900 CFM V. 1200 CFM Dyno anyone??
 

The debate continues. I know, I thought this had been put to rest too.. But the little voice in my head is screaming at me.. 1200 CFM is TOO MUCH CARB!!!!!

So what to do?? I ordered a pair of nifty Barry Grant Road Demon 525 CFM carbs prepared to love the results.. I did love the results.. Except the standard Ford 8V linkage doesn't clear their oh so sexy float bowls.. Doh.. Does anyone have actual or virtual experience (dyno 2000 program) with a set of Holley 1850-2, 600 CFM carbs. with vacuum secondaries V. the Holley 0-9776 450 CFM carbs. with mechanical secondaries..

How much is lost with the 600's when employed with a standard med rise 427, ok.. 433 if you include the .015 over bore @ 10.5:1, 306 degree duration cam at .050 With heads employing a flat tappet, roller rocker 2.25" /1.75" valves (tunnel port valves).. We know at a volumetric efficiency of .95 you "need" little more than 730 CFM..

That is a net of 40% over carburation with the 600's.. 900 CFM is 20%.. What if you re jet the 450's to .060 primary jets V. .058 (a 10%increase) and use the standard (plate secondaries) Does it help or hurt the equation?... Numbers never lie.. They just confuse us.. We know what grouchy did.. What should I do.. Then there is that 4v highrise I saw on e-bay for $1,000.00 Hmmm.


Any thoughts?? Sorry.. (in advance)

Larger carbs. will always (with few exceptions) make more ultimate hp. than smaller ones. What suffers is driveability and torque in the low end and mid range.

Ive played with Desktop Dyno., I don't think you want to rely on this software vs. real world experiance. Hopefully somebody that has done this already can shed some light.

What does the program say? pick any similar application.. 454 chevy or 440 mopar.. 1200 CFM except under the severest conditions 13-14:1 is too much. Isn't it?

The program always says more hp. with bigger carb. no mater what. Desktop Dyno is on the net for free if you know where to look. E-mail me if you would like the details of how to get it. All kinds of cool stuff, movies that arre only a few days old, software gallore (XP pro anybody?) any song you can imagine.

I'm still convinced you will never get the secondaries to open all the way, how much or how little I really don't know.. I have seen the demo versions you are talking about.

Thanks,

Smaller jets
 

Should give you better bottom end...at least this is my understanding...what do you motor gurus (nuts :3DSMILE: ) Think about this?

Michael

No demo version here, full blown program. I just got done playing with the program, it has been a while. Started at 500 cfm on a mild FE Ford. Went all the way up to 2,600 cfm, just kept making more hp. Pretty much true to the real world, but the car would not be driveable.

4V Highrise will not fit in a Cobra without a tall hood scoop. Also would need heads to go with it. You would also need special custom made headers.

The cam you speak of is total duration (306 degrees), not at .050.

I will try to run the numbers the best I can. If you give me the exact cam, we can get closer. Have the heads been ported at all?

900 CFM:

435 hp @ 6,500 rpm
388 lb ft tq @ 5,000 rpm


1,200 CFM:

446 hp @ 6,500 rpm
393 lb ft tq @ 5,000 rpm


2,400 CFM:

461 hp @ 7,500 rpm
401 lb ft tq @ 5,500 rpm


I guess you can't believe everything a computer says. Is your intake a single or dual plane?

I have a 401cid 390 with two 600 1850's on the Ford Al dual plane manifold. The cam is the Ford B cam from the 64 big ford cars. 324 deg. adv., 245 deg. @ 50, Lift is .524. Solid lifter. Too much duration for most but I like it. Engine runs real strong from 3000-6000. However it seems to load up at under 2000 rpm and feels much better when it has its guts rung out.

You need to talk to mr0077. He has a pair of 390 cfm vac. sec. Holleys on his 427 MR and I can tell you it FLIES! Drivability is very good and he really doesn't have all of the bugs worked out yet. I have a set of 390s on my 351 Cleveland and they work well also. They seem to be very flexible and drivable carbs.

Dave is right...I just swapped the 390 and a Ford dual plane for a 780 on an Edelbrock Performer RPM, and both drivability and performance are significantly up...winds like a demon until my coconuts turn into peanuts, very crisp low-end throttle response and easy to drive. Very satisfied (and looks WAY COOL!)
I'm gonna put on a pair of 600's in the very near future and see how (bad?) they do, compared to the 390's, I'll let you know.

Thanks Ken..

I have a set of 600's but they are pretty old.. Maybe that will be a good project for next spring, rebuild them and see how the car acts..

Good point about the 4V highrise being too tall Jeff.. It looks like a sidewinder but taller..

The 390cfm NASCAR Holley is an interesting choice, originally intended for spec. racing it is an excellent carb. I think the 780 cfm you get is way more than enough, but I own the 450's now..

The nice thing about the 390's and the 450's is the lack of a choke and smog ports.. The 525 Demons had as many ports as I have seen on a carb. fine if you need it but unsightly if you dont..

Regards,

Big is not always better. Here is some info from an HP "Auto math" book I occasionally find interesting. First the formulas...

Air capacity =(rpm*displacement)/2
1728 is cubic inches in a cubic foot
CFM= (rpm*displacement)/(2*1728)
3456=2*1728

so...

Theoretical cfm= (RPM*Displacement)/3456
Volumetric efficiency= (Actual cfm/theoretical cfm)*100
standard engine cfm= ((rpm*displacement)/3456)*.85
Performance engine cfm= ((rpm*displacement)/3456)*1.1


A performance example from the book... Using a 650 cfm holley a 350 comaro turned a 1/4 mile in 14.35 at 96.05. only change was to a 800 cfm Holley now it runs 14.61 at 95.44. Book recommends run the formulas. If they fall between sizes go with the smaller one. May not be cool or help bragging rights, but it may be a better performer.

We always run 450 Holleys, mech secondary. I have run them on strong 454 stroker med riser to stock ish 428's, to cross rammed 427's. I think its a perfect match for the FE, the mech secondaries are very preciese. Most of all 450's are DIRT CHEAP, 390's are more expensive. If I remember, last set I bought was 165 each from Summit. You can email me if you have any specifics, but its a bolt on

Yes.. $175 each with free shipping and no tax.. I own two pair already... (anyone want a rebuildable set)

Regards,