# Direct drive SBC

Discussion in 'Chevy' started by Natty Bumpo, Oct 24, 2011.

1. Jul 4, 2014

### Jeffd

#### Well-Known Member

Joined:
Dec 15, 2011
Messages:
114
102
Location:
Overland Park, Kansas USA
Some real world facts:

The V8 in the Legend delivered at least 500 hp to a 90" diameter 125 lb Hartzell CS prop. (2:1 re-drive ratio, 4500 max crankshaft rpm).

I flew the V8 Legend some 250 hrs or so, full power every take-off ( I estimate 250+ take-offs), plenty of full power climbs to 18,000 ft, lots of aerobatics and high G maneuvering, some time on the Reno pylon course, CAFE Foundation evaluation, including multiple top speed runs, etc.

Never a problem or complaint from the Geschwender re-drive.

Jeff Ackland
Altitude Group LLC

MARCVINI and rv6ejguy like this.
2. Jul 4, 2014

### Autodidact

#### Well-Known Member

Joined:
Oct 21, 2009
Messages:
4,513
799
Location:
Oklahoma
Yay, the EPI-ENG site is back up! And, I'll admit that that he does paint a less optimistic than possible picture of hy-vo chain drives, for example,

That's pretty dismal sounding, for sure.

But he did say "using Morse engineering data". The Morse company would probably rate it's chain as conservatively as it could; it's just good enginneering CYA, and results in a better than predicted durability and as a result, a better reputation for the product. EPI also says that under that scenario, a 3" wide chain would have "reasonable life expectancy", and if the chain is rated very conservatively then it could be that in actual use the 2.5" will handle what the 3" is rated for. So, the point goes to the experimenters - at least to some extent - since we're talking about results that have not been strictly quantified by the kind of testing that a large corporation can afford to do. In other words, how far beyond the factory rating of the chain can you go without a "run it and see if it breaks" process? Every machine has it's breaking point, and that doesn't make it a bad machine. Racing is a more harsh use than full power climbs and aerobatics and may have stressed that engine/gearbox combination too far; this can cause engine failure or PSRU failure either one, depending on which is the weak link, and could be due to the type of crank coupling. Racing is a different animal than sport flying. Marc, if the Geschwender PSRU was adequate for racing, then why was it changed? The fact that Sweet Dreams just unofficially broke three FAI records (which are under review by the FAI) does seem to suggest that the EPI guy (now, what is his name, I wonder?) is a good engineer, and does good design work.

In my post on transmissibility, I also mentioned that the principle could be found in text books on torsional vibration, and that is why I felt comfortable making the post, because I didn't have to rely on the EPI website alone as my source for information. I wanted to make the point that there are some assumptions that can be made about torsional vibration, and the way engines operate, so that a good system can be designed from scratch that, by the principles of its conception, excludes most of the bad possibilities, and doesn't require the kind of calculation that is difficult to do.

There is no reason to denigrate the work of an obviously competent engineer. The results had with the GP-5 put EPI ENG squarely in the same realm of "proveability" that Stol, and others who have had tangible success are in. I think that this "experimenters against engineers" thing that seems to come up occasionally is unproductive. And I'm not an engineer! If anyone should resent them, it's me. I do love machines, though, and they have always been made a little bit better by the work of engineers, such as Harry Ricardo, who applied mathematics and theory to combustion chamber design in the early days and improved the power and efficiency over what empiricists had been able to do. And how can you have a good turbocharger without someone who can do the calculations to design an efficient impeller?

The EPI site is an example of generosity, with lots of good information provided for free, and a list of books to read much like what we have here on HBA. And I don't think he is dragging the rest of us down, or that he has nothing valuable to contribute, on the contrary.

That,
, otherwise why would he post up such a large amount of purely technical, and very helpful data? It goes far beyond the typical sales spiel.

And that's how I've always thought of you; looking on your web site and seeing the modifications you made to the belt PSRU, and the cooling system, and the engine, and nearly every aspect of the engine/installation, I thought "that's what engineers do".

rv6ejguy likes this.
3. Jul 5, 2014

### Autodidact

#### Well-Known Member

Joined:
Oct 21, 2009
Messages:
4,513
799
Location:
Oklahoma
And the saga continues. What a massive thread! I wonder if Natty ever follows this still?

4. Jul 5, 2014

### Brian Clayton

#### Well-Known Member

Joined:
Dec 7, 2012
Messages:
1,042
528
Location:
Ivey, Ga and Centerville,Tn
63 pages on discussion of "how to bolt a prop on a SBC for direct drive". I didnt really think it was going to be that hard...

5. Jul 5, 2014

### MARCVINI

#### Well-Known Member

Joined:
Apr 16, 2014
Messages:
295
12
Location:
Pitanga/Paraná/Brazil
This Aero V8 thing is bigger than life, my friend, and it, for sure, sparkles passionate opinions wherever it is talked about.

You can be sure that, regardless of each others diferences, something great will come up.

Marcvini

Last edited: Jul 5, 2014
6. Jul 9, 2014

### nerobro

#### Well-Known Member

Joined:
Nov 6, 2011
Messages:
1,109
312
Location:
Northern Illinois
While we're on direct drive. I found someone who's turning more than 4500rpm direct drive. And a 46" prop.

