Historical Rod ratio L/R improvement information links

[xctasy]

See the following. General statements, citing a David Vizard article, that was also done via the Richard Holdener on the same SuperFlow 902 Engine Dyno at 300 rpm per second SAE Gross. 5.545, 5.7 and 6.00 inch rod tests that others have done as well that show No Change in power or torque with a Rod ratio change between 1.483 and 2.00 ratio limits, using 302 to 400 cube Small Block Gen 1 Chev combinations with Fullile style heads with moderate 230 CFM head flow.

"https://www.speed-talk.com/forum/viewtopic.php?f=1&t=2066"

Elseware, others are frequently sceptical about any Rod ratio improvements giving Any performance improvements.

I'm journalling those historical links that affirm that a HP or Lb-ft improvement happens with a Rod ratio improvement within certain 1.40 to 2.4 Rod ratio ranges. Based on the evidence, I say it is a true thing. It's primarily happens when an engine is "Air flow limited", or where air pump CFM exceeds total engine combo intake air flow.

I also include links that don't prove an increase in power with a numerically higher rod ratio. This is about free talk, not eliminating desenting information or info that is contrary to a certain theory I might be trying to prove.

First "https://fordsix.com/threads/interesting-read-about-rod-length-ratio.18599/".

"https://fordsix.com/threads/crossflow-conrod-lengths.11741/"

Stan57 or "57Stan", the Super Atlantic 4AGE comparison

"https://fordsix.com/threads/250-vs-200-rev-limits.77066/"

Proofs:

1.Gene Berg (No SAE proven sources)

2. Chrysler Bible Performance verses Rod ratio test ( Not conclusive, the test was a rod to stroke ratio verses power and torque on various sizes of 4.04 bore LA small blocks from 340, 368 and to 410 Cubic inches with 3.31, 3.58 and 4.00 with the same 6.123 rod, and differing Cam Lobe Center Angles) See For A bodies Only. A fuller explaintion, I've not seen "https://www.forabodiesonly.com/mopar/threads/more-connecting-rod-length-theory-questions.190630/"

3. Ford's SAE gross tests on 200/221/250 on line sixes with no changes but stroke and Rod ratio (Not conclusive but anecdotal)

4. David Vizards A series Tests. Test A, 1293 cc A series with 5.75 verses 6.00 inch rod. 1:47.23 to 1:49.23 on

Vale the late FordSixer Ron B ( Ronbaom) who showed me this David Vizard 1994 Australian Brisbane seminar on Youtube.


Test B, 1399 or 1435 cc engine verses 1549 or 1559 cc long stroke engine. Full dyno tests including frictional resistance calculations. (First Conclusive proofs are 1 and 2).

5. Ford's move to long rods on the 4.0 liter Intech and Barra engine (anecdotal) and 5.6 liter Stoker ( anectodal).

6. Bill in Indy's 240 long rod 300 cubic in line six test ( Engine Analyser).

"
http://fordsix.com/forum/viewtopic.php?f=2&t=42347

Originally Posted by xctasy
Okay, I've got a really good one for you. I can't find conclusive info elseware.

With the only change being a shorter piston to compensate, take the stock 6.21" rod, and shove an 6.58" rod in it, and then compare the ideal power increase for any application. I recon 3 hp gain at 147 hp stock, perhaps 4 hp gain for any 200 hp modifed combination.


This is a rod ratio sensitivelty test, and it seams to work best when the stock rod ratio isn't very good. David Vizard, Phil Irving and most specialist engine builders have often talked about the advantages, but I've seen no scientific 'apples matches apples' comparisons aside from SAE papers.

Originally Posted by pssnmn1
ok this the figures for xctasy's 6.21 to 6.58 rod ratio question.

stock engine stock 6.21 rod
peak h.p. 147@3500 peak tq 250ft/lbs@2000

stock engine 6.58 rod
h.p. 151@3000 tq 261@2000

after rebuild stock rod
h.p. 197@4000 tq 310@2000

after rebuild 6.58 rod
h.p. 202@3500 tq 324@2000



interesting changes"

7. The need for good SAE approved info to validate a "proof" ( Anecdotal)

"https://fordsix.com/threads/sizing-exhaust-header-site.66242/"

 

[Firepower354]

Right up there with oil and deity choices, for arguments... "Ideal" is nonsense.
Peak power/torque is less a measure than area under the curve, methinks. Circle track, Lingenfelter, et al.
No part of an engine design, stands alone. A tight web of overlapping function/effect, negates most generalizations in these experiments.
But, the short rod accelerates from TDC faster, initially. What that translates to, is the Paul Harvey.
Burn time, dwell and the detonation potential, piston acceleration vs intake port flow, ad infinitum.

I like 1.7:1 but settle for as short an adequately strong piston as practical, all the stroke that fits the block and/or rules, and a rod that fills the space between.

 

[twentyover]

Partially related-

I have an ongoing project building an MGC (2.9l 6cyl BMC engine.) 3.28 bore x 3.5" stroke. Stock rod length is 6.60". Piston had a 4" long skirt. The reason I went to a 7.2" Pauter rod was weight- with polished beams, the C rod weighed 1070 grams, the piston was 490 grams.

The 7.2" Pauter rod is 690 grams (and I had the big ends tabbed for early SBC rod bearings.) We also anticipate a 100 gram savings on the piston, so saving just shy of 3 kg before we lighten the crank. And almost 20 lb off the flywheel, hoping the motor will sing.

Not particularly relevant to the conversation, but perhaps an interesting data point.

Another idea/project I'm toying with is a stroker C motor, using aftermarket Ford Flathead rods @ 7". . Stoking the crank would eliminate the problem of the flattie motor rods big end being too narrow for the C journal. And keep me away from requiring a $2000 set of custom rods

 

[Firepower354]

Partially related-

I have an ongoing project building an MGC (2.9l 6cyl BMC engine.) 3.28 bore x 3.5" stroke. Stock rod length is 6.60". Piston had a 4" long skirt. The reason I went to a 7.2" Pauter rod was weight- with polished beams, the C rod weighed 1070 grams, the piston was 490 grams.

The 7.2" Pauter rod is 690 grams (and I had the big ends tabbed for early SBC rod bearings.) We also anticipate a 100 gram savings on the piston, so saving just shy of 3 kg before we lighten the crank. And almost 20 lb off the flywheel, hoping the motor will sing.

Not particularly relevant to the conversation, but perhaps an interesting data point.

Another idea/project I'm toying with is a stroker C motor, using aftermarket Ford Flathead rods @ 7". . Stoking the crank would eliminate the problem of the flattie motor rods big end being too narrow for the C journal. And keep me away from requiring a $2000 set of custom rods

Plenty of new and racey stuff leaves the rod a lot narrower than the journal, allowing a big radius and reducing side drag from the oil. Piston-guided rods take care of that. Best to have EDM oiling to the pin, or at least generous ring land to pin drains.

Jag early rods, slant six, 226 Willys, I was looking at a lot of options in those length ranges. That pesky OEM rods catalog...