I don't think my 64mm likes higher rpms or its just that I'm losing rail pressure an tons of power after 3200 rpm
limits on lb7 rods?
- Thread starter jonathancasey19
- Start date
No, a 64mm charger isn't going to allow high RPM operation. About 3000rpm peak, then power gently declines. That's about the size of a stock charger.
So its basicaly a worthless turbo?
guess ill have to upgrade to a min of a 66 if not a 472? but then towing suffers?
It's a little bigger than the LB7 charger, and perhaps flows better depending on the turbine, but not big enough to move peak RPM up much.
For towing low peak HP rpm is better, so you have the right charger size. You can tow with a big charger, but it's more hassle.
For towing low peak HP rpm is better, so you have the right charger size. You can tow with a big charger, but it's more hassle.
The smaller of the two chargers normally dictates the HP curve location. Sometimes it moves up a bit when gated, but from the curves I've seen it seldom moves it up much, maybe 200 RPM.
With twins, volume of air supplied isn't related to big charger, only the pressure you can make.
When I ran a GT42 + GT55 twin setup, the peak HP RPM was lower than a single GT45, and about identical to GT42 single, but with more area under the curve, which makes it harder to detorque.
When I ran a GT42 + GT55 twin setup, the peak HP RPM was lower than a single GT45, and about identical to GT42 single, but with more area under the curve, which makes it harder to detorque.
Pat, what do you think about the 4094, how much peak useful RPM do you think we could gain, and also is there a noticeable difference from the 4088 and the 4094 for towing?
The 4088 is about the biggest you want to run if you are towing heavy IMO.
About the 4094? That was one model I never personally tested. It sounded like a very good idea, but I'm no longer convinced it's good choice. Most folk didn't set the world on fire running it, and I'm not sure it's even better than the 88.
As you might remember, I ran a 4088 into the 11's at high altitude (LACR) and towed a car and trailer to the track. The tow vehicle was quicker than the Corvette on the trailer.
About the 4094? That was one model I never personally tested. It sounded like a very good idea, but I'm no longer convinced it's good choice. Most folk didn't set the world on fire running it, and I'm not sure it's even better than the 88.
As you might remember, I ran a 4088 into the 11's at high altitude (LACR) and towed a car and trailer to the track. The tow vehicle was quicker than the Corvette on the trailer.
I know he said it depended on turbine a little to so just let him know what size mine was guess I'll check into a bigger Turbo
Think of the turbine as the motor, and the compressor wheel like a cam.
No matter what you do with the turbine, the compressor wheel is going act the same at the same shaft RPM. A big compressor wheel needs a big motor (turbine) to drive it.
You could hook the compressor wheel to a gearbox and drive it off the crankshaft and it would have the same peak HP rpm. In fact, that's what a centrifugal blower is (Paxton, etc).
But if you have too much backpressure at higher RPM's, the turbine chokes the engine down. There is a right size turbine for a given engine displacement and compressor wheel. Too tight, and it makes power earlier, but chokes peak compressor output, too loose, and there isn't enough power to get the compressor wheel to target RPM at peak HP rpm. It will supply the right power as you rev further, but now the compressor is going out of it's target area and becomes inefficient.
No matter what you do with the turbine, the compressor wheel is going act the same at the same shaft RPM. A big compressor wheel needs a big motor (turbine) to drive it.
You could hook the compressor wheel to a gearbox and drive it off the crankshaft and it would have the same peak HP rpm. In fact, that's what a centrifugal blower is (Paxton, etc).
But if you have too much backpressure at higher RPM's, the turbine chokes the engine down. There is a right size turbine for a given engine displacement and compressor wheel. Too tight, and it makes power earlier, but chokes peak compressor output, too loose, and there isn't enough power to get the compressor wheel to target RPM at peak HP rpm. It will supply the right power as you rev further, but now the compressor is going out of it's target area and becomes inefficient.
What is interesting about the Dmax, is that the turbo and fuel system are so evenly matched. Putting a bigger turbo on a stock engine doesn't show big gains. Putting a big fuel system on with a stock charger does little also.
But increase both at the same time? WOW!
That the factory charger and fuel system can double the engine output through tuning alone is also incredible. But it's almost like GM knew what the limits of tuning were when they designed the engine. It will handle max tuning fairly well, but when you go past that point significantly, the hard parts are in harm's way. Did they test the engine at max fuel and max boost, then detune it so it lives a very long time? That would be my guess. But you can't sustain 500rwhp for extended periods anyhow.
But increase both at the same time? WOW!
That the factory charger and fuel system can double the engine output through tuning alone is also incredible. But it's almost like GM knew what the limits of tuning were when they designed the engine. It will handle max tuning fairly well, but when you go past that point significantly, the hard parts are in harm's way. Did they test the engine at max fuel and max boost, then detune it so it lives a very long time? That would be my guess. But you can't sustain 500rwhp for extended periods anyhow.