GM LS3 Hot Cam

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TXFlyGuy

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[HR][/HR]We have an LS3 6.2 V8 installed in our plane. In stock form, at cruise altitude between 9,000 and 11,000 feet, using 3600 rpm (1890 prop) for power, we will get 180hp. With the Hot Cam our horsepower goes up to 217, or a 20% increase.

This is figuring a 3% power loss per thousand feet, and a standard day.

Would the resulting increase in IAS, and the extra climb performance make the new cam worthwhile? The kit is $500. And, the cam in question is a bone stock GM LS3 component.

Hoping that some of you "engine gurus" will have some good input!
 

Kyle Boatright

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Very much a judgement call. When you modify a system that is functioning properly, you may make things better, or you may make things worse. Perhaps the shop goofs up the cam install. Perhaps the additional power pushes your PSRU over the edge. On the other hand, improved climb and speed are always nice.

Personally, I wouldn't make the conversion unless I already had the engine apart.
 

TXFlyGuy

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The goal is not to increase power much over 300hp, but to have a better performing engine at cruise altitudes between 7,000 and 10,000 feet. The horsepower gain averages plus 33 with the Hot Cam.
The other positive note, is that the 300hp can be obtained at a lower rpm, which should be beneficial for the entire drive train.
Cam swaps are pretty simple and straightforward. Any competent shop would be able to do it.
 

cheapracer

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Darn easy job for big changes that can just as easily be reverted back to where you were if you're not happy, so it's a "Yes" in my book.
 

TXFlyGuy

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Well, the question is...is 305 sea level hp (Hot Cam / 3600rpm) worth the change? Stock cam is 265hp at sea level. At altitude (10,000), this would be 213hp vs. 185hp.

This data is taken from the GM Performance charts, and I figured in a 3% / thousand feet power loss. I am now in discussion with Comp Cams. They are looking at a custom grind tailored to performance from 2800 - 4200 rpm. They said this is a first for them!

image0_1.jpg
 
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TFF

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You might make more HP but it will change the characteristic of the engine probably. Unlike a car pulling back the power will not matter much because you have the windmill effect of the prop, but engine acceleration when you need power like a go around might have the engine bucking and coughing if its too much. Cams change the hp but most of the time they move the powerband and if you loose a power spot you were using, your trade is probably not worth it. P51 is not a P51 without a supercharger. I would be more inclined to add a Paxton or like and use it to normalize at your 10,000 ft; you also get to keep your short stack exhaust.
 

TXFlyGuy

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A supercharger is not doable, for a number of reasons. Here is the Hot Cam chart:
Scan.jpg

Based on data from the Van's forum, I would estimate an increase in cruise speed of 7 to 9 mph, which is not that much. But the ROC would improve significantly.
 
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TXFlyGuy

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The GM LS3 Hot Cam would give us a solid 13% - 14% power increase at all altitudes. I would guess that would be good for 6 to 9 mph increase, but would improve the ROC by a much bigger margin. The standard T-51D (V8) will easily achieve climb rates of 3,000 FPM or greater. The supercharged T-51 (Honda V6) would do the same in climb, and cruise at 210mph IAS @8000'. Most Honda and Suzuki owners report econ cruise speeds of 170 - 180 mph IAS.

The T-51 Mustang will easily do 232 mph IAS at 5500', with the new high speed wing, and the V8 or V12. Add a conservative 8 mph to that and you get 240. I'll take that!

A simple cam swap nets 40 to 50 hp with the LS3. There are several performance websites that have experimented with this, and with published dyno lab results. Just a cam swap, nothing else. The LS3 responds well to this as it already has great breathing heads.

"Using just a cam, we managed to increase the power output of the LS3 from 496 hp to 573 hp, while torque was up from 491 lb-ft to 526 lb-ft."

http://www.enginelabs.com/engine-tec...e-engine-dyno/

http://www.superchevy.com/how-to/eng...ick-boomerang/
 

Toobuilder

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The hot cam may buy you some benefit but if a cam manufacturer is going to do a custom grind at your lower RPM levels, do it. The idea to build an optimum cam at 4500 and below is essentially unheard of in the automotive performance world. The LS-3 heads are excellent castings right out of the box and outflow all but the most exotic SBC race heads of just a few years ago. Tie that to a cam profile that tops out at 4500 RPM and you will have a real winner.

And before you get too far down the road and Comp Cams lawyers get involved, make sure you tell them this is for an "airboat".
 

TXFlyGuy

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The hot cam may buy you some benefit but if a cam manufacturer is going to do a custom grind at your lower RPM levels, do it. The idea to build an optimum cam at 4500 and below is essentially unheard of in the automotive performance world. The LS-3 heads are excellent castings right out of the box and outflow all but the most exotic SBC race heads of just a few years ago. Tie that to a cam profile that tops out at 4500 RPM and you will have a real winner.

