[jbDC9]

So I recently hit the 200 hr mark on my QB RV-8 and thought I'd share my experiences with the 4 into 1 exhaust system installed, just in case anyone else is considering such a system...

The original reason I went with this system was noise; the usual Vetterman type exhaust is just too loud for me and has a sharp, barking kinda quality to it. I called up Aircraft Exhaust Technologies (since merged with AWI) and asked about their crossover system with mufflers. Chris steered me towards the 4 to 1 system instead, saying it performs like a Powerflow tuned pipe, flows lotsa air, and the sharp exhaust note is mellowed out from blending the 4 separate stacks into one collector pipe. "Great!" says I, ship it!

I have no gripes at all about the pipes themselves; they're good quality, very well made and are holding up fine so far. My main beef is how the system interacts with the RV-8 airframe. I suppose that from the outside the noise is mellowed out, but from inside it was pretty noisy and buzzy with quite a bit of vibration through the floor... but since I've never flown in another -8, I had no basis for comparison on the noise/vibration level; I figured that it was normal -8 behavior. The noise/buzziness was worse at high AOAs and low airspeed. Also, in the pattern on base and final with the power pulled back there was quite a bit of popping and backfiring from the stack.

My first hint of trouble from the noise/vibration came at the 140 hour mark with cracks appearing in the forward belly skin between the gear legs; ref my previous post here - http://www.vansairforce.com/community/showthread.php?t=18402. I patched the cracks and figured that'd be the end of it. But alas, it wasn't to be. A few weeks ago (200 hrs) I was under the belly again wiping it down and I found a two more cracks just forward of the original ones. Well now, that does it; this pipe has gotta go! But first, I called AWI to see what could be done; it was suggested to try a down turned pipe tip. I had it within a week and had a local muffler shop weld it on. The end result? Holy-freakin'-moly, it's like a whole different airplane. It's much quieter and smoother than before, even with high power and AOA with low speed; methinks this will end the vibration and skin cracking problems. And, as an added bonus, the popping and backfiring at low power settings appears to have been eliminated; after 5 or 6 trips around the patch I didn't hear one pop or fart from the stack. Yea! I wish I'd known about such a simple fix 180 hours ago.

I don't know if any other RVs with 4 into 1 systems have had similar problems, but in my case it's been a real pain in the neck. If you're considering this exhaust or are already running one and if the noise/vibration seem excessive, put on a down turned tip before the skin cracks get started.

 

[Adam]

Thanks John, This could not be more timely. I have just 4 hr on my RV-8 and Ive been telling others that my 4 into 1 feels like someone is knocking on the bottom skin. I was going to call them this week to find out what I could do but thought that I would put more hours on first, think I call them tomorrow.

Adam Silverstein
RV-8 4Hrs

 

[LifeofReiley]

I actually heard about your ordeal while I was in Houston a couple of weeks ago. The story I got was that you had considerable damage (cracks) to the fuselage and were not very happy. I'm glad you've worked things out.

 

[brenegan]

Did they charge you for the tip or send it gratis? Do you have any pics of the cracks?

 

[jbDC9]

Nope, no free lunch; the new tip was $65-70... but that's a small price to pay though when my alternative was to scrap or try to sell the original system and blow another $950 or so on a new crossover type.

Here are a coupla pics of the original cracks; they were along the floor ribs around the rivet holes.

And here's the ugly aftermath; yuck. I've wondered if I should replace that skin, but it'd be a big job... and the patches are uniform in size and shape, down on the belly... might not be quite as noticeable after a paint job. I'm talking myself into just living with it. Live and learn I guess.

 

[brenegan]

Thanks for sharing. I am thinking of going for the 4-in-1 when I get to that point, so i'll make a note to get the tip as well. Your patch job looks good.

 

[JordanGrant]

Cleaner belly?

Hey, John. I have a standard Vetterman 4-into-2 crossover, but I was wondering about putting down-turned tips on mine for noise and for cleanliness. As you continue to fly with your new setup, I'd be curious to know if your belly stays cleaner now.

