Carb suggestions for FE 390 - Ford Muscle Forums : Ford Muscle Cars Tech Forum
 
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post #1 of 13 (permalink) Old 08-09-2016, 06:41 PM Thread Starter
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Carb suggestions for FE 390

Finally finished with the FE. I posted months ago regarding a quench issue, which led to block work and a complete engine rebuild to get things right. Added forged L2291 30 over flat top pistons and forged rods, along with an edelbrock performer rpm intake, comp cams XE274H cam, DUI HEI distributor, rebuilt C6 and 3000 rpm stall. Quench is around .042. I'm running 3.70 rear gears. Right now, the only decent carb I have is a 600cfm edelbrock, which was enough to see if the engine ran. Drove the car this weekend, ran really well, but I think the carb is too small for the motor. Any suggestions on correct carb? I'm thinking 650, but have read about several running 750's. Thanks
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post #2 of 13 (permalink) Old 08-10-2016, 04:10 AM
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Re: Carb suggestions for FE 390

I just delivered one last week, milder, same tight quench, ported heads, but has a CJ-copy cam and a Performer 390 intake (don't like those intakes for an FE, but that's what he had) and we used a Street Avenger 670, it was very happy.

I have also run a 3310 750 Holley on my own 396FE in my 4x4 before I built the 445 stroker (396 was a Holley Dominator Intake and a 270H cam). On that one, a swap to a blue accel pump cam made all the difference in the world and really ran nice.

For yours, with the 3.70 gears I would pick either but with the big cam and intake, I'd prefer the 750. If you want a hand choke, the 3310s can be had pretty cheap too, I don't see any reason to go smaller though

Another option is a 428CJ carb, they are very nice running carburetors, but not cheap by the time you buy one and have it rebuilt. However, the downleg boosters work real well and a lot of guys consider them a value. Nice thing is if you have Hooker headers, they likely have the choke tube and you also get a hot air automatic choke.

If you haven't be sure to tune that ignition curve too, it makes quite a difference for part throttle performance especially with your cam choice

70 Sportsroof, 427 FE/489 cid, TKO-600, 31 spline 4.10, A/C. modified Mass-flo EFI/reprogrammed A9L/CnC ported Victor.

Last edited by My427stang; 08-10-2016 at 04:13 AM.
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post #3 of 13 (permalink) Old 08-10-2016, 06:02 AM
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Re: Carb suggestions for FE 390

Ross makes good suggestions.

Having worked on a few of them locally, I really like the Quickfuel Slayer carburetors.
All the benefits of an expensive carb but with a small price tag.
If I had to buy a carb brand new for a budget build, it'd be a slayer.

drew

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1963.5 Galaxie 446FE/c6
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post #4 of 13 (permalink) Old 08-10-2016, 09:53 AM
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Re: Carb suggestions for FE 390

As a side-note, I would chime-in with Ross and suggest a thorough timing examination and of other tuning parameters. For example, a stock 4100 (580 cfm) made 440hp on the dyno, and although a larger carb could make a few more peak HP you should not be seeing any loss at less than that rpm. If anything, it should be better with the higher velocity of the smaller carb, if the Edel was tuned correctly. The point is, and tuning and carb design aside; at less than peak HP, a larger carb should not benefit power. Likewise, any potential benefit at peak HP can be pre-determined with a vacuum gauge if it indicates a flow restriction at the carb. Just sayin'.

David

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post #5 of 13 (permalink) Old 08-13-2016, 06:48 PM Thread Starter
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Re: Carb suggestions for FE 390

my edelbrock 600 is a 1406 model. From what I read it's geared more for fuel economy and not recommended for use with the RPM manifolds. Just ordered a Holley 670 Street Avenger. I'm thinking it should perform much better with the Holley.....hopefully.
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post #6 of 13 (permalink) Old 08-13-2016, 08:45 PM
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Re: Carb suggestions for FE 390

Yes, the 1406 could perform well, but would require more involved re-tuning than the 670. I would agree that is a good choice. The 670 will need tuning also—just not as much.

David

PS: Using the conventional CFM = CID * RPM * (VE / 3456) formula, I ran your build and it would be most responsive without losing top-end power using a good carb design in the 500 CFM range. Up to maybe 550 or so with good exhaust system and if you did some light porting work (actually ranging from 466 to 541 cfm). The 670 will not be quite as responsive and snappy (the vacuum secondaries save it there), but with good and thorough tuning should be a good all-around driver and you get to keep your bragging rights–which is actually more important than outright performance in many builds.

