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16 Apr 2002, 10:00 (Ref:261873)
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#1 | ||
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Racer
Join Date: Dec 1999
Posts: 330
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Exhaust Lengths
I have recently had a flowed manifold (header) and system built for my GP1 Dolomite, primarily to gain greater torque mid-range, something the Dolomite has previosly lacked. I have read several of CCC Mags Dave Walker's Techie articles regarding the subject, but wondered whether any of you had your own theories or maths regarding lengths of Primary and Secondary pipes?
Dolomite is 4Cyl 16V GP1Cam MaxRpm 8250 Regards Chris |
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16 Apr 2002, 11:13 (Ref:261934)
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#2 | ||
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Veteran
Join Date: Oct 2001
Posts: 544
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Have a look at Four-stroke performance tuning by A. Graham Bell (£18). He has formulas and ideas for exhausts and the full engine. His book can be got from the Haynes books web site as well as other places.
The formula he used to work the full length of the exhaust out is 850*ED all divided by the rpm you want the engine tuned for, and that value -3. These are in inches btw, but of course can be converted to SI units. Where ED is 180 + the number of degrees the exhaust valve opens before BDC. so 850 * (180+90) = 229500. So then 229500/ 5000 rpm = 45.9. and then 45.9 -3 = 42.9 inches, (1089.66mm) which is the full length of the exhaust, including all manifold primary and secondary pipes. Maths lesson over  There are also forumla for Internal diameter's. I know there are lots of other ideas out there but I hope that has been some help. Last edited by Tony_Simpson; 16 Apr 2002 at 11:15. |
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17 Apr 2002, 09:13 (Ref:262801)
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#3 | ||
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Racer
Join Date: Dec 1999
Posts: 330
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Thanks for the info Tony. I'll have to check out the book!
However varying the lengths of the primaries (and possibly secondaries) does have dramatic effects on torque and power results. Any info on this specifically? Chris |
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17 Apr 2002, 10:22 (Ref:262858)
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#4 | ||
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Veteran
Join Date: Oct 2001
Posts: 544
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Yes this book has some info on changing the lengths of the primaries. It all comes down to where you want the engines power/torque band to start. With the headers you could make them smaller by 1/8" and shift the power band down by 500/600 rpm, or make them bigger by 1/8" and shift the range up by about the same amount. It says that some engines work with having the exhaust (total) lengths changed will have a similar effect.
Do you have unequal length primaries at all? If so from the formula, it would say give a correct value of 30" then change the lengths of the four to 28", 30", 32", 34". This has the effect of widening the torque curve, thus giving a more drivable engine. Also it has info of stepped headers, going from 1 7/8" to 2", then up to 2 1/8". Again widening the torque area. It is all trial and error really. Hope that it is a bit more help. |
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22 Apr 2002, 09:19 (Ref:267087)
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#5 | ||
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Racer
Join Date: Dec 1999
Posts: 330
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Tony...take a look at the following...Thought this might be of interest to you...
Spin-Tech Mufflers and Dr Gas Chris |
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5 Sep 2002, 13:37 (Ref:373768)
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#6 | ||
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Racer
Join Date: Dec 1999
Posts: 330
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and here's the other AV8rirl
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