 

[Ironflight]

And here's the ugly aftermath; yuck. I've wondered if I should replace that skin, but it'd be a big job... and the patches are uniform in size and shape, down on the belly... might not be quite as noticeable after a paint job. I'm talking myself into just living with it. Live and learn I guess.

Oh, they're not so bad.....Take a look under a Grumman single sometime John....they have all sorts of "patches" that look just like that - reinforcement plates to keep installed stuff in the cockpit from pulling through the honeycomb. No one will ever notice them once it's painted - unless you go around pointing them out!!

Now "Get thee to a paint shop!!"

Paul

 

[Nuisance]

I went through some of this a few years ago.

linky

Recently, after changing to the ECI cold sump, I switched to the Vetterman 4 pipe exhaust. I don't believe I suffered any performance loss. Actually, I think the "tuned exhaust" is a bunch of hokey, unless you restrict your flying to one altitude.

look here in the middle of the page

I found the 4 pipe to be much quieter. It is also easier to fair in the bottom of the cowl for less drag. It is also cheaper. With the cold sump, I am going faster than before.

Have fun!

 

[AndyRV7]

Reminds me of a 69 Chevelle I had a while back. I swapped the exhaust and could only get the pipes back to the rear axle (into the mufflers) the first day I worked on it. I went to an air show with my family that day and the sound inside the car was literally deafening. It wasn't so much loud as it was like a tremendous pressure in your ears. I guess that was just a lower frequency. Then, I got the pipes finished and out the back of the car. I couldn't believe how much noise (and potential hazard) it made just having the mufflers end under the floor boards. So your story of just pointing the flow away from the fuse is something I can fully appreciate.

 

[gmcjetpilot]

THANKS! for the INFO

The original reason I went with this system was noise; the usual Vetterman type exhaust is just too loud for me and has a sharp, barking kinda quality to it.

(AWI) Chris steered me towards the 4 to 1 system blending the 4 separate stacks into one collector pipe. "Great!" says I, ship it!

Well one thing, 4-into-1 is superior in performance, but I have never heard they where quieter or had a more mellow exhaust note, especially verses a cross-over.

The cracking thing freaks me out a little, but I suppose its possible that "sonic" fatigue was happening, causing the cracks. The thing that freaks me out is the belly has fairly thick skins, and it happened in such a short amount of time, 200 hours. It will be interesting to see if more cracks start. I HOPE NOT.

From your well written post & observations it seems to be a direct correlation between the pipes & skin cracks. However it's not conclusive evidence. Is it possible that the cracks where going to happen anyway for other reason? (which I have no idea, just saying). It's suspicious that they happened across the same station, like the exhaust was working that area.

I've not heard of belly cracks before, with any pipes, but that does not mean it can't happen. I have heard of complaints of more floor vibration and noise with the 4-into-1. The down-turn seems to have solved your issue dramatically, which I'm glad for.

I understand fatigue in aerospace structure from an engineering standpoint. Flush rivets in sheet metal are not as highly "fatigue rated" as protruding rivets for example. Also dimple in sheet is even less fatigue resistant. Sonic fatigue can by low stress but HIGH CYCLE. All besides stop drilling/deburing the crack, your patch should extend beyond the damage by two rows. The ones you have look fine, but if you need help with repairs let me know off-line and email me.

Good luck and thanks for sharing your experience.

 

[gmcjetpilot]

A "Bunch of Hokey"?

Recently, after changing to the ECI cold sump, I switched to the Vetterman 4 pipe exhaust. I don't believe I suffered any performance loss. Actually, I think the "tuned exhaust" is a bunch of hokey, unless you restrict your flying to one altitude.

Contraire mon frair.

Now wait a second, tuned exhaust is a "bunch of hokey"?

First 4-into-4 singles is actually a good exhaust system, with it's own merits. Not losing does not surprise me. Your new 4-into-4 exhaust is STILL a tuned exhaust. The length of the pipes and diameters are not arbitrary. I think you'll find your pipes are still all matched length at about 34"-38" long at 1.75" dia. Yes? Than they are "tuned". You are right that altitude and power does affect the ideal pipe "tuning". However you start with a sweet spot and where you will be most of the time. All pipes will be affected the same unless they have some way to vary their geometry as you climb and engine makes less power and ambient pressure goes down. Still "tuning" is valid and based on real facts and physics. On the other hand its not a holy grail just part of the big picture.

