Compression questions

[Zebrahead]

Ok, I searched around a little bit, but the information I wanted was sketchy at best, so here goes. I have a 93 240 (that would be a KA24DE) and am interested in increasing compression in my cylinders. I'm not much of a mechanic, therefore my knowledge is pretty limited. If anyone (and by "anyone" i mean "Dauntless") could explain to me how increasing compression is done, what is involved, and how much it all costs, and what kind of gains i could expect.

I thank you for your patience in the times of a newbie.

So far all I've done is intake/lower/strut bar. I plan to get an ACT clutch and exhaust, and from there, we'll see.

Thanks a lot,Nick.

[Daunttless]

You may wish to go look at the other post you put up. : )

Raising compression is done by changing your combustion chamber. Basically, Higher compression ratios produce more power, up to a point. The more you compress the air/fuel mixture, however, the more likely it is to spontaneously burst into flame (prior to the spark plug igniting it). Higher octane gasolines prevent this sort of early combustion.

The easiest way to raise compression on a DE: Put in KA24E pistons. I think each piston is about 40-50 dollars a piece, putting you at about 200 new from Nissan motorsports. However, your block has to be taken apart to do this, and while you block is apart I'd suggest a rebuild kit ($300-400) to replace all your gaskets, seals and rings, I'd also suggest boring the block to 90mm if you are going to buy the pistons, might as well go slightly overbored.

As far as gains, intake/headers/exhaust and 11.1:1 compression ( 8.6:1 KA24E pistons ) will put you over 200 horsepower. I don't know the exact power output, but it will be around there. However, unless you do the work yourself it will be expensive. You'll need the pistons and rebuild kit, you'll need machine work, boring out your cylinder walls, and while they do that you might as well port and polish your head. Several hundred dollars there, several hundred for the pistons, 350 or so for the headers, 200-500 for the exhaust, dependant upon what you get, and 400 for the rebuild kit. If you have someone else do the rebuild, expect a lot of hours in labor. All in all expect like 2000 dollars. : ) You'll be pushing over 200 Naturally Aspirated horsepower, but it does come at a price unfortunately. You'll also be pretty much topped out unless you go hardcore N/A power which would cost even more. However, you will have a fresh engine to work with, with 0 miles on it. The downside is that you can't go turbo because of the compression ratio. The other downside is you'll hit a wall, and wont' be able to easily increase power. This is why most people go turbo. Good luck with everything, the only truly necessary part is the pistons and rings, and you can get stock KA24E pistons that will fit your block if you take it apart and do it yourself. Good luck! Let me know if I missed anything, I'll update. : )

[Zebrahead]

That's quite a bit, 1/2 a turbo. I don't plan to go turbo because a. it'll cost a helluva lot, and b. they heavily wear engines, and KA's don't last more than a few years w/ turbos (i think you said that.)

So If i go for just the pistons and rings, what will i be increasing the compression to?

Pistons (~ $200) + Rings (~ $50???) + Labor (~ $200)?

Is the estimate of around $500 correct?

Should I just as well do cams as well while the block is apart? Any suggestions?

Thanks for the response,Nick.

[YochTown240]

Okay im totally lost now i was thinking of gettin new pistons for my ka24e yes the SOHC and its from a 1990...ive looked into the 9.1:1 pistons they sell on nissanmotorsports BUT do i already have these in my engine??

[trpower7]

Ok, what will raise compression in your engines is pistons with a higher compression ratio. I think the stock pistons on a DOHC (91 and up KA24DE) are an 8.6 to 1 ratio. The stock pistons from an SOHC (90 and below, KA24E) are an 11.1 to 1 ration. These pistons can be had from Nissan for cheap, they are just stock parts. You can walk over to the local dealership and ask for a piston and ring set for a KA24E and get them handed to you. Then get ready to have fun ripping the block apart, taking the head apart, sending it to a machine shop, getting the block itself bored out, head ported and polished, as well as your intake manifold. Then get a rebuild kit and start putting everything back in with new seals and whatnot. I would also suggest getting a 5-angle valve grind done while you've got it out. If you do all this, intake/exhaust/headers/ECU/maybe even upgraded ignition, you should have a 200 plus HP naturally aspirated engine. Got it?

[TrunkMonkey]

I think the stock pistons on a DOHC (91 and up KA24DE) are an 8.6 to 1 ratio.9.0:1The stock pistons from an SOHC (90 and below, KA24E) are an 11.1 to 1 ration.8.6:1 (early 89s had 9.1:1) if you put these pistons in a dohc it will give you an 11.1:1 compression ratio.(the early 89 9.1:1 pistons will bump compression up to 11.7:1)

[trpower7]

Sorry, I guess I always thought of it in final ratio after the swap.

[Zebrahead]

I just installed Windows XP and I lost a bunch of links to car sites. What are the nismo parts sites? One's that actually have online catalouges, mind you.

Thanks,Nick

P.S. Do I have to overbore my cylinders if I get the ka24e pistons? Or do they fit?

[Zebrahead]

Daunt? I wanna do the minimum to achieve a higher compression/more HP. Any ideas? What'll be the damage, price-wise?

Nick

[Zebrahead]

Daunt? anyone?

Nick

[Daunttless]

The KA24E pistons will be a direct swap, a lot of times when people replace their pistons they rebore their cylinder walls, its a way of refreshing the engine, and if you were going to have them rebored, you might as well overbore them 1mm and buy the overbored pistons.

However, hypothetically damage wise, asuming absolutely nothing is wrong with your motor, and you do all the work yourself, it will probably cost you like 200 dollars for the pistons. ~$200

Suggested damage would be 200 for the pistons, like 400 for the rebuild kit, and if I remember all you need is headers for I/H/E, so I"d get those for 350. ~$600

Maximum would be overbored pistons to 90, overboring your cylinder walls, getting a port and polish of your head, rebuild kit, headers, and JWT reprogram. That would be about ~$1900

[Daunttless]

If you did nothing else but raise your compression ratio, you'd probably gain 10-20 horsepower. In conjunction with a reprogram, I/H/E, overbored, and a port and polish you'd be around or over 200 horsepower.

[Zebrahead]

Thank you for your infinite knowledge! About $800-900 for 10-20HP to the wheels is a great buy. Screw wheels!

Thanks,Nick

[Daunttless]

Hehe, yeah, that should have been like 900 not 600. : ) Good Luck with everything!

[b3aspire]

For ZebraHead,

here is a website for nismo parts http://www.courtesyparts.com/ , this place sells everything you would find in the 2002 Nissan Motorsports Competition Parts Catalog. It is a Nissan dealership in Texas.

[Zebrahead]

At courtesyparts.com, they carry the KA24E pistons that increase compression from 8.6:1 to 9.1:1. But it says "SOHC 12-valve engine only"?

If I put them in my KA24DE, it will increase the compression to . . . 11.1:1 you said?

Will there be any risk of damage? Theres got to be a reason it says "SOHC only."

ThanksNick.