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Last edited by PSIG; 08-13-2016 at 09:13 PM. Reason: Ran carb flow numbers
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post #7 of 13 (permalink) Old 08-14-2016, 05:00 PM
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Re: Carb suggestions for FE 390

That 670 will likely be a significant improvement, but be very sure you are getting full throttle.

I'd be interested in what you are running for heads and headers though. If stock C8AE-H, C6AE-R or C7AE-A heads, that combo won't breathe too deeply and the 670 will be plenty, as it is likely a 5000 rpm peak and somewhere in the 360-375 hp range. However, if you have a good set of worked low risers, CJs, or Edels, that's easily a 400+ hp motor and it'll want to breathe deeper and longer, the 670 will still do fine, just at the bottom end of good, I'd rather see a 735 CJ carb or some flavor of 750 on it

I know this wasn't the question, but if you are running bone stock, or nearly stock heads, that engine will be a completely different animal if you get the intake ports in the 280 cfm range, either by better heads or by working yours. A pretty achievable number at .550 lift on any of the castings listed above if willing to spend the cash and the cam you have will take advantage of it. FYI as cast, those listed above are in the 220 cfm range and very turbulent, hard to break 400 hp, even if pulling on them hard with a big inch engine

FWIW, the good thing is that average port flow in an FE RPM intake is about 300 cfm, so anything you do on the head side adds power and RPM without hurting low end due to the small change in overall runner volume on a short FE head, port matching that intake to a med riser head is even better and will let that intake flow in the 325-340 range, it's a good piece.

Regardless, where you are now, you have a very nice combo, strong but smart street cam for a 390, tight quench, the right intake, carb's in the ball park now, as long as the timing curve is there and you have a decent exhaust system, it should run very well

EDIT: Just want to make sure I don't look like I am stepping on any toes. David's math is spot-on and matches every recommendation you will get out there from the carb shops, and in terms of cubic inches and RPM, those numbers are good. However, whether it's a harmonic issue of the long intake ports on an FE dual plane or some other factor, in my experience, FEs like it when you err on the big side.

Even the 428 CJ, which was undercammed, minimal overlap, low lift, improved but still poor exhaust manifolds, and a crappy stock exhaust was real happy with a 735. Granted, it had approx 32 more cubes than you, but sub .500 lift, no significant 5th cycle (overlap) effect, a poor timing curve, and in most cases, had to be able to run on any swill nationwide, so it was far less of a deep breather than you built

Remember, a carb is not an intake port. The intake port is fed out of the plenum which acts as a big reserve to dampen what happens in each port and in the case of an intake port, smaller (but adequate) helps. A carb only becomes too big when you do not have enough airflow across the booster to tune the main circuit properly at the RPM you are asking it to perform.

It is not an extension of the intake port, it is essentially an extension of the plenum. I don't want to get too crazy about it, because you are absolutely on the right track with your build, but among others, if interested, David Vizard wrote about "understanding boosters" in (I think), Understanding Holley Carbs, and explains it pretty well.

70 Sportsroof, 427 FE/489 cid, TKO-600, 31 spline 4.10, A/C. modified Mass-flo EFI/reprogrammed A9L/CnC ported Victor.

Last edited by My427stang; 08-14-2016 at 05:23 PM. Reason: Added info
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post #8 of 13 (permalink) Old 08-14-2016, 08:59 PM
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Re: Carb suggestions for FE 390


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post #9 of 13 (permalink) Old 08-18-2016, 05:11 PM Thread Starter
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Re: Carb suggestions for FE 390

Thanks for the great feedback as always. Tried the 670 today and it's a night and day difference / improvement over what I had. The 670 has a stumble in it when I first hit the gas, or idling at stop signs, but really takes off after that. I have to look into that part, maybe accelerator pump, not sure yet. Need to recheck timing. Running 93 octane. Motor does not get hot, but radiator overflow spits water out in small gasps for about 5 minutes after I've driven it. I filled the entire system full of water when adding fluids, could be too much water, could be air in the system, not sure. Compression ratio is right at 10 to 1, so I guess I'm on the edge for stock C6AER heads.
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post #10 of 13 (permalink) Old 08-20-2016, 02:20 PM
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Re: Carb suggestions for FE 390

I would look very closely for vacuum leaks first, not old ones, but ones you may have caused with the carb swap.

