Thread: 6" con. rod in 383?

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what are advantages and disadvantages of running 6" connecting rod compaired to 5.7" connecting rod in 383 stroker motor?

Advantages, less side wall thrust. Disadvantages, have to clearance block and make sure that THE RODS CLEAR THE CAMSHAFT LOBES.

Ditto!

One advantage not mentioned above is that you might be able to run 87 octane or at least one grade lower than with the 5.7 rods because the longer rod slows the piston down near TDC and lessens detonation, depending on the CR you are using.

Don Shillady
Retired Scientist/teen rodder

Would be tight, definitely going to have to use a small base circle cam. Not sure all the additional expense and labor would be worth it to have a longer rod......

http://purplesagetradingpost.com/sum...%20engine.html

There is a reference article showing the effect of longer rods in a 350, not a 383, but the priniciple should apply to the 383 as long as you can solve the problems of the tight inner space between the crank and cam which is made even tighter with the long rods. Another good news/bad news tradeoff is that the pistons need to have higher pin positions. On the one hand that probably reduces piston rocking and side slap but on the other hand the higher pin position makes it tricky to place the rings on the piston away from the pin hole. Maybe Dave S. could build one of these within the cu in limitation for his track car. I suspect this information is out there among the track racers but it requires more than usual engine rebuild assembly so there are probably few of these engines on the street. I considered this build up but figured it was beyond my talent and wallet.

Don Shillady
Retired Scientist/teen rodder

thanks all for replys other than less wall thrust being only adv.not really worth doing 6" rods for real fast legal street car

Here's some interesting reading on the subject from Isky Cams. See Tech Tip 2005 by Ron Iskenderian....
http://www.iskycams.com/techtips.php

Originally Posted by Don Shillady

http://purplesagetradingpost.com/sum...%20engine.html
Maybe Dave S. could build one of these within the cu in limitation for his track car. I suspect this information is out there among the track racers but it requires more than usual engine rebuild assembly so there are probably few of these engines on the street. I considered this build up but figured it was beyond my talent and wallet.

Don Shillady
Retired Scientist/teen rodder

We're limited to stock rods, 5.7".... no long rods allowed....

ok. I currently have 2 383 motors with 6" rods. One has H beam and Mech. roller cam, the other Eagle SIR Hydr. 106 LS cam. The H beams cleared the Roller cam no problem. The grinding on the block was no different then with a 5.7 rod. The Sir Rods hit the cam lobes on 2 cylinders. A quick grind on the back side of the rods and it was fixed. As far as block clearance... same on both. No disadvantage in block clearance. The pistons on both motors have a oil support ring that has to go on after the rods have been mated to the pistons. The set up seems to work just fine. Havent blown either motor up yet despite 7000 - 8000 rpm on the roller motor, and 6500 on the Hydraulic one. basically either way works just fine.

The longer rod will hold the piston on TDC longer, making for better detonation, as for performance, you will not notice the difference, except in your back pocket.

if you are already changing pistons and rods, and own a die grinder the cost is the same for 5.7 or 6.0" rods. Personally i like to run the 6" ones. but what i do with them isnt your daily driver. I think this subject could be argued for a while. For the record, I dont use them for a HP gain. Just to decrease angle. Plus its fun to say i have a long rod. HAHA

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.