Carb venturis (Tweeked)
- Thread starter T.J.
- Start date
Dave Calkins
Registered User
Anchorage, Alaska
Yeah TJ,
Your original mention months ago of the modified venturi didn't impress me much either.
For me, it's hard to believe that a venturi shape change could boost HP by nearly 7%, or about 10HP.
Is he reducing the volume of the space the venturi occupies enough to free-up the induction flow?
We couldn't be talking about a simple "more complete vaporization" of the fuel providing these gains, NO?
As long as the dyno tests are honest (same engine, same dyno, no other variables than the venturi change) then I have to believe the claims.
Keep us posted. This sounds like FREE horsepower to me!!!!
Dave Calkins.
PS You guys get much snow down your way on the last couple of lows?
We finally have about 10 inches in town, here.
Your original mention months ago of the modified venturi didn't impress me much either.
For me, it's hard to believe that a venturi shape change could boost HP by nearly 7%, or about 10HP.
Is he reducing the volume of the space the venturi occupies enough to free-up the induction flow?
We couldn't be talking about a simple "more complete vaporization" of the fuel providing these gains, NO?
As long as the dyno tests are honest (same engine, same dyno, no other variables than the venturi change) then I have to believe the claims.
Keep us posted. This sounds like FREE horsepower to me!!!!
Dave Calkins.
PS You guys get much snow down your way on the last couple of lows?
We finally have about 10 inches in town, here.
Dave Calkins
Registered User
Anchorage, Alaska
Maybe some guys who've used the Ellison throttle bodies could comment on the HP gains, and whether they provide less obstruction than, say, a good old Marvel Schebler.
Dave Calkins.
Dave Calkins.
VENTURIS
When the TPI corvettes came out, Everyone was looking at raising H.P. One of the first mods we made was fooling around with the entrance to the throttle bodies. We found we could gain H.P. on a stock engine by installing a swerl plate to smooth the air flow. We messed around with a lot of plates. The upshot was we could gain 5-12 H.P. on a stock motor.I think the modified venturis on the M.S. carbs could equal or better this. Just an opinion. Tim Ayers
When the TPI corvettes came out, Everyone was looking at raising H.P. One of the first mods we made was fooling around with the entrance to the throttle bodies. We found we could gain H.P. on a stock engine by installing a swerl plate to smooth the air flow. We messed around with a lot of plates. The upshot was we could gain 5-12 H.P. on a stock motor.I think the modified venturis on the M.S. carbs could equal or better this. Just an opinion. Tim Ayers
ground loop
Registered User
Anchorage
The claims seem excessive for the type of mod we are talking about here!
Gaining horsepower and low end torque at the same time is difficult with carb modifications.
2-3 hp seems reasonable to me, but unless it as dependable as the original it probably isn't worth it.
Gaining horsepower and low end torque at the same time is difficult with carb modifications.
2-3 hp seems reasonable to me, but unless it as dependable as the original it probably isn't worth it.
Luke_theDrifter
Registered User
Dillingham, Alaska
Greetings TJ,
Add me to the list of folks to keep posted on the venturi.
........> On the subject of gaining poines, whats your thoughts on the small alternator driven (gear driven) from the assy. case, versus a regular alternator driven by belt in reguards to HP? Most race cars, from Sprint cars to Nascar Cup series machines drive everything directly, no belts. I realize some of this is for reliability, but I'm sure they must see some HP gain. For the sake of argument if a belt driven alternator, is "robbing" 3-5 poines??? while in full charge mode, what would a gear driven alternator use? Would it be about the same and a mute point, or could we see at least a couple of ponies?
On take off, when asking the plane to produce the max. HP, its' easy enough to turn off the master so the alternator isn't charging, no load, then turn it back on once underway,........ but the belt is still taking some.....any idea of how much?
By the way....we've been in the mid-Feb thaw over here, (not as bad as last year) mid 30's or higher. Today, Pres. day, we finally sarted to see winter wx conditions again, maybe some snow by Wednsday.
Good flying...>Byron
PS. Another ol' coot that don't impress easily by every new fan-dangled bell & whistle made for a Cub..................
Add me to the list of folks to keep posted on the venturi.
........> On the subject of gaining poines, whats your thoughts on the small alternator driven (gear driven) from the assy. case, versus a regular alternator driven by belt in reguards to HP? Most race cars, from Sprint cars to Nascar Cup series machines drive everything directly, no belts. I realize some of this is for reliability, but I'm sure they must see some HP gain. For the sake of argument if a belt driven alternator, is "robbing" 3-5 poines??? while in full charge mode, what would a gear driven alternator use? Would it be about the same and a mute point, or could we see at least a couple of ponies?
