Good morning class! Today we are going to learn about the how’s and why’s about stroker kits. My goal is to debunk some myth’s and common misconceptions about stroking a big or small block Chrysler. As someone who has built National Championship quality racing engines for over 20 years I will share specific information about bearing clearances, bore notching and much more information. This is really required for properly building a stroker engine. I will also ”in clear terms and detail” explain what questions you need to ask so you can purchase a stroker kit that is truly “ready to go” when you receive it.
We built our first big block stroker engine in the fall of 1988. “Back in the day” the only way to build a stroker engine for a Chrysler was to buy a billet crank or weld and offset grind a stock crankshaft. Since billet cranks are machined out a solid piece of steel they are very expensive ($2800+ in 88’) and took over 12 weeks to make. This was not a practical option for us. That left us to use welded strokers. Welded strokers evolved out of weld repairing damaged steel crankshafts. Someone figure out: instead of welding the journal to repair it, one could just weld on the top half of the rod journal and then offset grind it to increase the stroke. People have been doing this since the late 40’s!! While this worked well, you still are starting with a 1053 steel crankshaft that was never intended to make serious power. Not to mention any factory 440 steel crank is now 40+ year old and most likely has seen a pretty hard life.
Fast forward to1992. Mopar Performance releases the 3.75 & 4.15 stroke crankshafts. While they are a little bit more money than a welded stroker, they are brand new and can be ordered off the shelf and into you hot little hands in days not weeks! Mopar decided on a 4.15 stroker crankshaft because it makes exactly 500” in a 440 block that is bored + .060. These stroker crankshafts were made by Norton Foundries. This was a company that was in Fostoria OH that made OEM production cranks for the big 3. These cranks could be purchased for around $1200 and once balanced could be dropped right in to a properly prepared 440 block . Due to Norton’s experience with the OEM’s they held very consistent bearing sizing (clearances). These consistent bearing tolerances made them very friendly to the end user.
After decades of convincing people to spend the money on aftermarket aluminum heads, the first question people ask is why? Some assume it might be cheaper, but unfortunately that is not the case. Honestly, well ported Performer RPM heads will flow as much air, weight less, and features a closed chamber for quench. Since they are made out of aluminum repairs are easy if anything ever does go wrong.
Then next question is the same as the first, why? “906” iron heads are hard and difficult to port. They also are now at least 40 years old and need valve guide work, new valves, and hardened exhaust seat for unleaded compatibility, BUT if you have a 68-70 ½ Chrysler product, these are the correct heads for your mopar big block. Since the 68-70 ½ years might be considered the “premium” years for mopars of value, there are a large amount of people who want to improve engine output, but still maintain the OEM appearance. These CNC’ed 906 heads are not only for hot street cars but for a number of OEM appearing class racing organizations like FAST (factory appearing stock tire).
To meet the demand of this niche’ market we now offer CNC porting for 906 heads. I have been asked many times about programs for other castings such as 452 heads. The problem is that because iron is much harder than aluminum, it takes more machine time to port the heads. The iron heads are also harder on tooling. Because of these reasons, CNC porting iron is more expensive than aluminum. Honestly, In a performance application other than OEM appearing, you are better off upgrading to an aftermarket aluminum head for a hot street or bracket racing application. Our CNC ported 906 heads are specifically designed for class racing and people with certain year cars that want to maintain OEM appearance.
EVERYONE is obsessed with flow numbers. While they are important they are not everything to making power. To sooth the information junkies that exist out there, here are the flow numbers.
Head flowed w/2.14-1.81 valves, 45 degree VJ, 2.375 bore, no ex tube.
As you can see the ex easily flows over 70% of the intake and with 313 cfm you can easily support well over 650 HP.
For Muscle Motors to supply complete heads that feature: CNC porting with polished chambers, Stainless valves, new bronze guide liners honed to size, hardened exhaust seats, surface milled, any hydraulic or solid cam springs, 10 degree locks and retainers, new seals and are fully assembled, $2299 outright, no core charge. If you send your core heads deduct $200.
