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| [GMCnet] More on FiTech questions [message #301250] |
Sun, 29 May 2016 14:16  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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Hi Gordon,
Letting the ECU control spark seems to be popular with people who are confident they have a reliable knock sensor installed in a location that can properly distinguish between pre detonation and other engine noises as it allows the system to dial in more advance under certain situations. To do so without a properly working knock sensor would be very risky to the health of the engine. By advancing more it appears to be possible to wring out one or perhaps even more mpg.
If you do not have such a knock sensor, then the electronic HEI distributor is a great choice if the mechanical advance mechanism is set to the needs of our 12000 pound motorhomes and if the vacuum advance also works properly. The HEI was used on millions of cars and trucks contemporary to our coaches with great success. Olds never did design and test a factory installed knock sensor on either the 455 pr the 403 that I am aware of. In fact a 403 was I believe the last GM carbureted engine to pass the ever more stringent emissions tests in all 50 states when finally phased out in the early 90s. It used an HEI distributor.
I use the HEI with the 600 hp (the only one available when I bought mine) FiTech EFI in my 1977 Clasco at the recommendation of the FiTech tech support people. It works well for our application. If the factory had ever designed a knock sensor for trucks using our gearing and our engines, I would probably use the ECU controlled spark that is standard with the FiTech 600 hp unit. The 400 hp unit does away with ECU spark control in order to sell at a $200 lower price point. Check with FiTech, but my understanding is their ECU spark control will NOT work with an HEI distributor, it requires a two wire distributor with the advance mechanism locked out.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed & hand crafted
in the 1907 former Masonic Temple building
in historic Kerby, OR
http://jerrywork.com
........
Message: 9
Date: Sat, 28 May 2016 13:04:24 -0600
From: Gordon Gibson
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] More on FiTech questions
Message-ID:
Content-Type: text/plain; charset="utf-8"
Jerry
I really appreciate your posts on installing a Fitech in one of your coaches - comments like this plus the fact that I was going to have to bear the
cost of buying a rebuilt Quadrajet to finish off my coach were what prompted me to go the Fitech route.
Full disclosure - although I have rebuilt old cars and motorcycles, my mechanical knowledge of anything more modern that the mid-60s is sorely
lacking. But rest assured - I am having the FI installed by a professional.
I specifically chose the 600 based on the understanding that the FI's computer module would control the spark advance of my "pointless" distributor.
Do I understand that according to Fitech, most of their customers stick with good old mechanical and vacuum spark control? And if this is the case,
any reason why? Is this what you did as well?
Thanks
Gordon
1976 23' Norris Upfit
Montreal West, Quebec, Canada
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] More on FiTech questions [message #301253 is a reply to message #301250] |
Sun, 29 May 2016 16:06  |
Dan Gibb
Messages: 24
Registered: May 2015
Location: Tucson, Arizona
Karma: 0
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Junior Member |
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Howdy Hi everybody,
I just purchased the 400 FiTech, haven't installed it yet. Am I the only one who has gotten the 400? Or does someone else have it too? From what everyone has read or used shouldn't it also work on our engines?
Dan Gibb
1977 Eleganza II
Tucson, Az
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| Re: [GMCnet] More on FiTech questions [message #301270 is a reply to message #301250] |
Mon, 30 May 2016 07:14 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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glwgmc wrote on Sun, 29 May 2016 15:16Hi Gordon,
Letting the ECU control spark seems to be popular with people who are confident they have a reliable knock sensor installed in a location that can properly distinguish between pre detonation and other engine noises as it allows the system to dial in more advance under certain situations. To do so without a properly working knock sensor would be very risky to the health of the engine. By advancing more it appears to be possible to wring out one or perhaps even more mpg.
If you do not have such a knock sensor, then the electronic HEI distributor is a great choice if the mechanical advance mechanism is set to the needs of our 12000 pound motorhomes and if the vacuum advance also works properly. The HEI was used on millions of cars and trucks contemporary to our coaches with great success. Olds never did design and test a factory installed knock sensor on either the 455 pr the 403 that I am aware of. In fact a 403 was I believe the last GM carbureted engine to pass the ever more stringent emissions tests in all 50 states when finally phased out in the early 90s. It used an HEI distributor.
I use the HEI with the 600 hp (the only one available when I bought mine) FiTech EFI in my 1977 Clasco at the recommendation of the FiTech tech support people. It works well for our application. If the factory had ever designed a knock sensor for trucks using our gearing and our engines, I would probably use the ECU controlled spark that is standard with the FiTech 600 hp unit. The 400 hp unit does away with ECU spark control in order to sell at a $200 lower price point. Check with FiTech, but my understanding is their ECU spark control will NOT work with an HEI distributor, it requires a two wire distributor with the advance mechanism locked out.
Jerry
Jerry et al,
Knock sensors were never an emission issue, but have always been a performance (including CAFE) and warranty issue. It is not as easy to do as one would hope. On the Chrysler 4.7 program. We cast a block with 9 extra bosses and had each of those machined to accept a sensor. Then it went to to a development cell where it had to be installed with the intended mount system on a subframe and an R4OD transmission. Then it was rung out with all the sensor outputs tracked by a data acquisition system and then the two tied winners were evaluated.
I am actually sort of impressed that the people here have been successful with putting knock sensors on 403, 455 and 500 blocks.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] More on FiTech questions [message #301296 is a reply to message #301250] |
Mon, 30 May 2016 19:03 |
gibsongo
Messages: 116
Registered: October 2012
Location: Montreal West, Quebec, Ca...
