I need suggestions on size of carb (vacuum secondarys) for my 557 stroker, 9.3:1 CR, Stealth dual plane intake, mildly ported and cleaned-up DOVE heads, stock rockers, cam=204/214 @ .050, .479/.504 lift with a C6 and 410 diffs in an otherwise stock '76 F250 4X4. This is a "street stupid" daily driver. It'll probably never see over 5 grand on the tach.

 

At 100% volumetric efficiency 557 cubic inches at 5500 RPM will require 887 cfm.

Brad

 

Brad, How do you think it will run with a Holly 750, vacuum secondary, for street use?

 

Using a 750 carb will result in great bottom end response, but loss of a good portion of your overall HP (DD predicts anywhere from 30-75 HP, depending on cam selection).

Also, you need a lot more cam for 557 cubes, even for a mild motor. A stock-spec cam on a 460 cubic inch engine will positively strangle your 557 ci stroker. I tried a couple of difference cam profiles for max low-rpm torque and driveability. All the sims were run with a 900 cfm carb and 2.25" header primaries.

Your cam specs
HP - 467 @ 4500
Torque - 636 @ 2000 (torque falls off rapidly after 2500 RPM and is under 500 lb-ft @ 4000 rpm)

Comp Cams 280H
HP - 502 @ 5000
Torque - 606 @ 3500 (torque remains above 595 lb-ft from 2000 to 4500 RPM)

Lunati 00096
HP - 485 @ 5000
Torque - 626 @ 2500 (remains above 600 lb-ft @ 4000 rpm)

And to try something a little on the wild side, I through in a hydraulic roller cam just to see what would happen. Pay attention here....

Crane 325-2S-12
HP - 583 @ 5500
Torque - 656 @ 3500 (torque remains above 640 lb-ft from 2500 to 4500 RPM)

Lunati 516A1LUN
HP - 576 @ 5000
Torque 672 @ 3500 (torque remains above 640 lb-ft from 2000 to 4500 rpm)

 

I want to keep the lift down around .500" to run stock rockers and I want to be able to get from one gas station to the next on my 40 gallon fill-ups. I also don't want to twist-off all of the drive-line parts on this pristine, original paint, very stock (except for bigger wheels and tires) '76, F250, 4X4, C6, 410 diffs., daily driver, truck. I see the Lunati 00096 has .516/.543 lift and I'm told I can't run stock rockers with that lift. New rockers don't cost much and a different set of springs are affordable. As a 60 year old dentist who has over hotrodded almost every other project I've done, I'm trying to be really sensible on this one. I only went to the 557 because the parts were so cheap on eBay, I thought, "Why not?" I'll have to think this one out and I sincerely appreciate your help. Any other rationale you can provide is welcome.

 

If you can afford to build a 550+ cubic inch stroker then you have the money for a set of better rockers that will handle the cam this engine needs to breath propertly.

If you are putting all your money in the stroker short block and none anywhere else then I respectfully suggest you ditch the idea. Take the extra two grand you're going to spend getting the short block prepped and put it into better parts for a standard 460. You'll have a much better result.

Also, you mentioned economy as an issue. I've got really bad news - if you build it, this monster is going to drink fuel at a rate that will make a Greyhound bus seem absolutely miserly in comparison no matter what you do.

I think I know why you asked about the 750 carb earlier. You are thinking that the smaller carb will get you better fuel economy. Wrong - way, way, very, very, wrong. All a smaller carb will do is choke your big inch engine. It takes X amount of fuel for Y amount of air flow to support proper combustion. Changing the carb size does not change the physics involved, it just means you can flow less air and you are effectively negating all the extra cubic inches you just spent a coupla grand to create.

You mentioned wanting a sensible build. Okay, here's one...
-Standard block with a .030 bore and a new set of 9.5:1 cast pistons.
-A kick-butt balancing job on the rotating assembly
-A set of C8, C9, or D0 heads with a good valve job and some port matching, and retrofitted with adjustable, roller-tipped stamped steel rockers and a good set of properly matched valve springs.
-A Lunati 90460LUN cam
-Roller lifters
-A Cloyes double-row roller timing chain set
-A Weiand Stealth intake
-A 750 CFM vac secondary carb
-A set of GOOD headers with 1-3/4 or 1-7/8 primaries and 3" collectors
-A quality rebuilt factory distributor and Duraspark (factory) ignition box to light everything off.

With a little careful shopping you can build this entire setup for about what the stroker kit and machine work alone would cost on your 557. It will be more pleasant, break less parts, sound really nice, be very streetable, and be relatively fuel efficient (or at least as efficient as a 460 in a 5000lb 4WD truck can be).

DD predicts 496 lb/ft torque and 453 HP with this build. The low-end torque curve is nice and fat with at least 480 lb-ft on tap from 2500 RPM to almost 5000 RPM. Darned respectable for a mild 460 and plenty of grunt to pull around your truck in fine fashion.

