Great day at the dyno!

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a70duster

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Hello all, last Friday (3/21/25) I went to a dyno shop in Denver for my first time. ALL my tuning has been either at the 1/4 mile track or street-butt-dyno. I have a method down that I thought worked fine. First some background...

Three years ago I resurrected my '70 Duster drag car that sat for 20 years. I made it to Bandimere the last month before they closed in Oct 2023. It was so busy there that I barely got four runs in. I was also dealing with intermittent demons so I never got a chance to deal with tuning. Plus the car was pretty well dialed in 20 years ago.

Summer of 2024 test and tune schedule was Fridays at Pueblo (3 hours away). I switched from $12 110 Sunoco to E85 ($2.25). I added E85 metering plates and bumped up the jet 10 sizes. It seems like the car was fine just running 3 - 4 tenths slower. I was also having a little struggle with the cam and the torque converter. Again I didn't play with timing or jet changes because of mechanical issues.

Over last winter I ironed out all the issues and desided to try a dyno. The shop I went to had an owner that was down to earth, super friendly, let you tune the car while on the dyno and let you operate the car. The 1st run showed how bad my tune was. AFR started at 17:1 and crept into 15:1. The owner stopped my run at 5k RPM and said the car was WAY TOO LEAN.

So after 5 dyno runs of bumping up the jet sizes (and having a header bolt back out and dump a gallon of coolant) I got best power via the carb.

The next two runs were on 100 HP NOS and the final two runs consisted of bumping the timing from 35° to 40° for best power.

After I was done with 90 minutes of dyno time the car picked up at least 40 HP across the board AND tuned out a dangerous lean condition. The NOS runs showed me that the AFR were safe. I got A LOT done. That was the BEST $150 I spent on the car.

Red is my first run, blue is best power NA and green is the best NOS run.

20250321_140849.jpg
 
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The car is a 1970 Plymouth Duster with a 383 and 440 crank. The car runs low 11s at 5600 ft elevation. I've gotten a few runs in the 10s.

20250321_112207.jpg
 
a70duster said:
Thanks, as I was infomed ethanol burns slower than petrol. Also air/fuel burns slower at higher elevations. Repeated runs on the dyno consistently showed a power increase.
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What heads are you running, how much compression and heat range of spark plug.

Also, is this a curve or locked out?
 
I'll drop this in here because I had to look it up.

I've burned a lot of methanol in my life but never ethanol. As I expected the advice given the to the OP was wrong.

Here is the truth.


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No, E85 burns faster than gasoline, not slower, due to its higher volatility and faster ignition time.

Here's a more detailed explanation:
  • Faster Ignition and Flame Propagation:
    E85 fuel has a faster ignition time and flame propagation compared to gasoline.

  • Higher Cylinder Pressure and Power:
    This faster burning leads to higher cylinder pressure, which can result in increased engine torque and power, potentially gaining up to 20%.

  • Cooler Burning:
    While it burns faster, E85 also burns cooler than gasoline, meaning less heat buildup in the engine.

  • Lower Energy Density:
    Ethanol, the primary component of E85, contains less energy per unit volume than gasoline, which can lead to a decrease in fuel economy.

  • Increased Exhaust Gas Flow:
    The faster burning of E85 can also lead to increased exhaust gas flow, which can allow turbos to spool quicker.

That is way too much timing unless the OP has some iron head.
 
Newbomb Turk said:
I'll drop this in here because I had to look it up.

I've burned a lot of methanol in my life but never ethanol. As I expected the advice given the to the OP was wrong.

Here is the truth.


AI Overview
Learn more

No, E85 burns faster than gasoline, not slower, due to its higher volatility and faster ignition time.

Here's a more detailed explanation:
  • Faster Ignition and Flame Propagation:
    E85 fuel has a faster ignition time and flame propagation compared to gasoline.

  • Higher Cylinder Pressure and Power:
    This faster burning leads to higher cylinder pressure, which can result in increased engine torque and power, potentially gaining up to 20%.

  • Cooler Burning:
    While it burns faster, E85 also burns cooler than gasoline, meaning less heat buildup in the engine.

  • Lower Energy Density:
    Ethanol, the primary component of E85, contains less energy per unit volume than gasoline, which can lead to a decrease in fuel economy.

  • Increased Exhaust Gas Flow:
    The faster burning of E85 can also lead to increased exhaust gas flow, which can allow turbos to spool quicker.
That is way too much timing unless the OP has some iron head.
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For reference only, the few turbo big block mopars I’ve crossed paths with made the best power NA (no boost) in the 37-39 degree range with typical 906 heads.

The turbo motorhome 440 they tested on engine masters made best power before boost at 42 degrees on westechs dyno. It had mid 70s smog heads on it and 7:1 compression
 
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E85 has a very high latent heat of vaporization, not quite to the level of methanol but much higher than gasoline. Typically if you can run more timing with e85 than you did on gas it’s because the the combo on gas was octane limited.
 
TT5.9mag said:
For reference only, the few turbo big block mopars I’ve crossed paths with made the best power NA (no boost) in the 37-39 degree range with typical 906 heads.

