How to determine Redline?

What does it--piston speed, quality of rotating assy, (I've even heard valve float)? I've always thought that SB rev higher than BB, but I've seen some factory SB tachs at 5300, and BB at 6K+. Say if you have an L48, and you swap in a balanced forged SCAT rotating assy, how would you determine the 'redline?'

Run it up till it explodes, then back off 200RPM?:idea:

I don't know if you can determine the red line without sacrificing a test motor,and like Bird said when it let's go back it off 200-500 rpm or more and you have the red line.

I've heard of a calculation based on the relation of piston speed, bore diameter and mass.

BBShark said:

I've heard of a calculation based on the relation of piston speed, bore diameter and mass.

Click to expand...

There has to be more. I have seen different redlines on SBC's that were all the same except for C/R and cam. :flash:

With an all forged bottom end and I think your redline is going to be determined by your camshaft and valve springs more than anything else.

I would check with your cam manufacturer. Cranecams lists redlines and such on their website.

Lets just say there is a slight, VERY slight difference from a NASCAR engine or John Force's engine at 50 grand/copy and anything we are likely to build, by about 3000 rpm......

:stirpot::lol::devil:

youll generally find that 4000 FPM of piston speed with stock parts or 4500fpm with good quality forged parts is the reasonable limit on the lower end stress, but the valve control issues tend to become the limiting factor before the lower assembly causes problems, hitting the engines redline doesn,t mean the engines going to sustain damage, but it generally induces significant stress, stress that WILL eventually cause DAMAGE, it might happen instantly or require hundreds of repetitions BUT it will eventually happen if its exceeded

generally hydrolic lifters max out at about 6500rpm or lower
and stock rockers and valve trains rarely control valves well even with solid lifters above 7000-7500 rpm



http://www.csgnetwork.com/pistonspeedcalc.html

grumpyvette said:

youll generally find that 4000 FPM of piston speed with stock parts or 4500fpm with good quality forged parts is the reasonable limit on the lower end stress, but the valve control issues tend to become the limiting factor before the lower assembly causes problems

generally hydrolic lifters max out at about 6500rpm or lower
and stock rockers and valve trains rarely control valves well even with solid lifters above 7000-7500 rpm



http://www.csgnetwork.com/pistonspeedcalc.html

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GRACIOUS!!! A 3.48 stroke at 7500RPM=4350FPM; I take it 6500 is a safe bet (depending on the cam). Thanks everybody (most of my co-workers reiterated B2B, kwplot34).

keep in mind thats max PEAKengine rpm, that should only rarely be reached ,your engine will NEVER stay together if subjected to those rpms consistantly for more that brief moments before shifting, hold any engine at redline for more than a few seconds and bad things are likely to happen:crap:

keep in mind thats max PEAK engine rpms, that should only rarely be reached ,your engine will NEVER stay together if subjected to those rpms consistantly for more that brief moments before shifting, hold any engine at redline for more than a few seconds and bad and expensive things are likely to happen:crap:

run it on an engine dyno, the operator should be able to tell you everything you need to know, although it will probably cost you $400 for the info.
redvetracr

grumpyvette said:

keep in mind thats max PEAKengine rpm, that should only rarely be reached ,your engine will NEVER stay together if subjected to those rpms consistantly for more that brief moments before shifting, hold any engine at redline for more than a few seconds and bad things are likely to happen:crap:

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If you put a little thought into your build up and have a quality balance job the piston speed is not a limitation. It is not really a concern. The valve train will always fail first.

It takes big heads and cams to have the ability to spin a motor fast enough to blow it's self up.

Most motor builds the power drops off so fast that more rpm is point less.

I am a firm believer in digital sequential rev limiters

So I was thinking about the new LS7. One of the interesting things about it was that at the last minute they changed from forged to hyper pistons.

With their 7000rpm redline: that is 4666 fpm

I'm set at 6800 with hydraulic rollers

I hit the rev limiter a few times in this vid

[ame]http://www.youtube.com/watch?v=TlBURRMDllc[/ame]

I think this is a bit over 7000

The valves floated a bit

[ame]http://www.youtube.com/watch?v=mx1v-eHzWI8[/ame]

I have my rev limilter set at 6500 rpm,i have had the tach buried over 7k a couple of times,i have know idea what the motor was spinning since the tach only goes to 7k. That was before i put the digital rev limiter in.

There are two types of "redline" to consider. The one where you components are physically at the point of yield and the one that relates to the power band of the engine.

We ran major customer's 8.2L BBC for 200 hours on the dyno at full load and 4500-5500 r.p.m. This had to be successfully completed to ensure the durability of the final product. The only time the engine was stopped was to change oil at set intervals. No failures are acceptable. This was part of the development work on a re-manufacturing program.

By the way, General Motors recommendations from years past for factory High Performance BBC's were as follows:

396-427 Circle Track and Road Race 6600-7000 R.P.M.
454 Circle Track and Road Race 6200-6600 R.P.M.

396-427 Drag Race 7600 R.P.M.
454 Drag Race 7200 R.P.M.

These recommendations were for the factory engines, L-78, L-72, L-88, ZL-1, LS-6, LS-7. Etc. The difference between the 396-427 and 454 limits is due to the increased piston speed that cam with the longer 454 stroke.

I just run it until it quits making power, then I shift.:thumbs: