8.6:1 Truck pistons in a 240

[WAbernethy]

I'm in the process of rebuilding my engine and when it came time to order the engine kit, I wanted to see if I could do better than stock for my turbo. The only performance set I could find was a set of 8.5:1 Ross pistons for 500 bucks. Looking at my shop manual, I noticed that the stock compression for the truck's KA24E was 8.6:1 and mine was 9.1:1. To make a long story short, I called a Nissan dealer in BFE and talked to Billy Bob Redneck to see if I could use the truck pistons in my 240. It should work fine. So, I'm going to lower the copression to 8.6:1 with stock pistons for the truck. Should be pretty sweet, they are dished vs. the flattop ones. I ordered them from flatlander yesterday. I'm also getting them 20 over which might bring the compression to 8.7:1. Anybody else try this setup?

[bruinbear714]

I'm in the process of rebuilding my engine and when it came time to order the engine kit, I wanted to see if I could do better than stock for my turbo. The only performance set I could find was a set of 8.5:1 Ross pistons for 500 bucks. Looking at my shop manual, I noticed that the stock compression for the truck's KA24E was 8.6:1 and mine was 9.1:1. To make a long story short, I called a Nissan dealer in BFE and talked to Billy Bob Redneck to see if I could use the truck pistons in my 240. It should work fine. So, I'm going to lower the copression to 8.6:1 with stock pistons for the truck. Should be pretty sweet, they are dished vs. the flattop ones. I ordered them from flatlander yesterday. I'm also getting them 20 over which might bring the compression to 8.7:1. Anybody else try this setup?

If you're talking about rebuilding the KA24DE with the KA24E truck engine's 8.6:1 pistons, you're not going to get 8.6 compression in your KA24DE when its in there because the two engines are slightly different. You'll get something a lot higher like 11.x:1.

If you're going 0.02" overbore, then why not just get the ross pistons? That'll give you 8.5:1 and not some other compression ratio.

[TrunkMonkey]

I'm in the process of rebuilding my engine and when it came time to order the engine kit, I wanted to see if I could do better than stock for my turbo. The only performance set I could find was a set of 8.5:1 Ross pistons for 500 bucks. Looking at my shop manual, I noticed that the stock compression for the truck's KA24E was 8.6:1 and mine was 9.1:1. To make a long story short, I called a Nissan dealer in BFE and talked to Billy Bob Redneck to see if I could use the truck pistons in my 240. It should work fine. So, I'm going to lower the copression to 8.6:1 with stock pistons for the truck. Should be pretty sweet, they are dished vs. the flattop ones. I ordered them from flatlander yesterday. I'm also getting them 20 over which might bring the compression to 8.7:1. Anybody else try this setup?

you have a '90 with a ka24e, right?

your compression ratio is already 8.6:1. ignore the fsm. early '89s have 9.1:1 while later '89s and all 90s have 8.6:1. there's a technical service bulletin that covers this.

-demetrius

[WAbernethy]

I think you have that backwards. The early 89's have the 8.6:1 while all others have 9.1:1. I know that I have flat top pistons, so they must be the higher of the two cr's because the ones I'm getting are dished. The reason for not buying the Ross set: it costs $500+ just for the pistons. I'm getting a complete kit for $300.

[andrave]

you can get the ross a lot cheaper than that. The main weak spot of the pistons is the ring lands... you might as well spring for the extra 100 bucks and get some decent pistons, check ka24de.com out or raceeng.com .

[WAbernethy]

Didn't see anything new there. Not sure what you're talking about for an extra 100 bucks. They had the same Ross pistons for the same 500 bucks. I did see alot of stuff for the DE.

I don't see the ring lands being a problem unless I have some serious detonation issues. My old ones held up fine to 160k miles with the last 10k miles or so being under boost. I ran as high as 9psi and only had some detonation after hard runs where the I/C became heatsoaked. I/E when we dynoed it. I never had any problems on the street. I might go as high as 15 psi after this is done but I'm getting the BTM to help prevent any detonation issues and my fuel system will be more than adequate. I don't know why so many people are hung up on the stock ring lands being too small unless you are going for some high numbers. If your ring lands fail on a setup with 10-12psi, you must have other problems.

Here's a puzzle for you....If the stock 9.1:1 CR KA24E pistons will make something like 11.1:1 in a DE, what will those 10.5:1 DE pistons make in a SOHC? Looks to me like it would be < 9:1.

[andrave]

raceeng.com has a couple different pistons for the E for under 500 dollars. so I guess you didn't look long enough. Anyway if it was me and I was spending 300 bucks on stock pistons I'd go ahead and spend an extra 100-150 dollars and get forged ones. If you think otherwise, thats fine with me.The ring lands aren't a problem unless you detonate. at 10-12 psi it doesn't take anything more than a bad tank of gas to detonate. Thats why the ring lands can be a problem for cars driven on the street. If you are careful with your management, fuel system, and what you put in your tank, they probably won't be a problem.

[WAbernethy]

Well as it turns out the pistons are not going to work. Everything was going smoothly until I realized that the pistons that I got don't use the same connecting rods. Our piston pins use C clips and these pins are press in. The guy at the machine shop said that wouldn't work. This blows! I guess I will return them and order some different ones. I'll look at the forged stuff you all are talking about but these were only 138 for the set from flatlander.

Back to my question from before:

If the stock 9.1:1 CR KA24E pistons will make something like 11.1:1 in a DE, what will those 10.5:1 DE pistons make in a SOHC?

I just looked on flatlander again and all I see for the SOHC is that Ross set that I can't afford. They do have alot more to choose from in the DOHC models.