[Diy_efi] TPI cam limit.

[Becker, Damon Damon]

Wild cams do better on and sometimes require a richer mixture, more
advance and a higher idle speed.  Evaluate your stock ECU for these
types of requirements and consider aftermarket engine management if you
can't meet this.   

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
On Behalf Of John Gross
Sent: Saturday, November 26, 2005 9:08 PM
To: diy_efi at diy-efi.org
Subject: RE: [Diy_efi] TPI cam limit.

One major reason a lot of people have problems with larger cams on EFI
engines is because people aren't willing to raise the idle speed of the
engine.  You can't have an engine with a stock 600 rpm idle and a cam
with lots of duration and a narrow LSA.  On a 383 LT1, with 224/230
duration and a 113 LSA, I had a hard time getting the idle under 900
rpm.  At 900 rpm, however, the engine would idle smoothly, not jump
around or hunt, both at temp and cold.  BTW, that was a MAP car.  On the
engines we build a work, I can't tell you the cam numbers, but there is
definitely non-stock duration on the cams, and the engines absolutely
will not idle below 1300 rpm.  They find a comfortable idle at 1600-1700
rpm, however.

Long story short, placing a "cam limit" on an particular engine when
talking about idle quality is really only valid if you're talking about
trying to retain stock idle RPM.  If you're willing to raise the idle
speed to help retain the idle quality, you'll quickly run out of
manifold at speed on a TPI before you have idle problems.



>From: "Becker, Damon (Damon)" <damonb at avaya.com>
>Reply-To: diy_efi at diy-efi.org
>To: <diy_efi at diy-efi.org>
>Subject: RE: [Diy_efi] TPI cam limit.
>Date: Sat, 26 Nov 2005 20:41:52 -0700
>
>Filtration can help, along with vacuum manifolds (pneumatic receivers) 
>and such.  You can also "tune around" this type of thing by allowing 
>for a flat spot in the idle fuel tables.  If none of this works, then 
>you can go with a hybrid controller (hybrid speed-density and alpha-N).
>Camming an engine can frequently require the transition to an EMS to 
>correctly control the engine, depending on how your original ECU was 
>setup.
>
>If you are in the Denver area and need help with this, I am more than 
>happy to help you out.
>
>   _____
>
>From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
>On Behalf Of Joe Boucher
>Sent: Saturday, November 26, 2005 7:10 PM
>To: diy_efi at diy-efi.org
>Subject: [Diy_efi] TPI cam limit.
>
>
>I saw a reference just a few days ago claiming the practical cam input 
>lobe timing limit at .050' lift is 205 degrees.  Primarily the vacuum 
>signal jumps around too much.
>
>Is there a similar limit on the MAP driven TPI systems?
>
>Thanks,
>
>Joe B


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