Second, many builders going from cross-over to 4-into-1 have found performance increase. The engine turns more rpms with fixed prop and they pick up speed. It has also been shown on dynos that "Headers" improve performance. Most race cars have tuned headers. On the other hand the fastest of the fast, top fuel and funny car have separate stacks. All exhaust systems have their own charm, 4-into-1, 4-into-4, cross-over and others. There is just basic physics & design. Like everything there are trade-offs however. No one thing is going to be a panacea (cure for all).

The down side of 4-into-1 on a Lyc is the scavenging is so good, that the stock Lycoming cam restricts the full advantage of 4-into-1. It's not really a disadvantage only that the exhaust is no longer the restrictive component the cam is.

The basis of saying all this is NOT a "bunch of hokey" is from Cafe Foundation dot ORG. The reports on aircraft exhaust are found here:

http://cafefoundation.org/v2/research_reports.php

They found the the 4-into-1 was BEST overall. They also found the 4-into-4 was pretty good as well. The cross over had some charm, but the balance due to pipe lengths was a negative. The worst was the "Y" pipe, dumping #1 & #3 (same side of engine) into one and #2 & #4 into one. Its the easiest pipes to make but not great for performance. No free lunch, absolute perfect everything in aerospace design.

Now the LOSS part of using down turns is open to debate. My feeling from reports like this one above, is down turns clearly give less floor pounding and noise. I would say there is contribution of exhaust thrust facing aft but it's small that its not worth it for the nose and vibrations. RV's already have a pretty well faired in exhaust system, verses a Cessna, with a stove pipe sticking out at right angles to the airflow. I don't think a 90 degree down turn is needed. A 45 degree turn is probably good enough.

PS nice work, I've followed your work for a while. Good stuff.

 

[Nuisance]

I worked with Larry Vetterman a couple of months ago on this subject. He sent me 4 straight extensions, and by measuring and cutting I made all 4 pipes the same length. I don't remember the exact length, but George is about right. I remember there was 10 inches difference from longest to shortest before I added the extensions.

Flight testing showed no speed benefit, actually a slight decrease, and the afterfiring on short final was very bad (I actually have no idea why this changed). So, I am back to what is pictured on the web page I referenced previously.

My memory of tuned pipes is that it is proportional to the rpm of interest, and that at 2700 rpm, the optimum length would be about 80". You see these 'bundle of snakes' tuned exhaust system on racing cars that run at 8-12 thousand rpm. There are plenty of variables of course, one of them being air density (i.e. now you have to pick the altitude you want to tune for). That is why it is of less interest to all around flyers, though if you want to target wide open throttle at 1000 msl for racing, you can just figure out where to put 80" of 4 pipes. The reason the 4 into 1 system is supposed to work better is that a cylinder gets a reflection from the previous one to fire, so the pipes can be shorter. I think it works better in theory than in practice.

All of this comes from a conversation I had with Kevin Murray of Sky Dynamics, who was one of the pioneers of the 4 into 1 exhaust.

I have spent plenty of time pouring over the CAFE test results, and while I think they did a lot of great work, they missed the mark alot too. I bet if they could do it again the results might change. There is a lot more available these days.

Ken Tunnel of Lycon told me that they did a lot of the testing of the Powerflow (certified) tuned exhaust system. That is the one with the collector that hangs down almost back to the gear legs on a 172. As part of this testing, he found the 4 into 1 tied with the Powerflow, the 4 into 4 next, and the crossover the lowest horsepower producer. This of course is all at one altitude (ground level in Visalia, CA).

Best, John

 

[jbDC9]

The cracking thing freaks me out a little, but I suppose its possible that "sonic" fatigue was happening, causing the cracks. The thing that freaks me out is the belly has fairly thick skins, and it happened in such a short amount of time, 200 hours. It will be interesting to see if more cracks start. I HOPE NOT.

