65CrewCabPW
eastern Oregon
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Daveinet wrote:What no offer for cheese with my wine? 
I do wonder about the cam for a couple of reasons. Most comment that you need a different cam to run fuel injection. The after market fuel injection manufacturers all say we can make it work with the original cam. But does that hurt the efficiency? I have no idea. This verssion of the 502 is the HT or high torque version, so the cam is set up for torque. But is it as good as it could be without sacrificing any significant power? I also have no idea on that either. As much as I've been around engines, I don't have the experience to interpret cam timing into good or bad efficiency. In the past, I have installed an offset key to lower the torque peak, but I don't think this motor needs that as the original design was for the torque peak at 2800 rpm. Edelbrock claims this intake shifts the torque peak to 3500 rpm, just by improving the breathing. Is the fact that the intake shifts the torque peak higher than the OEM design, does that make it less efficient? Is that a mismatch? I have no idea.
First, let me state, I'm a Mopar guy, so I have little familiarity with the GM engine. I just know that in the pursuit of MPG, I would NEVER choose a GM engine over a Chrysler, but that gets into an engineering discussion that runs over even my head at times.
Let me make some educated guesses, here...
1. Any cam that puts your peak torque at 3800 RPM is going to have a lot of overlap or reversion of exhaust back into the cylinder at low speeds. This is exaggerated by smaller throttle openings, especially with headers if they are not anti-reversion and/or designed for higher rpm, rather than low to mid range torque. This reversion or overlap ends up killing your burn efficiency at low speed by lowering the temperature and slowing burn rate. So, I would say that your cam's too large for the purpose you wish to have. For one, it appears to take your peak torque and efficiency into far too high RPM range for economy. My GUESS. I offer it free, and likely to be worth roughly what you just paid for it. I would have chosen something that peaks torque somewhere near the 2500, even if it decreases horsepower.
2. An accleration run should not be done in 1st, it should be done in 2nd, and you should have a mild curve, one that starts west or right and then south a little above your cruise rpm. If it's near flat, something is strange. I would be tempted to get an air-fuel gauge or monitor, they're not expensive, and you can watch real time A/F readout on your dash.
3. Your acceleration curve says that even though it feels like a rocket at lower speeds, it may not be running as efficiently as it should. You should be able to find the best timing curves for this engine and have it burned into your control computer.
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Takereasy
South Texas near Victoria
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Dave, what is the actual cam specs? Do you know? If it were me, I'd be looking way less than 300 on the overall duration, maybe around 275 degrees or so. I don't much care about lift unless we start talking intake design, but the duration / timing will have more to do with "what" you should be running for intake and exhaust. This will, along with intake and exhaust systems, dictate your optimal power band.
You best pulling power/effeciency will be torque peak - 10% so you stay within your Droop torque band. Of course that percentage is based on what you provide as well.
If your cam timing is too high, and you never cruise or pull within it's band, you will never experience the effeciency of the engine.
IE. Why build a HD TC88 for 6500 RPM if you always stay between 2500 and 3500?
Richard
* This post was
edited 06/26/08 09:58pm by Takereasy *
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Takereasy
South Texas near Victoria
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I just read 65CrewCab's post and most of it is on the money, except for the fact that mopar would beat out GM for MPg. I never could fill up my 69 RT if I left it idling. But again, it wasn't very effecient unless it was smoking the tires at 60 mph. Heck, I don't remember that 440 Mag ever being effecient.
I bet your cam'd up to much and you "are" going to suffer especially with your 10% overdrive. You double screwed yourself. You built a motor that likes rpm, but turned around and geared it to turn less rpm. You need to run it around in second to see how the mileage turns out. Keep it around 3000 or better the entire trip.
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Gale Hawkins
Murray, KY
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So Dave has built a hot rod engine to drag around a house?
65crewcabPW that was a good write up. I never really understood the cam factor before. I knew it was for racing and they did not idle well afterwards but I did not know what was going on at low RPM.
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Daveinet
il
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I think there is some confusion about what I have - maybe. Here is the engine specs:
Quote:
Horsepower 338 @ 4500 RPM
Torque 512 ft/lbs @ 2850 RPM
Compression Ratio 8.75:1
Block Gen VI Cast Iron
Crankshaft Forged 1053 Steel
Cylinder Heads Cast Iron Small Oval Port Gen V
Valve Size 2.065" Intake/1.720" Exhaust
Camshaft Type Hydraulic Roller
Camshaft Lift .480" Intake/.483" Exhaust
Camshaft Duration @ .050" 204° Intake/209° Exhaust
The cam did not change, it is still the OEM cam as shown above. The intake from Edelbrock is what caused the shift from 2800 to 3500 in the torque peak. Below is the graph from Edelbrock:
I'm assuming I get a little more because the above graph is for stock exhaust, where I'm running Tri-Y headers. Any more thoughts?
