Custom Race Header Power Loss.

[CREngines]

something to try would be to take the old header and shorten it to the same length as the new one and run the new collector/pipe length and go back on the dyno. That should answer both questions. If it picks up more then the original setup then it is/was a diameter problem. If it is still down then the primary will not work at that length. (at least not without some other change)

[german4inline]

Just cut the bundle of your header after the bottom curve. Prepare 4 or 5 tube sections in order to make them stick onto the cut tubes to vary the lenght of the header. Run on the dyno and vary the lenghts until you´re happy. Don´t forget to match the sparking and fuel. With 20 hp difference it has to be considered.

In the 90ths, I had an Opel engine ( 6 cyl., 4 L displ.) on the dyno. Header was very nice,self made from the employee of an aftermarket exhaust company, it was Dia. 45 mm out. I adviced him to reduce it to 42 mm. We gained 27 bhp and 30 Nm of torque. Unfortunatly, I don´t know more the absolutly lenghts after almost 20 years passing by, but they were identical to each other. Anyway I believe your dia. is on the biggest acceptable range and you will gain more when decreasing the primaries and match the lengths as told above.

[jimmysxxl]

Thanks all for your valuable input. I'm gonna give the header one more shot and try Advancing the exhaust see if it improves drastically or not. or else i am planning on removing the collector and converting it to a 4-2-1.

[nitro2]

To work at the same rpm a big primary has to be longer than a small primary.

[lada ok]

All these calculations are for i/d or o/d ?

hi jimmy, if it's any use , my calc works out to 24.9 " from the EXHAUST VALVE
the I/D of the P / pipe is 42 mm
" " " " S / " " 60 mm length is .... 24.9 " or x 2, x 3 &c

these calcs are for a STRAIGHT pipe ! with all the bends, you may want to add 10 - 15 % more to pipe diam

[jimmysxxl]

The ID of the pipes re 45.3mm to be exact and the length from the face of the Head is 55cm so its Exactly as you propose. That's what makes it so weird,even if those calculations aren't optimal it shouldn't perform so poorly.

[Strange Magic]

The loss of power is simple. It's because it has a great loss of exhaust air speed which has a significant impact on your intake charge. Ones experience with an application could significantly vary from someone else's experience with a similar application, and that is simply due to valve timing events, assuming that your volumes on the intake side and engine displacement is very much of the same.

[John Wallace]

Can you post the engine specs?
(bore/stroke/valve sizes/cam specs, etc)

I don't have any figures for this engine but using a wikipedia stuff, I get that the collector is too small diameter, the primary length pipe is too long, and possibly the primary diameter is too large.

Pipe Max uses OD of pipe.
Is your specs ID or OD pipe?

[jimmysxxl]

Header Primaries is at 1.88inches OD collector chocke is 2.28 OD Tailpipe is 2.5inches OD. 0.06 pipe thickness
Engine specs are as follows
Bore: 3.18
Stroke: 3.42
Int Valves: 1.29 x2
Ex Valves: 1.1 x2
Static CR: 12.7
Cams : 305 Seat Timing, 265@1mm for both cams. 12mm Lift Intake - 11.5 Lift Exhaust with 0 Lash. Exh Open 55BBDC@1mm

[vwchuck]

Re-run with the correct AFR and you may be suprised. 9 to 1 to 12.5 to 1 AFR is a significant amount of power.

[jimmysxxl]

Usually is the other way around. Although i did re-tune and the power loss is evident.

[vwchuck]

Once you got the AFR back to where it was supposed to be how much power loss was there?

[jimmysxxl]

i Didnt even bother going to the dyno it was really dissapointing i dont like to estimate number but 20hp less from 5500-7500 and around 5-10 hp less from 7500-9100

[JoePorting]

Thanks all for your valuable input. I'm gonna give the header one more shot and try Advancing the exhaust see if it improves drastically or not. or else i am planning on removing the collector and converting it to a 4-2-1.

Wouldn't you want to retard the exhaust? Sounds to me like the exhaust valves are opening too early. The last 10% or so of the combustion process might be going out the tail pipes. I would shorten the exhaust duration overall.

[jimmysxxl]

Unfortunatly i can't retard the exhaust because V2V will be an issue. I was thinking of advancing in order to reduce overlap to improve midrange operation but it would be a lost cause anyway.