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Old 03-14-2014, 12:27 AM
Jarrett Jarrett is offline
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J32A2 "CL-S" vs. J35A8 "RL" pistons

The information about these pistons as they apply to use in hybrid engines that's being given out is jus tplain wrong. People seem to think that because an engine has a given compression ratio that the numerical value follows that piston everywhere it goes. This may be in large part because the aftermarket piston companies advertise pistons by their compression ratios instead of dish/dome volumes. They are usually selling to a specific application, not something that's going to be used in a custom setup. It's generally a lot easier for them to do it this way.

So what does this mean for us? Well, it means that if I were to look up information about building a hybrid J-series with a J35A3 rotating assembly beneath J32A2 heads I would usually find information telling me about the necessary piston changes I would need to make. I would be told that the "RL" pistons from the J35A8 would yield 11.0:1 compression and that if I wanted to play it a little more safe that I should use "CL-S" pistons from the J32A2. Ignoring the nomenclature by which these pistons are referred I'm left to think that the person(s) giving this information out have simply never been inside an engine before.

Let's assume that you have a given engine X with known, constant dimensions. Let's say that it's a 6-cylinder engine with an 89mm bore and an 86mm stroke giving it a 3210cc displacement. The crankshaft throw is 43mm (stroke/2), the rod length is 162mm, the compression height is 30mm and the piston-to-deck height is negligible for this particular exercise. The piston dome has a volume of +2cc and the combustion chamber is roughly 58cc once a 4cc headgasket volume is factored in.

Those numbers would all equate to a bottom dead center (BDC) volume of 591.2cc and a top dead center volume of 56.1cc. If we agree that a ratio is a comparison of numbers then the definition of a compression ratio worded "the ratio of a cylinder's largest volume (BDC) to its smallest volume(TDC)" is easy to understand. In this case (591.2cc/56.1cc) equals roughly 10.54:1 CR. Again, this is engine X, our basis for comparison.

Now, suppose we want to increase the performance of the performance of engine X by increasing its stroke. A 93mm stroke sounds nice. Since the throw of the crankshaft is now 3.5mm longer then either the rod length, compression height or piston-to-deck clearance will have to change in order to accommodate. Possibly more than one or all three. Let's just assume that it's the rod length alone to keep things simple. This will force us to use a 158.5mm-long rod. So again, we have a 6-cylinder engine with an 89mm bore and a 93mm stoke giving it a 3471cc displacement. The crankshaft throw is 46.5mm (stroke/2), the rod length is 158.5mm, the compression height is 30mm and the piston-to-deck height is still negligible. The piston dome has a volume of +2cc and the combustion chamber is roughly 58cc once a 4cc headgasket volume is factored in.

Since the piston is unchanged from the previous assembly many would assume that it has the same compression ratio. However, since the crankshaft has now moved the piston an additional 3.5mm further down the cylinder the volume at BDC has increased another 43.5cc. Add that additional volume to the original BDC and you get 634.7cc at BDC. Divide that by the volume at TDC which has remained unchanged and you know have somewhere near 11.3:1 CR using the same pistons in a 93mm-stroke combination vs. the original 86mm.

What does this mean? It means that the entire time you've been told that the "CL-S" pistons were the safer option in a hybrid build because they were 10.5:1 vs. 11.0:1 you were being fed incorrect information by people who had no clue what they were talking about. You were actually using pistons that had an even higher compression ratio than the ones you thought best to avoid. Or, if you chose to go to the "RL" pistons for a higher compression ratio, then you wasted the money as you likely already had a J32A2 base that this was being built on. If not, then the J32A2 pistons would certainly have been the cheaper alternative. The incorrect information has been "common knowledge" for way longer than it should have been.
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Old 03-14-2014, 10:07 AM
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Re: J32A2 "CL-S" vs. J35A8 "RL" pistons

Ok, so, for my J35a3 swap, which pistons should I use?
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Old 03-14-2014, 01:27 PM
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Re: J32A2 "CL-S" vs. J35A8 "RL" pistons

You can use four 2-cycle pistons for all I care. I'm not trying to say one is better than the other. I'm just saying that the information that has been presented previously is wrong and it's been passed along because no one seems to understand engine internals these days.
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Old 03-16-2014, 10:25 PM
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Re: J32A2 "CL-S" vs. J35A8 "RL" pistons

Nice rant.

cliffs - do your own homework or consult someone who actually knows what they're doing when buying, researching, and planning parts for your Honda v6 engine build.
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Old 03-21-2014, 05:22 PM
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Re: J32A2 "CL-S" vs. J35A8 "RL" pistons

---Jarret - your not Youngone51 are you? He's in Texas too i think. Didn't know if maybe you are using a different screen name over here or what. If your not the same guy, then disregard please.


hmmmm. I agree somewhat. It's been discussed before.