Dave
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Hikerdogs
Wisconsin
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Joined: 08/23/2004
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I think your sampling period for a determining mileage is too short and too early in the game. It took almost 12,000 miles to thoroughly break in our Ford V10. We started with a little over 7 mpg but by the time we had 12,000 miles on the clock we consistently got over 9 mpg.
Last week we drove 400 miles to Indianapolis towing our Jeep Wrangler and got 8.5 mpg on the way there. On the way back we drove the same course at the same speeds and only got 7.8 mpg. The weather and traffic were nearly identical yet the mileage varied almost 10%.
Another thing to consider is the ethanol mixed in with the gas. It can be up to 10%. Ethanol will only give about 80% of the mileage of gasoline. If you were unlucky enough to fill up at a station that had the 10 % mix it could reduce your mileage.
Hikerdogs
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Mike Hohnstein
Germantown, Wi
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I have a P-30 in a Airstream classic. Fresh reman 454 by an unknown rebuilder, but it runs well. The PO had the reman installed.
I added headers and a OD transmission. Lost all the emission******and expected great things.
6.5 mpg @ 2600 @ 65 mph pulling a 240D toad. PO told me he always got 8,running 3500 rpm but no toad. I dunno. The 502 is bigger than the 454, duh.
It occures to me there might be a reason Chevy used a 366 in thier vocational medium duties forever.
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Daveinet
il
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Hikerdogs wrote:
Last week we drove 400 miles to Indianapolis towing our Jeep Wrangler and got 8.5 mpg on the way there. On the way back we drove the same course at the same speeds and only got 7.8 mpg. The weather and traffic were nearly identical yet the mileage varied almost 10%. I think I have the answer, it was last week I made that same trip on I65. That's nearly the same mileage I got, so it was the week and the location and had nothing to do with the engine tunning, size and gearing.
Seriously though, it is encouraging that your mileage improved by 2 mpg once the engine was broken in. If I increase by 1 mpg once the engine was fully broken in, I'd be happy.
You know with the investment of this engine and everything I've done to it, I'm anal/paranoid about every aspect of it. Yes, we calibrated the fuel injection, but is it right? Which gearing should I run? Should I install a 4L85E? Will it make it worse or better? Is my cool ram air intake tubes good or bad? I have my head buried in the computer display datalogging every time I drive it anywhere. I have no idea where I've been or what everyone else saw on the way. I'm watching injector pulsewidth, O2 sensor, INT/BLM, throttle position, MAP sensor, instead of enjoying the scenery. Somebody tell me to chill.
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jeepman71
Colorado 80634
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Dave,
One thought that I don't think was mentioned is the exhaust in comparison to the total changes made. I see you are using the same exhaust that you used for the old (454) motor so the thought is that it should be fine. You are running about 11% more cubic inches. This is going to like a little more air flow. The air flow was addressed on one end of the motor but not the other.
Sounds like a fun project, good luck.
Jim
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Jim83Itasca
La Quinta Calif
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Joined: 09/16/2003
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I think there is some confusion about what I have - maybe. Here is the engine specs:
Quote:
Horsepower 338 @ 4500 RPM
Torque 512 ft/lbs @ 2850 RPM
Compression Ratio 8.75:1
Block Gen VI Cast Iron
Crankshaft Forged 1053 Steel
Cylinder Heads Cast Iron Small Oval Port Gen V
Valve Size 2.065" Intake/1.720" Exhaust
Camshaft Type Hydraulic Roller
Camshaft Lift .480" Intake/.483" Exhaust
Camshaft Duration @ .050" 204° Intake/209° Exhaust
That roller cam is dang near (close is dang near) perfect.....My 496 will have a torque monster (206 I)..(213 ex) @0.50 with a 112 LSA...
I don't understand which way you "keyed" your cam (advanced/retarded) but either way I doubt if you hurt it that much......
Now you also wrote "My A/F ratio is 14.XX which IF thats at cruise is way to FAT, I prefer a 15.2 idle, 14.9 cruise @3000 RPM and a 12.9 with a hill climb pushing the throttle wayyyyy down....That engine will have zero problems with a 3000 RPM and a 14.9 A/F ratio....
Your money and choice, Hope you can find the correct setup...
Jim
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