Keeping true to my mantra, here are the details of what I had in the MS460 I prepaired for the build-off.
I began by buying three pistons: 372BB, 064 Meteor, and 038 Magnum Meteor. The 372BB piston was not an attractive option to me at all. The skirts are no wider than the OEM piston, windows had to be cut, and it's not my favorite brand of piston. I went with the 038 piston. The 064 and 038 Mag pistons are very similiar. There are two main differences. The 064 has much longer skirts, and has thinner rings. I didn't realize until too late that the 038 rings were thicker. If I had it to do over, I'd go with a 064 piston. Both the 064 and 038 pistons have to be widened between the wrist pin bosses in order to fit over the rod.
Nik will have to clarify, but I we cut either a .030" or .035" popup. Because of the taller pin to crown height of the 038 piston, very little had to be taken off the cylinder base.
Once I had a piston to work with, I proceeded to porting the cylinder. I was able to go a full 70% of bore diameter on the intake and exhaust ports. I had to be very careful not to widen the very top of the intake port, due to the location of the ring locating pins. I did not raise the exhaust at all, since I wanted RPMs and torque. IIRC, the exhaust was around 102° at that point. Copmpression was 202 PSI.
I advanced the ignition timing about 8°. This is only about 1/2 the width of the key.
I also opened up the carb venturi about 1mm. Care must be taken to not thin the area where the nozzle comes through, or you're like to end up with it leaking.
I put it all together and headed to Andres, where he was testing the MS441 C-M. The 460 saw was VERY disappointing. It had VERY little more than a stock saw. I knew I had my work cut out for me at that point. No way could I deliver this raffle saw and build-off saw running like this.
I first tried putting the ignition timing back to stock. That didn't help.
So, I went back to degree my MS440/460 hybrid cylinder. It's an excellent running saw. I was shocked to find that it only has 14° of blowdown. It's a Mahle 046/460 cylinder, and that's how it came. Jeremy confirmed this by degreeing another early Mahle 046 cylinder and found it to only have 15°. I went back in the raffle saw and raised the transfers to 115°. It made a big improvement. I then went back in and raised the exhaust to 98°. I ended up with 17° of blowdown, with the exhaust at 98° and the transfers at 115°.
I still wasn't happy with it. I again advanced the timing 8° like I originally had it. It definately made a real difference.
I still wanted more. So, back in I went again, and did nothing other than remove the bottom ring. It suprised me by picking up several hundred RPMs in the cut. It was only after to talking to Jeremy again that I realized that the 064 had thinner rings. If getting rid of the bottom ring made that much difference, going to a thinner one could only help. This is why I'd go with the 064 piston if I had it to do over.
Are you thinking I'm crazy for going with that little blowdown and numbers that high? In talking with Jeremy about his build, he was experiencing some of the same frustrations. I finally talked him into raising his transfers, and he experienced the same improvement I did. He passed the info on to Randy, and you see where that got me Bottom line, this recipe works, and it works very well.
Is a popup and piston swap required for a great running 460? No. Some of the great running saws in this build-off had stock pistons and no popup. They may not make the winner at a race, but they're certainly not required to build a great running saw.
Here are the final numbers in this saw.
Exhaust - 98°
Transfers - 115°
Intake - 83°
Blowdown - 17°
Squish - .019"
Compression - 190 PSI
I began by buying three pistons: 372BB, 064 Meteor, and 038 Magnum Meteor. The 372BB piston was not an attractive option to me at all. The skirts are no wider than the OEM piston, windows had to be cut, and it's not my favorite brand of piston. I went with the 038 piston. The 064 and 038 Mag pistons are very similiar. There are two main differences. The 064 has much longer skirts, and has thinner rings. I didn't realize until too late that the 038 rings were thicker. If I had it to do over, I'd go with a 064 piston. Both the 064 and 038 pistons have to be widened between the wrist pin bosses in order to fit over the rod.
Nik will have to clarify, but I we cut either a .030" or .035" popup. Because of the taller pin to crown height of the 038 piston, very little had to be taken off the cylinder base.
Once I had a piston to work with, I proceeded to porting the cylinder. I was able to go a full 70% of bore diameter on the intake and exhaust ports. I had to be very careful not to widen the very top of the intake port, due to the location of the ring locating pins. I did not raise the exhaust at all, since I wanted RPMs and torque. IIRC, the exhaust was around 102° at that point. Copmpression was 202 PSI.
I advanced the ignition timing about 8°. This is only about 1/2 the width of the key.
I also opened up the carb venturi about 1mm. Care must be taken to not thin the area where the nozzle comes through, or you're like to end up with it leaking.
I put it all together and headed to Andres, where he was testing the MS441 C-M. The 460 saw was VERY disappointing. It had VERY little more than a stock saw. I knew I had my work cut out for me at that point. No way could I deliver this raffle saw and build-off saw running like this.
I first tried putting the ignition timing back to stock. That didn't help.
So, I went back to degree my MS440/460 hybrid cylinder. It's an excellent running saw. I was shocked to find that it only has 14° of blowdown. It's a Mahle 046/460 cylinder, and that's how it came. Jeremy confirmed this by degreeing another early Mahle 046 cylinder and found it to only have 15°. I went back in the raffle saw and raised the transfers to 115°. It made a big improvement. I then went back in and raised the exhaust to 98°. I ended up with 17° of blowdown, with the exhaust at 98° and the transfers at 115°.
I still wasn't happy with it. I again advanced the timing 8° like I originally had it. It definately made a real difference.
I still wanted more. So, back in I went again, and did nothing other than remove the bottom ring. It suprised me by picking up several hundred RPMs in the cut. It was only after to talking to Jeremy again that I realized that the 064 had thinner rings. If getting rid of the bottom ring made that much difference, going to a thinner one could only help. This is why I'd go with the 064 piston if I had it to do over.
Are you thinking I'm crazy for going with that little blowdown and numbers that high? In talking with Jeremy about his build, he was experiencing some of the same frustrations. I finally talked him into raising his transfers, and he experienced the same improvement I did. He passed the info on to Randy, and you see where that got me Bottom line, this recipe works, and it works very well.
Is a popup and piston swap required for a great running 460? No. Some of the great running saws in this build-off had stock pistons and no popup. They may not make the winner at a race, but they're certainly not required to build a great running saw.
Here are the final numbers in this saw.
Exhaust - 98°
Transfers - 115°
Intake - 83°
Blowdown - 17°
Squish - .019"
Compression - 190 PSI