3.6 race headers
05-07-2003, 10:29 PM
#1
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3.6 race headers
Can anyone recommend the proper size headers for a race only 3.6 ? It seems the largest diameter I can find is 1 3/4 " Would 1 7/8 " dia. be the
ideal size ? Is bigger better? Thanks for the input ! BTW- I run open exhaust, with megaphones.
ideal size ? Is bigger better? Thanks for the input ! BTW- I run open exhaust, with megaphones.
05-07-2003, 11:00 PM
#2
Race Car
It depends on the mods you've made to the 3.6. Stock motors don't benefit a whole lot from tuned pipes. Your motor sounds like it would, but it's not a simple project.
05-07-2003, 11:35 PM
#3
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Jack,
J&E 12.5:1 CR pistons, GE 100 cams, case vented, crank knife edged, RSR fly wheel,slide valves, RS valves,Varioram heads, ported to 43.5 mm intake, race valve springs, solid rockers, basic mods.
Thanks!
J&E 12.5:1 CR pistons, GE 100 cams, case vented, crank knife edged, RSR fly wheel,slide valves, RS valves,Varioram heads, ported to 43.5 mm intake, race valve springs, solid rockers, basic mods.
Thanks!
05-08-2003, 11:08 AM
#5
Howard:
I would guess that 1 5/8-in. headers would be good for you. Some people like 1.75 for all-out 3.8 race motors--it's a matter of personal choice.
Ideally, you would have to go to the dyno with the pipes and play around with lengths to get the best tune. Off-the-shelf headers would only get you so far.
Your basic design options are:
1) RSR knockoffs, which are short-tune pipes that shoot straight out the back and, thus, are hard to hang mufflers on. Factory design is very good, tho.
2) Long-tube headers such as Cargraphic or S-CAR-GO, which are *supposed* to make some torque because the pipes are equal-length or close to it.
3) Some custom variation on the above.
Your Varioram is kinda restrictive--think about putting single throttles on or an RSR tuned-resonance induction. Gotta flow more air...
I would guess that 1 5/8-in. headers would be good for you. Some people like 1.75 for all-out 3.8 race motors--it's a matter of personal choice.
Ideally, you would have to go to the dyno with the pipes and play around with lengths to get the best tune. Off-the-shelf headers would only get you so far.
Your basic design options are:
1) RSR knockoffs, which are short-tune pipes that shoot straight out the back and, thus, are hard to hang mufflers on. Factory design is very good, tho.
2) Long-tube headers such as Cargraphic or S-CAR-GO, which are *supposed* to make some torque because the pipes are equal-length or close to it.
3) Some custom variation on the above.
Your Varioram is kinda restrictive--think about putting single throttles on or an RSR tuned-resonance induction. Gotta flow more air...
05-08-2003, 11:11 AM
#6
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by DCLee:
<strong>Howard:
I would guess that 1 5/8-in. headers would be good for you. Some people like 1.75 for all-out 3.8 race motors--it's a matter of personal choice.
Ideally, you would have to go to the dyno with the pipes and play around with lengths to get the best tune. Off-the-shelf headers would only get you so far.
Your basic design options are:
1) RSR knockoffs, which are short-tube pipes that shoot straight out the back and, thus, are hard to hang mufflers on. Factory design is very good, tho.
2) Long-tube headers such as Cargraphic or S-CAR-GO, which are *supposed* to make some torque because the pipes are equal-length or close to it.
3) Some custom variation on the above.
Your Varioram is kinda restrictive--think about putting single throttles on or an RSR tuned-resonance induction. Gotta flow more air...</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">
<strong>Howard:
I would guess that 1 5/8-in. headers would be good for you. Some people like 1.75 for all-out 3.8 race motors--it's a matter of personal choice.
Ideally, you would have to go to the dyno with the pipes and play around with lengths to get the best tune. Off-the-shelf headers would only get you so far.
Your basic design options are:
1) RSR knockoffs, which are short-tube pipes that shoot straight out the back and, thus, are hard to hang mufflers on. Factory design is very good, tho.
2) Long-tube headers such as Cargraphic or S-CAR-GO, which are *supposed* to make some torque because the pipes are equal-length or close to it.
3) Some custom variation on the above.
Your Varioram is kinda restrictive--think about putting single throttles on or an RSR tuned-resonance induction. Gotta flow more air...</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">
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05-08-2003, 12:11 PM
#8
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DJF1,
I did the work myself, except the crank mod. It's difficult to say how much I've spent for the engine but parts alone were in the $11k range. I built the engine from a case I bought on Ebay, P and C's from Ebay as well. I made the billet throttle bodies and slide valves. The other parts are from various suppliers. I would guess if a race shop built this motor it would be well over $20k .
