I have a 427 BBC that is running 11:1 compression ratio, heads with a 325 cc intake runner , cam shaft 287-305 Adv/Duration 2000-5900 RPM Range Lift:.510 Intake/.495 Exhaust, a tunnel ram 2500-8000 rpm set up with dual Holley 600 cfm carbs with a Muncie 4-speed tranny. This is going to be in a street/strip car however I am hearing from half of the people I talk to that this thing is going to lag in power and acceleration and basically fall flat on it's face on the street. They said I am going to be better off going with a single 800-850 cfm carb and an intake like a performer rpm air gap manifold or a victor jr for the torque and hp level good for the street. I have heard other people say they have and have ran tunnel rams without a problem whatsoever and little or no lag at all. I am kind of worried that with the dual 600 cfm carbs I might have too much cfm for the motor. I got that tunnel ram/carb package from jegs

http://www.jegs.com/p/Edelbrock/755829/10002/-1/11937

It's like everyone I talk to has a different opinion. I am just curious what I should do, whether I should keep what I have or switch to the single carb set up?  

Yes a single 4bbl will have better bottom end and if you were going to change it I would recomend the victor intake instead of the air gap manifold a buddy of mine has a BBC with a tunnel ram and he runs on the street but he is using two 450CFM holley carbs.  

You have grossly overfed this engine. You friends have something right, the engine will fall flat on its face, but I'm not sure if they have the cause right...

325 cc's are by far too large for a 427 running under 6000 rpm. Please realize that there are 427 small block Chevys that will be making just as much peak horsepower (if not more) than you will with port volumes less than 75% of that value.

A tunnel ram would be a great way to pickup velocity and improve fuel atomization but I'm afraid you're not going to find one small enough for your engine off the shelf. So, I would have to recommend going back down to a single carb as well, preferably a dual plane intake to try to help re-gain all the torque you will lose with those horridly large cylinder heads.

Please realize that you cannot have too much airflow CFM for the engine but you can have induction velocity too low causing poor fuel atomization, puddling, and lean burns, etcetera. If you think you have too much carb CFM maybe you could... improve booster signal strength, use a four-hole spacer to elongate the venturi, use plenum divider or dual plane intake, etcetera...  

Well there are some good and bad things. The bad thing is I listened to my uncle on this one. The good thing is the engine is not hooked up yet so I still have time to change it over. According to John Barret he adv to change the cam, change the intake, and change to a double pumper 750 cfm carb and I should be ok. The heads are actually the matching numbers factory 69 427 heads  

I never said that GM had it figured out in the 1960's...

What doesn't help is 'camming down' from let's say for example a solid L88 cam of old. Less efficient cylinder head designs need more duration to make the same power as port shapes that breathe easier. But especially if they're numbers matching I don't want to discourage you from using them but just wanted you to realize there's a lot of potential tied up in an pair of aftermarket ovals...  

Yeah I know. I will probably go with a set of afr heads or some other heads when the car is completely finished. Right now I am starting to run low on money since this nova has been built from the frame up so I have a few things left to do to get it done. I'm going to go ahead and get an intake and carb ordered tonight.  

I called AFR about 2 weeks ago and they don't have the magnum 265cc or the ported version the 290cc ovals in production yet dispite listing them in afr catalog and website, my put together 427 bbc wants me to replace the 269 Merlins to lose weight and gain more cfm's.Brodix race rite,Darts new 270 oval, TrickFlow and Edelbrock that were tested in CarCraft recently performed quite well on a 496 bbc food for thought.WIEDER  

Sorry so asorbed in cylinder heads lately I agree something like a rpm intake 750 carb combo is better for street WIEDER  

Yeah I actually got lucky and found someone to buy my intake, carbs, and stuff so I am going to order my new intake and carb in the next day or so. I am trying to decide between the quick fuel ss, holley double pumper, or the might demon carbs any suggestions?  

You can't beat the original L-72 intake carb combo. 750 cfm Holley and high-rise aluminum intake.  

I went ahead and got an Edelbrock RPM Air Gap intake since it was ina  better rpm range for low to mid range power and matched up with my cam and I got a Quick Fuel Q Series 750 CFM Carb. I'll let everyone know how it works out. Is there any advantage to running a space?  

I'll assume there was a typo there and you meant 'spacer'...

Most conventional spacers are tuning aids and nothing more. Open spacers add plenum volume and more area for the carb to 'dump' into. This can add some top-end horsepower potential and in the case of a dual plane gives some extra communication between all the cylinders and all of the carb at once, even though slight. A lot of aftermarket intake manifolds are built with the plenum volume on the small side to accomodate smaller displacement engines of the same family and to allow the tuning of added displacement. For example, with a Performer RPM on a mild 454 some would guess that a 1-inch open spacer would perform best, but it's really dependent on the individual engine in question.

4-hole spacers elongate the venturi and increase velocity of the charge going through the carburetor slightly. As I'm sure you know velocity is good in many situations. It can improve power throughout the rpm range if the induction speed is slightly slow but like I said it's nothing earth-shattering.

Tapered spacers sometimes are called a combination of both but in reality they reduce velocity underneath the carburetor and allow for easier transitions from the carb to the runners. These can show major gains in top-end power in some situations but are most notably used with 4500-flange carburetors.

Shear plates or anti-reversion plates are useful below and beyond the engine's normal operating band. They of course try to isolate the booster from unwanted pressure waves that make their way to the carb. Some argue that these are only effective on engines with very large camshafts that bring on these low speed reversion situations that the spacer is supposed to 'tune-out.'  

Hello, i'll share my combo with you for comparison..
1986 monte carlo ss
'70 402cid BBC, 454 pass car heads,250cc runners, fully-ported with 2.25/ 1.88" valves, 5-piece big-tube headers, performer rpm air-gap with HVH "street sweeper" one inch spacer.
camshaft is a comp soild-lifter #11-679-5, 252/260 duration @.050" , .598/.598" lift, 290/298 advertised..
10.5:1CR, i want some aluminum 290's to replace the 049 heads..
the key to making it all work was the BG 750 mighty demon carb and a custom  4-hole 1" tapered spacer..originally i was using a 850 speed demon, engine ran poorly on the sreet, then i discovered from BG that the cam had too much duration at .050" for the speed demon calibration..ordered the 750 mighty demon next day.
night n day is all i can say, estimated 575+hp..
mid 10's at 125 w/o braking a sweat
It aint no slouch...lol

The 600's were way too big for the 427..period
holley 450cfm tunnel-ram carbs would have worked fairly well..still over-carbureted at 900cfm
BG 750 MD works well with the rpm air-gap manifold and HVH spacer..the street sweeper is a tapered 4-hole unit designed to work with the rpm manifold.

i see you already got a carb so here is a link to the spacer..ST4150-4
http://www.highvelocityheads.com/ss.htm

HTH, george  

Something doesn't make much sense here...

Tech at Barry Grant said that you had too much duration for the 'tune' of the 850 carb so they sent you a smaller carb?

By the way will you please clarify you had a 402 or a 427 there?  

What size heads and brand would you recommend?