III. OFF-ROAD MODIFICATIONS
In this group of sections we will discuss modifications using the parts mentioned earlier and some special racing parts which will provide increased power and durability. We will look at the various systems separately first and then tie these systems together into the various complete race engine packages.
A. Ignition System
Chrysler's new electronic ignition system which was introduced on the slant six engine in 1973 is the best ignition system available. The vacuum advance model electronic ignition conversion package PN P3690789 for the slant six includes a distributor PN P3690788, control box PN P4120505, wiring hamess and ballast resistor.
The next level up for higher rpm race cars is the chrome box system (P4120534 box). The highest output system currently available for race cars is the gold box P4120600 which is designed to offer the performance of other race ignitions (see later section) with more reliability and for less expense. See Chapter 19.
The H.P. electronic distributor does not need to be recurved since it has a race advance curve built into it.
The race electronic distributor with the vacuum advance is recurved to have full advance by 2000 rpm which is more suited to general high performance use.
The maximum total spark advance for the slant six engines should be set to 32 degrees. The damper should be clearly marked for both TDC and 32 degrees advance.
All electronic ignition systems, both standard and multi-spark, require a special voltage regulator PN P3690732 when installed on the 1969 and earlier cars. This is a constant output voltage regulator and, if it is not used, the control box will be burned out.
A good ignition is only as good as its spark plug wires. There are two types of high performance spark plug wires available, metal core and suppression. The suppression wires PN P3690806 are a good choice for a general high performance car. A race car must use solid metal core wires P3690805 to obtain the high rpm performance required. The spark plug wires should not be crossed one over the other anywhere between the distributor cap and the plugs. Use ignition wire separators PN P4007667 to keep the wires from crossing or getting too close to each other.
The wires should be kept away from any metal object. If the plug wires do get near metal, such as the valve cover, then more insulation should be added in the area of contact. These tips on plug wires must be followed if the high energy ignition systems, such as the Gold Box P4120600 are to be used.
A new lightweight battery-in-the-trunk kit PN P3690934 is available and a good investment for a bracket racer.
For racing or other high performance applications with a modified, non-stock engine, it may be necessary to use a spark plug which is one or two steps colder than standard. Colder than standard plugs used under normal type driving conditions will provide short plug life as they are more likely to foul. If plug fouling is experienced with a high performance two or four barrel engine under normal conditions, a warmer plug may be necessary to extend plug life.
The plug gap should be .040" with the high output coil PN P3690560 and .060" with the multi-spark ignition.
The standard spark plug for the slant six is a N-14Y. If the end plugs tend to foul during warmup, the cylinders #1 and #6 may want a hotter plug such as a N-18Y. For high performance applications, the N-10Y or N-12Y should be adequate.
Locating the colder race plugs can be difficult and you may be having a hard time locating high performance spark plugs! Direct Connection's got all of those hard-to-get Champion spark plugs in stock for every engine.
P4286562 N60Y - Champion P4286563 N63Y - Champion P4286564 N7YC - Champion, (replaces N65Y) P4286565 N9YC - Champion, (replaces N66Y)
Note: These are all colder than the N-10Y mentioned above. These plugs are for racing only.
B. Cooling System
The stock cooling system is adequate to keep operating temperatures to accepted levels. However, several components may be changed to reduce power losses in the system.
A viscous fan drive, PN 2003059, and fan, PN 2585376, will bolt on in place of the stock components to reduce the fan resistance at high engine speeds. The same effect or result can be obtained by using a plastic flex-fan. Be sure that these larger fan units have adequate radiator clearance.
NOTE: If the viscous fan is to be used, be sure to check for clearance to the radiator. The minimum clearance should be 3/4 inch.
For most high performance off-road applications, a high engine temperature is undesirable. For these applications, install a 160 degree thermostat, PN 3514174, which will help the engine run cooler. NOTE -Most" summer" thermostats currently available are in the 180-185 degree range. Winter thermostats are around 195 degrees.
3. Electric Cooling Fans
These 12-volt electric cooling fans are highly efficient auxiliary bolt-ons for street rods, race cars and compact or medium sized vehicles. They can be installed in front or in back of your radiator, quickly and easily. Unlike conventional belt drive fans, the electric fan will not rob engine horsepower. Three sizes are offered, with and without thermostat. Materials used in construction are of the latest tehnology Application recommendations listed below. Use as a guide only due to variances in engine compartment/cooling systems design.
