The Ford 400 V8 has never been a popular motor for hot-rodding, but that doesn't mean it has no potential as a performance motor. With its 4 inch stroke crankshaft (the longest stroke of any Ford V8) and its canted valve cylinder heads (sourced from the 351 Cleveland) a hot-rodded 400 makes a tire shredding performance motor with power akin to the 428 Cobra Jet. It's more of a torque monster, rather than a charging rhino like the smaller 351 Cleveland.
Most of the hot-rod parts for the 351C also fit the 400; i.e. water pumps, oil pumps, fuel pumps, distributors, camshafts, timing sets, harmonic dampeners, oil pans and most importantly the 351C heads. The block, crankshaft and connecting rods are manufactured to the same standards as the 351 Cleveland's block, crankshaft and connecting rods; they are durable enough for naturally aspirated high performance street motors and low-buck amateur racing applications.
The 400s wrist pin compression height of 1.65" is identical to the 351C compression height. The one wonky dimension of the 400 is its 0.065" deck clearance; the 400s piston is almost twice as deep in the hole at top dead center as the 351C's piston. The increase in deck clearance and approximately 16 cc dishes in the piston domes give the 400 a compression ratio of 8.0:1. Reducing the deck clearance and increasing the compression ratio must be incorporated into the strategy of hot-rodding the 400.
My formula for hot-rodding the 400 includes boosting the compression ratio to 10.0:1, pistons with greater compression height (in order to decrease the deck clearance) and open combustion chamber cylinder heads. I have a preference for flat top pistons, and a preference to keep the deck clearance in the range of 0.010" to 0.035".
Replacement of the 400s pistons is necessary for any type of performance build-up. Piston replacement creates the opportunity to boost the 400s static compression and decrease the deck clearance without resorting to modification of other castings; such as decking the block, installing off-set bushings in the connecting rods or milling the heads excessively. This simplifies motor assembly. However if you search the Summit Racing catalog you'll discover pistons are only available from a limited number of manufacturers (Keith Black and Sealed Power) and all of the pistons listed for the 400 are cast pistons with the production 1.65" compression height and dished tops of various volumes.
I ordered a set of custom pistons for the 400 I hot-rodded decades ago. Using custom pistons allowed me to specify a piston that met all the parameters of my application without the need for additional machine work or additional custom parts. The pistons were directly installed in the motor as "drop-in" parts without the need to mill the cylinder heads, deck the block, or bush the connecting rods. I used standard thickness head gaskets, and the deck clearance was a very normal 0.030"; none of the dimensions were extreme or wonky, the dimensions of the motor remained conservative and factory-like. The pistons were specified with flat tops and a 1.685" compression height which yielded my target compression ratio of 10.0:1 using D2ZE (351 Cobra Jet) 4V head castings having 75cc open style combustion chambers. These pistons would yield a compression ratio of 9.7:1 with cylinder heads having 78cc combustion chambers.
The spec for those pistons was:
- Forged aluminum
- 351C 4V style flat top (notched for 4V valves)
- 400 size wrist pin (0.9752")
- Pressed wrist pins
- Wrist pin height = 1.685"
- Standard ring package
Ordering custom pistons is not absolutely necessary however, thanks to T Meyer who offers 3 pistons for the 400 which are manufactured by Keith Black exclusively for T Meyer Inc.
(1) KB2347 is a cast hyper piston with a 13cc dished dome and 1.71" compression height. This piston will provide 9.2:1 to 9.4:1 compression with cylinder heads having 78cc combustion chambers (OEM heads). This piston is designed for a deck clearance of 0.005" in an un-milled block.
(2) KB2344 is a cast hyper piston with a 30cc dished dome and 1.71" compression height. This piston is designed very specifically for the Australian 302C cylinder heads having small (2V) intake ports and quench style 58cc combustion chambers. The piston was designed to provide 9.4:1 to 9.6:1 compression with that cylinder head.
Modern high swirl combustion chambers offer improved thermal efficiency compared to older designs; one trait of the high swirl combustion chambers is a requirement for less total ignition advance. Altering the piston domes also changes the amount of total ignition advance required by a motor. Domed pistons usually require more ignition advance while dished pistons combined with zero deck clearance usually require less ignition advance. It is assumed that the reduction in required total ignition advance indicates an improvement in thermal efficiency, as in the case of high swirl combustion chambers. This is the reasoning behind this piston and cylinder head combination.
(3) KB2334 is a forged piston with a flat top (2cc valve notch) and 1.72" compression height. This piston will provide 10.4:1 to 10.6:1 compression with cylinder heads having 78cc combustion chambers (OEM heads). This piston has a 0.927" Chevy size wrist pin, which I assume is designed to work in conjunction with bushed factory connecting rods. With its forged construction, floating pins and high compression it appears this piston was intended for racing motors or perhaps motors equipped with alloy heads.
These T Meyer Inc. pistons offer options in hot-rodding the 400 that weren't available decades ago.
