Carb Selection

750 or 850 on a Magnum 408 build

  • Holley 750 HP

    Votes: 16 27.6%

  • Holley 850 HP

    Votes: 14 24.1%

  • Quickfuel Q750

    Votes: 14 24.1%

  • Quickfuel Q850

    Votes: 14 24.1%
  • Total voters
    58
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moparspares

moparspares

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I know this has been covered before but there is varied opinion on either a 750cfm or 850cfm for a 408.

My 408 build is

Magnum Engine
Probe Forged Pistons with eagle rods
Compression roughly 10.5
RPM Edelbrock heads
Cam Lift intake .568 Duration 236
I have both RPM Air gap and M1 but will use the airgap I think
3500 PTC Stall convertor 727 with 8.75 3.91 gears in a Duster

The double pumper carbs im thinking about are

Holley 750 HP
Holley 850 HP
Quickfuel Q750
Quickfuel Q850
 
I'm a big fan of the Quick Fuel -AN carbs. They have annular boosters which makes a big difference for street driving and throttle response.

The QF carbs are a little nicer than the Holley's, too, IMO.
 
My machinest and dyno guy has always claimed mopar like more carb and bigger plenum due to their anemic heads. I've see the results 1st hand on 2 big blocks he built for me. I'd go 850 and the HP series carb is tough to beat.
 
roccodart440 said:
My machinest and dyno guy has always claimed mopar like more carb and bigger plenum due to their anemic heads. I've see the results 1st hand on 2 big blocks he built for me. I'd go 850 and the HP series carb is tough to beat.
Click to expand...

Think about what he's saying. Mopar heads are FAR from anemic. The reason they like more carb and bigger plenums is because they have superior heads compared to other small blocks. Mopar small block heads are by far the best flowing small block heads stock to stock industry wide......even including some of the best "bow tie" heads made.
 
I run an AED HO 850(modified Holley)on my 408 Eddy headed small block.I also have to friends that run the AED 750(383 BB-Eddy heads)and a 422sb-W2 heads with the AED950.I,ve been running this carb without issues,other than jetting up or down(weather)for 4 yrs.Summit Racing now carries the full AED line of carbs at great prices.:D
 
RustyRatRod said:
Think about what he's saying. Mopar heads are FAR from anemic. The reason they like more carb and bigger plenums is because they have superior heads compared to other small blocks. Mopar small block heads are by far the best flowing small block heads stock to stock industry wide......even including some of the best "bow tie" heads made.
Click to expand...

Read my post, "big block". If you think big block mopars have the best flowing heads you have some reasearch to do.
 
roccodart440 said:
Read my post, "big block". If you think big block mopars have the best flowing heads you have some reasearch to do.
Click to expand...

Rob said small block.

but if you want to talk big blocks... i know a guy with a 7 sec comaro
runs a big block

guess what heads? brodix BB4's

not factory LOL i wonduhr why

but then you have 8 sec hemi darts/cudas all over the place running IRON hemi heads. put that in your pipe and smoke it.
 
to the thread starter: if this is a strip car there would be no reason to go with a 750.

if it's a street car the 750 would give you a little more street response and maybe better mileage.
 
moparlover said:
Rob said small block.

but if you want to talk big blocks... i know a guy with a 7 sec comaro
runs a big block

guess what heads? brodix BB4's

not factory LOL i wonduhr why

but then you have 8 sec hemi darts/cudas all over the place running IRON hemi heads. put that in your pipe and smoke it.
Click to expand...

Actually he said 408 and my mind went into big block mode.. The words small and block were never in the title or in the original post.

How many of us have or have ever had or will have a 426 or larger old school hemi? Ok, moving on. Most will have a B or RB, not of the max wedge variety either. What's the highest HP 383 and 440 mopar ever made? And what are the factory flow numbers on the B/Rb heads? What were the valve sizes in those heads? Yes, there aftermarket heads that flow, they are expensive and utilize Max wedge ports, raised ports, offest rockers etc. Not factory design.

I've had many mopars as well as my current BB dart. I love mopars. I'm not dissilusioned though to think mopar is the best end all be all in engineering. All the brands have different areas of ups and downs.

To the OP. I don't think you can go wrong with any of the choices you gave but the 850 hp will likely yield max performance.
 