P4349202 12" Fan without thermostat - for 6 cyl. engines.
P4349203 12" Fan with thermostat - for 6 cyl. engines.
For high speed race engines a small diameter crank Pulley and large diameter alternator and water pump pulleys are desirable. Aftermarket sources have these pulleys available, and they feature a deep groove design. A race engine should use a 3/8 fan belt.
C. Oiling System
The pressure provided by the standard oil pump can be increased by installing the black spring PN 2406677 mentioned earlier.
The windage tray P3690274 can be installed to increase engine power output. This tray attaches to the main bearing bolts similar to a 340. The following parts are needed to install the tray: four 340 main cap screws PN 6027355, eight (two per bolt) Hemi main bolt washers PN 2468135, and four tray attaching screws (PN 6023092). (All parts included in windage tray attaching package PN P3690939.)
If the 340 head bolts are shortened to the correct six cylinder bolt length and no main bolt washers used, the tray will be too close to the crank and will hit making a tinny sound. If the bolt shortening is done or interference occurs for some other reason, spacers or washers will have to be added between the windage tray and the head of the main cap bolt. Be sure that the crank doesn't interfere with the tray before the pan is reinstalled. Loctite the windage tray bolts.
The minimum clearance between the tray and the crank-rods should be .125".
The dipstick may rattle against the tray with engine vibration. It can be carefully bent a slight amount so that the rattle goes away.
In high speed, fully modified engines provision must be made for more oil flow through the main bearings to the rod bearings. One way to achieve this is to groove the crankshaft. A better way is to use the upper main bearing shells in the main caps. (It will be necessary to file down the locating tabs to allow the grooves to align.) These tabs merely locate the bearings. The tabs do not prevent rotation; the inserts are "crushed" by the cap to prevent rotation.
The oil sump should be greatly enlarged so that the oil level is at least six inches below the crankshaft's path. At least six quarts capacity is necessary as shown in Figure 2-1. The oil pickup should be converted to a swinging-type unit. The parts to use are PN 2406678 and PN 2406679. The swinging pickup enlarged-sump system should have proper baffles that will enable the pickup too stay covered under acceleration and deceleration. We strongly recommend using the high capacity oil pump P4286740 in all high performance applications.
In a high mileage, extreme serviced engine you may experience rear main bearing oil leakage. This problem can be solved easily by installing these specially engineered bearings. The bearings feature special diagonal cut grooves to prevent leakage at the rear main.
P4349040 Slant Six, 1960-76 with Forged Crank
P4349041 Slant Six, 1976-84 with Cast Crank
The Direct Connection filter P4007513 is engineered to meet the demands of heavy-duty and high performance applications and is recommended for all engines.
Oiling Tip: use nylon insert oil pan screws P4120613 (pkg.).
D. Full Race Oiling System
The race oil pan should be designed similar to Figure 2-2. The first item to check before building a race pan is to determine the lowest point of the connecting rod travel and the relationship of this point to the pan rail. The dimensions given in Figure 2-2 are measured from the lowest point in the rod travel not from the pan rail. This means that the pan must be made deeper than the dimension in the figure by the amount that the lowest point in the rod travel is below the pan rail or bottom of the block.
The in-car clearances should always be checked carefully before making the pan. The important items to watch for are header clearance, steering linkage clearance, K-member clearance, and ground clearance. The K-member will interfere with the front requiring a notch in the front of the pan or in the K-member. Any notch put in the pan should be kept to an absolute minimum or eliminated completely if at all possible.
The steering center link will usually pass through the center of the pan. This can be done by welding a tube through the pan. Again, this tube should only be large enough to allow the installation of the center link and also to provide learance during the lock-to-lock travel of the steering linkage. If the rules allow it in the class, the engine can be removed and the center link dropped or reshaped so that the tube through the pan is not required. Any reshaping or changing of the center link should be done carefully so that the relationship of the end holes is not changed at all. If one of these points is moved, it will change the toe pattern of the front suspension which could be very dangerous in a drag vehicle.
