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Discussion Starter #1
Maximum Average Piston Speed (redline) is the rpm level where stress starts to damage parts,both the engines lower end strength and the engines valve float limits will have a huge effect on the engine ability to safely operate in the upper rpm ranges, most stock hydrolic lifter engines tend to float the valves by about 6000rpm due to weak stock springs and lifter pump-up so even if the bottom end can take the strain the piston smacking a valve will destroy the engine, keep that in mind!


Crank stroke x rpm divided by 6 = Piston speed in feet per minute.
Conservative speed is 4000fpm, but lightweight aftermarket parts can hit 5000fpm.

http://www.prestage.com/Car+Math/Engine+Building+Calculators/Calculate+Piston+Speed/default.aspx

http://users.erols.com/srweiss/calcrpm.htm

http://www.prestage.com/Car+Math/Engine+Building+Calculators/default.aspx


4000 feet per minute (FPM) of piston speed is generally considered max useing basically stock parts in a chevy v8. now no one in their right mind will tell you you can,t exceed that speed slightly but STRESS IS CUMULATIVE and if you EXCEED that speed regularly ,sooner or later IT WILL eventually FAIL!
4000fpm=48000 inches per minute
your crank stroke X 2= distance travelled bye the piston in ONE REVOLUTION
while its very true that its unlikely to fail the first or even the 100th time you exceed redline you are stressing the parts and the strain on those parts due to rpm levels climbs MUCH FASTER AS THE RPMS INCREASE than the RPMS,example the strain on parts spining 6000rpm is not double the strain imparted by 3000rpm, its more like 4-8 times higher (rod angles , rod stroke ratios, total stroke length, piston weight, crank counter weights, internal verus external ballance, etc. vary the results)
examples
327=7384 rpm
350=6857 rpm
383=6400 rpm
454=6000 rpm (454 big blocks with the 3/8 rods should not push that limit too hard, the aftermarket 7/16 rods and lighter weight pistons, can easily handle 7000rpm in a CORRECTLY set up engine)
 

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So, you are saying do not push a 350 past 6800? My friend has a LT4 like mine with a GM optional Hot cam and DRM reprogrammed his OBD II and he shifts at 7000 and he pulls my LT4 from 6300 to 7000 a car length in every gear and I shift at 6300 RPM?? How about NASCAR engines at 9000 plus????:huh:
 

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LAB said:
How about NASCAR engines at 9000 plus????:huh:
Nascar engine are run for 200-500 mile and are torn apart and rebuilt. In contrast top fuelers are run 1/4 mile and rebuilt (or at the least, torn apart and checked). Can you imagine going to the grocery and stopping 6 or 8 time to re-build the engine. grumpyvette makes some very good point. Part of my job at work is to track machine failure and to predict future failures. On a lot of our ewuipment we can back off the speed by 10% and double the life expectanct of the component part. BIG cost savings
 

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Discussion Starter #5 (Edited)
LAB
"So, you are saying do not push a 350 past 6800?"

yeah, push it past 6800rpm too many times and your looking for major replcement costs

"NASCAR engines at 9000 plus????"

NO PROBLEM, IF you spend close to $30,000 on parts, for each engine, and tear it down for inspection every 1000 miles MINIMUM for a TOTAL rebuild!


its only a matter of time before he destroys that LT4 (IF) hes really pulling 7000rpms on a regular basis, a few missed shifts, enought time,at those rpm levels, a few extra rpms and the engine will eventully fail!

84 GRANDSPORT
"So my 383 can go 6400 rpm's! "
"if the valvetrain and lower engines correctly clearanced and the engines running fairly new valve springs, the oil systems set up correctly,ETC. yeah you should be able to reach 6400rpm IF THE PROPPER CAM AND VALVE TRAIN GEOMETRY WAS USED AND THE REST OF THE COMPONENTS ARE CORRECTLY MATCHED, but I would not run that high with a stock cam and valve train
 

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grumpyvette said:
LAB
"So, you are saying do not push a 350 past 6800?"

yeah, puss it past 6800rpm to many times and your looking for major replcement costs


its only a matter of time before he destroys that LT4 (IF) hes really pulling 7000rpms on a regular basis, a few missed shifts, enought time,at those rpm levels, a few extra rpms and the engine will eventully fail!

84 GRANDSPORT
"So my 383 can go 6400 rpm's! "
"if the valvetrain and lower engines correctly clearanced and the engines running fairly new valve springs, the oil systems set up correctly,ETC. yeah you should be able to reach 6400rpm IF THE PROPPER CAM AND VALVE TRAIN GEOMETRY WAS USED AND THE REST OF THE COMPONENTS ARE CORRECTLY MATCHED
Thanks Grumpy Vette...I dont go that high but next time I race I am gonna....I hit 6000 1 time & it took it no problem! :)
 

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GrumpyVette,
Thanks for the advice, I will pass it on to my friend. Notice I shift at Stock Redline as I too read that the LT4 rods(powered metal) were not as strong as the 1970 LT1 Forged crank and rods from back then.(un happy when I found out that the 96 LT4 FI engine had a cast crank and rods) Read LT1 differences from the LT4 on the LT4 web site.:(
 
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