Do you use the piston-to-deck height from the piston itself, or the engine block?

I've always heard that you use the numer from the actual piston itself.

Example?

PCT pistons in a GS-R engine.

The CR calculatior asks for piston-to-deck clearance.

Would I not use the number for the B16B since that's what piston I'm using, or do I use the number for the GS-R since that's what block it is?

TIA.

 

Just making an educated guess here since no one has replied...I'd say measure from the piston. There a few dozen piston types that you can use on a given block. I would assume that if you calculate from the block your results would be inaccurate because pistons change and block deck is constant.

 

Yes that's what I'm saying.

Here's proof IMO that the piston, not the block, is what will change the piston-to-deck numbers:

Here, read this chart:

http://www.muller.net/sonny/cr...t.gif

See how the same D series blocks are yielding different piston-to-deck numbers?

Wonder why?

...because the PISTON itself determines the piston-to-deck clearance, not the actual block or head y0.

Look at the D16A1 engines listed there.

One is a 1986-1987 D16A1 with the PG6 piston and it reads a piston-to-deck clearance of .000.

Now look at the 1988-1989 D16A6 engine listed with the P29 pistons - the piston-to-deck clearance for that engine is .040.

this is what i posted in rebuttal to some guy telling me that the Cr I posted up are wrong. He is using the B18C1 piston-to-deck clearance with a B16B piston'd GS-R build-up.

I told him that his error in CR could be the difference between detonating and ruining thousands of work, or playing it safe until he can get to a dyno.

He's telling me that PCT pistons in an otherwise stock GS-R only yield like 12:1 CR with the GS-R head and all.

In fact, here's exactly what he said:

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">I don't know what you did, but you sure as hell didn't calculate that correctly.

Using C-Speeds Calculator:

B18C1 Block, B18C1 Head, PCT Pistons, OEM Headgasket, OEM B18 Piston-to-Deck Height = 12.042422511586593

B18C1 Block, B16A Head, PCT Pistons, OEM Headgasket, OEM B18 Piston-to-Deck Height = 11.751778779507741
</TD></TR></TABLE>

Wrong answer IMO.

 

the piston to deck height is determened by the rod and crank. The piston itself is not attached to the block.
PCT pistons in a GsR block (with standard piston to deck clearance of 30 thousanths) would be 12.0:1

 

Different engines of course would have different piston to deck height numbers.
Thats why B16's (and B17's I think have differnet piston to deck heights than the B18's and B20's)
If you got into custom fabs, you could obviously change where the wrist pin is, so that would change the piston-deck height.

 

What about wrist pin placement on the piston bro?

Why is it that otherwise identical D16A6 engines (only difference is the pistons themselves) have different piston-to-deck clearance numbers then?

The rods and cranks are the exact same on the 1987 D16A1 as the 1988 D16A1, yet they both have different piston-to-deck clearance numbers - why?

 

it must be the placement of the wrist pins,
but I've always assumed that was a standard thing on most honda motors. The rods are different on the older ones, I know that (because they are stronger, so maybe they are shorter too)
Plus, maybe someone fucked up, and its really 40 thousanths on both of them.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by -KangaRod- &raquo;</TD></TR><TR><TD CLASS="quote">it must be the placement of the wrist pins,
but I've always assumed that was a standard thing on most honda motors. The rods are different on the older ones, I know that (because they are stronger, so maybe they are shorter too)
Plus, maybe someone fucked up, and its really 40 thousanths on both of them.
</TD></TR></TABLE>

Well why is it when I put the 1986-1987 PG6 pistons in a D16A6 block the edges of the pistons sit perfectly level and are rated at .000 piston-to-deck clearance, but when I put the P29s in the same block the edges of the piston sit below the deck and those are rated at .040 too?

Here's a pic of a P29 in a D16A6 block of mine - The piston is all the way to the top:



See how the edge sits slightly lower than the deck?

That looks to be correct if we're using the .040 piston-to-deck clearance, right?

From what I've seen personally the 1986-1987 rods are the same length as the 1988-1989 ones, but the difference is in thickness as opposed to length.

I think Honda places the P29 (high dome) piston slightly lower on the rod to compensate for such a high dome when compard to the flat top PG6 piston.

 

I agree 100% the pistons wrist pin location affects deck clearance.

 

haha,
I'm a little bit in over my head here.
Usually the piston - deck height is relative to the other side of the deck no?
I've always though that the greater the piston-deck height, the higher the compression would be (as in one block with 30 thousanths would have greater compression if head and pistons were the same as one with 20 thousanths)

 

Oh, another post.

I'm not going to say anything is definite. What I am going to say is that you would have to measure the distance from the wrist pin hole to the top of the piston. This would explain everything. I think they are the same for ITR and CTR, but I COULD be wrong.

Anyone have one of each? Want to measure them???

