L98 internals and weak spots.

[devilfish]

Hello

Im going to rebuild my engine due to a bad leakdown result.
My plan is to go with some forged pistons ( +0.30), ARP rod and , main bolts.
My question is if this will make my engine handel more power, or is it a waste of money to install this products on a stock L98?
Myaby the rods and crank ar the weak parts?
My goal is 420hp at the crank, shifting at 6000rpm. Then mayby a 75hk nitrous shot.
Thank you..

 

[devilfish]

no one?

 

[Ken]

Weekends are generally slow. Give it time, someone (a lot of people) will be offering their opinions before long.

By the way, I'm going to move this to the "Mods" forum where you'll get more modification feedback I hope.

 

[rrubel]

I'll pipe in here... was doing some research recently for my required rebuild. The guy who's doing it is using TRW forged pistons, ARP connectors for everything, a ZZ3 crank, and LT1 con rods. He claims that the con rods become the weak point in this setup, because they're cast instead of forged, but he also says they're the strongest that GM uses outside of dedicated race engines. My GM Performance Parts book shows only one set of con rods for 350 non-racing engines, which are what's standard in the LT1 and LT4, and it says they're good to 500 HP. I believe the crank is forged in the ZZ3 engine, but cast in the L98 and LT1. The ZZ4 has a forged one, but also it's noted that you can ONLY use it in a ZZ4... No max HP is given.

My engine is supposed to be able to handle 500 HP without problem, and 6K RPM for hours at a time. My goal is 425 at the crank, NA. No juice...
[RICHR]

 

[devilfish]

thanks..

Same goal for me, but i am going to use the stock crank, stock rods, and fordge pistons. ARP bolts everywhere. How about the 2 bolt mains, are those a weak spot?

 

[-=Jeff=-]

thanks..

Same goal for me, but i am going to use the stock crank, stock rods, and fordge pistons. ARP bolts everywhere. How about the 2 bolt mains, are those a weak spot?

Considering you are going to use Nitrous, I recommend forged Connecting rods as well as a forged crank, Better to do it all now then when it breaks again.

Also I would suggest Main stud instead of bolts for the 2 bolt main. you could go to splayed 4 bolt mains in the block if you wanted. All depends how tough you want the bottom end to be. I spin my motor to 6200 rpms at the track only pretty much and have Hypereutectic pistons, LT1 rods, and a Scat Steel crank. I chose those parts at the time as I was not planning on nitrous or any power adder.

 

[taegdh]

All the previous replies are applicable, but the big question is: "What do you want the HP to do?"

Are you looking to do some NHRA or IHRA Drag racing with that go juice? Then definitely go with all FORGED INNARDS uncluding roller rockers and cam/lifters.

Are you looking to "light to light" on the street and through the urban canyons but feel the need for high revolutions, FORGED INNARDS again.

The cast parts just don't hold up once you get much beyond about 5K RPM.

In both cases you're going to have to get a plenum and short "opened" runners to get the higher revolutions out of the engine, along with enlarged valves, both in and out, along with a good porting job. $$$$$$$$

The long runners on your engine were designed to produce high air velocity, but they also limit the amount air in to the combustion chamber. They do work very well for producing lots of low end torque. (Note the next time you're out there cruisin, give it a little run and you'll see how athsmatic they get above 4800 RPM) These systems were designed for lots of low end torque, get off the line and through the turns properly and in a hurry.

There are tradeoffs in each system, so you have to ask yourself, a number of other things! Where do you want the HP/Torque to really kick in?
If You're going to have it on the street, will the CARB/EPA people get into the picture, how will it drive on the street, Will my tranny and rear end hold up?

Three Rules Which I have learned the hard way!
1. Set your goals! (Realistic yet challenging!)
2. Do your homework, on what has to be done to do reach those goals.
3. Don't skimp! If you don't have the money now, you're best putting off any mods until you have all your assets plus 20 percent, in place to do the job right the first time. Nothing is more infuriating and discouraging than to run out of money in the middle and not being able to finish the job in a timely manner.

 

[devilfish]

thanks for your replys. Im sorry for be unclear. Let me state my goals and parts im going to use:

Car is a 6spd 1991 vette.

Magnafluxed and cleand block.
I got the hot cam kit
with 1.6 rrs
Lt1 intake conversion
Trick Flow 23" heads
Hooker headers + 3" free flow exhaust, no cat
Fidanza alu FW
30" injectors
Bigger fuel pump
adj fpr
Dyno tuned by me.

