Quote:
Originally Posted by jessrayo
The limits of the LT1 engine are all very closely intertwined around 550 whp. GM developed this engine to make 450 hp and when you exceed that you run into multiple problems.
1. Fuel - you oversimplify with the LT4 pump and injectors. The car has both a low pressure side fuel system (electric in-tank pump) and a high pressure (mechanical) pump system. The biggest power boost can be gained by upgrading the low side pump. Not a lot of discussion about this because it is easy. Any of the pump upgrades from gen5 port injected cars can be used to supplement the low side.
High side upgrades are the main limiting factor in these engines. It is really hard to get the amount of fuel required to make big power through a tiny direct injector in a fraction of a second. High side upgrades currently can be done with a cam (increased lobe size gives more pump from mechanical pump), pump upgrade, or injector upgrade. Because the car uses direct injection these options are very limited. To this day very few aftermarket parts exist that are better than the stock GM parts and those that do exist are very expensive. Lingenfelter sells a 1000hp pump and injector set for $6000 and that is as far as I know the only direct injection system than can dyno 1000hp period. No other systems can touch this power level stand alone. The GM stock LT4 pump and injectors will give you around 800 hp max and it is really best to run them as a set. The injectors are designed to run a certain fuel pressure. The LT1 pump and injectors were developed along side each other and so were the LT4 parts. You can run the LT4 injectors on the LT1 pump but they are not as efficient and same with the LT4 pump with LT1 injectors.
Perhaps the easiest way to overcome this direct injection fuel restriction is to add a port injection system on top of the direct system. This is exactly what GM did to get the power they wanted from the new ZR1 corvette engine. Many builders have done this to make big power builds but so far the factory computer does not support this and the aftermarket is a cluster of not well tested products. There is no doubt in my mind this is the direction we are heading to beat the limits of direct injection but the tech is still relatively new.
2. Compression - The stock LT1 is 11.5 to 1 compression. Boost has a multiplication effect on the compression ratio of an engine and when you add a forced induction system you are very limited in the boost you can give the engine before the fuel is so compressed you get detonation. If you run alcohol this not an issue but most of the fuel sold in the USA is less than 10% alcohol. In reality that means unless you are making specialty purchases of fuel like E85 or race gas the LT1 engine is only going to safely make about 650 whp on a tune where you could drive the car across the country and buy gas at the pump.
3. Piston and ring design - the LT1 was not designed to run boost and many, many people that have boosted the LT1 engine over 600whp have experienced an engine failure related to pistons, rings or even rods. To be honest the previous GM LS pistons and rings were better able to handle boost than these new LT1 engines. The stock LT1 engine really needs a piston and ring upgrade if you plan to take the engine over 600 whp and run it hard.
In my opinion the LT1 is about a 600 whp max engine without major upgrades. The LT4 is about a 1000whp engine without major upgrades because GM adjusted the compression ratio and piston and ring problems. So, not just the LT1 injectors or mechanical pump but a cluster of limitations.
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I appreciate your post. I'm sure a lot of people will learn from this, but this is far from my first venture with a boosted engine.
High compression puts the limit on your fueling, not the piston. You can run fat or higher octane to get around this.
I don't think "600whp" is the limit. Since we want to talk about over simplifying the limit is posed by ignition timing and fuel, as it's been well documented that lt1 pistons are the issue. It's also been suggested that the ring gap is inconsistent from GM. We can't put a "limit" on this part until we've established that 600whp is not a functional number.
First because dyno numbers are a joke. The only realistically accurate way to compare power is trap speed with similar DA, similar weight and similar drive train. Otherwise it's a crapshoot. A dyno is a tuning tool. Not a ruler to measure your dick with.
Next power delivery is different for power adder. Roots have a lot more load low end that can change in combustion chamber conditions on a long pull, compared to even just a centrifugal blower. The increase in torque of a roots blower will also mean much more rod load as well. But more grand scheme, you can't compare "600whp" from a big 2.9 whipple to "600whp" to that of a turbo, na, or even nitrous. Parasitic loss is different for each, meaning that the piston and rod loads experienced in each are different.
Then that means even more for fuel system. Blower cars need more injector and pump than non blower cars. Cam timing is different for each, which means valve overlap is different for each, meaning dynamic compression is different for each. Which means different combustion chamber temps across the strokes.
Lastly the lt1 has been pretty well proven on the c7. Yes the load is lower on the c7 due to less weight, but I think a lot of people are being steered shy of the lt1's actual functional potential from a few bad experiences. It might be that GM uses less consistent tolerances on the SS than the c7, but without further probing we can't say for sure.
Again, I appreciate your post. I'm sure a lot of people will learn something for it. We can take tangents all day. Down the road I'm sure plenty of people will google and find these posts and learn something new. But I created this thread to try to answer a specific question, that personally the last 6 months of reading have yet to shed any direct light. Your post, and this may come across harsh, however well intended puts us nowhere closer to an answer of the topic at hand.