Project Thread LS 400 Single Turbo

[stevechumo]

The rod fails at 7 psi means there gotta be a serious problem with timing or something else, even though the rod is skinny.

 

[Arnout]

The rod fails at 7 psi means there gotta be a serious problem with timing or something else, even though the rod is skinny.

7 PSI on a T88 is already a lot of air & power. There was nothing wrong with timing, we were running very conservative and also there was no sign of detonation at all (nothing on the pistons).
Also timing doesn't kill rods. How can it?

 

[stevechumo]

7 PSI on a T88 is already a lot of air & power. There was nothing wrong with timing, we were running very conservative and also there was no sign of detonation at all (nothing on the pistons).
Also timing doesn't kill rods. How can it?

If your boost gauge is measured in the intake manifold, then 7 psi on a T3 or T88 is pretty much the same because that's how much pressurized air there is. If your timing is so advanced, that'll kill the rods while the rods are moving up.

There're something wrong with the forum server here. I didn't post any pictures but they just keep finding their ways into my posts. LOL

 

[Arnout]

So you're saying that it doesn't matter what turbo you have, if the boost pressure is the same you are making the same amount of power?

 

[spf_lexus]

Gotta remember boost in general is a measure of restriction not pressures. The uz manifold will make your turbo work harder to achieve the air flow you want but nevertheless it WILL flow more cfm per psi than a smaller turbo, period. Will it be a night and day 7psi? possibly. Imagine a single t25 on a 1uz versus a 35r on the same engine, it will make more hp for the same given psi with the weakness being it's inherant lag. Problem is, when you want to raise 7psi to 14psi you will loose a lot of the large frame advantage since all the massive flow at high rpm is working against a low efficiency manifold, with the lag in the first place. If you rework the lower manifold to a short strsight runner design you will pick up serious power at 4k and above. I have seen a few dyno sheets before/after stock and it really shows the bottleneck up top.


Perfect example is my 4.7 project. I am expecting my 1uz 7psi w/ stock heads to drop down to 4-5psi with stock heads but 4.7L block swap. The stock intake restriction is still there but it has a larger cylinder volume to fill before the restriction kicks in. Nevertheless I will loose some hp potential because of the stock mani. Cool part is that at 4-5psi I will make more than I did at 7psi.

 

[JustenGT8]

Not really, Steve is largely correct in that 7psi of air is 7psi of air, but there are a few complicating factors.

For starters, boost isn't a magical thing that suddenly starts, it's just a continuation of increasing pressure above ambient pressure. In absolute terms an engine (at sea level) is seeing 14.7psi of 'boost' all the time. So just like an n/a engine that has an airflow 'need' a turbo engine operates exactly the same.

Airflow NOT going into an engine at an rpm creating 7psi will be the same for a large or small turbo...it's airflow and gives no fark for what made it The difference is the airflow from a larger turbo will likely (bit not necessarily) be cooler and denser and that's where the extra hp can come from. This difference in density can be quiet significant.

 

[stevechumo]

Justen,
You're a detail oriented man. 7 psi is still 7 psi (pound per square inch and it's a unit of pressure), and you're correct that there're other factors involving to make more power.

 

[XR8tt]

Sheesh lets not forget back pressure on the exhaust side!!
Big engines have a lot of exhaust.. You cannot fit a 500 h.p turbo that may work on a SR20 [2ltr] onto a stout 4.0 engine.. Even though your goal is around 500 h.p..
You have to try and read compressor / turbine maps to find the best combination..
Fitting a smallish turbine tends to bring on a rush of power.. While a better sized A.R turbine may be slower spooling BUT much more tractable..
Being load sensitive they can spool or atleast supply boost at much lower rpm with load... My 5.4 TT Ford spools produces boost at 1200 rpm when pulling the car & trailer.. But being manual and driving with no load it spools up around 2800 rpm..

http://www.turborides.com/article9.html
How to read comp maps??
http://www.turborides.com/modules.php?name=Sections&op=viewarticle&id=13

 

[JustenGT8]

Justen,
You're a detail oriented man. 7 psi is still 7 psi (pound per square inch and it's a unit of pressure), and you're correct that there're other factors involving to make more power.

