I want expert advice!

Do you really need to have a forged steel crankshaft and some trick H-beam rods in a small block chevy street motor that stays below 6500 RPM's and makes around 600 flywheel HP?

I think way to many guys spend way too much money on their street driven short blocks. Is this high dollar reciprocating assembly stuff really required?

Forged pistons and good rings, of course, but billet crankshafts and $800 connecting rods?!

Old timers/Experts, please shed some light on this subject for me.

 

HELLO................Hello................hello... .................................................. .................................................. ..Anybody out there?

 

For an N/A application, up to 6.5k RPM and 600 HP, high dollar cranks and rods probably are overkill. IMO, I think many folks subscribe to the logic that they may not need the high $$ stuff now, but they want to leave their options open to heavily spray the engine in the future, or some other plan that may otherwise require a forged crank/rods.

I may be foolish with my money, as I could have built my stroker much cheaper with a Scat 9000 cast crank and I-beams, but I chose the additional security a few more dollars offered.

 

IMHO 500rwhp NA just needs a Scat crank. Once you add blowers or N2O into then we start talking forged cranks.

A set of Eagles is not that high in price for rods compared to a good cheap I beam like the Scat. The L19 versions of the Eagles are nice and when you get into boost are worth the extra cash.

FWIW the only guy I have ever seen need a set of Olvier Billet rods in his short block is Rich for a street car. 600-700hp doesn't need them if it's going on the street.

Bret

 

Listen to Bret.

Rich Krause

 

Do as you wish, but....

I just broke my stock crankshaft, and all I was pushing was 338 rwhp and 348 rwtq.

Although I had a set of drag radials on the car when I done it. Along with a 2000 rpm clutch dump. but it still shouldn't have broke, I've seen a lot more thrown at them than this.

Oh well, I've already purchased the crankshaft, and looking for h-beam rods. I already had forged pistons, so I should be good to go this time.

Maybee I had the lemon crank.

Just my.02

D Moss

 

From a spectator standpoint, it's tough to say why some cranks break and others don't. Could be a million different factors or just a combination of a few...... harmonics, tolerances, who knows.

I put ~500rwhp (never dynoed, just a guess) and a dual stage progressive nitrous hit to an old steel GM crank, arias forged pistons and pink rods for 3 seasons of dragstrip duty (refresh in between) before a connecting rod finally windowed the block. It's always just a matter of when. But people were amazed that is stayed together as long as it did. Of course I am quite **** about oil filter inspection and preventive maintanence. I also don't mind paying for precision machine work.

A cast crank is good for the majority of street builds. Just make life easy on it by using lighter pistons/rods and keep the harmonics out with a good aftermarket balancer. Balancing is a good idea too.

-Mindgame

 

Unfortunately the motor is only as good as the weakest part.

I just wish it was possible to determine which part would break.

Murphys law always determines that, meaning the part that will cause the most damage usually breaks (like a connecting rod) which ruins the block, pistons, usually the cam & sometimes even the head(s). I recommend to err on the safe side to protect my investment. Do you need billet? No, but a decent replacement rod would not be a waste of money either considering the consequences of a broken one.

Cast cranks are not generally breakage prone under 500-550 HP either.

The only thing to consider is that you may not need race parts, but can you afford to do it twice if it does break after using
OEM parts the first time.

 

The guy on the Eagle tech line told me yesterday that 500hp is the limit on their cast cranks and 5140 rods that they sell in Jegs. How much over that do you guys think I can push it? They didn't tell me an RPM range.

Wouldn't a boosted engine be better on the bottom end than a nitrous engine?

 

A boosted engine's bottom end is under stress all the time, a nitrous engine is only stressed when the juice is flowing.

If we are talking about centrifigal superchargers, the boost comes in linearly in proportion to RPM, whereas nitrous shocks the bottom end as the juice all comes in at once.

Then again, you dont have to worry about tensile strength with a nitrous motor as much as with a blown or high compression n/a motor.

I think it goes back and forth depending on how often you spray and how often you see boost.

 

A boosted application is a boosted application IMO, whether it be nitrous or a blower. A blower/turbo application is not stressed "all the time" because under light accel and cruise you are not under boost. Nitrous can be progressively controlled just like boost.
Guy here locally has run 11.20's@121MPH with a stock cast crank, stock rods and good pistons(internally balanced). With a 4 speed and a 5.13 gear shifting at 7300 RPM, All motor, in a 3rd gen. With 462 casting "double humps" no less. We even drove it around on the street.
Guys on this board on making 460 or better at the flywheel on stock bottom ends all motor.
I personally do not see the need for a 4340 crank until the 525 or so flywheel mark as long as it's balanced right. JMO


David

 

Let's put it this way. My car has gone mid 11's on nitrous with cast pistons, stock PM rods and a cast crank. I flog my car on the street because low 12's is more than enough power to try to hook up on the street. I only run nitrous at the track when:
A. I know I have good gas in the car
B. I can afford to put good gas in the car
C. When the car is running cool

3 things that a boosted application may or may not be able to insure.

All I am saying is a boosted application has the oppurtunity to see more boost than a nitrous application has to see nitrous in most cases unless you want to go through a bottle every few days.