Two things...
Thread Starter
Registered User
Joined: Mar 2004
Posts: 405
Likes: 0
From: miami springs
Ebay V-afc2 FOR 285 good or bad?
285 aint bad for one of these right...? they got three left and just about 2 hours till sale is done. This is just to drop the v-tec.
285 aint bad for one of these right...? they got three left and just about 2 hours till sale is done. This is just to drop the v-tec.
1 hour left 
Registered User
Joined: Oct 2000
Posts: 7,134
Likes: 3
From: Columbia, MD
Rings are a story for another day, but I'm not talking about shortening the stroke. You can leave the stroke alone if you beef up the rods. There's a large difference in tensile/compression stresses between 7,500 and 9,000 rpms (44%, to be more specific).
The main idea that I think gets glossed over too often in these types of discussions is the sheer piston speeds that were starting from. People wouldn't think too long and hard about doubling the limit on a 3,500 rpm machine to 7,000 (although it would take some work). But ask someone to up a 9,000 machine to 18,000 for similar money, and they'll probably pee themselves laughing. As speeds become higher, you're not just fighting stress from the controlled spark explosions, you're beginning to approach the material's stress limit for staying together in one piece.
Take a 10' long piece of aluminum tubing and swing it at 60 rpm over your head (let's assume you could actually do that). It's touch work, but doable with those materials. Now increase the length of the tube to 1 mile...assuming you could still spin it at 60 rpm, the tube would snap because the tensile strength of the material would give up long before then. This is akin to increasing the stroke. Now, keep the tube at 10', but increase the speed to 9,000 rpm. Again, the tube will snap because you've exceeded its tensile strength (actually, the rotational inertia will be too great and it'll snap off a few inches form your hand).
The point is, you have to beef up the tube (i.e., conrod) if you want to lengthen the stroke or increase the speed. You may get away with an extra 500 or 1,000 rpm, I can't say what the materials limit is, but you will eventually reach a point that no matter what you've done to the top end, the bottom end will need adjustment. Lucky for most, many engines come from the factory with a LOT of leeway built in (such as Supras), but our engine is sadly not one of those. We have a fairly limited margin of error.
The main idea that I think gets glossed over too often in these types of discussions is the sheer piston speeds that were starting from. People wouldn't think too long and hard about doubling the limit on a 3,500 rpm machine to 7,000 (although it would take some work). But ask someone to up a 9,000 machine to 18,000 for similar money, and they'll probably pee themselves laughing. As speeds become higher, you're not just fighting stress from the controlled spark explosions, you're beginning to approach the material's stress limit for staying together in one piece.
Take a 10' long piece of aluminum tubing and swing it at 60 rpm over your head (let's assume you could actually do that). It's touch work, but doable with those materials. Now increase the length of the tube to 1 mile...assuming you could still spin it at 60 rpm, the tube would snap because the tensile strength of the material would give up long before then. This is akin to increasing the stroke. Now, keep the tube at 10', but increase the speed to 9,000 rpm. Again, the tube will snap because you've exceeded its tensile strength (actually, the rotational inertia will be too great and it'll snap off a few inches form your hand).
The point is, you have to beef up the tube (i.e., conrod) if you want to lengthen the stroke or increase the speed. You may get away with an extra 500 or 1,000 rpm, I can't say what the materials limit is, but you will eventually reach a point that no matter what you've done to the top end, the bottom end will need adjustment. Lucky for most, many engines come from the factory with a LOT of leeway built in (such as Supras), but our engine is sadly not one of those. We have a fairly limited margin of error.
:
