How much boost?

[ptyEvoIII]

Hi! guys, first time to post in this section, I`m new so, sorry in advance if this is a lame question or out of place.

o.k., this is the problem: right now my Evo is in my brother`s shop, because it overheated and over boost about two month ago, because of this, I bought the MLS headgasket, ARP headstuds, timing belt kit, refresh the head and block, and did the machining work so I can put WISECO 9.0:1 .020 overbore pistons in it...

when we took out the piston one of the rods was bended, the real question here is: how much boost can take the engine with this work and the mods on my signature, the last time I drove it, was putting 17 psi, of boost...

I open a thread because the question have to do with my car setup, and don´t think much people have my specific path or way to go...so I think search was very usefull, correct me if i`m wrong.

thanks in advance,


P.D. : petbeemer, I hope you can answer me this question because I know you are the man here!!

[petbeemer]

sounds about the same as our own e4 m8 tbh
Bill drove it everyday without fault then one particular day it sounded un-healthy,we stripped it down and found a bent rod!
months latter after the rebuild i decided to let him loose with an avcr as boost was always a let down on the rollers.
After fitting the avcr and trying to set up to run 1.6ish i noticed the record function was showing over 2.0bar boost even though while driving it wasn't anywhere near that figure and we where trying to get it up!
we latter realised it was the usual actuator problem and the motor was indeed hitting silly amounts of boost!
That in itself didn't kill the rod but a combination i reckon on how power was applied with the boost spiking at the same time

[ptyEvoIII]

yeah! sound very close to what you describe!

he was boosting 10 psi, when I took it to my brother shop for a little heating problem, vaccumm was 20 hg/mm. that was a Friday, when I was driving it Saturday it suddendly overboost to around 20psi, in idle was like 15 hg/mm, that was the first sign of something wrong...then we notice serious blow by issues, suspect the headgasket

we put the headgasket, ARP bolts, and new timming belt kit, take the head to a machining shop (was fine), bottom looks good, so we put everything back together... I drove it around the block, spike 'till 17 psi, and once again blow by...

so we took out the motor, do the machining work for brand new forged pistons, and hope to solve the problem! nevertheless i`m a little worried about spiking to 17 psi again and bend another rod (I bought a new one for the bend one)...My concern is how much boost can hold with all this work...and if you can tell me what other thing to look?

[petbeemer]

Originally Posted by ptyEvoIII

yeah! sound very close to what you describe!

he was boosting 10 psi, when I took it to my brother shop for a little heating problem, vaccumm was 20 hg/mm. that was a Friday, when I was driving it Saturday it suddendly overboost to around 20psi, in idle was like 15 hg/mm, that was the first sign of something wrong...then we notice serious blow by issues, suspect the headgasket

we put the headgasket, ARP bolts, and new timming belt kit, take the head to a machining shop (was fine), bottom looks good, so we put everything back together... I drove it around the block, spike 'till 17 psi, and once again blow by...

so we took out the motor, do the machining work for brand new forged pistons, and hope to solve the problem! nevertheless i`m a little worried about spiking to 17 psi again and bend another rod (I bought a new one for the bend one)...My concern is how much boost can hold with all this work...and if you can tell me what other thing to look?

Pretty sure that they can take good amounts of boost and much more than 17psi so long as its stable and not spiking.
The problem lies with not being able to record how much it spikes because its so fast when it does it,even the record function on the avcr didn't record the full value of the spike i doubt.
But plenty of cars ive messed with have run 1.6bar happily,Si's evo9 although slighlty newer designed rods was running 1.8bar with an idiot behind the wheel everyday/night

[ptyEvoIII]

thanks bro!! i´m much more better and safe, I`m waiting to put together again the car to start testing it...nevertheless, I just talk to my brother and tell him to check the actuator, a think is a 1 bar actuator because in the beginning was boosting 14.7 psi

[andrewzaragoza]

im not familiar with the early models of evos but for the evo 8 & 9 there are a lot of them boosting around 22-23 psi on pump gas. for these models of evo the first thing the usually gives way are the rod bolts when they around above 400whp. i guess if you opened your engine up then might as well do a full rebuild on it. so that it could handle much more power that you will ever need. just my 2 cents.