My '77 460 is getting stripped down to go for a refresh. Probably will need .030" over bore/pistons. From what I have read in this forum, forged pistons seem to be the safe bet for a 500 or so HP 460. The debate over excessive ring gap for hypereutetic pistons has me concerned. I got a set of D0VE-C heads that are going to the head shop this week for a cleanup, valve job, and mild bowl work. Flat top pistons are probably what I will end up with. (Approx. 10:1 with the D0VE heads, I guess.) I am getting an Edelbrock 750 carb and Comp Cams 4X4 cam & lifters and roller rockers.

Are there any brands of forged pistons that you have good luck with? I would like to not spend a fortune, but for a few bucks more, good forged pistons seem like a good investment. Please let me know what your experience has been. I guess I should have pistons in hand before the machine shop bores/hones.

(BTW: I do not seem to be able to do a search, except of the entire web site. Did this change? Thanks)

 

I'm running TRW LF2404-F30 forged pistons with C9 heads (same as D0VE).
This yields about 9.5:1 compression (with porting/polishing you will end up with about 78cc chambers).

As far as ring gap goes, follow the piston manufacturer's specs and forget evrything else. Within the manuf's spec range; larger gap for racing, nitrous; smaller for street.

 

Was probably my post that led to some of your confusion about ring gaps on hyper pistons. Sorry about that, but the physics behind it dictate that the gap should be set according to the heat the ring will experience. Hyper pistons reflect more heat upward and; hence, need a larger gap. Hyper pistons are more efficient due to this heat reflection and light weight and carbon doesn't build as readily. Forged piston are much stronger and heavier, yet, they soak up heat easier than hypers, and they expand more than hypers. Forged pistons need a larger bore than hypers so they can expand to fit; therefore, they slap when cold. If your building a brute force engine, go with forged. Hypers can crack and explode and destroy your engine, although KB claims this hasn't been reported to them in 4 years. Whatever you choose to do, the gap should be set according to the expected heat. If you set it for racing and spend 90% of your time cruising, your gap will be too big 90% of the time and hot gases will be blowing by the ring, possibly scoring the cylinder. If you set it for cruising and spend 90% of your time racing, then you will break the top land off the piston. Manufacturers recommendations are just that, recommendations. I'm sure if you ask Ford, they would recommend putting it back the way it came from the factory. Why would they say anything else? So, who do you listen to? The manufacturers or the people who have had success? Either way, nobody will warranty anything. Just some thoughts for you. You should definitely have pistons in hand before doing any cylinder work. Oh, which 4x4 cam were you planning to go with? I was thinking about one too for my 509 with hyper pistons. Just asking cause it doesn't sound like a cam with a need for forged pistons, although it does have alot of lift.

 

Thought I'd rattle a bit more. Why not go .060 over? I hear alot of guys who have gone .110 and beyond with 460 blocks. .060 is not unreasonable. Ask around about that. What I did anyway. Also, your gonna have some monster compression with those DOVE heads aren't you? Have you given any thought to quench distance? Seems another good arguement for hyper pistons, since they dont expand and aren't very heavy. I was thinking, if you set the quench when engine is cold with forged pistons, isn't it possible for the forged piston to expand enough to smack the head when hot? Also, due to the weight of the forged piston, isn't rod selection very important so the piston never smacks the head? Rods are really expensive and if you get new ones, you might as well stroke it too and get a kit. See http://www.speedomotive.com/Building%20Tips.htm and http://www.speedomotive.com/Stroker%20Kits.htm Good luck

 

For your application, you could use forged or hyperkintic pistons. Quench is a combination of deck clearance, cylinder head combustion chamber shape and cam duration. With 10.0:1 c/r, a cam with longer than 225 duration or so on the exhaust side and a deck clearance of .035 max, you should have good quench and be able to avoid detonation using iron heads.

If you go with forged pistons, TRWs are your most economical choice and will be fine for your application. Forged piston contraction/expansion is on the skirts, not the top of the piston.

