Hi guys I was bored the other day and did some calculations on franken s2k motors , or motors with a combo of ap1 and ap2 parts. Mainly rods crank and pistons. From the calcs I found 2 desirable combinations The first is for the Na guys. If you use an ap1 piston with ap2 crank and rods you net a 11.8 compression ratio, which I think is close to the Jdm piston. I think the Na guys probably already know about this combo.

And secondly and more importantly for us Forced induction guys, using an ap2 piston with ap1 cranks and rods nets us an 10.35 compression ratio ! I know this is still not an ideal compression ratio for turbo, but it may be a step up from the stock set up for the following reasons.

1. Ap2 piston is identical to the Ap1 piston except for the piston dome and oil holes

2. Ap2 piston is almost 9 grams lighter than the ap1 piston.

3. Ap2 piston has better oil wiper hole placement. Below the oil wiper rings, see pic.


So if you decided to go with this setup you could benefit from the lower compression ratio, allowing you to run more boost or have a greater factor of safety, all while maintaining the factory quench pads. Also you could benefit from the lighter piston allowing you to spin the motor faster. And lastly you would consume less oil due to the better oiling hole placement.
Right now Im wondering if anyone has tried this combination? It seems like a cheap way to gain some power or safety factor for people who refuse to use a head gasket. Although Im not sure if it would be worth it just to lower you compression ratio by .65. I guess the real question would be how much more boost / power could I run with this setup on pump gas? Just my thoughts, any feedback appreciated. thanks


Oh yea I almost forgot the ap1 crank with ap2 piston and rods nets you a 7.1 compression ratio !! wow this might work with a really big turbo, however the stock quench distance goes all to hell with this configuration.


Here are my excel calcs, sorry for the shity pic, Im having trouble importing a decent photo.

Ap1 piston is on the left, notice the oil holes are in the middle of the oil wipers.

 

Can anyone else verify that they've seen it done. Sounds something I could do.

 

this only helps ap1s tho ryte??

 

Well since you would have both ap1 and ap2 parts, technically you would be an Ap1-2 hybrid But to answer your question the block is the same, but it would be much harder to convert an ap2 because you would have to change the crank and rods, instead of just the pistons like in an ap1. but on the other hand if you convert an ap2 you will already have a good set of pistons. You would just need to get an ap1 crank and rods. But on the downside you would lose .2 liters of displacement if you converted an ap2, maybee not worth it.

 

This is some very interesting and good information. I think the 10.35 CR wouldn't be bad at all.

I'd like to see Inline maybe try this to see what they think.

 

wow....this sounds really interesting. I want to try this. I would think + 2-3psi extra could be achieved as the stock CR is 11.10... 10.35 is a nice drop.

 

Boy im really behind on knowledge here . I had no idea Ap1/Ap2 pistons were different ! That is some good info An Ap2 piston in my Ap1

 

AP2 engines have a different stroke...so the CR appears to be the same but the AP2 piston has a lot less dome...which actually might help the burn on a FI engine as most FI pistons have a dish rather than a dome.

 

sounds like some cool info. I know a lot of built engines run at 10:1 which is pretty good especially with how well our engines flow and how efficent they are. excited to hear what the tuners out there think of this. My miles are getting high a cheap oem rebuild would be nice.

 

If anyone has a set of good condition ap2 pistons I would love to be the guinea pig for this. I have a freshly honed block on my work bench waiting for some pistons. I was going to build a 2.2 liter but this sounds more interesting!.