# FWF Chevy LS V8 engines and PRSU's currently installed and flying on OEM and homebuilt aircraft

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#### roxburg

##### Member
You are in for an expensive surprise.

BJC
If you read my comments about 3" above yours, or looked at the above pictures - you would have noticed that my dad already has an MT 3 blade, constant speed propeller and I know exactly how much it costs - so why would I be surprised?

#### BJC

##### Well-Known Member
HBA Supporter
If you read my comments about 3" above yours, or looked at the above pictures - you would have noticed that my dad already has an MT 3 blade, constant speed propeller and I know exactly how much it costs - so why would I be surprised?
I did read it. In fact, I quoted the part of your posting that I was commenting on.
]roxburg said:
an MT carbon fiber, three blade, constant speed prop. It has no life limited parts and never needs an overhaul.
If you believe that the seals have unlimited life, or you believe that the propeller never will need an overhaul, then I believe that you are in for an expensive surprise.

BJC

#### Toobuilder

##### Well-Known Member
HBA Supporter
Log Member
Are you suggesting that the LS engine produces 200 more HP than the old aircraft engine AND gets better milage? If so, the airplane violates physical law and should be in the Smithsonian for study.

I'm as big a fan of flying LS engines as anyone, but let's not blow sunshine up people's backsides to sell the concept. Adding 30 pounds behind the seats to make up for several hundred extra pounds FWF is not a small thing you can just gloss over. It is a huge engineering compromise and is a deal breaker unto itself for many people. As for the "difficulty" in managing an air cooled engine - that's largely solved with the relatively simple addition of EFI. I have an EFI Lycoming 540 and I have yet to touch ANY control but the starter button to get the fire lit (hot or cold), and the mixture control is purely optional during flight. I'd also be happy to compare BSFC numbers with an LS conversion, and certainly TBO.

I'm very happy to see any LS flying, but don't let that taste of success blind you to the fact that the basic Lycoming architecture, refined over decades, is pretty **** solid. Throw some of that EFI magic at one and most of the difficult management issues melt away and it's suddenly a very strong performer.

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#### Toobuilder

##### Well-Known Member
HBA Supporter
Log Member
I did read it. In fact, I quoted the part of your posting that I was commenting on.

If you believe that the seals have unlimited life, or you believe that the propeller never will need an overhaul, then I believe that you are in for an expensive surprise.

BJC
Oh indeed! Several friends with MT props that have "bent over" during the "never needed" overhaul process. Hoffman too. Another very expensive proposition to own. Must be a German thing

#### Turd Ferguson

##### Well-Known Member
I'm all in favor of alternative engines as well but if someone wants to extol the virtues of a conversion they should work on transparency because the 'good' does come with 'bad' and hiding or glossing over that fact doesn't make it go away.

#### rv7charlie

##### Well-Known Member
Can I walk on both sides of this fence?

I'm not a fan of Bud Warren's design choices, but kudos for doing *something*. And while I don't think a C172 is the perfect application for an LS motor, I think that it's worth remembering that *everything* is a compromise.

There are lots of stock C172s and Cherokee 140s that fly as 2 seat aircraft in the mountain states; that's the only way they can operate there. I suspect that even with 30 lbs of ballast, that LS 172 probably makes a pretty impressive 2 seat a/c; perhaps even near STOL level performance. Consider a salvage 172 bought with no engine, the cheapest aluminum LS truck motor, an airboat redrive, and a big fixed pitch prop. With a bit of mechanical aptitude, you could own a 2 seat super performing a/c for not a lot more than a new ultralite might cost. It certainly wouldn't be able to take full advantage of the LS motor's power, but how many homebuilts actually can? And do you really care? At the low cruise power levels you'd be using, fuel economy should be pretty impressive; certainly no worse than a 'stock' Lyc. BSFC has the potential to be better, simply because the engine isn't having to work as hard, and there's no point in pushing it beyond Lyc numbers in cruise, because trying to go any faster is just pushing a brick though the air.

Yes, owners (and especially, sellers) should be transparent about the compromises required, but we should also be able to weigh the compromises intelligently. The 172 isn't the 'best' airframe for the engine, but try affording a better fit, like a C206.

In these discussions, I always think about the original Pietenpol. Ultralite performance with a 400 lb engine. But everything about the airplane was dirt cheap to build, including purchase of the powerplant. You could have gotten the mission accomplished at probably 1/3 the weight, but at 30 times the cost. Where do you compromise?

Charlie

#### Andreas K

##### Member
If you are seriously considering installing a Chevy aluminum block V8 for your aircraft - there are a number of fly-by-night companies out there offering all kinds of deals and overstating the performance capabilities plus ease of installation of their FWF kits. Please do your due diligence, check the credentials of the people behind the product. How many of their kits are actually in the air. How many have more than 100 hours of air time? How long have they been in business?

#### roxburg

##### Member
Curious as to what updates you are referring to? And how that would make installation cheaper and faster. The FAA revised Part 23 in 2017 and I’m not aware of any further pending changes. A non-certificated powerplant will never be approved for installation in any normal category airplane. Not in my lifetime.