The two baffles shown in Figure 2-2 should be sealed on the three sides next to the actual pan sides. No oil should be able to pass between the baffle and the sides of the pan or the effectiveness of the baffle is greatly reduced. The swinging pickup is available from Milodon in Van Nuys, California. The oil sump should be designed so that the swinging pickup can swing to the rear of the pan on acceleration and to the front of the pan on deceleration. The pickup should stop within 1/2" of the back and front of the pan sump.
The sump should be filled with six to eight quarts of oil.
Note: Before installing any parts in engine, make sure that they are free of welding scale, dirt, or any other foreign matter.
Refer to the oiling system Chapter 18 for further information.
E. Fresh Air System
A good fresh air system can increase a car's performance without affecting much else. A hood scoop such as that used on the 1969 Road Runner or Super Bee 440-6 bbl. PN P3412057 (scoop only) can be attached to your standard hood. The air cleaner should be modified so that it is sealed to the hood. Foam rubber can be used as the seal. There are also complete hoods for some cars that already have a good scoop such as the 1969 Road Runner or 1970 challenger T/A. Small scoops are of no value. A scoop should have 30 in. sq. of opening to be effective. See Chassis Book P4349341.
F. Fuel System
A race car in Formula Stock or Modified Production or similar race cars should use two Carter 4594 electric pumps PN P4007038 in parallel. Parallel means having two inlets and two outlets rather than one pump feeding into the second pump. The mechanical pump should also be used. The recommended fuel line is 3/8" diameter and it should be the same diameter from the electric pumps to the carburetor(s). Only one Carter pump should be used in "Stock" (with mechanical pump).
The electric pump(s) should be hooked up so that it only works when the key is in the "ON" position. A separate switch in conjunction with the ignition key is optional.
G. Induction System
The intake manifold and carburetor make up the engine's induction system. The slant six has used a one barrel, a two barrel and a four barrel intake manifold on production engines. There is an aluminum version of both the one barrel and the two barrel manifolds. The Hyper Pak four manifold is no longer available, but a four barrel manifold is available from the Direct Connection Program, PN P3690801 as is an aluminum two barrel intake P4286281.
For any racing application, the carburetor must be specially jetted for proper fuel distribution. The intake manifolds mentioned above can be used with different carburetors, after-market manifolds or the manifold heat blocked, all of which require the carb to be jetted differently for each application. The following sections will cover the more popular choices.
SPECIAL NOTE: Because of the constant changes that occur in racing, the latest up-to-date carburetor and intake manifold information for the racing packages is covered in Chapter 21.
2. Single Barrels
Any 170 cu. in. slant six having a small BBS carburetor (1-1/4" diameter venturi) will produce about 5% more power when the 225 cu. in BBS carburetor (1-11/32" diameter venturi) is installed. These two carburetors can be identified by measuring their throttle bore diameter. The larger carburetor has a 1-11/16" diameter throttle bore and the smaller carburetor has a 1-9/16" diameter throttle bore. All 170 manual transmission jobs and the 1960-1961 170 with automatic transmission have the smaller carburetor.
3. Two Barrels
a. Two Barrel Conversion Available from Mopar
A two barrel setup (as used on the 225 cu. in. export and marine engine) is available from Mopar as follows:
Intake Manifold PN 2806816 Carter 2 Bbl. Carb. PN 3462779 (1.44 throttle bore) Air Cleaner PN 2465310
b. Do-it-yourself Two Barrel
The two barrel carburetor from any 318 V-8 engine (without CAP package) can be used as shown in Figure 2-3. It is larger and shouldn't need to be rejetted.
c. "B" Engine Two Barrel
The larger two barrel from a 361 or 383 can be installed as in b above. However, low speed driveability in cold weather may be unsatisfactory for general use.
2 Bbl. Manifold Iron 4041042 Alum. 4095066
2 Bbl. Carb. Man. 4027757 Auto. 4027721
If above parts are not available see Section 6 on the next page.
d. Four Barrel
The AFB from the 273 power pack can be adapted to the 225 six cylinder. The four barrel bores must be centered on the standard six cylinder inlet manifold's plenum chamber.
e. 3-2 Barrels - Race Only
Three Weber dual carburetors 48 IDA will improve engine output nicely compared to Hyper-Pak inlet manifold and carburetor on the slant six. Obviously, a hand fabricated inlet manifold would be required; one cylinder per Weber throttle bore.
