[Gmecm] 7730 Maximum RPM limit

[Ryan Hess]

Welp, I wrote a QBasic program to pulse the parallel port, and hooked my laptop directly to the computer in car.  I tried taking some datalogs with tunerpro RT and freescan, and both have confirmed the findings...  It appears as though RPM/25 is directly reported via the ALDL stream.  It is sent as a single byte, which means that at a maximum of 255, the reported rpm value is 6375.  This is where it apparently maxes out.  I'm kind of surprised I hadn't noticed this before, but I guess the amount of time I spend above 6375 is minimal and close to my revlimiter, so....

I guess my next question is, how much work (ha!) would it be to turn RPM/25 into a 2 byte value?  Or...  would it be even simpler to change the rpm/25 measuring routine into an rpm/35 or 40??  What kind of complications am I looking at here?  Thanks all,

Ryan


Ryan Hess <rgmecm at yahoo.com> wrote: Interesting.  If that's true, I wonder if I can cut out unnecessary function calls (EGR, CCP, air injection, whatever else I can find) to increase that...  What is the failure mode when this limit is reached?  Does it just act like a revlimiter, or crash, or ??  Thanks btw...  it does help.

Ryan

Bill Shaw  wrote: Don't know for sure (which is why I kept my mouth shut!) but I seem to
remember reading about 7300 being the limit due to processing speed.

let us know what you find on the bench :-)

Bill

> From: Ryan Hess 
> Reply-To: gmecm at diy-efi.org
> Date: Mon, 17 Apr 2006 16:03:17 -0700 (PDT)
> To: gmecm at diy-efi.org
> Subject: Re: [Gmecm] 7730 Maximum RPM limit
> 
> I guess I'll have to build a test bench and find out myself, eh?  Or are you
> guys always this slow in replying? :-p
> 
> Ryan
> 
> Ryan Hess  wrote: Hi again,
> 
> I'm currently running a northstar on a 7730, using the DIS $a1.   Currently I
> have the revlimit set to 6500, and it works great, I've hit  it occasionally.
> However, I will be upgrading  to some better heads soon, which will allow me
> to rev even higher  without valve float.  7500 seems to be the magic number.
> After a rebuilt bottom end (I don't know for sure if I'd go this far...  but
> want to leave my options open), 8500 would be possible.  Now,  after reading
> about LT1 computers hiccupping at high rpm, my question  is- has anyone ever
> tested the "max rpm" the 7730 can handle and/or  have any guesstimates?  How
> does processor speed compare to other  aftermarket ECM's capable of high RPM?
> (eg holley, haltec,  etc)  I assume they run faster processors with more
> bloated  compiled code, so I wonder if they're in the same place "speed wise".
> 
> Ryan
> 
> 
> 
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