[Gmecm] 7730 Maximum RPM limit

Wed Apr 19 01:01:50 UTC 2006

Yeah, I found the ref period in the code.  Looks like it recognizes speeds above 6375, it just doesn't report them via the ALDL.  For tuning, having the engine speed reported is of critical importance.  Additionally, when running 7500 or 8500 rpm, having the tables cover that extra RPM would be of benefit.  VE and PE would probably be the biggest ones here, since spark shouldn't change much anyways.

Ryan

Darren Freed <darrenfreed at shaw.ca> wrote: What, specifically, do you want to do?  Extend tables?  If simply rev limit, that is based on a 2 byte value (ref period).  I've run my 3400DOHC up to 7500 rpm with a '7730 and also with a '6401 (sefi, which, btw, stays sefi all the way up, verified on the pcm bench) with no difficulty - ie the ecm didn't take a big dump.

darren

----- Original Message -----
From: Ryan Hess 
Date: Tuesday, April 18, 2006 10:34 am
Subject: Re: [Gmecm] 7730 Maximum RPM limit

> 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  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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