• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Converting a 150hp to 160hp or is it 10:1?

Lawn Dart

Registered User
Las Vegas, Nv
I hear a lot about this modification of swapping out your 7:1 pistons in a stock WD-150hp-O320-A2B with 10:1 pistons and heavy wall wrist pins, and then calling it a 160hp-O320-A2B?.

I?ve read enough about it to know that I am thoroughly confused! :roll:

From the posts that I?ve read, no one has been specific about how to go about this.

I read that some people change the cylinders to choked barrels (cylinder bore is tapered up by TDC) and others don?t. I read that some just change the pistons, rings and pins, but I don?t know what the part #s are and I can?t find anything on Lycoming that suggests that they made 10:1 pistons for any O320.

I see that if you convert a 150hp to a 160hp you stamp a ?C? at the end of the model # (is that right?) but I still don?t know exactly what all is involved in the 160hp conversion (part #s, machining, log book work, etc)

And lastly, I?m totally mixed up about this whole 150 to 160 and 7:1 to 10:1 connection.
I?m no engine shop, but I?ve built enough to doubt that raising the compression 3 whole points in a 320 cubic inch engine is only going to raise the HP 10 horse?

I promise that if I blow the heads off of my stock straight barrels, I won?t hold you responsible!!

Anybody??

PM me if you?d rather.
 
Howdy Lawn Dart,

I'm trying to remeber the commpresion increase for the 150hp to the 160hp??? If my memory serves me correctly I think I remeber asking the same questions, ie; increase compresion to 10:1, when I changed to the 160hp. From what I gathered there seems to me a big mis-conseption about the 10:1 compresion ratio. I'm sure someone who builds engines for a living can give you the exact numbers, part numbers and so forth. Once again from memory I think its' more going from 7:1 to like 7 1/2 or 8:1.

At any rate, if you're not familar w/ the "new exhaust" system for Cubs, built by Leading Edge in Alaska you might check it out. I know for sure I seen more of a performace increase w/ the "tuned" exhaust than any other one single thing I've ever done to a Cub. I'm not trying to advertise for this company, however this new exhaust system really works! You can find them at; www.borntoperform.com or call them; 888-534-3343.

Anyway, even before I changed the guts of the engine to 160hp I put on the new stainless steel "tuned" exhaust system on. With the nature of how all the FAA rules work, the guy making the exaust system can't advertise a horsepower increase w/o going through a BUNCH more stuff to STC the O-320 engine to a higher hp rating. My true-life experince w/ the new exhaust was an increase of 200-300 rpm on the take off roll
( YES!..nearly 300 rpm more) and a very noticable increase in climb performance.
To make a long story short you can increase to 160+ hp just by adding the "tuned" exhaust. In other words I'm certain I have seen AT LEAST 10 hp increase w/ the exhaust. Based on info I'm hearing from other folks w/ the exhuast, and my own experince, it is commonly acsepted that we're seeing a "real-life" increase of 13-16 more ponies.
Then take into consideration if you have the ol' stock O-320 that has been juiced up to make 160 (higher compresion), plus you now have the fancy exhaust and the math comes out to slighly more than a O-360 will produce. (180hp) Best of all you still have the wieght of the O-320, and a stock cowling.
If I keep typing I'm sure I could produce some challanges from the 180hp guys, but as I mentioned earlier I KNOW what I've seen for preformance.

.......>Byron
 
Cavy, Diggler's numers are quite close, though the 150 is actually rated at a bit more than 150 hp at 2700 rpm, and the 160 is a little more than 160.

Supposedly the limit for mogas is 11.2:1, but I'd be very hesitant about running more than 10.5:1, and even then, only on avgas while running about 100 degrees rich of peak. Lycon sells 10.5:1 pistons at a reasonable price. I'm running H2AD pistons at the moment, and am quite pleased with them. Am going to switch them to another plane and replace them with 10.5 as a Christmas present to myself.
All the best,
JimC
 
Lawn Dart said:
I hear a lot about this modification of swapping out your 7:1 pistons in a stock WD-150hp-O320-A2B with 10:1 pistons and heavy wall wrist pins, and then calling it a 160hp-O320-A2B?.

