2BBL"s are measured at 3" HG and 4 BBL's are measured at 1.5" HG to get CFM ratings. So don't even try to compare 2BBL CFM ratings to 4BBL CFM ratings or vise versa. They have no correlation to each other.

If you are using a vac secondary Carb you can not really over size the carb on the engine, to a point, the primary venturi air speed is what actuates the secondary's. Basically you cant over carb with a Vac secondary carb as the carb will only feed what the engine requires if set up properly
. If the primary venturi air speed never gets high enough to over comes the spring pressure in the in the secondary vac can, the secondary's will never open.
Carb sizing is more critical on mech secondary carb's as you can over carb and have the engine fall on it's face. This for the most part is a non issue with vac secondary carbs.

The larger primary's on a bigger vac secondary carb may negatively impact acceleration and fuel economy but generally this is only an issue once start way over sizing.
Smaller Primaries will allow for better off line acceleration and cruise economy. This is in part why the quadra jet has been as popular as it is.

 

Well first off Summits carb size calculator doesn't state what its for 2V or 4V. It just says 85% for street vehicles comes in at 371 CFM. using DD2000, switching from 351 CFM @ 3" HG to 500 or even 600 CFM @ 1.5" HG shows no more than a 7 HP increase using flow data with E7 heads. Tells me that switching from a 351 CFM 2V to a 600 CFM 4V doesn't give much of a increase which tells me the 351 CFM 2V isn't too small to hinder the engine. Plus from what I have heard the E7 heads flow the same as the older heads, just smaller chambers for a higher compression. So if that is correct then I don't truly believe running a Edelbrock intake and a 600 CFM or even a 500 CFM Summit carb would cause a noticeable performance increase to justify the expense.

That is what I am getting at.

Also looking at the photo of the 500 CFM Summit carb, both primary and secondary throttle blades are marked 172 and they appear to be the same size. I couldn't say on the 600 CFM as they just have a generic photo from the angle showing the kit.

I am also kind of curious why the 600 CFM Summit carb is a good $20 cheaper than the 500 CFM carb.

Now if the summit calculator is showing the recommended CFM for a 4V well then I cant get any thing close. Closest I can get is 500 CFM which is considerably more than the recommended 371 CFM. I also have a gut feeling I will have to play with the jets as well. Saw a guy state on his old mustang he went from the Summit 600 CFM to the 500 CFM for his 302 cause the 600 had a raw fuel smell that it was too rich but the 500 is just right.

 

Matt is right on how they measure 2v & 4v carbs.
If you are looking for a better v2 carb to bolt to your stock intake manifold look at the Holley 2300 v2 that comes in 350 and 500 cfm, go for the 500cfm one.
I am running the 500cfm on my AMC 304 in place of the motorcraft 2100 I could not get to run right.

If you want to go for a v4 I would go with a Holley 600 vacuum. I have one on a AMC 360 but would not think twice to run it on my 304.

Any one know what make/size carb was used on the Ford 289 / 271hp hipo motors? I don't remember but want to say Holley 600cfm.
Dave ----

 

Yes I know how they measure CFM at 2V and 4V, Ive used DD2000 enough over the years to know the 3" and 1.5" HG measurements. That is beside the point though as I am trying to end up with a carb that will not be way to over sized. If I over size it where the secondary never open up cause the engine doesn't need it then why even waste the money on buying the carb if it is always running on just 2 barrels. That is my concern. That is also why I am avoided the edelbrock quadrajunk carbs as they are not vacuum secondaries but weighted mechanical secondaries and that will just be even worse for me than a vacuum secondary that will meter the fuel as the engine needs more.

If the engine will run right and the secondaries will be functional with the 500 CFM on the 302 that will turn no more than 4500 rpm then sure I will run it. But I find it very hard to justify $300 for the carb and another $300 for the Edelbrock intake if its not going to run off all four barrels cause its sized too big, it runs too rich for me, or it just doesn't give me any boost to performance.

Then there is also the big thing if the size of the summit carb if its the same size dimension wise as the old Ford 4V carbs, if so then it should fit under my stock airfilter. If not if its longer then I might not be able to use my stock airfilter.