From your well written post & observations it seems to be a direct correlation between the pipes & skin cracks. However it's not conclusive evidence. Is it possible that the cracks where going to happen anyway for other reason? (which I have no idea, just saying). It's suspicious that they happened across the same station, like the exhaust was working that area.

Good points, but I can't really imagine cracks starting in this location for any other reason; I've read of other -8s having a crack here and there on the cooling ramp skin, mine has one small crack around a rivet head there as well... the ramp skin seems pretty light and flimsy. But I've not read about or heard of another -8 with a tendency to crack in this location. For comparison, I've looked at numerous other -8s with standard exhaust systems including Paul's ship with 600+ hrs and Danny's with 900+ hrs... and no cracks on the belly between the gear legs. That, coupled with the huge reduction in noise and vibration with the new down turned tip on my machine has me 99.9% sure that the straight pipe was causing the problem. Now I just have to put another 50 hours or so on it to see if it's a done deal.

Why, oh why didn't I just stick with my original plan of a crossover system with dual mufflers?

No one will ever notice them once it's painted - unless you go around pointing them out!!

Now "Get thee to a paint shop!!"

No kidding, I gotta learn to refrain from pointing down there and saying "Look at this mess!" And the paint shop?? Oh, the horror! Does that mean I actually have to decide on colors and a scheme?? Seriously, I have no real plan yet for scheme or colors; it's driving my wife nuts. I suppose that I should at least get on the waiting list at a shop, that'd pressure me to make a decision!

 

[gmcjetpilot]

Excellent

I worked with Larry Vetterman a couple of months ago on this subject.................

As part of this testing, he found the 4 into 1 tied with the Powerflow, the 4 into 4 next, and the crossover the lowest horsepower producer. This of course is all at one altitude (ground level in Visalia, CA).

Best, John

Interesting John good stuff as usual. I agree the optimal to make power is longer than 38 inches but than we have some practical limits. Cafe tested straight pipes of 32.25" long with diff dia. 1.625, 1.75 and 1.875, and they did OK.

I found this simple formula I plucked off the "internets".

.....850 (180 + N)
L = ------------- - P
...........RPM


where
L = length of pipe in inches
N = degree before BDC exhaust valve opens
P = distance from exhaust valve to manifold
RPM = desired RPM

Guessing at N and P and calculating for 2,500 rpm.

.....850 (180 + 180)
L = -------------- - 2 in = 122 cm = 48 inch pipe length.
...........2,500


"The diameter of the pipe needs to be calculated so that the volume of the exhaust pipe attached to each cylinder is twice the volume of each cylinder. The exact diameter of the pipe, incidentally, is not critical and should only be used as a guide in determining which standard sized pipe diameter should be used."

Volume of each cyl on a Lyc 360 cu-in / 4 = 90 cu-in

pi r^2 * L = 2 * Vol
pi r^2 * 48 in = 2 * 90 cu-in
r = 1.93 in
Pipe Dia = 3.8 in dia - a nonsense answer clearly, but working backwards using 1.75" dia and solving for L = 58", is actually pretty close.

According to Cafe the ideal header primary is 28-36” plus secondary + collector length appeared optimize at 20-30”. So the total would be in the 48" to 66" total length range. The crude formula gave me 48" and 58".

Cafe talks about fancy programs that account for "Doppler phenomenon occurring in an exhaust pipe because the sonic exhaust wave is riding on the “wind” of the streaming mass flow of fuel and air." I have no idea? As you say John, RPM and altitude changes so you can "TUNE" only so close. Induction geometry can improve with "tuning" as well of course. The 993 Porsche has a variable-length intake runners they call the "Varioram" system. This addressed the inherent compromise between high-RPM power production and low-RPM torque production. It's first of its kind to be employed on production vehicles. The first 993's did not have "Varioram" and made about 12 hp less and little less torque at higher RPM. Not a big difference, but it shows if you vary intake and exhaust geometry you make more power.

 

[Adam]

Hay John, would post a picture of what the exhaust looks like now with the down turn!
Thanks

 

[jbDC9]

Hey John, would you post a picture of what the exhaust looks like now with the down turn!

Well, I would, but I forgot to take a pic of it... I'll be outta town for a few days, but I'll get a shot and post it or email it to ya next week.

