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Engine Masters rod ratio test results

General engine tech -- Drag Racing to Circle Track

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David Redszus
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Re: Engine Masters rod ratio test results

Post by David Redszus » Mon Mar 09, 2020 11:57 am

digger wrote:
Sat Mar 07, 2020 5:47 pm
David Redszus wrote:
Sat Mar 07, 2020 3:01 pm
its probably better to try and understand why
Digger, you are asking for trouble. :)

While it seems easy to understand measured values, even without an appreciation of measurement error,
it becomes a real son of a biitch to understand WHY.
friction hurts BSFC, negative work hurts BSFC.
Should we be looking at BSFC or BMEP?
For a performance engine. I don't much care about BSFC but care a lot about BMEP.

A change in fuels could easily affect BSFC without impacting BMEP.

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Re: Engine Masters rod ratio test results

Post by LoganD » Mon Mar 09, 2020 1:04 pm

This wasn't a very accurate test, I wouldn't read into this too much. The variables were not well controlled.

To do this right you'd need an oil conditioning unit, a water conditioning unit, a complete intake air conditioning unit, and a dyno that uses an electric motor with at least two torque meters for averaging. I'd prefer to see a fuel conditioning unit as well.

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Re: Engine Masters rod ratio test results

Post by digger » Mon Mar 09, 2020 4:48 pm

David Redszus wrote:
Mon Mar 09, 2020 11:57 am
digger wrote:
Sat Mar 07, 2020 5:47 pm
David Redszus wrote:
Sat Mar 07, 2020 3:01 pm

Digger, you are asking for trouble. :)

While it seems easy to understand measured values, even without an appreciation of measurement error,
it becomes a real son of a biitch to understand WHY.
friction hurts BSFC, negative work hurts BSFC.
Should we be looking at BSFC or BMEP?
For a performance engine. I don't much care about BSFC but care a lot about BMEP.

A change in fuels could easily affect BSFC without impacting BMEP.
BMEP tells you the net outcome, but BSFC might help to understand some of the underlying reasons but ideally other data is available as well

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Re: Engine Masters rod ratio test results

Post by gmrocket » Mon Mar 09, 2020 4:54 pm

digger wrote:
Fri Mar 06, 2020 9:08 pm
gmrocket wrote:
Fri Mar 06, 2020 5:42 pm
digger wrote:
Fri Mar 06, 2020 4:21 pm
like i said much higher? or just a bit higher....
You said it was the opposite..

That the long rod had a higher bsfc
at the 5,700 the number i gave was not a good number for the short rod as it was at the extreme end not an average
at 3,000 i said the long rod was was better

in both cases it was still a small difference not a huge difference like you said

its probably better to try and understand why
Nope, never said it was huge.

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Re: Engine Masters rod ratio test results

Post by gmrocket » Mon Mar 09, 2020 4:56 pm

LoganD wrote:
Mon Mar 09, 2020 1:04 pm
This wasn't a very accurate test, I wouldn't read into this too much. The variables were not well controlled.

To do this right you'd need an oil conditioning unit, a water conditioning unit, a complete intake air conditioning unit, and a dyno that uses an electric motor with at least two torque meters for averaging. I'd prefer to see a fuel conditioning unit as well.
Yup, from the little data provided it was all over the place..inlet 10deg is enough to make up the difference

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Re: Engine Masters rod ratio test results

Post by gmrocket » Mon Mar 09, 2020 5:03 pm

David Redszus wrote:
Mon Mar 09, 2020 11:57 am
digger wrote:
Sat Mar 07, 2020 5:47 pm
David Redszus wrote:
Sat Mar 07, 2020 3:01 pm

Digger, you are asking for trouble. :)

While it seems easy to understand measured values, even without an appreciation of measurement error,
it becomes a real son of a biitch to understand WHY.
friction hurts BSFC, negative work hurts BSFC.
Should we be looking at BSFC or BMEP?
For a performance engine. I don't much care about BSFC but care a lot about BMEP.

A change in fuels could easily affect BSFC without impacting BMEP.
Isn’t BSFC in this case worthwhile comparing identical engines with just a rod ratio change?

I agree ,I wouldn’t care what the BSFC was if it made more power. Not including if fuel efficiency was a concern

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Re: Engine Masters rod ratio test results

Post by Stan Weiss » Mon Mar 09, 2020 6:27 pm

I would want to look at BSFC while also looking a fuel lbs/hr, A/F ratio, and scfm /ve%.

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Re: Engine Masters rod ratio test results

Post by Tuner » Mon Mar 09, 2020 9:49 pm

gmrocket wrote:
Mon Mar 09, 2020 5:03 pm
David Redszus wrote:
Mon Mar 09, 2020 11:57 am
digger wrote:
Sat Mar 07, 2020 5:47 pm


friction hurts BSFC, negative work hurts BSFC.
Should we be looking at BSFC or BMEP?
For a performance engine. I don't much care about BSFC but care a lot about BMEP.

A change in fuels could easily affect BSFC without impacting BMEP.
Isn’t BSFC in this case worthwhile comparing identical engines with just a rod ratio change?