Well i was mostly agreeing with you Steve

All psi's are not created equal though. Here's a good example...pump up a tyre to 20psi...now heat it up....pressure will rise to say 30psi.....now let 10psi out to get back to the original 20psi.....still 20psi eh but less air Same deal with turbos

 

[stevechumo]

You are now taking another factor in it due to heat. Heat expands and creates more pressure. If you're talking about air volumn and its density, then it's not measured by psi. I didn't score really good in my physics class, but you keep calling for it. That's why I majored in Management of Information System. A physics drop-out as you can say. Here are some good readings about physics on density: http://en.wikipedia.org/wiki/Density

 

[hungryforinfo]

You are now taking another factor in it due to heat. Heat expands and creates more pressure. If you're talking about air volumn and its density, then it's not measured by psi. I didn't score really good in my physics class, but you keep calling for it. That's why I majored in Management of Information System. A physics drop-out as you can say. Here are some good readings about physics on density: http://en.wikipedia.org/wiki/Density

He is right, what he also said a post or so ago about airflow from a larger turbo possibly being cooler and denser stands true, and means that the big one wont be working as close to its limit thereby producing less heat, and the cycle continues.

Great reading in here btw, thanks guys.

 

[JustenGT8]

You are now taking another factor in it due to heat. Heat expands and creates more pressure. If you're talking about air volumn and its density, then it's not measured by psi. I didn't score really good in my physics class, but you keep calling for it. That's why I majored in Management of Information System. A physics drop-out as you can say. Here are some good readings about physics on density: http://en.wikipedia.org/wiki/Density

Dare i say a little knowledge is a dangerous thing Steve

What is controlling the turbo? The wastegate. and what's controlling the WG, the pressure line...the only reason you have 7psi is because that's what you are telling the turbo to deliver.

So, you have a small turbo putting out LESS dense HOTTER air at the 7psi limit.

Your bigger turbo does exactly the same thing but the air is COOLER and MORE dense same 7psi but more air mass.

The engine flow won't effect this as apart from some inertia issues moving heavier air the volume is still the same so flow for the 2 setup is still the same.

Got it now

 

[Arnout]

The rod fails at 7 psi means there gotta be a serious problem with timing or something else, even though the rod is skinny.

So this is rubbish

 

[Thermactor]

So this is rubbish

How much power would you say is the limit for the skinny rodded motor? 330rear wheel horsepower or the like?

 

[stevechumo]

Those are the basics in building a turbo system and I already knew that. I've had built more than a handful of successful turbo systems. What I initially mentioned is about the 7 psi of boost that breaks the rod. I've run 11 psi on a T60-1 (smaller than the T88) and the intake air temperature is only around 105 F when the engine is in full operation. I can touch and hold the intake pipe near the TB for a along time. And when the BOV releases the air, I only feel it's a little warm. I now run T67-1 and the intake temp is still the same. With a much bigger T88, the air can be cooler, but I don't think the air temperature will be that much significant colder. A guesstimated air temp number?

By theory and let's say a fact, bigger turbo will produce cooler air (more O2 density), but how much cooler air it'll produce and how much more power is created from the cooler air will need to be on specific numbers. This will give an idea of that bigger turbo with cooler air that makes more power killing the rods or it's because of something else.

If I have an efficient intercooler on a smaller turbo, I can still have the cool air that makes up for the small size. If the temps from both small and big systems are the same with the same psi, then that'll be equal. I never denied the factor of air density when I initially started the post, but I just brought up the first issue that comes to mind.

 

[JustenGT8]

If I have an efficient intercooler on a smaller turbo, I can still have the cool air that makes up for the small size. If the temps from both small and big systems are the same with the same psi, then that'll be equal. I never denied the factor of air density when I initially started the post, but I just brought up the first issue that comes to mind.

No arguments on that score

 

[Arnout]

How much power would you say is the limit for the skinny rodded motor? 330rear wheel horsepower or the like?

The skinny rods are very very skinny and on top of that the material casting is really weak. It's some weird powder pressure rod or something. It breaks so freaking early, I would throw them away even when you have charge air. Any boost will break them!

 

[stevechumo]

No arguments on that score

You just have to make me work so hard, don't you?

 

[Thermactor]

The skinny rods are very very skinny and on top of that the material casting is really weak. It's some weird powder pressure rod or something. It breaks so freaking early, I would throw them away even when you have charge air. Any boost will break them!

Wow, thanks for that news. I will have to run a huge blower pulley and go very easy on my motor then. Maybe I'll stop at 330 crank horsepower (vs. 260 stock)

 

[JustenGT8]

The skinny rods are very very skinny and on top of that the material casting is really weak. It's some weird powder pressure rod or something. It breaks so freaking early, I would throw them away even when you have charge air. Any boost will break them!

They are a powdered sintered forging just like the early rods just weanie for n/a revs rather than boosted torque. A good process but can't take as much bending force as normal forged rods so do seem to snap pretty easy under boost.