Honda, Acura, Project Honda Civic EJ, EK, B18c1, long rod, rod ratio, engine build, eagle, K1 connecting rods, stroker, Castillo's crankshaft specialists, arp 2000 bolts, Chuck Johnson, Annie Sam, QR25DE, bearing

Project Honda Civic EJ

Building the B18C1 Engine Part 2:  Improving Rod Ratio
Words by Chuck Johnson
Pics by Joe Lu
Our main goal for Project Honda Civic EJ is to build a formidable, yet reasonably economical weekend warrior.  However, we didn't want our "budget" project scope to limit us to merely rebuilding a stock configuration B18C1.  Admittedly, we also wanted the challenge of trying something new rather than simply building another stroker B-series.    
In recent months, there has been a lot of talk on MotoIQ about lengthening connecting rods to improve an engine's rod to stroke ratio.  Specifically, a few weeks ago we covered how Mike and I managed to shoehorn a Honda H22 rod into a Nissan SR20VE to improve its rod ratio from 1.58:1 to 1.66:1, but what is rod ratio and why all the recent talk?  
Rod Ratio 101 (nerds skip ahead)
Before I get started, I've found that some of our less nerdy readers (you know the ones with prospering social lives and non-imaginary, super hot girlfriends) are confusing rod to stroke ratio with stroking an engine.  Before I go any further, let me clarify that “stroking" an engine is increasing its displacement by lengthening the “throw" of the crankshaft.  For example, the Honda D16A1 1.6 liter has a stroke of 90 MM where as a 1.5 liter D15B has a stroke of 84.5 MM.  The 5.5 MM longer crankshaft "throw" (or stroke) of the D16A1 is what makes it slightly larger in displacement although the two engines have the same bores of 75 MM.  Simply put, increasing stroke increases an engine's displacement and has little to do with improving an engine's rod ratio. 
Honda, Acura, Project Honda Civic EJ, EK, B18c1, long rod, rod ratio, engine build, eagle, K1 connecting rods, stroker, Castillo's crankshaft specialists, arp 2000 bolts, Chuck Johnson, Annie Sam, QR25DE, bearing 
Rod to stroke ratio is merely a means of expressing the relationship between an engine's rod length and its stroke.  As an example, we can calculate an SR20DET's rod ratio by dividing its rod length of 136.3 MM by it's stroke of 86 MM.  This simple math will yield a rod ratio of 1.58:1.  So why fiddle with an engine's rod ratio?  In brief, improving rod ratio: 
  1. Reduces piston acceleration increasing the piston's dwell time near TDC, which could improve scavenging at high RPM.  
  2. Reduces piston side loads, which translates into a reduction in friction as well as piston skirt and cylinder wear. 
  3. Positions the piston higher in the cylinder to take advantage of peak cylinder pressures.

For a more in depth explanation of the effects of rod ratio, check out Khiem Dinh's article here. 

Conceptualizing the Long Rod
After the experiment with Mike's SR20VE yielded some promising results, I figured why not try it the other way around this time and use a Nissan connecting rod in a Honda engine?   When we first conceptualized the SR20 long rod engine, the H22A rod caught my eye because it shared the same big end bore diameter of 2.008" as the SR20DE.  A quick review of both FSMs would reveal that the two engines also shared a common crank pin diameter.  This meant that the bearing shells were the same thickness and the combination would most likely work.
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Dusty Duster
Dusty Dusterlink
Monday, October 31, 2011 6:04 AM
I'm very curious to see the results on a dyno graph.
Monday, October 31, 2011 6:40 AM
"Machinists, how could nerds live without 'em?"

Good machinist are greatly undervalued in today's society IMHO.

My brother was an ASE certified engine machinist. Watching him work was like watching an artist paint.
Monday, October 31, 2011 9:05 AM
On what applications does Honda use WPC?
Mike Kojima
Mike Kojimalink
Monday, October 31, 2011 9:57 AM
Most of them
Monday, October 31, 2011 10:03 AM
You said you will start assembling this motor when the parts come back from treatment. But what pistons are you using? Did I miss that part?
I'm also very curious about the dyno graph. Any possibility that there will be a similarly built stock rod ratio motor for a direct comparison?
Der Bruce
Der Brucelink
Monday, October 31, 2011 11:47 AM
Good stuff guys, looking forward to the dyno run! Chuck, let me know if you ever want to try something different than the CutterSil. It's a little too old school!
Dusty Duster
Dusty Dusterlink
Monday, October 31, 2011 11:50 AM
Do you think the top-end gains are going to be worth all the effort of getting those connecting rods to fit?
Chuck Johnson
Chuck Johnsonlink
Monday, October 31, 2011 5:28 PM
@jeffballs- No you didn't miss the part about the pistons. We'll be covering those in a later article as they're still being manufactured by JE. The pistons will be high compression with a shorter pin height to accommodate the longer rod.

