Low Compression Pistons vs New Shortblock

[SilverTipp]

For when I upgrade to a turbo ... I would like to lower the compression to better protect the engine.

What am I missing out on by just changing the pistons instead of a block? How much can the stock rods handle, etc.?

Any info is appreciated!

[JP]

if I was going to the effort of pulling down an engine to do the pistons, I'd switch to stronger rods for the minimal extra cost. The majority of engine failures I've seen so far have been snapped rods

[Reaper]

450 - 600whp is where the rods have issues. What fuel are you planning on using? Theres a growing number of us on stock engines over 400whp on e85 without problems.

[mrk1]

I agree with @JP. If you have everything out you probably just should change them. And you can reuse your block provided it's in good shape. Most people go with a short block if they toast the original one or are real short on time.

[DBW]

I plan to build mine at some point, forged pistons and rods. But I will keep it high comp since all I ever run is e85.

[shiro]

Speaking from personal experience and now having a built engine (by FullBlown ) it would be extremely wise to build your whole short block if you plan on doing any internals.

My first turbo on this car was a Greddy running E85 and pushing about 11-14psi. After 600miles of having my turbo on one of my rods broke and perfectly punched a hole through my short block. My tune at the time was pushing 300whp. It's kind of a pain in the a$$ shopping for a new short block (ended up buying a whole engine for a good deal). This might not happen to you since there are a lot of people pushing 14psi (E85) and not having any issues with stock. But honestly, these stock rods are garbage. I've talked to a few Subaru techs and they didn't seem to be too impressed when they did an analysis of my blown engine (since Toyota wouldn't touch the damn thing lol).

My new build is a 10.0:1 compression ratio built short block with Full Blown 1000hp rods. I also decided to go with Full Blown's turbo kit because of the flexibility. The car is a beast now and not too much lag from the 12.5:1. I'm pushing 18psi (E85) right now with just over 400whp and still have more room for play. I'm really happy with how LJ at FullBlown did on the car. I would shoot them a message for sure on your engine. They have some good options and knowledgable people.

Hope this helps!!

[arghx7]

Originally Posted by shiro

Speaking from personal experience and now having a built engine (by FullBlown ) it would be extremely wise to build your whole short block if you plan on doing any internals.

My first turbo on this car was a Greddy running E85 and pushing about 11-14psi. After 600miles of having my turbo on one of my rods broke and perfectly punched a whole through my short block. My tune at the time was pushing 300whp.

As I've mentioned in other threads, the limiting factor on the rods may be the peak cylinder pressure. That's determined by knock events, and in the case of E85 operation spark timing. I know that sounds a bit confusing.

If you have a significant knock/preignition event, your cylinder pressure will spike very high and can damage something. The rods seem to be one of the limiting factors. However, you can also stress the hell out of the engine by high loads (high indicated mean effective pressure/combustion torque) at more advanced spark timing on E85. This is why you hear "oh I blew my engine at this horsepower" "no, my engine could do this power and it never had a problem." It depends on the combustion pressure, which depends (simply put) on load and spark timing. When you advance the timing on race fuel/E85 and boost, you start running more like a diesel. And then shit can get real.

[SilverTipp]

Thanks guys! Good to know. Sounds like a full blown shortblock might be the way to go since the pistons + rods I'm looking at would be about 2k together plus more labor and time than swapping a block.

I'm planning on running both E85 + 93.

[King Tut]

Originally Posted by shiro

But honestly, these stock rods are garbage. I've talked to a few Subaru techs and they didn't seem to be too impressed when they did an analysis of my blown engine (since Toyota wouldn't touch the damn thing lol).

Will you be making a post with any pictures and info on the results of the teardown or did I already miss it?

[King Tut]

I think that throwing in a set of rods and lower compression pistons to really press the limits on 93 octane in this motor is what I would do.

[shiro]

Originally Posted by King Tut

Will you be making a post with any pictures and info on the results of the teardown or did I already miss it?

Absolutely! Probably not in the next two week since I've been tasked with finishing my graduate studies papers and some side documents for work. But I want to incorporate all this into a nice personal journal. It should be pretty interesting

[SmsAlSuwaidi]

Originally Posted by King Tut

I think that throwing in a set of rods and lower compression pistons to really press the limits on 93 octane in this motor is what I would do.

this

just like @Dipstik-sportech over 420 with maple syrup gas is impressive