Improving the rod/stroke ratio of the a20

[Accordtheory]

According to a post I just read, rods for the B18 A/B and B20B/Z will fit our engines, provided our pistons are modified for a larger wristpin. The length of these rods is 5.394", or 137mm. Our engines have a 3.58", or 91mm stroke, which calculates out to a miserable 1.5:1 rod/stroke ratio. Fuck that. I highly doubt that the wristpin could be moved up enough with custom pistons to significantly alter this ratio, so now what are the remaining options? The only thing I can come up with is a crank with a shorter stroke. Does anyone know if any other honda cranks will fit the A20? A good rod/stroke ratio is more important to me than a loss in displacement, as my turbo will more than compensate for this. Someone, please tell me something good about bore spacing and parts interchangeability!

[Sean]

1.5 is not that bad. to think im trying to build a stroker. leave well enough alone. not all the b series rods fit either.theres also a lack of piston compression hiegth. an as of right now im not sure about cranks.your chasing a ghost. the long stroke is what makes the a20 a great motor. it doesnt have a large bore so it takes stroke to make the displacment what it is. im not sure where you guys come up with this crazy stuff. if we didnt have a iron block and an open deck then yes i would be concerned with piston thrust wall side loading. but im not. also the Diamond pistons are barrel skirt to help with the less then ideal 1.5 R/S

[Justin86]

I would trust Sean on this one. He has done the research and if this set-up is so bad then I don't think he would be tell everyone else about it.

[Accordtheory]

The rod/stroke ratio is just another piece of the puzzle, and if you can build an engine with a good foundation, why not do it? 1.5:1 is a lousy ratio, how many engines do you know of that have a ratio worse than this? The A20, with 3 valves/cylinder, heavy cast iron block, long ass 91mm stroke, etc, etc, doesn't sound too great to me...but I am still going for my 380hp goal. The "ideal" ratio is 1.75:1, and one of the best engines Honda builds, the B16, has a rod/stroke of 1.74:1, and my 240Z has a ratio of 1.8:1. When you build a 350 chevy, you use a 6 inch rod (instead of the 5.7") to improve the ratio, if you know what you are doing. Hopefully my A20 will survive the intercooled boost from my big 16G with the stock ratio, but I'm still going to to look into this anyway. I read about a guy who built a supercharged d16z6 and DEstroked the engine, as well as adding deck height, to achieve a closer to ideal ratio. The engine produced 487hp and around 350ft/lb from 1.55 litres., with a static compression ratio of 11.2:1, on pump gas. (featured in Hot Rod magazine) So I am not opposed to destroking the engine, especially with forced induction. I emailed Diamond Pistons to see if there is any possibility of locating the wristpin higher up, but they haven't replied yet...although I'm not too optimistic about this anyway. What I would really like to do is destroke the engine, use the Eagle special length 5.967" rods, and use flat top forged pistons with a static compression ratio of around 10:1. If anyone finds out anything relevant to this, please let me know!

[Justin86]

Well it will probably cost more with your set up but if you belive it will make more power in the long run then do it. The point on this thread is to get the rods at a cheaper price. To get the forged rods for the A20 cost a lot more then the $370 it cost for the D blocks. Well maybe you can get the longer rods that are available for the D blocks.

[Sean]

the reall advatabge to long rods is the increased dwell time at TDC and the lower pistons speeds. with what your planning to do theres really little sense in worrying about the Rod ratio unless your gonna be runnign over 8500rpm for extended periods. yet agains 1.5:1 isnt great but its not that bad. the b16 has a high R/S becuase it has a pathetically long stroke. and they didnt want to make a pistons they weighed 9,000,000 lbs. so they made the rod longer. look around at hondas other 2.0L and larger engines. the a20a has one of the best 2.0L honda rod ratios around. keep the stroke make the TQ and life goes one. as for dealing with pistons thurst load from the BAD r/s well thats in teh skirt of the piston and with a good coating its pretty minimal problem to deal with. also there is no crank im aware of right now that will drop in and reduce the stroke.

[K-MOD]

Try the JDM A18 it's only a 1.8 liter so it should have a shorter stroke. If the bore is the same(82.7) then it would have a stroke of 87-88mm instead of 91mm. Contact www.mnrracing.com. Whatever price they give you I'll beat it.

[Sean]

ok lets put this in really simpel terms

tq x rpm / 5250 = HP

if you reduce the stroke youll loose TQ then makless HP. just something to think about.

[Accordtheory]

"Simpel terms"? ha ha Anyway, all I'm saying is that I would rather have a b16 than a b18c...Why does the b16 almost always have more output than the b18c when boosted by identical or very similar systems? Did you check out the civic connected to the link about the carbon fiber intake manifold, way over 400whp? Damn... B16: Shorter stroke, better rod/stroke ratio, smaller displacement. I still like the idea of destroking the 2.0 to maybe 1.9L...

[Sean]

the b16 has more outptu b look a the Tq curve. what TQ curve. does it even mkae TQ. ? no. no need. look at the rpm they have to turn ( read exspensive bottom end parts and vavltrian. ) take the big motor and enjoy it TQ output. ive made over 200WHP without revving over 5500RPM !!!!! never see a b16 do that !

[Justin86]

I would rather have a flat hp and tq curve then one that is straight up and down and make over 500 hp.