4. Slant Six Carburetor Calibrations
Hyper-Pak Manifold (possible to use aftermarket manifold like Offenhauser)
Carter AFB 4294S (Chrysler No. 2843111) should be used. This carburetor is used on the 1967-273 CI 235 HP engine with the manual transmission. Earlier carburetors used with this engine and manual transmission can also be used.
This carburetor should be modified as follows:
a. Replace the metering rods with No. 16-480 (.068-.065-.051)
b. Replace the throttle arm side secondary jet with No. 120-181 (.0492)
c. Replace the choke side secondary jet with No. 120-365 (.065)
Modified Standard Manifold
The above carburetor is also used with this manifold and should be installed with the primary throttle bores towards the front of the car.
The carburetor should be modified as follows:
a. Replace metering rods with No. 16-177 (.067-.0655-.064)
b. Replace primary jets with No. 120-386 (.086)
This calibration may be too lean for a highly modified engine in which case a richer mixture should be used.
5. Four-Barrel Carburetor for all Slant Six Engines
A carburetor that gives proper fuel mixture and distribution characteristics for the six cylinder engine using a Hyper-Pak intake manifold or a modified standard intake manifold can be made from a Carter model 3854-S carburetor. This carburetor is used on the 1965 and later 273 cubic inch high performance engine. The modifications are as follows:
a. Replace the metering rods with No. 16-177 rods (.067-.065-.055" Dia.)
b. Replace the throttle side secondary jets with No. 120-181 jets (.049" Dia.)
c. Replace the choke side secondary jet with No. 120-386 jets (.065" Dia.)
d. Replace the pump jet clusters with cluster No. 48-264S
The throttle linkage will have to be fabricated to match the installation.
Special Note: We only recommend the 4 BBL package for racing.
6. Carb and Manifold Update
In the last couple years several new intake manifolds and carburetors have been introduced for the slant six. Although they have all been produced on the 225, they will fit the 170 and 198 also.
In 1975 an aluminum intake manifold PN 3837608 for the one barrel was introduced on the Feather Duster package. In 1977 the Super Six two barrel package was introduced. This package has an aluminum two barrel manifold PN 4095066 and two barrel carb PN 4027721. This is a standard-type Carter two barrel with 1.44" throttle bores.
The problem with the 2 BBL intakes listed in this section and early ones is that they are not available. Ordering the number listed gets you a superseded manifold made of cast iron. The 2 BBL intake that you want to order is D.C. part number P4286781. The carb (2 BBL) to use with this manifold is PN P4286782. This package is also the best for dual purpose performance. Larger two barrels should be used for higher performance before the 4 BBL is installed for all-out racing.
H. Camshafts and Valve Gear
The '71-77 camshaft (244 degree duration .410" lift) is a good choice for the older engine which had only a 232 degree duration .400" lift cam. No other special pieces would be required.
The next step up would be the Hyper-Pak cam (276 degree duration .430" lift) which is borderline for driveability even when used with a manual transmission and a high numerical axle ratio. The Hyper-Pak cam is not recommended for use with an automatic transmission. The H.D. valve springs from a 340 (PN 2863439) are required with this camshaft. It also is very difficult to obtain. We recommend the next step because it offers more performance with less duration.
The next step up in hot rod camshafts is the PN P4286679, which is a 268 degree duration .460" lift design. This is a good cam for general high performance applications with a high numerical axle ratio. The 340 valve spring should be used with this cam also.
The race cam for the slant six that is carried by the D.C. Program is the PN P4286681 which has a duration of 276 degrees and .490" lift. This cam should use the new high performance spring PN P3614542 or P3412068.
These last two 6 cylinder cams are brand new designs and represent the highest state of camshaft development to date. Most 6 cylinders aren't going to be in need of any bigger cams but they are available.
It appears that the Racer Brown ST-21, STX-21 and STX-22 should perform well in fully modified engines. Racer Brown pushrods, retainers, valve springs, and so on should be used. No slant six dynamometer work has been done at Chrysler with these cams, but these cams have produced power very well in the Chrysler wedge head V-8's. The STX-21 has a. 560" lift, while the STX-22 has .590" lift. If in doubt, use the smaller D.C. profiles listed above.
