boxBoxegg

Hi folks, new to this wonderful place you call Scionlife.com... I have been an xB owner for well over a year, clocked about 23k miles and am very happy with my vehicle. However, once warranty time expires, I was possibly going to experiment with this tiny 1.5. I'm moderately experienced with vehicles, and I am extremely familiar with the Toyota product. I am surprised how few people talk about compression ratios in proportion to raising the HP in our vehicles (mind you, w/o forced induction) I have tinkered with compression ratios in my past Toyotas. I've never had problems with my older ones taking the strain. Obviously I was using a higher octane to fend of any demons that stress could create.

Likewise in this application could a thinner head gasket, like in my older vehicles, be a good source of reliable HP gain? regarded its within reason? obviously I'm not thinking 15.1 or something of that source, but maybe a 12.5.1 safely. I do know the 2ZZ-FE runs about that, before anyone corrects me, I know the internals in the 2ZZ are more made for that. Oh, another thing I have installed just a header on my vehicle to start, I tried a intake and wasn't all that impressed with it. This car is not made for speed, else I'd still have my All-Trac granted I was looking for that, but It is a hobby of mine to tear things down and "improve" upon them, I think many others in this forum share this feeling with me. Anyone who has endeavored into this mod please give me some feedback as to reliability and results, real and "butt" dynos accepted ;) Everyone thanks for your feedback and/ or ideas.

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Simplyscion

throw a Prius bottom end in your box...they have a 13.5:1 compression ratio.

BrianxB

Do you understand what determines CR?


Anyway, the 2zz in the Celica isnt built to handle much more compression than that. Trust me. The valves are quite thin. Take it from someone who has pulled his own head a few times.

Simplyscion

I think I might have an idea...thanks for your input

x_rayted711

Thats what I'm saying...I really don't think that just because the prius has 13.5:1 CR, that it is the bottom end doing it. Some of us need to read up on this and see what actually raises CR.
Back on topic...I don't think a thinner gasket is available. I may be wrong, but I would think you'd have to contact felpro and have one custom made.

dave72

I'm not going to touch that one (but it sounds like you already have).


Instead of just installing a thinner gasket try having the head machined for a higher compression. I'm not sure how much material you can take off, but a good machine shop should know. You could always refer to a service manual.

While the shop is working on it they can open up the ports a little to allow more airflow. This would probably cost a few hundred bucks but will yield more power.

jwa276

makes me wonder if any other mods would be necessary with doing that. also makes me want to see someone else do it first.. hahaha

-jon

dave72

Opening the ports will accentuate any of the other "breathing" mods that have beed done (intake, headers, exhaust) and milling the contact surface down will definetly up the compression. Care would need to be used to avoid taking off too much material (or else the pistons will make contact with the head), but again, a good machine shop will know how much is too much.

I've never done this to a Scion (or any Toyota engine), but I have had it done on several other cars. It WILL work.

siopaojoe

mill the head...it'll be under $100 and worth it in the end

soros151

Do anyone know the milling limit and how much to achieve 11.5:1 in CR at least?

x_rayted711

The head and block would have to be "CCed" to get an exact CR.

soros151

DANG... I didn't want to spend time with the lexan screen and the antifreeze and measuring.

x_rayted711

Well, due to the cam timing and valve overlap, these engines never see the actual physical CR...Just like the prius...It is 13.5:1, but the piston, cylinder, and head never see that.

soros151

Yhea, I saw the real physical CR for a prius is of 9.X:1. Can't remember it correctly.

Scorpius01

Where is everyone getting thier info on the Prius's engine?
Do not know 100%, do not post what you 'think' something is.

The Prius has a 'physical' compression ratio of 13.0 to 1.

x_rayted711

So I was off by half a point. Sorry. I'll be more 'aware' of what I post and who I post to. Thanks for the correction, though.

soros151

Are we feeling picky?

I meant to say that the effective compression ratio of the Prius is lower due to the Atkinson Cycle.

Better?