When I hot-rodded a 400 V8 I chose the 4V Cobra Jet heads as the least expensive route to high air flow cylinder heads. This reflected the mind-set of that era that a serious performance motor had to be equipped with the big valve big port 4V heads. I also had several sets of Cobra Jet heads stacked in the garage so there was no additional expense involved in that selection. The drawback to the choice of 4V heads was the necessity to use intake manifold spacers, but I learned that really wasn't that big of a drawback, the spacers installed easily and didn't look bad either. Some people didn't even notice the spacers until I point them out.
Even though I chose to use 4V heads it doesn't mean you have to use them too, many people prefer the smaller port heads, while others prefer not to spend additional money on replacement heads. The small port heads are certainly capable of supporting elevated horsepower output and performance. Any pre-1975 small port (i.e. 2V) open chamber iron head can be used for a performance build.
Cylinder Head Choices:
- 1970 351C 2V .................. Nominal combustion chamber volume is 76.2 cc.
- 1971 - 1974 351C 2V......... Nominal combustion chamber volume is 78.4 cc.
- 1971 - 1974 400 .............. Nominal combustion chamber volume is 78.4 cc.
- 1971 - 1972 Cobra Jet 4V... Nominal combustion chamber volume is 75.4 cc
The heads listed above have combustion chamber volumes in the range of 75 cc to 78 cc which are ideal for building a 400 cubic inch performance street motor because the compression ratio we want to obtain can be achieved with flat top pistons, a reasonable 0.030" deck clearance and a standard 0.040" thick head gasket; they also compliment the off-the-shelf T Meyer/Keith Black KB2347 pistons. The heads found on the 1975 and later 351M and 400 are not recommended because the exhaust ports were modified for thermactor air injection and do not flow as well as the earlier heads.
Open Combustion Chambers
Some enthusiasts are under the misconception that Cleveland cylinder heads with quench chambers are more resistant to detonation and make more horsepower. Although this may be true in regards to the small block Chevy I know from experience this does not apply to the 335 series Ford cylinder heads. I have built two high performance street motors using open chamber 4V cylinder heads (D2ZE castings sourced from 1972 Cobra Jet motors), both motors had 10.0:1 compression ratio. One was an actual 351 Cobra Jet installed in a 1972 Mustang, the other a 400 V8 installed in a pick-up truck. Both motors ran without a hint of detonation on 91 octane pump gas without having to reduce the amount of ignition advance. (US/Canadian 91 octane gasoline is equivalent to 95 octane anywhere else in the world). The 351 Cobra Jet was dyno'd and made just as much horsepower as similar motors I had hot-rodded using quench chamber heads. I also know there have been many racers over the years that quietly used open chamber heads in their high compression Cleveland race motors along with their own proprietary piston dome designs. They wouldn't have done this if they weren't competitive.
There is one quote in Ford's Off Highway (i.e. racing) parts book of 1972 about the differences between open and closed combustion chambers:
Quote: "Quench chambers encourage a swirling action of the incoming air-fuel charge. This improves mixture ... especially at low rpm ... when the mixture travels at relatively low velocity. This causes a more complete burning of the fuel and better low rpm torque ... Open chamber designs ... There's no quench area and valves are less shrouded; thereby encouraging excellent breathing. However, you sacrifice some of the good low rpm torque advantage associated with the quench chamber ... As of this date (1972) Ford has not developed a special pop-up piston that will give 12:1 or 13:1 ratio with open chamber heads. Thus the quench head is recommended. However this doesn't preclude use of open chamber heads. If you elect to go this route, it simply means you will have to work with a piston manufacturer to develop an appropriate piston design."
This quote is straight from the Ford engineers who designed the 351C. They made no mention of detonation, no mention of a big horsepower difference; the main difference is low rpm torque, which won't be a problem with a 400 cubic inch motor. They also suggested the use of the open chamber cylinder head for racing; they wouldn't have made that suggestion if the performance of the open style combustion chamber was inherently inferior to the quench style combustion chamber.
For a basic performance street motor I recommend choosing a two-plane intake manifold in order to emphasize the power band in the rpm where the motor will be operated the majority of the time and to maximize manifold vacuum for the power brakes, PCV system and distributor vacuum advance.
I chose the Shelby (same as Blue Thunder) dual plane intake manifold for the 400 I hot-rodded. The manifold is designed for the 351C 4V, therefore installation required Weiand manifold spacer plates. Weiand also manufactures the model 8010 "Action Plus" dual plane intake manifold which is an excellent small port (2V) head manifold. The "Action Plus" manifold is designed specifically for the 400, therefore it requires no spacer plates for installation.
Although I recommend a dual plane intake manifold that doesn't limit your choices, some enthusiasts may want the racy looks or top-end power of a single plane manifold. The choice is yours. And there are plenty of choices thanks to Price Motorsport Engineering (PME) and T Meyer Inc. who sell adapter plates to allow utilization of 351C 2V or 4V intake manifolds on the 400. The PME #AP-29 2V adapter plate provides the choice of using any 351C-2V intake manifold in conjunction with 2V heads. The PME #AP-30 4V adapter plate provides the choice of using any 351C-4V intake manifolds in conjunction with 4V heads.
