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Topic: Carb size calculator (Read 8040 times) previous topic - next topic

Carb size calculator

I wonder how many people over size their carburetors. I found this to be interresting, I hope it will be helpful the the site.
http://www.gtsparkplugs.com/CarbCFMCalc.html
88 Cougar LS 5.0 .030 over, ported E7s with GT40 valves & trickflow springs, Proform roller rockers, HO cam, removed air silencer, K&N filter, smog pump delete, 2.25" dual flowmasters, Pacestter H-pipe & headers, HO computer, 65mm TB, Explorer intake, 19# injecters, 3.45s, rebuilt posi, and TCI shift kit.

Carb size calculator

Reply #1 –
i laugh when people say they have a 750 on a mild 302.. anyone who knows anything about a 302 knows that's overkill lol

Carb size calculator

Reply #2 –
I was pretty surprized that it only recommends a 600 CFM for the engine that I'd like to build. I was going to run my 650 with with my Torker 2. I guess Im going to use my 600 and sale the 650 and Torker so I can buy an Edelbrock RPM Perfromer.
Engine size - 306
Max RPM - 6500
Volumetric Efficiency - .85
Carburetor Type - Modified
Carburetor Size CFM - 600 CFM
88 Cougar LS 5.0 .030 over, ported E7s with GT40 valves & trickflow springs, Proform roller rockers, HO cam, removed air silencer, K&N filter, smog pump delete, 2.25" dual flowmasters, Pacestter H-pipe & headers, HO computer, 65mm TB, Explorer intake, 19# injecters, 3.45s, rebuilt posi, and TCI shift kit.

Carb size calculator

Reply #3 –
NONONONONONONONONONONONO.. use the torker! and you can't really go by a simple calculator like that.. it doesn't account for what's hiding below the intake

Carb size calculator

Reply #4 –
Everything depends on the combination you are using . The single biggest decision is the cam IMHO
Fox-less at the moment

Carb size calculator

Reply #5 –
In my experience those caluculators have little basis in the world of performance.  Maybe it's good for a stock engine, can't say, I've never had one in a project car.

I haven't run anything smaller than a modified 750 on 306 w/a 6,500 RPM shift point.

If you want to go fast, look elsewhere for advice on the right carb.

"the single biggest decision is the cam"  Bingo!  There's a comment I can get behind.

Carb size calculator

Reply #6 –
Dont forget about the cylinder heads.
88 Cougar LS 5.0 .030 over, ported E7s with GT40 valves & trickflow springs, Proform roller rockers, HO cam, removed air silencer, K&N filter, smog pump delete, 2.25" dual flowmasters, Pacestter H-pipe & headers, HO computer, 65mm TB, Explorer intake, 19# injecters, 3.45s, rebuilt posi, and TCI shift kit.

Carb size calculator

Reply #7 –
I figured it was off. Because I ran a 450CFM holley on my 2.3 ranger, and it ran great.
88 Cougar LS 5.0 .030 over, ported E7s with GT40 valves & trickflow springs, Proform roller rockers, HO cam, removed air silencer, K&N filter, smog pump delete, 2.25" dual flowmasters, Pacestter H-pipe & headers, HO computer, 65mm TB, Explorer intake, 19# injecters, 3.45s, rebuilt posi, and TCI shift kit.

Carb size calculator

Reply #8 –
cam and intake are what you need to pay the most attention to.. are you going to run a x-303 and an edelbrock performer 302 intake together and get great power? HELL NO.. your intake has to flow to the standards of what the cam wants to drawl into the cylinders// which also leads to ditching stock, low performance heads like E7's for something better, like GT40p's or something of the sort.. it all comes down to how much flow the intake/head combo will really want/need..

Carb size calculator

Reply #9 –
I plan on running 650, Torker, ported GT40s, SRP pistons, F303 or TrickFlow stage 2, and so on.
We'll see money is very tight.
I cant make up my mind on the cam, I can get the F303 for $50 used. I've heard that a F cam is a good blower cam. ;)
88 Cougar LS 5.0 .030 over, ported E7s with GT40 valves & trickflow springs, Proform roller rockers, HO cam, removed air silencer, K&N filter, smog pump delete, 2.25" dual flowmasters, Pacestter H-pipe & headers, HO computer, 65mm TB, Explorer intake, 19# injecters, 3.45s, rebuilt posi, and TCI shift kit.

