SP20 boost pressure/power = broken rods?

[Octane]

Hey guys, haven't been back here for a while....
Just want to ask a Q about the FS-DE (SP20) engine in relation to adding some boost. Now from reading posts on this site and some of the forum members here giving good advice in the past I seem to remember that the weak points in there engines are the rods.

I know one or two of you have done turbo installs yourselves or with overseas kits etc etc... whats the general consensus about boost pressure/power levels before you run into reliability problems on these engines?

And also, the power you can get out of the stock injectors before running over say 90% duty cycle, maybe a malpassi might need to be added in there too to squeeze a bit more out? I think the stock fuel pump should be able to handle a minor increase in power.

We are thinking of running a T28 off a sr20det (not a T25g), or something around the same size (a turbo off an old single turbo 300zx would be nicer).
A 450x300x76mm intercooler is already on order.
A 2.5" exhaust
A microtech running the show (had to be sent back cause the sensors were not compatible with the computer they sent up, since its the first for this engine).
A malpassi IF needed, and fuel pump if needed.

All of this combined should run around 8psi through the normal wastegate actuator, maybe spike to 9psi... is this too much boost or power for these rods (tuned correctly of course, no pinging, running rich), whats your thoughts???? I gather this should net around a 70-80% gain, ie., around 170-180KW at flywheel.
Octane

 

[twilightprotege]

yes long time no speak! welcome back!

on our 9.7:1 comp ratio, i wouldnt be going over 6psi tops, but that's still good for 160kw @ fly i'm pretty sure. stock injectors can handle 170kw @ fly too. they are actually quite large for a 98kw engine.

so yeah, 9psi and our crappy rods and higher comp ration than the americans - expect a rod to go anytime even with the best tuning you can possibly do.

 

[Octane]

With the 9.7:1 compression ratio, its a little high, but there's no problem running 8-9psi with an intercooler, I wouldn't go any higher, especially on a hot day..... but the rod thing is a worry.....

So your thinking that we should be aiming for as little boost as possible? I would have thought the engines would have been stronger, considering it is a new engine, better metalurgy etc... ohh well...

I think the 2.25" exhaust and cat thats already on there should do then, help restrict it a little, keep the boost down as much as we can, and make up a dump pipe to suit the 2.25"...

6-7psi should be fine for 60-70%, with a large improvement in torque at mid range when boost is on, should be much more driveable, without being too close to doing a rod in.
Octane Anyone elses experiences?

 

[twilightprotege]

even at low boost you'll be pushing the boundry of the rods. dont forget it's torque that makes things go boom, not hp.

i would strongly advise against turbo over 4psi on the 2.0L. the 1.8 is another story because the rod ratio is much less and the compression is 9.1:1

 

[Octane]

I thought the only difference between the 1.8 is its destroked (or the other way round if the rods are shorter).
Torque and horsepower are related, a turbo will make more torque in the midrange than a 'high revving NA' engine.

Hmmm, ok, hang on. Lets just say that boost pressure is not in the equation (as it only helps stuff more air in the cylinder, and theoretically raise the compression). While there would be a small amount of extra pressure put on the piston/rods by this, the main determinant is power made.

Hence a naturally aspirated engine making 150HP would be similar in 'stress' that a turbo engine at 150hp would be, right? Well then lets take compression ratio out of this, and say that what the US guys are making power wise before they have reliability problems with the rods. I am not so sure of this, cause a big turbo running 9psi, makes a heeeap more power than a small turbo running 9psi.

Which leads me to the point, these rods give up at a certain 'stress' level. Be it high rpm loading, or too much power (stress) for the rods to handle.

So does someone know what power output some of the US guys (or someone from here who has experienced it) are running reliably? I guess I'm just finding it hard to believe that around 160KW out of this engine could cause rod failure. I'm thinking 200KW (or 200HP@wheels) would be stretching it, but not as small as the increase we are looking at.
Opinions?
Octane?

 

[twilightprotege]

yes the 1.8 is de stroked and the rods are the same length. so it has a much higher rod ratio which is better for strength.

also, 150hp from NA and turbo will give the same stress yes, but only if the power curves are equal. pretty much always, a turbo will have more power down low - and that's where the torque is and that's when you'll have problems

at the moment we're pretty sure the rods give out to pressure, not rpm. rpm doesnt help though.

reliably, the yanks can run 180whp. and yes, a big turbo at 9psi will make more power than a small turbo @ 9psi because of heat and a smaller turbo is more restrictive for the exhaust gases. another thing to point out, a turbo on a standard engine making 9psi wont make as much power as a turbo on a free flowing intake path (ie head work etc) on less psi. psi is just the pressure in the system, so a more restrictive system needs more psi to make the same amount of power

 

[Octane]

Okey dokey....

Yep, absolutely correct about the turbo making more power in the mid and upper range, its essentially a turbo bolted onto a stock motor, stock cams designed for good mid-range etc...