For my 400 V8 build I used a Ford sourced 780 cfm vacuum secondary Holley carburetor. Those carburetors were a bit expensive but they were calibrated very well for the type of motors that I built (motors that had to pass a tailpipe emission inspection) and provided better drivability than any generic out-of-the-box Holley carburetor I could purchase at the hot-rod parts emporium. Unfortunately that option is not available today.
People will argue over carburetor size, but I see no problem in recommending a 735cfm to 780 cfm carburetor for a 400 cubic inch motor, especially if it is used in conjunction with a dual plane intake manifold. My recommendation for a 400 cubic inch street motor equipped with a dual plane manifold is a 735/750/780 cfm carburetor. This is a carburetor with 1-11/16" throttle blades and 1-3/8" venturi throats. The carburetor I'd recommend will have an electric choke, Ford kick-down linkage and vacuum secondaries for smooth street operation and for best performance with automatic transmissions. I also prefer carbs with annular boosters. If you're going to use an out of the box carburetor stay away from Holley; choose Quick Fuel Technology carburetors instead. QFT carburetors are price competitive with Holley yet offer more features, they are tuned better out of the box and they are easier to fine tune.
- Demon Carburetors #1402020VFE 750 CFM, vacuum secondary carburetor with annular boosters.
- Quick Fuel Technology #SS-735-VS 735 cfm vacuum secondary carburetor with down-leg boosters
- Quick Fuel Technology #SS-780-VS 780 cfm vacuum secondary carburetor with down-leg boosters
A smaller carburetor may be a better choice for single plane intake manifolds, for heavy vehicles, for high geared vehicles, for towing or off-road vehicles, or for drivers wanting to maximize low rpm performance at the expense of upper rpm performance.
- Demon Carburetors #1282020VFE 650 CFM, vacuum secondary carburetor with annular boosters.
- Quick Fuel Technology #SS-680-VS 680 cfm vacuum secondary carburetor with down-leg boosters
Demon carbs have had their quality control issues. But the vacuum secondary Demon carburetors I've listed are the only carburetors in this configuration having both an electric choke and annular boosters. They are great carbs if youre willing to buy one risking the possibility it needs work out of the box. If that risk seems illogical to you then you'll be better off using a Quick Fuel Technology carb instead of a Demon carb.
The off-the-shelf camshaft I most often used in the 1970s was a hydraulic version of the Boss 351 camshaft, having the following specs:
- 290°/290° advertised duration
- 219°/219° duration @ 0.050
- 62° overlap
- 0.505"/0.505" valve lift
- 114° lobe separation angle
This cam turned a 351 into a hot performer that operated over a wide power band with Boss 351 type street manners. It was amazing how the 400 was a torque monster with the same camshaft installed in it; the extra cubic inches tamed both the camshaft and the large port 4V heads. I'm not suggesting you use this camshaft; I merely wanted to demonstrate how the extra cubic inches of a 400 V8 will tame the performance of a camshaft designed for a 351.
Recommending a camshaft is inherently difficult to do without specific information about the vehicle, how the vehicle shall be used, and the drivers expectations. One cam I feel safe in recommending is Crane Cam's part no. 523801, grind no. H-278-2. This is another wide power band type camshaft with good street manners that will work in a variety of applications. Remember this cam was designed for a 351; therefore it will be much more "civilized" in a 400 V8. The specs:
- 278°/290° advertised duration
- 222°/234° duration @ 0.050
- 56° overlap
- 0.539"/0.534" valve lift
- 114° lobe separation angle
The factory distributor will interfere with the intake manifold if the PME manifold spacers are used. In that situation plan to use an aftermarket distributor that has more clearance between the block and distributor housing. My recommendation would be the MSD model 8477.
Off-the-shelf exhaust headers for the tall deck 400 are available, but the manufacturers and applications are limited. To my knowledge there are no off-the-shelf headers for the 400 with 4V heads. Some fabrication may be needed, trial fitting headers for other applications may provide a solution, or universal shorty headers like those made by Sanderson may be a viable choice. If you should find there are no headers for your application it should not discourage your plans; paying someone else to manufacture custom make exhaust headers is always a possibility, but that will inflate the cost of your engine project by several hundred dollars.
Those are the specific concerns for building a tall deck 335 series, 400 V8 performance motor. All the usual concerns related to building the 351C for performance apply to this motor as well so I won't rehash that information here.
In summary, the 400 I hot-rodded long ago was equipped with custom flat top pistons having a compression height of 1.685", open chamber 4V heads (1972 Cobra Jet heads), 10.0:1 compression, a Shelby manifold and a 780 Holley. That motor was a hot performer in a Ford pick-up truck. However, that is only one possible way to go about it. A person may wish to avoid the use of custom ordered pistons, 4V heads, or intake manifold spacers; or a person may prefer a motor with a milder state of tune. In those situations a build-up including T Meyer/Keith Black KB2347 pistons, small port (2V) cylinder heads, 9.4:1 compression, the Weiand 8010 "Action Plus" intake manifold and a 680 QFT carburetor may fit the bill.
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