Hi all. I was on the net last night. And found an Aussie firm that makes extractors . They claim a horsepower increase of between 10 and 25 % depending on the motor. Could this right ? I'm about to put some "Genie" s on my Datto . I would be stoked if I could get that sort of power increase.
What do you think ?

they probably had a built motor with big cam, twin webers and a stock manifold, then put extractors on and measured power

Well if you build a madly wild V8, and then use a stock factory exhaust system (with lots of exhuasts and emmsion controls), then put some very open headers and exhaust im sure some of those figures are concivable. The Ls1 is good example of doing minimal internal work and lots of external changes (chips, exhaust, re-map etc) and making alot of big gains.

Opening up any motor and letting it breather alot more will always gain benefits (specailly worked motors).

The 25% increase from just changing to headers not going to happen, thats on the very extreme level. Thats why they say from 10-25% never give any specfic gains.

I understand that all extractors will give a slight (couple of %) increase in power, but also the type of extractors will alter where the engine makes it's peak torque in the rpm range.

So the further you move that torque range into the higher rpm bracket - technically the more "power" your engine will have.

As power = (roughly) torque x rpm.

I vaugely understand that the 4 into 1 type extractor make their best torque higher up the rpm range than 4 into 2 into 1 - so would be considered to have more power (even if the torque is the same)

--- If any of that makes any sense ---

Building upon what has already been said, it really depends upon what elase has been done to your engine. Real power gains are made by reducing the air flow restriction in and out of the engine. If you put beautiful extractors on an engien with the standard intake and carby, you will hardly get any gain, as it will still be restricted by the intake. But vice versa, if you have twin webbers and lots of headwork with restrictive extractors, you will also have small gains. For example I have heard of a power increase of around 30% after proper tuned length extractors were put on an otherwise worked engine.

cheers

Everyone I've talked to that knows about A series motors suggests extractors but says I'm better off sticking with the stock carbie.
Just what I've heard from a few different mechanics.

Theres no way youll never get 10 let alone 25% from putting them on a stock engine.The best youll be able to do there is maybe 3-4% little bit more on newer cars.

The only way you'll ever get 25% is if you have something like an F1 or pro stock engine with a ####ed 5mm exhaust on it.

I understand so far. But what does proper tuned length entail and who do I see to do that. I think that my muffler guy has done a great job on my car (from the fire wall back) but I don't know if he could determine a tuned length.Quote:

I have had a set of extractors added to my white 120y coupe with standard A12 motor.
It's definately a better performer now but I don't reckon it's gained a huge increase in power.

Quote:

Its done on math 24" should be good.

If your running an open exhaust then you really need to look harder at other stuff like collector tuning but not for a street car.