I see this everywhere. I know forged is stronger and needed in high boost applications, but what exactly is the difference? Obviously I can infer the forged items are forged and the cast are cast, and I get how it would be done, but somebody explain the processes to me and why forged is so much stronger, if you don't mind. Thanks.

RP
Zach

 

Cast parts are made from material that is poured into a mold and subsequently finish machined to shape. Forged parts are created from a slug of metal formed in a press under tremendous pressure, resulting in a much more dense and stronger finished part. The parts are then finish machined in the same manner as cast parts. The bottom line is that a forged piston, for example, will be a much stronger, and more durable part under high stress than a cast piston would be.

 

Ah thank you that's exactly what I was looking for!

RP
Zach

 

The organization of the atoms of the material in its crystalized state are different between the two manufacturing processes. The tensile strength and ability to resist fracture are much more pronounced in a forged item.

 

hkiefus...you strike me as an engineer type...

No paticular reason, lol.

RP
Zach

 

Actually, hypertueric pistons are the best choice for a forced induction engine, as they are dimensionally stable under load/temperature and are often very light.

The problem is people often get detonation from poor or unfinished tuning, and blow holes through them. Stronger = more brittle when it comes to pistons.

 

Frederic you hit the nail on the head. With a proper tune the hyperuetectics can outlive the forged pistons and produce more power as well. Folks are finally catching on.

 

But do you still need to run lower CR with hyperuetectics to increase longevity?

-Kerry

 

Compression ratio is directly related to the state of tune. The richer you're willing to make the mixture and the later you're willing to run your ignition timing the higher the compression ratio can be relative to a given amount of boost. However richer mixtures and later timing mean less power. This is why it can be an advantage to lower the static CR of the engine and then compensate with more boost. Niether forged or hyperuetectic pistons will survive the detonation caused by a bad state of tune. The material or method of piston manufacturing do not establish the paramaters for an acceptable compression ratio.

 

I like hyperuetectics even though I struggle to spell it correctly Have 'em in my supercharged FWD Continental, as well as the old twin-turbo Dodge 451 stroker pickup.

I'm not sure people are catching on, because when people ask me what's in the engine they generally don't like the answer, and insist my piston choices are insane and ridiculous.

This is another thing that frustrates me with many people. For example, I have a good friend with a supercharged, 351W early 90's mustang with all the usual do-dads. Nicely tuned car (smooth throughout the RPM band), handled well, and so on. But when I put my wideband o2 into the exhaust (no cats on this car), it was obvious the car had significantly more to give. Out of 40 LED's, 20 red indicating degree of lean, 20 green for rich, even at WOT none of the green LED"s lit up. None. Not one. Not even a flicker.

We adjusted the EFI tables using his laptop, and after three or four "runs" down an empty road at WOT, we had the car running even better. At WOT most of the green LED's light, and we knew the engine was burning the extra fuel because temps went down and the tailpipe didn't smell like gasoline vapor.

I've been telling people for years... engines want fuel. Forced induction engines want more fuel. Why not give it what it wants?

My friend was very pleased actually. He got noticable power increase measured by the infamous non-calibrated ***-o-meter.

I am just baffled at how poorly tuned many supercharged/turbocharged vehicles are. Another friend brought his big turbo'd import to a "professional tuning shop" and after much money and much effort, the car was very fast. Still, my wideband indicated lean lean lean. So, we fixed that too though he had to operate the software since I wasn't familiar with it. Now that car runs really well.

I'll stop ranting now.

The problem is gasoline. Gasoline is a highly volatile, unstable fuel (as compared to other fuels) and is where most of the problems occur.

Diesel engine for example, run a 18:1 compression ratio. Propane/natural gas engines often have compression ratios in the 14:1-18:1 range as well. The higher the compression ratio, the higher economy you can get out of the fuel.

This is primarily why diesel engines get better mileage per CID or CC than an identically sized gasoline engine.

Gasoline vapor can ignite from a spark (which is what we want), or from a really hot surface (pistons, valves, chambers) which sharp edges aggrevate. This is why often times with a forced induction engine, effort is put into smoothing out the rough spots inside and removing casting flash, burrs, and sharp edges. Often times the top edge of the pistons are rounded as well.

