"safe" boost on a stock 3sgte?

[barryogen]

A n00b mate of mine asked me to find out what amount of boost is "safe" on a stock 3sgte from a 1997 Caldina(ST215) with ~75000kms.

He says it has some exhaust work(looks fairly stock apart from the tip to me), and a pod filter, but is otherwise stock.

I'd imagine the answer I get here is going to be along the lines of "leave it as stock unless you are doing fueling etc" or similar, right?

I guess the question is more what amount of boost can the factory turbo give that the stock injectors can give appropriate fuel to?

[barryogen]

anyone?

[strx7]

std boost and not more than a fraction higher

14-15psi is std from memory, and 17-18psi on run of the mill 96 = 3 pistons left.

you could up it to 17psi but MAKE SURE it gets 98 octane and nothing less.

[barryogen]

std boost and not more than a fraction higher

14-15psi is std from memory, and 17-18psi on run of the mill 96 = 3 pistons left.

you could up it to 17psi but MAKE SURE it gets 98 octane and nothing less.

figured... is it a limit of the fueling or something else?

[Adydas]

I personally would find using 98 and running that boost to just mean your delaying the damage, if you can melt a piston @ 15-16psi using 96 do you really think adding 2 more octane points is going to Save the day, Im more likely to belive it just adds a tiny cusion..

Pillows dont stop the pain, they just reduce it....

[fivebob]

Safe boost regardless of octane is the stock level of boost (about 13-14PSI), anymore than that and you risk cracked ringlands in hotter weather. You could add a couple of lbs in cooler weather, but whether or not it is "safe" is debateable.

[fivebob]

figured... is it a limit of the fueling or something else?

There's plenty of fuel. The limit is 9:1 compression, stock ignition curve which is tuned for 100 octane, and the stock interwarmer (+ hot weather)

[barryogen]

There's plenty of fuel. The limit is 9:1 compression, stock ignition curve which is tuned for 100 octane, and the stock interwarmer (+ hot weather)

right, so only easy way around it is ECU to take care of ignition curve(or retard the timing a bit), lower compression pistons, and change to a front mount(or atleast something better than top mount)...

He's going to love being told this... he's a cheap bast@rd... don't be surprised if you hear from me again looking for a new engine for him in summer.

[Akane]

There's plenty of fuel. The limit is 9:1 compression, stock ignition curve which is tuned for 100 octane, and the stock interwarmer (+ hot weather)

There are EVO 7's running crazy amount of "boost" (power) through their factory engine, and AFAIK they're 9:1 as well, what's stopping the caldina running so high (besides the ign curve and the pathetic intercooler)? Would it be down to the piston and head design and squish areas? I wouldn't be suprised if that'st he case as EVO's has come from a long way and they're more refined.

[fivebob]

Well for starters the 4G63 is an interference engine, so it hasn't got deep valve pockets machined into it. All the 3S pistons that I have seen have cracked close to the point where the piston is thinnest due to the valve pocket. Also the machining of these valve pockets leaves sharp edges which make very good stress risers.

Next is the squish area, which is less on the Caldina engine than other 3S-GTEs, due to the way the piston is machined. Squish has been proven to reduce detonation, but for some reason this method of detonation control has fallen out of favour with engine manufacturers. Only problem on a turbo engine is that there's often too much clearance between piston and head to make squish effective.

My guess is that if the cut outs were machined with a small radius it would be less likely to crack ring lands, detonation could be reduced with more squish area, but the piston to head clearance might need to be reduced.

One thing I have noticed is that the 3S-GTE is essentially an oil cooled engine, and while it has an oil cooler, it's the wrong sort of cooler when it comes to a highly loaded engine. As load goes up water temp increases and oil cooling capacity decreases. As the oil temp increases so does combustion chamber temp and detonation soon follows.

[JIZRAG]

Id say leave it stock boost, 3sgte's arent very strong motors in stock form. Ask PRYMAL about his experience with them. he smashed a piston to shreds running 17psi and running higher fuel pressure than stock.

Id suggest just get a full exhaust and give it a gud service etc and leave it at that, they were never meant to go quik unless u start swapping turbo's and ECU's then it just gets expensive

[fivebob]

Id say leave it stock boost, 3sgte's are very strong motors in stock form. if you approach modifying them in a sensible manner

Corrected for truth
BTW you can extract 500HP from the stock internals if you do it properly, and it's as reliable as any other 500HP 2 litre engine that is built on a budget

[Dell'Orto]

Id say leave it stock boost, 3sgte's arent very strong motors in stock form. Ask PRYMAL about his experience with them. he smashed a piston to shreds running 17psi and running higher fuel pressure than stock.

Bollocks to that, I accidentally hit 20psi (or more) on more than one occasion in my MR2 without it popping

[Boosted_162]

Just look at Al's old SW20! It was regulary raced on more than 17psi

[dougsop]

Id say leave it stock boost, 3sgte's are very strong motors in stock form. if you approach modifying them in a sensible manner

Corrected for truth
BTW you can extract 500HP from the stock internals if you do it properly, and it's as reliable as any other 500HP 2 litre engine that is built on a budget

any idea on how ?

[Anth_555]

Ask PRYMAL about his experience with them.

it wasnt his block that let him down, from what im told it had the worng ecu in it

[strx7]

if its tuned correctly and has the right bolt ons they'll make good power reliably.

[barryogen]

thanks guys, I think that we have suitably scared him into doing it properly if at all.