Ageing cars w/ speed density
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Joined: Jun 2005
Posts: 1,834
From: Indiana
100k LT1 + Speed Density = Bad perfomance
I have heard that since my car 93' uses speed density and thus a table to calculate the fuel mixture not MAF, as the engine gets older since it doesnt have MAF to compensate for engine deterioration it still used the old tables it used when it was brand new which can lead to a loss of perfomance in a older engine. I got 100k. Is this correct? Should I get a mail order tune?
Last edited by Jazsun; Nov 4, 2005 at 10:08 AM.
Thread Starter
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Joined: Jun 2005
Posts: 1,834
From: Indiana
Re: Ageing cars w/ speed density
Oh yeah my gas millage sucks to I get like 13-14mpg in city. Duno if thats normal but it seems a little low considering the sticker was 17 and I do have some mods which should freeup some millage. I have replaced everything that I can to help millage such as plugs/o2s/wires...except fuel filer hmmm maby I should anyways im not complaining just asking if I should get my pcm tuned I could use a little more perfomance too.
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Joined: Aug 2002
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From: Scottsdale AZ
Re: Ageing cars w/ speed density
As far as proformance, I think mine got better or stayed the same. Heck it trapped 102.5 with just a catback, cai, and 3.42's and its an auto. All with well over 100k on it.
As for the MPG all those mods you have done also make the car faster and more fun to drive. That can be counter productive in your quest for better savings. But yours sounds about right for city.
Faded
As for the MPG all those mods you have done also make the car faster and more fun to drive. That can be counter productive in your quest for better savings. But yours sounds about right for city.
Faded
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From: Hell was full so they sent me to NJ
Re: Ageing cars w/ speed density
The only difference between speed-density and MAF is the way the PCM gets the number for mass air flow. In the MAF system, it comes directly from the MAF sensor. In speed-density, the PCM does an internal calculation which involves RPM, displacement and a value for volumetric efficincy (VE) from a lookup table. And then it adjust things based on the density of air, using the MAP and IAT sensor data.
It all comes down to how good are the VE tables? If something has altered the engine's "breathing', the tables lose accuracy. That could be the simple result of a CAI or a set of headers. "Age" would seem to be a minor consideration, maybe things like ring wear or valve leakage that affects VE.... but I wouldn't necessarily sign a 100K mile 93 up for AARP membership based on that small affect. Your performance mods will have made a larger difference than the "aging".
It all comes down to how good are the VE tables? If something has altered the engine's "breathing', the tables lose accuracy. That could be the simple result of a CAI or a set of headers. "Age" would seem to be a minor consideration, maybe things like ring wear or valve leakage that affects VE.... but I wouldn't necessarily sign a 100K mile 93 up for AARP membership based on that small affect. Your performance mods will have made a larger difference than the "aging".
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