On take off, when asking the plane to produce the max. HP, its' easy enough to turn off the master so the alternator isn't charging, no load, then turn it back on once underway,........ but the belt is still taking some.....any idea of how much?
By the way....we've been in the mid-Feb thaw over here, (not as bad as last year) mid 30's or higher. Today, Pres. day, we finally sarted to see winter wx conditions again, maybe some snow by Wednsday.
Good flying...>Byron
PS. Another ol' coot that don't impress easily by every new fan-dangled bell & whistle made for a Cub..................
fobjob
MEMBER
Salt Lake City, Utah
For every 8 amps produced by the gen/alternator, you would lose 1.1 HP plus friction losses (minor)....assuming 13.8 volts and typical efficiencies...
OOPS...gotta quit doing this stuff in my head...I meant 80 amps/1.1 HP....that's 72 amps/HP.....not real significant...unless you can feel the difference.
OOPS...gotta quit doing this stuff in my head...I meant 80 amps/1.1 HP....that's 72 amps/HP.....not real significant...unless you can feel the difference.
SuperCub MD
Registered User
Collins, Wisconsin
Anybody ever mess around with the intake riser?
The straight bore is about 1.8" all the way up, which roughly matches the -12 or -32 carb throat. The old standard taper bore startes over 2" on the bottom and tapers to about 1.8" at the top creating a second venturi on the riser. The -12 carb is used on the taper bore, and -32 on the straight. Either riser and carb can be used on the 150/160. Has anyone ever tried each set up back to back to compare?
Lyc made the taper riser first, then switched to all straight riser. A obvious reason for the change may be that the straight would be a heck of a lot easier and cheaper to manufacture. I wonder if there may be some advantange to the taper.
The straight bore is about 1.8" all the way up, which roughly matches the -12 or -32 carb throat. The old standard taper bore startes over 2" on the bottom and tapers to about 1.8" at the top creating a second venturi on the riser. The -12 carb is used on the taper bore, and -32 on the straight. Either riser and carb can be used on the 150/160. Has anyone ever tried each set up back to back to compare?
Lyc made the taper riser first, then switched to all straight riser. A obvious reason for the change may be that the straight would be a heck of a lot easier and cheaper to manufacture. I wonder if there may be some advantange to the taper.
Steve Pierce
BENEFACTOR
Graham, TX
I remember a Service Bulletin on carb icing on some twins (probably Apaches) that Lycoming remedied by adding the tapered riser. I will look it up when I go to the shop and let you know what it says.
fobjob
MEMBER
Salt Lake City, Utah
The tapered riser was ~2.5 inch diameter and matched the -12 carb, which was standard pre 1959 on the O-320-A2A . The -12 had some rich mixture at cruise and mixture distribution issues (hot cylinders) and it was recommended that (I think by Piper) the -12 be changed to a -32 carb, which had the smaller 1.94 inch throat diameter. To make the tapered riser work with the new carb, a riser adaptor was made by Lycoming, and SB258 was issued. Lycoming then made the engine sump with the straight riser, which was designated the O320-A2B.
Which is where I am now. Installed the riser adaptor ($138) and got back about 10 HP, moved some temps around in the engine....but Lycoming thinks now that the hot #4 cylinder is due to the -32 carb, and probably the one-piece-venturi.....(turbulence)
In the spirit of this thread, the formula one racers take their O-200's and weld fins on the inside of their intake risers(not allowed to modify carbs) and spin the air to get HP increases and low temperature distributions between cylinders.
I wish I'd learn this stuff by reading this site instead of having to go through the experience.
Which is where I am now. Installed the riser adaptor ($138) and got back about 10 HP, moved some temps around in the engine....but Lycoming thinks now that the hot #4 cylinder is due to the -32 carb, and probably the one-piece-venturi.....(turbulence)
In the spirit of this thread, the formula one racers take their O-200's and weld fins on the inside of their intake risers(not allowed to modify carbs) and spin the air to get HP increases and low temperature distributions between cylinders.