 

George, what kind of rods would recommend for that engine in the case of forged and the case of hypereutectics? Also, would you place any rpm restrictions in either case if stock rods were to be used?

I concede to you that forged iron pistons see most expansion at the skirt, but isn't there some expansion in all directions due to the crystalline structure of the metal? Or is this expansion negligible in the axial direction?

The way I reason it, the crystals expand in all directions almost equally and because the crystals are arrainged in a circle, this expansion is cumulative around the skirt. If you add up the expansion of each crystal around the circumference of the piston, you get the expansion seen at the skirt. Is this right?

Worthy questions for a worthy man, thanks George.

 

Forged "iron" pistons?

 

For my combination I went with Trw forged pistons,and truck rods. One of the reason I picked forged over hyper is strength, and possibly I am a little old school, you know stronger is better. Also I plan on turbocharging my 460. Part of the problem with the forged piston is when cold they are actualy slightly oval and expand round as they warm up, but most of this does take place in the skirt area. Eric

 

Oops, that should read aluminum, not iron My mind was on iron for some reason, thanks Bill.

 

Stock rods to 6000rpm, CJ/truck to 6500 (people run them to 7000 without problems, but..) and H-beam of varying degrees of strength dependent on hp requirements over that.

I don't know the physics or metallurgy of forged aluminum pistons, but continual friction on the thinner skirts creates constant expansion to a working level as versus periodic combustion heat on the much thicker dome and pin bosses. Steel pistons wouldn't be affected, but their weight factor makes them prohibitive. The compromise is hyperkinetic pistons, an alloy that doesn't have the strength of forged aluminum, but does have less tendency for expansion. And they cost less.

Aluminum rods are stressed in a manner that requires extra tolerances for stretch (to avoid valves meeting pistons at calculated rod operating stress)and are normally replaced at frequent intervals as aluminum fatigues quickly when compared to steel when subjected to direct stress, but are easier on crankshafts than steel rods because of their ability to contract/expand.

An engineer could provide us with accurate definitions, but it's all basically compromise and refinement in achieving higher performance from an invention that's well over 100-years-old. When you look at some of the current offerings from say Mercedes Benz, or GM/Holden's LS1/LS6, the 385 is indeed a technical dinosaur. But it puts out a lot of hp/tq for a relatively modest amount of money. And cost/hp is an important guideline in our hobby.

 

George, looks like you know your metallurgy to me. The fact that aluminum fatigues over time completely slipped my mind, but is very true. I would think especially so in a cast form. I also did not know the heat due to friction in the skirt is higher than that from combustion, or maybe your just saying the skirt is so thin compared to the dome that even smaller heats affect skirt expansion more. Is that true for nitrous and/or supercharging as well?

Is hyperkinetic another term for hypereutectic, or is that another animal? Eutectic is a mixture with a melting point lower than that of any other mixture of the same constituents. Hypereutectic just means it has more of what made it eutectic, in the case of pistons, it would be silicon. Kinetic relates energy of motion.

According to my trusty machinery's handbook, the coefficient of expansion for aluminium alloys in terms of micro inches per inch-degrees F range from 12.8 for 2011 alloy to 13.1 for 7075. Cast steel with 3% carbon is 7. While malleable iron is 7.5. Most other irons range from 5.8-6.2. Stainless can range from 5.2 to 9.6 depending on composition. Forging is never mentioned here. But in any case, it seems that aluminum can expand nearly twice as much as iron based alloys at a given temperature. I wonder why they don't forge out hypereutectics and have the best of both worlds?

I agree with you about the 385 series giving alot of HP/$$$. I am enjoying building mine up and even though I'm replacing everything but the block, I still don't have a fortune into it.

I also enjoy corresponding with you and appreciate the learning opportunity, I hope to continue.

 

Hyperkinetic is the result of multiple postings of hypereutectic degraded by lack of spell checkers and, I would assume, laziness. I used hypereurectic in a post on another forum and somebody asked me if it was a new type of piston or similar to hyperkinetic. As I understand it, silicone is an added ingredient.

