Question about pistons and boring

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A

ambryatim

New Member
Ok, I did search and did not find my answer. So, here goes. I have an LS block that was run as an LS/VTEC with the stock pistons. Now, before I purchase new pistons what would qualify for me to bore or just hone (cross hatches) out the cylinders, I was wondering if I have to go up in size or if the 81mm (nippon or ycp) pistons would fit in the cylinders. I have yet to measure the bore of the cylinder, but how close are these pistons (really) to the proclaimed diameter of 81mm??? Bigger or just a tad small. There is a small lip at the top of the cylinder liner that you can hang your nail on but, no major gouges.

Thanks in advance on the advice.
 
Measure your cylinder diameters, then check those against the tolerances specified in your service manual. You can also check the recommended piston to wall clearance of whatever pistons you're going to use (only if you have them in hand) and then see if the cylinder walls are within spec. If you don't have any damage to the walls, chances are that you can use them with a new set of standard sizes pistons.

One thing to note- forged aluminum pistons expand more than your OEM cast pistons, so a forged set of 81mm pistons could require a slightly larger bore to cover the larger piston to wall clearance. That bore can be done easier than a full rebore on an engine.

By the way, welcome to the site- and please be patient! Most people aren't even awake this early to answer a question that was posted at 11pm central time.
 
Calesta thank you. No, I do not have the pistons in hand that is why I asked the question so, I could decide on what piston to buy 81mm or 81.25mm. I dont have any scoring or scratches on the liners but, there is a lip at the top on cylinder #1 that you can catch your nail on just a little. Oh, and I guess I need to put where I am from in my avatar (Denton, TX). But, again thank you for your advise. I plan on running cast pistons (Nippon or YCP). I am in the process of doing an LS/VTEC :rolleyes:, just want to get everything right.
 
Compression

Well, since I am building an LS/VTEC I was wondering about the compression. I know most recommend an 11:1 and up ratio but here is my delima. My company will pay for my fuel but not 93 octane only 87. So, I was thinking of going with P72 pistons with a GSR head and that would give me roughly a 10.2:1 ratio and run octane boost. Any suggestions??
 
The link is in my signature.

If you're going to run octane booster, it's going to get REALLY expensive. I don't really trust them either. Maybe you can cut a deal with your company to only pay the 87 octane price and you make up the difference?
 
I was going to have my b18b block bored to 82mm just to make sure the walls were all cleaned up and already had the pistons in hand though which were 11.1:1 . Sorry to thread jack but if your looking for parts for an ls vtec build check out my for sale thread I have everything needed to build an ls vtec except bearings and gaskets and everything except head and block is brand new. https://hondaswap.com/parts-sale-trade-wanted/b-series-engine-parts-new-good-deals-156980/
 
No, problem for "jacking" but, I will be going NA and plan on using Nippon (NPR) or YCP pistons. Maybe sometime in the future I will in stall a JRSC. But, until then I will just stick with some cast pistons.
 
Bore

Well, I checked the cylinder bore on the LS block. The readings that I got were 3.185" to 3.188" on all cylinders. Not to bad, I guess. I am worried about going to much on the bore due to increase in compression with the larger surface area of the new pistons. I was thinking of 81.25mm but 81.50mm would be fine also, I just have to see if the pistons I want are offered in that size.

FYI here is a link to a pretty cool Compression Calculator for B series engines.:cool:
B-Series CR Calculator

On a side note I did not think that Honda offered OEM pistons in a 81.50mm variety just 81.25mm.:confused:
 
Calesta said:
The link is in my signature.

If you're going to run octane booster, it's going to get REALLY expensive. I don't really trust them either. Maybe you can cut a deal with your company to only pay the 87 octane price and you make up the difference?
Click to expand...


:( The link does not work.:(
 
different pistons will require different cylinder wall clearances. some manufacturers specify only a .003 in clearance while some need as much as .007in clearance. if youre building a new engine, you're really better off having the block bored and honed to the next avaliable oversize piston that you want to use. this will enure you have a perfectly straight bore, with proper side clearances. not to mention you will have the proper finish on the bore to seat your rings.
ask your machine shop if they bore match each piston. even the highest quality pistons will not all be exactly the same size, the differenced will be slight, but can make a difference. it also says a lot about the reputation of the machine shop. if they say yes they do it, they prolly know their stuff. if they tell you no or "it dont matter" you might wana move on.
 
Yea that was the first thing the guy told me. "Bring in your pistons so we can bore the cylinder to match the piston." So, yea they know what they are doing, been doing it since the 60's and get this they are only going to charge me $8.00 per cylinder to "bore match the cylinders"!!!! To the pistons of course.

And does anyone know (going out on a limb here) what the clearences of the Nippon (NPR) pistons are??
Also the YCP, haven't decided on which I will be getting.
 
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