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  #16 (permalink)  
Old 06-18-2008, 11:52 AM
406cu.in. of tire smokin' fun
 

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They stopped the "winter mix" of 10% ethanol at the end of last month. That just brings stoich down to 14.1 anyway. I'm not sure how that relates to WOT AFR, but the fuel I put in it should have been the good stuff.

If it is misfiring at higher RPM's, how do you find something like that? Like I said, the plugs look identical to me, there doesn't appear to be any vacuum/exhaust leaks, the exhaust temps at the headers are close, and the compression is good on all of the cylinders. Any other tests I'm missing?

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  #17 (permalink)  
Old 06-18-2008, 02:19 PM
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Originally Posted by Pre-Tuner
Oldbogie, I'm just South of you in Tacoma.

When I started this project, I was only hoping for 100 more HP than what I started with, which would put me at 300 at the crank. Of course I hope for more, but I didn't want to be completely disappointed when my 400 HP dreams were squashed by 300 reality.

I am running a 454 TBI with small 454 injectors. The 350 injectors were rated at 68#; the ones I have are the smallest 454 injectors at 75#. 80# and 90# are also available. The actual throttle body is a Holley, but the injectors are GM since the Holley ones are aweful. I'm running 18psi to these injectors at WOT and the spray looks good when I'm parked and I rev it up.

Everyone I've talked to seems to think that this engine combo should make it's peak power at 12.3-12.8:1 AFR, which is part of the reason that I think that it being 11:1 is a problem. It should have fallen over way before getting that rich.

I'm not sure what you're saying about it's possible to be over fueled and still be lean, because the way I see it "lean" by definition is under fueled. If I'm wrong, please explain it to me.

The engine only has about 3500 miles on it and I have checked the compression about 1000 miles ago. Everything seemed great then, and it doesn't run any different now.

The O2 system the dyno place had they said was calibrated. They were also surprised by the fuel requirements so they changed the sensor with no change in results. My WB also reports rich.

I'm running a 170* thermostat and this was on a 69* day.

I haven't decided yet if I'm going to replace just the Y-pipe or the headers also. We'll see where that leaves me.
Let me start with fuel from a latter comment of yours, Tacoma is somewhat off my beaten path though I do get to Pyuallup now and then when taking my wife's PRIUS into the Toyota dealer where she bought the thing for scheduled maintenance. But as far as alcohol in fuel goes, in Seattle and Everett, the two ends of my day to daily life, 10-12% ethanol is in the fuel year around.

What I was saying about an engine running as if it were lean but not showing on the AF tester is that engines, especially carburated or TBI engines that are running a cold manifold (large ports or throttle bores also exacerbate this problem) have mixture atomization and distribution problems. To get to a sufficiently homogeneous mixture that will burn adequately, it is possible that an excessively rich mixture has to be used. The excess fuel in this case is just thrown away to be burnt in the exhaust manifolds if an AIR system is present and or in the catalytic converter. you have to keep in mind that an O2 sensor only reads the available oxygen content and makes assumptions based on throttle position, load from the vehicle and manifold vacuum as to how that relates to mixture ratio. This is not a measurement of mixture ratio per-se, it's a computed guesstimate.

With a 170 thermostat the fueling program in the computer may still be in cold start mode. The 454 TBI is quite large for a 350, untill you get up around 5000 RPM you just can't get enough velocity to escape reversion which is a feature of this kind of cam. So you can get into a place where the intake isn't hot enough to adequately vaporize the fuel into the passing air and reversion is pumping mixture back out the TBI. All of this is a compromise, you've got to find what the engine likes rather than assume that there's power in cold air, it isn't that easy.

The cam you're using is pushing the upper limits of the sensors to adequately discriminate small changes in loading, throttle position and how that relates to manifold pressure. This isn't an issue of computer programming, this is a problem of getting adequate signal discrimination from the sensors. Edlebrock will only go to a 194/214 degree cam with TBI. When idle vacuum decreases to around 14 inches MAP managed systems start having real problems with adequate sensory discrimination. Getting into this much cam timing with MAP TPIS is about the only organization I know of that is willing to go there with these systems, I suspect they use better sensors than those of these earlier factory systems.