Brad

 

Well Brad we're getting together a little late in the project but I'm ready to listen to your suggestions to finish it off. I actually started off as you thought I should with the nice sensible 460 but, as usual, I got off track. Here's where I am. Beautifully prepped .080" over block, balanced rotating assembly consisting of 4.5" Scat 9000 crank, Scat H-beam 6.7" rods, Probe 51cc dished pistons. Nicely prepped , mildly ported DOVE heads with Ferrea 1.75"/ 2.19" valves and Comp 926-16 springs and a Stealth dual plane intake. I've assembled the short block but could easily swap out the cam and even install better springs and get a set of rockers. Tranny is a C6 I built pretty tough. Whada'ya think?

 

Some things to think about in your build. I'm doing the same thing but only a 502.

Don't ask me why but fords always love more carb than called for. I would worry about running a 750, it may run lean towards the top and that is not good. I'm thinking about running a 950 holley with 750 ventuies. I heard nothing but good things about this setup. Throttle response like a 750 but flow capability of a 950. The other option would be a 850 with anular boosters.

Bigger cam means different stall converter. I will have mine custom built and if you have any doubts do the same thing. Don't go cheap in this department. With your current cam you might be ok stock but I would still ask the pro's.

Brad can I have you run my numbers again please.

Block
Stroke = 4.125
Bore = 4.40
Rods = 6.7
Pistons = 33cc D-shaped dish
Zero deck and balanced

Heads
Intake = 2.25, flow 320 @.500
Exhaust = 1.76, flow 200@.500

Intake, 460 Air-Gap. I would use stealth figures for this.

Cam
C/L = 110.7
Intake = 233.5@.050, lift .575
Exhaust = 243.7@.050, lift .576

 

I'm thinking it's time for a tunnel ram and dual 550's or if you can drop that CR a little bit you could top it off with an 8-71 blower. Don't want to starve it . . . Brad is 100% correct about running a carb with too little flow.

 

Well, Brad, you've made me come to my senses. I actually ordered the cam I listed when I planned on building a solid, mildly tweaked 460. You are absolutely correct, with 557 cubes, the engine can use a ton of cam. I probably couldn't hardly over cam it. I am, however, still going to be conservative and go with the Comp 280H, a set of their Magnum rockers and stick with my 926 Comp springs. I'll have to install guide plates of course. I'll send my Holly 750 back to Summit and get an 850.

Thanks to everyone for all of their suggestions and I'm open to more.

 

You might want to look at the Barry Grant 850. BG's venturi work is usually very nice and it's not uncommon to see one of his 850s actually flow upwards of 900 cfm. They are a little pricier than a Holley, but I thing the expense is justified.

Make sure that the springs you have won't be binding with the cam. A 280H actually isn't just a whole lot of cam and you shouldn't have any binding issues, but it always pays to make sure. The roller lifters and roller tipped rockers are always a good idea just to get rid of some parasitic power loss (figure an extra 7-10 HP). Be sure to use a good timing chain - I have come to prefer the Cloyes double row full roller unit. Dead reliable, strong as heck, and not real expensive compared to some other options.

With the extra cubes you will want to get larger primaries on the headers. 2.25-2.5" minumum. The headers normarlly recommended for torque on a 460 (1.75" or so) will be too small for your added displacement.

Oh, almost forgot... High Volume Fuel Pump. A standard unit may not be able to keep up with your monster mill.

Your engine is going to be a mild mannered torque monster! Enjoy the heck out of it and keep us posted on the build. tmyers mentioned getting a little higher stall converter. Maybe, but you have a ton of torque on tap right off idle and the cam is going to accentuate the off-idle response. I'd probably stick with a stock stall unit that's built to take the torque you're going to be making.

What ignition system will you be using?

Brad

 

tmyers..

I reran the sim with the numbers you posted...

RPM HP / Torque
2000 174 / 456
2500 230 / 484
3000 283 / 495
3500 345 / 518
4000 409 / 537
4500 468 / 546
5000 511 / 536
5500 540 / 515
6000 549 / 481
6500 539 / 436

Brad

 

Thanks Brad. These are the numbers I get with Engine analizer 3.0

RPM HP / Torque
1500 44 / 154
2000 108 / 283
2500 187 / 392
3000 282 / 494
3500 380 / 570
4000 459 / 602
4500 524 / 612
5000 569 / 598
5500 589 / 562
6000 571/ 500

I don't know the why this stuff is so hard to get good figures though. Wish I had the money for the real good DD's.

I think I'm going to plug in the Lunitic cam.

 

Brad the lunitc cam is a mech roller by the way.

 

tmyers - I ran the sim above using a plain hydraulic lifter. I reran it with the hydraulic roller profile. You will likey

RPM HP / Torque
2000 227 / 596
2500 290 / 609
3000 352 / 616
3500 416 / 624
4000 476 / 625
4500 528 / 616
5000 563 / 536
5500 575 / 592
6000 557 / 549
6500 527 / 488

Brad