Larger Holley Carb or MSD Atomic EFI?? Opinions?

[BS CUDA]

 Ok its that time - time I finally decide on Larger Carb or thinking MSD Atomic EFI. Currently running an 870 Holley on a 500CI stroker - 520HP and 620FT LBS peak, 727 trans, 4.10 Auburn 8 3/4 in a full weight '74 Cuda. The car is really fun but I can never seem to stop looking for more power / better ET's. It has run a best 12.08 @ 112 MPH @5000 ft in Calgary. I am thinking maybe 1000 cfm carb should enhance these #'s but continually tuning / jetting is getting a little tiring. The Atomic EFI runs a 1000 CFM throttle body and is good to 620hp with the big pump and should eliminate tuning. I will be hauling this car to various tracks this year as Calgary's in done. I would love to see this car in the mid 11's and am sure it has it.... Carb swap = $800.00ish and always tuning, EFI 2500.00ish and 0 tuning.  Your thoughts?    Oh yeah the car is a street / strip car - never drives more than an hour from home unless on a trailer due to $1.30 per litre premium and high RPM.

[PlumCraZRT]

Seems to me you should be making more than 520hp with 500ci.  I can't imagine the carb is really hurting your numbers that much.

What heads/cam/intake you running?

[BS CUDA]

Yeah I know - it is a `mild`stroker - the intake is a Edelbrock Performer RPM, Edelbrock performer rpm heads, and cam is Comp 21-225-4 Grind XE284H-10. I purchased this engine already built At the time the Dyno sheets looked impressive to me compared to the run down 440 that was in the car. And yes I know a set of Indys, bigger cam etc would awaken the beast  but big $$$$ as a package.

[HP_Cuda]

What kind of rpms you pulling on your 1/4 mile? 6k 7k 8k?

If you are only pulling 6k then you are at 100% Volumetric efficiency:
http://www.cuda-challenger.com/cc/index.php?topic=84870.0

The Performer intakes are made for low end torque so if you want to improve your 1/4 mile times then you might look into a single plane manifold to gain more top end power.

You could also just go and do a dyno tune. The dyno's are usually around $300 bucks and then they will charge you extra for the amount of time and tinkering after that. ymmv

[Killer_Mopar]

Just my I dont have the MSD atomic EFI, but I recently added FAST EZ-EFI to my car and recommend it to everyone. I went with the FAST system because it was cheaper and had been out for a while so it is well tested. The MSD kit plugs into their ignition system and doesnt require a return line, but I don't think the return line-less system is a positive thing. Anyhow, the EZ-EFI kit is one of the best modifications I have done to the car - it smoothed my idle out and the car runs/drives a ton better, the tune is 1000% better than it was with my carb. It is really a night and day difference. Thats not to say it doesnt have a few drawbacks (mostly $$$$). I also wouldnt recommend the kit with the external fuel pump as it is overly loud in my opinion (to the point where Im going to an in-tank fuel pump). That is my only real complaint, everything else has performed beyond my expectations.

[ragtopdodge]

FYI with the MSD unit...if you want to get returnless, then you have to run full rubber (or braided) hoses from the tank to the EFI.  I.e. no hard lines.

[BS CUDA]

HP - I understand the formula and see there is skepticism in regards to such. I ran a 770 Holley prior to the 870. I picked up 3 tenths and a few mile per hour when I switched to the 870. I am pulling roughly 6300RPM in the 1/4 and will look at the single plane - perhaps the Victor if I can get it under the hood

Killer - thanks for the positives on the EFI. I have looked at all the EFI setups currently available, in my opinion the MSD just looks better although it is currently limited to single carb and no power adders. The Fast EFI is a very close second due to its proven abilities and time tested... if EFI is chosen.

RagTop - I will be running with the return line as by MSD returnless "test" you would have to live in Alaska or further north to run returnless effectively. I already run a 1/2" pickup with 1/2" braided rubber front to back.

Keep the Info coming folks. I love this site and the information and opinions all users have.

