Big Block Intake/Carb Upgrade

The below article was originally written in early 2001. See the follow-up under that too.

Weekend Project Tip #1

Best Intake Carburetor Conversion for a Stock 400CI

Dave Schultz aka BK

The general consensus on the best intake and Carburetor for a stock 400ci, which will give you more power, no conversion hassles, is 50 state legal, and still give you enough induction to upgrade your heads, exhaust, and cam is:

I was able to purchase all of the above at Summit Racing for $461.80. Future weekends projects can include a cam that is packaged as part of this set. Many people also felt that the Edelbrock RPM would be a good choice – but it doesn’t have the provisions for EGR, which may keep you from passing inspection.

The car originally had a lean-burn system on it — so I also bought a Mopar Performance electronic ignition (orange box), a Mopar Performance air cleaner with a K&N element, a matching set of Mopar Performance valve covers and Felpro blue gaskets.

Magnums with a big block have minimal hood clearance — so you will need a shorter filter element. Use a piece of playdoh on the air cleaner and close it easily to check your hood to air cleaner clearance.

Installation of the above took about an afternoon following the instructions. Most of the time was spent drilling the valve covers and standing in the Help Aisle of the parts store putting together the grommets and hoses needed for the PCV to air cleaner.

Major performance improvement with these changes. Click on the below photos to see the full-size versions.

UPDATE December 2005

While the ignition and carburetion greatly improved the power over stock, and the valve covers and air cleaner improved the under hood appearance — I always had problems with bogging on the carb when I put a hotter 400 (from a street racer) in the car. This is sort of an epilog of the above.

I replaced the Edelbrock Performer 750 (which is the old AFB design — they’ve since released two friendlier versions — one being the AVS) with a Holley Street Avenger — but that carb would backfire so hard it would slam the choke butterfly shut. I then went back to the Edelbrock Performer and called Edelbrock’s technical department. Many phone cals and many jet/metering rod/spring changes — and it only got worse. The guy who does my racing carbs is Jesse Bigs from Bigs Performance. I told him of the issue and he build me a Holley 735 Vac Sec carb that cured all of that. So if I were doing this all over again — I’d have Jesse (ask for a Moparstyle discount) build be a carb over using the Performer 750. If I was sold to use an out of the box Edelbrock — I would try the Thunder Series AVS or their Street Performance EPS. Below are some photos of what my engine bay looks like in 2005.

As far as the Mopar Performance electronic ignition conversion — it is much better than the lean burn system — but for real power (if you will be tweaking the motor some) you might want to consider going with a MSD 6, MSD Billet distributor and MSD Blaster II coil. Use MSD 8.8 mm wires. This is the ignition system used for the lower horsepower drag cars because of a controllable rev limiter and a hotter and more consistent spark. Between the Mopar Performance and the MSD (but for the Mopar Performance price) is the FPO ignition system. Call Don at FPO and ask for a Moparstyle discount. For Mopar Performance stuff — call Wes and Mancini Racing and ask for a Moparstyle discount. You find out more about these vendors in the Forums.

On the air cleaner — since you have to use a shorter air cleaner element (see above) I’d suggest what we use on my kid’s racecars — the new Xtreme toppers by K&N. The top also breathes allowing you to pump more air into the motor. See photo below.