New exhaust system!

[pandamonius_maximus]

i have very little technical knowlege, just the "suck it and see" type (i have built and played with a few)

and a 2mm raise in diameter doesnt sound like it will affect the power too much, probably raise power, if anything.

so maybe it was the putty thing?

Yes, I really cant think of anything else that it could've been tbh.

 

[jug]

dont talk down at me. I am not an idiot.

i meant no offence, i think you have misinterperated my post.

a 2mm raise in diameter doesnt sound like it will affect the power too much, probably raise power, if anything.

raise power and lower torque, in my experience an increase in 2/3mm would not cause serious problems.

the main difference in terms of back pressure is caused by the change in bends. a 90degree bend is much more restrictive. exhaust designers usually stick by the rule of 40degrees, and never go past 45degrees. that is fine if you want to lower back pressure, but in this situation you really dont want to do that because your engine lacks torque more than it lacks power and torque is especially important on 4wd because torque is what gets your wheels turning (not power!), and its much more difficult to get the wheels turning on a 4wd car, so you really need torque to get it moving.


if you have a carb you are lucky because you can compensate for the effect of your new exhaust. you can keep the extra power it gives you and also give yourself more torque. to do that you need to rejet the carb (try 2 sizes up), this will mean you get more fuel into the cylinders, so the amount that is lost through scavenging does not result in underfueling and a loss of torque. best of both worlds! only problem is fuel consumption will increase.

 

[pandamonius_maximus]

Yes, do excuse me for jumping to the conclusion that you were having a go! I had had a very long day and the reply "is this a genuine thread" had got me a little wound up before too. You were only trying to help and in fact say the same as I have been thinking. That running in the exhaust sounds like a load of rubbish unless your talking about noise and carbon build up.

Back on topic, the old exhaust did have 90 degree bends in it. So would have much more restriction. I am not too sure how more restriction causes more torque though. Not arguing with you there though, as it rings a bell in my head aswell. I thought that the restriction in a sharp bend would be more detrimental overall than just more narrow pipe. Having said that, the old one with two 90 degree bends in it wasnt that bad. So perhaps thats proof of the more torque given by more restriction (up to a point of course, otherwise we'd all be fitting high ratio boxes and straws for exhausts! ).

As for fitting new jets to the carb, might pass on that for the moment as fuel consumption isnt brilliant atm as it is
New engine soon I hope too, :yum: and it will have more capacity and might even prefer the new exhaust aswell.

Cheers,
Si

 

[jug]

I am not too sure how more restriction causes more torque though.

it reduces scavenging, thats all.

at the other end of the scale if you increase back pressure too much you will have too little scavenging and then you also lose torque.

you need the correct amount of scavenging to make sure you get all the exhaust gas into the exhaust but none of the unburnt air and fuel.

 

[pandamonius_maximus]

it reduces scavenging, thats all.

at the other end of the scale if you increase back pressure too much you will have too little scavenging and then you also lose torque.

you need the correct amount of scavenging to make sure you get all the exhaust gas into the exhaust but none of the unburnt air and fuel.

Cool! that makes more sence. And so if you have too much scavenging this will alter the air fuel ratio which earlier suggestion that the carb might need to be set up better and which is also what you said earlier today.

The peices are falling nicely into place :devil: