Some time ago I had the opportunity to purchase a 331 stroker motor with a Vortech supercharger on it. I was considering just dropping the entire setup into my 94GT. The price was fantastic, and it had a handful of parts on it that I could sell to offset the price because I couldn't use the parts or I already had those parts. I'm not going to get into the buying / selling aspect or listing all the parts out.
Once I had the engine home, I used an endoscope with my laptop to look into the cylinders through the spark plug holes to see what the cylinder walls looked like. The didn't look bad, but I did see some scoring on one or two of the cylinders. I made the decision to have the engine freshened by my engine builder.
A little more about the engine. It is a 4.030 bore by 3.25 stroke for a 331 displacement. Heads are AFR 185, outlaw series topped with SVO A315 3/8 stud mount rockers. The pistons are dished for a boosted application, not sure what camshaft is in it.
I bought this motor knowing that it was an aftermarket ford block. Before I brought it to my builder I knew that there was an R in the lifter valley and XXX and XXX on either bank of the lifter valley. I came to learn that the block is nicknamed the Mexican R Block or more specifically the M-625-B50 block. This is good news, its actually a decent block! The other thing I was told is that the bottom was filled, which can also be an advantage making the block more rigid to hold more power.
I finally got the engine to MCRP in Easton. Mike did the work on the 306 that is currently in the car, and it runs absolutely fantastic. Once the block was disassembled, I stopped in to see him and talk about it. It turns out that the block is filled to the water jackets. This isn't good for a street application (even with an oil cooler) because the cylinder walls have no way to be cooled. This engine was in a street / strip car that saw minimal cruise time so that was OK. I plan on cruising a LOT and that wasn't a good thing. What happens is that the extra heat eventually wipes the cross hatching from the cylinder walls and that creates blow by and needs to be freshened pretty regularly. I didn't like what I was hearing.
Let me take a step back for a minute. My goal for this engine was to give me at least 100 more RWHP than my current engine, which put down 250RWHP on the chassis dyno with 300 torque. It is REALLY a fun car to drive right now. A 331 with AFR 185's was certainly able to hit my new goal without a power adder. I already knew I was going to get a custom cam for it, and we would need to replace the dished pistons with something suitable for a naturally aspirated application. So back to the issue with the block being filled. I made the decision to go with an aftermarket block, which would have much more potential down the road anyway. I asked Mike to order a big bore Dart SHP block which is a 4.125 bore. The same crank and rods will be used from the original motor, but with a Mahle piston that will yield 10.5:1 compression. The 3.25 stroke with the 4.125 bore works out to be just about 347 cubic inches. It also means that we will be making closer to 400RWHP, and hopefully more. Now that we had a solid foundation, it was time to outfit the block with some nice accessories.
Valvetrain - I decided to go with a shaft mount rocker setup from LGM. The ratio is 1.6. To stay with the stud mount rockers, they really need to be upgraded to 7/16 and then even more with a girdle. This starts to get expensive, and requires a tall valve cover. The shaft mount rocker setup is even more stable than the 7/16 stud mount setup with the girdle and should still fit under a stock height valve cover ). Yes they are more money, but to me the trade off is worth it!
Intake Manifold, TB and CAI - This is the new Trick Flow R EFI intake (Not the box R). RPM range is 7250 and it should clear the trick flow stock height valve covers with no problems. I'm going with a professional products 75mm throttle body to match the 75mm opening on the intake. I also have the elbow for the intake that is necessary for 94/95 model years. I'm likely going to have to make my own cold air intake for this setup. It will need to be 101mm or 4 inches to accommodate the BA2400 mass air sensor and housing I'm going to use.
Camshaft and Balancer - Romac Gold series balancer, 28oz was sourced from FlowtechInduction.com along with a custom grind camshaft to tie everything together. Spring recommendation from Ed will be given to Mike before the final assembly. The cam that is currently in the 306 that is in the car was also sourced from Ed. He took into consideration the 94/95 ECU being a little bit temperamental with aftermarket cams. I'll say this - tuning the 306 with the Moates Quarterhorse and Binary Editor was a lot easier with a cam that is friendly to the ECU! Ed does good work!
Shortblock - Dart SHP 4.125 by 3.25 stroke. Probe crank and rods, Mahle piston, 10.5 to 1 compression.
I already have 60lb injectors, so I won't need to change injectors. I also sourced a RAM billet aluminum 28oz flywheel.
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