Another help me with my carb selection thread...

[bth0320]

So I have read many an opinion on which carb is best but being new to all of this, I figured I would reach out to get some opinions more specific to my set up. When I bought the 68 RR, the 383 short block was already complete as follows:

4.31 bore (60 over)
3.395 stroke
JE domed pistons .500 height (not sure of cc's but guess around 11) - zero deck and plan on using .040 gasket
Comp Cam XE285HL - 241/247 @ .050 with .545 lift

I have since bought the Edelbrock performer RPM intake/aluminum heads (84cc closed chamber) and in the process of buying everything else I need to put this thing together.

I was originally looking at the Eddy Thunder AVS carbs as I hear they are much easier to tune for guys like me without much experience. I am guessing I may have vacuum issues with my set up?

Also keep in mind that I am in Denver so much higher altitude....

Any suggestions on brand/size would be greatly appreciated!!

 

[RustyRatRod]

I would use a Holley style of some sort.

 

[fatecaptured]

I have had mostly carter/edelbrock carb experience. Which i'm not a carb pro. But they are pretty simple. I have the thunder series carb. Haven't run it yet. I also have two carters. The afb is really basic from what I gather. Holley is the most used and favored of them all. My choice for a holley would be a double pumper. I read mechanical secondary's are the way to go for performance. Demon seems to be a step up from the holley with improved features.

I recommend this video:http://chucker54.stores.yahoo.net/howtosutupee.html
I've watched it like three times. It's very good at explaining things and offers good carb tuning tips. Hope this helps.

 

[747mopar]

Look at all of the professional drag racers, I doubt you'll see any Edelbrocks under they're hoods. I had one and they are deffinetly easy to work on but I had issues with it leaking out of the throttle plate shaft and it vapor locked regularly. You likely wouldn't have the vapor lock issue, mine was on a ford 460 that had a pretty hot cat iron intake. Holley's and Demons are my first choice and they are not hard to tune or work on. My 2cents

 

[Meep-Meep]

First you need to decide how you will use the car. If for street use then I would not use a Holley double pumper or anything else that is considered a race carb. Get a street carb that has well balanced fuel metering circuits. Carbs also rely on vacuum to work properly and the cam you have is pretty big and might mess with carb calibrations because of low vacuum. Flat top pistons even at zero deck on a 383 do not equate to a lot of compression so you may have a bit of a mismatch there. For street you want to stay on the small side of the CFM rating for best all around performance. Get an accurate compression spec by CC-ing everything then pick a cam that is best suited for that number. For pump 91 I hope you have no more than 9.5:1 and you might be able to squeeze 10:1 with AL heads.

 

[Rems440]

Go for HOLLEY 4150hp 750 cfm vaccum secondaries .I have a simular set up to yours and its just a great carb.Has screw in air bleeds too!

 

[451Mopar]

Here in Denver, just about any carb you choose will need some adjustments. Because of the cam and altitude, I would use a Holley style carb.
I have not used the Quick fuel carburetors, but they are well priced for the features they have. The HR-780-VS (Vacuum secondary, electric choke, dual feed bowls, 780 cfm, adjustable air bleeds and restrictions.) $408.80 from summit racing.

I have used Holley street avenger carbs and they do not have the screw in restrictions, and both needed the idle restrictions enlarged.

 

[747mopar]

First you need to decide how you will use the car. If for street use then I would not use a Holley double pumper or anything else that is considered a race carb. Get a street carb that has well balanced fuel metering circuits. Carbs also rely on vacuum to work properly and the cam you have is pretty big and might mess with carb calibrations because of low vacuum. Flat top pistons even at zero deck on a 383 do not equate to a lot of compression so you may have a bit of a mismatch there. For street you want to stay on the small side of the CFM rating for best all around performance. Get an accurate compression spec by CC-ing everything then pick a cam that is best suited for that number. For pump 91 I hope you have no more than 9.5:1 and you might be able to squeeze 10:1 with AL heads.

Good advice, When I was choosing one for mine I talked to a lot of people about which to buy, it seamed to be well excepted that a heavier car 3,200 lb or more needed vac. sec. I did the math and went with the 870cfm street advenger.

 

[67 coronet]

gonna get lots of opinions on this one.meep hit it pretty good,as usual.you need to choose a carb based on what you are doing with the car and all modifications to that car.overall weight and final gear ratios can have a big effect on wich carb you should choose.summit racing has a cfm calculator on there site and it has two different formulas depending on race vs street use.

 

[bth0320]

Thanks everyone for you advice....I have checked out the calculators but how to you determine max rpm? Is there a general range for the 383's? I plugged in 6,000 and based on 396 ci, I am coming up with about 600cfm.

Just as a little more information, this is mostly for street use. The new TC that came with the car has no numbers anywhere and no idea of the stall but guessing 3000 based on the cam....I plan on running 3.73 to 3.91 gears to help.

