I posted earlier but can't add or change anything.
Anybody with musical knowledge that can advise me how long and how large to make the size of the megaphones?
I posted earlier but can't add or change anything.
Anybody with musical knowledge that can advise me how long and how large to make the size of the megaphones?
The magic formula is don't ;)
I know software like dynomation will spit out numbers for you but that assumes the megaphone is right off the collector, I don't think it has any tuning value at the end of a tail pipe will should help make it louder I guess.
In reply to mke :
The goal in part is to add volume to the exhaust note. It's also to change the tone. More Clarinet than Tuba.
Enzo Ferrari traded torque for tone in his cars. He was able to do that because those 3.0 liter engines revved so willingly to high rpm.
I noticed that as his engines got larger he lost that tone. So there is no way I can get my 5.3 liter engine singing like his 3.0 liters but I'd like to approach it. Yes I too will trade power for sound. Racing after all is about fun.
The bigger the pipes the deeper the tone. If you're goal is to get the highest tone possible maybe consider running 4 small pipes back below is a ferrari 275 exhaust...its 4 pipes. This is how they did it 250-412. The engine headers are 3-1, but you see the 1st pipe is a 2-1 collector as there is hp gain with a 6-3-1 setup, but then they split it to run it out...and that is probably the sound you are looking for. The muffler size shape/design matters quite a bit too.
After that it was dual exhaust which is lighter and flows better,but will have a much deeper tone and it what you seem to want to avoid.
A megaphone on the end...that will make it louder, there is a reason megaphones are shaped like that after all, but it will also deepen the tone which I think is the opposite of what you probably want.
In reply to mke :
No mufflers on a race car. But headers really don't gain too much because of the even (60 degrees ) firing order ( unlike a V8 where adjacent cylinders may be anywhere from 90 degrees to 270 degrees apart)
Robert Knodt did a before and after dyno test on his racing XJS V12 using carefully measure pipe lengths for his headers. There was only 20 horsepower difference. To get that 20 horsepower basically he had to block off any airflow in the engine compartment. There couldn't have been any weight difference to fit all that tube in the engine compartment. The stock cast Iron manifolds (4 of them ) weighed a little over 3 pounds each.
AJ6 engineering (on stock street cars) found 30 horsepower gain using 2&1/2" pipes off the iron manifolds for 48 ". Then collected both pipes per side out under the IRS and to the resonator.
I'll trade some power and use smaller pipes, but what sort of taper in the megaphones will yield the highest note? I've got around 36 inches to work with
All engines love tuned exhaust...I have have no comment on any testing other than a V12 likes 6-2-1 then an X pipe where possible (aka all modern ferrari 12s, I couldn't fit one) because a 6-1 collector just doesn't work very well. Log type manifold are better than no manifolds and since you have them and its a challenge build they win :)
The length coming off the cast manifold will act like the collector, 48" is long but for a below 6k engine might be good....it would be like the 1st reflection I think? For peak hp most header collectors are tuned usually tuned to the 5th or 6th reflection but any tuned length is better than an untuned length. The collector helps most for pulling up the midrange.
Back to megaphones. You are building them because you want them so I'd say just build what looks the way you want it to look. A megaphone at the end of the pipe will amplify whatever is in the pipe so I'm pretty sure using the pipes to damp the low freq stuff is the most important and the megaphone is a decoration. As a general rule flow like the expansion angle to be about 6 degrees to no more then 12 so maybe use that as a guide so the megaphone at least isn't costing hp.
That's great advice. Yes 48" is set for the stock camshafts which flattens. out at 5500 rpm.. so I can crunch numbers and calculate what the ISKY XM3 cams will provide.
The trouble is the Isky XM 3 only gives a little over .400 lift and 210 duration. ( peak right about 6750 rpm) I'm not sure the XM 4 or 5 can be achieved on the stock camshafts. Nobody has any billets around anymore. ( and on my budget I couldn't afford them if there were)
I'd prefer those if possible. I don't need anything under 3500 rpm on the race track.
210@0.050" lift"? that pretty mild...well...very mild in a 2V engine. Webcamshafts can weld up your cams and grind whatever you please but I think its about $100/lobe.
In reply to mke :
stock is .375 lift and 256 duration XM3 is .404 lift and 310 duration
My bad.
That sounds like advertised duration which is honestly a meaningless number, what is the 0.050" or similar? Advertised includes accel/decel ramps so they can literally make it anything they want without actually changing anything because the valve aren't actually open. The standards for comparing cam durations are 1mm or 0.050"...so you know its open. performance wise the standard is .006" of actual valve lift, which means lash+.006" because that is about where meaningful flow starts and ends.
