Carb choise question....
Race Director
Joined: Oct 2000
Posts: 15,009
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From: central FL, near the beach.
Hey folks...Just got home and verfied with heads I have...
Dart Iron Eagle 180 w/ 74cc combustion chamber and 2.02 intake valve diameter
http://www.dartheads.com/manager/upl...IRON%20SBC.pdf
I really think I might have to go and pick up on of those intake manifolds especially at that price. I really think I should upgrade the carb anyway based on what I have been reading and what is another $50, right?
Dart Iron Eagle 180 w/ 74cc combustion chamber and 2.02 intake valve diameter
http://www.dartheads.com/manager/upl...IRON%20SBC.pdf
I really think I might have to go and pick up on of those intake manifolds especially at that price. I really think I should upgrade the carb anyway based on what I have been reading and what is another $50, right?
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
I think in the near term, I may start by changing out the carb.
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
So sounds like I need to go big or gom home...i.e. replace the carb, heads and intake. Funds are definitely not in line for right now. Maybe either later this winter or in the spring. In the meantime, any issue with simply upgrading the carb right now and going to 750cfm and then saving up for the heads and intake? Will a 750 be too much for my current set-up?
Team Owner
Joined: Jul 2001
Posts: 182,997
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From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Team Owner
Joined: Jul 2001
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From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Rule of thumb is about: 180 cc = 430 HP, 200 cc = 450 HP, 215 cc = 475 HP, 230 cc = 500 HP..
That's if the engine is a pump gas engine with a flat tapped cam.. With high compression or significant porting work, more power is possible.. (in the end it comes down to actual flow numbers of the heads) A roller cam with more lift and duration could also raise those numbers.
Last edited by GrandSportC3; Sep 21, 2007 at 08:44 AM.
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
180 cc will not get you anywhere close to 500 HP... You just can't flow enough air/fuel through those little runners.. For 500 HP, you'll need about 230 cc intake runners and 2.08 valves. It's probably doable with 215 cc intake runners with a lot of porting.. Port velocity is another factor but even with great port velocity, 180 cc intake runners will not get you close to 500 HP..
Rule of thumb is about: 180 cc = 430 HP, 200 cc = 450 HP, 215 cc = 475 HP, 230 cc = 500 HP..
That's if the engine is a pump gas engine with a flat tapped cam.. With high compression or significant porting work, more power is possible.. (in the end it comes down to actual flow numbers of the heads) A roller cam with more lift and duration could also raise those numbers.
Rule of thumb is about: 180 cc = 430 HP, 200 cc = 450 HP, 215 cc = 475 HP, 230 cc = 500 HP..
That's if the engine is a pump gas engine with a flat tapped cam.. With high compression or significant porting work, more power is possible.. (in the end it comes down to actual flow numbers of the heads) A roller cam with more lift and duration could also raise those numbers.
Team Owner
Joined: Jul 2001
Posts: 182,997
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From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
I used to have a '69 Vette with a 383 that had 170 cc intake runner heads and I ran a 4779 Holley (750 cfm - mech. secondaries) and it worked great. Engine made about 430 flywheel HP. The heads had some porting done, so they flowed slightly better than standard 170 cc heads.. That 383 was very similar to what you have.. My cam in that motor was 230/230 degrees @ .050 and .505 lift.
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Race Director
Joined: Oct 2000
Posts: 15,009
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From: central FL, near the beach.
the only downside is poor mpg. if 9-13 mpg doesn't bother you(without o2 sensor tuning)
a 4779 will be a blast. OD gets even worse sometimes
.
oliver
isn't the 80528 set up for better mpg?
i'm not sure.
a 4779 will be a blast. OD gets even worse sometimes
.
oliver
isn't the 80528 set up for better mpg?
i'm not sure.
Team Owner
Joined: Jul 2001
Posts: 182,997
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From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
http://store.summitracing.com/partde...5&autoview=sku
Instructor
Joined: Jul 2007
Posts: 245
Likes: 2
From: Hope Indiana
Carburetor's should be sized for a given displacement at a maximum speed with the assumption of a volumetric efficiency. Vol.eff. is where things like duration and port flow rates come into effect.
Use the following formula:
CID x max RPM x vol.eff. / 3456 = CFM
So for your 383, assuming a max rpm of 6000, even at 100% vol.eff. your max CFM needed is only 665.
Safety Car
Joined: Oct 2000
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From: Southern Indiana
Race Director
Joined: Oct 2000
Posts: 15,009
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From: central FL, near the beach.
very easy to win $$$$$$ when ignorant guys tell u it is junk. Thanks for posting Tim
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
when ignorant guys tell u it is junk. Thanks for posting Tim 
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,677
Likes: 1
From: Potomac Falls VA
Carb sizing is a little more complicated than "bigger is better" as most people think. A big "hole" in your intake system at WOT drives down charge velocities and can lead to low torque, ie. you may flow a lot of air but if you flow it slowly you may never fill the cylinder.
Carburetor's should be sized for a given displacement at a maximum speed with the assumption of a volumetric efficiency. Vol.eff. is where things like duration and port flow rates come into effect.
Use the following formula:
CID x max RPM x vol.eff. / 3456 = CFM
So for your 383, assuming a max rpm of 6000, even at 100% vol.eff. your max CFM needed is only 665.
Carburetor's should be sized for a given displacement at a maximum speed with the assumption of a volumetric efficiency. Vol.eff. is where things like duration and port flow rates come into effect.
Use the following formula:
CID x max RPM x vol.eff. / 3456 = CFM
So for your 383, assuming a max rpm of 6000, even at 100% vol.eff. your max CFM needed is only 665.
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
With that you can't even use a 750 on a 454!!!
If you start thinking too much and start treating it like rocket science you will never figure it out.
If a 383 can't handle just a 750 DP then move the decimal point back one to a 3.83 liter!!!!!
Instructor
Joined: Jul 2007
Posts: 245
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From: Hope Indiana
It's a pretty simple flow calculation based on the volume an engine can breathe. I suppose you can call is "HOO HA!" but it's simply not.
I'm not saying that a 383 can't "handle" a 750 DP. But you're compromising charge velocity for flow area that you just don't need. I suppose if you don't like it then you can keep tuning your engine in your own way.
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
You can make a 750 run on a 305 or a 454 with the right tuning parts, but a calculator isn't one of them.
Race Director
Joined: Oct 2000
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From: central FL, near the beach.