Forged internals not for D.D???

[blink]

Was reading a thread from 2011, which stated that forged internals aren't good for a daily driver? Is this true?

And if yes then why?

I just want my new motor to last me , is it really better to buy an OEM long block?
What else would I need to buy to have the oem one work?

[Skym]

From what I understand, the reason behind that is due to forged pistons expand at different rate to cast pistons. Cast pistons expand quicker (can drive engine from when it's cold), but are weaker when it comes to engine knocking. Basically don't make engine knock with cast pistons (play it safe with ECU tune). With forged engine, warm it up (gives time to close the clearances) before driving.

I gather heat is the limiting factor with cast pistons. If get too hot, they expand too much and piston rings get jammed into cylinder walls and breaks ringlands (especially if ringlands are thin) or break due to knock. I gather that's why running a rich tune, lower boost levels (lower cylinder temps), conservative ignition timing (to prevent knock) is key to making a cast piston engine last. Basically is what factory does, but is a bit too rich to take into account leaking intake, exhaust manifolds, adding exhaust, weak fuelpump, clogged fuel filter, etc.

Like alot of people say, it's all in the ECU tune.

This goes more indepth into what the differences are between cast, forged pistons -

http://www.motorcycleproject.com/motorcycle/text/cows-pistons.html

It's for motorcycles, but similar applies to car engines.

[blink]

Wow thank you skym, you really do have perfect answers to everything =p


So would you recommend buying an OEM long block?
How much additional costs would be involved after an oem block, turbos? and what else would be required

[NismoS-tune]

Buy my near new built engine. It's good for big power, just doesn't fit in my new WRX project haha

[gezed]

It isn't necessarily true, companies like Supertech makes forged pistons with relatively high silicon content, the so called 4032 alloy

This material is not as "ductile" or flexible as the conventional 2618 alloy used by CP and Wiseco but they do offer significantly better durability compared to the OEM pistons

I did a lot of research on the 2 types of forged pistons and decided to go with Supertech because the 4032 alloy does not expand as much as the 2618 which means they tend to have smaller piston to wall clearance and that really helps extend the life of the internals for day to day use where cold start-ups is common

The Supertech 4032 forged pistons will definitely not be as resilient as the CP and Wiseco's 2618 pistons though

[Skym]

Not perfect answers, but my interpretation of what I understand / learnt about the subject.

Also from what I understand, the other benefit of forged pistons is weight (lighter). Forged pistons put less stress on conrods (inertial load) at same rpm (engine is more reliable). It's something like every 1000rpm = 3 tons of inertial load (not actual figures, but get the idea). That's why conrods (even H beam conrods) snap like twigs and put a hole in side of block when rev engine outside factory rev limit's. If stay within factory rev limit's, shouldn't have a problem.

The lower boost level is to put less stress on ringlands as well, not just drop cylinder temps. Most tuners say limit is around 20psi with RB26, RB25, etc cast pistons (I gather bigger than stock turbo's, so hard to say what that would be with stock turbo's or single turbo, etc) when used on racetrack, drifting, etc. I noticed on dyno you can push past that psi limit. Another way to reduce stress on cast piston ringlands is to drop compression into high 7's (as done with Group-A RB20DET running 1.7bar x 14.5psi = 24.65psi + forged pistons). But it affect's off boost performance. That's why RB25DET has higher compression, to improve off boost performance (where engine is most of the time when used on the street), but limit's boost level you can run.

For cooling cast pistons factory use oil squirters on bottom of cylinders (found only on turbocharged engines). But if your oiltemps are higher than they should be, the oil squirters aren't going to help cool the cast pistons (or forged).

Shouldn't excede 90 degrees max with oiltemps on racetrack or road. At 100 degrees+ is where factory recommended 7.5w30 oil (or slightly better than factory oil, w40) start to break down. A w50 is usually used on racetrack. That's the other thing, I think oil viscousity changes with forged pistons due to clearances (run slighty thicker oil). Best to ask oil experts before running thicker oil.

About your engine, usually if pushing ECU tune or exceding 600hp or 20psi with RB26 you fit forged pistons and reuse stock I beam conrods with ARP conrod bolts (when on a budget 700hp at engine build, but mainly used with around 460hp at engine on low boost). Same with block if it doesn't have cracks. N1 short block if can find one, as N1 block, N1 pistons, N1 oilpump (with Reimax gears), N1 waterpump (racetrack), etc is better.

Why 600hp, because there's supposedly a 100hp per cylinder limit with cast pistons.

If you look at Nurburgring N1 GTR with 500hp, N1 cast? pistons (redesigned, stronger? ringlands).

500hp / 6 cylinders = 83.333333333333333333333333333333hp. It's below 100hp per cylinder, so should be reliable while running N1 cast pistons. I think some forged pistons are good to 900hp+.

[blink]

Thank you gezed, I will read up about those.


Skym, So main concern for the cold days is to have the proper cooling system, correct? Will lower rad heater hoses, help warming it up on cold days too? Like will getting warming systems be beneficial?

What would you consider too cold to drive in?


Oh I'm not looking for anymore than 400hp. 3-4 is good at the moment for me =]

[Skym]

If starting in snowy conditions, warming up radiator, etc might help with higher coolant temps, ECU not running engine too rich.

If can get oiltemps up, the hotter oil via oilsquirters on bottom of cylinders squirting oil onto underside of pistons might help to make forged pistons heat up and expand quicker. But if forged pistons expand too quickly, will they crack????

Don't know, never driven in snowy conditions. But I would think when coolant is rock solid.

400hp at engine can be done with a boost up of stock engine (with metal headgasket, sump baffles, 600cc injectors, fuelpump, Z32 AFM + plugs x 2, ECU retune, boost controller, breathing mods, etc), if stock engine still has good compression. Adding bigger N1 turbo's will make that easier to achieve with stock engine. At 1bar N1 turbo's should produce between I think was 440hp? (R33 N1 turbo's) or 455-460hp (R34 N1 turbo's) at engine with stock cams, ECU retune, removed restrictions, etc. I think max for R34 N1 turbo's with N1 engine is 550hp at engine with metal headgasket, Mines cams, 600cc injectors, etc.

[Dragon Humper]

If you can swing it, always run forged internals. You will get a little piston slap in the mornings when dead cold but it's no biggie. Just allow more time to warm up, and run the stock thermo in the colder months. You only need to warm up for about 3 min. longer.

Cast pistons do not expand nearly as much as forged from dead cold, that's why OEM likes them. They are cheap, get the job done, don't consume as much oil when cold (which affects cold start emissions) and don't make any funny noises to make the dummy general public complain.


If you are running a stockish twin setup, run forged, they cope with the hotter air of small/responsive turbos and the odd tuning booboo much better than cast.




Jon.