1. Retainers & Keepers
The standard steel retainer can be used with the standard type springs such as the 340. An aluminum retainer PN P3412067 can also be used with these springs. This aluminum retainer can also be used with the race valve springs. An Apollo titanium retainer PN P4007178 can be used for race competition. If required, there is a 3/8" stem lash cap P3690763 that can be used.
There are three designs of lock grooves used on valves. There are hardened valve stem locks or keepers available for each design for the 3/8" stem slant six valves.
1 Groove P3690797
2 Groove P3690856
3 Groove P3690857
The standard 170 and 225 mechanical lifter pushrods are acceptable for most purposes. If the block and heads have been milled excessively, the length of the standard pushrods may be unacceptable. If this is the case or a custom length pushrod is desired, the pushrod kit PN P4007284 (which will make 16 pushrods - 4 extra) is recommended. Individual replacements (which will make one pushrod) are available under PN P3690988. (Total of 12 required, no tool included.)
3. Degree Bushing
The B-RB engines use a pin in the end of the camshaft to locate the cam in relation to the cam sprocket. By using offset bushings (package of 4 - PN P3690936) inserted into the sprocket, the installed centerline of the camshaft can be changed (advanced or retarded).
4. Timing Chain
For heavy duty use, there is a roller timing chain setup available. Cam Sprocket P4007715, Crank Sprocket P3690280, Roller Chain P3690279.
5. Viton Valve Seals
The viton valve seals (P4120492) are sold as a package of sixteen - 8 intake and 8 exhaust. Only 12 used on 6. They are not the same. The short one goes on the exhaust valve.
Note: If dual springs are used, then use PC package P3690963.
6. Valve Spring Recommendations
6 Cylinder Valve Spring Recommendations
Camshaft Duration Lift Valve Spring ------------------------------------------------------------ P4120243 244 .436 P4286813 P4286679 268 .460 P4120249 P4286681 276 .490 P3412068
The three camshafts listed above use a standard style mechanical tappet P4286774. This can be used as service replacement on all production 6 cylinder mechanical cams. The aftermarket cams (Racer Brown, Crane etc) may use a different style. Be sure to check with the manufacturer.
8. Notching the Piston for Valve Clearance
In many cases when large, long duration and/or high lift camshafts are installed in stock engines, a notch in the piston is required. The proper location for these notches is shown in Figure 2-4. As a general rule camshafts in the 225 of 290 degree duration and longer will require a notch. The '72-77 low compression engines aren't as critical as the earlier 170, 198 engines. This holds true only as long as the heads have not been milled or the block decked. Clearances in the 170 are also much closer and camshafts bigger than stock should be checked for valve-to-piston clearance.
J. Cylinder Heads
The cylinder heads on the slant six engine are very straight forward and require very little special or custom machining or other items. The head is very rigid and very few head gasket problems are ever encountered especially if the steel gasket is used. There are several special considerations which we will cover in the next few sections.
1. Big Valves
The standard six cylinder valves are 1.62" inlet and 1.36" dia. exhaust. Bigger valves can be installed as follows:
Exhaust Valve (Oversize)
The 1957 Dodge V-8 exhaust valve #1827958 makes a very convenient oversize valve for the slant six. The head diameter is 1.5" or .140" oversize and the length is satisfactory. It is necessary to provide a clearance notch at the top of the bore. Outdated info see below. Included for reference only.
Inlet Valve (Oversize)
The 1-3/4" dia. 1634744 exhaust valve from the 1957 or 1958 Chrysler 392 V-8 can be made into a .130" oversize inlet valve. However, it is necessary to reduce its length by .270" and cut three more lock grooves down the stem. No bore notch is required for clearance for this oversize inlet valve. Outdated info see below.
Oversize Intake and Exhaust Valves Update
The two paragraphs above list oversize valves from older Chrysler engines. These work fine but may be very hard to find today. This can be solved by using D.C. intake valve P4286785 which has a 1.70" diameter and exhaust valve P4206786 which has a 1.44" diameter. No bore notch is required with either of these valves.
2. High Flow with Standard Valve Diameters
Oversize valves are expensive and involve much more work, bigger cuts etc. In many cases the racer is looking for more performance but without the added expense and extra grinding. High flow, standard diameter valves are ideal for this application: Intake P4286783, Exhaust P4286784. They are interchangeable with the stock ones but they're backcut to help flow more air which helps increase horsepower.