Another thing is the timed ignition port on this carb, my truck currently is running manifold vacuum for the dist, tried to run ported and I could not get the truck to idle smooth had to run manifold vacuum to get the truck to idle smooth. Maybe wont be a problem with the 4V but changing as much as I would be changing I just don't know what to expect.

 

The E7 head do not flow as much as the older heads. the flow 10-20 CFM per port less than the older heads at most all valve lifts.

The CFM calculator on Summits site is CFM @1.5" hg again you cant use 2BBL CFMs rating for ANY kind of comparison to 4BBL's.

You wont lose any peak HP with the 600CFM carb, and it's cheaper just due to the volume sold.
The 500CFM carb will offer an edge on off the line acceleration and potential cruise economy with the sacrifice of top end power.

All carb calculators ten to under size the carb CFM this has been dyno proven time and time again. They give you a ball park that is all.

And all Carbs out of the box are set up to allow an engine to start that it is. They need to be tuned and fuel air ratio's checked. The idle air circuit will need to be adjusted for idle F/A mix and jetting adjusted to optimize the mani circuit F/A ratio. . Size of the carb has NO correlation as to how rich or lean it will run that is dependent on jetting and other adjustments.

 

We just tested this on Thursday with my 302 on the dyno. Brand new 600 CFM 4bbl Holley 4160 with vacuum secondaries. The technician put a zip-tie on the secondary throttle plate shaft so we could see if the secondaries were opening, and they were.

 

1) which older heads are you talking about. Cause me I was informed that smog era heads from the early 80`s don't flow any more than the E7 heads but they have larger chambers. I don't care what heads flowed back in the 60`s and 70`s as I am dealing with stock ford head castings from 82.

2) Where does it say what the calculator on Summits site is for? All it says is and I quote



No where does it state 1.5" HG or 3" HG. So I like to know where is the proof that this is 1.5" and not 3" or just some generic number that would be safe for either 2V or 4V.

3) Yes, I know smaller primary side of the carb will improve throttle response, same with smaller intake port volume will improve vacuum signal to allow for faster response. With that said this is a street truck, not going to be raced. Just something driven every day and used like a truck. It will be on the highway most of the time running 75 - 85 mph after I move. Why I am really originally looked at a roller engine from a late model vehicle as a transplant so it will in conjunction with the proper 5w20 oil put less drag on the engine and should net me better gas mileage than if I was running 10w30 or 20w50.

4) I know the carb has to be adjusted to the engine in question. But some carbs only can be jetted so small from available jets for said carb. if its way too over sized even playing with jets you cant lean it out enough. Saw a few reviews posted about this issue with the 600 CFM. I prefer not to deal with a headache like that. I prefer to go with something that can be adjusted and tuned easily without having to get way to deep into it. As far as jetting goes I don't mind playing with jets. I just prefer not to do it if I don't have to. That's why everyone recommended a edelbrock carb as they are jetted on the lean side compared to holley being jetted on the rich side. I probably will have to go down one or two jet sizes anyways as Summit carb I hear is built by holley for summit so it probably is set on the rich side as well.

 

Did they have to go rejetting the carb?

I don't mind running the 600 CFM. I just hate the thought of having to disassemble the carb multiple times to play with jets to get the fuel mixture right. I do want it set right so I can get as good gas mileage as I could. I don't know if I could run a O2 sensor for a AF ratio to set the engine, the headers I am looking at has one O2 fitting but its only on driver side. Nothing on passenger side so I cant check passenger side. Plus I think might be a bitch to put the plug in once I am done.

 

We had to put slightly larger jets in my 600CFM Holley. Stock jets in the 4160 are #66, and we installed #68's. A/F ratio was pretty good after that. That is with the Explorer GT40 heads...not sure how much more they are flowing over E7"s, or my original D8's. That was on the dyno however, so installed on my truck with a proper exhaust, I may very well have to reinstall the stock size jets. I'm at sea level I should mention, so we have air you can wear.

If you're just using this thing as a daily driver street vehicle and don't want or need the extra power, just stick a 2bbl on it.

 

Yep right now im at about 25 ft above sea level after I move its going to be around 200 feet above sea level.

