Discussion in 'Chevy' started by TXFlyGuy, Oct 8, 2016.
In the middle of reading your post, it changed to Hmmmmmmm. What's up?
Rethought what I was going to say. There is a lot to consider on how to interpret what PW said. Lets use 100 HP and 3000 and 4000 rpms for ease of calculation.
An engine would produce 131.3 lbs ft of torque to make 100 HP at 4000 rpms.
The same engine would need to produce 175 lbs ft of torque at 3000 rpms for 100 HP.
If you divide by the number of cylinders being used,
131.3/6= 21.88 131.3/8=16.41 175/6=29.16 175/8=21.87
Looking at it that way, yes he is correct. But looking at the overall application I think its a moot point. Its just a mechanical relationship that applies to all engines. At your normal cruise rpm, the V8 will have smaller impulses than a 6 so what does it matter if at exactly 25% fewer rpms it matches the V6. Its gonna match the V6 somewhere as it goes from idle to WOT and back to cruise.
If you compare it to a 4 cylinder at 2700 rpms, each cylinder would be making 48.62 lbs ft of torque while a 6 would need 32.41 and your V8 would be at 24.31 each time the piston imparted twist into the crank throw. Seems pretty good to me.
I agree, it's a moot point. The drive train will be able to handle the torque and hp. We are only talking about 300 - 325hp. No way we can ever use the full potential of the LS3 & Hot Cam...almost 500hp.
The 402 cid LS engine in our P85 uses the GM Hot Cam. Works well with the Catto 3-blde, 80" diameter prop. Craig Catto said the max helical tip speed for this prop is .94 Mach and he is right - WOT runs show that the prop pulls right up to this point. The allowable tip speed with this prop lets us to spin the engine to 5000 rpm with the 1.8:1 re-drive. It is my understanding that tip chord and thickness play a significant role in max usable tip speed.
This is one reason why we are looking forward to Titan's new 96" prop, a complete new and more efficient airfoil design.
With the new prop, which looks like a Hamilton-Standard P-51 propeller, perhaps we will be able to turn the engine a bit faster. This naturally will allow more power.
Titan is also considering a better gear ratio to allow the prop to spin slow, while the engine spins fast. I am not an engineer, but I think this would make for a very efficient combination.
Here is the dyno data taken straight from GMPP:
We are having the dyno testing and break in done now. The first numbers are coming in at 10% greater than the GM data. Using 100LL, we will tune the ECU for max spark, then back off just a bit. This will give 20 percent more hp than the previous charted data.
example: 390 hp @4500 rpm is now 468hp.
310 hp @3600 rpm is now 372 hp.
What flutter analysis / testing has been done on the design that you are having built? Have any flown with the HP that you are installing?
The airframe has been fully flutter tested during inflight trials. No T-51 has flown with this much power.
Vne is published at 250 mph IAS.
Do you mean TAS?
250 indicated is a very spooky place at the high altitudes you intend to fly this machine.
Also, what is meant by "fully" flutter tested?
First let me say that I'm a fan of your project and wish you success. That being said, I have to wonder about the numbers thay are supplying you with. GM was historically known for understating their HP ratings. That allowed them to run in lower stock classes at the drag strip and win over competitors who had over rated their product. Later, I think insurance rates affected ratings. When they sell a crate LS3 with the Hot Cam its rated at 480 hp. My understanding is they easily make that and often exceed it somewhat (10HP+). Usually the best initial help is to lower the exhaust backpressure with headers. That gives a sizeable increase. In your setup with the short exhaust stacks you cannot take advantage of exhaust tuning to extract additional power. You won't have any backpressure though, so I don't know what to expect. I will say that the amount of additional HP they are claiming just through tuning sounds a bit more than I would expect (Opinion). I do agree
with BJC,s apparent concerns about maybe too much power and redrive strength. When you change ratios you also increase the torque output the shaft is dealing with. Best of Luck
PS: Hows the header coating doing?
Just kiddin BJ !
Make sure your dyno guy knows that you want real HP, not bar bragging HP...
The cam info in post 26 looks very suitable.
You may well need to redo flutter testing for the higher speeds you'll hit.
I just looked at the brochure. Cruise 150-180mph and vne of 215mph. Vne should be 1.26 cruise, vd should be 1.4 cruise. Vne is a bit too low for standard cruise. Titan does know what you are doing?
Our speeds will not exceed Vne, although our cruise will be close to it. The data I supplied here is straight from the dyno shop in Houston, with the 10% - 20% increase by using 100LL versus 93 Octane pump gas.
The flutter testing was accomplished by Titan's Chief Test Pilot. Putting the airplane nose down, WOT, and doing everything he could to induce flutter. It never occurred. The standard wing is nearly spin proof also. You can force it into a spin, and maybe get one turn. That's it.
We have the new high speed wing. It will easily cruise at 240 mph.
The ceramic coating will happen soon. In Arlington, Texas.
Dyno places often inflate HP. Customers are much happier with big HP, so 'correction' factors tend to get overapplied. You don't want to order a prop designed for inflated HP.
10-20% seems a big increase for 100ll, what cr is it running?
Does the dyno place know this is for an aircraft and will spend hours at high throttle? 'Boat' should work if 'aircraft' is a bad word
The tune for car racing is different to endurance. Cars don't hold high throttle for long.
Please explain this. I would like to understand why.
I think the shop knows. They are a high end race programming aftermarket shop catering to customers who will be running their engines hard, near WOT at the track.
Call Titan Aircraft. Ask to speak to Bill Koleno or John Williams. They can tell you better than I can. Our wing is not the standard wing, and is more prone to spin.
The fat wing is extremely reluctant to spin. You really have to force it, and then you might get almost a full turn. For this reason, aerobatics that involve spins do not work with this wing.
The standard wing is a 24', high lift airfoil. The high speed wing is 28', and much more symmetrical (thin).
Yes, ten to twenty percent is a large number. The numbers are what they are. Pretty hard to fake it when the owner is standing there. There is no reason to, and if word got out, it would be detrimental to their reputation.
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