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View Full Version : When building a custom engine-rev limit?



HyperDonzi
03-15-2004, 02:25 PM
Say you built a custom engine, how would you know what to set the rev limiter at? Determined by the cam I would guess?

Ranman
03-15-2004, 02:37 PM
The cam will determine the basic power band (HP and torque curves). If I were building a custom engine, it would be on an engine dyno for tuning when finished. From the dyno you will get the HP and torque curves. I would use this info to set the rev limit at slightly past the HP peak.

CDMA
03-15-2004, 02:43 PM
Build engine. Rev it up till it blows up. Rebuild engine and set rev limiter 3 rpm bellow fatal level. ;) ;) ;)

Chris

Last Tango
03-15-2004, 02:45 PM
A long time ago in a galaxy far far away I read an article that said to determine SHIFT points in your drag racing engine, run it on the dyno to determine rpm for max peak HP. The SHIFT point would be 10% higher than that. To me, that seems like a good RPM to set the rev limiter until the engine is broken in. After that, one can probably add an additional 10% from the HP Peak (total 20%) But keep in mind that max RPM at WOT in a race car lasts for a just moment. WOT in a boat lasts for a lot longer...
Probably of no help here, but then again...

BUIZILLA
03-15-2004, 02:52 PM
I can only speak from 30+ years drag racing experience, but we have found our best shift points to be about 200 rpm past peak HP dyno readings. We try and run out the back door, about 400-500 rpm past peak hp readings. As for boats, I shoot for propping at the exact peak rpm, maybe 100 higher. This isn't the bible, just what worked for us.

J :sombrero:

your opinion may vary

Rootsy
03-15-2004, 03:09 PM
it's a totally arbitrary thing tommie... dependent upon many factors. Valvetrain rpm capability, bottom end capability, driveline capability...

therefore the rev limiter should be set based upon the capability of the motor and it's internal components and whatever it is attached to... the main purpose of the rev limiter is to keep things from breaking...

GEOO
03-15-2004, 03:31 PM
Chris, :frown: That was my secret formula!!!

Seams like the question is pretty well answered.

I was nervous when they said they were going to take mine to 7000 on the dyno. (I forgot to mention the rev limiter was set at 6800rpm.) You should of seen the look on my face when she hit the 6800rpm rev limiter (hard). the engine almosted danced off the dyno stand. (they laughed and said my rods are a little longer now?) :eek:

HyperDonzi
03-15-2004, 03:38 PM
Poodle, nothing yet, but who knows what the future holds ;)