3. Valve Grinding
The intake and exhaust valve seats and the intake valve face have a 45 degree angle. The exhaust valve face has a 43 degree angle. The concentricity of the valve seat should be measured using a dial indicator. Total runout should not exceed .002" (total indicator reading). The width of the intake seats should be .060" to .090". The exhaust seat width should be .045" to .060". It must be remembered that the further the valve seats sink into the ports, the less horsepower the engine will produce. Never sink the valves to equalize the combustion chamber volumes. Although it is not legal for Stock and Super Stock racing, the full radius or multi-angle valve job (see Figure 2-5) is a performance improvement over the standard valve job.
For NHRA stock or super stock valve job, the following rules apply:
The valve must be faced at factory specification angle, and the seat angle must also meet factory specs. The valve seat may be narrowed from the top with any angle less than the seat angle, but not to exceed 1/4 inch larger than the valve head (see diagram). The maximum width for valve seat and bottom cut may not exceed 1/4 inch when measured together (top of seat to bottom of cut). See Figure 2-6.
4. Bracket Valve Job
In class racing (SS/A, F/S, B/SM etc.) there are very specific rules regarding valve work and seat modifications. In bracket racing, however, there are no rules regarding valve grinding. Therefore, we can have a special "bracket valve job", sometimes referred to as a competition valve job. The valve part is relatively easy. Production wedge valves have a small ski-jump on their backside just below the seat itself. The "backcut" removes this (see Figure 2-7).
Backcut angles vary from 20 to 35 degrees depending upon the engine. Backcut valves are available for the 6 cylinder engines (see section 2). Backcutting the valve tends to make the valve seat narrower, for which we strongly recommend that bronzewall valve guides be installed in the head.
Modification of the valve seat in the head is not as easy to explain. The valve seat itself is 45 degrees, standard. The throat or approach angle is 70 degrees, but sometimes 65 degrees is used because the orbital grinder used to grind the seats occasionally will "chatter" at 70. relatively speaking, the 70 degree cut in the throat removes a lot of material, which leaves a sharp edge at the bottom 70 degree machine cut as it transfers to the "as cast" port. (See Figure 2-8).
This sharp edge should be removed very carefully with a hand grinder so that it blends smoothly into both the cast port and the 70 degree machined cut. It is very important to keep to a minimum the metal removed and to maintain the 70 degree cut - although it may be narrower than it was originally. Extra caution should be used on the port's "short side" to keep as much radius as possible.
5. Valve Guide Cutting
To install the dual valve spring PN P3412068, or P3614542 or other race type valve springs, the inner spring seat needs to be narrowed and also its height of the guide needs to be cut down. See Figure 2-9 for details. It is also recommended that for the high lift cams, such as the Super Stock roller cams, that the stock valve guide height be shortened by .100". For Super Stock and fully modified drag race only engines, valve seals are not used but the valve guide clearance is decreased to .001" on both intake and exhaust valves.
K. Short Block
When assembling a slant six engine, most of the miscellaneous small parts such as cam bearings, timing chain and sprockets, rear main seal, camshaft plug and freeze plugs are the same between the various engine sizes.
When reassembling your short block you'll need a variety of Plastigauge (P4286819) to measure bearing clearances. This popular assortment includes one blue strip for .004-.009" tolerances, two red strips for .002-.006" tolerances and two green strips for .001"-.003" tolerances. Each strip is 12" long.
A chemical kit belongs on every mechanic's work bench...for life's mechanical frustrations, like baked-on gaskets, and for assuring proper seals, for assembly lubing, freeing up nuts and dozens of other uses. Eleven separate chemical products in each kit: Silicone RTV; Gasket Remover; Lubriplate; Spray White Lube; Anaerobic Gasket Maker; Lock'N Seal; Brake and Carb Cleaner; Penetrating Fluid; Spray Gasket Adhesive; Thread Sealant with Teflon; and Hand Cleaner. Everything you'll need to spare a headache is in this convenience kit. P4286559. We suggest having this kit on hand before you start rebuilding your short block.
If the head or block or both have been milled a total of .080" or more, we recommend using hardened washers P4120457 on the head bolts upon reassembly.
