Got a few questions about overboring a B18C motor to 84mm. Just thought I'd ask the question here since I'm getting jack for response on another board. Hopefully all you H series engine guru's have some experience with B engines.
1) Where do you get the pistons? Can you just use a B20 piston on a B18C rod? I know the strokes are different (89mm in the B20, 87.2 in the B18C) but are the rods the same? Wrist pin, length? For example, my car has an H22A1 I believe is a pressed in wrist pin vs the H22A4 which uses a "floating" wrist pin which prevents me from using an H22A4 piston in my H22A1 engine.
2) Do you need to modify the head to compensate for the larger bore? If the combustion chamber was designed to an 81mm bore would an 84 bore create a "lip" between the head and piston?
3) When you put in an 84mm piston, what do you bore and hone the cyclinder to? Do you need to add anything to account for the rings? Or does 84 mm refer to the actual bore and and hone diamter and the actual piston is 83.?? and the rings take up the remaining diamter? (just a general engine building question)
4) If you use a B20 piston, are the pistons the same height (center of wrist pin to combustion surface of piston)? Or should you always measure your clearances between the pistons and valve?
Originally posted by DrSeus 1) Where do you get the pistons? Can you just use a B20 piston on a B18C rod? I know the strokes are different (89mm in the B20, 87.2 in the B18C) but are the rods the same? Wrist pin, length? For example, my car has an H22A1 I believe is a pressed in wrist pin vs the H22A4 which uses a "floating" wrist pin which prevents me from using an H22A4 piston in my H22A1 engine.
I believe they are the same, as long as they are B20B/Z parts and NOT B20A. You will obviously have to check. I know there are companies that make specific stroker kits and pistons for all the B series, so...
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2) Do you need to modify the head to compensate for the larger bore? If the combustion chamber was designed to an 81mm bore would an 84 bore create a "lip" between the head and piston?
Ideally, yes. In reality, no. The difference in power unless you are FI or going with some wild output will not be much. Ideally, though, you would want the CC to match the head perfectly.
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3) When you put in an 84mm piston, what do you bore and hone the cyclinder to? Do you need to add anything to account for the rings? Or does 84 mm refer to the actual bore and and hone diamter and the actual piston is 83.?? and the rings take up the remaining diamter? (just a general engine building question)
I would suggest reading up on the Helms manual for your car and get an engine building/blueprinting book (Motorbooks, etc.) from your local bookstore or barnesandnoble.com.
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4) If you use a B20 piston, are the pistons the same height (center of wrist pin to combustion surface of piston)? Or should you always measure your clearances between the pistons and valve?
The height I think is the same but you ALWAYS measure your clearances (clay the motor). Depending on valve size and cam lift and head milling you may put the valves too close and have to enlarge the valve reliefs in the piston.
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Thanks for any help.
You're welcome even if it's OT. I think these are good questions regardless of the motor.
Hmm trying to bump up the displacement of a B18C motor. I could just go with a B20 bottom end but everything I've heard is that is can't rev easily due to a poor R/S ratio. So I wanted to keep the same stroke and use the same rods so I can still rev. I've driven my friend's GSR and it's a bit lacking in the oomph department so I was hoping that the bump in displacement would help it a little.
I'll check my helm's unfortunately I only have the one for my prelude. I ordered a bunch of books from Amazon about engine building and turbocharging. These should answer my general questions like about boring and honing. (Maximum Boost - Corky Bell, Honda Builder's Handbook - Pettitt, Honda/Acura Engine Performance - Kojima). Have come yet but hopefully soon. Are there any other books you recommend?
The bump in displacement will help a little but not much, and it will help it across the board. The stroke is what will give you the low-end "oomph," and it's an unfortunate tradeoff. Keeping other parameters fixed, changing the stroke will worsen the r/s ratio and inherently limit your top end RPM (without other work).
Are you planning to boost? If so, I would leave the sleeves the stock size to preserve the strength, even if you decide to sleeve the block. In order to keep the sleeve strong with an overbored engine, the sleeve will have to take up more room in the water jacket than the stock sleeves. This can cause cooling problems, especially on a boosted engine, and even on an NA engine.
As for the R/S ratio, I wouldn't worry too much about it. Here's the numbers I have. If they are incorrect, someone let me know.
B18C
Stroke: 87.2mm
Rod Length: 137.9mm
Rod Ratio: 1.581
B20
Stroke: 89mm
Rod Length: 137mm
Rod Ratio: 1.539
It's a difference, obviously, but it's a difference of 0.042. Maybe enough to make a difference, but unless you're running the engine at 10 tenths (like a race engine) the difference is probably not noticable.
If you're boosting, I would say go for a B18C block and crank, and just turn up the boost, especially if you plan to sleeve. If you're going NA, I would say a B20VTEC would be the way to go.
I don't have any direct experience with the B series engines, but I did a TON of research into them when I was planning to buy a CRX.
Like Todd said, for oomph, you need stroke, not necessarily displacement.
Originally posted by DrSeus Hmm trying to bump up the displacement of a B18C motor. I could just go with a B20 bottom end but everything I've heard is that is can't rev easily due to a poor R/S ratio. So I wanted to keep the same stroke and use the same rods so I can still rev. I've driven my friend's GSR and it's a bit lacking in the oomph department so I was hoping that the bump in displacement would help it a little.
I'll check my helm's unfortunately I only have the one for my prelude. I ordered a bunch of books from Amazon about engine building and turbocharging. These should answer my general questions like about boring and honing. (Maximum Boost - Corky Bell, Honda Builder's Handbook - Pettitt, Honda/Acura Engine Performance - Kojima). Have come yet but hopefully soon. Are there any other books you recommend?
Thanks. Sorry for being so OT.
Well you can't increase the stroke and keep a good RS/R without a deck plate or something. Or a custom longer rod and a custom piston with a relocated wirst pin...
Thanks for all the suggestions. Guess it's back to doing some research to see if I can find some actual info concerning the wrist pin. I'll check the various sights suggested.
FYI the "grand" plan was to turbo the B18. I just figured since I was resleeving I would try to take advantage with a larger bore since the Darton MID setup has the same OD if you use an 81mm or an 84mm bore. I was thinking up picking up an Integra and making it a project car. Both to see what it possible and what I can do myself.
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I think these are good questions regardless of the motor.
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