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Original Message
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| Study cylinder wall requirements for race engines. |
| By Dave Shoe - 10/01/2001 9:53:02 AM; IP 216.243.158.15 |
I don't mean going to school to study, I mean you should check around and learn the critical importance of healthy cylinder walls.
Thin walls do conduct excessive heat to the coolant (reducing power and causing overheating and the need for larger radiators, etc) and the cylinders do shatter more easily than properly-bored cylinders, however, cylinders also transmit headbolt torque through the block to ruggedly connect the cranksaddles to the head and they also help clamp the head gasket by adding rigidity to the block. Additionally, thin cylinders flex during use, increasing operating friction and preventing proper ring sealing.
It's easy to build a wimpy FE (or any engine) by boring without regards to the design of cylinder cores. I've read (and commented on) magazine stories where the dippy writers bored out a 390 block to make a 428 engine without sonic checking the block to see if it was cast with the heavy cylinder walls (it wasn't a heavy-wall type of block). While looking at the cylinder deck these knotheads said, "look at all the meat between those cylinders (of the 390 block). We would take it out to the biger 427 bore, but we don't want to pay extra for the pistons". Not only did they build a wafer-thin 428 engine (and write about it in Car Craft mag, July99), but they suggested they were willing to bore until they hit water, except they couldn't afford pistons. They insulted the FE many times during the article (e.g.: "This engine will never see the high side of 5000 RPM, etc), so why would any FE engine builder want to take their advice. Sadly, a rash of "bore and stroke to 428" articles came out about then, some sorta "follow the leader" thing, I guess.
Many folk have commented in these forums on cylinder characteristics and FE engines. You might try the search feature and look for such words as "sonic" or "jacket"or "core" as a starter.
If you seek another analogy which more obviously paints a picture of what is going on, you might think about simply offset-grinding a 390 nodular crank to the 410/428 specification. while the crank may still be quite sturdy, the rod journals will be visually thinner and the more flexible crank now has a lower resonance frequency, so damping becomes more important. Chevy engines may have smaller rod journals, but Chevy engines were designed for forged crankshafts, which allow this. FE journals were designed for nodular crankshafts. Other issues become factors, such as the drilled oil passages will occasionally break through where the journal was turned down, causing oil to leak.
If you do end up turning a 390 into a 428, you might just find yourself with a thinner wallet, a broken engine, and a hankering to start playing with Chevy crate motors. On the other hand, if you have a heavy-cylindered 361/391 block, you might do O.K. with it (only a sonic map will tell you in advance).
Shoe. |
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