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#### TXFlyGuy

##### Well-Known Member
Most of you know this, but our LS376-495 will do 525 hp. With our Autoflight-New Zealand PSRU we are limited to 412 hp at a max rpm of 4500.

The gearbox has a good record in T-51 Mustangs.

#### roxburg

##### Member
The G-limit of an airplane in standard category is +3.8, utility +4.4 G's. If you pull 3 G's you can certainly feel it. Why do you think a Cessna is rated 3.8?
Hard landings, turbulence, wake turbulence, avoiding a bird or plane that you see last second. So if you inadvertently pull 4 G's do you expect the wings to fall off? I don't. But at 4 G's I would have the airplane inspected for structural damage. The same applies to that gearbox. There is value in knowing that limit. That has nothing to do with air combat or acrobatics. What if it can't handle 3.8 G's but only 2.5? Do you have to de-rate your plane to make it legal? When do you tear that gearbox apart after a hard landing?
You do realize that we are talking about home built aircraft here? There is no such thing as a product liability guarantee, or insurance in this catagory. I don't think you will ever find a PSRU manufacturer who is willing to go through all the testing to see what their PSRU can withstand, let alone the astronomical costs associated with those tests. Especially, when more than half of the ones I talked to, did not even know what NDT testing was, let alone how to use it to improve the quality of their product. Good luck trying to find a PSRU manufacturer who tests their product to failure, just to get some data to give you a ball park figure for a 'G' limit. You would probably be better off just installing a good quality ballistic recovery parachute - if you are that worried about exceeding 'G' limits.

#### Orange4sky

##### Member
Someone correct me if I'm wrong, (as if you needed an invitation) but I think that you don't really have to worry about the effect of Gs on a typical PRSU. You have to worry about the effect of the weight of PRSU on the aircraft but I would think the forces acting on it internally far outweigh the effect of Gs on it. Am I wrong?

HBA Supporter
Log Member
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#### Orange4sky

##### Member
LOL. Oh Geez. Tough crowd. Gravity forces. That's plural. Apostrophe-s can be possesive or a contraction. Is G's really a contraction of Gravity forces? I didn't think so. It seems that g-forces or "4.4 g" without an s is the correct way to use the term in this context:

The unit g is not one of the SI units, which uses "g" for gram. Also, "g" should not be confused with "G", which is the standard symbol for the gravitational constant.

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#### TFF

##### Well-Known Member
Lots of PRSUs are weak on G ratings. A number don’t seem to have the bearings or structure for steep turns much less aerobatics. Straight and level preferred. Pulling off a great alternative engine is many times graded like just pulling off flight. If it happens, it’s a win. Not all are bad, but not many can claim good.

Extra weight always sucks. You are loosing capacity dealing with it. If it weighs 50 lbs more, you have to carry 50 lbs less to stay even.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Hello, looks like you did a lot of research. What is the g-limit of your dad's gearbox? I couldn't find any specs on AutoPsru's website.

Thanks
Andi
G limits are probably not a big deal in a PSRU as that is just prop weight times g's times whatever the moment arm is between the outer prop bearing and the CG of the prop.

What I am harping upon on any PSRU is what are the gyroscopic moment limits of each box or limits on prop MMOI and combine yaw/pitch rotation rates. This comes from MMOI of the prop times rotation speed of the prop (in rad/s) times combined yaw and pitch rotation speed (also in rad/s). It only takes a spin entry to make some really huge moments on the prop shaft.

Some PSRU makers have never even thought about this... oh, and just saying " no acrobatics" is not much protection. Wing drops in stalls, spin entries, and people wiggling the stick can all make decent instantaneous yaw and pitch rotation rates, even if only briefly.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Is there any failure history of the centrifugal clutch on a V8 aero conversion?
Would you use one on your project and why?
Interested in knowing this too.

Most PSRU go with flexible couplings to drive the natural frequency of the flywheel-prop system significantly below idle, and then they just power through that resonance during the acceleration from firing speed to idle speed. AutoPSRU avoids this mode with the clutch, which engages above the resonance speed. They do seem to have a bunch of parts, cost, and weight that other systems do not carry.

Billski

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Why would knowing the 'G' limit be of any value when it is installed in one of the most generic, stable, easy to fly aircraft in the world?
The only reason you might want to know 'G' limit is if you install it in a Mustang or Spitfire and intend to try your hand at air combat.
C172 is an airplane certified for +3.8/-1.52 g's. Since this particular C172 also has a lot more power than most Skyhawks, it might be capable of higher cruise speeds too. All of these things hint at being able to approach the g limits of the airplane, either intentionally or inadvertently. Examples might include maneuvers required for the commercial test, collision avoidance, unintentional severe turbulence penetration, etc. If the gearbox further limits the g's that the airplane should be exposed to seems to be a pertinent question. Moderator Mode On - If you do not know the answer to a question or will not answer, saying so is OK and preferable here on hba.com to rediculing the poster. Moderator Mode Off.

Billski