Factory pistons have the pin offset to reduce piston slap. By reversing the offset (reversing the piston) engine friction can be reduced. Forged racing pistons for the slant six are available from TRW (their part no. L2125F). Other manufacturers such as Forged-True and Venolia also offer forged pistons for the six.
It is possible to make the dome too high and too sharp which can have an adverse effect on the output of the engine. If this is the case, then some of the blocking dome should be removed and some of the steep angles and sharp edges should be rounded over.
2. Connecting Rods
Do not increase connecting rod side clearance beyond the specified .017" (the acceptable range is .008" to .017"). Excessive side clearance increases the oil demand of the engine as a result of excessive oil leakage past the rods. Increasing oil demand reduces the oil available for lubrication and cooling at high speeds.
Rods from the cast crank engines are unique and are not interchangeable with any of the other slant six rods. All the slant six rods use a pressed pin. For any heavy duty application the high strength rod bolts and nuts should be used.
3. Engine Break-In with Rough Bore Finish
When chrome flashed rings are used, the cylinder bore finish should be 30-40 micro inches. This is fairly rough compared to production bore finish of 20-30 micro inches. Use a medium stone and clean it frequently to avoid scratching the bores. The cross hatch angle should be 45 degrees - 60 degrees (included angle).
The proper break-in procedure with the above bore finish is:
Number Shift Cycles Shift Speed 10 @ part throttle 3500 5 @ part throttle 5000 cool down to dead cold 3 @ part throttle 6000 3 @ open throttle 6500 cool down. RACE
NOTE: Engine should not get over 180 degrees during the break-in cycle.
4. Engine Break-In with Smooth Bore Finish
With the new smooth hone finish (AN 501 Sunnen stone-wet) on the cylinder walls, the following procedure should be used for engine break-in:
Each run should consist of short interval 1/2 to 2/3 load bursts.
5-6 runs total beginning at 4500 rpm
Increasing the engine speed each time approximately 500 rpm.
Final run of break-in cycle - Max power rpm.
NOTE: Engine should not get over 180 degrees during break-in cycle.
It is not necessary to balance an engine using production parts (crankshaft, rods, pistons) for dragstrip use. Production balance tolerances are more than adequate. A race engine should be balanced.
6. Head Gasket
If trouble is experienced with blowing head gaskets in modified high compression engines, a steel head gasket (PN P4286789) ('60-'80) is also available.
A composition gasket P4286790 ('81-'84) is also available. The comp gasket will fit on the older engines and is recommended for gasket sealing problems.
The only production part available to stroke the six is in the installation of the 225 crank into the 198 engine. This requires the 225 crank and rods. Likewise, any specially made stroker crank will also require either special rods or special pistons or both. The assembly should be rebalanced.
8. Honing Plates
For the serious all-out race engine, honing plates are recommended. Honing plates from other engines like the A or Hemi won't work on the slant six engines because the head bolts are located in the wrong place. Honing plates for the slant six engines are not readily available at this time.
L. Exhaust System
The special exhaust pipe, muffler and exhaust manifolds from the Hyper Pak six are no longer available.
1. Mufflers and Pipes
The exhaust system from the '75-76 Feather Duster and Dart Light is the best system currently available. The large dia. pipe from the manifold to the converter is PN 4004379. The catalytic converter and pipe assembly is PN 4004147, while the muffler is PN 4004381. This is a bolt-in system on the various '67-76 "A" body cars.
For hot rod applications, the large diameter pipe PN 4004379 can be adapted to a street hemi muffler PN 2781300 for a low restriction exhaust.
Cylinders 1-2-3 should exhaust through 1-1/8" or 1-3/4" O.D. pipes about forty inches long into a cloverleaf collector and then through a 2-1/2" O.D. outlet pipe much like current V-8 Super Stock practice. Cylinders 3-4-5 should have a duplicate system. See Figure 2-10.
The Direct Connection six cylinder headers PN P4007602 are a 15/8 x 40 primary with 2-1/2 collector design which fit the '67-76 A-Body and '62-74 B & E Body.
M. Compression Ratio
Up to .090" can be removed from the slant six cylinder head. The slant six cylinder head has an especially thick lower deck surface.
