Max safe RPM on stock bottom, and LT4 question?
12-22-2009, 10:18 AM
#1
Max safe RPM on stock bottom, and LT4 question? 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?
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?
12-22-2009, 11:04 AM
#3
Some guys have eclipsed close to 7k rpm on the stock bottom end. As long as it's in good shape and you have good oil pressure 6500 rpm shouldn't be a problem. Don't expect it to last long if you spin it higher than that on a daily basis though.
And the LT4 had a higher rev limit because the cam/valvetrain had higher peak HP.
And the LT4 had a higher rev limit because the cam/valvetrain had higher peak HP.
12-22-2009, 11:10 AM
#4
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with new rings and bearings you should be able to spin the shortblock pretty high. Now if you have 90k of hard miles on it things are going to be a bit different.
12-22-2009, 11:33 AM
#7
Good to hear, I have found a cheap cop Caprice LT1 with 80k on it, and want to use the shortblock and then go LE2 with it shifting around 6400. I will still be putting in a new Melling pump with high pressure spring and Canton pan for a little added insurance. This should be an ok combo if maintained well, right?
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12-22-2009, 12:28 PM
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I was shifting at 6400 on my stock bottom end, but I have a high pressure oil pump which should help keep it healthy for long.
Until my opti decided to die. Its either from a water puddle I drove through in the dark at work, or from spinning shifting at 6400 everyday whenever I got the chance.
Until my opti decided to die. Its either from a water puddle I drove through in the dark at work, or from spinning shifting at 6400 everyday whenever I got the chance.
12-22-2009, 03:38 PM
#11
If it's a stock and never rebuilt motor with stock clearances on the bearings the rpm capability might be a bit lower than a "built" stock bottom with ARP bolts, Clevite 77 bearings, a Melling Hi Vol pump, and .002 clearances which is a bit looser than stock was. I tend to think the bearing clearance and oil pump make the most difference when you are talking about stock bottom ends at this range of RPM (but I could be wrong).... I think 6500 is okay with the a high volume pump and 20/50 oil...
12-22-2009, 05:19 PM
#12
Biggest difference in the LT4 shortblock is going to be the fractured cap rods. I do not know if they used a different rodbolt or if the pistons were lighter, those would be other key pieces of information to know.
The 4-bolt main doesn't mean much LT1s are more prone to rod bearing failure at high rpms than mains and IMO most mains that do spin happen from debris from a rod bearing starting to let go.
Again IMO tyhe rod bearing issue is more a rod bolt one, if the rod bolts stretch a little it lets the cap wiggle and the bearing gets eaten. Fractured cap rods locate the cap MUCH more positively, harder to rebuild though as instead of machining the parting line and rehoning they need to be bored oversize and special bearings used.
The 4-bolt main doesn't mean much LT1s are more prone to rod bearing failure at high rpms than mains and IMO most mains that do spin happen from debris from a rod bearing starting to let go.
Again IMO tyhe rod bearing issue is more a rod bolt one, if the rod bolts stretch a little it lets the cap wiggle and the bearing gets eaten. Fractured cap rods locate the cap MUCH more positively, harder to rebuild though as instead of machining the parting line and rehoning they need to be bored oversize and special bearings used.
12-22-2009, 08:01 PM
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the lt4 also had a better crank and pistons not sure about the rod i spin my lt4 up past 6500 at the track but its not a dd but i did have an lt1 spin a rod
12-22-2009, 08:04 PM
#17
The LT4 crank had undercut and rolled fillets, seeing as nobody is breaking the stock LT1 crank on a heads/cam application I fail to see the big benefit.
I also question the "better" pistons, I was under the impression they were just higher compression. Do you have any data to support your "better" statement?
I already covered how the rods were actually better.
a LOT of us have taken stock LT1 shortblocks to 6500 and beyond.
I also question the "better" pistons, I was under the impression they were just higher compression. Do you have any data to support your "better" statement?
I already covered how the rods were actually better.
a LOT of us have taken stock LT1 shortblocks to 6500 and beyond.
12-22-2009, 10:35 PM
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Good to hear, I have found a cheap cop Caprice LT1 with 80k on it, and want to use the shortblock and then go LE2 with it shifting around 6400. I will still be putting in a new Melling pump with high pressure spring and Canton pan for a little added insurance. This should be an ok combo if maintained well, right?
If your going as far as to replace the oil pump, Throw some arp rod bolts in there and eliminate the biggest fault in the bottom end.