im under the impression forged steel is lighter and stronger than cast but i know its much more expensive, but in my quest to build an everyday driver (except in winter) 383 that would see more normal driving than racing would it be worth it to spend the extra cash on a forged crank and pistons? id like to have the best but im wondering if the difference is worth the cost? any suggestions, facts, or opinions are appreciated.

Russ

 

Forged isn't lighter, it's just stronger for the same weight.

For "normal" driving, it wouldn't be worth the extra expense. For potential future power upgrades, or when the need-for-speed bug bites you, it would be a good idea.

 

you can step up from gray cast to nodular iron and have more strength at less cost than forged, hyper pistons are stronger than cast and at less cost tham forged, and lighter too, actually hyper pistons have a higher tensil strength than forged ,but also are not as ductile

 

i was thinking about a supercharger add-on about this time next year or bottle feeding the car, would the nodular crank /hyp. pistons hold up to either or both of these?

Russ

 

power adder = forged

 

A lot of times forged pistons are lighter because they use less material to make them. Nodular Iron is pretty tough. The real key to having a long lasting engine and rotating assembly is good balance. Forged Steel does of course help, but you can attain really high power levels with pistons, cranks and rods that aren't forged too if they are balanced properly.

 

Actually cast pistons are generally garbage. Don't even consider them.

 

A forged piston will weigh more than a normal cast or hyper piston. Take a look at the weight of them sometime.

 

On the contrary:

A multi-season points winner here, who's always at the top of some class's points race any given season, who runs an engine building shop for a living, races a '37 Chevy pickup with a dual-quad roots 383. Now, this pickup weighs 3900 pounds going down the track. He shifts at 6500 RPMs, runs 13.3's at this altitude consistently. At Topeka last year, it ran 11.9's on one carb (he was trying to slow it down to meet the 12.0-sec rule).

He uses cast pistons. Says they last as long as forged as long as you don't lean it out. But, what does he know?

 

I'll say it again cast pistons are junk. The instant they even smell detonation they generally break even at relatively low power levels. Let's not forget the piston probably undergoes the most stress out of any part of your engine and it's wise not to cheap out on some crap that will break if you lean out (which unfortunately can happen to the best of us at really unforseen times!). Also there is a feeling in my gut that says they WILL break once you reach really high levels of horsepower.

A cast piston is made in this fashion -

There is a mold! They pour molten steel into it! They let it harden! This is the really short/sweet answer.

A hypereuratic piston is made from a cast but it has approximately 15-18% silicone in its material. This greatly strengthens the piston.

A forged piston is created by packing the material (aluminum and steel are both used) tightly together with a huge press. This creates a much denser and stronger grain.

"If you plan to build a hot street engine of any kind, forged pistons are the only intelligent choice." John Lingenfelter

Lingenfelter also feels that if you add compression or forced induction your cast pistons will be destined for a pretty short linespan as well.. Never said anything about them being "Ok" if you don't lean out... Cast pistons are crap don't cheap out on pistons. If there is one thing in your engine (besides the cylinder heads) that you shouldn't cheap out on, it's pistons. Cast Rods, Cranks, they do much better than cast pistons because they do not see near as much energy as the piston. Remember the piston is basically the mechanical catalyst and it has to absorb tremendous forces of combustion... anwyway ya whatever. I don't wanna give someone bad advice, how about you?

 

Really? Well, what you say isnt true. Theres more I could say, but I'll be nice though.

Hyper pistons, while stronger, are much more prone to cracking into little pieces than normal cast pistons are. MUCH more. If you're at all worried about recommending cast pistons to someone, you should be even more worried about recommending hypers.

Cast pistons are not that prone to breaking from detonation. My dads pickup took 7 years of detonation (and believe me, it did it alot.. like every time you drove it) to disintegrate a ring land off the piston. The 68 Grand Prix we had spent the last 10 years of its life with us detonating its little heart away due to lousy gasoline out here in California (it was built in the days of 108 octane at the pump, and had 10.75:1 compression with cast pistons and cast iron heads... 375 SAE Net HP if you want numbers) and even the day we sold it, it had excellent compression and never used any oil whatsoever. Your statement of them breaking even at 'The instant they even smell detonation' is so untrue I couldnt emphasize it enough.

 

even though you say that cast pistons will hold up which i believe you, my concern is that if i were to buy forged pistons, would the extra money be worth it? would i get a noticably better, longer lasting engine for the extra cash, and not just pistons, crank and rods too?

 

It all depends on what you plan on doing with the car. If you are considering a power adder like nitrous or boost at some point in time, even the slightest chance (it is a 383 youre talking about) then I would run forged, period. If not, there is nothing wrong with a cast piston. I've put tons of miles on them, some of those in fairly decent HP engines and they have been holding up just fine thank you. I even have the fabled brittle KB Hypers in another car here and it has 11k miles and no signs of problems, contrary to popular doomsday predictions on the internet. I think its more important what sort of abuse you plan on dealing the engine and that it wasnt assembled incorrectly. Remember that many factory engines use cast pistons. I dont think I have to search around for proof of how well people have done on factory shortblocks.

 

Ok I stand corrected. I've heard that hyper pistons dont have much give, but are stronger in some areas. Anyway, most cast pistons won't stand up to that kind of abuse. A friend of mine had an old 86 tempo that he drove the crap out of. It had serious fuel issues and detonation was constant. Believe me it didn't take long for the pistons, crank and rods to break. Mind you i'm sure that car was never well taken care of.

 

For nitrous... nodular crank yes... cast pistons NOOOO!

 

In all fairness, this builder will only use two brands of pistons out there. So, just "any ol' cast piston" isn't the case.

But, the blanket statement that "cast pistons are junk" isn't the case, either.

 

Call Scat and get there 9000 series lightweight crank--H-Beam Rods and SRP pistons. My sons running high 11's with 8-8500rpm shifts with no problems.
The above rotating assembly is under $1300.00

 

Stock cast cranks will hold up under moderate abuse. So will stock rods. If it were me, I would keep a stock crank, have the stock rods resized w/ARP bolts, and a set of cheap TRW forged pistons. I had a 355 in a tubbed S-10 that started out with a 150 shot, and then got moved up to a 225 shot. I ran over 30 bottles through it in one summer, and never had any problems. I sprayed it quite a few times on 93 octane fuel also. Just keep up with your timing and fuel pressure, and you should be dependable for many years to come. BTW I shifted this engine at 7700.

 

Actually stock cast rods and cranks can take a lot of abuse if they are balanced properly and are well maintained. Using quality bolts is important too. Generally bolts that are the same material you are using them in are best as they will share similar flex/warp charactaristics and stay tight longer.