As for the dyno, I'm hoping that Skunk will have a relative comparison for us to bench mark against.

@Jason- I know that American Honda applies WPC treatment to many of their dirt bikes, like CRF 450, that use a bushing-less steel on steel connecting rod and floating wrist pin combination. Steel on steel (without a bronze bushing on the pin end of the rod) usually doesn't play well together, but WPC seems to help prevent gauling from occuring.

@Dusty- I actually enjoyed the challenge of figuring out how to make the long rod combination fit so it wasn't really that much "work." Even if it doesn't net measurable results, it's still a good learning experience... that is a long as it's not a totally gutless pig.
Monday, October 31, 2011 11:17 PM
Where do you get your crayons? ;)
Tuesday, November 01, 2011 1:36 PM
Mike, wouldn't it be easier to just order longer rods? I did this 8 years ago on my B18C block B20/VTEC setup- went from 5.397" rods to 5.534" with the pin moved up in the piston by .137". That got the rod ratio up to 1.58 from 1.54, and I didn't have to mess with the crankshaft- just ordered the right length Eagle rods and Wiseco pistons. Ask Khiem, he should remember...

That engine didn't end well because of a stupid piston to wall clearance issue, but I did see another 10lbft on the dyno across most of the rev range compared to the previous build with similar compression and the original stroke geometry. I don't know that you could attibute all of the torque gain to the better ratio, but that was about the only difference between builds at that point.
Micah McMahan
Micah McMahanlink
Monday, November 07, 2011 7:21 AM
If you wanted custom rods, they're just a phone call away. 4340 or 300M; L19 or 625 bolts...I or H-beam.

Did you guys do the math to see the reduction on reciprocating mass?
Chuck Johnson
Chuck Johnsonlink
Monday, November 07, 2011 7:34 PM
In our case, it was cheaper to use an off the shelf rod and modify it, but not everyone has access to a full machine shop. I'm not sure what the cost or lead-time is on a set of custom rods cost but getting the crank ground and rods modified is pretty cheap.

We'll talk about the reduction in mass in the next engine build article.
Monday, November 07, 2011 7:39 PM
Chuck, the Eagle rods that I bought at the custom length cost me the exact same as a normal set of B18A/B length rods. They were right around $500 from what I remember, maybe less.
Mike Kojima
Mike Kojimalink
Tuesday, November 08, 2011 7:30 PM
Eagle does not do custom rods. At least they didnt used to as little as last year.
Tuesday, November 08, 2011 9:20 PM
Ok Mike, then either they used to back in 2003 or they just offered this length for B series blocks as one of their normal off the shelf rod lengths- point is, they were available in 5.534" with B series ends in an H beam configuration.


5.531". My mistake.
Tuesday, November 08, 2011 9:29 PM
Ok, digging a little further... looks like Eagle offers B18A/B18B/B20 compatible rods in 5.394, 5.531 (140.49mm), 5.862 (148.89mm) and 5.967 inches (151.56mm) as standard fitments per their web site, all at a list price of $400.
Chuck Johnson
Chuck Johnsonlink
Wednesday, November 09, 2011 6:02 PM

The 5.862 and 5.967 rod would both be too long for the B18C1 stroke and block height. Basically neither of the two would leave room for a piston with a realistic pin height and 3 ring configuration. The 5.394 rod is actually shorter than the OE B18C1 rod which is 5.433. Must be for a stroker or another B-motor? This leaves the 5.531 rod as the only good option, but the QR rod is still .100 longer. The difference in rod ratio is small at 1.61 vs. 1.64, but I wanted to maximize the rod ratio to increase the chances of seeing a measurable difference in performance.
Monday, October 08, 2012 3:24 PM
I like what you're saying phunky buddha. I've always thought the ultimate B-motor would use the Eagle 151.56mm rods in a 226mm Dart block with a stock stroke. Then the rod ratio would be 1.75. I just never had the resources to do it. Sounds good in theory
Monday, October 08, 2012 7:34 PM
Chuck, a year late- but the 5.394in rod is 137mm, which is the same as the B18A/B OEM rod length- gives the 1.54 ratio with the 89mm crank.

venenon, I don't know that I necessarily subscribe to 1.75 being the "ideal" ratio- it all depends on the torque curve shape you're going for and the strength of the parts you have plus how high you want to spin- but it doesn't take a Dart block and a ton of money to fab up a deck plate. :)
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