- Feb 20, 2006
Ford's supercharged Mod motors
Readers of Autoblog know that I'm not a huge fan of the naturally-aspirated Ford modular V8s that are available here in the US, but stick a supercharger on these motors and my opinion changes substantially. Let's take a closer look at the two forced-induction versions; the lame-duck 5.4L DOHC engine used in the Ford GT, and its closely-related sibling that will soon see use in the Mustang Shelby GT500.
Due to this engine's similarities to Cadillac's supercharged Northstar, it's tempting to make comparisons between the two engines, and so I'll do exactly that.
A look at the camshaft chain drive shows that one large chain drives the exhaust cams off the crankshaft, while a short intermediate chain then transfers rotation to the intake cams. This strategy allows the use of a smaller sprocket on the intake cam, and the subsequent reduction of bulk at the upper corners of the head (compare this to the Northstar, which uses two equally-sized sprockets on each cam). The downside is an increase in length, complexity, and noise; this is a huge "small block" engine, despite its modest displacement.
See that log-style cast-iron exhaust manifold? To the eye, it sure doesn't look very efficient. It'll be interesting to see how much room is left in the S197 engine bay by the time this tall-deck DOHC monster is shoehorned into place, but hopefully there's enough space to squeeze in a pair of proper headers.
The serpentine belt is also used to drive the supercharger. It'll be interesting to see how the aftermarket modifies that to allow the use of a cogged belt to drive the blower.
That fuel rail appears much larger than what we'd typically find (the Northstar's rail looks tiny in comparison), and it feeds one injector per cylinder.
This is a lovely-looking Roots blower, but how long until someone mounts a twin-screw unit? It'll be interesting to see what Whipple and Kenne Bell offer for those sickos who just can't be satisfied with smaller blower pulleys. Note that the blower discharges downward into the intercooler, which is a bit more typical than Cadillac's upside-down airflow path.
There's the oil cap, and just above and behind it is the crankcase breather. Follow that tube up to the blower housing, and you can see the vacuum actuator for the supercharger bypass valve right behind it. When the throttle is closed enough to draw a vacuum, this system bypasses the compressor for additional efficiency.
Is that a reduced-diameter multi-plate clutch that we see? Yummy - hopefully it's enough to hold up to the sort of abuse that this engine will be capable of doling out at the dragstrip. The skeletonized flywheel looks to be much lighter than what we'd normally see in a production application. I'm thinking that this engine will provide the definition for "throttle response".
Note the relatively deep sump - hopefully that's sufficient to maintain oiling during high-g cornering, as I suspect that many owners will want to do more than just quarter-mile straight-line blasts.
That's one beefy bottom end, but we can see just how small the pistons are in relation to the exterior dimensions of the engine. That 3.66" bore limits the engine's ability to breathe, even with four valves, but this becomes much less of an issue once that supercharger starts to work its magic. Regardless, note that Ford isn't really keen on showing off the intake and exhaust ports in its cutaway displays.
The dish in these pistons is larger in diameter and not as deep as those found in the Northstar's pistons. That lends itself to a bit less desirable combustion chamber shape, but likely also allows for a higher pin position and more thickness in the piston crown (the latter is especially important to those who will be pushing this engine to the limit). This is a fine example of the tradeoffs and compromises that must be made when designing an engine.
Now, on to the Ford GT engine:
See that big cogged belt, mounted low on the engine? That drives the pump for the dry-sump oiling system, which is employed to reduce the packaging height of the engine. The sump that we pointed out on the Shelby's engine is eliminated, allowing the engine to sit lower in the chassis. It brings with it some oiling improvements as well, especially under high lateral loadings. 'Tis not inexpensive or simple, however.
Methinks there are more than a few horsepower to be found by replacing those exhaust manifolds with a proper header.
If you're an oxygen molecule that was unfortunate enough to enter the GT's intake track, this is one of the last things you see before you die:
After a trip through the dual 70mm throttle body (I'd estimate its rated airflow somewhere well north of 1250 CFM), the intake charge is compressed in a twin-screw supercharger:
There, it's discharged downward through an intercooler. Note the use of two fuel injectors for each cylinder. Only one is used at idle and low throttle openings, which allows for fine metering of the injected fuel. Get into the loud pedal far enough, and the second injector comes online to ensure that sufficient fuel is available to keep up with the supercharger's cylinder-filling efforts.
At the upper edge of this photo, we find the four black coil-on-plug (COP) assemblies. Once again, note the relatively small size of the cylinders relative to the overall bulk of the complete package.
To no one's surprise, we find the same cam drive arrangement.
The transaxle is seriously gorgeous - it seems a shame that it likely won't see use in other Ford products.
As we can see, there are indeed differences between these two engines, but they're not huge. The Ford GT puts down well over 500 HP to the rear wheels despite its 550 HP rating; will the Shelby prove its 475 HP rating to be equally pessimistic? We're anxious to find out, and it should be interesting to see how much work is required to bring the Shelby's output up to the same level as its much more expensive cousin. We're betting that it won't take much.