# LS-3 Powered Velocity

Discussion in 'Chevy' started by rv6ejguy, Mar 27, 2019.

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1. May 9, 2019

### BBerson

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Of course, direct drive can run 2900 or more depending on the prop diameter. Might go supersonic on takeoff like a C-180.
One way to get a lighter direct drive is copy the VW evolution.
The original 1200 cc was converted to almost double displacement with just a few extra pounds to increase the power to weight ratio at low rpm.
So start with a half size engine and double the displacement, if that is possible.

Last edited: May 9, 2019
2. May 9, 2019

### Toobuilder

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300hp @ 2700 is 584 foot pounds torque.

To get 584 lb/ft out of 413ci needs 211 psi BMEP. Pretty hefty for a NA engine.

Using a more realistic BMEP of 175 drives the displacement to 501 to get the 584.

Running the numbers backwards using 413ci and 175 BMEP gives you 486 for torque, which computes to 248hp.

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3. May 9, 2019

### Vigilant1

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One difference between a 413ci LS3 at 2700 RPM and a similar displacement Lycoming is that liquid cooling of the LS3 that would help mitigate any head/exhaust valve temp issues that would otherwise result from trying to squeeze out high HP/ci.

4. May 9, 2019

### revkev6

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has anyone run the numbers on a turbocharged LS engine direct drive?? IMO this would be the best option of all. I would imagine a smallish single turbo setup could be designed to be optimized for under 3k rpm and hit the HP target. weight could be similar to or less than the reduction drive without the harmonic issues. then you also have the benefit of not losing hp at altitude.

couple problems that would pop up direct drive are:
prop low on the engine
thrust bearing.

5. May 9, 2019

### Winginitt

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Thanks, that makes more sense. The website posted below showed a VNE of 215 for the T-51. In addition to the wing change, is anything being done
to insure flutter doesn't become a problem ? I have to say that those appear to be some pretty substantial changes. I know you have gone through a
long and expensive and probably frustrating process to see this dream come true. so I'm looking forward to seeing it fly successfully.
http://www.titanaircraft.com/t-51d.php

Below is a dyno readout for a "torque optimized" 427 smallblock Chevy....not an LS. As you can see, at 2800 rpms it produced 282 HP. Simply adding a slight increase in RPMs
to 3000 jumps the HP to 309. Thats an increase of 27 hp for 200 rpms. The thing to note here is the dramatic increase in HP available with small increases in Tip Speed. This is a much more substantial increase than whats available from comparable aero engines because of the efficiency of newer technology. Remember that 2700 is not anything more than a suitable rpm for aero engine designs. It is not an absolute. Props running at 2000 rpms will be more efficient than those at 2700 and those at 3000. The question then becomes whether a propellor optimized for 3000 rpms can actually give a better result because it has a more significant HP increase to work with. In other words, if an engine only gains 10 HP with a 300 rpm increase is compared to an engine that gains nearly 30 HP....a builder may benefit or at least achieve a result equal to a 2700 rpm engine with less HP. If you split the difference between 251 HP @2600 and 282 HP @ 2800 you end up with 266 HP @ 2700 rpms. Thats more than sufficient HP for the majority of homebuilt airplanes. So unless someone needs more than 266 HP, there is no benefit to a reduction drive on a 427 LS engine.

An LS designed engine built for torque should be able to at least match the dyno numbers below because producing power is all about airflow, and the LS head design is superior to the old smallblock Chevy. At any rate, its easy to see that a properly built torque engine can produce significant HP without a reduction drive. The issue comes when you move down in HP requirements, say down below 200 HP. At that point the weight of the LS V8 even with direct drive may be too much for many homebuilts. Then you need to be selective about smaller and lighter engines ....maybe with a redrive. Maybe a Rover or Small Ford. There is no one solution thats always best.

Note the valve size used with this 427. The upper rpm HP is only 512 @5400 rpm then falls off. If this engine were built for high rpms it would make a lot more HP. Building for a purpose changes where you get the power at. Thats why I believe that a scratch built LS is a better choice than a crate engine.

http://www.titanaircraft.com/t-51d.php

Last edited: May 9, 2019
6. May 9, 2019

### rv6ejguy

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A turbo DD is the way to go to get a better power to weight ratio as Reg Clarke did on the Subaru Dragonflies. He never had any issues with crank thrust bearings. These handle the clutch pressure plate forces (many hundreds of pounds) in the car so they are more robust than many people think. I'd be more worried about crank bending loads, especially with heavy props and a crank extension.

