625 Road Demon to be happy or replace?

[juit 34]

Displacement CFM Needs

289/302ci 453 cfm

351ci 550 cfm

390ci 609 cfm

428ci 668 cfm

 

 

I think were with sec mech

 

but with the vacum sec the engine only takes what it needs of the sec

Edited October 17, 2014 by juit

[jholmes217 65]

Hi,

 

I´m Tom from Germany. I am proud to drive a 69' mustang coupe J

 

By the way, where in Germany are you if you don't mind me asking? I did three tours there with the U.S. Army. I was stationed in Zweibrucken, Bamberg, and Heidelberg. Loved every tour!

[barnett468 418]

Displacement CFM Needs

289/302ci 453 cfm

351ci 550 cfm

390ci 609 cfm

428ci 668 cfm

 

 

I think were with sec mech

 

but with the vacuum sec the engine only takes what it needs of the sec

 

actually that is not correct or realistic. any of those engines with even the slightest bit of hp all need at least 75 cfm more.

 

heres a realistic estimate of the minimum sizes.

 

289 - 600 cfm (this was factory on the 271 hi po. the shelby had 715 which was a little big.)

302 - 600

boss 302 - had a 780

351 - 650

boss 351 - had a 780

390 - 650

428 - 700 (735 was stock on the cobra jet which was no rocket ship high hp engine.)

Edited October 18, 2014 by barnett468

[RogerC 136]

actually that is not correct or realistic. any of those engines with even the slightest bit of hp all need at least 75 cfm more.

 

heres a realistic estimate of the minimum sizes.

 

289 - 600 cfm (this was factory on the 271 hi po. the shelby had 715 which was a little big.)

302 - 600

boss 302 - had a 780

351 - 650

boss 351 - had a 780

390 - 650

428 - 700 (735 was stock on the cobra jet which was no rocket ship high hp engine.)

 

+2

Though you covered boss 351s, I believe all 4V clevelands came with a 780. I've posted elsewhere in the forums about 351C carb requirements but don't have the time right now to look it up to check.

[juit 34]

at holley they told me that 302 needs a 570

 

600 was a lil over carbed

 

don't take my word on this, I found all this on car craft mag

 

with the 600 that I have on my 302 my car runs rich all the time, on the road also

 

respond very very good but its running very very rich

Edited October 18, 2014 by juit

[barnett468 418]

at holley they told me that 302 needs a 570

 

600 was a lil over carbed

 

dont take my word on this I ound all this on car craft mag

 

with the 600 that I have on my 302 my car runs rich all the time, on the road also

 

respond very very good but its running very very rich

 

ok, the box stock 4 barrel carb on a box stock ford is....550 cfm. my listings are NOT for box stock engines, however, i have driven around 10 zillion box stock type engines that were bored .030" - ,040" over with stock type or very close to stock type cams and they run fine with a 600 cfm holley straight leg booster non smog vacuum secondary carb with the heavy secondary spring in them on eddy performer manifolds.

 

if you put an rpm manifold on them, they will run poorly off the bottom.

 

if you do not run the heavy spring they typically bog a bit when the secondaries open.

 

you can run a 750 on a stock 302 engine and it will NOT run rich if it is properly jetted and you don't floor it from a dead stop.

 

if you have a 600 cfm, your carb size is not your prob, its simply impossible.

.

Edited October 18, 2014 by barnett468

[juit 34]

what color spring U recomed?

[barnett468 418]

what color spring U recomed?

well i have no idea what is wrong with your carb. the springs are colored. the heaviest will open the secondaries the latest and slowest so you will be running on 2 barrels most of the time. this will eliminate bogging from them opening to soon but it will not eliminate bogging from improper jetting.

.

[shaun071 62]

unless that is a box stock 2 barrel you need at least a 670 cfm and for a moderate or higher hp 4 barrel you need a 750.

 

That was my thoughts. The 351 has 214/224 cam closed chamber Aussie heads etc. It's mild but I don't want to starve it. I suppose if the secondaries are tuned to open later milage would be ok as well. The coupe will be almost daily driven.

