"Dieseling" and generally running like $%!

[LEB Ben]

^^^Denied access at work...but please school me. So am I to believe from your posts that you don't believe he can go too big?????? Now I'm no newbie to carbs and can handle my own and no where have I ever seen anyone advise more than 750cfm carb for a stock engine. To advise more than a 750cfm carb for a stock street used engine is down right ridiculous. I'm not saying it can't be done...but you'll have to know more than the average joe to accomplish it and have it be right.

 

[dragogt]

^^^Denied access at work...but please school me. So am I to believe from your posts that you don't believe he can go too big?????? Now I'm no newbie to carbs and can handle my own and no where have I ever seen anyone advise more than 750cfm carb for a stock engine. To advise more than a 750cfm carb for a stock street used engine is down right ridiculous. I'm not saying it can't be done...but you'll have to know more than the average joe to accomplish it and have it be right.

Yes you can go too big, but you have to remember

1. The carb is going to act like a restriction in and of its self..

2. Even a Stock rebuild "should be more efficient than what they were 20 years ago..

3. Carbs now days are more responsive than they were 20 years ago..

From the Pro-Systems link I posted earlier..

Well that formula is still being quoted by magazines and companies etc...but times have changed and carburetors are operating on almost immeasurable amounts of vacuum. 10 years ago a carburetor would require 10 inches of water to pull signal and shear fuel. Now they can can pull and shear fuel at only 3. Remember 20.4 inches of water (wet) is the cfm rating guide with reputable designers so we aren't looking to match cfm requirements with cfm ratings.

20.4 = 1.5 hg.

You can see that going from 10 inches of water as a requirement at launch to only 3 inches as a requirement really allows a serious increase in cfm size. This removal of restriction really pays off in cylinder head flow numbers and hp of course. Imagine altering this upstream restrictor when flowing your heads.

Because, most of you have specific application designs, a custom shop/unit is typically the plan.

In the future, use this calculation as a general rule on a modified carburetor:

CID x RPM x V.E. / 2820 = CFM
350 x 6600 x .9 / 2820 = 737 CFM

Now you'll be a little closer.

One more thing..

As promised, here are the '07 Explorer 4.0L SOHC pics.

TB is 70mm tapered down to 63mm and MAF is 64mm entrance tapered out to 83mm connection with air hose.* .... air transition is 64-->83-->70-->63* *:wonder:

Added:

Valves DIA: 1.815"/1.539"
Lobe Lift: .259"
Valve Lift: .472"
Ratio: 1.82:1

Here's another "detail" regarding the air hose connector for your evaluation...... see the added resonance chambers?

​

So why would Ford put a 70mm TB on a 4.0 238CI IIRC???????

 

[LEB Ben]

I read that...and in theory I agree to it, but let's be real...most guys aren't coming close to those optimal numbers. Not tomention, who knows what you're starting with...I can't tell you how many engines I've pulled from fields thrown in a rig, crossed my fingers it would run and hold up. And experience tells me, the bigger carbs on those engines don't work...and that's what the majority of joe blows do. I can also say I think with the 400 in the Bronco now, there's no way I could throw a 750cfm carb on there and have it be happier than it is now with a 650cfm carb...same with Red. So I'll agree, in theory...sure...but real world...not buying it on the whole. To me, that info is kinda like watching Powerblock TV and the guys telling you how easy X mod is...well no $hit when you have a whole shop available to you and you're dealing with brand clean parts.

 

[dragogt]

Yeah, but thats why you Test and Tune; Or run it down the "Track"..

If your just going to pull it out of the box and not do any kind of tuning with it, then ya I could that.. But why leave it as is when with a little bit of tuning it could run better and probably get better mpgs at the same time...

put a coffee straw in your mouth and try and breath through it, see how well that works out for ya...

http://www.460ford.com/forum/showthread.php?t=108428

Stock Twin blade throttle body sizes:

EFI 460 - 52mm

V10 - 57mm

99-04 Lightning -

96-02 4V Cobra - 62mm

03-04 Cobra - 65mm

^^ Whats that tell you...