Carb size calculator

Reply #10 –
If money's really tight, don't spend on parts that don't match.  Wait and get the right ones.  A $50 cam that works poorly is a lousy buy, particularly if you have to buy another to get it run right.

General guidelines I have learned: 
Example #1: Big heads, single plane intake, big carb, big exhaust, little cam (custom), power from idle to as high it's built to spin. Good idle, lots of vacuum, good gas mileage, easy to live with.
Example #2: Small heads, small carb, dual plane intake, small exhaust, big cam like a Stage 2 (OTS) = soggy low end, peaky power band, low vacuum for power brakes, poor idle, crummy gas mileage and miserable to live with. 

I've done builds at both ends.  Example #2 really sucks.  Spent all the cash on trying to get togehter and running and don't have funds to get it to run right.  Example #1 takes more saving and planning, but it's sooo much more satisfying to have it work right!

We all have our learning curves.  I did #2 builds until I learned better.  Wish I knew better earlier!  I would have save a bunch of time & money.

Hope you have good luck which ever one you choose.

Carb size calculator

Reply #11 –
Quote from: Bruce M;346833
I plan on running 650, Torker, ported GT40s, SRP pistons, F303 or TrickFlow stage 2, and so on.
We'll see money is very tight.
I cant make up my mind on the cam, I can get the F303 for $50 used. I've heard that a F cam is a good blower cam. ;)


i learned to stay away from the FRPP letter cams, there is a much better selection out there that work 10 times better.. but the rest of your desired combo sounds good.. the gt40p's on my 306 are amazing.. i spent roughly 3 weeks(not constant, but a little here, and little there) porting them and made sure all the ports were matched with my digital caliper.. that's the #1 key factor, you don't want cylinders running lean.. i also port matched my intake as well, which makes it flow amazingly.. i have nothing but great things to say about those heads, the motor is a pure power house with a pretty small cam
 
Quote from: 86T-bird;346837
I've done builds at both ends.  Example #2 really sucks. .


x2, i think everyone learns a few do's and don'ts from building 1 like example #2

Carb size calculator

Reply #12 –
Letter cams make great paperweights......I'd actually like to get one and make a table lamp out of it.

A TFS stage 2 is too much cam to be used with GT-40's IMHO.
-- 05 Mustang GT-Whipplecharged !!
--87 5.0 Trick Flow Heads & Intake - Custom Cam - Many other goodies...3100Lbs...Low12's!

Carb size calculator

Reply #13 –
Quote from: V8Demon;346847
Letter cams make great paperweights......I'd actually like to get one and make a table lamp out of it.

good idea!

Carb size calculator

Reply #14 –
Quote from: 86T-bird;346837
If money's really tight, don't spend on parts that don't match.  Wait and get the right ones.  A $50 cam that works poorly is a lousy buy, particularly if you have to buy another to get it run right.

General guidelines I have learned: 
Example #1: Big heads, single plane intake, big carb, big exhaust, little cam (custom), power from idle to as high it's built to spin. Good idle, lots of vacuum, good gas mileage, easy to live with.
Example #2: Small heads, small carb, dual plane intake, small exhaust, big cam like a Stage 2 (OTS) = soggy low end, peaky power band, low vacuum for power brakes, poor idle, crummy gas mileage and miserable to live with. 

I've done builds at both ends.  Example #2 really sucks.  Spent all the cash on trying to get togehter and running and don't have funds to get it to run right.  Example #1 takes more saving and planning, but it's sooo much more satisfying to have it work right!

We all have our learning curves.  I did #2 builds until I learned better.  Wish I knew better earlier!  I would have save a bunch of time & money.

Hope you have good luck which ever one you choose.

 I would like to add an op-ed  to this.... #2 type build if done with some thought can be just fine for some people ,it depends on what the the car is going to be used for.
 If going as  fast as possible is your goal then #1 all the way ,
But for a daily driver that you just want a *little* more than stock  that will NEVER see a track if the proper cam is chosen to match all the other components #2 type of build  works just fine and when I say #2 build , I think Gt40s are "small heads "  but they can be cammed to get decent mileage and vacuum as well as increased power with OTS parts .
  Engines are not "one size fits all"  First you need to be honest with yourself as to what you want and how much do you want to spend .
 Again I say" the single biggest decision is the cam"
Fox-less at the moment