Don Terrill’s Speed-Talk

take a look at the data between the two engines during steady state peak TQ test.

The conditions were kinda different..air inlet temp about 10 deg diff as well as other stuff

The steady state peak TQ test also showed the short rod had a much higher bsfc making the same TQ

gmrocket wrote: ↑Fri Mar 06, 2020 12:45 am take a look at the data between the two engines during steady state peak TQ test.

The conditions were kinda different..air inlet temp about 10 deg diff as well as other stuff

The steady state peak TQ test also showed the short rod had a much higher bsfc making the same TQ

you sure about that ?

BSFC
rpm/long/short
3000/0.535/0.560
5700/0.455/0.436

the short rod was 8-10F hotter IAT

digger wrote: ↑Fri Mar 06, 2020 5:51 am

gmrocket wrote: ↑Fri Mar 06, 2020 12:45 am take a look at the data between the two engines during steady state peak TQ test.

The conditions were kinda different..air inlet temp about 10 deg diff as well as other stuff

The steady state peak TQ test also showed the short rod had a much higher bsfc making the same TQ

you sure about that ?

BSFC
rpm/long/short
3000/0.535/0.560
5700/0.455/0.436

the short rod was 8-10F hotter IAT

Ya I’m sure about it at peak TQ which is where you should get your best #’s

Video in slo mo , and don’t include the jump in the numbers as he backs off the throttle that’s where you got the .455 from

Long rod first @5700 low .419 hi .429 avg .424 622.9

Short rod @5800 low .433 hi .445 avg .439 621.2

Long rod slightly better on both counts at 100 lower

The 3000 steady state was meaningless to me..it’s so far under the power band you can have funky stuff going on in the intake....even though at steady state both made indentical TQ

like i said much higher? or just a bit higher....

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

Is there a difference in NVH with longer/shorter rods?

Daryl

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

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.

Here’s my takeaway from this particular test.

The long rod was clearly better on the bottom end from 4K thru about 5.2k, the difference is clear on the overlay graph. I wonder why they didn’t point that out and tell us the difference? It’s more noticeable than the tiny difference at the top end.

The below peak TQ was more noticeable to me.

The short rod had a small gain above 7k to 7.5k

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.

Were any of these comparison tests done with the spark advance curve optimized from the lowest to highest RPM, perhaps in 500 RPM steps or ? In any case, was the difference in best advance for peak output at all engine speeds accounted for? It seems to me that engines of the 'short rod' variety want more advance from torque peak to power peak.

it would have been good to see the differences in airflow using a hat flow meter.

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

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.

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.