Heading down the 383 path and wrestling with what length rods to use. To bad the damn search doesn't work since this has no doubt been beaten to death.

Plan is to build an engine with a 6300rpm hp peak so it will need to survive to 6500/6600. Goal is ~420hp-430hp at the wheels (on a Dynojet). Primary use is on a road course for track days and HPDEs...ie I'll use the low end grunt of a 383 to get out of the corners and need the hp for the straights

Cam is tbd, but figure in the 230/236 range for duration and high 5xx for lift with 112 LC. I do drive the car on the street on occasion so it will need some civility.

Probably going with Lloyd Elliot heads (LE2) since AFRs are beyond what I want to spend. (I'll be in touch Lloyd )

Internal balance SCAT or Eagle forged 4340 crank, SPEC lightweight flywheel and ATI damper.

Current engine has 11.3:1 static CR with no issues and the 383 will be about the same.

Keep in mind that on a road course the engine will spend a LOT more than just a few seconds above 5000rpm. During some track days I've logged the better part of 4 hours on the course.

Looking at the SCAT 4340 H-beam Q-lite rods just need to decide on length.

I have concerns regarding the 6" rods in the areas of high rpm piston stability and having the pin in the oil ring land. Less weight (due to lighter piston) is goodness as is a better rod/stroke ratio. Reverse of all the above is true for the 5.7 rod.

Thoughts?

 

007,
I like your approach and the components that you've chosen, please keep us informed.

R/Noland

P.S. PM Sent

 

http://www.iskycams.com/techtips.php#2005

 

I'm also in this (deciding what rods/pistons to get for my 383 build)
right now, but I plan to rev my engine to 7500.

Link that rodj posted, makes me wonder!
I was almost sure that I'll go with 6" rods!

 

#007
Don't rule out 5.85" or 5.875 rods also as an option.I run a 396 3.875 stroke crank with 5.875 rods and the wrist pin does not enter the oil ring boundary. A 383/3.750 with a 5.875 rod I would think would work fine for that application with sustained high rpm and wanting to stay out of the oil groove.
Rick

 

The difference in performance and durability in your application is virtually a draw. Espc using off the shelf componets.

At <6500RPM (sustained) a good quality 5.7" rod will be fine. I have turned 400SBC's with GM 5.7 "X rods" more RPM back when we didn't know any better and aftermarket rod availibility wasn't what it is today....

On the other hand piston stability and the wrist pin intersecting the oil ring should not be a concern with the 6" rod. It's a well proven combination in the SBC and very few people ever have any problems.

Don't ge too wrapped around the axel about it. With something as insignifigant in an engine as Rod Length, it takes a real big change to make a noticeable difference. Going from a 1.52 stroke to rod ratio to a 1.6 stroke to rod ration is not a big change. The actual difference in HP and TQ peaks between the 2 is about 200-300rpm.

If you want to get wrapped around the axel about it and do some real research. Jerry Stahl (the Super Stock racer and header mfg) has a good synopsis on his web site about rod length.

http://www.stahlheaders.com/Lit_Rod%20Length.htm

Considering your planning to run it on a road course - I would suggest you spend time finding the lightest weight crank, rods and pistons you can afford. The Scat Q Lite rod is a good peice for little $$$. If you like I could make some recommendations for the other parts.

Will

 

Sent you a PM

 

RKLESSDRIVER is right, rod length in a 383 is close to irrelevant. 5.7 or 6.0 at 6500 rpm's has alot more to do with balance than rod length. Go with whatever the builder of the rotating asm is happy with, you will not know the diff if it's well balanced. I built a few 302's for a 5.0 class and we put 6.25" rods in one of them compared to the 5.7 we normally used and it did'nt make enough difference to make it worth doing on purpose. The engine was a little more playful and reved easier, it wanted more compression, but the total power under the curve was not significantly changed only the throttle response seemed to change a little snappier. Have fun

 

thats soudns excatly like what i have in mind for my GS

Update us what you find! I will be very interested in all you research!

GS POWAR!