But it's still a cast piston, subject to strength limitations presented by molecular structure eliminated in the forging process. I don't know why silicone isn't added to forged pistons, maybe it is. Cost certainly can't be a factor, because when you get into custom forged pistons a few dollars of material wouldn't be an issue. I'd think that while the inclusion of silicone (an oil byproduct converted to polymer status) might add lubricity to a cast piston, perhaps it's not compatible with the forging processes/equipment used to make forged pistons or dilutes the material strength.

I think hypereutectic pistons are suitable for most performance applications up to about 6500rpm. People certainly use them at higher rpms, and a lot of people do spray them. However, there are plenty of reports of skirt failure from side thrust at higher rpms and being sprayed which don't occur in the same engines with forged pistons. To me, that's a you get what you pay for situation. If I'm putting a few thousand dollars into a short block, an additional $2-300 for forged pistons seems like good insurance.

 

Thank you kindly for all your teriffic input. I am a mechanical engineer and I am learning from this forum!!! I will measure the bores this week, and from those dimensions, determine what oversize pistons I need, and look for a set of them before having boring done. Probably TRW forged.

I hesitate to use the stock rods, due to the sharp corner at bolt site (how do you spell "stress riser?!" The football head shaped bolts/rods would reduce the stress risers. I would like to get a set of them rebuilt, cause I have thrown rods in a coupla engines years ago (283 Chevy, 292 Ford, so you see I'm not 18 years old!)
Thanks again for your help. I'll keep you informed as to the progress.

BTW: Do I need special valves and/or seats installed in the D0VE heads to use today's unleaded pump gas?

 

Hardened exhaust valve seats provide nearly as much controversy as a discussion on motor oil, mufflers or Ford vrs Chevy. Two important considerations are:

Lots of older vehicles with pre-hardened valve seats are still operating on unleaded gas without problems. I've torn down a lot of early 385 heads that had no sign of seat erosion and I knew they were operated on unleaded fuel for many years.

The switch to hardened seats began about the same time as vehicle manufacturers began using catalytic converters to meet EPA exhaust emission standards. Early cats produced a lot of heat (look at the exhaust shielding on some '70/80s vehicles) that reduced the ability of the exhaust port to dissapate heat, resulting in much higher valve/seat temperatures than a mufflered system without cats.

I've put a lot of hard miles on 385s (none with catalytic converters) without hardened valve seats and, to date, experienced no valve seat erosion.

 

I'm glad to be on either end of a good learning experience. The schools aren't what they used to be. Maybe if you go to MIT of something, but the experience I had, anybody could pass, and did. College prep classes in High school had me freaked out that University class would be tough or something. I'd be lucky to get an instructor that spoke english as a primary language and the tests where all open book and notes with calculators. Nobody ever fails, if you do you get bonus questions to raise your grade.
Go one on one with folks like George and then grab a few books to see why he is RIGHT; that is the best way to learn. Nothing takes the place of experience.

Dyerstown, if your gonna get rods anyway and if your planning on spending 300-500 for them, why not consider a stroker kit? You get forged H-beam rods, forged pistons, a nice crank, all the bearings and rings (name brand), and free shipping for around $1500 or so. http://www.speedomotive.com/Stroker%20Kits.htm
I made the decision after I found my crank needed machining anyway. $90 is what I was quoted. I also had the broached style rods.

Here is a quote from KB's site http://www.kb-silvolite.com/page02.htm
Eutectic alloys exhibit good strength and are economical to produce. Hypereutectic pistons have a silicon content above 12%. Silvolite’s KB Signature Series pistons use an alloy containing 16-18% silicon. In addition to greater strength, scuff and seizure resistance, the hypereutectic will improve groove wear and resist cracking in the crown area where operating temperatures are severe.

It is the primary silicon that gives the hypereutectic its thermal and wear characteristics. The primary silicon acts as small insulators keeping the heat in the combustion chamber and prevents heat transfer, thus allowing the rest of the piston to run cooler. Hypereutectic aluminum has 15% less thermal expansion than conventional piston alloys.