I wish I'd learn this stuff by reading this site instead of having to go through the experience.
fobjob
MEMBER
Salt Lake City, Utah
I cracked my carb this weekend and found that the venturi is a mess as far as casting flash is concerned. Since the air whistles through there at 259 MPH,(assuming 320 cu. in. per revolution?)(maybe only half that?) the poor casting and the huge structure supporting the siphon tube and blocking at least 1/3 of the throat sure looks like a place to create trouble. Cleaned up the venturi leading and trailing edges with a half-round needle file, and smoothed the inside of the inner venturi(having a spoiler at the max thickness point of an airfoil doesn't seem like a good thing) Test flight Wednesday. With my past experiments , I'm not expecting anything....
recalculate: 65 mph to 100mph depending on whether the valve is open....
recalculate: 65 mph to 100mph depending on whether the valve is open....
fobjob
MEMBER
Salt Lake City, Utah
Flew the cub Tues. after smoothing out the carb venturi...ambient temp was 43F, quite a change from last time,(73F) but here's what happened:
CHT 405 #4, 330 #2...
EGT range 1400-1500, 1370 full rich, full power.
oil temp 155F
I think it leaned mixtures overall, and cooled #2 more than #4. (430-405=25;
390-330=60)Full power was unchanged by the fuel consumption test, in spite of lower density altitude. Prop RPM was higher, but I didn't note it....I remember it was about 2560 rpm ....meaning that full power did increase, but fuel consumption at full rich dropped. I think that people who are suffering from over-rich symptoms since changing to the one piece venturi would probably benefit from smoothing away the casting flash.
The overheating #4 mystery remains so, but I think spinning the air in the
intake manifold would eliminate that possibility. (even if it didn't cure it)
My next exercise in futility is to finally pay attention to the suggestion that I check the induction tubes again, very carefully. Next week will be a lot warmer here on planet Utah, and I'll run some more numbers.
----------------------------------------------------------------------------------
I'm not a mechanic; ignore everything I say. All normal and Cosmic disclaimers apply.
CHT 405 #4, 330 #2...
EGT range 1400-1500, 1370 full rich, full power.
oil temp 155F
I think it leaned mixtures overall, and cooled #2 more than #4. (430-405=25;
390-330=60)Full power was unchanged by the fuel consumption test, in spite of lower density altitude. Prop RPM was higher, but I didn't note it....I remember it was about 2560 rpm ....meaning that full power did increase, but fuel consumption at full rich dropped. I think that people who are suffering from over-rich symptoms since changing to the one piece venturi would probably benefit from smoothing away the casting flash.
The overheating #4 mystery remains so, but I think spinning the air in the
intake manifold would eliminate that possibility. (even if it didn't cure it)
My next exercise in futility is to finally pay attention to the suggestion that I check the induction tubes again, very carefully. Next week will be a lot warmer here on planet Utah, and I'll run some more numbers.
----------------------------------------------------------------------------------
I'm not a mechanic; ignore everything I say. All normal and Cosmic disclaimers apply.
B
bearsnack
Which exhaust system are you using? Do you possibly have a better exhaust flow on the cooler cylinder?
B
bearsnack
My train of thought was going the wrong way, I think your right about the induction pipes. They have been a flawed system in my opinion all along. They get the job done but ineffeciently. I was thinking that leftover exhaust from a higher backpressure cylinder Vs. a lower BP cylinder would change the whole combustion fuel/air ratio to provide a different CHT, or a slightly different mixture. I may be way behind on this and you can tell me what you know.
T.J.
Registered User
Alaska
Well I finally got an update from the guy with the tweeked venturi. He sent me some dyno sheets from Lycon. After looking them over a while, I notice they are not very useful. The best "run" was done with his venturi and the engine leaned. The other "runs" were done rich.
This is not the full report. I pulled data from it to post.
One thing I did notice, the difference between a square air cleaner and a round one.
Another thing I noted which is not shown above is the max RPM.
Stock, Round.....2593RPM.
Stock, Square....2657RPM.
Venturi, Round...2650RPM.
Venturi, Square..2657RPM.
I'll get hold of him and see if he has any data without the mod, in the lean condition. I hear Lycon is running one of his venturis in a go fast experimental race plane.
Verdict still out.
This is not the full report. I pulled data from it to post.
One thing I did notice, the difference between a square air cleaner and a round one.
Another thing I noted which is not shown above is the max RPM.
Stock, Round.....2593RPM.
Stock, Square....2657RPM.
Venturi, Round...2650RPM.
Venturi, Square..2657RPM.
I'll get hold of him and see if he has any data without the mod, in the lean condition. I hear Lycon is running one of his venturis in a go fast experimental race plane.
Verdict still out.
