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Broke 1000 HP yesterday at 6,000 rpm, but our fuel injectors were too small or we would have gotten more.
These were 80 Lb injectors that have served us well through the last several builds, but this build has different and better cams and heads so we are flowing much more. The chart below shows where the injectors maxed out, approx.. 5300 rpm. We made this with only 18 psi of boost - most of it is motor.
We are ordering up new injectors and we’ll go back at it!
How we did our HP calculation: 839 HP at the tire equals 987.6 HP at the engine when using a 15% drivetrain loss factor. But, the dyno operators do a lot of dynos on Corvettes with the Tremec T56 just like mine, and they said the right drive line loss number for that transaxle 18%. When I use that, then engine HP is 1023.2 HP.
It’s only temporary anyway, as we should be back at the dyno with larger injectors in just a week or so.
It looks like you have your road race setup....that is a SILLY amount of HP for road courses.....talk about NASA GTSU.... Even with monster slicks your gonna have a very hard time putting power down...but I guess the torque curve rising WITH RPM should make getting off the corners a bit easier...still 600+ftlbs at the minimum is quite a bit more than any other race 928 has ever made
What upcoming race/event will this monster debut at?
I'm registered to be at the Arkansas Mile put on by the East Coast Timing Assoc. (same sanctioning body as the SCTA for Bonneville rules/regs).
I have 3 weeks to prepare and its going to be close but I think we'll make it. We are supposed to be there Sept. 28th-30.
The new fuel injectors arrive Wednesday (115 lb/hr) and we will pop them in and get back to the dyno to tune. It's going to be tight.
One big question we have is whether our clutch can hold it. So far, yes. My last clutch was slipping on 900 HP and 825 lb ft of torque... so we changed it out to a different custom clutch that is supposed to hold 850 lb ft of torque. So far, it is.
But with the new injectors I will be higher still and I worry about this clutch...
Here is the new idler pulley added to the timing belt system after we broke a timing belt at Road America. It controls harmonics in the long, unsupported belt run from the water pump to the left head that the Gates engineers felt contributed to our belt failure. We bent all our valves on that! The engineers explained that that the belt was probably vibrating there, especially when I downshifted, and that is what broke the fibers in the back of the belt, allowing it to snap. The idler pulley keeps it running true, no harmonic waves, and providing better (more accurate) cam timing to the left bank. I believe them, so I designed this idler pulley to do just that. We've also added the Gates Race timing belt too.
Note that the Porsche engineers already provided an idler pulley for just this purpose on the right side, between the water pump and the right cam sprocket. This was the longest unsupported belt run, and the idler pulley they provided on the toothed side of the belt keeps that section of the belt from vibrating up and down and breaking the belt fibers. It would seem at my HP level and rapid accel/decel with large/wide race slicks, a similar idler pulley is now also needed on the left bank.
Interesting. What’s the fuel pressure and duty cycle of the 80 lbs injectors at peak power in these runs?
The timing belt engineers should be able to calculate the resonant frequency of the belt section based on the unsupported length. I doubt it is resonance, because resonance only breaks parts like this in uses where a constant rpm is held for a long time, like with boats. And simple belt flapping would cause the belt to jump and gear to skip, but belt would break, at least not first.
I think that the only timing belt breakages that we’ve had posted here have been with aftermarket cams and springs?
Here’s presentation about how they analyze these. The suppliers went to full computer analysis in the mid 1990’s. But I’m thinking that the pre-1990’s design rules of thumb and simple analytics supporting them would also be very useful for us hot rodders. http://www.leonardointegration.it/en...e_Analysis.pdf
140%. They went to 100% duty cycle by 5500 rpm, and 140% duty cycle by 6300. Meaning, they were locked open from about 5300 rpm-on. The only fuel gains we were getting were from the 1:1 FPR increasing fuel pressure [per pound of boost.
The mode of failure that I had (straight across the belt) is commonly caused by a belt being folded in storage or shipment, they said. Or the severe resonance of a harmonic wave. And yes, we certainly have after-market spring rates and valves and cams in play!
08-31-2018, 03:48 PM
1020 HP and out of fuel!