John

 

[DanH]

<<Guessing at N and P and calculating for 2,500 rpm.>>

Bit long on your "exhaust valve open" (N) guess. 180 before BDC is TDC <g>

Closer to reality is 65 BBC, so:

.....850 (180 + 65)
L = -------------- - 2 in = 81.3 inch pipe length.
...........2,500

My memory about tuned pipes agrees with John's...and so does your formula.

 

[rv6ejguy]

Induction geometry can improve with "tuning" as well of course. The 993 Porsche has a variable-length intake runners they call the "Varioram" system. This addressed the inherent compromise between high-RPM power production and low-RPM torque production. It's first of its kind to be employed on production vehicles. The first 993's did not have "Varioram" and made about 12 hp less and little less torque at higher RPM.

Nissan (VG30E), Subaru (EG33D) and Audi had variable intake length systems in production well before the 993 introduced it. Many engines use it today in conjunction with VVT. Mazda used it to win LeMans in 1991. I don't think you'll see this on an aircraft power plant any time soon with a narrow operational rpm band. Even fixed length induction runners can show major gains if made to the correct length. My new manifold is tuned for best gains in the 4000-4500 rpm range.

 

[garnt.piper]

4-1?

I built an assymmetric 4-1 for my RV-4, and initially I tried to keep the exit pipe as long and close to the floor as possible to align with the airflow. Noise and heat beat me, so I shortened it, put a 45? turned down tip on it, and now noise is very acceptable, both inside and out. The heat under my right foot is still a bit uncomfortable on a warm day though! In applying CAFE data, most systems don't have a long or large enough tailpipe. The CAFE argument, as I read it, is that by keeping a large mass of exhaust gas moving down the tailpipe the momentum of it helps scavenge the cylinders. Most people don't like a great long tailpipe hanging out in the breeze. The skydynamics 4-1 have a large diameter tailpipe and a bellmouth exit - this gives a longer effective length, I believe. Paser looked into exhausts with his Mustang II, and found that 4 straight pipes were best for speed (tuned for half wavelength I think), and equalising EGTs, but he developed slightly more power with a crossover system.
I'll probably opt for 4 individual pipes in the next iteration.

 

[gmcjetpilot]

<<Guessing at N and P and calculating for 2,500 rpm.>>

Bit long on your "exhaust valve open" (N) guess. 180 before BDC is TDC <g>

Closer to reality is 65 BBC, so:

.....850 (180 + 65)
L = -------------- - 2 in = 81.3 inch pipe length.
...........2,500

My memory about tuned pipes agrees with John's...and so does your formula.

Yep you are right 180 deg did seem like a lot. I was going on then Cafe Foundation report. I think that is what they used.

N = degree before BDC exhaust valve opens

(opens means either start to open or full open? You are probably right its BTDC fully open.)

I was confused about what N means, start or fully open. Thanks for the info. I'd like to have the specs on a Lyc cam, any one have them? It would be easy enough to put a degree wheel on the crank & turn the engine through, noting dial gauges on the push rods.

 

[DanH]

<<opens means either start to open or full open?>>

"Starts to open" is the meaning of the spec, although not completely true. Most cams have a clearance ramp to gently take up any valve train slack and accelerate the valve components. The spec specifies the point were the valve is actually off the seat some small arbitrary distance, like .020 or 1mm or whatever the cam and/or engine designer picked out of the air. In theory it is the point where the valve is open enough to start flowing air.

When somebody quotes cam timing, your first question is "at what lift?" There is no universal standard. I have no idea what valve lift Lycoming uses to specify timing.

In general, peak cylinder pressure is somewhere in the area of 14 ATDC. The exhaust valve opens somewhere beyond 90 ATDC but well before BDC, the typical design range being 80 to 40 BBDC. This is the blowdown period. Mechanical advantage is decreasing; no point in holding the expanding gas in the cylinder any longer. It is more efficient to use the remaining cylinder pressure to vent exhaust mass. The rising piston after BDC is working against relatively little pressure; Elvis has already left the building.

