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Old 11-24-2015, 10:36 AM   #201 (permalink)
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Originally Posted by Formula413 View Post
I will never give up my LT1!

I never thought of that, very interesting. I'll have to give this more consideration and research. I'm leaning towards a Mazda3 with the Skyactive direct injection engine for my next car.
Hey Formula, are you referring to the 1st gen LT1 of 1970-72, the opt spark LT1, or the new released for 2014 6.2L GDI LT1. The new GDI engines are more efficient than any previous LS or LT (at least until the intake valves begin to coke to the point of disrupting the airflow, after that they degrade quite quickly in efficiency). The LS was more efficient than the 90's LT1 due to a much more robust PCM and improved cylinder head design as well. After a GDI engine's intake valves begin to build more than a light deposit (generally 5-10k miles depending on engine and make) the airflow into each cylinder is affected so the cylinders with the more severe build-up (those closest to the point of entry, the PCV connection to the intake manifold) will have less air entering so they run richer, the ones with the least amount of coking, those furthest from the point of ingestion, will run leaner as the upstream O2 sensor for that bank is reading the bank as a cumulative whole, so the PCM commands the same fuel amount for all cylinders in that bank, so they soon become less efficient in not only power and fuel economy, but also hydrocarbons released from a less complete burn.

As designed when new, they are a good deal more efficient for the following reasons:

Fuel is atomized far better exiting the injector at 2000-3000 PSI than 45-55.

Compression ratio is much higher (11.5:1 common vs old 9.5:1 or so) due to
the elimination of fuel present during the compression stroke. The fuel is not introduced until mere milliseconds before ignition, and this requires a different complex topography of the piston top resulting in most of the fuel being burned before it can make contact with most of the piston top.

The greater amount of ignition timing advance also produces a more efficient burn and thus more power/MPG.

So tons of advantages to GDI, just the unexpected negative of fuel no longer touching the backsides of the intake valves allows deposits to begin forming as soon as the engine is run, and as there is no cooling spray of fuel either, the valves operate at a far higher temperature than port injection, so these are not soft deposits like the carbureted or port injection engines of past, but very hard crystalline bakes on deposits, thus the wear to the guides as every cycle that valve makes is pulling this abrasive coating into the softer guide (most are bronze alloy) as well.


Anyone wanting more in depth discussion or questions answered, just ask. I am not able to spend much time due to work load, but always willing to share as this is the field I work in daily.


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Old 11-24-2015, 12:25 PM   #202 (permalink)
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Quote:
Originally Posted by GDI Tech View Post
Hey Formula, are you referring to the 1st gen LT1 of 1970-72, the opt spark LT1, or the new released for 2014 6.2L GDI LT1.
The Opti LT1 found in my 1997 Firebird Formula. 102,000 miles on the original Opti and still running great. I did put a new cap and rotor on when I changed the water pump.

Just curious, what would you suggest if I'm looking at a GDI car with 70-80K miles on it?
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Old 12-09-2015, 04:25 PM   #203 (permalink)
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I would really want to check valve guides for excessive wear. This takes a bit of work, and the old "wiggle test" is not accurate, so it is measuring the amount of deflection the valve can move side to side in the guide. Then if possible, remove the throttle body and use a boroscope to look into the runners until you see one of the intake valves up close.

What make/model/year/engine are you looking at? I can give you better tips.
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Old 12-09-2015, 06:07 PM   #204 (permalink)
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What make/model/year/engine are you looking at? I can give you better tips.
2012 or newer Mazda 3 with the 2.0 Skyactive engine.
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Old 12-10-2015, 11:00 AM   #205 (permalink)
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Good car. Yes, follow what I described but that intake manifold is internally shaped with the long runners curling around it is near impossible to get a boroscope into a runner and to the valves. So removing the IM is the best. Do not be alarmed at the deposits unless they are more than twice the original size of the valve, they are not hard to clean on these as the intake manifold is in the front of the engine. Then with the IM removed you can look into the ports and there will be 2 intake valves per port. Pick one that the valves are fully open, or turn engine over until one is. Then with a needle nose pliers you can grab a valve and "wiggle" it. It should barely have any deflection side to side. If it seems excessive then at higher RPM's the valves are unstable and would need head removed and old guides pressed out and new ones installed.

Be aware all GDI engines will have this coking pretty severe. Mazda, like all the newer GDI engines has this issue on the pretty severe side, but it is a great engine design.

So to summarize, if you do not have the opportunity to remove the IM, just drive the car and look for misfire codes, etc. You know from your F body when an engine is running well. Make sure to check oil level before you start it also. If it runs/rides/drives good then just deal with the manual intake valve cleaning after the purchase. If you need step by step instructions, I will be happy to provide them.

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Old 03-29-2016, 11:49 AM   #206 (permalink)
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Good list - but why side mirror abscent or remove - I am very used to it and cant go without it
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Old 09-16-2016, 07:59 PM   #207 (permalink)
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what about spark plugs? What are the best a spark plugs to increase mpg?
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Old 09-17-2016, 11:38 AM   #208 (permalink)
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Originally Posted by sunita83 View Post
Good list - but why side mirror abscent or remove - I am very used to it and cant go without it
There's a small improvement in aerodynamics when the mirror is removed. Most people don't feel the gain is worth the inconvenience. Some people have tried internal side view mirrors which are not a perfect solution.
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what about spark plugs? What are the best a spark plugs to increase mpg?
It's unlikely you would see any improvement as long as your plugs are the correct ones for your car and clean/properly gapped.
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Old 09-18-2016, 09:32 PM   #209 (permalink)
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what about spark plugs? What are the best a spark plugs to increase mpg?
I have seen some ignition coil packs claim to give better economy, but have never tested them myself.
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Old 09-19-2016, 08:43 AM   #210 (permalink)
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The best spark plugs are OE spec.

Cars' machine spirits are picky about the plugs you give them and while a "better" plug may be better in some other application, it's not the plug that the engineers designed your engine around.

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Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

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