How do you determine the size of your header?

[Tobi/DFL]

After reading the great thread about mouse motors I recognised that obviously some of the little beasts use pretty large headers for their engine size. Is there a formula similar to those formulas you can use when you want to find a starting point with your jets and venturis?

What header size would you recommend for the following engine:

2176cc (78.4x94mm), W 140, Bugpack ratio rockers (advertised as 1 : 1.25 but in fact 1 : 1.31), welded 040 heads with 44/37.5mm valves, oval ports, 11:1 CR (runs on 100 octane Shell V-power), 48 IDAs (42mm venturis, 180 main, 120 air, 60 idle, F11 emulsion tubes, third hole bored, enlarged float bowls. Jetted with the help of a LM1 wideband lambda meter) on short race Trim manifolds. The current header is a 1 5/8" bugpack which is shortened about 1" to use a large flange. The muffler ist a CB Performance merged dual quiet pack which is shortend as well (about 1.5") to get a large flange fitted. In that trim (but without the current jetting and ignition timing) the engine made 198.56 bhp at 6770rpm and 237.3 Nm of torque (don´t know how much that´s in ft.lbs.?) at 5130rpm.

I think that the mufflers are quite restrictive so I´m currently welding a custom dual quiet pack as I don´t like the look of today´s turbo mufflers. The tubing from the flange to and through the mufflers is 2 1/8" and after the mufflers its diameter is 2 1/4". The flange is 2.5" in diameter. Do you think that I could make a little more power in the higher rpms with this set-up or should I change to a 1 3/4" header or even bigger? Currently it seems like the engine is lacking a little bit of top end power.

Currently the engine sees limited street use but it must remain driveable so it mustn´t have no power until 4000rpm. Do you think that a 2" header would be way to big or would make the engine anything but fun to drive?

Your opinions please!
Bye,

Tobi

[richie]

1 3/4,            I think 2" would be way to big,

cheers richie,uk

[Tobi/DFL]

Thanks, Richie!

[Tom G.]

Hi my friend...

Did you use the mufflers, which i have given to you...? I think if you use them, it is a first step to get down in backpressure instead of your cool but restrictive dual quiets with such a too small diameter for your power range...But it is allways incredible to see that you have produce 196 ?HP...I know the engine and it is really impresive for 2,2l..So what can you expected if you have the bigger ones on it?:-))
If you also change the header to 1 3/4" it could cost you a little tourque in the lower RPM ranges...I would go for 2 steps..1 step the mufflers...if you notice a HP gain and it is enough...let it go...if it is not so much you can go to step 2 to change also the header to max. 1 3/4....



Good luck
Regards
Tom

[Tobi/DFL]

Hi Tom!

Yes, the mufflers I will use are the ones you sold me 2 years ago. The tubings however are not the ones you sold me as those were not of good quality (the bends were crap) so I´ve ordered them from Jegs. The greatest problem at the moment seems to be getting the stainless steel tailpipes flared like they are usually are on old dual quiet packs. I will have an attempt in the next days at a friend´s garage who has a 20 ton. press.

i guess I will in fact use the old 1 5/8" header at first to see if the engine has more top end power with the new mufflers.
Bye,

Tobi

[benssp]

What if, (in my case) i'm running a 1776 with an 1 3/4" header and am downsizing to an 1 5/8", would i have much of an issue in the step between the exhaust port and the header?

[richie]

What if, (in my case) i'm running a 1776 with an 1 3/4" header and am downsizing to an 1 5/8", would i have much of an issue in the step between the exhaust port and the header?

No,I would doubt you ex port is anywhere near 1 5/8 let alone 1 3/4 so should be nothing to worry about.

cheers richie,uk

[benssp]

cheers richie, it actually is opened up to 1 3/4" I got some 1 3/4" gaskets from bernie and they line up perfectly, I have no problems with the bigger header and like the sound it mjakes at 7.5K, just want to see if my times drop with an 1 5/8" header

[Peter Shattock]

Ben, that is one hell of an exhaust port on a 1776, I know you said you had Tony looking at the heads, it will be interesting to see how things work out. I'll try a 1"3/4 header at some point this year so I'll let you know how I get on but my exhaust port is way less than 1"5/8 currently but I do run a 1"5/8 header (small flange).

See you at the AGM no doubt

[benssp]

hi Pete, I could lend you mine if you like, there's a nice turbo muffler attached to it too, although i think it's too shiney for your liking!





Speak to you soon

[Peter Shattock]

I think your right I think I'll stick with my old GB dual QP's, they might not be the most efficient but you cant beat the look not to mention the thrashy sound! Thanks for the offer but I think Phil said I could have a blast with his old header when the time comes and his is also a small flange 1"3/4 which I'm keen to try first.   

Thanks for the offer though, I’ll keep you posted. Have you heard back from Bugpack yet about the valves?

[Fastbrit]

Hey Ben, do you want to sell me your muffler? You won't be needing it any time soon... 

[benssp]

Hey Ben, do you want to sell me your muffler? You won't be needing it any time soon... 

not a chance Sir

I had to beg they guy who had it to sell it to me, it cost me a pair of Flat4 Fuchs! it's a lovely handmade piece by a man you know, Uk Hot Rod Supremo Jon Golding

p.s PK tells me your gearing up for next year, can't wait to see the car run

pps. what are you doing with your lexan windows?

[Fastbrit]

Hey Ben, do you want to sell me your muffler? You won't be needing it any time soon... 

not a chance Sir

I had to beg they guy who had it to sell it to me, it cost me a pair of Flat4 Fuchs! it's a lovely handmade piece by a man you know, Uk Hot Rod Supremo Jon Golding

p.s PK tells me your gearing up for next year, can't wait to see the car run

pps. what are you doing with your lexan windows?

Oh, swapping them for your muffler, probably...

[benssp]

http://www.volkszone.com/VZi/showthread.php?p=4037643#post4037643   THIS ANY USE TO YOU KEITH?

[Fastbrit]

http://www.volkszone.com/VZi/showthread.php?p=4037643#post4037643   THIS ANY USE TO YOU KEITH?

Ta, but it's for a Bus. 

[JS]

How do you determine the size of your header really? I understand that you can try out different sizes, but is there a relatively simple formula to calculate the diameter of the tubing?