I’ve read enough about it to know that I am thoroughly confused! :roll:

From the posts that I’ve read, no one has been specific about how to go about this.

I read that some people change the cylinders to choked barrels (cylinder bore is tapered up by TDC) and others don’t. I read that some just change the pistons, rings and pins

Basically what you are asking about is the two certified ways to convert to 160 hp. Both are for the wide deck engine only. Both of these certified ways give you 8.5 to 1 like diggler said.
One way is to use all parts that are compatible with a Lycoming 0-320-B2B engine. this includes Choked cyls, higher comp pistons, rings, and heavy wall piston pins. If you use the Lycoming Parts book, and the Service Letter on changing the Data Plate, you then fill out a 337 referencing all the changes and data used, alter the data plate and you now have a Lycoming 0320-B2B 160 HP engine.

The second way is to purchase an STC that allows you to convert your 0-320-A2B Wide deck engine to 160 hp without changing the straight wall cyls. You simply Install B2B pistons, rings and heavy wall Piston Pins, (and exhaust valves if yours still have the early Wide Deck 150 hp valves) and rivet another data plate next to Lycomings Plate.

these are two Certified ways. There may be more by now that I am not familiar with and there are probably a dozen experimental ways to do it.
 
Thanks for the input guys, this sorta clears up the ol? wives tail about just dropping in a set of 10:1 pistons and calling it a 160hp.

Next question(s): I'd like to address another wives tail.

What sort of machine work is required to make this change?
I?ve never built one of these motors, so please excuse my ignorance, but in everything else that I?ve ever built, piston side wall clearance is everything! (hence the choked cylinders). Seems that I hear a lot of people suggesting that they have just swapped the pistons for another set and call it ?good? (clearance wise). Do people really do this to these motors? Are Lycoming?s tolerances so sloppy that this simple 'swap' is allowed?

And, (here I go showing my experience again) can the heads be unscrewed from the cylinders for the purpose of working on them? (valve work, porting, etc) I assume they can?t, (or shouldn?t be) but what say you?

Thanks again for your input, this is much closer to the type of info that I am looking for.
 
> What sort of machine work is required to make this change?<
None.
>t, piston side wall clearance is everything! (hence the
choked cylinders).<

True. And it will remain unchanged if you just swap out the pistons and pins. I suggest replacing the rod bearings and rod bolts while you have the cylinders off. The swap will take you about a day, most of which is spent messing about with the cooling baffling.


> Seems that I hear a lot of people suggesting that they have just swapped the pistons for another set and call it ?good? (clearance wise). Do people really do this to these motors?<

Yes they do. The swap leaves nominal clearances unchanged.

> Are Lycoming?s tolerances so sloppy that this simple 'swap' is allowed?<

I don't know that I'd call them sloppy, but yes.

> And, (here I go showing my experience again) can the heads be unscrewed from the cylinders for the purpose of working on them?<

They can, but I would strongly discourage attempting a 'do it yourself' project on head removal and replacement. Get a pro to do it, though there's really no need to do it at all.


> (valve work, porting, etc<

3 angle valve facing can help. The ports are already too large, but could benefit from reshaping.



> I assume they can?t, (or shouldn?t be) but what say you?<

They can, but there's no real need to.
JimC
 
Also, there used to be a mod that replaced Lycoming valves with larger Continental valves, but it tended to result in cracking the heads between the valve guides, so has sort of petered out.
JimC
 
Cavy get a copy if a Lycoming Direct Drive Overhaul manual and you will have all the answers about clearances. No as a normal practice you do not take the head off the barrel. Save the porting and polishing for the car stuff as it is one technology that doesn't transfer all that well to aircraft engines. ( in my opinion ) The tolerences in aircraft engines are huge when compared to a liquid cooled engine and the reason is that they have to operate over a large temp range that is less stable than liquid cooling. You may be an expert on say a chevy v-8, the mission for the v-8 and the lyc. are different . How many hours would the v-8 run at it's rated hp? I bet it isn't close to 2000 hrs.


