[Tim Corcoran]

I am going with a 4.181 bore and 4.25 stroke. There are a few reasons why I would prefer not to go to a 4.5 stroke. With my heads having a 71cc combustion chamber it would bring my static compression way too high, of course I could of ordered dished pistons to get my compression down. A longs stroke like 4.5 puts additional stress on the crank and the block, I don't want to push my luck with an OEM block. Longer the stroke the faster the piston speed thus shorter ring and bore life, I already have increased piston speed using 6.8 rods that's a tradeoff for less side loading on the cylinder wall and better cylinder filling since it dwells longer at TDC. If I were building a monster engine with an aftermarket block I'm not sure even then I would go with that large of a stroke. Many have done it with good results in my opinion it's not the best choice for me. I'm not going for max power I'm trying to stay in the low 10 second range for a reliable long lasting bracket engine and I don't want to put in a cage and window net.

[blueghoast]

I like the 4-inch stroke there assome, kind of the best of both worlds
Just thinking out load. Good Luck.

GT

[Stan Weiss]

Originally Posted by Tim Corcoran

I am going with a 4.181 bore and 4.25 stroke. There are a few reasons why I would prefer not to go to a 4.5 stroke. With my heads having a 71cc combustion chamber it would bring my static compression way too high, of course I could of ordered dished pistons to get my compression down. A longs stroke like 4.5 puts additional stress on the crank and the block, I don't want to push my luck with an OEM block. Longer the stroke the faster the piston speed thus shorter ring and bore life, I already have increased piston speed using 6.8 rods that's a tradeoff for less side loading on the cylinder wall and better cylinder filling since it dwells longer at TDC. If I were building a monster engine with an aftermarket block I'm not sure even then I would go with that large of a stroke. Many have done it with good results in my opinion it's not the best choice for me. I'm not going for max power I'm trying to stay in the low 10 second range for a reliable long lasting bracket engine and I don't want to put in a cage and window net.

Tom,
While increasing the rod length does change the piston velocity curve, where in the velocity curve are you looking at when you say velocity has increased? Peak velocity is actually reduced as you length the rod. You also move the point of peak velocity and where the rod and crank journal are at 90 degrees to each other farther ATDC.

Stan

[Tim Corcoran]

Originally Posted by Stan Weiss

Tom,
While increasing the rod length does change the piston velocity curve, where in the velocity curve are you looking at when you say velocity has increased? Peak velocity is actually reduced as you length the rod. You also move the point of peak velocity and where the rod and crank journal are at 90 degrees to each other farther ATDC.

Stan

It is my understanding that with a longer rod the piston dwells longer at TDC and gives more time for cylinder filling and this also increases piston speed at some point in the stroke over a shorter rod. I don't understand your statement that peak velocity is actually reduced with a longer rod or maybe my understanding is flawed.

[chiefbigb]

Stan is pretty smart. Your build is one that has been done by probably everyone in the race section 20 plus years ago. The higher block fill will probably net you higher oil temps and lower cooling system capacity. I hope it runs well and lasts many years.

[blueghoast]

I've got two motors that are hard blocked to the water pump holes
Both of these motors run cooler then any of my other engines.
On the street and at the track, I'm useaully running the motor in
the staging lane's to keep the temp up where it needs to be.

GT

[chiefbigb]

Do you monitor oil temp also?

[blueghoast]

Originally Posted by chiefbigb

Do you monitor oil temp also?

No I haven't done that yet

GT