Hi all,

Well I'm still researching and researching some more on how to build up my rocket block (1st step is to order DD2000 so I can plug some freakin' numbers!)...

Anyhoo, after looking (and drooling) at all the great cranks, rods, and pistons I'm wondering exactly how much worth there is in going light weight in the rotating assembly. Light weight parts obviously are extremely expensive, and while I'm not against spending the money to do it right the first time, I have my limits!

So my question is, exactly how much will I benefit from using light weight parts in the rotating assembly? IE, how much difference am I going to see using 570g rods vs 710g? Or a 40lb crank vs 58lb?

I'm aware that the lighter the rotating assembly, the quicker the engine response, but at 600+ HP, quick response may not necessarily be a _good_ thing! :eek:

Thanks,

Tony

 

I'm no expert, but I've asked my builder and others about this also.

His questions where, 1) Is this a drag motor or a roadrace?2) What heads/Intended RPM range. He went on to tell me that If it was going to see any street use that I would probally be wasting my time and Money buying a featherlite crank!

He did mention that a Drag motor is more likely to benifit from some mass on the crank while a circle track/road race motor would benefit from less mass. Now, he doesn't mean that the heaviest crank you can find would be ideal for drag, but just that a drag crank imposes severe twisting forces on the crank.

As for rods and pistons! I say go lightweight and forged. I think the weight reductions gained here have a similar effect to reducing crank weight. At least this was my approach.

KM

 

The light parts are almost never as strong as teh heavier parts but then again sometimes they are. As long as the parts are strong enough for the job you want them as light as possible for all types of racing. You may run a heavy flywheel for drag racing to get you out of the hole but believe me most drag race engine technology concentrates on losing rotating and reciprocating weight as well. The lighter pistons and rings actually seal better as long as the piston maintains it's shape under duress. Everything has it's limits including weight removal but any excess weight is simply lost power trapped in the engine due to inertia.

 

It's all back to the application again.

The light stuff is best IF the whole combo supports it. Like having a bunch of rev happy rotating parts and then sticking a Hyd roller cam in it. Sure it's better, but you aren't twisting that high. For sure the lightest pistons and rods are very worthwhile as they decrease the loads on everything else. But of course strength has to play in there too.

Crank weight to me is not as big an issue. It is just rotating weight just like a flywheel. Think of it as an extension of it. So if you built it with a light rotating assy, which probably has a healthy cam and big heads and all the cool stuff to make it rev, it will probably be a pig out of the hole unless you have some serious gearing in it. So then you have to throw a 30-40 lb flywheel on it to make it launch. Kind of defeats the whole deal.

I'd use any of the aftermarket H-beam reasonably priced rods and some relatively light pistons and pins for anything streetworthy. Use a good strong crank that will handle anything you throw at it. Remember, race motors are disassembled often and inspected. They also maximize everything else in the combo to take advantage of the trick stuff. Before i spent tons of extra dollars on trick bottom end stuff, I'd spend it on the heads and valvetrain. Very little power is gained in the bottom end. It mainly just has to stay together and support the top end.

Now this ought to open some good debate! :-)


Jim

 

I used to want alum rods till I learned the become brittle with age. Thought you mind find that interesting. :nono:

 

""Before i spent tons of extra dollars on trick bottom end stuff, I'd spend it on the heads and valvetrain. Very little power is gained in the bottom end. It mainly just has to stay together and support the top end.

Now this ought to open some good debate! :-)""

Jim,

That's by far some of the best advice probably ever seen on this forum and completely true!

The lighter reciprocating parts always help in-gear acceleration but can hamper drag race launching depending on how the car is set up. Cars that spend a lot of time already rolling and in the lower gears like an autocross optimized vette for instance will ge the most benefit.

 

ive run one of my lightweight asphalt modified motors on the street for several years and never noticed a difference on the street.on the track it used to come off the corners (circle track)alot better then standard weight stuff...lunati 38 lb knifeedged crank, wiseco ultralight pistons ,and crower rods and light weight wrist pins..also the lighter the piston the less area there is around the wrist pin so thats the first place itll break...for the street ill stick with heavier parts and longer life.

 

The real question should be: I'm trying to build XXX amount of cubic inches. What do you think the best most cost effective parts are?


I have a 3.750 4340 nice crank sitting on my floor for the past 1.5 years. it's in the 46 lbs class. Instead of using it I went with the big buck idea of 40 lbs 3.75 nitrided hollow ground mirror finish with oil repellant throws. My plan was 800 or better hp with a 250 shot of NO2.

Then i used 685 gram Manley Monster h beam bushed rods with JE light weight pistons with the three coatings. Thermal ceramic tops moly sides and oil repellant under coating.

The smarter choice on rods for street use is Oliver 585's or so. It would make for allot less stress. I only went with the big rods because I never had a failure in a alky injected 358 ci that did 9000 rpm every day down the 1/4.

light weight revs quicker and induces less stress on the block and bearings. I also went with 2.08 titanium intake valves for less stress in the solid roller cam train.


here is a pic of my crank




[Modified by gkull, 1:18 AM 6/1/2002]

 

Thanks for all of the great posts!

First it'll be a 427 small block (tall deck rocket block). I will be doing a partial block fill on it since I plan to be up in the 600+ HP range and 500+ on torque. Revs up to 6500 maybe 7000 if feasible. Still got a lot of homework to do. :)

Since I prefer that the engine be reliable first and foremost, I would rather overengineer it than to risk it on lighter parts if it really isn't going to make that much difference. Besides, as others have said, I'd rather sink the money into a good set of heads.

So, any recommendations on rotating components? I'm really leaning towards Manley H-beams (or Eagles), and JE pistons, but still up in the air about the crank. I wish Dyno2000 would hurry up and get here! :smash:

Tony