Thread: 6" con. rod in 383?

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In any of the mod. engines we build we will try and run the longest rod possible.
Other advantages over a shorter rod are less piston skirt wear and better ring sealing.

Tech1 posted a reference to several discussions by Ron Iskederian, one of which essentially says that the longer rod length only makes a small improvement in power. Clearly R. Iskederian is an independent thinker with a lot of experience, but almost all of his discussions negate current trends. I am particularly interested in the discussion of longer duration exhaust timing compared to the data in "Ryans Dyno tests".

http://www.ryanscarpage.50megs.com/combos1.html

In particular Ryan's Example 56 shows that the case of a cam with a longer duration exahust pattern still benefits from the use of 1.6 rockers only on the exhaust valves. This seems to say that both higher lift and longer duration help scavenge better. Maybe R. Iskederian's point is well taken for long duration cams but Ryan's Example 56 seems to say that for mild cams only a bit longer in duration than stock do need more exhaust duration and lift. I have wondered for quite a while why most of the Isky cams have equal duration for exhaust and intake patterns. I guess the point is well taken that the only way to actually figure this out is with actual dyno runs but boy these different views are confusing!

Don Shillady
Retired Scientist/teen rodder

Originally Posted by Don Shillady

Tech1 posted a reference to several discussions by Ron Iskederian, one of which essentially says that the longer rod length only makes a small improvement in power. Clearly R. Iskederian is an independent thinker with a lot of experience, but almost all of his discussions negate current trends. I am particularly interested in the discussion of longer duration exhaust timing compared to the data in "Ryans Dyno tests".

http://www.ryanscarpage.50megs.com/combos1.html

In particular Ryan's Example 56 shows that the case of a cam with a longer duration exahust pattern still benefits from the use of 1.6 rockers only on the exhaust valves. This seems to say that both higher lift and longer duration help scavenge better. Maybe R. Iskederian's point is well taken for long duration cams but Ryan's Example 56 seems to say that for mild cams only a bit longer in duration than stock do need more exhaust duration and lift. I have wondered for quite a while why most of the Isky cams have equal duration for exhaust and intake patterns. I guess the point is well taken that the only way to actually figure this out is with actual dyno runs but boy these different views are confusing!

Don Shillady
Retired Scientist/teen rodder

In our dyno testing over the years we have found hp gains by using a non-symmetrical camshaft.
With the intake ratio being so much greater to exhaust ratio in a 23 degree small block Chevy head we always try and favor the exhaust side by 4-6 degree's at .050.
In a good 18 degree head or 15 degree head we will close this by a couple of degree's.

In particular Ryan's Example 56 shows that the case of a cam with a longer duration exahust pattern still benefits from the use of 1.6 rockers only on the exhaust valves.

Don Shillady
Retired Scientist/teen rodder[/QUOTE]

Well the whole idea of split angle cams was so that they could get more flow out of the stock exhaust ports. This was mainly when we only had the old stock heads to work with. With the plethora of modern well designed good breathing heads on the market today you will see that the cam designers are coming back to a straight design of camshaft the timing events on the exhaust are exactly the same as the intake because the exhaust port flow designs ahve caught up with the intake flows.

Originally Posted by southerner

In particular Ryan's Example 56 shows that the case of a cam with a longer duration exahust pattern still benefits from the use of 1.6 rockers only on the exhaust valves.

Don Shillady
Retired Scientist/teen rodder

I am not sure what happened to the first post.

Originally Posted by erik erikson

[/SIZE]

Well the whole idea of split angle cams was so that they could get more flow out of the stock exhaust ports. This was mainly when we only had the old stock heads to work with. With the plethora of modern well designed good breathing heads on the market today you will see that the cam designers are coming back to a straight design of camshaft the timing events on the exhaust are exactly the same as the intake because the exhaust port flow designs ahve caught up with the intake flows.

On what heads has the exhaust caught up with the intake???

Originally Posted by erik erikson

On what heads has the exhaust caught up with the intake???

Well, figure of speech, I should of said that the newer head designs, edelbrock, airflow reasearch, dart, et all. flow a darn sight better out the exhaust than the stock chevy 1955 to 1986 head.