How stressfull is 4lbs of boost?

[AN89HATCH]

I am almost done gathering the parts for my kat, but the closer I get, the more im afraid im going to blow my engine :rolleyes My set up is as follows

log type manifoldTeo4h turbo (small)sr20 smic255 fuel pumpstill looking for 8:1 fmu (will this be to ritch for 4lbs of boost?)

My engine has 180k miles, but I compresion tested it all cylinders are above 155 and within 10% of each other. How stressfull Is 4lbs of boost? Most people I talked to say it will be ok, since the ka has low compression. I Will also retard timing around 1-2 degrees by the way it is a sohc thanks

[ziggy682]

It will be just fine as long as you have enough fuel and don't get any detonation. My KA-T has 189K and it runs just fine at 6psi. Once I tune it, I'll bump up to 8psi and see what happens.

[WDRacing]

With 4lbs and a FMU you'll be fine forever, the motor won't wear out any faster then it would in NA mode. 4 lbs is far from stressful so long as you don't detonate.

Brian

[Jookmasta]

i have an FMU; contact me at [email protected]BTW its a vortech 8:1 FMU. let me know

[C-Kwik]

Just consider that the peak cylinder pressure at about double the power output with a turbo is only about 50% higher than it would be NA. The bulk of the increase in average cylinder pressure occurs after the crank position where peak pressure occurs, which basically means it is spread out over the combustion stroke. Theoretically, doubling an engine's power output is achieved by doubling the pressure ratio(NA Motor would go from 1.0 to 2.0 BAR which is 14.7 psi of boost). So 4 psi would be significantly less.

[AN89HATCH]

Thanks guys, for 4-5 lbs of boost this is what I planed for fuel, 8:1 fmu, fuel 255 fuel pump, stock injectors, and a 300zx fuel filter, and the retard of timing 1-2 degrees. Is there anythign elese I should add, to garentee that I will not detonate? Or does this sound good? thanks

Jookmasta I sent you an email thanks

[Drift Machine]

For 4-5lbs of boost you don't really need to mess with the timing.

[Def]

For how cheaply you can get 370cc SR injectors nowadays, I would go with them at a minimum for a KA-T setup. 370cc's + an S-AFC and you definitely have enough fuel for 4-5 psi.

FMU's really aren't cheap(at least good ones), and IMO bring in just another variable to "mess up." You're still going to have to go to a dyno and really check out the AF ratio with the FMU to even know if you're in the ballpark, and you really have no way to tune out any lean or rich spots after that. FMUs always seem like more of a "ragged edge" setup where you are going into severe duty cycles and high pressures to squeeze enough fuel through your wussy stock injectors. Spend the extra little bit now and ensure you have plenty of fuel capacity in reserve.

I'd still retard the timing 1-2 degrees, as you really won't lose much power, but add a little bit more of a safety net. It seems that running only 4-5 psi you aren't so concerned with power, but reliability. So the name of the game is headroom and having a large safety net as far as reliability is concerned.

[AN89HATCH]

Do you guys think an safc+ 370 injectors are necesarry for only 4-5lbs of boost? with an 8:1 fmu, 255 fuel pump, and 4-5 lbs of boost on the ka24e, should this be alittle ritch?? or will it be close to being lean? Also im shooting for a reliable kat, with just alittle extra kick thanks guys

[Def]

The FMU setup will most likely get you the extra fuel you need, but you will have no way to make fine adjustments to the fuel delivery. You can only change the base fuel pressure a few psi or rising rate to make large changes over the whole powerband.

I seriously would *NOT* skimp on fuel delivery if you want a good running and reliable turbo setup. The FMU setup might get you by, but who's to say how good it will come out until you're finished.

FMUs cost over $100 by themselves. That will easily cover the cost of injectors. An S-AFC isn't all that expensive when you consider what a "failure" will cost. I'd even say something like a simple S-AFC would probably be added to your setup in the future when you see how sloppy the AF curve can be with a simple FMU setup.

It's just not a smart place to cut costs, especially when you're talking about only a couple of hundred dollars for a FAR superior setup.

[OP240sx]

I didn't think SR 370cc injectors fit a KA24E, it's top feed right whereas the SR is side feed.