Although the compression calculators come in around 10.5 to 1 on the compression, I am at 5,200 ft so assuming this will drop the compression at least half a point?

 

[67 coronet]

Thanks everyone for you advice....I have checked out the calculators but how to you determine max rpm? Is there a general range for the 383's? I plugged in 6,000 and based on 396 ci, I am coming up with about 600cfm.

Just as a little more information, this is mostly for street use. The new TC that came with the car has no numbers anywhere and no idea of the stall but guessing 3000 based on the cam....I plan on running 3.73 to 3.91 gears to help.

Although the compression calculators come in around 10.5 to 1 on the compression, I am at 5,200 ft so assuming this will drop the compression at least half a point?

normally max rpm is determined by your cam to start with.it will have an"operating range"and you should match your intake and carb choice to that.cam is kind the brain of the engine and air/fuel flow should be determined from that.

 

[451Mopar]

I looked at the numbers closer and that looks like a nice combination. It also looks like the crank is offset ground? Are you using GM rods?
Anyhow, with the piston at zero deck, 11cc dome, 9.9cc head gasket, 84cc heads, compression ratio should be 10.78:1.
I calculate total displacement at 396.25 CID.
With the Comp 21-228-4 (EX285HL) cam, the intake valve should close about (using stock 383 rod length) 68.5 degrees after BDC, so the dynamic compression ratio is right at 8:1. At sea level cranking compression pressure should be about 164 psi?, but at this altitude closer to 136 psi.
When I plug the info into the DynoSim5 simulator (at sea level, with the 780 cfm carb) it shows about 504 HP @ 6,000 RPM, 485 ft/lbs at 5,000 RPM. With a smaller 670 cfm carb the sim shows a power drop to 479 HP?
The bad news is when running the simulation at 6,000 ft altitude the 504 HP drops to 397 HP (same RPM.)
I will try uploading an image of the sea-level power curve.

 

[bth0320]

Thanks for running that simulation...amazing how much altitude affects everything! I don't believe the crank was ground but not sure and the rods were custom built by JE pistons is as much as I know right now. Unfortunately, the guy that was building this car passed away about 7 years ago and his dad has been storing the car until he finally sold it. No paperwork was found on the short block so trying to figure out what all has been done. Will likely go have the crank blue printed to be sure. Do you know any good crank folks in the Denver area?

 

[451Mopar]

Just curious because the stock stroke is 3.380 and you posted 3.395?
The JE piston #213683 is a 11cc dome big block Mopar piston with a compression height of 1.858, and uses a 0.990" pin, but with stock rods it would sit 0.066" below the deck, even with the 3.395" stroke, so if the rods were about 6.424" long that would bring the piston to zero deck?
On the other hand, the pistons could be custom compression height and the block could have been milled to get zero deck height?

 

[fatecaptured]

I have had mostly carter/edelbrock carb experience. Which i'm not a carb pro. But they are pretty simple. I have the thunder series carb. Haven't run it yet. I also have two carters. The afb is really basic from what I gather. Holley is the most used and favored of them all. My choice for a holley would be a double pumper. I read mechanical secondary's are the way to go for performance. Demon seems to be a step up from the holley with improved features.

I recommend this video:http://chucker54.stores.yahoo.net/howtosutupee.html
I've watched it like three times. It's very good at explaining things and offers good carb tuning tips. Hope this helps.

Yeah I should of elaborated on the double pumper statement a little more. The mechanical secondarys are for race , sorry.

 

[bth0320]

Just curious because the stock stroke is 3.380 and you posted 3.395?
The JE piston #213683 is a 11cc dome big block Mopar piston with a compression height of 1.858, and uses a 0.990" pin, but with stock rods it would sit 0.066" below the deck, even with the 3.395" stroke, so if the rods were about 6.424" long that would bring the piston to zero deck?
On the other hand, the pistons could be custom compression height and the block could have been milled to get zero deck height?

Not exactly sure to be honest....I do know they are custom pistons as there is an order number stamped on them. I called up JE and they had just a limited amount of information since the job was 7 years old...they gave me what specs they had but unfortunately didn't know the volume of the pistons or the rod length. All they knew was the bore, stroke, pin (which is .990) and dome height. I called the machine shop in the springs who I believe put this thing together but they have no records nor remember the motor at all. It sure is a good looking motor though! Lol Here is a pic....

 

[forphorty]

Used 3310 750 vac are cheap and easy to find and would work well. I like DPs myself and the old 4779 750 DP works well on a variety of engines. BTW, that XE285HL is pretty hot for a street 383, not going to make alot of low end power. Especially at your altitude. It's going to need plenty of converter. Think 3500+ http://www.moparmusclemagazine.com/techarticles/mopp_0209_383_engine_restore/viewall.html