rice_classic

Well, I've had my year or so off from racing and it time I started getting back in the game. I am starting with rebuilding my block and I don't know whether I should use .020 over or .040 over pistons.

I will be running two classes ITA and H4 (group 2 and 5) and want a piston that's legal, for starters. I've heard about some discrepency in the rules regarding .040's in Honda in Improved Touring so I'm on the fence. The motor I'm rebuilding had .020 over's and I think I should stick with them.

Is there is huge performance advantage between the .040 and .020 over pistons? Is there any reliability advantage?

I will be ordering the pistons as soon as I return from x-mas vacation and want to make sure I make the right decision the first time.

Any good advice is welcome.
Thank you in advance.

bosco500

If possible, I would certainly stick with the .20 over. Reason is that if you go .40 over and stick it, you will need a new block in most cases. The little bit of extra compression would not be worth it for me.

FlyZlow

The performance difference is negligible. If you calc the diff in displacement and static CR, you'll see that they're very similar. IIRC, diff in displacement is about 1% and CR might raise .02 or something. So, in general, I'd say stick w/ .020 over for the reason Bosco mentioned. If something happens to it, you can still punch it out to .040. However, if the block you have is already .020 and you want to clean it up, it may be worth going to a .040 over. These blocks are pretty cheap and not too hard to find in general.

I got my CRX .040 over pistons from Rivergate (found them on the web somehow). They came with rings and wrist pins for about $160. The rings seated right away and I never had any problems with them, so you may want to look them up.

- Scott

prkiller

It really depends how competitive you are and if your at that point of needing a little bit more. The extra .5cc is worth about 1 hp, and 4 tq on the dyno. That can make a difference when racing with someone that is VERY similar to you...
If your already at .020 over, I would say go .040 over to make sure you get the right piston to wall clearance!


Modified by prkiller at 5:21 PM 12/8/2005

CRX Lee

I have a set of new-in-box .040 over flat top pistons and rings that I may be selling soon if someone is interested. They changed my F Prod car from 10:1 to 12:1 compression for 2006 before I ever assembled the engine. I will now need to get some pop-up pistons for the higher compression.

I have a nice fresh block overbored to .040/1.0mm already but the high compression pistons seem to mostly be .020/.5mm overbore. Does anyone know of a .040/1.0mm piston available in the 11;1 to 12:1 compression range? I'd hate to have to have them custom made.

I had previously subscribed to the "bore it less now to leave room for later" thought but honestly the blocks are not expensive or hard to find compared to the money end effort put into a racing situation so are you really gaining much in the long run by saving little at first?

prkiller

Lee, pm'ed!

jisu009

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by prkiller &raquo;</TD></TR><TR><TD CLASS="quote">The extra .5cc is worth about 1 hp, and 4 tq on the dyno.
</TD></TR></TABLE>The math of it:

Stock 75x90mm = 1591.179 cc

.020 over = 1612.805 cc

.040 over = 1634.577 cc

The difference in cc's is 21.6263 or about 1.35% of total engine volume.

I estimated the increase in HP to be in the 1.65-1.8 range. Torque is probably 2-4 ft lbs.

I think there is benefit going with the .040 over piston, even with the additional weight of the lager piston.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by CRX Lee &raquo;</TD></TR><TR><TD CLASS="quote">
I had previously subscribed to the "bore it less now to leave room for later" thought but honestly the blocks are not expensive or hard to find compared to the money end effort put into a racing situation so are you really gaining much in the long run by saving little at first?</TD></TR></TABLE>

I agree. It's not like the D16A6 block is hard to find or expensive. I personally have 5 of them in my garage. The cost of boring from .020 to .040 is the same as boring from STD piston bore to .040 over, so there is nothing gained there. Assuming you rebuilt the block ever 2 seasons, you might be out $50-100 for a new block....if that.

That being said, as the IT rules read now, I don't see how they are legal.....BUT! I don't think ITAC will oust 75% of the front running hondas because they have .040 over pistons, which I believe is "within the spirit of the rules." I think it will come up in protest in '06 and they will clarify the rule to allow the Honda's to run a .040 over piston.

rice_classic

I think all the really competitive IT honda's up here all have .040 over pistons so I think I might be on that side of the fence.

I think I'll check out rivergate.

Knestis

The substance of the piston issue at it.com was, if 40-over pistons were never made available by the factory for a car, is it legal to run them at all? The rules require the factory parts "or their equivalent" and the (sound) argument went that, if a part was never made, how can anything be made to be equivalent to it??

Kirk (who is dealing with piston issues, too)

jisu009

What do you think will become of it? Anything?

Batoutahell

I'm surprised there hasn't been a formal protest of a 40-over piston. Isn't there a mandatory teardown at the ARRC?

CRX Lee

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Knestis &raquo;</TD></TR><TR><TD CLASS="quote">The substance of the piston issue at it.com was, if 40-over pistons were never made available by the factory for a car, is it legal to run them at all? The rules require the factory parts "or their equivalent" and the (sound) argument went that, if a part was never made, how can anything be made to be equivalent to it??</TD></TR></TABLE>
Been awhile since I looked at it but do the rules not say that you can overbore to .040" on an IT car. In my previous IT life, "or their equivolent" was understood by everyone as same shape (flat, domed, etc.) and same type (cast, forged, etc.) and there was never a ruckus. If you had flat, cast pistons of the allowed .040 bore then there was no issue.

