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[GMCnet] Fi Tech - any downwsides [message #299475] Fri, 22 April 2016 11:43 Go to previous message
glwgmc is currently offline  glwgmc   United States
Messages: 1014
Registered: June 2004
Karma:
Senior Member
I’m not John,

But, the answer is yes, the FiTech ignition control is an advance curve programmed into a table without a knock sensor. It needs a locked out standard distributor (not HEI) to work. Most of the FiTech support people with whom I have spoken say they run their own classic/muscle cars using the HEI distributor. When Dick Patterson discussed this with FiTech at a trade show, he found the curve to be about what he programs into his HEI units designed for our GMCs. I had him curve one of his HEI distributors for my FiTech application in the Clasco and it seems to perform well.

The 400hp unit was not available when I purchased my 600 hp unit from FiTech - or at least I was unaware of it at that time if it did exist then. The design of the throttle body is the injectors do not squirt directly into the area of the throttle butterfly plates. Instead they squirt into an annular chamber that runs all around the throttle body. Small holes in the inside of the throttle body direct the pressurized fuel from the injectors into the throttle body all around on top of the throttle butterfly plates which they say delivers better atomization. It is not clear to me whether there is any real world difference between the two sizes of injectors given this delivery mechanism. All I know is the 600 hp unit works very well for me. I had one person off line tell me I should be experiencing bogging issues given the size of the injectors in the 600 hp unit. I am not. The only anomaly I have experienced is on two occasions while trying to reset the manual idle air back to the factory setting (I improperly moved that adjustment during installation) I experienced a bog right off idle when first firing up the engine from a cold state and driving off immediately. I have not experienced that since I think I got the manual idle air back close to where it belongs.

Most of the folks who are using computer based spark control with a knock sensor say they are able to achieve more advance without pre-ignition and so experience perhaps a 1 (some even say 2) mpg gain in fuel mileage. Some say they do not. Using the HEI distributor curve in both the Clasco with the FiTech EFI and the Royale with a Patterson Qjet I can’t readily tell any difference in fuel mileage. There is a lot of difference in throttle response, altitude compensation, immediate starting, etc. Lots of variation in our old beasts, I guess.

Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR

glwork@mac.com
http://jerrywork.com

==============
Message: 12
Date: Fri, 22 Apr 2016 09:37:58 -0400
From: Ken Henderson
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Fi Tech - any downwsides
Message-ID:

Content-Type: text/plain; charset=UTF-8

John,

In addition to the restriction to points type distributors, it's my
understanding that the only ignition "control" is that the advance curve is
controlled by software tables. That is, there is no knock detector
providing feedback and real time control of advance.

Is that correct?

Thanks,

Ken H.

On Fri, Apr 22, 2016 at 8:53 AM, jhb1 wrote:

> Hi Gordon
>
> I originally ordered the 400hp unit but kept getting the delivery pushed
> back. I ended up ordering the 600hp unit the differences between the two are
> injector sizes and the 400hp unit does not support ignition control. The
> ignition control only works on points type distributors early models
> non-HEI.
> Hope this helps
> —
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Jerry & Sharon Work
78 Royale
Kerby, OR

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