In reply to mke :
I'm pretty sure Isky measures things @.050
The stock numbers date from about 1955 they've used the same camshaft since then. Both on the V12 with 2.76 stroke and their old WW2 based iron Six with a 4.17 stroke
frenchyd said:In reply to mke :
I'm pretty sure Isky measures things @.050
The stock numbers date from about 1955 they've used the same camshaft since then. Both on the V12 with 2.76 stroke and their old WW2 based iron Six with a 4.17 stroke
No, those are ridiculous duration numbers. I had a buddy running a 290@0.050" cam in his H-D drag bike, it needed 15:1 compression and a 5 jet carb to make it work. I ran a 270 in my H-D roadrace bike ...for pump gas is needed 11:1, I ran 12.25 100 octane, shifting at 9k rpm. The numbers you're kicking around are unworkable if they are 0.050", so no doubt those are advertise duration numbers.
A quick search turned up one of your old threads and these were the specs
"I think your stock cam is .375"L and (from memory) 211" duration at .050"?. The XM3 is (I think) .424"L 242 at .050"?."
These look right and were given to you by a cam grinder, I'd say use them as real. Its easy enough to check with a degree wheel and dial indicator so you are certain.
242@0.050 at the valve is what I have in the frankenferrai, its 246 at the cam with .452 lift (iirc). The 0.050" durartion numbers on the cam card are always 0 lash, so the most it could ever be at the valve. With the flow and valve sizes I have this will make peak hp at 9000-10500 depending in headers mostly and then installed lobe centers and and intake runner length also matter, or so says dynomation6 software.
Moderate flowing 2V heads I'd guess the same numbers would peak around 7k and that is almost exactly what ferrari used as their street grind on everything up through 1977. The race only P6 cams were I think 265@0.050 and and peaked aroun 8000-8500 but basically didn't run below 3500...guys tried but the webers just hated all the reversion, I did an EFI conversion for a guy with those cams and was able to get it idling at 1000 and diving decent, he was thrilled with the change.
From what I remember, if they're not right off the collector - not worth fooling with.
I downloaded the isky catalog, here are the correct numbers. The advertised duration number looks like its probably a 0.006" lift which is the standard for measuring seat to seat duration. Also note the numbers are at 0 lash, so lift at the valve is reduced by the lash numbers and duration also reduced about 5 degrees
Paul_VR6 (Forum Supporter) said:From what I remember, if they're not right off the collector - not worth fooling with.
Three reasons to use megaphones.
First the sound volume.
Second the tone
Third the shiny brass. Band instrument look.
In reply to mke :
I'll see what Crower can do. Bruce Crower developed the Group 44 heads and cams. I know that the British have developed V12 regrinds to a fine art but Kent cams wind up costing 3 times what American regrinds do plus air freight and import duty.
I don't know anything about megaphones or headers or cams, but I think you should run triple quad (quad triple?) exhaust just for the sound. 3 into 1 x 4 and aim the megaphones up so we can hear them. 
In reply to frenchyd :
Sorry, I thought you said you had the xm-3 cams. The specs look right for a 7k rpm engine which begs the question what is it you are trying to do with the cam and where are you getting your numbers?
Just putting in a cam with more duration or lift is unhelpful if it doesn't match everything else. You have stock cast log type manifolds and also stock heads and intakes? It sure sounds like its a 5500rpm 300hp engine just like the factory says it is. More duration will probably bump the hp/rpm a lift but the general rule is "I don't care is you're Jesus Christ himself, without air you can't make hp" ...and I'm not seeing/hearing about more air flow so generally in this situation all a bigger cam does is harm the low end while delivering nothing significant on top. All the parts need to match.
In reply to mke :
Oh. Air? Did I mention my pair of turbo's?
But those log manifold only cost 20 horsepower over a beautiful set of equal length Headers designed for the V12. Go to Camp Chaos on U Tube. Done by Robert Knodt
When TWR ( Jaguar V12) raced BMW in Group A (European touring car) they were required to use stock cast Iron manifolds and stock EFI system. They still made over 500 hp.
Ok, so why are you screwing around with cams that don't match the rest of the setup?
Megaphones at the end of tail pipes are decorations so decorate as you please, but all the talk about exhaust sound is moot with a turbo stuffed in there....it will sound like a turbo, just sayin
In reply to mke :
I do have a set of XM3 cams for a 6 cylinder. Not for the V12. Same specs. Jaguar has been using the same .375 lift 17 BTDC 59 ABDC 59 BBDC 17 ATDC since about 1955. On all their production engines.
I bought mine from Summit. They have a good choice of multiple lengths and diameters.
I always believe in go big or go home. YMMV
If it ain't broke.....
I'm sure it will be great, good luck!
In reply to mke :
That's part of the reason ( only a tiny part ) for the megaphones.
The only place to fit Turbo's is out of the engine bay under the fenders where they won't be seen. Since I'll be using E85 I'm hoping not to need intercoolers thus maybe fool some people. Distract them with megaphones. Then further confuse them with Castor bean oil dripped into the exhaust pipe.
Are you old enough to have smelled Castor Oil? In the early 1950's and post war in England they used castor bean oil as a lubricant because it was a better lubricant than mineral oil at the time. Very distinctive smell.
I'm not going to "win" the challenge but I do hope the guys leave an impression.
Racing has to be about fun. Or why do it?
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