lose torque on a 4-2-1

23rd August 2010, 19:12

is it ture you loose torque with a full decat system ? ive been told this and im just wondering cus i just purchased a manifold ...

23rd August 2010, 19:18

I've heard of shit but this is off the scale.

23rd August 2010, 19:18

Infact you've broken the bullshit scale you need to purchase a new one from :

www.whataretard.com

23rd August 2010, 19:20

There is such thing as "pulse" tuning yes. Sometimes a middle box/cat can act as a expansion box to help scavenge the next cycle of gases out of the cylinder head. Like a 2 Stroke. But thats high end tuning for race cars.

23rd August 2010, 19:22

High end tuning which doesnt fall into the same category as westcoast 1.4's i'd imagine, pack the brancher on and pack her off the limiter outside primary schools.

23rd August 2010, 19:24

True tbh Krys! lol.

23rd August 2010, 19:26

Sorry for the spam lol, in that kind of mood unfortunately for you.

23rd August 2010, 19:36

On a serious note, I spent a lot of time on Ricardo Wave when I was modelling an engine, and there was nothing to suggest a 4-1 was good for top end power and 4-2-1 were shite at top end.

Fucking about with 4-2-1 designs came up with some great figures with not much less top end than 4-1.

23rd August 2010, 19:40

So whats the blast with, more pressure with the 4 pipes directly to one? Does it really make any difference in comparison to the 4-2-1? or not worth bothering, anything over a cast iron mani? ^^

23rd August 2010, 19:53

Its all dependent on the rest of the engine like distance to valve head, cam profile, all that sort of shit, no one is better than the other per se; its just people have misconceptions about 4-1s being better for top end power.

I couldnt run tests for a VTS engine, ran it on a Zetec fiesta engine which is fairly similar. Woulda been nice to run comparisons of a standard vts mani and a supersprint.

The main thing with any mani is a balancing act between maintaining gas velocity and choking the engine, plus factoring in pulse tuning. The easy way to understand it is this: imagine your lungs are the engines cylinder. Open your mouth wide and suck in. Gas is going into the engine, but sound/pressure wave is coming out- this is the equivalent of the intake stroke. similar happens on the exhaust stroke, when you blow out. In each case, the sound/pressure wave can help to force gas in, or out, of the cylinder.

The more you change the shape of your mouth though, the harder it is to intake or expel air. Its the same principle really - theres an optimum size for your mouth (the manifold pipe) to be to get the gas in and out as fast as possible.

Theres slightly more to it, but thats about the basics of it, and an easy analogy that people can get their heads round.

23rd August 2010, 21:05

Quote:

Originally Posted by Colin

There is such thing as "pulse" tuning yes. Sometimes a middle box/cat can act as a expansion box to help scavenge the next cycle of gases out of the cylinder head. Like a 2 Stroke. But thats high end tuning for race cars.

Theres no benefit to an expansion box. The gases will slow as they enter, then speed up as they enter the exhaust pipe again, basically making no real difference.

Quote:

Originally Posted by Gabbastard

On a serious note, I spent a lot of time on Ricardo Wave when I was modelling an engine, and there was nothing to suggest a 4-1 was good for top end power and 4-2-1 were shite at top end.

Fucking about with 4-2-1 designs came up with some great figures with not much less top end than 4-1.

Theres no reason why a 4-2-1 cannot produce as much power. The only difference being a 4-2-1 can be optimised better for two points in the rev range rather than one.

Quote:

Originally Posted by Gabbastard

lots...

Good analogy

Virtually all the pulse tuning is done in the manifold so this is usually where the power can be made. The exhaust really is there to get the gases out as quickly as possible and to allow the use of silencers to quieten the sound. For example our new VW Lupo exhaust manifold gained 9bhp with a sports cat, but we were only able to gain a couple of bhp on the exhaust, which performed well as standard.

23rd August 2010, 21:34

Really good advice, never thought about that before with the two points in the rev range and one with the 4-1, very good input i'm sure it will be helpful to alot of people, thanks.

23rd August 2010, 22:09

I have just put a stainless 4-2-1 manifold on a VTR.

Everyone shouldn't ever bothered trying to squeeze an extra BHP or 2 from such small and crappy 8v engines like these.

I have noticed an increase in mid range torque but to be honest it's only on because the crap that was on before had rusted away and would fail an MOT.

If you are going to buy performance parts you should have / should buy a performance engine in the first place to notice any difference.

23rd August 2010, 22:34

Quote:

Originally Posted by outrage_uk

I have just put a stainless 4-2-1 manifold on a VTR.

Everyone shouldn't ever bothered trying to squeeze an extra BHP or 2 from such small and crappy 8v engines like these.

I have noticed an increase in mid range torque but to be honest it's only on because the crap that was on before had rusted away and would fail an MOT.

If you are going to buy performance parts you should have / should buy a performance engine in the first place to notice any difference.

Sometimes people want to stick with what they have and maximise that rather than try to chase bhp with the biggest engines possible. Nothing wrong with that..

23rd August 2010, 22:40

Quote:

Originally Posted by Gabbastard

On a serious note, I spent a lot of time on Ricardo Wave when I was modelling an engine, and there was nothing to suggest a 4-1 was good for top end power and 4-2-1 were shite at top end.

Fucking about with 4-2-1 designs came up with some great figures with not much less top end than 4-1.

interesting shit man. We've got Ricardo Wave and I jumped on to a machine thinking I had all the values for the variables and then realised I was WAY short of the mark.