RA95

Wondering about peak boost levels now my FMIC is fitted and car boosts high very easily.

Car has STI v6 block, early heads, forged pistons, uprated metal head gaskets and big head studs (as well as ecu/remap, injectors etc etc.)

What's a safe peak boost level for this configuration?

Local specialist showed me rods which had been bent by hitting too much peak boost, something I'm keen to avoid!!!

harvey

iTrader: (48)

The block is good for at least 2 bar but the pistons and rods will be the limitting factor but you do not state what make or give any other details as to other mods.

RA95

pistons will be ok they were previously upgraded along with block, and with almost everything else on the car. Only rods and crank are original STI v6.

Standard rods are still in there so they are definitely in danger then and will be next on the list before a turbo capable of running higher boost levels goes in.

harvey

iTrader: (48)

What pistons???
What boost to you think may be required?
I have seen O/E rods bent in the high 300s but that may have been with missuse. Around 1.5 /1.6 bar. By 400 bhp I would be starting to think about steel rods and it is best to fit them with a set of quality forged pistons.

exvaux

iTrader: (1)

standard sti5 typeR and im running 1.4 bar,has done since i got it 2 years ago

RA95

thanks harvey, sorry for being a bit vague about mods, sounds like top quality rods are required before I change anything else on car, and that's been recommended along with the turbo upgrade by my engine builder (who showed me the bent rod which was caused by running a standard rods build at 1.8 bar) as well as possibly the crank (although others have suggested the STI 6 crank is good for 450+)

Currently peaking at about 1.6 bar (VERY short peak periods) so should be safe for the moment. AVCr is set at 1.5bar and generally holds this from 4-7.8k RPM with no overshoot, except when I floor it in 3/4 gear up a hill or something which loads the car more. Under these conditions (and since I fitted a hooooge APS FMIC) flooring it causes the boost to surge initially but then level off at 1.5 bar.

Can't remember make of the pistons, it would be on the receipt somewhere but I can guarantee they are not crappy nor were they cheap. Specialist recommends only top quality parts normally cos he know's I will upgrade eventually. Block was a brand new STI v6 short motor, triple metal head gaskets (possibly lower compression ratio or something?) , pistons, lifters etc all changed. heads were ported and polished, along with 550cc Injectors, FPR, blitz SUS, PFC custom mapped.

Car is currently limited to approx 370bhp by the turbo (an educated guess, based on maxing out a TD05) It rolling roaded at 350bhp with the mods above but BEFORE the FMIC (so that's 350bhp with the original 1995 tiny slanty TMIC) on optimax + CVL.

Did get a few funny looks at the SIDC rolling road day when I did 350, since the brakes hadn't been upgraded at that point

silent running

Someone correct me if I'm wrong but isn't the strength or otherwise of the bottom end basically down to rpm and nothing more complex or exciting than that? I see a lot of threads talking about how certain power or boost levels will break stuff, surely it's down to the speed you want to run the engine at when you're loading it up?

harvey

iTrader: (48)

To run high boost levels you need good pistons so that is worth investigation. You also need good rods to run with these pistons. There is not much wrong with the OE Subaru crank and the latest STi 9/10 crank is as good as anything and reasonably priced.
On standard rods and pistons I would not run more than 1.4 or 1.5 bar but once these have been uprated, essentially you can run what you want providing your injectors and turbo are up to it.
In the past with a particular turbo, I found there was more power running at 1.85 bar than at 2.2 or 2.3 bar so it really depends on your choice of turbo as to what boost you run.