 

I would suggest going 5.85. doesnt push the pin up into the oil ring groove and is a tad longer than the 5.7. Lingenfelter used 5.85s in almost every LTx motor he built.

 

I built a very similar engine a few years ago. 7,000 plus RPM, LT4 383 stroker for street and occasional road course.
45lb crank, compatable with 5.7" rod, internal balance.
To keep my piston speed within reasonable limits at elevated RPMs, I went with the 'middle' choice of the 5.85" rod (Manley's I-beam, 580-590 grams, considered lightweight). A 6.00" H-beam is going to be rather heavy, even if it calls itself "LW". A 5.7" would have been my second choice.
This, of course, required a custom piston (Diamond, 480 grams, a tad heavy for my liking). The wrist pin barely poked into the oil ring groove, just enough to require the additional rail support.

Got it together, barely broken-in, two weeks later took it to an open track day. Spent most of the day above 5,000 RPM, lots of 6,000+plus RPM up and down shifting. Plenty of 3rd gear 7,000 RPM corner entrys, to avoid using 4th (4.10 rear gear, a bit much for this course). A little over 300 degree oil temps (stock C4 6 speed radiator, no oil cooler).
My brakes took a beating, but the engine never gave me a hint of trouble.
Drove the car home (well over 100 mile trip) with the A/C on!

 

Personally I would go with the 6" rod. Lighter rotation componets and a slightly more favorable rod angle.

 

Lot's of good info, thank to all. Gives me lots to think about.

This is going to be my winter project since rainy season starts here in the Pacific Northwest shortly...although this week is making me think it's arrived early

 

Slightly being the operative word

 

Go with the Mahle Powerpack pistons. The rings are thinner and moved up on these pistons so the wrist pin location is not a problem. The thin rings also free up horsepower, less friction. I had 6" rods in my 383 LT4 street only car, no problems. I also used Eagle rods and crank, all forged.

 

On the 383's we have been building we have used 6 inch rods as it does free up some unwanted friction in the engine and the pistons are a lot lighter compared to pistons that are used in a 5.7 or 5.850 rod.

The rods are either the 6 inch Compstar rods or the Scat I beams with 7/16 bolts.

The Callies Compstar crank is the best quality crank out there as far as sizing, roundness, straightness and journals that are right on from journal to jouranl.
we get 595.00 for those cranks.

Here is a link to one we dynoed a few weeks ago.
http://www.chevelles.com/forums/showthread.php?t=236517

 

I would run a 6 inch rod or longer in this application. I would not change the ring sizing though since it needs to go longer between rebuilds. Going with a smaller ring size decreases the longevity of the package; ok for an outlaw sprint car engine but not so much for someone a little less serious. Just my .02

 

There is not much difference in the rings. 1.5mm=.059" 1/16=.062" but the 1.5, 1.5, 3.0mm ring pack severly limits your ring choices as compared to the conventional 1/16, 1/16, 3/16 ring pack. For the life of me I don't know why Mahle offers their pistons with this stupid crap... then again maybe its just a maketing gimick to sell more rings.

You really need to go to a .043 or 1.2mm (.047) ring to get any weight or friction advantage over the tried and true 1/16 ring. Here you run into the same problems of limited ring choices and more money. None of which fly in a dual puprose - street car.

Also the oil ring eats more HP and causes more friction than the compression rings. You almost HAVE to run std tension oil rings for oil control so any advantage the .043 compression rings gave you is going to be nill on the street.

Carl:
That's a good price (over the counter retail) on a Compstar crank. I wish they would offer the 1pc rear seal ones in their Comet LW line.
Will

 

Is not the 1.5, 1.5, 3.0mm rings what GM now uses on the LS1 motors? Anyways I have selected the Mahle piston package for my buildup.

 

Using the Maule pistons for 6 inch rods there is no need for spacer rings and the Maule pistons have the tightest ring lands out there compared to waht we have been seeing with the other pistons out there.

Metric rings are very common in some of our high end builds.

Those cranks are what we sell them for, If we wated to get cheap we can buy 4340 cranks for 375.00 but they don't compare to a Callies.