EAA - EAA Experimenter - Aeromorph 75

Not only is it a heavily modified engine, it's also turning "crazy" rpm.

akwrencher and Brian Clayton like this.
7. Jul 9, 2014

### Brian Clayton

#### Well-Known Member

Joined:
Dec 7, 2012
Messages:
1,042
528
Location:
Ivey, Ga and Centerville,Tn
Thats pretty neat. I like outside the box thinkers....

8. Jul 9, 2014

### stol

#### Well-Known Member

Joined:
Feb 15, 2008
Messages:
497
145
Location:
Jackson Hole Wyoming
Agreed...... And I bet it was ALOT of work too.....

Also.... 4500 rpm's with a 46" diameter prop = still within reason.....

9. Jul 10, 2014

### Toobuilder

#### Well-Known Member

Joined:
Jan 20, 2010
Messages:
4,441
3,235
Location:
Mojave, Ca
I'll imagine that the piston speed (even at 4600 RPM) is well under that of a typical Lycoming.

10. Jul 10, 2014

### PTAirco

#### Well-Known Member

Joined:
Sep 21, 2003
Messages:
3,477
1,000
Location:
Corona CA
Tip speed on that prop is about Mach 0.803 at that speed. Quite reasonable, if not ideal.

11. Jul 10, 2014

### Toobuilder

#### Well-Known Member

Joined:
Jan 20, 2010
Messages:
4,441
3,235
Location:
Mojave, Ca
Concerning piston speed - the little VW based engine has 27 FPS @ 4500 RPM compared to the 32 FPS of a Lycoming 360 @ 2700. To match the piston speed, the Lyc would have to pull back to about 2250 RPM.

And to tie to this thread a SBC @ 3300 and a LS-3 @ 3200 match the piston speed of a 360/540 @ 2700

Considering piston speed is one of the main limiting factors on reciprocating engines, its a good illustration why short stroke engines seem to be screaming their guts out, but survive just fine.

Last edited: Jul 10, 2014
Brian Clayton likes this.
12. Jul 10, 2014

### crytes

#### Well-Known Member

Joined:
May 16, 2014
Messages:
140
12
Location:
Clarksville, TN / USA
So is there a rule of thumb for maximum piston speed? With the SBC parts availability you can order cranks with all kinds of strokes and tailor an engine you build to the piston speed and revolutions you want. I personally like the idea of going for maximum stroke to squeeze out more displacement but this increases piston speed unless you reduce engine speed.

13. Jul 11, 2014

### BJC

#### Well-Known Member

Joined:
Oct 7, 2013
Messages:
9,534
6,308
Location:
97FL, Florida, USA
OK for a slow-moving airplane.

14. Jul 12, 2014

### nerobro

#### Well-Known Member

Joined:
Nov 6, 2011
Messages:
1,109
312
Location:
Northern Illinois
Is 180mph slow?

15. Jul 12, 2014

### BJC

#### Well-Known Member

Joined:
Oct 7, 2013
Messages:
9,534
6,308
Location:
97FL, Florida, USA
No, it isn't. My grasp of the facts in this case was slow. :ermm:

Although at 60 F, 4700 RPM and 170 MPH, I get 0.88 Mach for the tip.

16. Jul 12, 2014

### stol

#### Well-Known Member

Joined:
Feb 15, 2008
Messages:
497
145
Location:
Jackson Hole Wyoming
Still a reasonable tip speed number....IMHO...

17. Jul 12, 2014

### henryk

#### Well-Known Member

Joined:
Mar 8, 2010
Messages:
4,695
448
Location:
krakow,poland
18. Jul 13, 2014

### ekimneirbo

#### Guest

Friday I went over to a friends house to see if I could help solve a problem on a truck belonging to another friend of his. The truck was a 58 Chevy with a high  build up. The original builder had been asking \$85K for the truck and ended up trading it to my friends friend. I was scared to touch anything on this flawless black beauty. The paint on the" frame "was nicer than anything I own. The point here is that it was basically a money is no object build, so they didn't cut corners on anything to save a few bucks. The engine was an LS2. The intake consisted of an electronic throttle body......with the MAF sensor fastened DIRECTLY to it, and a small rectangular air filter DIRECTLY in front of that. I know GM recommends at least a 10" straight length of tubing for the MAF sensor to work properly, but this setup worked just fine......over the full rpm spectrum. No driveability problems at all. Since the trucks useful rpm range is wider than the expected rpm range on a DDV8, I would think it
would pose no problems. I'm not sure if the setup came from "Street and Performance" in Mena AR or not, but thats at least where the air filter was from, and they are experts in adapting LS engines. I wish I had gotten a picture of the setup, but I failed to do so. Anyway, if the use of an elongated intake system is holding you back from considering the LS engine, then this is at least a little more food for thought.

19. Jul 17, 2014

### ekimneirbo

#### Guest

Got to see the truck again, so took some pictures this time. Here is what the MAF and throttlebody setup look like.

20. Jul 17, 2014

Joined:
Apr 16, 2014
Messages:
295