I agree ,I wouldn’t care what the BSFC was if it made more power. Not including if fuel efficiency was a concern
Isn’t BSFC in this case worthwhile comparing identical engines with just a rod ratio change?
None of it is worthwhile if the ignition advance curve for best output over the engine's entire operating range with each rod length combination is not determined.

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Re: Engine Masters rod ratio test results

Post by gmrocket » Mon Mar 09, 2020 10:07 pm

Tuner wrote:
Mon Mar 09, 2020 9:49 pm
gmrocket wrote:
Mon Mar 09, 2020 5:03 pm
David Redszus wrote:
Mon Mar 09, 2020 11:57 am


Should we be looking at BSFC or BMEP?
For a performance engine. I don't much care about BSFC but care a lot about BMEP.

A change in fuels could easily affect BSFC without impacting BMEP.
Isn’t BSFC in this case worthwhile comparing identical engines with just a rod ratio change?

I agree ,I wouldn’t care what the BSFC was if it made more power. Not including if fuel efficiency was a concern
Isn’t BSFC in this case worthwhile comparing identical engines with just a rod ratio change?
None of it is worthwhile if the ignition advance curve for best output over the engine's entire operating range with each rod length combination is not determined.
The pulls start at 4K, how much of a curve do you think is needed from that point?

They did test each engine for max power timing.

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Re: Engine Masters rod ratio test results

Post by Tuner » Mon Mar 09, 2020 11:19 pm

If the timing wasn't checked at 500 or at least 1000 RPM steps from lowest to highest over the range of interest how will anybody know? This is too big a factor to be ignored.

I've played this tune on lots of different engines but never with the same engine just changing the rod length, as this thread is about, so I recognize that in the variety of engines I've dealt with there is more to it than just rod length.

In my experience, some engines want 1 or 2 degrees per 1000 RPM and some want 2 or 3. The ones that like the most are usually in the short rod category. This trend is found in OEM factory service literature and "off road" tuning handbooks in which advance curve specifications are published.

With the common SBC example of circle track and road race engines I have done this enough times I am sure, beyond any doubt, that an advance curve that increases 1 to 1.5 deg. per 1000 RPM from 3000 to 8000 will give a distinct advantage in a field of others that all have "locked advance", in which case the locked advance is actually retarding about 1+ deg. per 1000 RPM due to ignition system slew rate.

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Re: Engine Masters rod ratio test results

Post by David Redszus » Tue Mar 10, 2020 12:45 pm

I've played this tune on lots of different engines but never with the same engine just changing the rod length, as this thread is about, so I recognize that in the variety of engines I've dealt with there is more to it than just rod length.

It sounds very easy to only change the rod length. But this also means a new piston with a different mass, a rod with a different mass and center of gravity relocation. Now we have G forces that are quite different. Changing only one thing at a time is almost never possible. Except on paper.
In my experience, some engines want 1 or 2 degrees per 1000 RPM and some want 2 or 3. The ones that like the most are usually in the short rod category.
Modern computerized ignition systems allow for the construction of
a complex ignition map using a number of input parameters. The result is an ignition advance curve that looks like the
Rocky Mountain Range. And it changes constantly, even under conditions we think are stable.

I have yet to meet the racer (or engine builder) who knows the actual timing curve of his engine while on the track.

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Re: Engine Masters rod ratio test results

Post by maxracesoftware » Tue Mar 10, 2020 12:58 pm

Stan Weiss wrote:
Mon Mar 09, 2020 12:35 am
Where are these dyno sheets at ?

If you have accurate dyno room weather data (BP, VP, TEMP), fuel lbs/hr and A/F ratio. SCFM can be calculated.

Stan
i'm likewise wondering :
Where are these dyno sheets at ???

anyone have a web Link to these Dyno Sheets ??
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Re: Engine Masters rod ratio test results

Post by Tuner » Tue Mar 10, 2020 4:54 pm

"I have yet to meet the racer (or engine builder) who knows the actual timing curve of his engine while on the track."
I don't know what to say. I thought you were acquainted with a better crowd than that. Perhaps you need to get out more.

I have confidence the curve seen on a distributor machine and confirmed in the engine, on a dyno or not, is what you get on the track.

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Re: Engine Masters rod ratio test results

Post by David Redszus » Tue Mar 10, 2020 5:49 pm

"I have yet to meet the racer (or engine builder) who knows the actual timing curve of his engine while on the track."
I have confidence the curve seen on a distributor machine and confirmed in the engine, on a dyno or not, is what you get on the track.
You're kidding, right?

For vintage ignitions tuned on a distributor machine, track results are very often affected by shaft end play,
point bounce and jitter, coil over heating, loose electrical connections, cylinder pressure and temperature variations and a whole bunch more.

For electronic ignitions we have measured ignition lag due to switching delays, heat buildup of coil and ignition box and a whole bunch more.

For mapped ignitions, we have measured variances from the map due to input errors, sensor errors and incorrect mapping. With multiple inputs used to drive ignition maps, it is often not possible to accurately predict actual curves.

The cool thing about ECUs and data loggers is that you can see and measure invisible variables.
The sad thing about ECUs and data loggers is that you can see and measure invisible variables.

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Re: Engine Masters rod ratio test results

Post by Tuner » Tue Mar 10, 2020 6:12 pm

As in all things, if you think so, or you don't, you're absolutely right.

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