And before you get too far down the road and Comp Cams lawyers get involved, make sure you tell them this is for an "airboat".
Yes! They were advised its for an off-road vehicle, sand dune type racing, as well as a Pikes Peak climb. I gave them the rpm profile of what we need, mainly from 3000 to 4200. Anything above that is a waste. The LS3 is a great candidate as it responds so well.

BTW...we have had more than one manufacturer hang up the phone as soon as the word "airplane" was mentioned.
 

TXFlyGuy

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Just heard from Crane Cams..."Sorry, we have nothing that will work for you."

Hope to hear back from Comp Cams with better news. The GM LS3 Hot Cam may be the best (only?) option.
 
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PW_Plack

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The other positive note, is that the 300hp can be obtained at a lower rpm, which should be beneficial for the entire drive train.
Can you explain the basis for this assumption? The same HP at lower RPM will mean larger torque pulses spaced at at longer intervals. You'll be hitting the drivetrain fewer times per second, but with a larger hammer. This also changes the torsional vibration picture.
 

TXFlyGuy

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Can you explain the basis for this assumption? The same HP at lower RPM will mean larger torque pulses spaced at at longer intervals. You'll be hitting the drivetrain fewer times per second, but with a larger hammer. This also changes the torsional vibration picture.
Just the long held theory that slower turning speeds equals less wear and tear.

Comp Cams contacted me, and they have a stock off the shelf cam that they claim will work for us.
 

wsimpso1

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The other positive note, is that the 300hp can be obtained at a lower rpm, which should be beneficial for the entire drive train.
You got it backwards. Making the same power at lower rpm means more torque at that new lower rpm than you had at the same power at a higher rpm. Power is torque time speed. Torque is the origin of mean force applied to every gear tooth, bearing, shaft, hub, and blade in your system. Increased torque and lower rpm may also make for larger amplitude firing pulses, which makes this change have both higher mean load plus bigger oscillations. It also means the engine internals run at higher forces to obtain the same power at lower rpm. While the engine itself will most likely be fine with it, and it might be a little more fuel efficient, I would check with your PSRU maker to see if they have a problem with the engine mod.

Billski
 

TXFlyGuy

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The PSRU has a design limit to withstand up to 600hp. The published numbers claim 300hp maximum, building in a large safety margin. There are no torque/rpm limits.

This is still 8 cylinders firing. If we shut down 2 cylinders, with the same power output, then I could envision issues.
 
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Winginit

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You got it backwards. Making the same power at lower rpm means more torque at that new lower rpm than you had at the same power at a higher rpm. Power is torque time speed. Torque is the origin of mean force applied to every gear tooth, bearing, shaft, hub, and blade in your system. Increased torque and lower rpm may also make for larger amplitude firing pulses, which makes this change have both higher mean load plus bigger oscillations. It also means the engine internals run at higher forces to obtain the same power at lower rpm. While the engine itself will most likely be fine with it, and it might be a little more fuel efficient, I would check with your PSRU maker to see if they have a problem with the engine mod.
While I agree with your point about making more torque at lower rpms increases the forces for each revolution, a question comes to mind. If someone designs a PSRU that is advertised for up to XXX HP, how would they know what the torque curve up to that point would look like? It might look like the stock LS3 430hp curve, or it could be something completely different as with the hot cam version. So isn't the manufacturer "implying" (?) that any torque curve that doesn't generate more than XXX HP is acceptable ? Second question. Shouldn't PSRUs be rated by torque capacity like transmissions rather than HP ?
 
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TXFlyGuy

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We have decided on the GM LS Hot Cam. A mild performance cam, and totally GM O/E.

GM claims a 15% increase in power output. The custom rod / engine websites actually show that GM's numbers are quite conservative. We are only interested in recouping some of the power lost at altitude, say from 9000 to 11000 feet.

The standard LS3 will do 270 hp @3600rpm, sea level, standard day. At 10,000', that drops to 189hp. With the Hot Cam, we will have 224hp at ten grand. Plus the bonus of better rate of climb. I like to cruise high, where it is cool and smooth, above most other traffic.
 

PW_Plack

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This is still 8 cylinders firing. If we shut down 2 cylinders, with the same power output, then I could envision issues.
If you make the same eight cylinders produce the same HP at 25% lower RPM, you've created the identical effect as switching to a V6 of equal power. Fewer power strokes in a given time interval require more power from each stroke.
 

TXFlyGuy

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If you make the same eight cylinders produce the same HP at 25% lower RPM, you've created the identical effect as switching to a V6 of equal power. Fewer power strokes in a given time interval require more power from each stroke.

I actually do not agree. Because, you still have 8 cylinders firing, and a smoother power distribution versus a V6. We will soon find out.
 

Winginit

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If you make the same eight cylinders produce the same HP at 25% lower RPM, you've created the identical effect as switching to a V6 of equal power. Fewer power strokes in a given time interval require more power from each stroke.


Hmmmm.
 
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