by terencejiminy Fri Mar 06, 2009 4:26 am
225 Slant/6 upgrades & mods for the economical owner/racer.
#1 = The best base to begin hopping up a Leaning Tower of Power is starting with the Forged Crank EARLY engines (Pre ‘ 76).
BLOCK:
Clean the block by Detergent Wash (Tide is best), BAKING, followed by a steam clean. Acid boiling has left acidic debris in a hidden places which can return and cause havoc with your hard work and precision machining.
The max bore factory recommended is .060”, which there are numerous pistons for this ( 3.460”) size.
A .100” over bore (or opening it up to 3.5”) is POSSIBLE (hopefully there WASN’T any casting shift during production) and allows more choices/options when shopping Aftermarket Pistons.
Note: Some Std. pistons for GM V-6’s are 3.5 from the factory. The Chevy VEGA 144 ci 4 banger piston is a good candidate too. Correcting the piston’s wrist pin bore to match Mopar rods is best done by reaming the PISTON wrist pin bore out to the Mopar measurement .9008” and using the factory press fit into the rod. This makes the wrist pin bore of the piston act as the bearing for this Piece.
Block filling (pouring in a special 2 part epoxy mixture into the lower part of the CLEANED block (up to ¼” below the freeze plug bores) for extra strength, CAN be done, but its need in a street or NON-ALL-OUT Drag racer (0 to 50hp Nitrous use and/or 9.5 to 1 or lower compression) is not necessary.
Chamfering the top of the lifter bores 45◦ X .125” (1/8”wide) to create a funnel effect for additional lube to the lifters IS recommended. In addition, restricting ONE of the oil return holes (one front and one rear) by ½ has been done. Do this by installing a small freeze plug in one front and one rear return hole and re-drilling it to ½ the size of the original hole.
Some people have stayed away from this and feel they facilitated the same results by installing a stand pipe into all 4 return holes that forces the oil level in the area up even with the top of the lifter when it is at its highest point (valve full open). A higher capacity oil pan/system (minimum 1 extra quart) is a must with this mod.
Decking the block up to .100” has been done, which raises the compression ratio, with a factory style flat top piston and rod, 0.5 to 0.8 of a point. I would deck the block AND head .050” each to accomplish the same results
CRANK:
#1 - FORGED ONLY = 1960 to 1976. 1968 to 1976 are most desired since they do NOT have the smaller crank center nub (1960 to 1967) that restricts certain performance T/converter usage.
An inline engine has little or no rebalance requirements due to the Physics involved. The factory balance of the slant’s forged crank is sufficient for RPM’s up to 7500.
Obviously a change in connecting rods needs the entire set to be equally re-weighed/balanced on the large or swing end and their total weight overall equalized.
The crank having a .001” polish, after regrind or from std, does wonders for long term bearing life and supports sufficient oiling.
RODS and PISTONS:
The factory FORGED CRANK RODS (1960 to 1976) are a BIG plus here. They are more than adequate for HP & racing use. It has even been a recent practice for builders of the Ford 460’s to use 225/6 rods in their all but ALL-OUT racing engines.
Mixing and matching of rods is an ongoing quest for the all out Slant. Recently the factory 198 slant’s rods have been surfacing as part of an HP combo with 2.2 and 2.5 Mopar 4cyl. NON-Turbo pistons. The 198 rod is .307” longer center to center which will bring the standard 8 to 1 - 225 piston up in the bore from its .140” in the hole to .167” up and OUT. Using the 2.2 piston will net you a .026” to .010” in the hole depending on how much you shave off the deck. QUENCH – SQUISH – QUENCH…….
The 2.2 - Zero Offset wrist pin Keith Black Piston comes in a 1.0 mm O/size that will work great in a 3.485 bore. Remember this is to be done to a block that has been checked for MINIMAL casting shift.
OILING: (There are volumes that could be printed here with upgrades to insure great oiling no matter what the application. Here are a couple of most interest)
The FIRST of the 2 MAJOR weaknesses with our Slants is the oiling system. By that I mean it isn’t a major issue for the short pass Drag Racer, but for oval track/road course/marine/towing and extended highway, it can be a killer.
That little drive gear on our oil pumps gets EATEN alive by the cam gear in long runs with a Hi-volume and/or Hi-pressure aftermarket pump.
I personally experienced this with my Oval Track, Super Six, Challenger back in the mid to late 70’s.
Changing the oil pump EVERY week became an expensive chore.
Be ALSO aware that after eating one of your oil pump gears OFF, the cam gear may very well be so damaged to where you may never get the life you got out of your FIRST pump gear.
The fix? Need to get some EXTRA lube to that little gear somehow no matter which pump gear you have. Brass or Iron. Here are 2 methods.
A. By routing (Gravity Fed) return oil from your rear lifter galley to this gear set (Cam Gear, Oil Pump Gear and Distributor Gear) you can accomplish added lubrication here.