Crash
GONE WEST
Nikiski Alaska
RMREBOB said:
You have to take these test stand results with a grain of salt (i.e. Bull Wooster). An engine sitting still in a test stand running a round or square filter in not real world. On a Super Cub bouncing down a strip is where you will see the difference. Charlie Center of Crosswinds STOL did real world testing of round versus square filter on take off and came back with the round filter pulling around 100 RPM more then square. Take care. Crash
I read somewhere where the round airfilter was good for a few horsepower increase. I can't find where that was at but will keep looking. Is there an STC that puts that on the early models with a square bracket filter? I've got an 0-290 and would like to get as much HP as possible (without spending $$$ to upgrade to a 150 hp). Truth is I really can't complain with the performance. It gets me off the ground fully loaded (and then some...) in a respectable distance and I usually indicate about 110 mph cruise.
SuperCub MD
Registered User
Collins, Wisconsin
In back 2 back thrust testing, the round filter pulled more on a stock 18-150. That was run it, change the lower cowl and airbox as fast as I could (just a few minutes), and run it again. That's as good of real world testing as I could get, take it for what it is worth.
In my testing, the biggest thing I found is that a lot of this testing is subjective, and subject to the smallest variables. You could test one engine/plane in certain conditions, then test another, or change the conditions just a little, and vary the results. My point is, it would not be wise to put a lot of faith in my testing, or anyone elses. Just because it works on someone elses plane/engine, does not necessarily mean it will work on yours. In other words, the disclaimer, "Results may vary".
In my testing, the biggest thing I found is that a lot of this testing is subjective, and subject to the smallest variables. You could test one engine/plane in certain conditions, then test another, or change the conditions just a little, and vary the results. My point is, it would not be wise to put a lot of faith in my testing, or anyone elses. Just because it works on someone elses plane/engine, does not necessarily mean it will work on yours. In other words, the disclaimer, "Results may vary".
T.J.
Registered User
Alaska
Mark;
Yep, I agree. What makes a difference on my plane may not work on yours.
I'm just the messenger here. I just posted the results from Lycons test.
I do however, agree with Jerry. It just makes sense to me that an opening faced into the air flow will produce more of a "ram" effect than a filter where the air has to make two 90 degree turns before it enters the carb.
Crash:
On a test stand you will get no "ram" air effect. I wonder if that would matter?
Yep, I agree. What makes a difference on my plane may not work on yours.
I'm just the messenger here. I just posted the results from Lycons test.
I do however, agree with Jerry. It just makes sense to me that an opening faced into the air flow will produce more of a "ram" effect than a filter where the air has to make two 90 degree turns before it enters the carb.
Crash:
On a test stand you will get no "ram" air effect. I wonder if that would matter?
Dave Calkins
Registered User
Anchorage, Alaska
anybody running a K&N round filter?
..talk about easy back-to-back testing among the old paper filter, Brackett, and the K&N.
As far as the ram-air effect of the square filter, I'm not totally convinced.
The scoop for the round filter acts as a constant pressure plenum. The two 90degree bend efficiency losses might be overcome by the constant pressure available and also the much greater surface area of the round filter.
The air on the square filter still has to likewise make one 90 in the airbox.
Which is more applicable to this discussion, pressure into the airbox, or amount of flow? We're ultimately limited by the carb throat area, right. And of course the filter style topic concerns air before the air even sees the carb heat valve and airbox vanes.
I brought this up so you smart guys could school me.
Thanks, DAVE
..talk about easy back-to-back testing among the old paper filter, Brackett, and the K&N.
As far as the ram-air effect of the square filter, I'm not totally convinced.
The scoop for the round filter acts as a constant pressure plenum. The two 90degree bend efficiency losses might be overcome by the constant pressure available and also the much greater surface area of the round filter.
The air on the square filter still has to likewise make one 90 in the airbox.
Which is more applicable to this discussion, pressure into the airbox, or amount of flow? We're ultimately limited by the carb throat area, right. And of course the filter style topic concerns air before the air even sees the carb heat valve and airbox vanes.
I brought this up so you smart guys could school me.
Thanks, DAVE
SuperCub MD
Registered User
Collins, Wisconsin
I also tested the square Brackett filter with the element removed. It picked up thrust with the element removed, and was equal in thrust to the round filter with the element installed. Interestingly, the round filter airbox and lower cowl lost a little thrust when the round filter element was removed. The best thrust was with the round airbox, filter, and cowl with the round filter installed.
Again, take it for what it is worth, but I'm curious if anyone else has tested this and come up with anything else.
Again, take it for what it is worth, but I'm curious if anyone else has tested this and come up with anything else.
Crash
GONE WEST
Nikiski Alaska
Why is it that Lycon keeps doing these apples to oranges comparisons? Take the same engine at the same mixture and compare it with and without the mod at least twice but better yet three times to make sure the results are the same. 7th grade science class experiment principals. Crash