I have a 408 built on a 92 Magnum block. My cam is 242/248 Dur@ .050, .3660/.3630 lift @ .050, 112° lobe sep. 549/544 gross valve lift. Pretty close to yours. I run an RPM air gap and my compression is 11.8:1. I ran an Edelbrock 800 for a year and had no issues, other than a rich condition which was likely timing rather than carb. I am (still) planning for an E85 conversion at some point, and since they run on Proform bodies, I changed to a Holley 750dp so I could get all the plumbing in place. The Holley has more power but needs a lot of adjusting and tinkering. It also runs rich, but again, that will be in the timing. I need to **** or get off the pot and either get a programmable MSD box, an E-curve distributor, or bushings for my existing MSD distributor. The 750 is more than enough for your motor. Mine turns 500hp and there is plenty of fuel. I recommend talking to Crackedback about how to set up the timing correctly. You will love this motor. Every time I drive it I can't help but smile and say "Holy **** this thing is fast!"
 
Of the choices provided, for the money, install the Holley 850 HP. Perfect fit for your combo and carb parts are at most Auto Zone type stores if you ever get in a bind and need a small part for it... 0.02
 
roccodart440 said:
Read my post, "big block". If you think big block mopars have the best flowing heads you have some reasearch to do.
Click to expand...

Sorry about that. I missed that part. While I agree with you, they ain't the worst. lol
 
roccodart440 said:
Read my post, "big block". If you think big block mopars have the best flowing heads you have some reasearch to do.
Click to expand...

Also, the thread is about small block heads. So I simply assumed.
 
moparlover said:
Rob said small block.

but if you want to talk big blocks... i know a guy with a 7 sec comaro
runs a big block

guess what heads? brodix BB4's

not factory LOL i wonduhr why

but then you have 8 sec hemi darts/cudas all over the place running IRON hemi heads. put that in your pipe and smoke it.
Click to expand...

Jim Laroy (IQ52) would have gotten 800 HP through factory IRON 906 heads had things gone right. I don't know how they were ported, but they were ported within the limitations of the stock ports. No tubes or anything fancy. Just good port work. Had the cooling accident not happened on the dyno, that engine would have seen 800 HP. It was well over 700 with leakdown on all cylinders after overheating and their quick allowed repair. It had like 56% leakdown on the worst cylinder and had leakdown on all the rest yet STILL made over 700 HP. Had he not been penalized for spending money on a high dollar crank I think he would have won the contest. In my eyes he did win, because he made the most TQ and HP. I shouldn't keep saying he.......it took their whole team. Those are a great bunch of guys. If you can port a 906 to flow 800 HP, I think big block Mopar iron heads are ok.
 
Mopar To Ya

My build is probably a touch more conservative than yours however I hope it will be in the vicinity of 420 - 450HP. My brother runs a Holley 750HP on a standard stroke 340 and it runs very good. I just thought with the extra 60 odd cubes going a little bigger. As I said in my original post members here are split between a 750 and 850. Economy for me is not an issue so I dont care if it uses a bit more fuel but of course I want the engine to run up to it's potential.
 
Would be interesting to see an Ede Thunder Series AVS 800 on a 408.
I bet it would work really well.
 
moparspares said:
Mopar To Ya

My build is probably a touch more conservative than yours however I hope it will be in the vicinity of 420 - 450HP. My brother runs a Holley 750HP on a standard stroke 340 and it runs very good. I just thought with the extra 60 odd cubes going a little bigger. As I said in my original post members here are split between a 750 and 850. Economy for me is not an issue so I dont care if it uses a bit more fuel but of course I want the engine to run up to it's potential.
Click to expand...

My Eddy 800 was too much for the motor. Too much fuel is just as power robbing as too little. An 850 is capable of dumping a LOT of fuel. Can't hurt to try. Especially if you have another carb to swap and try if you don't like it. You are going to love your stroker. The torque is absolutely impressive.
 
I have a crate 360 magnum the (300hp) in my 1991 half ton short bed 4x4 truck and after months of messing with an edelbrock I bit the bullet and bought a quick fuel super street series 680cfm vaccum secondary carburetor.
Buying that carburetor was the best move I ever made, I love it and I love it more and more everyday,It has billet metering blocks and billet base plate. Changeable idle air bleeds and idle feed restrictors and changeable high speed air bleeds. It has a 4 corner idle and changeable power valve channel restrictors. Tuning is basically unlimited on this carburetor. And the vaccum secondary adjustment is awesome, just turn a screw clockwise for sooner counter clockwise for later.
The guys at quick fuel are very knowledgeable and very friendly.
I voted for the quick fuel 750, and I would recommend the super street series.
 
Oh and I forgot to add, if it were me i'd run the 750cfm if most of your time will be on the street, if it's going to be on the track strictly then I'd probly run the 850.
But the 750 will give better throttle response on the street over the 850.
I know a guy running a 650cfm mighty demon on a 408 stroker and he said he switched to the 650cfm mighty demon from a 750cfm holley and he said he noticed a huge improvement in throttle response. I don't know his camshaft spec's. But he built it for a 4x4 truck.
 
If you do go 750, I have mine for sale, so that I can go to an E85 carb.
 
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