Hello, and welcome to the Slant Six Sanctum. Here you will find suggested combination for a streetable, economical slant six buildup, a summary of Car Craft's 225 buildup, some info on turbocharging a slant six, and a list of sources for slant six speed parts.
A (comparatively) high torque 225 on a budget
As with any engine buildup, there isn't one part that will make the engine. A well done high performance engine requires a well chosen combination of parts. The 225 cubic inch slant six is a long-stroke engine, with a stroke longer than a 440 big block. It has a very low redline, about 5,000 rpm. Consequently, a built up daily driver should be designed for low-end torque rather than high-winding horsepower.
The parts listed below are meant to improve the 225's excellent torque capabilities, while at the same time letting it breathe better at high RPM. Furthermore, they are meant to be as affordable and readily availible as possible.
Perhaps the best intake is, surprisingly, a factory piece. This is the "Super Six" two-barrel Carter carburetor and the accompanying single-plane intake manifold, which is readily availible in junkyards. It was most commonly installed on F-bodies (Aspens and Volares) and some trucks from '77-'80. For best results, the lean "smog" jetting of that era should be enriched somewhat. Getting rid of the undersized stock carb will make a big difference all on its own.
There are several other two-barrel intakes availible. A 350 cfm Holley two-barrel on a Clifford or Offenhauser intake manifold will work just as well as the Super Six setup. However, four-barrel carburetors are usually too big to use on all but the most heavily modified 225's.
Dual exhausts or a 6-into-1 header with a large diameter exhaust pipe can improve horsepower, torque, and mileage. If you want a very reliable, quiet, and leak-free exhaust, your best bet is a set of Dutra split manifolds. If you prefer headers, they are availible from Clifford Performance.
The .395" lift stock camshaft really doesn't provide enough lift for good performance. A good bumpstick can improve both low-end torque and horsepower, sometimes even mileage. I recommend a cam with between 260 and 270 degrees of advertised duration and as much lift as is practical, usually from .440" to .450". The Comp Cams High Energy 264S cam will work well, as will the cam that Clifford Performance installs in its 4.0 crate motors. Most other cam grinders offer similarly ground cams.
The 225's stock 8.4:1 compression ratio is easily improved by milling the cylinder head. Shaving 0.050" off it will yeild 9.0:1 compression. The adjustable rocker arms prevent the valve train geometry problems encountered when milling the head on other engines, and the manifold alignment problems milled heads can cause on V engines won't be a problem here.
Points are a nussaince on V-8s, but on slant sixes, they're absolutely intolerable. The distributor location makes them very difficult to adjust. I replaced my points with a Pertronix Ignitor and have not had any problems since. Other options include the Mopar Performance electronic conversion kit and an MSD ignition combined with an electronic distributor.
Although Car Craft denies that this was a worthwhile project, I beg to differ. It's a very good reality check to show just what might happen if you try a mild slant six buildup. In my case, it served to prevent me from attempting a similar buildup. At this point, I'm not sure if I'm going to just go the easy way and drop in a 360, or do something a bit more high tech than the bolt ons and headwork they used for the article. This article appeared in the November 1999 issue, and for more details, including some very informative pictures on slant six cylinder head ports, I suggest you get the back issue.
They started with a '67 Barracuda with a stock rebuilt '63 225 block, A-833 overdrive (out of an Aspen), and a 3.23:1 geared 7.25" rear axle. On 9" cheater slicks, this car ran a best time (uncorrected, at LACR) of 19.73 @ 68.3 mph, about the same as my '66 Dart (unrebuilt, probably 197,000 mile 225, A904, Super Six, and what I believe are 2.93:1 gears). They then installed the following modifications:
The results still weren't all that fast, a best time of 16.41 @ 83.6 mph. They suspected it might have been faster with a Sure-Grip and an electric fuel pump, as the engine seemed to stop pulling at around 1,000 feet. If those improvements could get it into the 15 second range, that might be good enough to take to the track without embarassing yourself, but it seems pretty clear that for some serious speed, it will take a bit more than what they used. However, I'm still not quite convinced that fooling around with slant sixes is a waste of time. Read on...
Recently, a new member on the Slant Six Mailing List announced that he had a 13 second Valiant powered by a 170. We assumed that it was a trailered race car, but were nevertheless fairly impressed. Imagine our surprise when we found out that it was a full bodied street car that even got decent in-town mileage! It's not magic or nitrous here - this seemingly impossible car is a reality thanks to turbocharging.
Since I don't have that much experience with turbos, and turbocharged slant sixes are still a rarity, this section will mainly be dedicated to links containing relevant information about turbocharging slant sixes.
Turbo Concepts - If you're not familiar with how turbos work, check this page out first. This explains all the important concepts, from the basic setups to how boost is controlled. Most of the information is concerned with Chrysler 2.2's.
Charlie Schimd's 1965 Valiant - This Valiant uses a draw through setup to make a 170 go like a 340.
Mr. Mopar's Page - Features a lowrider Plymouth powered by a draw through turbo, along with a detailed account of how he set up the engine.
Turbo 1968 Valiant - A blow through turbo setup, which is in the process of being converted to EFI.
Clifford Performance offers a wide variety of intakes, including two-barrel, four-barrel, tripple Webber carburetors, and fuel injection.
Offenhauser offers a four-barrel intake manifold availible through J.C. Whitney. They make a few other trick manifolds for the slant six, including one which allows you to run two stock single barrel carburetors.
Turbo City offers a throttle body injected intake for the slant six, based on the GM TPI system.
Clifford Performance sells a variety of headers, including dual exhaust ones and 6-into-1 units.
Mopar Performance also carried headers for both dual and single exhaust applications. Catalogs are availible at Chrysler / Dodge / Plymouth dealers.
Doug Dutra sells a dual exhaust manifold converstion for those who want more performance and fuel economy without the leaks and noise associated with tube headers.
Camshafts and Other Valvetrain Products
Competition Cams sells several high-torque grinds for the slant six, double roller timing chains, pushrods, and valve springs. Custom racing grinds are availible, too.
Clifford Performance, as you might expect, carries cams to match their other lines of slant six products.
The Mopar Performance catalog offers several slant six cams, too, from mild to wild.
The Mopar Performance electronic ignition kit will replace the breaker point ignition with a factory style electronic ignition. It's reasonably priced, reliable, and easy to find replacement parts for.
The Pertronix Ignitor is easy to install and the least expensive ticket to electronic ignition. It can also function as a pickup for an MSD ignition if you decide to upgrade but don't want to get rid of the stock distributor. It's availible from J.C. Whitney.
MSD Ignitions provide multiple sparks for each cylinder firing. People who have installed one on a slant six tell me it really smooths out the idle and makes a noticable difference in thw low RPM range.
For high-performance steel and titanium (!) rods for your slant six, contact:
Performance Automotive Warehouse offers several rebuild kits, from simple gasket, bearing, and ring sets to kits with reconditioned crankshafts and TRW forged pistons. They regulary advertise in Hot Rod Magazine and have a special discount for its readers. You can reach them at:
Nitrous Oxide Systems sells systems which can be installed without modification on a slant six if it already has a four-barrel Holley intake.
Turbo City sells turbo kits for the slant six. They require a lot of fabrication to install, however, as much of the ductwork is not included.
If anyone knows of any other performance parts sources for the slant six, please let me know.