Ceramic coatings are good to do as well, because it's a thermal insulator - it keeps the extreme heat inside the chamber, rather than allowing it to be absorbed by the piston, head, block, and so on. Engine runs cooler, and more heat in the chamber means more power, and more "ooopmh" against the turbo blades if the engine is turbocharged. Less heat absorbed by the block results in less heating of the oil, which means it lasts longer. Less heat also keeps tolerances closer meaning less blow-by.

Gasoline can also ignite uncontrollably under pressure, and often times why forced induction (i.e. increasing pressure) requires a lower C/R.

Since gasoline reacts violently to spark, pressure, and heat, and we can only control spark, we want to do things during engine building that will prevent pressure and heat from setting off the gasoline. A higher octane gasoline usually helps, as the octane slows down the burn rate of the gasoline, therefore a little preignition won't result in the entire intake charge going "pop" before the piston gets to TDC.

If you really play around with this... as I have... you'll discover something interesting.

Low compression, ceramic coated engine internals, with high amounts of boost, makes a ton of power, even of 87 octane. 87 octane burns faster than 93 octane, and that can be an advantage if your engine is built to take it.

After a lot of experiments on an engine dyno, using junkyard engines, I and several friends figured out that an insanely low compression, with large turbos that start to spool up off idle, can make significantly more power than the same engine with "normal" compression, and less boost. And, we didn't have the same detonation issues that a higher compression engine would have. We tested Buick V6's, Chevy 350's, and a Ford 302.

My old 75 dodge had a twin turbo, 451cid somewhat low compression engine (8:1), everything was smooth and coated. No real pinging, no detonation, nada. I could break transmissions, twist driveshafts, and leave rear-end parts on the asphalt "on demand". Or if I got lucky, the front suspension would extend itself to it's limit and the front tires would just "skate" on the surface of the roadway.

Think about this... most modern day cars have a 10:1 c/r. During the hot summer, don't they ping on occasion if you mash the throttle to the floor?

Imagine what would happen with a supercharger?

Of course what you do and the degree you do it depends on what you want to accomplish. Slapping on a supercharger kit into your F-series is fine, and you will feel the power increase for sure. But, there are limitations to the level of boost you can run and of course that limits the potential power.

My old dodge, like I said would extend the front suspension all the way if WOT occured from a standstill. It was silly fast, and it weighed 5700lbs since it was old and wasn't covered in cheap plastic like most newer cars. And, it was a long bed, extended cab.

 

Frederic, that was an awesome post, thank you very much!

RP
Zach

 

I appreciate the time you guys have spent in putting so much research into the field. It helps those of us without the time or cash flow understand the more in depth workings that a quick and dirty primer from a corporate skewed write-up leaves out.

However, the point of cash flow is brought out... you have to really dig deep to be able to, essentially, bullet proof the set-up. This isn't something that any old Joe Blow might be able to accomplish in his garage, in a weekend, for cheap.

-Kerry

 

You're welcome, but I did the research to prove a theory (big cubes + low compression + crazy boost = no detonation and tons of fun!) for my own selfish purposes. I share as I remember

I will have to disagree, only because I'm on my third big block, twin turbo stroker for a pickup, and I'm a cheap bastid in an extreme way. You have to be resourceful, and you don't have to buy $2500 in parts to make a nice forced induction engine.

For example, the twin-turbo Dodge engine, ended up being 451 cubes. It went like this:



$200 - Mopar 400cid "B" block (in above picture) fully loaded with accessories. Engine ran, had "okay" vacuum, and I chose to rebuild and stroke it in the garage, purchased from a friend who rolled his truck twice in the same summer.

$10 - warn out 440cid "RB" crank from a different friend.
$0 - turned down 440 crank journals to 400 journal size.
$0 - decked a set of 430 big-block Buick rods found in shoebox at local machine shop, in exchange for wiring two flourescent lights and repairing a wall switch.

$250 - engine rebuilder parts - bearings for crank/cam/rods, full gasket set, high volume oil pump.

$8 - eight pushrods out of a junkyard 440 mopar engine.

$150 - two junkyard T3 Ford thunderbird turbochargers.