[barnett468 418]

That was my thoughts. The 351 has 214/224 cam closed chamber Aussie heads etc. It's mild but I don't want to starve it. I suppose if the secondaries are tuned to open later milage would be ok as well. The coupe will be almost daily driven.

I would look sat a 670, 700 or 735 annular or downleg booster type carb. The mileage on any given engine is always related to the right foot, lol.

 

Yes, the later the seconds open, the better the mileage.

 

That duration on that cam is a bit too long on the ex compared to the intake. it would probably be happier with a comp cams xe262h or 268h.

 

Also FYI, you need at least 1 5/8" primary header tubes with that.

Edited October 20, 2014 by barnett468

[shaun071 62]

I had the engine in my daily driver for 6 years with 1 3/4" 4into1 long tubes. The reason for the longer duration on the exhaust was the engine was built for straight propane fuel. It ran very well, high 13/low 14 down the quarter in a 3700lb Aussie Falcon. I'm still remembering/learning about carbs since I've been playing with LPG fuelled cars for the last 15 years or so.

[Max Power 74]

ok, the box stock 4 barrel carb on a box stock ford is....550 cfm. my listings are NOT for box stock engines, however, i have driven around 10 zillion box stock type engines that were bored .030" - ,040" over with stock type or very close to stock type cams and they run fine with a 600 cfm holley straight leg booster non smog vacuum secondary carb with the heavy secondary spring in them on eddy performer manifolds.

 

if you put an rpm manifold on them, they will run poorly off the bottom.

 

if you do not run the heavy spring they typically bog a bit when the secondaries open.

 

you can run a 750 on a stock 302 engine and it will NOT run rich if it is properly jetted and you don't floor it from a dead stop.

 

if you have a 600 cfm, your carb size is not your prob, its simply impossible.

.

 

This is correct, and your previous as well.

 

There is no way 30 cfm makes even the remotest difference in carb sizing with proper tuning, especially with vacuum secondary carbs. Vacuum secondary carbs are in essence variable venturi carbs. With proper tuning, it is hard to overcarb with them. David Vizard wrote some great stuff of PHR a few years ago and got a 750 working great on a 5.0 liter engine.

 

As far as the charts go, they are fine for garden variety street cars, but there is a bit of a flaw in using straight rpm for cfm requirements in that it doesn't measure the rate of acceleration, just a mathematical equation. As we all know, rate of acceleration is what performance actually is.

 

I had a stock 390 GT in a 66 Comet Cyclone years ago, the 325hp 4v version, and from the factory it had about a 600cfm vacuum Holley. I swapped a 750 on there and the difference was measurable. The chart says 600, your butt says 750.

 

If a 600 is running rich on a 302, it's a tuning issue, plain and simple.

[barnett468 418]

I had a stock 390 GT in a 66 Comet Cyclone years ago, the 325hp 4v version, and from the factory...

oh yeah...factory fiberglass hood, veeeery cool. my friend has 4 67 427 r codes. i hate him...

 

 

.

[Max Power 74]

I used to like the 66 better, but over time have grown more fond of the 67 models. Fiberglass hoods, best looking wheel covers ever made, etc. Mine was a baby blue winter beater, as the back half was pretty rusty. There were a lot of 350 Nova drivers back in the day that saw my taillights. Most assumed I was running a 289. Chevy guys don't know their Fords very well.

 

Sadly, I rolled the car. Many times. Lucky to walk away from it. It was my 18 but not invincible moment.

[MUST 25]

Hey Guys,

 

thanks for the many replies. :thumbup1:

I have decided. I don´t know what is with the Demon cab, maybe installed wrong needles, or perhaps totally different things..

Your opinion and tips say, that the Demon is not the best and easiest choice, for me. So I'm going to buy a 570 CFM Street Avenger. And start over from scratch.

 

Thanks for the support!

 

Tom from Munich ;)

[barnett468 418]

ok great. just a suggestion, you might want to order the optional secondary spring kit with that is case you need or want to change the point they open at. also the sa carbs are jettied slightly lean so expect to do a little jetting.

 

what does a "sharp" camshaft mean?

 

if your engine revs to 5800 rpm, that carb will still work but it will be a little small imo.

 

if you have probs with hard starting when hot you might consider buying a phenolic spacer also.

.