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Madact · 11-23-2014, 05:33 PM

OK, got PipeMax... I've got to say, it's pretty impressive - enter stock valve specs, cam timings, volumetric efficiency etc., select "shorty header + muffler", and the predicted torque and HP values seem to hit the stock engine specs pretty darn close

which is good for confidence.

Anyhow, the length values seem to agree very much with previous calculations, using the tri-y street+muffler setting. Having done more calculations for a couple of different operating conditions though, I think the magic number may be 27" instead of 32".

Why is this? Well, the "standard" header formulae are based around the kind of exhaust gas temperatures you'd expect to see while racing, or near the end of a WOT dyno run (around 1485F, the default in PipeMax, gives numbers that agree with other formulae I've seen). Lower EGT brings the calculated lengths down, and 'cruising' EGT at part throttle & closed loop ECS control will a bit lower than 'race track'/dyno EGT... also, given the (future) head swap, other considerations are that exhaust gas recirculation also brings down EGT, while lean combustion raises it - not sure which will be dominant. If anyone a civic HX with an installed EGT sensor is reading this, some input would be great

So, picking some numbers out of the air (and this thread what are typical gasoline exhaust temperatures? - Diesel Forum - TheDieselStop.com), I've also run calculations for EGT=1000F at low RPMs and EGT=1200F in the mid range.

The really, really cool thing here is that it seems that Physics has thrown us a bone here, and the exhaust system will 'tune itself' to higher RPMs if you're stomping the accelarator for extended periods. Meaning when it's tuned for cruising at low RPM, it's also, by lucky coincidence, not too far out for being thrashed around at WOT in the high RPMs...

The other interesting thing here, is that the recommended primary diameters are a bit smaller than I was previously thinking from other formulae... based on this, it looks like a 1.25" OD primary may be a better choice than the 1.5" (all diameters below are O.D., by the way)

----------
Many numbers follow
----------

"Low range" calculations:

Vtec-e "low cam":
Setting "3100rpm" max HP at 90% VE, at 1:9.7 compression:
59.4 to 62.7", "operating range" 1000-3500 rpm
* 3100rpm is guess for the max HP RPM, based on promotional material, theoretical/illustrative graphs for the D15Z7, and staring at the bumps on a bunch of D16Y5 dyno graphs from the internet.

Same RPMs for non-VTEC:
Setting "3100rpm" max HP at 85% VE, 1:9.4 compression:
61.9 to 65.2", "operating range" 1100-3600 rpm
* Cam specs appear to change only the pipe diameters & predicted performance here, not the pipe design, but as I understand it, non-VTEC has lower volumetric efficiency as the cams can't be so well optimised.
*** And with EGT set to 1000F:
53.2 to 56.5

"Mid range" calculations, based on peak HP at 6400 (design spec - D16Y8 quotes 6800rpm max HP, but that's past the VTEC switchover):

Standard cam, using D16Y8 specs:
Setting "6400rpm" max HP at 98% VE, 1:9.7 compression:
25.6 to 28.8", "operating range" 4400-6900 rpm, 1st segment diameter 1.212 (or 1.412 for "higher RPM power, possible TQ loss")

D16Y4 guess, using D16Y8 standard cam specs because I couldn't find anything for the Y4:
Setting "6400rpm" max HP at 95% VE, 1:9.4 compression:
26.2 to 29.5", "operating range" 4400-6900 rpm, 1st segment diameter 1.2 (or 1.4 for "higher RPM power, possible TQ loss")
*** And with EGT set to 1200F:
24.4 to 27.6"

"Mid range" calculations, based on peak HP at 5800 (de-tuning peak power for wider torque):

Standard cam, using D16Y8 specs:
Setting "5800rpm" max HP at 98% VE, 1:9.7 compression:
28.5 to 31.8", "operating range" 3800-6300 rpm, 1st segment diameter 1.157 (or 1.357 for "higher RPM power, possible TQ loss")

D16Y4 guess, using D16Y8 standard cam specs because I couldn't find anything for the Y4:
Setting "5800rpm" max HP at 95% VE, 1:9.4 compression:
29.3 to 32.6", "operating range" 3800-6300 rpm, 1st segment diameter 1.145 (or 1.354 for "higher RPM power, possible TQ loss")
*** And with EGT set to 1200F:
27.2 to 30.5"

"High range" calculations:

Standard cam, using D16Y8 specs:
Setting "6800rpm" max HP at 102% VE, 1:9.7 compression:
23.2 to 26.5", "operating range" 4400-6900 rpm, 1st segment diameter 1.404 (or 1.604 for "higher RPM power, possible TQ loss")
At "7000rpm" max HP, same settings - as I have no data for the D15Z7 high cam:
22.5 to 25.7" 1st segment diameter 1.423 (or 1.623 for "higher RPM power, possible TQ loss")

