SPANKY LS1

iTrader: (24)

I keep seeing people say that cars with forged bottom ends dyno lower than those with stock bottom ends. Why is this, weight of components, right? I have been doing some research, and found that most forged pistons are lighter than stock ones. Now, if comparing a stock shortblock and a shortblock with stock rods and crank and forged pistons (that are lighter than stock pistons), wouldn't the motor with the forged (lighter) pistons make more power, everything else being equal?

Shawn

HumpinSS

iTrader: (1)

dejavu

DanZ28

iTrader: (5)

It should make more power I would think as well. I didn't notice less HP with my forged bottom end, but I didn't do swap for swap comparison either. You would think that a better built and correctly balanced/blueprinted motor would put out slightly better numbers than stock. Are there actually lower numbers being seen?

Dan

jrp

iTrader: (16)

i think its just an excuse on poor setup *shrug*

WS-Sick

Aren't the internals heavier? If so, would that not rob some horsepower?

gomer

iTrader: (13)

I asked a couple of engine builders the same question and they told me that ring tension had alot to do with it. I'd like to get input in this thread from Futral, AP, Thunder, and some of the other LSx engine builders.

Bo White

iTrader: (59)

A local had a Eagle 383 w/ a 238/240 cam and it revved pretty damn fast IMO.

Inspector12

iTrader: (29)

Mine made the same if not more. Just my experience though. And Spanky is right most forged pistons and rotating asyemblies are lighter. I can only guess that the heavier rotating mass is actually helping rather than hurting? Who knows for sure. Good topic for discussion. I would like to hear more peoples stories with this. The day these guys dynoed was the weather comparable same dyno what exactly changed. I mean if tires can change numbers on a dyno other things can also.

ROGERSPERF.

Lets assume all being equal and all we swapped out were pistons rods crank.No other mods.The lighter rotating assembly would show a power increase under the curve but if you held it at a set rpm say 5000 it would not make any differance on what the parts weight.they would both make lets say 500 hp.I build a lot of circle track engines and we look for the lightest rotating assembly we can use so the car will get off the corner.The rotating assembly in a winston cup car at daytona is a lot heaver then at say bristol.The inertia of the weight of the assembly we help keep the engine rpms up.So if you us a water brake dyno and the use a inertia dyno the inertia dyno will almost allways show more power the the water brake dyno.

Wild85

iTrader: (1)

Forged pistons, need a looser piston to bore clearance, (hope i used the right term) because they expand more than a cast or hyp piston, forged pistons usually burn more oil than the other pistons for this reason.

ROGERSPERF.

Stock ring package on a LS1 is 1.5 1.5 3mm if you put pistons in that have a ring package of 1/16 1/16 3/16 you will lose power.There is power in a thin light tension ring package.Not so light though that you would need a vacum pump or e-vac system to help out the oil ring.

ROGERSPERF.

I will disagree with you on that most forged pistons today run .004 clearance if you put in a forged piston and it use more oil i would find a new shop or at least ask the shop how they prep the cylinder walls for ring seal.This is wear the oil is going not because of the piston you choose.

DavidNJ

RogersPerf.,

Which track do you build engnes for?

David

ROGERSPERF.

Motordrome in pittsburg jennerstown an ppms dirt track in pittsburg and i,am doing a hooters pro cup engine wright now.I also have done some busch north engines.

LSonederfull

I would say forged pistons could lose power because they usually have valve reliefs that lower compression and unless gas ported, hypereutectic cast pistons have harder ringland surfaces and less expansion so ring seal and control should be better than forged. Compounding the ring seal aspect is the looser fit piston to cylinder wall that forged pistons require, this hurts seal compared to cast.Denser cast hypereutectic should reflect more heat energy than thinner lighter forged pistons also. Just some food for thought.

Full-Force

iTrader: (11)

this post is nonsense

forged, cast who cares

usually aftermarket bottom ends are gonna be lighter than stock

you aint gonna buy a high dollar set of forged pistons that are heavier than stock ... thats one of the claims to fame of good pistons is lightweight

i think someone is full of

ROGERSPERF.

We are talking about oil use.With the thin rings used today you need tight piston wall clearance if you used piston in the old days that needed .010 clearnce then i would say yes oil may be a problem.Once the shiny top of your piston gets coated with carbon the benafits of heat reflection have gone unless it is a race engine that gets torn down alot and you can remove the carbon.The reason for the use of hyper pistons in todays car is so your mom can,t complane about the piston noise when she starts it up in the morning..0008 to .0015 clearance.with hyper any thing more and you will start to here noise like your LS1 had with the recall.

Race Car Driver

Well, I'll let you know how much power my FMS 347 makes versus stock LS1, within the next month. I will predict 420 or so on the new FMS motor versus 309 rwhp stock.

MakoLS1

Forged bottom ends can take alot more nitrous. I dont know if a forged bottom end absorbes horsepower but i never heard of that before. Sometimes you have to sacrifice hp to go faster. I did with my th400 and moser 12 bolt. Well worth it, might hurt on the dyno but help at the track where it counts.

Another_User

Because people that can afford forged internals can afford a "pro" tune, and "pro" tunes are poopie?