck but I don't think it would hold up with that gear ratio and nobody makes a 3.08 or 3.73 gear set for the series 2 carrier so I don't know if I should change get a series 3 carrier and gear set for that rear end or for the truck 12 bolt, and will the 3.08 12 bolt open rear get me by until I save up the money for the propper rear end solution?

Thanks in advance for all help. You guys are a great wealth of knowlege and I'm somewhat new to the technical aspects of hot rodding though I do have a basic grasp on what will generally make things go faster or slower.
That's alot of cam for "mostly street" and if your not enjoying the small stall you have now your going to hate what that cam will actually require to idle and be right. 373 and 3000 won't cut it, will it work? Depends on your level of tolarence, but you will be much happier with a 355-373 and the stall you have now. If you want to keep it brutal, 3500 - 4000 stall, 750 dp, and 411 gears and hope it never hooks cause you will lunch that 10 bolt.
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Old 01-16-2013, 11:21 PM
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I honestly have no idea about the heads. The story I was given is " There's an old circle track guy in the Denver Co. area that built these heads for all the circle track guys within at least a couple hundred mile radius, about 15-20 years ago. He wouldn't divulge his source for the bare heads. They have no casting #'s and never did. they weren't ground off, they were never there." My boss had this motor in his 41 willy's, which I rode in, and it ran strong. I can't say it ran right because as I said I'm new to the technical stuff, but it ran strong. He did say that when he first built the motor he had an 850cfm Demon carb that was setup by a performance shop on the car and kept sucking the fuel bowls dry, under what conditions I don't know. He also said it has very little vacuum which creates a problem for my power brakes but I can get an electric vacuum pump for that. Seems there's alot of heresay but I do know it's a strong motor in great shape. If I put my 600cfm edelbrock on there, will it run? I have a Q-Jet on my other 350, but it could use a rebuild. Would it get me by?
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Old 01-16-2013, 11:33 PM
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The 600 will work,not a perfect match.You can get a vacuum canister for your brakes. Try that before you buy a vacuum pump. Low vacuum on my car mostly bothers the head lights,brakes work ok as I keep the revs up if Im sport driving.When driving in traffic I notice a firmer pedal. I g
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Old 01-16-2013, 11:35 PM
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Confused about carbs, need help.

The best way to go would be to buy an Eaton 3series carrrier, Motive 373 ring and Pinion. The GM corporate (big 10) rear is just as heavy duty as that 12 bolt. Get the 30 spline carrier and a pair of moser axles. A Hughes GM40 stall converter will help that cam shaft you have. Try a Holley or Demon 750 DP carburetor with that Victor JR. intake.
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