I get this call about a year ago from a racer/friend of mine. Tracy Sons is an accomplished big buck bracket racer that uses Mopar power. Tracy asked me “if there was a wedge head that would run significantly faster than his current 440-1 engine.” I wanted to know how much faster? Tracy asked if we could build him something that would run 4.60s’ in the 1/8, 7.40 in the 1/4 (most big dollar bracket races are run on 1/8 mile) in his 1875 lb dragster. Tracy continued that: it must be a low RPM, low maintenance, and run on relatively cheap race gas (no Gucci $12 a gal oxygenated fuel). I said sure, no sweat!
I would build this combo with B1-PSO heads. You may ask (because Tracy did) “What are B1-PSO heads?” PSO stands for “Pro Stock Option” this was the very first head that Wayne County used back in the late 80’s when Darryl Alderman went NHRA Pro Stock racing. Externally the head looks exactly the same as a traditional B1 head. The intake and exhaust port openings are in the stock location. The difference is that the ports are raised within the head. This gives the head more short side radius and the roof is also higher in the casting. This requires a longer valve and special drilling of rocker stand location. What this means is you can get A LOT more airflow thru the head. Typical B1 heads flow anywhere from 400-420 CFM. The PSO’s will flow over 475 CFM with our CNC porting!!! Tracy already had an aluminum wedge block, headers, B1 intake, etc so that is why we went PSO heads instead of a Predator. Predators will still make the most power but for low RPM/low maintenance, I feel the PSO is a better choice.
I decided that Tracy’s 4.500 bore block needed new life so I bored and honed it out to 4.530, that with a 4.500 crank makes 580” engine. Next the heads 2.400, 1.81 valve combo with our CNC porting gives us a Killer cylinder head. NOTE: PSO head come with head bolt, intake and exhaust bolt holes and that is IT! We had to drill the head for valve guide angle and location, valve seat location, rocker stand location, etc, etc. THESE ARE NOT FOR A NOVICE ENGINE BUILDER. Anyway, castings were now machined, ported and ready to assemble. I then drilled the head for typical B1 oil drain backs (required). I used stainless steel valves (yes I said Stainless) with 11/32 stems. I believe there is no need for titanium when the RPM’s are kept so low. Since I was location the rockers where ever I wanted I made sure we had a valve long enough to have 2.100 installed height spring. This will allow a “big cam” at a later date if we want to make a change. I choose a cam to keep the peak power below 7000 RPM and peak torque below 5500 RPM’s. A different cam with more lift, duration and lobe separation would make more power but it would also need compression and RPM, two big No No’s on the project. What we ended up with was a single 4bbl engine that runs great on 110 octane fuel, and makes peak power of 1004 HP @ 6500 and peak torque of 850 Ft/lbs @ 5300!! All of this with 31 degrees timing!
A Predator head is a symmetrical port cylinder head that is designed to fit on a 4.800 bore spacing block. It features an oval intake port that is deigned for maximum airflow with minimal cross sectional area. Port volume starts @ just over 420 cc’s and can get as big a 480 cc’s max ported. It uses valves that are 6.800” long (almost 2” loner than a stock 440 valve) and has a 2.400 intake and 1.850 exhaust valve. The intake and exhaust valves are both canted. What this means is the valves open on a compound angle. As the valve lift increases the valve actually moves towards the centerline of the bore. This increases the unshrouding of the valve as valve lift increases (more lift/more flow= more power!) Out of the box, with the correct valve job and blending of the seat the heads will flow over 485 cfm on a 4.500 bore. Properly ported the heads are capably of flowing over 530. Combustion chambers come CNC ‘ed and will start life around 85 cc.
The head can be ordered with a Wedge or Hemi head bolt pattern. This allows for “off the shelf” availability of many different choices for gasket thickness and design. The Hemi or Wedge bolt pattern availability allows the user to use a preexisting short block (B1, Indy and Hemi) and this way you can upgrade your engine program to a better flowing cylinder head without have to buy everything from scratch.
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