B. By tapping into the main oil gallery just rearward of the oil pump area you can provide pressurized oil to this spot with better results. This requires a 1/8” tube aimed right at the gear contact point to minimize ware.
CAMSHAFTS:
The hottest cam for the Slant FROM THE FACTORY was the PN#2205620 for the Hyper Pak 4bbl package back in the early 60’s. This cam can still be purchased from Melling Tool Co., there PN# RPD-3.
The hottest (but still fairly mild) most recent Factory cam is out of all 1971 – 1977 Slants. PN# 3512639.
Then there are aftermarket bump sticks that must be chosen by what you want to do with your slant and what combination you want to assemble to make it all work.
HEADS:
This is the OTHER weakness of the Slant. There’s only so much you can pass through this chunk of cast iron gang……..
Up to .100” has been shaved off for increased Comp. Ratio numbers.
Match Porting (head to Gasket and manifolds to Gasket) is a MUST and Polishing is highly recommended.
Over size valves are recommended but remember there is a combination of diameter and the lift of the cam and the finished bore size the all play into making this work. Valve relief’s ground into the upper edge of the cylinder, in that little 3.5” bore, unshroud the valve but:
A. Decreases the compression ratio, again.
B. Creates glow points (sharp edges) for pre-ignition to happen at High RPMs.
Big valves can increase the flow into and out of the combustion chamber but what about the proven fact that the side of those valves facing the cylinder walls actually shrouds that part of the opening, taking away from the new bigger size you just put in? Better to go with a BIT bigger valves (1.70” Intake and 1.44” Exhaust) and make up for it with LIFT in the cam. With pistons higher in the bore eyebrows may have to be cut into the pistons for this increased lift. Oops, there goes some of that increased compression you gained again.
I’ve always used stock 318 intake and exhaust valves, with springs, retainers and keepers from a ’68 / ’69 - 340.
INTAKES:
Hard to believe but with only a comfortable (achieved economically) max of 235.8 ci (using the 2.2 .040” O/Bore Pistons) you can still only get so much Air and Fuel through your engine. 4bbls LOOK great, but do you need (and can you efficiently combust) all that CFM?
LOOK AT THE PORTS IN THE HEAD. HELLO !!!!!!
Chrysler engineers PROVED in the mid to late 60’s that slants can only handle so much flow through them.
They developed 275 gross HP from a 225 using basically off the shelf parts. Yes they used a 4bbl Hyper Pack intake but with the small 4bbl from the Commando 273 Package. The factory Super-6 (2bbl) was only 260 CFM.
They also proved the BEST cylinder filling/flow (stock head) up to 6500 rpms was realized with the old 2 X 1bbl (with twin 190CFM factory 1bbls) Offy intake, as this has the closest equal length runners of any manifold, short of that famous Go & Show Slant 6 T-bucket (XR-6 ?) that had 6 motorcycle side drafts on a hand made intake. Try and sync/equalize THOSE in.
The best head work will only get you to 6750 useful rpms before the head won’t handle any more. Before the heat from the exhaust port, Siamese next to your intake port, compromises the nice cold intake charge going in.
I know that there has been 7500 rpm 170’s that have held their own up to this speed but remember LESS CUBIC INCHES were going in and coming out. I only ran my 234 slants to 6500 rpms. That is where the torque dropped off dramatically. The horsepower FELL off at 6000. This again was using an oval track cam profile, lots of lift but not so wide on the duration.
I have seen many intake attempts and using the Super-6 2bbl factory aluminum intake is a good economical starting point. 4bbl intakes, but with 2bbl (Holley / Ford 2V pattern) adapters with the carb bores front to rear, are better. A 390 Holley 2bbl works GREAT on this manifold. The 500 2bbl is bordering on overkill unless a complete head porting and valve train program is followed. 650 is the max.
Remember that in the original FACTORY Slant/6 Mods guide they recomend a 2bbl mounting plate mounted with the venturis front to back not side to side for best all around cylinder filling.
Production and linkage issues killed THAT set-up at the factory for economy reasons when the 2 bbl Slant manifold came out for marine use in the early to mid 60's. These same issues prevailed with the Pass Car and Light Truck Super 6 in the mid 70's.
EXHAUST:
I used a split FACTORY cast iron exhaust on my oval track car. This matched my cylinders (1-2-3 into one & 4-5-6 into the other) in a 120◦ firing configuration for BEST scavenging.
Headers look cool, sound a bit better BUT dissipate TORQUE.
For an up to 390 cfm 2bbl Slant, street and periodic drag racing, using a STOCK exhaust manifold with its outlet bored to 2 ¼” ID 3” deep works wonders.
A 2 ¼” ID ALL THE WAY BACK, smooth flowing system, is a must.
Terry Bogusz