For less than 250hp, an LS is really too heavy for most airframes and lots of planes are built for more power than that- Glasair, Velocity, Lancair Legacy, IV etc. These do best on 300+hp and the need a redrive to get the right prop (available) on there. Finding an efficient prop for a DD could be a problem in this power range if you exceed 2700 rpm. Prop efficiency takes a bigger hit with higher mach number and as you reduce the diameter to keep this in check, TO and climb performance can suffer. You need a big excess in power to get decent performance with a DD auto engine and FP prop.

7. May 9, 2019

### plncraze

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A good reference for direct drive with a Chevy 350 is Vance Jaqua's article in Contact! Magazine many years ago. There are many compromises all in the name of simplicity.

8. May 10, 2019

### TXFlyGuy

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With regards to the posted Vne on the T-51, and flutter testing, the new wing was originally designed for racing at Reno, with speeds exceeding 300 mph in mind. The Titan website will not show anything on this wing as it is no longer available. That 275 number has been backed off, to 250.

With a 90" prop, a DD V8 would never work.

Looking at doing a twin V4 setup. No, not really.

9. May 10, 2019

### tailwind

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Interesting discussion. I have a bit of experience on the direct drive side as i have a v8 tailwind. It is 300 inch olds, resleved and 300b crank. 10.5 to 1 cr. It produces about 160hp at 2800 rpm. I am seeing about 185 mph at 8000ft density alt. 2800 rpm 10.5 gal/hr.
Tom

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10. May 10, 2019

### tailwind

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And all up powerplant weight, radiators, drive prop, coolant, 356lbs.

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11. May 10, 2019

### BBerson

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12. May 10, 2019

### TXFlyGuy

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2600 rpm is the max prop (90") limit. At that power, the V8 direct drive would put out far less than the 400 hp we have available. And we plan to cruise that prop at a nice, efficient, 1765 rpm. That is 3900 engine rpm.

13. May 10, 2019

### BBerson

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Max continuous. I think my friend ran his at 2900 for brief takeoff. Sure, to get a good power to weight ratio for direct drive you need a bigger and lighter engine . Would need to be custom made like the old Curtis V8’s. But instead of a 9 foot prop and 1400 rpm, go with a much higher rpm and smaller prop for higher cruise speeds.
Maybe look at V-12. V engines are shorter, so a V -12 might be the crank torsion limit.

Last edited: May 10, 2019
14. May 10, 2019

### mm4440

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Hi Ross, I posted on another thread where 250 HP from a complex V-6 is planed. The direct drive LS leaves about 1/2 its potential HP untapped. would be expensive to build. A "stock" V-6 with a PSRU might be the better choice in the 250-300 HP range. All it takes is lime and money.

Murry

at 8:32
A 496c in. LS based normally aspirated pump gas street engine; 600+ hp but look at the first, 2800 rpm dyno numbers. 316 hp, 592 #' TQ.
NRE is local to me, big power engine and car builder. With a direct drive and lower red line, lighter valve springs for lower stress on valve train could be used. I do not think you need to change the cam. A big inch LS means an aftermarket racing block and other parts. Inverting a V-8 is straightforward, you make sure oil can drain to an external sump tank that connects the valve covers and a suction line to the inlet of the oil pump. A dry sump is not needed but can be done with GM parts. Simple is better.

Murry

15. May 10, 2019

### mm4440

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I have been down the V-6 vs V-8 battle for a Mustang replica project in the early 1990s, before the LS engines were born. One lesson learned was no one wants a V-6 when a V-8 is available. The T-51 was originally 100 HP Rotax powered? The performance of the replicas has been
disappointing with the exception of the Thunder Mustangs. There is a replica from Germany where they have reproduced all the warts of a production aluminum Mustang in molded Carbon. Performance takes second place to accurate modeling.

16. May 10, 2019

### TXFlyGuy

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You are mostly correct. But you need to factor in what the original expectations were/are with regards to the replica, and it's performance.
The T-51 actually flew quite well with 100 hp, or so I am told. Today with 400 hp on tap, and a host of aerodynamic improvements, the airplane is much more respectable. The Titan Mustang has most likely evolved far beyond what the original vision was for the aircraft.

We all wish the new company in Europe luck. It seems they have not gotten off to a good start.

