Ken/Fred, sorry if this is the wrong place to ask this, if it is no biggie

As some of my recent posts here have shown, I am beginning to gather some ideas together for my Stroker rebuild for next year.

I've gotten some great ideas, but unfortunately, now I'm confused more.

I've heard that a light recriprocating assembly is key to paking NA power, but I don't hear of many LT1 guys running AL rods. I also notice that most AL rods are 0.10" shorter than the nominal specs (5.7", 6.0", etc...)

I also wonder people's thoughts on the lifetime of AL rods. Mainly, are they best for strip only, or will they last as mainly a daily driver w/ occasional street/strip runs? I worry about AL stretching too much.


I also hear theories that stock rods are fine for NA motors. If I want a long Rod, is the Impy 6.00" Rods a halfway decent setup?

Lastly, there is my favorite topic rod length.

For a NA Motor with no plans whatsoever of N20/Blower/Turbo I'd think that a long rod, stroker could be driveable with 12.5:1 compression on pump gas.

I've seen Rods of the following lengths:
5.7, 5.85, 6.00, 6.125, 6.250

With a 383, where does the length put the wristpin at a dangerously high point? Like Rich K. posted on a recent thread, he believes the key to NA power is high rev's and I'd think you can maximize that by having the longest rods possible.

Thanks in advance, guys

 

My understanding is Al rods stretch and therefore need to be resized every so often. Not a big deal on a race motor that gets torn apart regularly but a little inconvienient on a street car.

I really would not bother with any OEM rods. Not when there are plenty of choices in forged rods for under $300. By the time you pay to replace the rod bolts and resize used ones its not worth it IMO.

As far as rod length all of the really knowledgeable people I've talk to say its really a non-issue with a street motor. While longer rods are definately a good idea its not worth compromising the piston to get it either.

 

I've read different pieces on rod-length, and I think it's somewhat of a non-issue. The rod-stroke ratio differences between say a 5.7" and 6.0" rod are so small that I don't see it impacting performance on anything other than a pure, max-effort racing engine.

As for aluminum rods... they are race only parts. Aside from the stretching issue, you have to warm them up before really driving them. I.E. you gotta warm up the engine before you can go make a pass at the strip. They are definitely not suited for anything that is going to be driven on the street much.

 

Looks like I'll stick to some good, forged rods.

Not to get off topic, but where can you get a good set of forged rods for $300? I'm not saying I don't believe you, but I haven't found any in that range?

Thanks for the insight guys

"There is a reason why everybody does a 383 a certain way..."

I'm now finding out why I just hate to do something because everybody else does without knowing why.

 

A light weight rotating assembly won't actually create HP, but it will take less hp to accelerate it. The biggest benefit is that light parts create much less stress at high rpms. The high rpm's is what will get your HP in an NA engine. High rpms + big heads + big cam = lots of HP. Grab a copy of David Vizard's book on small block chevy rotating assemblies. There is some great information there, pertaining to rod lengths, dwell times, piston acceleration, etc...

 

I hope I can shed some light on the rod length for you. There is something called rod angle. If there is to much piston above or below the wrist pin it will it will push harder on the sides of the cylinder walls. W/5.7 rods there is to much above and 6.0 to much below. After speaking with Lingenfelter I understand why the 5.850 rod is the best choise for the 383. Lunati prefers to use the 5.875 rod and shorter piston which is what is in our383 LT1. Not haveing the proper rod angle will cause more wear and shorter life.

 

Try:

http://www.flatlanderracing.com/cribeamscat.html
http://www.competitionproducts.com/page66.html
http://www.speedomotive.com/rods1.htm
http://www.strokermotor.com/DESCatalog/page5.html
http://www.sdpc2000.com/cart.asp?act...tart&catid=390

I'm not saying these are the best rods out there but they're definately stronger than the OEM pieces. If you think you'll need something stronger Eagle H-Beam rods are supposedly just about bulletproof for a bit more money.

Good Luck!

 

This (http://www.aros.net/~rbuck/rick/rodstudy.htm) is an interesting analysis of different rod lengths. The author concludes that there is minimal difference but that: "There are real gains to be had by going to longer rods but they are small, usually a lot less than 2 percent. However, the hard-core racers are grasping at every tiny bit of performance and can justify the expense. For the more average rodder I would suggest staying with the rod length specified by the factory. Money would be far better spent on improving the heads, cam, and induction and exhaust systems. (and perhaps a supercharger...)"

I think his analysis is overly simplistic because it is strictly a mechanical analysis and does not include the dynamic effects of the intake port, exhaust port, and most importantly cam timing. This (http://www.stahlheaders.com/Lit_Rod%20Length.htm) analysis is a lot more sophisticated. The lesson here is that rod ratio is a more complicated subject than it first appears.

My own conclusion is that if your are building a high revving setup you want a relatively long rod. A low revving setup should use a relatively shorter rod, especially if a supercharger is used. The best supporting link I am aware of is here at (http://victorylibrary.com/mopar/rod-tech-c.htm.).

What appeals to me most about long rods for a high rev NA setup is the lower peak piston acceleration and the lighter (shorter) pistons. This helps keep parts from breaking! What appeals about short rods, especially for a low rev setup with a blower, is that the increased piston acceleration away from TDC provides a larger effective chamber volume, which in turn is filled with more fuel and air by the positive manifold pressure. The result is more power. In addition, peak cylinder pressure will be lower due to the higher piston acceleration. This helps preserve the mechanical integrity of the piston crown and reduce the tendency toward detonation (always an issue for a SC motor).

But these differences are subtle. With the combos 99.99% of us are talking about this is all interesting theory of no practical use. One thing that is silly though is worrying about wear. Even for the 99.99% of the "rest of us" we aren't tying to spec out a motor to last 100K miles. It's not gonna happen with hard use, high specific power output, high revs, etc. It will break long before it wears out .

If you get the "cheap" rods, at least get strong rod bolts.

Rich Krause

 

Wow, guys thanks for the boat-load of info. I always like to research the hell out of something before I get involved, and this will help!

Z28tt:
Thanks for the info, I'm going to have to pick up a copy of that book, sounds like a very interesting read.

gearhead3:
That sounds very familiar. I've seen a lot of guys running boost, run 5.85 rods.

Soma07:
Mucho Gracias for the links. I Like the sound of Eagle's but my Wallet begs me for a less costly rod.

Rich:
Thanks also for the links and words of wisdom. I hope to be able to follow both your theories as I have two 94's. The 383NA will be the (red) one for my Fiancee' and my (Teal) one will probably have a blower on it...but that's after the red one, because it's got 47k more miles than mine. I'm definitely going to bookmark those links...Good Stuff....Not "watered down" info like what usually appears in magazines

 

Something to consider... GM, when given the ability to design a clean sheet motor (i.e., LS1) they picked a 3.62" stroke with a 6.1" rod, which is a 1.685 rod/stroke ratio.