Extractors

[Jase]

Whats optimum header length for four into one extractors?

Just looking into how close i can get for my small amount of space

for the v8 in the gemi

[Guest vvega]

44" per primary

[BobbyBreeze]

I'm no expert, but i would think the optimum length completely depends on cam timing, port length/shapes, compression ratio etc.

i.e. its not as simple as saying 'what is the optimum length'

[Guest vvega]

its for a v8 so forget about tuned pulse scavanging beacause the paired cylanders are on different sides of the engine(unless you want pipes going over and under your engine)

exeptions been a flatplane crank .. v8

also you are right tuned pulse extractors work on lots of calculations .. and even then it will still take you 10-20 sets on the dyno to find the best curve for you application

hope that explains the 44" BTW 1 3/4" primarys please 2 1/2 " main pipe ... or no main pipe

[Testament]

the main factor is the rpm you want them tuned for - cam timing and pipe diameter have some effect but rpm is the key one. shorter pipes = higher rpm, longer pipes = lower rpm. 5000rpm is about 1m/40" in length. so as vvega says 44" is good for a pushrod v8 that isnt going to be pulling heaps of rpm.

This is just tuning for 1st or 2nd harmonic on an individual cylinder, not tuning for pressure waves from one cylinder to scavenge another cylinder.

also remember, tuning for max torque is the ideal. Yes you hardly ever see extractors of this length - its not because it doesnt work, its because its hard to fit them in, and the cars that it really matters for (race cars) are usually pulling high rpm so they have shorter pipes anyway.

[Guest vvega]

also bigger pipe = shorter pipes as well

a 2" primary is shorter that a 1 3/4 ... but the smaller will help v.e more

[BobbyBreeze]

Yeah, a mate was just using the Ricardo engine simulation software to try and improve on the exhaust system for Formula Fords. In the end the calculations ended up being close to pointless, and dyno time with different configurations were much more useful.

I know some factory v8 setups use an X pipe or Y pipe connecting each bank, would there be any point in doing that?

Also, Wayne, i assume the 44" would be too long for high revving 4 bangers etc?

[Guest vvega]

how high ?

a 2" 44" primary should see you to 10,000 on a 2 litre

16,500 will see you with a 23" 1.5 " primary on a 4 cyl 600cc ... (titainum honda works exhaust off a race bike) ... made 140 hp @ rear wheel

remember engines are just air pumps so a given cfm of though put regardless of engine config will still require similar fuel similar total intake length tuning and similar divided exhaust length tuning

prolly just confusing the issue really

its also funny you cant really go to long ..... but been to short will castrate you

the balance pipe is for sound mostly .. they sound bizare without it though it can lift midrange gogo if you do manage to fluke it

8 into 2 into one is one of the best sounding IMO shame my uz has such a shit exhaust system ...

[Testament]

2" primarys on a 2Litre 4cyl, too big. 1.5" should be plenty for all but the most extreme - better to be on the small side really.

[Guest vvega]

reving to 10k is getting fairly extreme

this combo was used on a cosworth makeing 300 hp so its a fair good bet

[Jase]

so these are pointless then other than looking tidy

[Unclejake]

^ Variable length primarys are not entirely without their advocates but the great majority of people that actually know what they are doing would vomit on those just for fun (despite how nicely built they look to be). Presumably the build requires the minumum space intrustion over performance (given that the exhaust also comes out the front )

They must have been done like that for a reason.

Is that a V8 or a V6? Hard to tell

[Guest vvega]

^ Variable length primarys are not entirely without their advocates but the great majority of people that actually know what they are doing would vomit on those just for fun (despite how nicely built they look to be). Presumably the build requires the minumum space intrustion over performance (given that the exhaust also comes out the front )

this man knows stuff and things

[Jase]

so to make sure your lengths are all equal do you fill them with water or something to make sure the volumes are all the same on the primaries

or just use a string of pingpong balls(or similar primary sized ball) mounted on two thick pieces of copper wire (twisted together) to form the shape needed to get to the collector at an equal length?

well thats how i would do it?

[Jase]

rover v8^ in mini

[Unclejake]

rover v8^ in mini

Two wrongs don't make a right

[UTERUS]

Flexible electrical conduit with some stiff wire inside to hold its shape would be the go for mocking up the headers.

[Jase]

haha the build work on it is impressive to say the least its on

http://www.retrorides.proboards86.com/i ... read=37234

check it out

so four strings of pingpong balls bent around like pipe cleaners to get the shape needed for each primary should work ok i think?

[Guest vvega]

how ever it works out is good

then you can just get a muffler man to bend the shape... or do it with mandrel bends

will still need some fine tuning .. but its the easiest way

[Jase]

thats sounds like a plan mandrels would be good

but a bit fiddley,

might get the first set bent but keep the forms from each set,

i'm going to have to run forward as well then loop back down the passengers side