As far as chassis dynos go, I not convinced that you can relate anything from those things into crankshaft horsepower. While the industry would have everyone believe that there's only a 20 percent loss in the drive train, I know that Ford engineering in a rear wheel drive vehicle with an automatic transmission considers the installed power loss as read at the rear wheels to be as high as 47%, this is extremely vaiable with gear ratios as well. Most purveyors of chassis dynos do this with the transmission in second gear, the purpose is to hold driveshaft revs down as these things are known to come out when turning fast. In this gear the engine is turning fast thus the accessory and exhaust losses are maximized. An automatic with a locking converter isn't so that loss is maxed and if you're running a high stall converter it's worse. Then you've got the losses in the differential which are considerable and if it's a posi or a locker, higher still. There are also considerable losses in the tires. For comparison a person can push a the weight of a 5 ton 4 steel wheel rail road truck on flat steel rail. The same person cannot push a rubber tired 5 ton street driven truck on flat concrete. So there is a lot of power lost just to move the tire. Also, the chassis dyno cannot read any power beyond where the tire breaks traction. So there are a lot of effects that can make the results of a chassis dyno run look a lot different, had that engine been run on a crankshaft dyno.

All-in-all the fudge factors with these things are getting to be a major portion of what the engine is even capable of, so I begin to develop a lot of disbelief in these numbers. If you read Car and Driver and have some techncial expertise in automobiles, over the past few years you'd think these new cars are built to a whole new set of physics rules. Reading the fine print you find that these guys do a lot of "Dry Labbing" rather than testing. Top speed in an overdrive gear being calculated at the engine's red line. I've seen damn few engines capable of reaching red line in 1 to 1 drive let alone in overdrive.

As far as your engine is concerned, if it wants 11 to 1 mixtures as the place where maximum power is being developed, then let it have it and stop worrying about what the experts say it should be, it is what it is.

Bogie
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  #18 (permalink)  
Old 06-18-2008, 11:17 PM
406cu.in. of tire smokin' fun
 

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We have fuel delivered to the place I work (not a gas station though), and the guy delivering said the winter mix stopped at the end of last month. This makes sense because I noticed an increase in mileage from my daily driver. The "may contain 10% Ethanol" stickers stay on the fuel pumps all year long. Maybe it's different where you are???

The manifold isn't really any different than what came with it, other than being compatible with vortec heads. It still has coolant flowing through the casting and it isn't some monster that makes the air cleaner stick up any higher than the original one did. I don't know how cold this would make it. Also, I am using very little acceleration enrichment (pump shot) which tells me that I'm not losing much fuel atomization in the manifold.

As for the TBI being too large, the size of the 350 TBI can only flow so much air to meet horsepower requirements. I can't remember the numbers, but I remember purchasing it because it was going to end up being a bottleneck for me. At higher RPMs, there is a ton of air flow so I doubt improper fuel atomization could be my issue, especially with the near double PSI I'm running to the injectors.

The wideband O2 sensor doesn't give the ECM any information at all. It is a completely different system that doesn't have anything to do with the TPS, MAP, or any of the other sensors. I just use it as a tool to log data. I understand it could be reading wrong though, especially with a misfire. It is calibrated in a separate process to fresh air. This is the only sensor that would really be affected by what I'm doing. It's an older system and there are only two sensors that a big cam would have any effect on; the MAP and O2, and I'm not using an O2.


It idles at 16-17 in vacuum. This is closer to the limit, but not to the point of being inaccurate. In the programming there is a MAP filter which will smooth out the reading (because of the fluctuations at idle) and will help correct for cams that are too large. I haven't even had to increase it because my idle is just fine. Aside from that, my problem is at WOT and the MAP sensor is reading that just fine. At WOT I'm at 100-101 MAP which means my air intake, intake manifold, and TBI are not presenting any air resistance problems.

The colder thermostat doesn't have any effect on the ECM because I'm running open loop anyway. The ECM only needs to see 160 degrees to go into closed loop, or my ECM does anyway.

I'm less concerned about the actual dyno numbers because I know there is wide speculation about losses and the accuracy in general. The fact that this engine needs 11:1 AFR when every other engine needs less is where my concern lies. I've seen dyno slips of guys that have nearly identical setups with the exact same transmissions and rearend gears putting out far more HP with far less fuel. Inaccuracies aside, there are huge number differences.

There is something different about my setup that isn't right yet and I need to find out what it is. Other than WOT, the truck runs great, even under higher loads up hills.
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  #19 (permalink)  
Old 08-12-2008, 10:02 PM
406cu.in. of tire smokin' fun
 

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Found the problem! I haven't dyno'd it yet, so I don't have hard evidence but she runs a LOT better. I was looking into changing the Y-Pipe and decided to change the headers to ceramic coated ones while I was there. The headers aren't much different but the Y-Pipe is now 2.5" instead of 1 7/8". Right off the bat I noticed that it was running more and more pig rich as I was making the RPMs rise, indicating that opening the exhaust worked. Before it took 11:1 to make the most power and now 11:1 was making me lose power as it should have in the first place. I spent an hour last night tuning it down and it runs a whole lot better. Like I said, I haven't been to the dyno yet, but I'm guessing it's a 20HP gain or more at the wheels.
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