$30 - black pipe to make exhaust manifolds
$20 - steel for header plates and turbo flanges.

$15 - edelbrock aluminum "streetmaster" intake from a swap meet.

$20 - 1" aluminum round stock to make injector bungs on the drill press, using bits to drill the inside, and a file for the outside.



$30 - "Durafix" aluminum soldering rods to attach bungs to intake.

$50 - carbide rotary cutters/deburrers for intense porting effort.

$20 - GM ECM 1227749 from a friend.
$0 - random wiring snips from junked cars
$5 - solder to make new harness.
$1 - electrical tape for new harness.
---------
$651

That's approximately what I spent (including tools) to make the 451cid stroker. The wiring didn't have a direct cost because everytime I went to the junkyard for anything, I'd snip a few connectors here and there and the guy running the cash collection booth didn't care about a few connectors. I spliced everything together and made a complete harness. Just took a while to have enough connectors to make a full harness.

I honed the cylinder walls the monkey way - stones on a springy thing in a hand drill, which I borrowed from a friend. Not a perfect job but it was good enough.

Add to that the cost of techline coating for the piston tops, chambers and valve heads was about $50-60 at the time if I remember correctly. It was just enough for two coats, something like 16oz or thereabouts.

So there's the worlds cheapest stroker, in dodge flavor.

Regarding longetivity, our dyno testing/experiments also proved that RPMs killl engines faster than boost.

20psi extra in the combustion chamber is piddly as compared to the square of the RPM / force when the piston changes direction at TDC. For every 1000 RPM increase, the load on all the "stuff" is squared. This is one of two reasons why my twin turbo stroker projects always have silly redlines - 4000-4500 or thereabouts.

With the tires/gearing in my F350 crewcab, at a "decided" 4000 rpm redline I'd be doing about 135 in 5th gear. Silly.

The engine I'm building for my F350 crewcab, will be about 500cid. With a target/goal of 1000 ft-lbs of torque, that's about 2 ft-lbs per cid. That's not very high actually because the RPMs aren't that high. By keeping the RPMs low, nothing is going to break. Instead, I can turbocharge and add large amounts of boost and make the power that way.

500cid, 4000 RPM with 30psi of boost will survive much longer than 500cid, 6000rpm with 10psi of boost. And, I can use reasonably stock, cast, crappy, nearly free unloved parts too and assemble it in the garage at my leisure, and not open a revolving credit account with places like Summit Racing.

Of course you're welcomed to "wrench with your wallet" and buy a racing block for $1200, a stroker kit for $1500-1900, THEN buy all the bearings, pushrods, rockers, and so on and make yourself a very nice stroker for about $3500-4500 depending if you shop around or just buy everything from one vendor for convienence. Or you could pay a machine shop to do everything.

Was it a perfect engine? Nope. Was it cheap? Heck yes! Was it fun? Absolutely.

Pop the clutch in 2nd and the front tires came right off the ground, assuming something behind the flywheel didn't spit out parts. Trannies, driveshafts, and rear diffs had a very low survival rate on this truck, when I put slicks on it. DOT tires weren't too bad because they'd break free and smoke, acting as fuses.

Anyway, not breaking *****, but instead trying to illustrate a point, having done this twice now, working on my third.

 

^ Remind me again, why is it I'm moderating this forum (instead of you)?

P.S. You did put 16 pushrods in that engine didn't you? Did you have eight of are the intakes simply opened by that silly amount of boost you run?

 

Because the FTE bestowed great responsibility upon you, and I got an FTE t-shirt instead

The intake pushrods were off a 440 "rb"I found in the junkyard. They are a hair longer than the stock 400 "B" pushrods because the 440 has a taller deck height. "RB" stands for "raised block" BTW Anyway, the exhaust pushrods and rockers were stock, and the intake side had longer pushrods to compensate for the higher point where the pushrod meets the rockers, because I used fancy rockers instead of stock parts. Why? Because I had them handy, they fit the stock rocker pivots, and had a slightly longer leverage which means the intake valves would extend further into the chambers, allowing for more airflow.

They wouldn't hit the pistons since the c/r was lower and the engine didn't see enough RPM to cause valve float.