For example, removal of .090" will raise the compression ratio of a 225 engine from 8 to 1 up to 9.5 to 1. Removal of .090" will raise the compression ratio of a 170 engine from 8 to 1 to 10 to 1.
Using high quality gasoline such as Sunoco 260, compression ratios between 11 and 12 to 1 should perform satisfactorily on the dragstrip. "West Coast" pistons would be required to attain ratios this high. Step seal "Dykes" top piston rings should also be used because they lower engine friction at high speeds. Forged racing pistons should be fitted at .008" to .010" clearance.
The following charts show the resulting compression ratios from a variety of deck heights, cylinder head volume and bore sizes.
SPECIALL NOTE: Domed pistons and Dykes rings eadily available for the slant six.
COMPRESSION RATIO - 170 CUBIC INCH ENGINE
Cylinder Deck Head Std. Compression Ratio Height Volume Bore .020 oversize .040 oversize --------------------------------------------------------------------- -.040 54.00 8.39 8.46 8.54 52.50 8.57 8.65 8.72 51.00 8.76 8.84 8.91 -.020 54.00 8.75 8.83 8.92 52.50 8.95 9.04 9.12 51.00 9.16 9.25 9.34 .00 54.00 9.16 9.25 9.34 52.50 9.38 9.47 9.55 51.00 9.61 9.71 9.81
COMPRESSION RATIO - 198 CUBIC INCH ENGINE
Cylinder Deck Head Std. Compression Ratio Height Volume Bore .020 Oversize .040 Oversize ---------------------------------------------------------------------- -.075 54.00 8.95 9.02 9.10 52.50 9.13 9.20 9.28 51.00 9.31 9.39 9.47 -.055 54.00 9.31 9.39 9.47 52.50 9.51 9.59 9.67 51.00 9.71 9.79 9.88 -.035 54.00 9.71 9.79 9.89 52.50 9.92 10.01 10.11 51.00 10.15 10.24 10.34
COMPRESSION RATIO - 225 CUBIC INCH ENGINE
Cylinder Deck Head Std. Compression Ratio Height Volume Bore .020 Oversize .040 Oversize ---------------------------------------------------------------------- -.140 54.00 8.89 8.95 9.02 52.50 9.04 9.11 9.17 51.00 9.20 9.27 9.34 -.120 52.00 9.20 9.27 9.34 52.50 9.37 9.44 9.51 51.00 9.54 9.61 9.69 -.100 54.00 9.54 9.61 9.69 52.50 9.72 19.80 9.88 -51-00 9.90 9.99 10.07
NOTE: All compression ratio figures are with a standard steel head gasket with a compressed height of .020".
N. Boring and Milling Specifications
All the 1970-1976 slant six engines can be overbored .060" maximum. The thin-wall lighter weight 1977-1982 blocks shouldn't be bored past .030" oversize.
However, if the engine is to be used for high output racing purposes, the cylinder wall thickness should be checked to be sure that that particular block doesn't have a bad case of core shift. The cylinder wall thickness should be the same all the way around or thicker on the major thrust side, i.e. passenger side, of the cylinder bore as installed in the car.
Milling the cylinder head will reduce its volume and increase the engine's compression ratio. To reduce the chamber volume one cc., mill the head .0063". The intake manifold surface doesn't have to be milled.
O. Engine Clearances
Conn. Piston Engine Brg. Clear. Rod Side To-Well Ring Disp. Rods & Mains clearance Clearance End Gap ------------------------------------------------------------------ 225 .0015/.0025 .008/.017 .0015/.002 .011/.015 198 .0015/.0025 .008/.017 .0015/.002 .011/.015 170 .0015/.0025 .008/.017 .0015/.002 .011/.015
P. Torque Specs
Connecting Rod Nut - Std. 45 ft lbs. H.D. 50-55 with oil Cylinder Head Bolt 65 Main Bearing Cap Bolt 85 Spark Plug 30 Camshaft Lock Bolt 35 Carb to Manifold Nut 30 Exhaust Manifold Nut 10 Flywheel to Crankshaft 55 Flex Plate to Crankshaft 55 Flex Plate to Converter 270 in lbs. Intake to Exhaust Manifold Bolt 200 in lbs. Rocker Shaft Bracket Bolt 30 ft lbs.
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