I did the work myself, except the crank mod. It's difficult to say how much I've spent for the engine but parts alone were in the $11k range. I built the engine from a case I bought on Ebay, P and C's from Ebay as well. I made the billet throttle bodies and slide valves. The other parts are from various suppliers. I would guess if a race shop built this motor it would be well over $20k .
05-08-2003, 09:49 PM
#9
You want the smallest pipe that will handle the full flow at max rpm. 1 5/8" thru 1 7/8" will all work ok but give slightly different torque characteristics. The factory used 42mm up thru 3.6 race motors so thats a guide. The most common size over here seems to be 1 3/4"
Another issue is length, longer moves torque down the rev range and smears it out a bit, shorter will give a narrower power band up high. So the type of track you drive most will point you in a direction.
lengths seem to run from ~17" up to ~31"
Another issue will be the collector and transitions, there are lots of theories here This seems to be an important area w/ closely held knowledge. The length, taper and reverse cones(if any) of your megaphones further complicates things.
If $ is not an object S-Car-Go seems to have headers that are well thought of.
Your cams have lots of overlap so a pure guess would be 1 3/4" header ~31" long, stepped collector and A/R rings. Hopefuly w/ reverse cones on the megaphones. This will enhance torque and broaden the power band a bit.
Further tuning can be done by shortening or lengthening the megaphones. If they operate at the same frequency as the headers power band will be narrower, if you can get them to work out of phase w/ the headers powerband will be widened.
Another issue is length, longer moves torque down the rev range and smears it out a bit, shorter will give a narrower power band up high. So the type of track you drive most will point you in a direction.
lengths seem to run from ~17" up to ~31"
Another issue will be the collector and transitions, there are lots of theories here This seems to be an important area w/ closely held knowledge. The length, taper and reverse cones(if any) of your megaphones further complicates things.
If $ is not an object S-Car-Go seems to have headers that are well thought of.
Your cams have lots of overlap so a pure guess would be 1 3/4" header ~31" long, stepped collector and A/R rings. Hopefuly w/ reverse cones on the megaphones. This will enhance torque and broaden the power band a bit.
Further tuning can be done by shortening or lengthening the megaphones. If they operate at the same frequency as the headers power band will be narrower, if you can get them to work out of phase w/ the headers powerband will be widened.
05-08-2003, 11:15 PM
#10
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Thanks Bill,
I checked the S-Car-Go setup, and it IS a little pricey...$3500 . MSDS has headers for $549, Smart Racing about the same, it's confusing.
About this "reverse cone" and A/R rings? I would imagine the reverse cone is similar to an expansion chamber? I have not seen that at the track yet. The 996 Cup cars seem to run a longer tube with short megaphones, and they are loud!
My home track is WSIR, which is a high RPM, high speed track, mostly top gear in the 6500-7000 RPM range. So it seems a higher torque open exhaust would be in order for me. I was kicking around the idea of going with MSDS, cutting the tubes just before the collector, extending the collector out 12" and running a 12" megaphone. I just don't have any data on tube diameter and length and how it affects HP/torque.......more research. Thanks for your help, and the valuable information !
I checked the S-Car-Go setup, and it IS a little pricey...$3500 . MSDS has headers for $549, Smart Racing about the same, it's confusing.
About this "reverse cone" and A/R rings? I would imagine the reverse cone is similar to an expansion chamber? I have not seen that at the track yet. The 996 Cup cars seem to run a longer tube with short megaphones, and they are loud!
My home track is WSIR, which is a high RPM, high speed track, mostly top gear in the 6500-7000 RPM range. So it seems a higher torque open exhaust would be in order for me. I was kicking around the idea of going with MSDS, cutting the tubes just before the collector, extending the collector out 12" and running a 12" megaphone. I just don't have any data on tube diameter and length and how it affects HP/torque.......more research. Thanks for your help, and the valuable information !
05-08-2003, 11:42 PM
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Our 3.6ltr Boxster Racer runs a Huntley Racing EFI system with TWM throttle bodies, 12.8:1 comp JE Pistons, CMW heads, Custom Huntley Racing Cams, Pauter rods, Knife edged/lightened/perp drilled crank, etc.... We made a S/S 1 7/8" header with true merge collector into S/S reverse cone megaphones and found that to be the best for our application (we tried 1 5/8" and 1 3/4" on our dyno). I would go no smaller than 1 3/4" and likely the 1 7/8" like we run. We made 355 HP at the wheels.
05-08-2003, 11:45 PM
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P.S. We will build more of these if there is a demand. Mid engine ONLY at this time. Heck we might make a 911 set if there is enough demand. The headers would be $1700 and the merge collectors with tips another $1000.
05-09-2003, 02:07 AM
#13
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In the open wheel race car arena, stepped headers are a current trend. Basically the primary tubes are stepped up about 1/8"ID halfway through the primary tubes. Of course this is for a 2.65L V-8.