Karma: 0
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Senior Member |
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Hi Jerry
Thanks for the answer. I'll stick with the HEI distributor controlling timing via vacuum, etc.
Gordon
Gordon Gibson
1976 23" Norris Upfit
Montreal West, Quebec, Canada
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| Re: [GMCnet] More on FiTech questions [message #301349 is a reply to message #301250] |
Tue, 31 May 2016 20:17 |
rvanwin
Messages: 325
Registered: April 2007
Location: Battlefield, MO
Karma: 6
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Senior Member |
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glwgmc wrote on Sun, 29 May 2016 14:16Hi Gordon,
Letting the ECU control spark seems to be popular with people who are confident they have a reliable knock sensor installed in a location that can properly distinguish between pre detonation and other engine noises as it allows the system to dial in more advance under certain situations. To do so without a properly working knock sensor would be very risky to the health of the engine. By advancing more it appears to be possible to wring out one or perhaps even more mpg.
I have wanted to chime in here to clarify some of the misconceptions of how knock sensors (KS) are used in our application. The implications from most are that without a proper KS (and one was never engineered for the 455 or 403) you should not let the computer control the spark advance (SA). I think that is a false assumption and should not hold anyone back from desiring or proceeding with using a computer controlled distributor or our engines. There are several reasons for implementing an electronic fuel injection (EFI) system for fuel management. It precisely meters fuel under all conditions: cold starts and warmup (minimizes washing down of cylinder walls); altitude changes; immediate start-ups; immediate shut downs; higher pressure in fuel lines minimizing vapor lock (if pumps are installed properly). There are many excellent solutions for doing just fuel management: FiTech, MSD Atomic, Holley, Meqasquirt, FAST, Howell with EBL, each with advantages and disadvantages but most do an excellent job of metering fuel with self learning capabilities (either automatic or semi-automatic). In all cases, I think one will "feel" an increase in responsiveness over a Q-Jet. The amount of "feel" will probably be determined based on how well the Q-Jet is tuned. I suspect there are not many Q-Jets that are tuned to their optimum due to age, wear, etc. However, a well tuned Q-Jet will perform similarly to a fuel management only Throttle Body Injection (TBI) system and probably won't see too much difference in fuel economy. In fact, I don't think you can do too much to get better fuel economy because it takes fuel to push a 12,000 pound vehicle with a large frontal area through the air).
Most EFI systems, even the early ones back in the 80s, also controlled spark. Why? Partly to help meet emission standards, but, also, for increased performance. Most early implementations used KS as an added safeguard for the engines. Early KS implementations did not provide full protection for engines simply because the technology and engineering was not that sophisticated. Modern day KS implementation and Computer Controlled Spark does a great job, and, in fact, can detect excessive knocks when using lower octane fuels and will allow the engine to run with less than recommended octane without excessive damage (although not recommended).
I'm hearing people say they wouldn't run a computer controlled distributor on our engines because the KS sensor is not engineered for our engines and cannot protect the engine. By the same token, then you should not use a mechanically controlled distributor because there are absolutely no protection for the engine other than how good your hearing is. When I tune an EFI system that also controls the spark, I tune in much the same way you would tune a mechanically controlled distributor. I have a couple of known good spark tables (spark curves if you will) that I start with. Depending on how aggressive someone wants to be, I then increase the spark until the KS starts showing me some knocks in certain cells. At this point, I don't rely on the KS to continue to "protect" the engine, but pull out SA in those cells were knocks occur. It actually takes less SA retard to prevent knocking than it does to stop knocking once started. So what is done with a mechanically controlled distributor? You either use a very conservative initial spark advance setting with a timing light or if you want to be more aggressive you increase the initial SA setting. Then, if you hear knocks (pinging) when under heavy load you pull over to the side of the road and retard timing by twisting the distributor to retard SA. You now have effectively retarded spark by let's say 2 degrees across the complete spark curve. When I'm tuning SA on an efi system, I have up to 200 cells in which I can advance or retard timing. Typically, our engines are knock limited only when under heavy loads and that affects anywhere from 6 to 12 cells. I can change those to eliminate knocks and keep the other cells at an optimum setting for performance and fuel economy. It is the spark that can allow you to steal a couple more mpg in some cases (there's no guarantee in claiming better fuel economy with EFI because there are lots of factors involved with the health of an engine).
Bottom line is that I don't rely on the KS to continually notify the Electronic Control Module (ECM) that spark needs to be retarded but, rather, use it as a tuning tool and a protection mechanism if something happens to the engine that causes knocks to start occurring when previously there were none. This can be caused by getting a load of bad gas, something causing hot spots in the cylinder, a spark plug failure, etc. On my engine, I usually see the display monitor showing Knock counts at about the same time that I start to hear some slight pinging. The ECM reduces SA in 4 degree increments until the knocks stop then reintroduces SA until back to what is commanded or until new knocks occur. These changes are instantaneous I believe that saved my engine when I had a spark plug that failed. With a mechanically controlled distributor, I may have lost an engine. Also, the ECM has SA adders and subtractors based on various conditions (sensors inputs such as coolant temperature, inlet air temperature, change in throttle position (delta measurement), change in vacuum (measured by MAPP sensor and is also a delta measurement), etc. These all can mitigate the chances of knocks.
So, KS is a tool, not perfect in our application but good for tuning and good as a backup "protection" mechanism. Just as in the 80s and early 90s, the KS was not perfect but used as a backup "protection" mechanism.
If anyone is not installing an efi system solely because they are concerned that a KS will allow damage to their engine, then hopefully this discussion will dispell that notion. Sorry to be so long winded, but these discussions are difficult in just a few words.
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO
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