 

the difference from the center of the wrist pin on a PCT piston will be way more than the difference between the P73-AOO piston. I dunno how many of you have seen a PCT piston, but that think is a mountain!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by -KangaRod- &raquo;</TD></TR><TR><TD CLASS="quote">haha,
I'm a little bit in over my head here.
Usually the piston - deck height is relative to the other side of the deck no?
I've always though that the greater the piston-deck height, the higher the compression would be (as in one block with 30 thousanths would have greater compression if head and pistons were the same as one with 20 thousanths)</TD></TR></TABLE>

Well I know for sure that a neagative value for piston-to-deck clearance means that the piston is actually out of the hole.

I'd imagine that if everything else remains constant (dome cc, rod length, crank, head cc, etc.) and the only thing you change is the piston-to-deck clearance from .040 (piston edge sits lower in the hole) to a .000 (piston edge sits dead even with the edge of the cylinder) that the .000 value will increase the CR ratio.

Correct?

You're basically creating a smaller area for combustion when you bring the edge of the piston closer to the very edge of the top of the cylinder, right?

 

I didn't mean from the top of the dome, I meant top where its supposed to be measured against the block

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AzSi22 &raquo;</TD></TR><TR><TD CLASS="quote">I didn't mean from the top of the dome, I meant top where its supposed to be measured against the block</TD></TR></TABLE>

I know what you mean.

I'm sure that the value is measured from the very edge/lowest point of the piston top or else those P29 slugs would have a way negative value because the domes definately stick out of the cylinder as evidenced by my pic up there.

 

no, the one with the .040 will have a higher compression than the one with a .000 value. its a negative value so it takes away from the combustion chamber size / increases the compression ratio. There must be a standardized way of measuring it.
Oh where are tho H-T Gods!

 

Bump for the night crew.

 

If I remember correctly, the distance from the center of the wrist pin to the top outer edge of the ctr is about .010" higher than the gsr.

 

deck height clearance...distance from top of the piston(not dome) to the top of block @TDC

compression height...distance from center of wrist pin to top of the piston(not dome)

calculating compression you use deck height clearance (not comp. height)

the bigger the deck height clearance the lower th piston sits in the block(lower comp)

 

Ding ding!

Round two!

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by -KangaRod- &raquo;</TD></TR><TR><TD CLASS="quote">no, the one with the .040 will have a higher compression than the one with a .000 value. its a negative value so it takes away from the combustion chamber size / increases the compression ratio. There must be a standardized way of measuring it.
Oh where are tho H-T Gods!</TD></TR></TABLE>

Actually .040 is a positive value, which means that the edge of the piston sits .040 below/inside the cylinder.

 

Based upon the numbers from this data chart &lt; http://raceseek.com/honda_specs.htm &gt;, and this equation:

Piston-to-deck height clearance = Deck Height -[.5(Stroke) + CTC Rod Length + Piston Compression Height]

I've run the calculations before and I think it came out to +.0085". Which we will relate to as .0085" below the deck to keep conventions familiar to what's already being used in this discussion.

Actual measurements came closer to being .000" (exhaust side of the crown) and +.002" on the intake side of the crown. Since we were/are using a quench-padded P72 head with a B18C block, crank, and rods, there were other things I had to consider as well, like the piston orientation arrow that is -.0145" (.0145" above the deck), the "S" and "IN" markings that also come up above the deck.

You can find pics of the measurements here:
https://honda-tech.com/zerothread?id=579672

BTW, those measurements and any subsequent compression calculations reflect the following (for our engine, which may be slightly different from everybody else's with respect to the chambers and headgasket):

PCT .25OS pistons
B18C block, crank, and rods
Either .040" or .043" or .045" headgasket, depending on what Cometic has to offer
P72 Head reworked by Portflow, but I haven't cc'd the chambers yet, so I don't know how much Tom opened up the chambers and sunk the valves. I'll put those up later on when I have the time to cc them.


Modified by IN VTEC at 12:19 PM 9/11/2003

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fox297 &raquo;</TD></TR><TR><TD CLASS="quote">If I remember correctly, the distance from the center of the wrist pin to the top outer edge of the ctr is about .010" higher than the gsr.</TD></TR></TABLE>

According to Larry at Endyn, the compression height of the PCT's is .027" more than the GS-R piston (but I've also seen .029" more based upon a P72-A0 comp height = 1.181" instead of the 1.183" that Larry uses), and .020" more than than the USDM ITR piston.

 

Hmm, ok, so whats the final answer?

 

Final answer to...?

I'm sure you could figure out all you needed to know (whatever that may be) from the measurements I've taken and the pictures as proof.

If you're referring to our engine, I just ordered a Cometic .045" MLS head gasket. That only leaves the combustion chamber cc'ing left to do.

Oops, I forgot to add that we'll be shaving all the markings on the pistons, polishing, and maybe deepening the valve relief pockets a little. That'll increase the total chamber volume and lower the compression ratio slightly. I'll have to cc those too...but hopefully I can find a cheaper way of doing it rather than buying a set of sleeves and machining them.


Modified by IN VTEC at 12:35 PM 9/11/2003