[Chryco Psycho]

the formula doesn't work , I continually got faster stepping from 850-950-1050
 I build an EFI system using SDSEFI computer based in Calgary , 1200 CFM T body & 75 lb/ hr injectors .
If the budget can handle it I would recommend the EFI , you can use a pre drilled Eddy Victor intake & rails all in for $400 . it will out run a carb system in drivability & performance . I would budget closer to $4500 for EFI all said & done though .
 If the budget is not there I would recommend a 1050 Proform race series carb

 

[moparmaniac59]

I'll bet if you take that same $4500 bucks and have some decent head work done (porting/polish) and a good flowing 1000 cfm carb, you'll have a far faster car than by just using the EFI system alone. Just my 

                                                                       Matt B.

[BS CUDA]

I do like the set it and forget it aspect of the EFI - as for $4500 not happening(that would almost cover the AlterKtion - future conversation). The box kits all avg $2500.00 which is almost affordable. I do like the 1050 Proform carb as it has vacuum ports(brakes  ) and is easily adaptable to a street/ strip car and a 1/3 the cost of EFI.    ..............................

Still undecided!!!

[BS CUDA]

Matt, you may be right. Also future adaptability is probably better in regards to further performance enhancements.

[HP2]

I do like the set it and forget it aspect of the EFI - as for $4500 not happening(that would almost cover the AlterKtion - future conversation).

True, but the Alterkation is only worth  .08 in e.t. reduction using the .1 per 100 pounds theory.  The EFi should net you more than that.

[HP_Cuda]

If the formula doesn't work then I'd suggest you get to work rewriting physics books! 

The reason folks don't get the formula is because they haven't dyno'd their car and know the point of dimishing returns for their powerplant. Meaning if you push your motor past a certain point you are no longer getting horsepower then followed by torque. If you know you will be running your motor to 7k rpms then the formula will work for *aspirated carbs* as it's been done for many many years.

the formula doesn't work , I continually got faster steeping from 850-950-1050 begin_of_the_skype_highlighting              850-950-1050      end_of_the_skype_highlighting begin_of_the_skype_highlighting              850-950-1050      end_of_the_skype_highlighting
 I build an EFI system using SDSEFI computer based in Calgary , 1200 CFM T body & 75 lb/ hr injectors .
If the budget can handle it I would recommend the EFI , you can use a pre drilled Eddy Victor intake & rails all in for $400 . it will out run a carb system in drivability & performance . I would budget closer to $4500 for EFI all said & done though .
 If the budget is not there I would recommend a 1050 Proform race series carb

[Chryco Psycho]

Maybe But who says the carbs ratings are accurate + it is also possble to get beyond 100% efficiency with mild ram effect in the intake @ higher RPM . My 440 duster seriously gained MPH & dropped ET every time I went to a larger carb , sure I was past 100% effciency but the car ran faster with a larger carb , I was shifting the 440 @ 7000 RPM but 1050 is past 100% by the formula . Altitude has an effect as well , the air flow may be the same but the air is less dense , I was running @ 4000 ' .
 BS also lives in the Calgary Area which is the same altitude , often the air quality was equal to about 6000' + altitude .
 I have also dynoed numerous cars & the 2x the CI formula seems to be more accurate .
 Even the carb flow #s are not equal , the fatoryused the 800 TQ on the 340 & 360 small blocks , the Six pack rated @ 1350 cfm was put on the 340 although they rate 2bbls at 3" of vacuum & 4 bbls @ 1.5 " which affects the carb rating , as a 4 bbl the 6 pack is closer to 950 CFM , but puting that much carb even on a 440 is way over 100% given a 6000 RPM redline .
 I guess the point is The volumetric efficiency of a 440 at what vacuum / is the engine drawing to ratethe carb flow at . , if it is less than 1" a 1050 may only be flowing 750 CFM according to the formula

[HP_Cuda]

I agree altitude does have a factor in it. 2 x the CI is surprising to me and I haven't experienced that before.

A high lift cam also can effect the cfm draw but I digress.

In all my musclecar building experience I have found many many people stick HUGE carbs on motors which will never get to even 80% VE and they are wasting their money. Now if you spent 8-10k on an engine build we might be talking but otherwise its cool to say you have a 750 Double pumper!!!