It would be nice for you, or anyone, to prove the theory on paper vs applying that theory to a build, then showing some numbers.

We don't really know what compression ratios we are running because people talk, but never prove it with real data/numbers/flowbench data, etc.

Take into account the head porting that some of us are doing and then your theory you listed above, may become skewed.




** I posted this because, way back in the day 1 guy stated the combination of a J30A1 low end with J35A3 heads would not work due to the valves would hit the pistons --- As he stated on paper....

I had NVA-AV6 do that build combination in real life and it worked. I guinea pigged my own engine and proved that theory wrong.

So, if you would be so kind as to actually prove the theory in a real build with real data you would make a great contribution to the community and debunk the misleading info on the J-series that is still out there.

Last edited by WHEEELMAN; 03-21-2014 at 05:27 PM.
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Old 03-24-2014, 05:33 AM
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Re: J32A2 "CL-S" vs. J35A8 "RL" pistons

I am not yungone501. His name is Robert and he lives in Plano, TX. My name is Jarrett and I'm down south in Houston, TX. I have met him, and he is very knowledgeable on the J-series engines. To be honest, most of my experience comes from H/F-series builds in the past for my CB-model Accords. I currently own three of those and had two others previously.

Anyway, I can certainly show some proof, but it will take some time as I don't really have a lot of time for my projects. I've recently purchased a couple of CL-S 6-speed cars from Copart auctions and I'm in the middle of doing body work on the one I'll be keeping, removing parts from the donor, swapping one of the engine/trannies into a friend's '98 CG2 and putting the rest of the parts leftover into my own CG2 to keep as a spare. So, before a build happens I have a lot of housekeeping to do. I did, however, purchase a J35A3 shortblock from Robert and will be purchasing his J37A rotating assembly soon now that his J25A has come in.

In response to your clearance issues with the valves, that is one area I did not really want to touch in my original post due to my lack of personal experience. What I do want to say on the matter is that I'm perfectly confident that there are people who have installed J32A2 heads onto J35A3/4 shortblocks, rotated the crankshaft and had absolutely no clearance issues whatsoever. I'm also confident that I could do the same and get the same results. What this determines is that I will not have clearance issues on the non-VTEC lobe of the camshaft. Unless I remove the rocker assembly to lock the pin that's oil pressure-activated on the VTEC rocker and reinstall, then there's no way that I'm going to open the valve to the full lift on a stand. You can have all the clearance in the world on the non-VTEC lobe but it won't mean anything once you hit VTEC if you don't have sufficient clearances there. But every moron and his dog is going to spout the information out of the hole in his face as fact as soon as he does the former.

Head porting has absolutely nothing to do with the compression ratio of an engine, unless of course you reshape the combustion chambers. Polishing them up will yield somewhat negligible increases in volume. By increasing the intake runner's flow rate you're increasing the amount of air going into a cylinder, but not the volume. So, the air inside the chamber will just be more dense than it would previously. This concept isn't that important to compression, though.

Head-swapping is also a little bit of a tough issue with J-series engines for me. I simply cannot wrap my mind around why someone would take a cylinder head with an 89mm-wide combustion chamber that's made to go on an 89mm-bore cylinder, and put it on a block with 86mm cylinders. There's now a 1.5mm ridge that runs the entire circumference of the block that is begging hot spots to form. It also drastically decreases the compression ratio as the volume of the chamber is significantly increased. This may be one of those situations where the power benefits outweigh the short-term disadvantages, but the hot spot issue is very real. Here's a thread I made on CB7Tuner that has good images I just drew up in paint. It's about F/H Frankenstein engines.

http://www.cb7tuner.com/vbb/showthread.php?t=187140


If you'd like, I can come up with some similar images that better illustrate the point of my original post soon. The engine build, as I explained, is being put off for now to focus on car repairs and clearing out some of the excess projects. It was nice to see some positive feedback!

Last edited by Jarrett; 03-24-2014 at 05:38 AM.
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Old 03-24-2014, 05:24 PM
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Re: J32A2 "CL-S" vs. J35A8 "RL" pistons

^
Thank you Jarrett. Intelligent discussion is much appreciated over here.

Please post new threads for any insight you discover and prove with your journey on the J-series.


Also, Acurazine.com has some super info on the J-series -- little bit in the 2nd gen CL section and tons in the 3rd Gen TL section. There are a few guys overe there who have dumped tons of cash into RnD on it, including cams with adjustable cam gears. There are more technical individuals over there, including youngone501.

But, if you know Robert....you got a very good source there too. I am familiar with his info...damn good info at that. I'm just an amatuer myself, but the info he presents helps me understand the J-series better.



peace,
Michael
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