what are advantages and disadvantages of running 6" connecting rod compaired to 5.7" connecting rod in 383 stroker motor?
Printable View
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!:toocool:
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
We're limited to stock rods, 5.7".... no long rods allowed....Quote:
Originally Posted by Don Shillady
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
In our dyno testing over the years we have found hp gains by using a non-symmetrical camshaft.Quote:
Originally Posted by Don Shillady
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. **)
I am not sure what happened to the first post.Quote:
Originally Posted by southerner
On what heads has the exhaust caught up with the intake???Quote:
Originally Posted by erik erikson
Weren't the long rods originally supposed to be a longevity deal to correct the rod aspect ration on some of the sroker engines???? Ran a long rod Windsor with a two ring piston and buttons on the dirt track, made good power and seemed to outlive the short rod version of the same engine displacement. Only problem was keeping the rings sealed, about 10 shows and the leakdown got a bit high.....
This year i built a long rod 383 with TS Gapless rings. I currently have over 40 shows on the motor in my Mod. Leak down is still almost nothing, and oil pressure is good. so i dont know. I do know this is the most i have ever gotten out of a dirt track motor without a freshen up.
Don't know if it was the rod or the two ring piston that caused the problems.... Curious what others thought..... 40 Shows is excellent on a circle burner!!!! Engine program for next year isn't dialed in completely yet, but I think we'll be freshening about every 20 shows......
:D :D :D 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.:rolleyes:Quote:
Originally Posted by erik erikson
for next year a Dart Block 427, flat top pistons, 6" rod, 49cc dart heads and a big fat Roller cam. Santa might just bring me the block and rotating assembly for Christmas!! I need to get rid of a couple Motors first though. Running out of places to put them right now. :P
Dave,the biggest problem we have is still the valve springs.Quote:
Originally Posted by Dave Severson
We have ran up to 25 night's on a couple engines and found springs that we a little weak for our likeing.
20 nights is a safe bet.
Erik, What kind of RPM do you run on your motors? Mine stay in the 7400 range. Valve springs have yet to be a problem for me. but i guess there is always a first time. I normally build these things and only run them one season. There is a good market out there for a well built Circle track motor. I get my use, someone else gets a good deal on a nice used motor. Although i always freshen them up before selling.
The 380 with a mech. cam turns to 7,800Quote:
Originally Posted by mod67
I know some of the sprint guys around here get in the 9000+ RPM range. they are constantly changing valve springs. Normally not a problem in the Modifieds.
We will be so limited with the cast iron non-ported heads and the 4412 carb, I would imagine rpm's would be in the 7200 to 7800 range, hopefully. This Super Stock class is really going to be a challenge with all the engine limitations.... Back to chassis set up and driver skill..... Greg realizes what a steep learning curve he is going to have, might even send him to one of the late model driving schools...... Any good ideas for some lightweigh 1.94's and 1.60's valves???? lol, no, we can't run titaniums!!!!!
Oh yeah, any good ideas for a steel stock stroke crank with a GM part number???? Can't be a GMPP piece, either......(sigh) I hate 50 pound cranks!!!!
Dave,take a mic. and check the stem in other words look for under-cut stems and also weigh your valves.We have found a lot of difference in valve weight over the years.Quote:
Originally Posted by Dave Severson
i have heard of hollow stems, but still SS and look normal. but of course thats just what i have heard... ;)
yup, that's the valves I looked at, Manyley makes a nice undercut valve, Weighed some of the Ferrara valves I had around here from Ford engines,, surprised how heavy they were.. Just thinking the old lighter valve train lives longer thing....
Here was an old Smokey Unik trick ! It's in the How to "Hot Rod Small Block Chevs" book, what you did was get the standard pressed rocker arm and lighten it a bit by making up a former as detailed in the book, put the rocker arm in and grind down the sides. The whole idea of the former was to lighten the rockers to a uniform weight and in such a way that it did not compromise rocker strength. So with your lighter valves rockers and retainers there was whole overall reciprocating mass drop over the whole valve train. I suppose it is just knocking off weight here and there that the whole weight saving adds up.
Kinda like the old deal that it's hard to find a place to take 100 pounds off a car, but not too hard to find 100 places to take off a pound, i guess....