i was talkin to a mate bout gettin extractors for my n/a vl6.he says that extractors make u loose compression,there for power,and response,is this true,or will it give me gains,and better response?

i think ur mate needs his head read extractors are one of the few things that give a worth while gain on n/a vl's.

Actually, if you get out your old physics textbook it will become obvious that anything you do to reduce backpressure in the exhaust system will result in a loss of compression. This does not neccessarily equate to a loss in power. As has been proven extractors will give you a decent gain on NA vl.

k yhanx for that

I'd say hes talking out of his arse! Depends on what he means by 'compression'? - Is he talking about cylinder compression? Nope, I cant see how extractors cause a loss of internal compression. (can you explain chioce_bro?) The only time the extractors have any affect on the cylinder pressure is on the exhaust stroke when the exhaust valves are open...better exhaust scavenging from a well designed exhaust can only be an advantage here. I think he may be talking about exhaust back-pressure? Even then, a well designed set of extractors will definitley be better than 99% of facotry exhaust manifolds too... Ta Damo

Who's talking out of who's arse you imbecile? Mate express your opinion, even though you shouldn't have one because you don't have a clue, but don't insult my intelligence. Ask any engineer this question and you will get a similar answer. Reducing backpressure reduces compression, it is a simple equation and has been known since the first combustion motors were built. Have a look at the restrictive chunks in a VL Exh. manifold and you will notice that they are not match ported to the head in any way shape or form. The result is increased back pressure ------> increased compression and if you remove it you decrease backpressure ----->decrease compression. That's not to say you are decreasing power though as I have already stated, your engine will rev better and so power will increase. If you can't see how the exhaust system has any bearing on the compression of the engine then you are most likely a 16 year old P plater as most people who insult me on this site are. Respect your wiser elders Sonny Jim.

Quote: Originally Posted by Choice_Bro Who's talking out of who's arse you imbecile? Mate express your opinion, even though you shouldn't have one because you don't have a clue, but don't insult my intelligence. Ask any engineer this question and you will get a similar answer. Reducing backpressure reduces compression, it is a simple equation and has been known since the first combustion motors were built. Have a look at the restrictive chunks in a VL Exh. manifold and you will notice that they are not match ported to the head in any way shape or form. The result is increased back pressure ------> increased compression and if you remove it you decrease backpressure ----->decrease compression. That's not to say you are decreasing power though as I have already stated, your engine will rev better and so power will increase. If you can't see how the exhaust system has any bearing on the compression of the engine then you are most likely a 16 year old P plater as most people who insult me on this site are. Respect your wiser elders Sonny Jim. 0wned

Whoa there big fella! Relax! Settle down an read my response, then re-read Nathan f's question. He starts with "I was talking to a mate......" I wasnt referring to you. I wasnt having a stab at you at all. Yep, I've asked you to expand a bit on your response, but hell, I though that was what this site was for? I've tried to do this as politley as possible, and again, I havent had a go at you, but have just asked a question in the hope that I might learn something new. As for the P-plater thing? I doubt there is alot of people on here older than me - were probably very close in age! I've been playing around with rallycars for the past 6 years or so (hence me only being able to afford a VL for a road car!) and have had a healthy interest in cars since I was small.....do I know it all? Hell no! This is the reason I'm asking the question of you. Have a look at my last sentence, I agree totally that reducing backpressure is benificial for an engine. Yep, I agree that replacing the stock manifold will allow better exhaust scavenging... BUT - I'm still at a loss as to how removing restriction in the exhaust & improving exhaust scavenging reduces the static compression ratio of the engine, therefore reducing performance? ie. how does it lessen the amount of compression the piston makes on the fuel/air mix during the compression stroke? (when both the exhaust & intake valves are closed?) Again, this is not a dig at you, not a challenge, and I dont need to start proving that mine is bigger than yours...just a question because there is something I dont quite understand. If you've still got a problem with the way I've responded here, PM me. Otherwise relax, us old fellas need to stick together. GoldVL - Owned? Nahhhh.....dont think so. (what the hell does 'owned' mean anyway?) Ta Damo

I think it may have some effect due to the overlap of exhaust and inlet valves. The inlet valve opens before the exhaust valve has fully closed. Not exactally sure how that relates to less compression, but thats my theory.

Yeah just a simple misunderstanding choice-bro..

Hornet, Yep good point. I've heard of a few race engines that have 'lost' the positive effects of their high compression builds with the switch to a more aggressive cam. But in this instance (just adding extractors to a stock engine) I would think valve timing would remain the same, hence giving the same compression ratio before & after? Thanks for the sane response!

Ok ok, I need an explaination here too Choice Bro. My understanding of what compression is in a cylinder referes to it's static ratio. That is, the ratio between gas in the cylinder before compression to after compression. ie, if the gas is reduced to one ninth of its uncrompressed volume, the compression ratio is 9:1. Thats just the definition that i can think of at the moment, and I don't understand how exhaust back pressure affects this. Is it because more exhaust gas can escape, hence leaving less matter in the combustion chamber or something? If so, I figure that the remaining matter in the chamber would be closer to pure air/fuel (hopefully closer to 14:1), hence more power? I'm just trying to logic my through it here, so correct me if i'm wrong please!

Quote: Originally Posted by Damo666 Hornet, Yep good point. I've heard of a few race engines that have 'lost' the positive effects of their high compression builds with the switch to a more aggressive cam. But in this instance (just adding extractors to a stock engine) I would think valve timing would remain the same, hence giving the same compression ratio before & after? Thanks for the sane response! Your right, the valve timming wont be changing. But i'm thinking MAYBE, by reducing backpressure, more gasses are being expelled on the exhaust stroke, meaning the cylinder is emptier on the start of the induction strock. So by the end of induction, there is less air in the cylinder to be compressed?? Just a theory. I'm not saying i agree or dissagree that fitting extractors reduces compression, i'm still sitting neutral on this one. The only way to find out would be to do a compression test on an engine before and after fitting a pair.

yeah thats what i was trying to say hornet. You reckon its right? it makes sense to me.

yep that makes sence to me aswell hornet & BC if the engine can't take enough air in (being non turbo), at least some of the exhuast air must remain in the combustion chamber to be mixed with the new air/fuel right ? isnt that why they say putting 3" exhausts on n/a's is stupid, because u still require a slight amount of back pressure on a N/A for optimum performance.

Yep sounds fair and putting 4" exhausts on the fully sik mirages too But i think that loosing some backpresure will gain performance, its like trying to find a nice equalibrium. I dont think too many people would disagree with me in saying that a 2.5" system with high flow cat and extractors would perform better than a standard setup. Some original photos have not been recovered yet.