Right now my concern is the vacuum tree that threads into the intake. This supplies manifold vacuum to the vacuum tree on the firewall as well as to the brake booster and the PCV valve. The Edelbrock intake does have a threaded port in Cylinder 4 intake runner but if I go with the EGR Edelbrock intake and run the EGR 4V plate I don't think I can use the vacuum tree as the EGR valve will sit over the port. The other port is under the throttle bracket mount area thus would be useless either way. I could omit the vacuum tree and use tees to connect to the carb itself but the PCV hook up on the Summit carb is up front the PCV is in the rear. Then all the vacuum lines are in the rear as well on the firewall. The emission vacuum lines I would omit as I would keep them intact on this engine and just make up new lines for my new setup. I was planned on getting the Edelbrock intake with the 4V to 2V adapter to run my 2150 for now. Just to save me some time from having to clean up my old intake for paint.

But I am thinking why not just go with the 4V and intake now if it will make a difference. Cause if I don't do it now and go with the 2V then there will be no reason for me to upgrade as I will be content with driving the truck vs working on it to make changes.

I do want as much power as I can get how ever. But I also want it set up properly where I wont be just wasting gas. Fuel down where I will be moving to is pushing $3 a gallon now but where I live currently its only $2.60. But now that $3 is for the cheap 89 octane. The 93 is pushing $3.40 as its ethanol free.

That's why I am going to run the shorty street headers by headman along with the off road Summit Y pipe so I can purchase a stock cat back exhaust system for my truck so I don't have to deal with a exhaust shop. Only question for myself is do I want to reuse the Thrush glass packs or do I want to get something nicer. Im curious how a new 5.0 mustang muffler would sound. We've been putting them on a lot of the retrofits we do at work and they sound great on the LS swaps. Havent heard one on a header equipped older ford engine though.

That's another thing I just remembered, if I don't run the EGR I will have to get a 1" spacer plate to raise the carb to the proper height with the Performer intake.

 

D9 Castings Which is what used till the E5 Castings. And any casting from D2 up used the same basic dimention core molds for the intake and exhaust. Actual flow testing was done on all available SBF heads By Ford Muscle magazine about 17 years ago, The E7's were the worst performing short of the small SBF heads from the 60's use on the 221/260 and the E5's. The ONLY advantage the E7"s have is the smaller chamber.
They can be ported to improve flow but bog stock they are not worth installing unless you are only looking to bump compression.
So don;t be a slave to the E7 myth.....
GT40's are a much better option.

All Carb calculators are done for 4V carbs NOT 2BB carbs basically NO one uses CFM calculators for 2BBL's. Why the hell would summit use 3"HG in their calculator to give CFM ratings that would not work with ANY 4BBL carb they sell ? And you can bet they sell 1000 times more 4BBL's than 2BBL's
Plus to convert from the 2BBL 3"HG CFM ratings to 1.5" HG CFM ratings is idiot simple just multiply 3"HG CFM ratings by 0.707 to give you 1.5"HG CFM ratings. This is not exact but is very close.
Your 351 CFM 2 BBL flows 177 CFM at 1.5"HG equivalent.
1BBL's are also rated at 3"HG.

The reason it was not he same for 2BBL"s and 4BBL's was the flow benches the carb manufactures had at the time (Holley) quite simply could not flow enough air at 3"HG to measure the the air flow on the then new 4BBL's but they could move enough air at 1.5"HG.

And even way over sized carbs can be jetted down as long small enough jests are available. Hell hows do you think people run the 875CFM Autolite inline's on a cross boss for install on 302's.
And better off to be a bit fat than lean no one has ever burnt up an an engine running it a bit fat.

 

1) Im not changing heads, I am getting a whole ****ing engine. My stock smog engine spun the balancer on the crank. This resulted in I guess egg shaping the crank so the 5/8 crank bolt wouldn't come out. Impact sheared it off in the crank with about 1" left in the crank. So the engine is trash to me. not worth it to pull the engine and throw a $150 crank in it and not reseal this leaking nearly 20 year old rebuilt engine. Also not worth it to not pull the heads and have the ****ty knurled valve guides replaced with new since the engine shop then didn't do the job right. So my option is buy a long block for a 80-86 or spend about $20 more and get a 94-96 302 with the explorer roller cam and the E7 heads. Just the roller cam is a upgrade as its a roller over a flat tappet. So no I am not looking at doing a head upgrade, I am getting a whole reman long block. The one I happen to settle on is a 94-96 truck 302 with the HO firing order, roller cam, and E7 heads. Considering this is such a newer engine I am trying to set it up properly. Why I have to buy a steel dist gear to replace my gear on the old DS2 style dist to make it compatible with a roller cam. I also am contemplating a 4V upgrade if it is an upgrade and will see me a noticeable difference in performance. If upgrading to the Edelbrock intake, the 500 cfm summit carb which also requires the summit kick down spring and perch kit along with the holley kick down extension does not give me a noticeable difference you can tell driving then I can not justify spending close to $500 in upgrades when I can just clean up and use my stock intake and stock 2150 carb. That is where this is all revolving around. Its about a upgrade that is noticeable while driving, I am not going to split hairs over 5 to 10 hp as I highly doubt 5 to 10 hp will be noticed on the street. Now if it will wake the engine up and make the engine run great and make the truck pull harder then yes I have no problem paying up to $500 for the parts to upgrade the intake system.