My goal is:
420 at the crank
Hiiiiiigh 11sec ( with slicks ) 1/4 times.

I got 2 ways i plan this rebuild
First is the cheap way, to use the stock crank,stock rods with ARP bolts everywhere, rezised rods after arp bolts, hyperxxx or forgde pistons running around 10:1 comp ratio.

Second plan:
New Scat 9000 Knife Edged 3.480 crank
Triton Engineering 4130 Forged I-Beam 6.000 Rods, with ARP Wav-Loc Bolts and Press Pin
Keith Black (KB) FT Hypereutectic Pistons
Internal balanced.
This will keep me on the edge of my budget. And I really dont have anny money left
I whant to keep it a 350 ( 355 ). I really dont need more torque.

The car is going to see the dragway around 4 times a year. Its going to be a higway warrior more then a stop light to stop light racer.

Thanks for your time.

 

[Ken]

Three Rules Which I have learned the hard way!
1. Set your goals! (Realistic yet challenging!)
2. Do your homework, on what has to be done to do reach those goals.
3. Don't skimp! If you don't have the money now, you're best putting off any mods until you have all your assets plus 20 percent, in place to do the job right the first time. Nothing is more infuriating and discouraging than to run out of money in the middle and not being able to finish the job in a timely manner.

... And it'll still drive ya nuts every now and then - "Murphy's Law" ya know.

_ken

 

[rrubel]

Will someone explain in small words what hypereutectic pistons are? I've been told they're just another fancy way of casting metal, and forged are still stronger. But HE's can be just as expensive as the forged.
[RICHR]

 

[Ken]

hy·per·eu·tec·tic (hi´p?r-y?-tek?tik) adjective
Having the minor component present in a larger amount than in the eutectic composition of the same components.

Excerpted from The American Heritage Dictionary of the English Language, Third Edition Copyright © 1992 by Houghton Mifflin Company. Electronic version licensed from Lernout & Hauspie Speech Products N.V., further reproduction and distribution restricted in accordance with the Copyright Law of the United States. All rights reserved.

 

[Ken]

eu·tec·tic (y?-tek?tik) adjective

1.Of, relating to, or formed at the lowest possible temperature of solidification for any mixture of specified constituents. Used especially of an alloy whose melting point is lower than that of any other alloy composed of the same constituents in different proportions.
2.Exhibiting the constitution or properties of such a solid.

noun

1.A eutectic mixture, solution, or alloy.
2.The eutectic temperature.


[From Greek eutektos, easily melted : eu-, eu- + tektos, melted (from tekein, to melt).]

Excerpted from The American Heritage Dictionary of the English Language, Third Edition Copyright © 1992 by Houghton Mifflin Company. Electronic version licensed from Lernout & Hauspie Speech Products N.V., further reproduction and distribution restricted in accordance with the Copyright Law of the United States. All rights reserved.

 

[Ken]

Hypereutectic pistons became the rage in the early '90s as they offered the reliability and lightweight of cast pistons but were resistant to higher cylinder temperatures.

The pistons are cast with a material high in silicone content to achieve the low expansion rate and cylinder wall tolerance of a common cast piston, with near forged piston strength.

Hypereutectic pistons are ideal for high-performance, naturally aspirated combinations that won't suffer under the strain of power adders like turbos or nitrous, which can quickly decompose this strong, but inflexible style of piston.

The pistons are priced economically, between pressure castings and forgings.

 

[Ken]

For some good reading regarding cast versus forged pistons, see: Tech Speak: Forged or Cast? Piston Basics

 

[devilfish]

mmm ok ,but have anyone anny coments on my setup and if my bottom going to take it?

 

[rrubel]

Thanks, Ken. A wealth of information, as always. So basically cast is worst, HE are middle, and forged are best - in terms of strength, not necessarily weight.
[RICHR]

 

[drags1998]

IMHO,Nothing but Forged pistons,stock rods are fine to500HP and 6000RPM If you can swing it 5140 or 4340 steel crank,4340 being the best!!!! If you are going to BEAT THIS THING LIKE YOU HATE IT, then buy a complete forged rotating assy. If you can restrain yourself, and be some where near HUMAN, A stock crank& rods are really quite strong!!

 

[Ken]

What I used in my 417 build:

• Eagle 4340 forged steel crankshaft
• Eagle pin fit 4340 H-beam 3-D forged steel connecting rods - 6.00"
• SRP forged aluminum pistons

If I ever get it to the point where I'm satisfied that I can take it to the strip, we'll see how well the bottom end holds up.

_ken