 

[LEB Ben]

^^^You have to admit dealing with an efi and carbed engine are two totally different animals. The OP is talking carbed. Also keep in mind, you can test and tune all you want...but you still have to figure out the optimal numbers...and the numbers you are referencing are optimal performance. Test and tune will yield completely different results when dealing with a stock 460 vs a 460 with a cam/headers vs. cam/headers/heads/intake vs a completely balanced and blue printed rig. So while, yes...great info from you, I take those as theoretical numbers and won't yield the same results depending on different engine builds. It's been proven through the test of time that on a stock to moderate 460, the average joe who wants something easy to work on and will be reliable is typically under 750cfm.


And that 750cfm QJ you say GM used on the 350 shows a bit of a discrepancy. By the logic you've posted, it came with a 750...but a simple stock rebuild with the advancements in technology should allow it to run a 950+cfm carb...it just doesn't work like that.

 

[1985 Ford F-150]

You can run numbers all day long and sit here and ***** about whats right and what aint but the only way that works is gettin a couple differnt size carbs and tryin each of em on the truck and see which runs best. On my 410 ive tried a 600 edelbrock a 750 edelbrock and a quadrajet for a small block. The 600 made it ping through mid range RPM with a load on the motor as much as I messed with the jets and rods it still wouldnt fix it. Went to a 750 edelbrock and couldnt get it to drive 10 miles without floodin out. Now its got a reman quadra jet on it and it runs like all get out. It dont flood the motor and it only pings when I romp on it and get into higher RPM (differnt problem I still need to fix). That 600 edelbrock that wouldnt work on my 410 works great on my 460 where a stock brand new holley didnt work as good also able to squeeze 11 MPG out of the pig with the edelbrock. Those two motors in particular dont get over 4000 RPM which is probly about the limit that the OP will have if not lower. Itll cost ya some money but in my opinion youll be money ahead the next time ya need a differnt size carb itll be sittin there on the shelf.

 

[dragogt]

^^^You have to admit dealing with an efi and carbed engine are two totally different animals. The OP is talking carbed. Also keep in mind, you can test and tune all you want...but you still have to figure out the optimal numbers...and the numbers you are referencing are optimal performance. Test and tune will yield completely different results when dealing with a stock 460 vs a 460 with a cam/headers vs. cam/headers/heads/intake vs a completely balanced and blue printed rig. So while, yes...great info from you, I take those as theoretical numbers and won't yield the same results depending on different engine builds. It's been proven through the test of time that on a stock to moderate 460, the average joe who wants something easy to work on and will be reliable is typically under 750cfm.


And that 750cfm QJ you say GM used on the 350 shows a bit of a discrepancy. By the logic you've posted, it came with a 750...but a simple stock rebuild with the advancements in technology should allow it to run a 950+cfm carb...it just doesn't work like that.

Different you say??

4 stroke engine - Check

Push rod engine - Check

Only thing different is the method of fuel delivery...

Any why not if you can streetably run a 750 on a 289/ 302???


[quote author=SteveL link=topic=15585.msg192368#msg192368 date=1250643600]
[quote author=Sixtyninemercury link=topic=15585.msg192361#msg192361 date=1250640592]
[quote author=liljoe07 link=topic=15585.msg192357#msg192357 date=1250637683]
Just because your asking, and no other reason. And I make no Claim to accuracy.

theoretical cfm = rpm x displacement / 3456

volumetric efficiency = actual cfm / theoretical cfm x 100

street carb cfm = rpm x displacement / 3456 x 0.85

racing carb cfm = rpm x displacement / 3456 x 1.1

[/quote]

LilJoe -- you know that those carb formulas are waaaay old school and aren't good for real driving! *The racing carb formula says that a 760CFM carb will be adequate for my 445" turning 6500RPM . . . hardly!* **:jawdrop:
[/quote]

Yep, thats why I have a 750cfm Holley on my 302... I didn't pay attention in math class...
[/quote]


[quote author=289nate link=topic=15585.msg278377#msg278377 date=1280515102]
Tom, I guess you aren't familiar with the carb guy I was referring to. *He had a Holley 850 main body and 950 base plate (which would equate to what Holley would call their 1000 cfm carb) running pretty good on my last very mild factory ported head 9:1 or less compression 289.