Luke_theDrifter I hate to tell you that just by bolting on the leading edge exhuast that you will not produce more than 150hp@ 2700 rpm (160hp@ 2700 rpm for the b2b ) on a stock engine. The only way to produce more hp in these engines is more compression ratio or more rpms ( above 2700). Now did you see a hp increase by removing the stock SC exhaust and installing the lees system? Probably and you might gain your 13-16 hp but it is not over the 150 or 160 hp as set by Lyc and the FAA on certification. Realistic #'s you probably went from 130 hp to 140 hp when you removed some back pressure.


Matt
 
Well said, Matt.

If anyone wants a QuattroPro spreadsheed that computes the horsepower gain due to compression ratio changes (based on change in thermodynamic efficiency), I will send it to you. The increases are nowhere near some of the numbers you see tossed about, but are still worth pursuing.
Jimc
 
At any rate, if you're not familar w/ the "new exhaust" system for Cubs, built by Leading Edge in Alaska you might check it out. I know for sure I seen more of a performace increase w/ the "tuned" exhaust than any other one single thing I've ever done to a Cub. I'm not trying to advertise for this company, however this new exhaust system really works! You can find them at; www.borntoperform.com or call them; 888-534-3343.

I just installed the new exhaust on my 160hp engine last week and cant tell any differnce.
 
I would like to see someone come out with an STC for the 10.5 to 1 pistons.
 
There are 10, 10.5, 11, and more available. But when you tell us, "problem is I fly Part 135 and need something STC or field approvable", you've just told us that you plan to go with 8.5:1.
All the best,
JimC
 
Does anyone know the advantages of a choked barrel? or why it should or shouldn't be used on a 8.5:1 piston?

For an experimental engine, I have a set of narrow deck chromed cylinders with 8.5:1 pistons, on a punched out case, mechanical lifter, 0-290d to make a 230lb engine. I need a photo of some cylinder base hold down plates so I can machine a set. I have an extra 3/8 inch of thread sticking out the top of the nuts on the stock 290 cylinders with hex nuts so I should have plenty of space for the hold down plates.
 
I talked to a guy at an engine shop today and he told me that they choked the cylinders because down south when it get's really hot out, the cylinders actually expand. Must cause loss of compression... ? Interesting.. therefore .. im thinking my plans should work, straight bore 8.5:1 pistons in the ND.. Has anyone ever heard differently?
 
If you don't choke the cylinder, when you get up to temp, you will be running reverse choke. The top expands more than the bottom.
 
I just converted my A2B to a B2B. If you go the STC route you need two STC's. One to convert the engine, the other to hang it on the airframe. Right now, I only know of one STC available to convert the engine and that is LyCon. Everybody else is out of the business. The LyCon STC spells out everything you need to do in terms of parts change out. There are severa STC'sl to hang on the airframes, Crosswind STOL seems like a good deal as he throws in the aft mounted oil cooler STC in the bargain. They are good folks I hear. Cubcrafters also has one, and that is the one I bought only because I have a Cubcrafters Cub and they both know the airplane and have been a big help on this project.
 
It doesn't require an STC to go from 150 to 160 hp, narrow or wide deck. Just re-stamp the data plate and make a log book entry. Both variations are on the same TCDS -- no STC required. But it does require an STC to install 160 hp in a Super Cub -- Cubcrafters has an all inclusive one.
 
Just a thought - my hotrod 0-360 weighs 260 pounds.
For 30 pounds you get more hp, more torque (very important for out of the hole performance) and much greater parts availability and at lower costs.

Bill
 
When you change a A2B to a B2B are the carb, air box, alternator, oil cooler, starter the same? In other words are you just switching out pistons and cylinders?
 
It doesn't require an STC to go from 150 to 160 hp, narrow or wide deck. Just re-stamp the data plate and make a log book entry. Both variations are on the same TCDS -- no STC required. But it does require an STC to install 160 hp in a Super Cub -- Cubcrafters has an all inclusive one.

That is correct however my understanding of via SB1304 is you can only stamp a "C" after the S/N, you cannot change the HP on the data plate, whereas an STC will allow rescribing of the data plate. Is that correct?
 
It is correct to stamp a "C" when making a change without an STC. Don't know about what happens with an STC. Basically, the "C" tells folks to look at the log book for more details.
 
Back
Top