pistons question

[Kwanza]

Originally posted by Flashmn
Well good for you.

You still crying over the 4AF carb bit? Get over it dude. It's very basic stuff you as a tech in training should know... You make it sound like he's gonna blow up his engine if he decides to throw down used pistons. You're not even considering specs... which is BASIC stuff when it comes to building motors.

Anyway... I'll again repeat. 4AGZ pistons will not reduce compression in a 4AFE or 7AFE. The compression chamber design of the 4/7AFE head is different from the 4AG so compression levels have been proven to increase. A celica dude tried to go this route to turbo his 7AFE and he ended up with compression in the 11 range. it'll probably be less in the 4AFE because of the stroke ratio differences, but compression levels will probably go up.

[Flashmn]

You still crying over the 4AF carb bit? Get over it dude

Why would I be, its not like its gonna crumble my world.

[TRDemon]

i did a compression test already and the results was
cyl1: 165psi
cyl2: 170psi
cyl3: 170psi
cyl4: 165psi

is that bad if i wanna charge it??

[Flashmn]

sounds ok to me.
The compressions arent really that important considering boost. If you have bad compression, you'd have large blowby (if it was pistonrings) or bad emissions (if it was bad valves). Its the compression ratio of the piston that is the important aspect.

[Pineapple]

Compression indicate the health of the engine. You'll kill the engine if you boost one that can't hold pressure. What's the point of boosting it if all the boost gonna go into the crank case?

Looks like you got good compression on all cylinder. I believe it should be between 140PSI-200PSI.

[Kwanza]

Originally posted by Flashmn
Why would I be, its not like its gonna crumble my world.

Yeah... but you sure do act like your panties are in a bunch.

Mild compression such as the 4AFE (9:5:1) isn't gonna be life threatning so long as you supply the fuel. High-compression and boost makes detonation a lot more dangerous, that's why boosted motors are lower compression. So long as you supply a good amount of fuel, you should be ok under modest boost level (up to 8-10 psi)...

[Flashmn]

Compression indicate the health of the engine. You'll kill the engine if you boost one that can't hold pressure.

True, it is...but you wont directly kill the engine, you'd get alot of blowby, which would basically kill your oils. (you cant exactly run a closed breather with a turbo, like you can do with an NA), which would kill the engine.

9.5:1 is boostable, just I wouldnt run very high boost with the 4A-F connecting rods, they arent exactly meant for boost applications. However, keep moderate boost and you'd be fine.

And detonation is dangerous with whatever compression you have. Just the tendency to detonate is lower with lower compression.

[TRDemon]

thanks guys for the info

[Pineapple]

Question: will blowby affect O2 reading?
Its not good to have boosted blowby in crankcase. The whole crankcase is kind of sealed. You may blow some seals and get oil leak. Also blowby will heat up the oil. You'll need a new engine very soon. Its not a good thing.

[Flashmn]

Its not good to have boosted blowby in crankcase. The whole crankcase is kind of sealed. You may blow some seals and get oil

Well you get blowby on naturally aspirated cars too, thats why you have the PCV(positive crankcase ventilation). Well having an open breather wouldnt affect emissions, having a clogged one would.

[TRDemon]

hey have a friend that turbocharge his car and his compression ratio is 10.3:1 isn't that risky but he got 10psi just before he blow the engine. but the thing is its a different car all together.
the thing is i'm going turbo charge but ONLY !!!!!!! 3psi

[TekPhobia]

Originally posted by TRDemon
hey have a friend that turbocharge his car and his compression ratio is 10.3:1 isn't that risky but he got 10psi just before he blow the engine. but the thing is its a different car all together.
the thing is i'm going turbo charge but ONLY !!!!!!! 3psi

Pfft...3psi isn't even worth it. You'll get 1psi @ WOT on a N/A motor. You know as well as I do you won't run 3psi for long...

-Tim

[TRDemon]

ok guys i'm serious, i only want 3psi but thanks for the info, i'll keep you all posted