Safe RPM for a 408" Magnum?
- Thread starter jbc426
- Start date
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This!
Ok here is the QUESTION!
When you raised you shift point. Did it give you a notable BETTER KICK in the PANTS with the shift??????
ANSWER
If YES! The eng has passed its max HP and was losing exceleration when you shifted!
IF NO! You were still in you power band!
"Non" Forged Piston.....i agree with others, your shortening you engs life at them RPM's.
MY 408 has similar compression, Bigger cam but less air flowing stock RHS heads. My ET Gets longer if i shift over 5800 rpm. This was a custom cam also, with the focus on bottom end torque to combat the High altitude i live at (6800 feet) and stockies Torque converter.
My Hyd Roller cam is a .562/.550 lift 243/247 @.050 Duration. ground on a 102 intake center line.
When you raised you shift point. Did it give you a notable BETTER KICK in the PANTS with the shift??????
ANSWER
If YES! The eng has passed its max HP and was losing exceleration when you shifted!
IF NO! You were still in you power band!
"Non" Forged Piston.....i agree with others, your shortening you engs life at them RPM's.
MY 408 has similar compression, Bigger cam but less air flowing stock RHS heads. My ET Gets longer if i shift over 5800 rpm. This was a custom cam also, with the focus on bottom end torque to combat the High altitude i live at (6800 feet) and stockies Torque converter.
My Hyd Roller cam is a .562/.550 lift 243/247 @.050 Duration. ground on a 102 intake center line.
After thing about that for a moment......
You raised your rev limiter not you shift point. so there was vary little or no more RPM before the shift.
IF you can lower the shift point, the theory still hold true.
I don't think you need the cam, altho if its a custom one. Don't think you can return it.
Lowering you shift point could make all the difference.
You raised your rev limiter not you shift point. so there was vary little or no more RPM before the shift.
IF you can lower the shift point, the theory still hold true.
I don't think you need the cam, altho if its a custom one. Don't think you can return it.
Lowering you shift point could make all the difference.
Rev it until it blows, then back off a couple hundred rpm....
Then you know how much RPM it can take...
Then you know how much RPM it can take...
jbc426
Well-Known Member
It is still pulling hard at the shift into 2nd. My piston speed is 4145.9 FPM at a max of 6200 rpm. The guys who make the KB pistons say that speed is fine, They regularly run their pistons at 4333.3 FPM and higher with no problems.
The new cam should give me a significant boost in torque and hp from 2000 rpm and up to my new higher rpm 1st to 2nd gear shift point. I have no intention of spinning it higher. It's somewhat rare that I wind it to 6200 rpm as it is. The car just gets moving too fast when the throttle is wide open. Things happen pretty quickly with this build as it is, and I don't want to be driving like on the street like that as a rule.
I think your to focus on making it go fast by throwing new parts on it when there more power to be had with you present package by making it shift sooner.
Everyone has said that your current cam will be out of breath by 55 to 5800 rpm but you insist on running it to 6200.
My car will pull well past 6500! it just runs faster if i shift it at 5800.
Which will take you more time, and money? governor work in the transmission? or a new cam,lifter and Valve Spring?
I don't have one of these 200r transmissions, so i don't know.......
Everyone has said that your current cam will be out of breath by 55 to 5800 rpm but you insist on running it to 6200.
My car will pull well past 6500! it just runs faster if i shift it at 5800.
Which will take you more time, and money? governor work in the transmission? or a new cam,lifter and Valve Spring?
I don't have one of these 200r transmissions, so i don't know.......
jbc426
Well-Known Member
Those that say the current cam is out of breath at 5500 to 5800 are correct. I can hear it nosing over for the last 500 rpm or so. Fortunately, that won't be the case for long. A cam better suited for my intended use, which is shifting at 6200 rpm, is on the way.
The Extreme Automatics Stage 2 200R4 is awesome as is. It's one of the best upgrades I've made on my car. I just needed to tweak the engine's tune a bit with a cam upgrade to take full advantage of it. Thanks to the input I've received on this post, I did some digging and found that 6500rpm is a safe max "recommended" rev limit for my bottom end. The motor should never even see that, as the first gear shift into second occurs at 6200rpm. The remaining gears shift near 5900 rpm.
I thought I would be happy with a mild cam, but I found myself wanting more from the beginning. The prospect of having 50 to 80 or more horsepower at 6200 rpm for the price of a cam, valve springs and some gaskets was just too much temptation for me. I will be the first to admit it. I LOVE cars and motorcycles with prodigious amounts of horsepower and torque not to mention the beautiful sound of a loping cam at idle.
I've been hooked on high horse power and torque since I was 10 years old. Obviously, there's no hope for me at this point. I seem to be able to tell when one of my vehicles have enough power. That number is 710 hp on my 1970 5-speed E-Body and 170 rear wheel horsepower on my street bike. This new cam should put me around 490+ with my daily driver A-Body. I'm thinking I'll have the 9's, 10's and 11's covered with the 3 vehicles. The die is cast, and the money has been spent. Thanks to each one of you for your input. I appreciate the time you took to post your thoughts.
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