If you want both P-51 performance and P-51 looks, you need a P-51.

17. May 10, 2019

### Toobuilder

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Last time I explored the DD LS concept the weight was theoretically equivalent to the AV 540 Lyc. Admittedly heavy for most kit aircraft, the real challenge was the lack of displacement from an alloy LS block to match the power of the Lyc. Limited (at that time) to less than 430 inches, the LS would need an exceptionally high BMEP. With the added bump to 500 ci now available, the LS reaches parity with the Lyc at an easily attainable 175 BMEP.

This is a good thing.

18. May 10, 2019

### Winginitt

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A turbo will always provide lots more power for a small amount of additional weight. Hard to beat them when you look at it from strictly a power gain vs weight gain comparison. Like you, I don't care for the direct drive conversions on larger engines that is just a prop extension and places all the leverage on the engine bearing. Clarke did a nice job on his Dragonfly and it seems to work well. I have seen other Subes with direct drive that work well and there is always the Gary Spencer Ford. Probably a lot of examples that I don't know about. I'm more in the vein of a direct drive which also provides a support bearing and possibly a thrust bearing in the design.

The site below shows a FWF for a Bearhawk. I think airplanes designed along these parameters rather than the sleek and fast glass designs would be a niche for a direct drive LS.
First, this FWF has a reduction drive included. With its 1.667 drive, 2700 rpm prop would mean about 4500 engine rpms and around 300 HP available (per dyno charts I have seen)
Advertised HP by vendor is 367 HP @4500. So thats a little questionable. Wet weight with all accessories is advertised as 580 lbs. Cost for FWF is $39,200 (Note:I believe this is a version of the former reduction drive that Bud Warren marketed as Geared Drives) Supposedly this airplane has been flying since 2010 but I did not look for any current information. https://www.autopsrus.com/bearhawk A basic crate LS3 480HP is available for about$7500. That means this FWF package costs an additional $31,700 above the engine costs. For that you get a reduction drive, an ECU,a wiring harness, and some programming. Not sure what else might be included,maybe the engine mount, but it doesn't include a propellor,or fuel pump. There certainly is a lot of room there for someone to build a cost effective LS3 on their own. Lets face it, most of us aren't going to drop$39K for an engine. Might as well get a Lyc for that money.

Now look at a version of the LS3 stroker that matches the numbers on the dyno chart above. If someone assembles one and gets 266 HP @2700 rpms he has about $31K left to buy an ECM,wiring harness,mount, and some programming. GM sells basic harnesses and off road ECMs without all the bells and whistles that assemblyline ECUs have. Figure about$1500. Or buy one from the larger aftermarket suppliers. If you welded up your Bearhawk, you can certainly make your own mount. So probably for about \$11K you can build a 266 HP engine that with a bearing supported direct drive should weigh at least 50 lbs less than the redrive engine package. Lets say you only get 250 HP....you still have something comparable to a large LYC powerwise. Its smoother and more efficient and has fuel injection to compensate for altitude. Running it at only 2700 should provide great economy and long life. Need more power.....just increase the rpms to 3000 and you have 300 HP. Just use a prop designed for that rpm.

There are other Bearhawks using different and less powerful conversions. These are usually lighter than the LS. Above, " Tailwind " mentioned his inverted Olds powered Tailwind direct drive conversion weighs 356 lbs.Might be a good choice for a Patrol or Piper replica. Engine selection has to start with the choice of airplane thats going to use it. There are viable engine combinations that use reduction drives and even turbos, just as there are many successful direct drives (Corvair, Sube, and even smallblock Chevies) Each builder has to decide whats important to their choice of airplane. My preference is to initially look to see if my needs can be met without a reduction drive which introduces weight, resonance, and cost into the equation. If someone can live with those factors they certainly can attain more HP than with direct drive. I know there are a lot of people who have used Subes in airplanes. Depending on what they want, they have used them with both direct and reduction and had satisfactory (to them) results. I just think that its not a "one size fits all" situation. The nuances of each conversion determine which option make prove satisfactory to each builder.

What is the current direction for best Sube choice for conversion? Weight /Power ?

19. May 10, 2019

### rv6ejguy

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The EJ257 4 cylinder turbo is a good choice for up to 225hp. Alternately, the EG33 six puts out the same power if you don't want a turbo. A number of both of these flying successfully for many years. Around 300-350 pounds with redrive.

20. May 10, 2019

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