Engine Masters rod ratio test results

General engine tech -- Drag Racing to Circle Track

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Stan Weiss
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Re: Engine Masters rod ratio test results

Post by Stan Weiss »

4.12" bore and 3.75" stroke. Piston location with 6.135" rod - red line (BBC engine) and 6.625" rod - green line (Pontiac engine).

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Re: Engine Masters rod ratio test results

Post by bobmc »

don't know what I am looking at in this graph, what do the columns represent? are the rows piston amounts of travel?
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Re: Engine Masters rod ratio test results

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bobmc wrote: Mon Mar 02, 2020 8:33 pm don't know what I am looking at in this graph, what do the columns represent? are the rows piston amounts of travel?
The columns are degrees ATDC in 2.5 degree increments. Starting @ 122.5 ATDC with the last line being BDC. Yes the numbers on the right hand side / y-axis is piston travel.

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Re: Engine Masters rod ratio test results

Post by Lizardracing »

Every time I see/hear/read one of these shows/articles that go about testing stuff I get the critical feeling that ratings and controversy are more important and cleverly hidden inside illegitimate ABA type testing. It’s really hard to take any of them serious when something kinda important is glossed over because it doesn’t fit a narrative.
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Re: Engine Masters rod ratio test results

Post by Mikej26 »

What I found of interest was the difference in ignition timing requirements. The longer rod ran best in the 34-38* advance range and the short rod ran best in the 40-42* range. What got my attention and had me scratching my head is they said the long rod was insensitive to timing and ran the same from 34-38* btdc, so they went with 38*. Wouldn’t it have made more sense to go with 34-35*?
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Re: Engine Masters rod ratio test results

Post by GARY C »

Lizardracing wrote: Mon Mar 02, 2020 9:07 pm Every time I see/hear/read one of these shows/articles that go about testing stuff I get the critical feeling that ratings and controversy are more important and cleverly hidden inside illegitimate ABA type testing. It’s really hard to take any of them serious when something kinda important is glossed over because it doesn’t fit a narrative.
After watching all of their shows and listening to their reasoning I get the idea that they are still doing mostly 1990's magazine articles, for example in this one Frieburger has wanted to do this test since 1997 and he seems oblivious to the fact that this has been hammered to death, both in discussion and testing and that just changing rod length is an invalid test. So I sent him a link to googlesearch/speedtalk/rod length/rod ratio. :)

They do have some cool stuff on dyno testing basic stuff that the pubic would encounter but they don't seem to take into account what has bee learned over the past decade. I also understand that they probably have a lot of money tied up in one 20 minute dyno video publication.
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Re: Engine Masters rod ratio test results

Post by digger »

so if you watch the video its 2 different short blocks, one has pin in oil ring. the torque is like 1-2 numbers different at peak and power about 10 numbers in 800hp at peak. the longer rod was better on the bottom end by around 10 numbers. at steady state at 3000 and 5700rpm they were within around a number so at the bottom end the differnce wasnt like when sweeping. not particulary conclusive
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Re: Engine Masters rod ratio test results

Post by BradH »

There was an article I read from a few years ago, right before NHRA Pro Stock switched to EFI, with one the the PS engine builders that touched on rod ratio. IIRC, he mentioned they couldn't reduce the rod ratios as their program evolved until the heads had progressed to where they could keep up with the induction requirements the shorter rod ratios "wanted".
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Re: Engine Masters rod ratio test results

Post by mag2555 »

The conclusions draw from these test remind me of the many decade's of Cam,Intake and header shoot outs in magazines that I have read where they never even bother to re-jet the Carb to further fine tune things, weather it was at the track or on the dyno!
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Re: Engine Masters rod ratio test results

Post by learner1 »

It's much easier to visualize the rod ratio and velocity differences if you graph it as piston position and using rod length extremes helps even more as a visualization tool. Now when you have a cam lobe profile ground using the rod ratio it makes sense and as Mike stated earlier the rod ratio test does nothing without a proper cam. I don't work as a professional engine builder anymore but even as a hobbyist i'll never buy another cam from anyone but Mike.
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Re: Engine Masters rod ratio test results

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learner1 wrote: Tue Mar 03, 2020 8:19 am It's much easier to visualize the rod ratio and velocity differences if you graph it as piston position and using rod length extremes helps even more as a visualization tool. Now when you have a cam lobe profile ground using the rod ratio it makes sense and as Mike stated earlier the rod ratio test does nothing without a proper cam. I don't work as a professional engine builder anymore but even as a hobbyist i'll never buy another cam from anyone but Mike.


That graphically shows it does change things.
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Re: Engine Masters rod ratio test results

Post by RevTheory »

ClassAct wrote: Tue Mar 03, 2020 10:05 am
learner1 wrote: Tue Mar 03, 2020 8:19 am It's much easier to visualize the rod ratio and velocity differences if you graph it as piston position and using rod length extremes helps even more as a visualization tool. Now when you have a cam lobe profile ground using the rod ratio it makes sense and as Mike stated earlier the rod ratio test does nothing without a proper cam. I don't work as a professional engine builder anymore but even as a hobbyist i'll never buy another cam from anyone but Mike.


That graphically shows it does change things.
Yeah, but with a 10" difference in rod length. How does it look at .3"?
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Re: Engine Masters rod ratio test results

Post by CamKing »

We've tested the heck out of different rod lengths in limited class circle track engines. There are a ton of circle track classes that limit you to 358ci, stock stroke, a compression limit, and unported production heads.
In these classes, Rod length is one of the few things that can be changed, so it's a great place to learn about the effects of rod length. One thing we've proven, as the rod/stroke ratio goes up, the engine wants an earlier intake valve closing point, for the same rpm power band. If you run a cam designed for the shorter rod/stroke ratio, with the longer rod, the intake closing is too late, and it'll hurt the power.
When we cam the engines correctly for the different rod lengths, we normally see the power between peak torque and peak hp to be very close, with the shorter rod making more power below peak torque, and the longer rod, carrying the power farther past peak hp.
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Re: Engine Masters rod ratio test results

Post by Stan Weiss »

These show piston travel, velocity, and acceleration from very small to very large rod length.

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Re: Engine Masters rod ratio test results

Post by piston guy »

pdq67 wrote: Mon Mar 02, 2020 4:27 pm
CGT wrote: Mon Mar 02, 2020 3:55 pm Shorter rod has more dwell at BDC, I can see that as more of an advantage then more dwell at TDC of the longer rod. Regardless, I haven't seen the test...but it would have to be pretty damn intricate, complex, and precise for me to get on board with results in either direction. And I'm doubtful it was any of those things.
Again, I guess I always thought a longer dwell at TDC due to a longer rod allowed more push time on the piston.

pdq67
How can it do that when the piston isn't moving? Same for "burn time" a couple of nano seconds does nothing.
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