26 replies to this topic

[crazi-85crx]

When you all say rods resized, I hope you might elaborate on that, do you mean just having the d16 pistons put on the ew rods? If so thats not too bad, then you can use the 1.5 rods and the 1.5 crank. That would be fairly simple......

No, by "resize" I mean running a hone (or whatever) over the part of the rods that touches the crank so they're round, because pressing the ARP bolts in may distort them I guess. You don't need to resize the rods if you're not using ARP bolts; the D16 piston will swap on in place of the ew pistons, no modifications needed.


And you do use the 1.5 rods and crank, with the 1.6 pistons.

[BGPKR]

I'm wanting to do this as well. Can used pistons be used or is it recommended to get new. What compession will the 86-87 piston yield?

[stevo911_]

This should help you out a little. . .

I was just looking at this pic again (thinking about building a hydra) and was looking at the pm7 pistons, does anyone know how they compare in compression to the 88-89 integra slugs? From the way the valve releifs are cut and the bits surrounding them it looks like they could be a bit higher compression but still with room for the valves?

[crazi-85crx]

I was just looking at this pic again (thinking about building a hydra) and was looking at the pm7 pistons, does anyone know how they compare in compression to the 88-89 integra slugs? From the way the valve releifs are cut and the bits surrounding them it looks like they could be a bit higher compression but still with room for the valves?

The PM7 does look slightly higher than the P29. But PM7's are only in the JDM 88-91 CRX, the USDM/CDM 88-91 CRX has pistons like one of the first two in the pic.

P29's FTW! lol

[stevo911_]

thats cool, do you remember what sort of compression ratio it pukes out or where I can find more specs on it? I'm kinda thinking about building a hydra engine now so we'll see what happens

[r4adkshn]

I was just looking at this pic again (thinking about building a hydra) and was looking at the pm7 pistons, does anyone know how they compare in compression to the 88-89 integra slugs? From the way the valve releifs are cut and the bits surrounding them it looks like they could be a bit higher compression but still with room for the valves?

same piston

[anjin]

I'm doing this on an early (86-88) ZC rebuild. From my investigations, the PM7 pistons have a larger dome capacity (7.2 cc) which raises the compression compared to the PG6B (1.5cc) , but they sit 1 mm lower in the hole (29 mm as opposed to 30mm distance to the centre of the pin from the top edge of the piston) which then loses some of the gain in compression. The PG6B pistons are flush with the top of the head, the PM7's sit below. The standard compression ratios are supposed to be 9.34 for the PG6B, and 9.56 for the PM7
Mill the block 1mm the PM7 pistons will get you 10.5. You can't/shouldn't mill the block with PG6B. and the PM7 and PG29 are supposed to be identical.

There are a couple of compression ratio calculators around which you can plug in blocks, pistons, gasket thickness, how much the head in milled and the block decked, rods etc, and boost; and get a cr figure. If you've worked in the combustion chamber to deshroud the valves you have to guesstimate the difference. It's an interesting exercise - thats where some of the above comes from


I have both sets of pistons available now, and once I have one PM7 on a rod I'll put it in and compare the valve clearances before deciding what to do for milling the block. FI, I have already milled the head 30 thou inch, and I'm waiting on a web cam to arrive, I'll post up the results when its done.

[stevo911_]

cool thanks for the info, i'm just starting a hydra build, but am thinking of milling the block a it and using the pm7's to kick the cr up a bit

[BGPKR]

I have done this for many years on my race engines and the only thing that need to be done is the stock block needs a .040 bore to fit those pistons. I would also recomend not shaving too much off the head. I always ran a 94 octane gas with these engines. I also would replace the rod bolts with ARP ones and get the rods resized while your at it. Any good machine shop will be able to do a boring and resize rods

I'm actually planning building the spare block I have lying around.
How exactly would the rods have to be resized? Could you be more specific?
Thanks

[GnarlyJ]

doodson,

if you dont mine me asking, what head, valvetrain, cam, intake, throttle body, etc are you using on this setup? I plan on sticking with the SI motor and putting 86-87 teg pistons and just want to know whats a good head setup.

Edited by GnarlyJ, 24 September 2007 - 08:07 PM.