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Don't forget to calibrate your altitude standing pressure in to the math, and would not throw more than 240psi total presssure at the stock block cylinder liners.
If above sea level, that can add boost to make up for standing air pressure being lower, but keep in mind before you drop back down to sea level, want to upsides the top pulley, so your not going over the 240psi cylinder pressure to start with.
Also, keep in mind that this is a TVS ,where is going to be making pressure right after idle, so torque is going to peak right after idle as well.
At 750hp, will be close to 750ft lbs of torque just off idle, will need to dail in TM into the tune, so your not blistering the tires every time you breath heaver on the gas pedal.
I agree about LS7 sleeves cracking. But the biggest factor I've been aware of is they are made of a very hard, brittle cast iron. Add to that their relatively thin wall thickness, and you have the tendency to crack. My take on the cracking has been more to do with detonation than pressure. I agree that pressure can cause the detonation, and cracking is cracking, regardless. As with most serious builds like this, the tune is absolutely critical to longevity......
Thank you for the feedback. I do not want to overcomplicate things, but I calculated these "in cylinder pressures" as you suggest here in this sheet using the static compression ratios. There are differences between the static and the dynamic compression ratios, and of course the amount of air volume you put through the engine. Lowering the compression ratio and adding boost is essentially "keeping the peak cylinder pressure before ignition the same but pumping more air and fuel through the engine, hence, making more power".
I guess that we can further advance this discussion if we focus on ignition timings. What ignition timing are these Lingenfelter LS7 twin-turbos at? What do you recommend? What boost retard per PSI? If the cylinder wall is the limiting factor, then I have to make dead sure no detonation occurs.
What boost retard per PSI? If the cylinder wall is the limiting factor, then I have to make dead sure no detonation occurs.
Now your catching on, and timing retard, and how far you can push the timing curb at red line to make more power, without running into detonation problems, all comes down to the octane rating off the fuel in the first place.
So will be blunt that 93 octane is not going to cut it with any kind of timing advance to make more power and not have detonation problems, so your back to either running on real E85 to get the octane rating as high as needed, or putting a meth kit into play so you can run on pump gas, and have the meth mix give the fuel the extra octane boost needed for under boost; so your not into the detonation problems from the fuel not having a high enough octane rating/ not able to push the timing to get you the extra powder you want.
Hell, just shaving the heads on a LS7 to increase its compression to 13-1, puts the motor out of the range of any petrol pump fuels available (93) with the amount you want to push the timing, short of running av gas 100 that has lead in it, so have to strip the cats before you destroy them with the leaded fuel.
Hence the reason that you can may way more power on a LS9, is not only do you increasing the boost pressure with smaller top pulley, but you either go to E85 or add meth kit, so you can push the timing without detonation problems with the increased octane fuel rating.
Heads and gaskets for the boosted LS7 build: I have a set of LS3 heads here and a set of LS9 heads. I suppose the LS9 heads are the better option here. Head gaskets: read that the 7x layer LS9 head gaskets are best, but they only feature a bore of 4.100. Unsure if that is a problem. What is the best thing to do here? Which head gasket would you recommend?
They differentiate between
"First Design Camshaft with Aluminum Blocks and Iron Blocks up to early 2009"
and
"Second Design Camshaft with Iron Block Only Late 2009 to Present"
Since we are talking about the LS7 aluminium block, I am in the first category here. I would still like to learn about the differences here in the camshaft design? Does anybody know?
Whole different ball game between a LS9 and LS7 motor.
Hence meat between the LS7 cylinder is not great, and why you can not throw a lot of pressure at the motor, before you pressure crack the cylinder liners between each cylinder.
LS7
While the LS9 block has a lot more meat between the cylinders since less displacement/ smaller pistons, and why you can push higher boost levels at the LS9.
So, regarding the TVS 2300 blower, way too much pressure/over kill that is going to pressure crack the cylinders if driven normaly, and really only need to push just enough pressure at the motor to over come the shortfall of the intake manifold not allowing the motor to breath to 7K instead.
So to short bus this, take a look at the below dyno and see how the motor can rev to 7K, but stop climbing in HP drastically around the 5.8K range.
So with about 7lbs of pressure to the LS7 that even one of the M122 BLOWER/CHEAP CADILLAC SUPERCHARGERS can pull off on the motor, will fit the bill. hence take the above graphs, and where the motor is making power to 5K, draw a line on that curb, to 7k, to what the motor can make when it can breath to 7K correctly.
So stock LS7 with headers, looking around 700/750, and don't need to upgrade the pistons or connection roads any stronger, since stock LS7 block is not going to take much more than about 7lbs of boost before the cylinder liners let go.
Hence block is 11-1, so at 14.7lbs of N/A at sea level, compression on cylinders is 161.7psi. With 7lb of boost, 14.7 goes to 21.7lbs times the 11 compression, and your at 238.7psi in the cylinders. Yes, you can drop the compression, add in more boost, but that 238.7 cylinder compression in the end, is going to be your limiting factor, due to the thin cylinder liners.
Thanks for posting this. Well, what do you think about the Lingenfelter twin turbo C5 Corvettes back in the day? They were 427CUI, basically the same thin walls compared to the LS7. These engines had over 15PSI of boost. They did that with much lower compression ratios. So if we replace pistons in that LS7, we can go down in compression. So if you drop compression to 9:1, we have 239PSI / 9 = 26,5 PSI. That is then 26,5-14,7=12PSI of boost and more power since you have more air and fuel to burn. You have the same peak cylinder pressure (roughly a factor of 10x after ignition, so 240PSI goes to 2400 PSI or 165atmospheres), but the pressure decay as the piston moves down is much slower, hence more overall pressure. Efficiency goes down a bit, but you have more power with the same peak pressures. On that note, compression ratio is one of the least reliable ways to make power. Best example: LS9 in stock has very low compression. The lower the compression ratio, the more robust the engine. Tuners often increase compression ratio, but that is not as reliable then making the power by other means (more air and more fuel with a lower compression ratio).
So overall, I totally agree with everything you write, and I hate high compression ratios, and the consequences, which is why I am going another way. I want margins as much as possible, so I am not looking at more than 6-7 PSI. In the world of reliability, you cannot add any boost to an 11:1 compression ratio. You can only add 6-7PSI of boost in case you turn down the compression ratio to 9:1. On the Lingenfelter C5, I turned the boost down to 6 PSI also.
Out of pure interest, where can you buy these M122 kits for LS engines? Found this for roughly 3k.
Unfortunately, these units take in the air from the back. So they would not work on a Corvette. This is the intake tubing that would sit between the firewall and the engine:
