I have read to keep the stock RPM <6300 to keep from spinning rod bearings, however the stock LT4 rev limiter is 6411 from the factory. What is so different about the LT4 bottom end that would allow the safe higher revs from the factory? Other than the 4-bolt main?

The The reason I am asking is when building a cammed stock block engine, if replacing the cam bearings and using a high pressure spring in a new Melling oil pump and Canton pan, is there any reason that a stock shortblock couldn't handle 6400 rpms safely if the stock LT4 can?

 

improved crank with undercutting and rolling. positive twist top piston rings.

 

For me the MAXIMUM SAFE RPM is the factory's REDLINE, not the cut off rev limiter. That's why it's there, right?

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

Which on the LT1 is nearly the same, 5750 I believe for the LT1 limiter, and we all know an LT1 can easily rev safely more than 5750.

 

You asked about the MAX SAFE RPM, right? So why re-invent the wheel?

GM set the REDLINE and the cut off is for those who choose to ignore or, in a rare case a runaway WOT engine.

If you REALLY want the Maximum SAFE rpm, stick to the factory redline. It's the RPM that GM, in their testing, shows to be the maximum SAFE rpm the engine should reach and still be SAFE. NOW, if you're determined to push the envelope, go for it.

Remember the line from Pulp Fiction when Travolta told Samuel L. Jackson that he was being pushed into the "RED" - implying he was about to BLOW? RED=Redline; RED=Danger.

Should you choose to ignore it, it's your call. I never do, but that's my call.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

While I agree with JakeJr's statement on a stock engine, I don't agree if it's using an aftermarket valve train. Most of the time, a maximum given by a engine manufacturer is limited by the weakest link. In the case of OHV emgines, that's the valve train. Improve the quality of the valve train and the rev limit increases.

There are a bunch of papers out there from the SAE and one or two from GM suggesting that the maximium engine speed for a cast rotating assembly is 4100 piston feet per minute. Change the materials and that number changes. Using 4100pfpm as a maximum, a Chevy small block with a 3.48 in stroke would turn about 7100rpm. That number is well above where the OBD-1 computer stops and significantly higher than the stock valve train would ever turn....

So, bottom line in my opinion is that you could run the LT4 cam and extract the maximum from it. Of course, this is all opinion and you should research it further before deciding. By the way, there is a difference in the LT4 crank Vs the stock LT1 crank...the fillets are undercut to relieve as much stress as possible at the crank journals....

 

The farther you go above redline the more risk you run. I am a bolt on car and beat the crap out of my car on the street turning 6300rpms and messed something up. Thinking a rod bolt, but regardless the higher you go the more risk.

 

Oh, yea! I agree. Once you begin changing parts to more performance oriented versions all bets are off and the recommendation then changes.

Yet, I still don't trust the stock rod bolts above the factory redline. Also, I don't like the stock main and rod bearing clearances, ESPECIALLY if they spec out on the tight end, like 0.0007"/0.0009"/0.0013".

To me, the problem is there's really no way of knowing without tearing into the engine and measuring to see what the factory sent you.

But that's just me. To each his own.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

Stock 5750-5800 would be the "safest", but I'd say under 6300 is considered "safe". Although as mentioned anything modded is going to be on borrowed time. Just like human life, everything must come to an end. My stock bottom end sees 7200 all the time and just wont quit

-Dustin-

 

So would you say upgrading to high pressure spring in new Melling pump and Canton pan and keeping the shifts at/under 6400 be ok?

 

I think that would be unnecessary, just keep shifts under 6400 and make sure you have good oil and pressure.

-Dustin-

 

replacing the cam bearings requires removal of the engine so it might be a good idea to put fresh bearings in the bottom end and ARP bolts, maybe even have your machine shop balance the stock assembly

 

Well I was asking because I already have the pump and pan, so it will be transferred to the 'new' engine once it goes in.

 

I missed the rebuild part of the post. I'd just have a QUALITY machine shop check and spec everything. Beware lots of machine shops are screwing LT1 guys over.

-Dustin-

 

Depends on how far "under" 6400 we're talking about. Most guys just trust to luck. Those who have engines that survive will say it's okay because their engines survived. Those who blow their engines or spin bearings check their bank account balances.

What you're bound to get are responses loaded with disclaimers like "should be", "might be", "probably will be", and things like that.

So ask the guys who say it's "okay", "fine" (or similar responses) to run 6400 if they'll cover the cost of the repairs should your engine blow. Wonder how many takers you'll get.

I suggest you don't let this Forum be your only source of information and feed-back. Check on several other Forums and compare the reported failures against the successes then choose your poison. If/when it blows, don't forget to do an autopsy.

"MAX SAFE", adhere to the redline, even then there's no guarantee.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!