Compression and more!

[ElHeffe86]

Ok... Im doin a K24 swap with K20a2 heads... So Ive run into some questions Im not sur about at all.... So here they are. For the pistons..... What bore; 87.0, 87.5, 88.0, 89.0, or 90.0. Now compression....a couple of these wont go with some of the bores... but I know yall know this already.... 9.0:1, 11.5:1, or 12.5:1. Now onto the valves. Intake size: 35mm, 35.5mm, or 36mm. Exhaust: 30mm, 30.5mm, or 31mm. So... again I don't know anything about the bore sizes, compression or sizes of the valves... SO any help would be outsanding. Thanks alot!

[talonXracer]

What are your plans for the block? and how deep is your wallet? Sounds like you need to do ALOT more research on your build.

[ElHeffe86]

What do you mean what are my plans for the block, and my wallet will be real deep within the timeframe i plan on doin this. Im buyin myself a K24 block and building it outta the car, then gonna drop it in once th full build is done. I know I have alot more research to do, Jus figure I would start out here among people who have done it before and have a vast knowledge on our "slumbering beasts". Thanks

[talonXracer]

Well you still have not said what the intended use will be, a DD, a strip car, a autoX car, a show queen?


The largest pistons you should go is 88mm, you can try 88.5, but it will be a biotch to tune and be very short lived.

Will you have the future resources to overhaul the engine again?

Do you want longeviety or max whp?

[ElHeffe]

O ok lol sorry, Im wanting to do autox in the car and if needed i will have the money to overhaul it again. I haven't definatly checked to see what a good hp/tq rating would be for this can yet for doin the autox and Im wantin a good mid way mix between longevity and max hp.

[Lucid Moments]

On the stock sleeves what I would do is to get 87.5mm pistons and have the bottom end bored to match. That leaves you room to bore it again if you have problems later. For compression it depends on what kind of gas you can get. I see you are in Ks so I assume you can get 93 pump? With that then I would go 12.5:1 and be prepared to spend a little money getting tuned and never put cheap gas in your car. Have you considered E85? I would love to run it but its availability down here is poor, but I expect in Ks it is probably pretty common. Something to think about anyway.

[ElHeffe]

Ya I was planning on doin an E85 swap. Im headin back home to IN in a couple months, so I have a garage that does amazing tunes back there. So I will have a good tune on it. Im getting the block re-sleeved too. Also all I run in my car is the 91 that is available in the area Im in. So would you still recommend the 87.5 and 12.5:1?

[Lucid Moments]

Ya I was planning on doin an E85 swap. Im headin back home to IN in a couple months, so I have a garage that does amazing tunes back there. So I will have a good tune on it. Im getting the block re-sleeved too. Also all I run in my car is the 91 that is available in the area Im in. So would you still recommend the 87.5 and 12.5:1?

Okay, E85 or 91 octane? Very different builds. For 91 octane I wouldn't go beyond about 11.5:1 compression. For E85 you can go much higher. Probably 14:1 or better, but not having done one I am not thoroughly versed in an E85 build so my knowledge is limited on them.

I am not a fan of aftermarket sleeves. I have had a couple of bad experiences with them, and my bad experiences were with top notch sleeves installed by a top notch company. Plus while I'm sure it may have happened, I have never even heard of a K-series motor having an issue with the sleeves. Unless you count a rod breaking and going through the sleeves a problem. That being said, with aftermarket sleeves you can go with a bigger bore. If I were going with aftermarket sleeves I would probably start with an 88mm bore. That leaves you room for a rebuild later on. With stock sleeves 87.5 is still where I would start.

[ElHeffe86]

Right now Im runnig the 91 octane cuz that's the "premium" around here, When I get my K24 block I am gonna start piecing it together. But if there have been no problems with the stock sleeves I will just run those. So what about the different valve sizes for the intake and exhaust?