11-23-2014, 05:33 PM	#54 (permalink)
Madact EcoModding Apprentice Join Date: Aug 2014 Location: Adelaide, Australia Posts: 120 Emerald - '97 Honda Civic CXi 90 day: 40.13 mpg (US) Thanks: 53 Thanked 53 Times in 32 Posts	OK, got PipeMax... I've got to say, it's pretty impressive - enter stock valve specs, cam timings, volumetric efficiency etc., select "shorty header + muffler", and the predicted torque and HP values seem to hit the stock engine specs pretty darn close which is good for confidence. Anyhow, the length values seem to agree very much with previous calculations, using the tri-y street+muffler setting. Having done more calculations for a couple of different operating conditions though, I think the magic number may be 27" instead of 32". Why is this? Well, the "standard" header formulae are based around the kind of exhaust gas temperatures you'd expect to see while racing, or near the end of a WOT dyno run (around 1485F, the default in PipeMax, gives numbers that agree with other formulae I've seen). Lower EGT brings the calculated lengths down, and 'cruising' EGT at part throttle & closed loop ECS control will a bit lower than 'race track'/dyno EGT... also, given the (future) head swap, other considerations are that exhaust gas recirculation also brings down EGT, while lean combustion raises it - not sure which will be dominant. If anyone a civic HX with an installed EGT sensor is reading this, some input would be great So, picking some numbers out of the air (and this thread what are typical gasoline exhaust temperatures? - Diesel Forum - TheDieselStop.com), I've also run calculations for EGT=1000F at low RPMs and EGT=1200F in the mid range. The really, really cool thing here is that it seems that Physics has thrown us a bone here, and the exhaust system will 'tune itself' to higher RPMs if you're stomping the accelarator for extended periods. Meaning when it's tuned for cruising at low RPM, it's also, by lucky coincidence, not too far out for being thrashed around at WOT in the high RPMs... The other interesting thing here, is that the recommended primary diameters are a bit smaller than I was previously thinking from other formulae... based on this, it looks like a 1.25" OD primary may be a better choice than the 1.5" (all diameters below are O.D., by the way) ---------- Many numbers follow ---------- "Low range" calculations: Vtec-e "low cam": Setting "3100rpm" max HP at 90% VE, at 1:9.7 compression: 59.4 to 62.7", "operating range" 1000-3500 rpm * 3100rpm is guess for the max HP RPM, based on promotional material, theoretical/illustrative graphs for the D15Z7, and staring at the bumps on a bunch of D16Y5 dyno graphs from the internet. Same RPMs for non-VTEC: Setting "3100rpm" max HP at 85% VE, 1:9.4 compression: 61.9 to 65.2", "operating range" 1100-3600 rpm * Cam specs appear to change only the pipe diameters & predicted performance here, not the pipe design, but as I understand it, non-VTEC has lower volumetric efficiency as the cams can't be so well optimised. * And with EGT set to 1000F: 53.2 to 56.5 "Mid range" calculations, based on peak HP at 6400 (design spec - D16Y8 quotes 6800rpm max HP, but that's past the VTEC switchover): Standard cam, using D16Y8 specs: Setting "6400rpm" max HP at 98% VE, 1:9.7 compression: 25.6 to 28.8", "operating range" 4400-6900 rpm, 1st segment diameter 1.212 (or 1.412 for "higher RPM power, possible TQ loss") D16Y4 guess, using D16Y8 standard cam specs because I couldn't find anything for the Y4: Setting "6400rpm" max HP at 95% VE, 1:9.4 compression: 26.2 to 29.5", "operating range" 4400-6900 rpm, 1st segment diameter 1.2 (or 1.4 for "higher RPM power, possible TQ loss") * And with EGT set to 1200F: 24.4 to 27.6" "Mid range" calculations, based on peak HP at 5800 (de-tuning peak power for wider torque): Standard cam, using D16Y8 specs: Setting "5800rpm" max HP at 98% VE, 1:9.7 compression: 28.5 to 31.8", "operating range" 3800-6300 rpm, 1st segment diameter 1.157 (or 1.357 for "higher RPM power, possible TQ loss") D16Y4 guess, using D16Y8 standard cam specs because I couldn't find anything for the Y4: Setting "5800rpm" max HP at 95% VE, 1:9.4 compression: 29.3 to 32.6", "operating range" 3800-6300 rpm, 1st segment diameter 1.145 (or 1.354 for "higher RPM power, possible TQ loss") *** And with EGT set to 1200F: 27.2 to 30.5" "High range" calculations: Standard cam, using D16Y8 specs: Setting "6800rpm" max HP at 102% VE, 1:9.7 compression: 23.2 to 26.5", "operating range" 4400-6900 rpm, 1st segment diameter 1.404 (or 1.604 for "higher RPM power, possible TQ loss") At "7000rpm" max HP, same settings - as I have no data for the D15Z7 high cam: 22.5 to 25.7" 1st segment diameter 1.423 (or 1.623 for "higher RPM power, possible TQ loss")