In addition to the low RPM = long pipe problem, I doubt a stock Lycoming cam has much overlap, pretty much a requirement for pulse tuning to increase VE by any significant percentage.

 

[rv6ejguy]

.050 valve lift is the figure most often used on domestic engines for comparing cam specs, 1mm or .040 more often for import engines. If you look at flow bench data, there is little significant airflow at lower lifts so these figures, while arbitrary, are more useful than zero lift specs in comparing duration.

From my dyno testing, the primary tube length for best results at 2700 rpm would be something on the order of 83 inches which agrees closely with some posts here. Try to fit that in an RV! The half wave length might be more manageable.

 

[gmcjetpilot]

Doha!

From my dyno testing, the primary tube length for best results at 2700 rpm would be something on the order of 83 inches which agrees closely with some posts here. Try to fit that in an RV! The half wave length might be more manageable.

You mean I'm wrong again, Doha!

Kind of hard to fit 82" pipes in a tractor plane. There is optimal and practical.

Looking at the graph and estimating timing specs I got:

Total lift - 0.360 inches
Overlap - ?? deg (overlap is ??, min 25 deg or 60 deg, less/more? depends on criteria)
Intake start to open - 10 degree BTDC (@ 0.040) (corrected degrees and @ lift criteria)
Exhaust stats to open - 37 deg BBDC (@ 0.040) (added)
Peak Exhaust valve lift @ 105 BTDC (corrected delted intake, added Exhaust, change deg to 105)
Peak Intake valve lift @ 105 ATDC. (corrected deleted exhaust, added Intake)
Duration of Intake / exhaust are both approx 220 deg using the 0.05" lift criteria​

This graph shows straight pipes of various lengths from 6" to 68". It shows the longer the better, but also shows the "header collector" is better. See Cafe Foundation Report. Reading between the lines, I gather 28"-32.5" is best for straight stacks, verses the theoretical 83", which they did not test. There's an issue with LONG pipes and the "reflected negative wave". Simply put as I understand it, you want the strongest savaging (neg pressure at exhaust valve opening), over the most degrees during overlap. This promotes exhaust evacuation which also promotes better intake charge.

You can see the "header" is better timed at the start of exhaust valve opening, broader and stronger negative pressure or savaging. The LONG 45.5" and 68" pipe has stronger savaging but is narrow and delayed. Boo, no good. So like all things, there are trade offs. 83" pipe may be better in theory but not in practice. The longer pipes means a delayed "reflected negative pulse energy". * So a 32.5" pipe may not be as strong but its timing is better.

The other part of the exhhaust is you need a special CAM to take advantage of that scavaging. You need a CAM that matches your pipes. As Dan pointed out the overlap of the stock cam is a little mild. **

Bottom line the header is generally better overall. The header they tested has length of 54" to 64" total = primary + secondary.

* "This reflecting, negative pulse energy is the basis of wave action tuning. The basic idea is to time the negative wave pulse reflection to coincide with the period of overlap - this low pressure helps to pull in a fresh intake charge as the intake valve is opening and helps to remove the residual exhaust gases before the exhaust valve closes. Typically this phenomenon is controlled by the length of the primary header pipe. Due to the 'critical timing' aspect of this tuning technique, there may be parts of the power curve where more harm than good is done."

** Cafe Foundation Report: "Camshaft timing must be suitably altered by making exhaust valve closure occur later and the overlap period of longer duration and higher lift. Many of the scavenging systems here do not exhibit as much effect upon the intake manifold pressure during the overlap as might occur if the camshaft had greater valve overlap.

 

[DanH]

<<Overlap - 90 deg, pretty mild>>

Actually 90 degrees would be pretty aggessive if it were true. I've drawn a red line across the lift plot at .040". Now what does overlap look like?

Yes, the collector exhaust as tested gave the best negative pressure at the right time (dark red on the graph). Sadly (and as noted by the CAFE folks), it is like putting lipstick on a pig....limited overlap doesn't allow it to do anything really useful.



<<Intake start to open - 180 degree BTDC (0.180" at 180 BTDC!)>>

No. Intake starts off the seat at about 30 BTDC, and if this graph is accurate it gets to .040" about 10 degrees BTDC.