2) Well I just did some looking into the calculators, they don't account for carbs. The calculators are nothing more than the following math formula.

CID x RPM = _______ x 0.85 = __________ / 3456 = CFM.

It has nothing to do with inch hg flow. This formula is for simply figuring what the engine is able to handle at a given RPM. Has zero to do with 1.5 or 3.0 in hg.

302 x 5500 = 1,661,000 x 0.85 = 1,411,850 / 3456 = 408 CFM.
302 x 5000 = 1,510,000 x 0.85 = 1,283,500 / 3456 = 371 CFM.

So show me where in the math formula is there an accounting for 1.5 or 3.0 in hg?

Plus further more this intake is good up to 5,500 rpm but Ive never seen this truck run past 4,500 rpm when floored. Now making more power it might change the operation of the torque converter and cause the transmission to shift differently but I don't see this engine ever turning 5,000 rpm.

302 x 4500 = 1,359,00 x 0.85 = 1,155,150 / 3456 = 334 CFM.

Which actually puts the requirement below what my 2V is capable of flowing. Now tell me if all I need is 334 CFM, then how would I be able to jet down a 500 CFM carb down enough to make it have the proper fuel mixture? Jet sizes are only offered in so many sizes and like I said before some people reviewed the 600 CFM and said it ran too rich for them and they couldn't jet it down low enough to work. That is what I want to avoid, I don't want to get the 500 CFM if I need a X jet but yet they don't offer an X jet. That basically means the money spent on the intake, carb, and all the parts to make it work with my truck was a waste of money.

3) Lets compare apples to apples here, I don't care about a 800+ CFM carb on a Boss 302, that doesn't mean **** to me because you didn't say anything about what RPM that engine is turning. If that engine is turning 7,000 rpm then yes that carb would probably be capable of being jetted right. But now if that engine turns no more than 5,000 rpm then 800+ CFM is way to ****ing big and I highly doubt you can jet it properly Not to mention at such a low rpm the large barrels will result in a sluggish throttle. Which is what I want to avoid. I already had a problem with my accelerator pump not squirting enough fuel to eliminate a stumble when accelerating from a stand still. Which is also another reason why if I can see a noticeable increase in performance running the 4V carb I will do it and make it work. That Accelerator pump looks like it uses holley style cams that can be swapped with different ones to change the squirt which is more adjustability than the three holes my 2150 has for adjustment.

 

Is there a way to tell a steel gear from a non steel gear?

I did some searching and found a post on here from 07 where a guy was told simply to look for a 302 HO/GT distributor that has the steel gear already and not to try and press the old one off and swap.

Well I did some searching and found a Cardone sells a New dist listed under a 82 F150 with a steel gear as well as a cast iron gear. There is also a listing for the same for World Power Systems, which I never heard of.

I replaced my dist a couple years back I cant remember if I did a whole new dist or a reman. But the thing is I got it locally and no mention of steel or cast iron gear. Now I am wondering if I might possibly have a steel gear dist in my truck already that I can reuse.

If not I am looking at $50 for the Cardone new dist with steel gear which is cheaper than buying just the gear for $65.

 

Again you are not fully understanding this stuff or how it is correlating to each other. But you are getting there.