Lets look at it this way.... since rpm and torque are used (with a factor) to calculate HP, this means that having a look at a dyno graph, just say the turbo engine is doing 3500-4000rpm, and is on full boost (say 6psi). At 3500-4000rpm, actual power output is probably no more than a stock engine with extractors and exhaust + filter at PEAK power output, of say 115KW... the thing is that the turbo motor then keeps building rpm and power output all the way to redline (depending on how restrictive things get, torque will drop off, and power will 'crest').

So given that torque is building or remaining relatively constant from 3500rpm and onwards, the actual stress on the engine at mid range rpm's is not as much as it is as revs rise and power output increases.
Hence, the turbo motor will be the more 'stressed' for a longer period than a NA engine making the same power because it is at high levels of torque for longer.... *phew*
The trick is to keep the 'stress' on the rods below a point where damage can be done, do this and you should never have a worry, start to get to the point of damaging them, and they will eventually let go, go waaaay past the point they are inteded to, and it'll blow on the dyno,

Ok, so your saying that reliably they are making around 180HP@wheels, I think that keeping the boost as low as the turbo will allow (hopefully 6psi through the actuator) will make around 160, maybe 170HP@wheels tops.
Octane......

 

[twilightprotege]

exactly. peak hp on an NA and turbo might be the same, but a turbo will have more power below peak (well it should).

i forgot to mention, but that 180whp for the yanks is with their 9.1:1 comp ratio as well

fyi, torque (lbs-ft or whatever it is) = (hp x 5252) / rpm so at 5252rpm, torque will always equal hp.

also, if you're not sure (since you're a rotary head - dont worry, i'll be a rotary head next - series 6 rx7 with a bridgeport 13b and big single turbo (prob T66 or equiv)), rod ratio is the ratio between the length of the rod and the stroke. i think the 2L has a rod ratio of 1.45. the 1.8 has a rod ratio of 1.57 which is much better. the lower the rod ratio the more movement the rod does from side to side which is bad for hp, but good for low down torque.

 

[Octane]

Yep yep, the longer rod has greater 'effective length' for those engineers out there.... hence more stress on the longer rod.
Point noted.

9.1:1 u say. Do both the 2.0L and the 1.8L have the same 9.1:1 compression ratio over there? Damn 9.1 is soooooo low, its like they wanted a turbo thrown on them

Octane

 

[twilightprotege]

actually the other way around. longer rod = better.

think of a triangle with a flat bottom and equal sides going to a point at the top. sorta like /_\

now make those sides short (ie short rod). see how great the angle is at the top of the triangle? now make the rods long. reducing that angle is the key to happy rod life. so you either do that by getting a shorter stroke (by why would you), or increasing the length of the rod

actually i dont know what the 1.8 is over there. shortly after the sp20/protege5 was available in america they made all the cars 2.0L

 

[Octane]

Ahhhh yep, understand what u mean now, I guess the power (depending ignition timing) is actually building very close to TDC, but mainly at TDC and just after TDC, where the rod is at its most susceptible because of the angle. It still does have some advantage becauise of the shorter rod, depends where the weak point of it is though, the 'I' section, or big end/small end connection??
Interesting stuff....
They made all the cars 2.0L...... lucky them....

This turbo job will still go ahead, will monitor the power output and not go over 6psi or much more than 160HP@wheels...... hopefully. Will post here when the job is done (hopefully soon!!)
Octane

 

[twilightprotege]

i think the problem is the centre of the rods.

if youre mate getting a new clutch? keeping the stock or only slightly firmer than stock is a good way to protect the gearbox and moving parts

 

[Octane]

He got that clutch we talked about a while back, from some place in brisbane, a fair few $$$ though. Its not a button clutch.... it has more clamping force and a better clutch face from what I know, but it is still a sprung centre. It will handle the turbo.

The 2nd gear cog is very beefy/chunky and I don't think he will have many problems. The 3rd gear was the one he has munched slightly. If it goes, a new one will be thrown in, he knows it would have eventually died if he kept up his usual driving style.

He now has the short shift kit and the kartman bushes or whatever..... and says that its soooo much easier and more precise. Plus he will go easier with the gears with the large increase in torque the turbo will give.

Fingers crossed anyways..... hehehehe.....
Octane

 

[twilightprotege]

oh yeah, forgot about that (dur)

has he had another go at the drags?

 

[Octane]

Nope, he hasn't been back to the track since the new clutch/short shift went in. He kept saying that he thought the clutch was always slipping. I think his best was a 15.91 @ around 86 MPH with some not so good 2.3 sec 60footers.

Guessing a mid-high 14 when the turbo is slapped on, I guess traction will become a major issue. Once she gets going though, should be good

The intercooler he was supposed to get in about a week, is gonna take another 3 or so weeks cause the guy got the wrong order from overseas.... a bigger cooler than what he needs... or can fit.... that sucks bad, hate waiting for stuff, especially after already waiting a month.
Octane