webbyj

So I was messing around with a d-series compression calculator online. According to that if I put pistons from a y7 in my y8 with a 2 layor head gasket it will give me 10.25 static compression and 10.0 effective compression at 1200 ft above see level. Can any one more experienced with building Honda engines confirm this? Or is this not a good idea with it being an interference engine.

ezone

That shouldn't matter, it's an interference engine no matter if you jack with it or not.


So I check wiki,
D16Y7 shows 9.4:1
D16Y8 shows 9.6:1


Now I'm wondering.....You're gonna install LOWER compression pistons, is that the plan?
Then use a thinner head gasket to try and raise compression again?

Seems like there should be an easier way.
Why not just install the thin head gasket on the Y8 as-is?
(NOTE: I deal with mostly stock stuff, not modified)

Note, you may want adjustable cam gear since a thin head gasket will alter cam timing.

webbyj

I want to build an all engine D series but still try to use low octane gas. To help achieve this I was going to up compression 1 point. I just wasn't sure if using a 2 layer head gasket was a good idea in general. I've never used a 2 layer before. Putting a 2 layer on the y8 would get me to 9.96 I think but not really where i want to be. That's according to the compression calculator I was using. I want to get 10:1 and run low octane gas, if thats possible. Plus I spun the #2 rod bearing in the y8 which chewed up the rod a little. I have a y7 I'm not using I was going to steal the rods out of. So I figured instead of paying the machine shop to take the Pistons off one set of rods and put them on another. I'd just take the rods and pistons out of the y7 and drop them in the y8. Or if I want to take the time and attempt the mine-me swap....build whatever it's called. I'm fairly new to hondas.

ezone

You should check that the spun rod bearing damaged the crank as well.

Also....Whenever a bearing gets damaged like that, metal debris can be pumped throughout the entire oiling system, that means there's a possibility of trash in the oil passages for the camshaft journals and the valvetrain/VTEC. If it hasn't made it all the way into the head it may have clogged up the oil control orifice in the block deck, if the block uses one of those.

So in short...I'd pull it all out. Strip it down til every last piece is off the block and head, and clean the hell out of the oil passages and everything because any leftover metal you miss can ruin all your hard work later on.

That spun rod bearing damaged the crank...(confirm this?) Since crank and rod are (probably) both damaged, I'd think you'd want to swap the crank/rods/pistons from the good engine. That's probably gonna mean new bearings and seals and stuff.


Or just get a decent used Y8 engine and start fresh?
GX pistons?


I'm wondering how the low compression Y7 pistons in the Y8 block would yield a higher figure than the stock higher compression Y8 pistons in the same block.
Something seems screwy here---- or did I read that all wrong?

Anyway........
Milling the head to raise compression is another possible avenue you could look into.


When you raise the compression but use low octane gas, you might need to back off the distributors base timing (or the ECM might do it via knock sensor) to reduce or stop knock, you could lose some power.

You might need to run higher octane to take advantage of the higher compression (and make this work as planned).

webbyj

Yeah I've already blown the engine apart. I just need to have the machine shop clean and inspect the block and crank. Plus have them take the head apart to clean and inspect it. I'm not sure how the y7 pistons up the compression either. That's one reason I was posting on here. Maybe the combustion chamber is smaller on the y8 head. As far as the knock sensor, I'm thinking about going to obd 1. That way I can get more out of the engine since obd 1 is more uhh....programmable is the word to use I guess. I am going to get a adjustable cam gear eventually. This is my first tuner engine I'm building so it's going to be a learning experience. All the other engines I built where carbureted. No computers and a lot simpler. Not to mention cheaper too. Gx pistons, what are those?

ezone

In the parts catalog the Y7/Y8 pistons have different part numbers so they are different, but the parts catalog does not tell what the difference is. I can only assume that's how the compression difference comes in. The shape and size of the piston top may be different. It won't be much if there is only 0.2 difference though.

You could cc a combustion chamber in each of the heads to see if they are the same volume



GX=CNG (compressed natural gas)
Wikipedia: D16B5, 12.5:1 compression ratio LOL
Also noticed D16W7 says 10.9:1

mac25

...What!!!!!!!! just no man some of this stuff is just wrong.

the y7 runs
bore: 75mm
stroke: 90mm
compression: 9.4 parts gas to 1 part fuel
stroke bore ratio: 1,2
rod/stroke ratio 1,52
rod length: 137mm
deck height: 212mm

the y8 runs
bore: 75mm same
stroke: 90mm same
compression: 9.6 to 1 higher
stroke/bore ratio: 1,2 same
rod/stroke ratio: 1,52 same
rod length: 137mm same
deck height: 212mm same


So if the ratios are the same, the deck height is the same but the compression is different then we know that either the crank shaft is different between blocks, the piston head shape is different or the head valve dome is different

Since the deck height is the same 212mm, that should mean that the height from the crankshaft center at TDC, to, the engine deck (where the head gasket sits) is the same. We also know that the rod length is the same.

Which it should be since the piston/rod lengths are identical, the blocks are identical and the crank is identical.

So the high compression must come from the y8 head having a lower volume than the y7 head, or, the piston shapes; where the higher compression pistons sit flatter than the low... or both.

I did some digging and found that Mindbomb pisted a picture with both pistons https://www.civicforums.com/forums/2...8-pistons.html

The y8 pistons do have a lower volume than the y7, creating higher compression, but the y7 head has a larger volume at 34.6cc than the y8 at 32.8....

So you will be making less than 9.6:1 compression, but close.

mac25

You could also try researching if you can use the d15b7 pistons with the d16 rods.

If the wrist pins line up and are the same size it should be possible but since the d15b7 normally runs

9.2:1 compression with
a shorter stroke, 84.5mm, and a shorter rod length 134mm

and the lowest piston dome volume of -1.5cc

if they were used in the d16y7 with a normal piston dome height of -7.4cc

you would have a massive compression ratio increase.

Asemech1980

I know this post is from last year however the answer is the d16y7 pistons will raise compression to around 10, even though the stock d16y7 is 9:4:1 and stock d16y8 is 9:6:1the combustion chambers in the y7 are 34.60 cc and y8 are 32.80cc. So you can slap a y8 head on your y7 engine and up the compression because of the smaller cc combustion chambers, and so it's the same deal if you put y7 pistons in y8 as long as you keep y8 head you can raise compression. Other ways of raising compression.decking block,shaving head and running thinner headgasket., but you can play around with that on.honda engine calculator.

ezone

Good info... I never had any info regarding combustion chamber sizes