<<Peak Intake valve lift @ 65 BTDC (as you said Dan)>>

No I didn't say that. I said an exhaust valve opening figure of 65 BBDC was close to reality for this kind of engine. It looks a little shorter in this graph. Peak intake lift in this graph is around 105 ATDC.

<<Peak Exhaust valve lift @ 105 ATDC.>>

Nope.

 

[SteinAir]

The other part of the exhhaust is you need a special CAM to take advantage of that scavaging. You need a CAM that matches your pipes. As Dan pointed out the overlap of the stock cam is a little mild.

Right on....and you do realize there are a couple high end "lyco" shops that'll grind a cam for you based on a number of variables for your new engine....everyone knows about the auto guys doing it, but it's not so common in Lycos. I had the cam mildly mod'd on the last 360 I built up, so I know it's available!

Cheers,
Stein

 

[Tbone]

exhaust ordered

Ordered my exhaust from John @ awi and he now fabricates the exhaust with the turn down installed, albiet for more $$. He said he was made aware of the cracks from some forum members.

 

[gmcjetpilot]

Thanks Dan

Thanks Dan for the analysis, corrections and opinion.

Peak intake lift in this graph is around 105 ATDC.

Yes I got it backwards exhaust & intake reversed, their peaks are around 105 btdc & 105 atdc respectfully.

I said an exhaust valve opening figure of 65 BBDC was close to reality for this kind of engine. It looks a little shorter in this graph.

I also missed your BBDC reference; yes it looks like only 37 degrees which is not much I guess? I'm a cam retard.

No. Intake starts off the seat at about 30 BTDC, and if this graph is accurate it gets to .040" about 10 degrees BTDC.

I see that and that is short. It looks like the graph is sagging or your RED line rising in the middle. It could be 20-25 deg BTDC? Clearly you could open that up with a custom cam. When I built small block Chevy's, for hot rods, picking the right grind was always a pain. Part of the reason is HOW Manufactures specify their Cam grind. There was no standard. Of course a Chevy has a red line at or over 6,000 rpm and 1/2 the displacement per cyl than a Lyc. Clearly cam technology can be applied to the Lyc. As Stein said. 'Ram' makes custom certified cams for Continentals. I don't think Lyc was dumb with cam grinds just conservative, which may be a good thing.

Sadly (and as noted by the CAFE folks), it is like putting lipstick on a pig....limited overlap doesn't allow it to do anything really useful.

Ha-ha the visual of lipstick'ed pig is funny, but I would not agree with "doesn't allow it to do anything really useful". Of course it depends what you compare a 4-into-1 to.

The Power Flow guys claim big HP gain going from stock Piper/Cessna stacks. Of course that may be just a indication how crummy stock pipes are. (?) However I think you get a few more pony's from experience and others comments by going 4-into-1.

Example, a guy went from cross-over to 4-into-1 and found his static RPM and in flight RPM increased along with speed. It did something. Quantifying it by the Cafe Report is hard because they measure pressures not HP, but their bottom line was the 4-into-1 is better overall.

As a practical matter 4-into-1 does not always fit as well as the cross over or 4-into-4 separates. They all WORK. A few extra HP is not going to make a lot of difference. I recall in my foggy memory numbers like 7-10 hp more for the 4-into-1. However a lot of 4-into-1 exhaust are compromised with short secondary (10") to make them fit better verses the ideal longer secondary pipe.

 

[AWI]

4 INTO 1 EXHAUST SYSTEM CHANGES

AEROSPACE WELDING MPLS, INC, has been talking to system users and watching these posts. We are now adding the tailpipe turn-down to every system as standard. The price increased from $1149 to $1188 for the extra time and materials. We will add the turn-down to previous systems if you send in the part. The cost is the price difference of $39 plus shipping. This offer is for AWI manufactured systems, not by the previous manufacturer.

Further news, due to a few problems of system fit in the field with nose wheel RV's, AWI has suspended production for re-designing. Getting the system around the nose wheel assembly without interference and still maintaining the enhanced performance is the challenge. There are some very tight areas involved. More news as it develops.