Look to the base of the carb for any unhooked hoses, or if you have to, look close at the gasket under the carb compared to your intake and carb.

First two things after a self-induced vacuum leak I would look for are:

1 - Accel pump adjustment. It's not tough to do, but you basically hold the throttle wide open (not running), then actuate the little accel pump arm with a screwdriver and make sure you have about .015 clearance between it and the big arm off the throttle linkage. That allows you a full stroke without bottoming the diaphragm

The second thing to look at for the accel pump is that it gives an immediate and solid stream. If its weak, you may need a new diaphragm (assuming this is a used cab, a new carb should have a good diaphragm, but you never know

2 - I would make sure I have the throttle set right. A good way to check is, warm the car up so the choke is fully open, then let it idle at normal idle speed. Pull the vacuum line off the pass side front metering block, if you have vacuum there, your primary throttle blades are too far open. That will cause you to be in the transition circuit and you won't have it when you need it. The choke has to be full open though. If it is this way, and you didn't have a vacuum leak to fix, then close the primary throttle blades and if you need more idle, there is an adjustment on the passenger rear, but you need to get it from the bottom

Now, if this is a used carb, there is possibly more to do, but I'll wait to hear from you

70 Sportsroof, 427 FE/489 cid, TKO-600, 31 spline 4.10, A/C. modified Mass-flo EFI/reprogrammed A9L/CnC ported Victor.
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post #11 of 13 (permalink) Old 08-23-2016, 10:14 AM
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Re: Carb suggestions for FE 390

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Originally Posted by James4164 View Post
Thanks for the great feedback as always. Tried the 670 today and it's a night and day difference / improvement over what I had. The 670 has a stumble in it when I first hit the gas, or idling at stop signs, but really takes off after that. I have to look into that part, maybe accelerator pump, not sure yet. Need to recheck timing. Running 93 octane. Motor does not get hot, but radiator overflow spits water out in small gasps for about 5 minutes after I've driven it. I filled the entire system full of water when adding fluids, could be too much water, could be air in the system, not sure. Compression ratio is right at 10 to 1, so I guess I'm on the edge for stock C6AER heads.
For the off idle, throttle tip in stumble I'll suggest what worked for me with my 670 Street Avenger. I don't see it listed anywhere what car this engine is in, but if it is in a big, heavy car, like mine, then the stumble could be a lean stumble. What solved my issue was going to a smaller squirter. If I remember correctly I installed a #24 squirter and it made all the difference in the world. The smaller squirter delivers the same volume of fuel from the accelerator pump except that it takes longer. The longer time to deliver the pump shot gives the engine time to get a heavier car moving without leaning out before transitioning to the regular circuits. My drives wonderfully with that change, so keep that in mind if for a tip-in, off idle stumble.

1970 XL, 351W originally 2V, now 4V
670 Street Avenger, Edlebrock Performer intake, Comp XE262H, Flowtech Headers
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post #12 of 13 (permalink) Old 09-01-2016, 06:26 PM Thread Starter
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Re: Carb suggestions for FE 390

Great feedback as always! I made "0" adjustments to carb, only worked with timing and idle speed. It took a couple times with timing light and idle speed adjustments before everything started to fall in place, or close to it. Initially I was at 14 deg. BTDC with an 1100 rpm idle in park, which would drop to around 850 in drive and just fall on its face. Now I'm at around 16 deg. BTDC at 850rpm in park, with pretty much same rpm in drive. (With Vac. Adv. disconnected and plugged for timing checks) I was around 34-36 deg. timing at 3000 rpm. No stumble out of carb now. Carb is new 670 holley street avenger, also using full length headers (Crites) and Hooker Aero chamber mufflers. Sounds great, runs much better. I'm thinking I still have more work to do with the timing to get it completely dialed in, but it's getting closer and is fun to drive.
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post #13 of 13 (permalink) Old 09-02-2016, 12:45 PM
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Re: Carb suggestions for FE 390

Did you adjust the idle a/f?

If primaries only, start at about 1 1/8 from bottom, and go in and out until you have the best idle, either by ear or with a vacuum gauge. If it is a 4 corner, start 3/4 out on all 4. If you haven't adjusted idle a/f, you likely have more to gain!

Thanks for reporting back!

70 Sportsroof, 427 FE/489 cid, TKO-600, 31 spline 4.10, A/C. modified Mass-flo EFI/reprogrammed A9L/CnC ported Victor.
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