JDogg

as far as i know honda did offer most of the single cam pistons in a 0.040 oversize version.

prkiller

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDogg &raquo;</TD></TR><TR><TD CLASS="quote">as far as i know honda did offer most of the single cam pistons in a 0.040 oversize version.</TD></TR></TABLE>

Not that I know of. You can't buy them now from Honda...

Only went up to .020 over!

CRX Lee

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDogg &raquo;</TD></TR><TR><TD CLASS="quote">as far as i know honda did offer most of the single cam pistons in a 0.040 oversize version.</TD></TR></TABLE>
Actually what I recall from the mid '90s from Honda was a .25 and .50 overbore piston and dummy me didn't realize that they were talking millemeters and I was thinking thousandths of an inch. I bought the .25s thinking at first they were .025 being afraid that a .50 was then bigger than the allowed .040 and thus illegal. Welcome to the translation from metric to English.

icarp

here it is

http://www.rivergate5speed.com/rivergate.html

icarp

JDogg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by CRX Lee &raquo;</TD></TR><TR><TD CLASS="quote">
Actually what I recall from the mid '90s from Honda was a .25 and .50 overbore piston and dummy me didn't realize that they were talking millemeters and I was thinking thousandths of an inch. I bought the .25s thinking at first they were .025 being afraid that a .50 was then bigger than the allowed .040 and thus illegal. Welcome to the translation from metric to English.</TD></TR></TABLE>

yeah, .25mm and .5mm... lol damn japenese

Knestis

Here's the text out of the 06 ITCS:

Engines may be bored to a maximum of .040 inch over
standard bore size. Factory oversize replacement pistons
or their exact equivalent shall be used. Cast or forged
equivalent pistons shall provide the same dome/dish/valve
relief configuration, ring thickness and spacing, pin height
relationship, weight, and compression ratio as factory
replacement oversize pistons. Piston rings are unrestricted.

Now, being what I thought was a Rules NERD, I am embarassed to admit that this caught me completely out of the blue. I have for - literally - decades shared the common interpretation that we could go 40 thou over as long as the pistons were the same configuration. Heck, I had a set of custom, forged +40 pistons made for the Alliance after a renter blew a hole in a stock one, 15 years ago.

Problem is, that is NOT what the rule says. If you haven't already, you should take a look at http://itforum.improvedtouring...=6652 and see what you think.

I'm of the opinion that this is one of those cases where the common interpretation is better and more reasonable than the letter of the rule. Problem is, that's not enough once the barn door is open and people are interpreting. Some wacky stuff can get rationalized that way.

K

JDogg

i think top line makes oversize replacement pistons.. i know they have ITR pistons in 1mm oversize, but with exact same dome/valvereliefs, etc

.RJ

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Knestis &raquo;</TD></TR><TR><TD CLASS="quote">Problem is, that is NOT what the rule says. If you haven't already, you should take a look at http://itforum.improvedtouring...=6652 and see what you think.</TD></TR></TABLE>

5 pages of incessant bickering. Again.

RJ - needs an advil and a beer

turfer

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ &raquo;</TD></TR><TR><TD CLASS="quote">

5 pages of incessant bickering. Again.

RJ - needs an advil and a beer</TD></TR></TABLE>

If you like that one, try this one out. http://itforum.improvedtouring...=6450

You'll be trading your advil for anvil to drop on your head.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Knestis &raquo;</TD></TR><TR><TD CLASS="quote">Now, being what I thought was a Rules NERD, I am embarassed to admit that this caught me completely out of the blue. I have for - literally - decades shared the common interpretation that we could go 40 thou over as long as the pistons were the same configuration.

Problem is, that is NOT what the rule says.

K</TD></TR></TABLE>

I certainly can't in good faith argue that .040 over is legal, anymore. I'll bet protests will be flying early next year and barring a revision to the GCR, they will be successful.

Rick

Hracer

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rice_classic &raquo;</TD></TR><TR><TD CLASS="quote">Is there is huge performance advantage between the .040 and .020 over pistons? Is there any reliability advantage?
</TD></TR></TABLE>
Some people say there is a little to be gained, however at the price of reliability and faster wear and tear. Honda pistons is what we've always used on both crx and integra simply because of the bulletproof reliability compared to the aftermarket 0.04 over stuff. I don’t dare enter that thread on IT.com, but the point that's been brought up on this thread about the legality is very interesting and might ruffle some feathers if pursued since probably a lot of people would now be deemed "illegal" in that regard. Well yet another reason to stick with Honda pistons and maybe now more people will, too. Pretty much all the power in an IT motor comes from a good head and header (and ecu tuning if the car responds well) anyway. We've also tried a few aftermarket oem replacements over the years in different areas of the car, but in the end we always ended up going with Honda parts, especially in the critical areas (such as calipers) where the quality makes all the difference.

.RJ

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by turfer &raquo;</TD></TR><TR><TD CLASS="quote">

If you like that one, try this one out. http://itforum.improvedtouring...=6450

You'll be trading your advil for anvil to drop on your head</TD></TR></TABLE>

Someone should ban that Banzai240 guy. Every time I open a thread there, he's in there flinging poo, being argumentative and generally unconstructive to the topic at hand.

turfer

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ &raquo;</TD></TR><TR><TD CLASS="quote">

Someone should ban that Banzai240 guy. Every time I open a thread there, he's in there flinging poo, being argumentative and generally unconstructive to the topic at hand.</TD></TR></TABLE>

And that is just one of our representative members of the ITAC.

Knestis

Interesting - he's arguably been largely responsible for most of the log un-jamming of the entire IT rule set over the last two years. It's possible to be pragmatic even while ACTUALLY CHANGING things.

K