IIRC, I thought you had to use CA18det 370's. No idea where to find them though.

[Def]

Actually, I think that's right. In that case though, you might be able to find injectors from another car that fit in fine that don't fit a KA24DE.

[Frozen240]

In my current setup I'm running with a 7:1 fmu, it works, but I have no control over the A/F ratios. I would really like to get some bigger injectors and a SAFC so I could have some adjustment at varying rpms. I've yet to dyno the car so I have no idea how rich/ lean it is.

[s13sr20chris]

you can add 1 psi for every 1000 rpm after the torque peak and cause almost zero additional strain on the engine.

[AN89HATCH]

you can add 1 psi for every 1000 rpm after the torque peak and cause almost zero additional strain on the engine.

so on a ka engine would this = 6psi?

[C-Kwik]

I've never actually heard of this myself. s13sr20chris, do you have any technical reasoning to explain why this is? My initial thought is that the least strain(other than tensile loads on the pistons and rods) at any psi would be near the torque peak where VE is highest.

AN89HATCH, if I am reading Chris's statement correctly, it sounds like he is saying you can add an additional 1 psi of boost for each 1000 RPM over the engine's torque peak(about 4400 RPM for the KA) without adding any more load to the motor. So if you boost 6 psi normally, then you can boost 7 psi at 5400 RPM and 8 psi at 6400 RPM and so on. But again, it's not making sense to me so I'd like to know the reasoning behind this.

[jdmfreak]

What are tensile loads?

[s13sr20chris]

after the torque peak when ve goes down there is more partial filling. maybe that should read less filling. its a generalization, but you can "replenish"(for lack of a better word) the lost cylinder filling by adding approx 1psi for every 1000 rpm. this is the same reasoning behind not spraying nitrous too low. another thing is that at higher rpm there is less time for detonation to happen. this allows you to run less octane(not really possible in the real world), more ign timing, or more boost. q45tech is the guy that explained it all to me.

[C-Kwik]

That's quite interesting. Maybe I should opt for a Profec E-01 afterall and use it to set boost by RPM as well. I'll have to do some thinking on it's effects on Efficiency and backpressure just to get an idea of potential results. Do you know if Q45tech posted that info on this site? If so I'll go look for it.

[ziggy682]

What are tensile loads?

Tensile loads are forces that pull on an object. Compression loads are forces that push on an object. Engine components can handle compression loads much better than tensile loads. Basically, when the piston pulls on the rod, that is a tensile load. When a piston is reaching TDC, the tensile loads are highest, because the piston wants to keep going up, so it pulls on the rod, and that's how it slows down. When combustion happens in a cylinder, the force pushes on the piston, and causes compression loads. The tensile and compression loads are acting in opposite directions, so they sort of cancel each other out. This is why you can turbocharge an engine, and double the stock horsepower without blowing up the engine, because it can handle the increased compression loads. However, if you tried to double the horsepower by just spinning the engine to higher rpm's, you would blow the engine because the rods would not stand up to the high tensile loads. That is why, when an engine is revved way too high, it often snaps a rod in half.

That's basically the short explanation. Corky Bell goes into some pretty good detail in "Maximum Boost." You should read it.

[s13sr20chris]

with the 1psi for every thou over the torque peak just search(im too lazy). his idea was to use a centrifugal supercharger on a q45 to just add 1 psi per thou over the torque peak. thats with no initial boost. obviously the heat load will go up as well as the compressive forces that ziggy mentioned. the benefit is that each individual "putt" will only load the reciprocating components the same as it otherwise would at the torque peak. or somewhere thereabout. its the rod stress at higher rpms that you have to worry about more than boost(so long as you stay out of detonation). tdc on the exhaust stroke can snap a rod much easier than the other forces are adding up(from the 1 psi per thou method). what does all this mean? how do we apply it? i dunno. the centrifugal supercharger would be easy because you could just gear it up. for a turbo you would need one heck of a fancy boost controller. im not sure that 1 psi every thou would make for ease of control in a corner. maybe .5 psi for every 500 rpm or even .25 psi for every 250. the smoother the better right?