Example:
Your 2BBL Carb flows 248CFM at 1.5" HG the 500CFM Holley Flows 500CFM at 1.5" HG

Your 2BBL Carb flows 351CFM at 3.0" HG the 500CFM Holley Flows approx 707CFM at 3.0" HG

And to confuse things even more there are wet and dry for the above "HG ratings.
Come carbs are given dry CFM ratings and others wet .
Changing from a wet rating to a dry rating would on average add 8% more CFM to the carb. Example – a carburetor rated on the wet four-barrel rating scale at 500 CFM would now amazingly flow 540 CFM
Don't think this was not done by carb manufactures either. (Cough cough Carter)
The calculation you are using for air flow requirements .
302 x 5500 = 1,661,000 x 0.85 = 1,411,850 / 3456 = 408 CFM.
302 x 5000 = 1,510,000 x 0.85 = 1,283,500 / 3456 = 371 CFM.

And exactly.

At what pressure drop are the above CFM ratings being calculated at,
This is something that has always been missing from this formula. And NO ONE seems to know either.

Is this formula calculating at Atmoshpere, or 1.5" HG, or what ?
The 3456 divisor constant has no explanation as to how it was arrived at, is it just plain old Atmospheric air volume movement. or is corrected to 1.5"HG to corresponding to CFM ratings for 4BBL carbs or is it 3"HG or some other arbitrary number. This is what you are missing using this formula to choose a carb.

We know at what "HG that carb's CFM are calculated at
If the above formula is not calculating at the same "HG as the carbs CFM are rated at the 2 will have no corresponding relation to each other in terms of finding the appropriate CFM rated carb.

Sort of like how 2BBL and 4BBL CFM ratings have no relation to each other. You can't use 2BBL CFM ratings to find an Equivalent CFM 4BBL or vise versa without converting one to the others "HG for CFM Ratings.

The above formula has always undersized carbs when using it to select a carb . This has been dyno proven many times.

The standard rule of thumb is don't exceed twice the CUI for 4BBL CFM on mildly built or stock type engines.


The smallest 4BBL carb fitted by Ford on the 302 has been 600CFM.
Will up grading to a 500 CFM 4 BBL yield more power than your stock 2BBL, absolutely it will, as it is capable of flowing almost 3 times the amount of air. And they are to be quite frank choked with the 2BBLS
Plus NO 500 CFM carb has ever been over sized on a 302 even smogged down stock ones.

Using some of these standard Auto formulas to find precise numbers can be very misleading if you do not understand all the intricacies involved,some of the formulas are flawed from the get go and you just can't take them at face value.

 

Well im not going to dig any more into the carb aspect. Lots of people are saying the 500 - 600 cfm is a good carb for the 302. Last one I read went more in depth on explaining the operation of the 2V vs 4V carb on an engine. Wont get into that on here as I am moving on past that.

The last one I read said basically the same as been said before, 500 cfm will feel snappier and would net better gas mileage when cruising on the primaries as they are smaller than in a 600 cfm. I wouldn't know about that as there is no photo of the Summit 600 cfm carb showing the throttle plates for me to compare.

But the last thing read though was that the 302 doesn't really need much help in the carb department stock is just fine, its the exhaust side that needs help.

Well I already have 89470 Headman Shorty Street headers. They are a 1 1/2" primary but are listed as using the stock flange collector, its also listed as 86-96. The search I did in the parts and illustration guide shows the 86 F150 has the same Y pipe and Manifolds as on the 80 - 85 models. Jegs also sells a 2" inlet 2 1/2" outlet off road Y pipe listed for fitting 84 - 86 F150-F250 as well as 85-95 5.0 Bronco and 87-95 F150-250 5.0. So basically this Y pipe will fit a 80-85 since its already been confirmed that Y pipe and manifolds are the same 80 - 86.
https://www.jegs.com/i/JEGS-Performa...830+4294827330

Only question now would be since I don't currently have an exhaust other than a thrush glass pack with a turn down, I was looking at Waldron Exhaust for their cat back exhaust system. They have a selection for stock, mild imposter, or imposter performance for the muffler options. The imposter performance is the best flowing but also can be loud. Im tempted to just spend the $270 for the stock muffler then go get dimensions off of it and find my own muffler. Would consider going stainless steel but not going to spend $440 when the off road Y pipe isn't even stainless steel itself. Also wondering about the use of band style exhaust clamps over the old style clamps. Ive used them in exhaust kits before and they seem to clamp good with no exhaust leak unlike the old style clamps.