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Author Topic:   building new hobby engine
Dirt Roller

Total posts: 8
posted August 11, 2005 05:20 AM  
Wanting to build new imca hobby motor has to be 9/1 flat piston 355cu in. dont know much about difference in 5.7 to a 6 in rod can someone explain what we can expect for difference. thanks

Dirt Freak

Total posts: 265
posted August 11, 2005 11:13 AM  
Find the article in HOT ROD "the 350 chevy should have built" this will help you with that question. you'll get a ton of views on this however here's a general idea:

there is theory behind rod length it all has to do with piston speed...a shorter rod has a faster piston speed (going near and away from TDC) while the longer has a slower piston speed. What does this mean? well a shorter rod can take advantage of a larger head better due to increased speed.....while on the other hand a longer rod is slower and spends more time around TDC absorbing more of the power from combustion putting a little more to the crank.

Also, think about the price when considering the benifit. 6.0 pistions tend to be more than 5.7's.

Dirt Freak

Total posts: 402
posted August 11, 2005 11:55 AM  
The difference isn't big enough t omake a difference in a hobby stock.

longer rods decrease bore wear with really short piston's. Angularity issue's as well.

Dirt Forum Champ
Total posts: 5390
posted August 11, 2005 08:19 PM  
The motor will rev significantly quicker from the 50-60 gram lighter pistons. That's worth about 5 times more than the actual change in length and piston speed.

Eagle 6" SIR rods are 8 grams heavier than the stock 5.7 rod I measured. A 6" rod piston is about 50-60 grams lighter than a 5.7" version.. and if you really want to go light, a 6.2" piston is almost 100 grams lighter than a 5.7" piece.

Dirt Forum Champ
Total posts: 5390
posted August 13, 2005 02:17 PM  
thats true raz but most imca races pay about 150 and i take your motor for 300 now your 2 grand in the hole to replace it . where a basic 355 from a good builder you would only be a grand to replace.guess it just depends on your budget. with imca the heads and cam are more benfit for the money

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