The turbo motorhome 440 they tested on engine masters made best power before boost at 42 degrees on westechs dyno. It had mid 70s smog heads on it and 7:1 compression
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That’s why I asked him what heads and what the curve looks like.

If he’s locked out he’s just killing torque and power all around peak TQ.
 
All right - lots of great input. Thanks for correcting me - I was passing out bad information.

The car
- 383 0.060" over
- 440 crank turned down to fit in a B block
- stock 383 rods
- JE "pop-up" pistons, 14.1:1 compression
- 906 cylinder heads with oversized valves
- Autolite 85 spark plugs
- roller cam with ~0.57" lift and ~240° duration
- ARP fasteners (heads, rods, mains)
- Factory mag pickup distribution with a CDI module, distributor is NOT locked out
- 727 with ~4500 stall converter
- 4.10 spool with 28x10.5x15 inch slicks

I tuned with Sunoco 110 25 years ago with timing and jetting. The best times I got were with 78 jets in an 850 Holley and 35° timing.
 
trimethylpentane is a reference only and should not be used to compare burn rates of typical gasolines (or e85 for that matter) as there are many many additives affecting burn rate in standard gasolines. The amount of lead time (timing advance) is more closely related to chamber type, style, and shape, as well as plug location and style of piston (dome, flat top etc) than the burn rate of the fuel being used.
 
a70duster said:
All right - lots of great input. Thanks for correcting me - I was passing out bad information.

The car
- 383 0.060" over
- 440 crank turned down to fit in a B block
- stock 383 rods
- JE "pop-up" pistons, 14.1:1 compression
- 906 cylinder heads with oversized valves
- Autolite 85 spark plugs
- roller cam with ~0.57" lift and ~240° duration
- ARP fasteners (heads, rods, mains)
- Factory mag pickup distribution with a CDI module, distributor is NOT locked out
- 727 with ~4500 stall converter
- 4.10 spool with 28x10.5x15 inch slicks

I tuned with Sunoco 110 25 years ago with timing and jetting. The best times I got were with 78 jets in an 850 Holley and 35° timing.
Click to expand...


Do you have a graph with torque on it?

Also do you remember you initial timing number and at what rpm the curve is in?

I’m not surprised with those heads at your timing numbers. Just curious about the shape of the curve.
 
Newbomb Turk said:
Do you have a graph with torque on it?

Also do you remember you initial timing number and at what rpm the curve is in?

I’m not surprised with those heads at your timing numbers. Just curious about the shape of the curve.
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I did not get a torque curve, the dyno guy and I were shooting for best power (his recommendation). I'd start the dyno run rolling in 3rd gear at ~3000, he'd signal me to floor it, RPM shot up from a loose converter, my tach then was at ~4000 for a couple of seconds and then the RPMs climbed to 6000 rpms. The run lasted about 10 seconds.

Initial timing was at 35° BTC and total timing is in by 3500. I don't lock out the distributor for the ease of starting the car.
 
TT5.9mag said:
trimethylpentane is a reference only and should not be used to compare burn rates of typical gasolines (or e85 for that matter) as there are many many additives affecting burn rate in standard gasolines. The amount of lead time (timing advance) is more closely related to chamber type, style, and shape, as well as plug location and style of piston (dome, flat top etc) than the burn rate of the fuel being used.
Click to expand...
I was tuning for best power. The jets could be a little bigger but I didn't have any jets larger that 98. Power went down a little when timing was set at 42°. I backed it down to 40° BTC.
 
a70duster said:
I did not get a torque curve, the dyno guy and I were shooting for best power (his recommendation). I'd start the dyno run rolling in 3rd gear at ~3000, he'd signal me to floor it, RPM shot up from a loose converter, my tach then was at ~4000 for a couple of seconds and then the RPMs climbed to 6000 rpms. The run lasted about 10 seconds.

Initial timing was at 35° BTC and total timing is in by 3500. I don't lock out the distributor for the ease of starting the car.
Click to expand...


Just so I’m clear, you have 35 degrees of timing at idle. Is that correct?
 
Newbomb Turk said:
Just so I’m clear, you have 35 degrees of timing at idle. Is that correct?
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I started at 35° timing. I got best power with 40° timing and left it at 40°. The whole power curve showed an increase at all RPMs with 40° advance. I have a Fluidamper style harmonic balancer and TDC does coincide with the timing marks at 0°.

At low idle timing drops to about 10° BTC. This value was BEFORE the bump in timing. Current idle timing should be around 15° BTC.
 
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So you have 10 degrees at idle and 40 all in before 3500. A 30 degree swing, that seems like a bunch.
 
Sorry for the confusion - I misread a question.

My distributor is a factory mag-pickup from a 400 that retains the mechanical advance. Vacuum advance has been removed. The distributor was initially set at 10° advance at idle and total advance of 35° would come on at ~3500. This didn't matter because of the stall converter which locked up at ~4500 when racing.

With the timing bumped up to 40° advance, the idle timing is probably at 15° BTC.

At the track I shift at 6500.

Per the dyno graph, if you were to overlay the 35° advance plot over the 40° plot, there is a noticeable hp improvement over the whole "RPM" range. The dyno shop didn't give me those graphs, just what you see from above.
 
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