Tom and Jayh, do you perceive there is a down side or just that there is no gain to be had on a mild combo? *If I had an intake that would fit a 75-90mm TB are there benefits to staying with a 75mm?

Will the degree each blade opens at each point of throttle depression be identical between say a 75 and 90mm TB? *Take a 650 and 850 Holley double pumper each with 1:1 linkage between the primary and secondary and you would have the same issue right? *You can always change the ratio the secondaries open on a double pumper. *Is there something similar with throttle bodies?
[/quote]

 

[Mil1ion]

If your engine is blowing raw fuel out the carb like Old Faithful ,IMO your timing gears and chain need replacing.

I still believe that 850 cfm is too much carb and you need to run a 650 cfm on the street

 

[dragogt]

So rejet the 850...

And have the airflow it needs with out the extra fuel.. Because I'll bet 10 dollars to a donut that a properly rejeted 850 will out perform a 6-750 on the street or strip...

http://www.summitracing.com/parts/HLY-36-181/

 

[LEB Ben]

So rejet the 850...

And have the airflow it needs with out the extra fuel.. Because I'll bet 10 dollars to a donut that a properly rejeted 850 will out perform a 6-750 on the street or strip...

http://www.summitracing.com/parts/HLY-36-181/

Believe me, I'm as much a proponent of proper tuning and rejetting as the next guy...but I guess we'll just have to agree to disagree on this topic.

 

[LEB Ben]

For the record Aaron...to an extent I do agree with the info you're posting. As I said before, the theory is good, but I don't think the real life numbers are. There comes a point where going bigger starts plateauing and then bigger is no longer better. If you have to continue to re-jet a carb to get it to run properly, why not just buy a carb more suitable in the first place? I'd bet 75% of all carb issues are due to over-carbing and/or not having the know how to tune properly. So I guess my question is, what and where is the cutoff point? You had once said 750cfm and up...is that safe to assume, you believe a 1050 Dominator will perform better than something in the tried and true 650-750 range?

 

[dragogt]

For the record Aaron...to an extent I do agree with the info you're posting. As I said before, the theory is good, but I don't think the real life numbers are. There comes a point where going bigger starts plateauing and then bigger is no longer better. If you have to continue to re-jet a carb to get it to run properly, why not just buy a carb more suitable in the first place? I'd bet 75% of all carb issues are due to over-carbing and/or not having the know how to tune properly. So I guess my question is, what and where is the cutoff point? You had once said 750cfm and up...is that safe to assume, you believe a 1050 Dominator will perform better than something in the tried and true 650-750 range?

How is it theory when the guys over on http://sbftech.com/index.php/board,1.0.html are doing this every day????

Like I said register (yeah I know you cant access it at work) get 10 post in and just do some reading in the Myths and Rumors section....


Jurgen, I'm sorry for dragging you into this; But will you please tell Ben what you've learned over there...

 

[LEB Ben]

^^^I'll sign up there and do the reading you posted if you call Tim at TMI and ask him what carb he'd recommend for a bone stock 460. Like I said, I'm not necessarily saying you're wrong, but where's the plateau, you can't just go infinitely bigger. And if you hop on 460ford, you'll see just as many threads and tech write-ups about staying in the 750-780cfm range for a stock to mild 460. I guess we'll just have to agree to disagree on this one bud.

 

[dragogt]

Don't get me wrong, I'm not saying you can can take a 850 out of the box Do Nothing to it and have it run perfectly..

But all things being equal a Properly set up 850 will Out Perform a 6-750....

 

[rjphillips]

If you are overfueling the carb at idle it will run on as it will if the idle is to fast. Are you checking the timing with the vacumn hose off and is the vacumn hose in the correct spot on the carb, no or not much vacumn at idle. Also make sure the secondary blades are completely closed at idle as this is a common Holley problem and it will induce a small bit of fuel at idle and want to keep running. Good luck. Also check float levels are correct.